- CEE - Nanyang Technological University

Transcription

CIVIL ENGINEERING
RESEARCH
ISSN 0219-0370 • No. 24 / 2011 • www.ntu.edu.sg/cee/research/bulletin/index.asp
SUSTAINABLE URBAN SYSTEMS
In 2000, the world population was 6.1 billion. The
Population Division of the United Nations projected that
this would grow to 8.9 billion by 2050, an increase of
nearly 47 per cent in 50 years.
Today, half the world’s population lives in urban areas.
By 2050, eight out of ten people on planet earth will be
living in cities. This prompted the Executive Secretary
of the International Convention on Biological Diversity
to say that “the battle for life on Earth will be won or
lost in cities”.
With the explosive growth in population and the unrelenting
shift to urbanization, successfully engineering and building
sustainable cities within limits imposed by the natural
environment is a huge challenge. Cities consume two-thirds
of total energy produced and generated over two-thirds
of global energy-related CO2 emissions. Cities impose
tremendous demand on natural resources such as clean water
and clean air. In their wakes, they created a huge volume
of waste that must be handled safely without impacting the
quality of modern urban living.
Dr Su Guaning, President NTU, in his opening remark at
the GlobalTech’s Workshop on Sustainable Urban Solutions,
held at Shanghai Jiaotong University, China on 03-May2010 said:
“For a long time, mankind has made fundamental
assumptions on Mother Nature that turn out to be grossly
inaccurate and highly dangerous. From a small population
dependent largely on processes of nature for our survival,
we have evolved and multiplied and acquired the powers
to transform nature for the good and the bad. No longer
can we take the impact of mankind as negligible and
the capacity of nature as infinite.” He commented that
“Unfortunately we are in the awkward situation where we
Cont’d on Pg 3
MESSAGE FROM THE CHAIR
ur School of Civil and
Environmental Engineering (CEE)
has continued its pace of rapid growth
over this past year strengthening its
research programmes in the sustainable
built environment domain. Early in
2010, CEE accounted for two of NTU’s four prestigious
awards in Singapore’s National Research Foundation
(NRF) Competitive Research Programme call on
Sustainable Urban Systems. These extremely competitive
awards of about S$10 million each saw faculty teams
across CEE’s three Divisions led by A/P Chu Jian and
A/P Wang Jing-Yuan winning awards in the development
of an underwater city and in sustainable urban waste
management, respectively. The feature article of this issue
of CEE Research Bulletin contains detailed descriptions
of both research programme which are ramping up.
and in building energy efficiency. Both are somewhat
non-traditional areas for the School and representative
of NTU’s renewed efforts in intensifying integrative
research as well as being aligned with NTU’s strategic
peak of excellence in Sustainable Earth. The first is the
establishment of NTU’s Institute of Catastrophe Risk
Management (ICRM) in January 2010 with CEE being
the key driving School and CEE Professor T-C Pan,
Dean of College of Engineering, being the Founding
Director. ICRM aims to become Asia’s leading research
institute in catastrophe risk management, helping those
at risk worldwide in general and Asia in particular. The
focus on Asia is because Asia suffers from having the
largest exposure and corresponding fatalities and losses
from recent major catastrophes but is the least prepared
from both societal and governmental fronts. Working
synergistically with other NTU colleges and institutions,
ICRM will undertake integrated risk assessment and
This year also saw CEE embarking on two new research
fronts, that specifically in catastrophe risk management
Cont’d on Pg 2
Dear friends:
O
IN FOCUS
Message from the Chair (Cont’d from Pg 1)
management of hazards and catastrophes, both natural and
man-made. As a start, ICRM is developing methodologies
for the rigorous assessment of seismic risk and flood
risk. These two efforts are led by CEE Emeritus
Professor C.N. Chen and CEE Professors Shuy E.B., Li
Bing and Kusno Megawati. Together with the Nanyang
Business School, ICRM has also secured PhD funding
for two students from Aon-Benfield, a global leading
reinsurance intermediary. One of the PhD students will
focus on catastrophes in maritime business and the other
on Asian motor liability. Additional post-doctoral fellow
funding is also secured from Willis Re, another global
reinsurance firm, for research into marine container and
cargo exposure/vulnerability, and for CEE to join the
Willis-Re Global Research Network. CEE Professors
Robert Tiong, Jasmine Lam and Chiew Sing Ping are
leading these efforts with the Aon-Benfield and WillisRe grants.
Civil Engineering Research • January 2011
The second research front is in energy efficiency for
buildings in tropical climates. Buildings in Singapore
account for 50% of the nation’s energy usage (the number
is about 40% in the US) representing the nation’s largest
energy demand. NTU, led by CEE and its School of
Electrical and Electronic Engineering (EEE), partnered
UC Berkeley thereby enabling Berkeley to establish its
Berkeley Education Alliance for Research in Singapore
(BEARS) under NRF’s CREATE scheme. BEARS will
have the Building Efficiency and Sustainability in the
Tropics (BEST) programme as its first programme. Under
BEST we will see Berkeley faculty partnering CEE and
EEE counterparts to develop and testbed technologies that
will significantly reduce the building energy demand. The
focus will be on self-optimizing building systems using a
combination of physics-based models, models of occupant
behavior, data driven models and smart sensing to deliver
custom environments that simultaneously optimizes
comfort and productivity, and minimizes energy and
environmental costs. The research teams aim to achieve
disruptive innovations in building energy systems which
will be vital in creating new knowledge for new buildings
and retrofitting of existing buildings. Professors Chiew
Sing Ping, Susanto Teng and Victor Chang and I will
be heading CEE efforts on this front.
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It is indeed most exciting to see these new large research
programmes developing over the course of the year.
Furthermore, these initiatives are coming on top of the
research centres and programmes started under NTU’s
Nanyang Environment and Water Research Institute
(NEWRI) with again CEE being the lead School and
which I have reported on in last year’s issue of CEE
Research Bulletin. On the flip side, these many new major
initiatives are placing dramatically increased demands
on CEE’s research infrastructure to the point that CEE
is now facing major shortages in office and laboratory
space at its N1-Block on campus. CEE currently has
over 240 PhD students and over 120 research staff
comprising research fellows, research associates and
project officers. We have thus embarked on several
major renovation projects that will see teaching and
research activities being consolidated to free up spaces
for research offices and laboratories. In particular, CEE
now has a new laboratory, the Central Environmental
and Science Engineering Laboratory, housing several
new instruments for environmental research and a new
Civil Engineering Materials Laboratory for green concrete
research. I encourage you, and particularly the alumni,
to visit and see the transformations first hand.
A key part of School management is to ensure that CEE’s
education and research programmes are of the highest
possible level in rigor and quality. Notably, CEE saw
visits by two key visiting committees this past year.
The first is by NTU’s College of Engineering Visiting
Committee and the second is by Singapore’s Ministry of
Education External Review Panel under the Ministry’s
Quality Assurance for Universities (QAFU) framework.
I am happy to report that CEE has received positive
comments and reviews by both committees. Furthermore,
our Bachelor of Engineering degree programmes formerly
accredited by UK’s Joint Board of Moderators (formed
by The Institution of Civil Engineers, the Institution of
Structural Engineers, the Institution of Highways and
Transportation, and the Institute of Highway Incorporated
Engineers), are now accredited by the Engineering
Accreditation Board of the Institution of Engineers
Singapore under the Washington Accord. At the individual
level, Dr Goh Kok Hui, a recent PhD graduate under the
supervision of Professor Lim Teik Thye, won one of the
World Future Foundation’s PhD Prize in Environmental
and Sustainability Research for his thesis on the sorption
of oxyanions on nanocrystalline Mg/Al layered double
hydroxides. CEE Professor T-C Pan, Dean of College of
Engineering, won the 2010 Defense Technology Prize for
work over the years in underground technology and rock
engineering, and thereby provided key support towards
the current developments of underground facilities in
Singapore.
CEE continues to be successful in attracting new,
high calibre faculty members over this past year.
Since January 2010 we welcomed 5 new faculty
members. They are Associate Professor Tarek Zayed
(Construction Engineering Management, PhD Purdue
University, 2001) Assistant Professors Lee Chang Soo
(Environmental Engineering, PhD Pohang University of
Science & Technology, 2005), Yang En-Hua (Civil and
Environmental Engineering, PhD University of Michigan,
2008), Philip Wong (Environmental Engineering and
Science, PhD Stanford University, 2010), Cheung Sai
Hung (Civil Engineering, PhD California Institute of
Technology, 2009).
I hope you find CEE Research Bulletin informative and
enjoyable. Please do e-mail me with your thoughts and
comments.
Edmond Lo
Chair, CEE
IN FOCUS
Sustainable Urban Systems (Cont’d from Pg 1)
need to know the impact of our actions on nature without
sufficient understanding of nature itself.”
city can be constructed using the approach proposed. Living
under seawater will be a reality in the near future.
He further announced at the workshop that, “a happy
coincidence of our prior preparation, the increase of
external funding as well as our convictions has resulted
in an explosion of energy and activities in the Sustainable
Earth Peak of Excellence of our NTU 2015 Strategy. It is
backed by a multi-year funding of S$700mil on a diverse
range of topics ranging from earthquake and volcanoes to
environmental engineering to biofilms to energy to water
resources to membrane technology.”
The proposed new approach has many advantages over
the existing practices. It makes multiple use of sea space
by making the space both above and below the reclaimed
land available for recreation, living or infrastructural
development. It combines reclamation, superstructure and
underground constructions in one and thus is the most
efficient and cost-effective approach for space creation
and utilization. When designed strategically, the cylindrical
structure groups can also function as effective shore
protection elements against extreme waves such as storm
surges or tsunami and seawater changes caused by global
warming. They can also be designed to create energy
using waves.
The School of Civil and Environmental Engineering is a
bulwark in the preparation and on-going effort to spearhead
the Sustainable Earth Peak of Excellence in NTU 2015
strategy. The School had won two Competitive Research
Programme (CRP) funded by the National Research
Foundation.
The first project titled “underwater infrastructure and
underwater city of the future” is focused on the exploration
of new approaches to land-use particularly in the nearshore environment. This research effort is particularly
timely and pertinent to land scarce Singapore where other
potential approaches to expanding land-space are severely
constrained.
The design and construction of the super large cylindrical
structures poses many challenges to both theories and
practice. These include (a) the development of new and
innovative construction materials that would allow the
massive concrete structures to be constructed economically
and last for hundreds of years; (b) innovative soil
improvement and foundation construction methods to
allow a proper control and prediction of the settlement
and bearing capacity under various loads; and (c) the
hydrodynamics and related coastal, environmental issues
The second project is titled “Sustainable Urban Waste
Management for 2020”. The main focus of the project is
directed at the decentralized “waste-to-resources’ concept,
targeting at the recycling, reclamation and reuse of all
forms of wastes generated in highly urbanized cities of
which Singapore is a prime test field.
The following provides a synopsis of the two CRPs.
CRP I:
UNDERWATER INFRASTRUCTURE AND
UNDERWATER CITY OF THE FUTURE
Figure 1. Use of large size cylindrical structures for space
creation underwater and for land reclamation above.
Figure 2. Use of large diameter cylindrical structures to form
seawalls and create space behind the seawall.
In land scarce Singapore, space creation is a key strategic
area that concerns the survivability and sustainability of the
Nation. At the present, we have been using underground
caverns and offshore reclamation for space creation. Both
methods may not be sustainable in the long run. A new
approach – going underwater is proposed to make use of
the sea space to construct underwater infrastructure and
at the same time use the top-side of the infrastructures
as reclaimed land (see Figure 1). Using the proposed
method, we no longer need to import fill materials for land
reclamation. The proposed method also allows the use of
our limited space even more efficiently and cost effectively.
Cylindrical structures can also be put together to form a
watertight seawall and thus create space behind the seawall
(see Figure. 2). What is more exciting is that underwater
3
IN FOCUS
and the possibility for harvesting wave energy. New
technology and innovative solutions are required to make
the idea a reality. It is proposed in this project to carry out
an intensive inter-disciplinary study to address problems
related to structural, geotechnical, hydrodynamic, risk
analysis, and socio-technical aspects. From the study, a
series of innovative methods, new materials, and new
construction technologies will be developed to make the
proposed approach technically feasible and cost-effective.
The scopes of the study include (a) in-depth study of the
mechanical properties and durability of new construction
materials including Ultra High Performance Concrete,
Self-Compacting Green Concrete, as well as innovative
cylindrical structural design using new forms of structural
members; (b) Innovative soil treatment and foundation
methods; and (c) hydrodynamic study and harvest of wave
energy. The innovative methods to be developed include
the use of green concrete and new reinforcement, new
methods for the installation of cylindrical structures such
as suction caissons without soil improvement, new methods
to address issues on vortex shedding, wave trapping and
movement of sand waves relevant to the founding of extra
large structures on the seabed, and methods to harness
wave energy.
The expected outcome of this research is the establishment
of a new, efficient and sustainable method for space creation
using less resource and to provide innovative solutions
to the challenges to make space creation and underwater
construction more cost-effective and socially attractive.
KEY MEMBERS OF PROGRAM TEAM:
Principal Investigator:
• Assoc Prof Chu Jian (CEE, NTU)
Co-Principal Investigators:
• Assoc Prof Susanto Teng (CEE, NTU)
• Assoc Prof Tan Soon Keat (CEE, NTU)
Collaborators:
• Assoc Prof Robert Tiong (CEE, NTU)
• Asst Prof Sulfikar Amir (AHSS, NTU);
• Mr Lam Kok Pang (JTC Corporation)
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Industrial collaborator:
• Surbana International Consultants
Overseas Collaborators:
• Mr Knut H. Andersen, Norwegian Geotechnical
Institute, Norway;
• Dr Dale Berner, Ben C. Gerwick Inc., USA;
• Prof Odd E. Gjorv, Norwegian University of Science
and Technology, Norway;
• Prof Richard S. Mercier, Offshore Technology
Research Centre, Texas A&M University, USA;
• Prof Andrew Whittle, MIT, USA
CRP II:
SUSTAINABLE URBAN WASTE MANAGEMENT
FOR 2020
INTRODUCTION
Waste is not waste. Much of our disposed waste should
not in fact be considered waste; they are simply misplaced
resources. Based on current waste management concepts,
these resources are normally buried in landfills or incinerated.
Such waste treatment/disposal approaches need to be revised
as natural resources are depleted. Waste becomes potential
sources for resource recovery. This is especially true for
land- and resource-scarce Singapore.
A successful proposal entitled “Sustainable Urban Waste
Management for 2020”, based on a decentralised “waste
to resources” concept, was recently awarded S$10 million
by the National Research Foundation (NRF) under its
Competitive Research Programme (CRP) funding scheme
to develop sustainable urban waste management solutions
for 2020 and beyond. The five-year programme is led by
Assoc Prof Wang J.Y. (lead PI) of the School of Civil and
Environmental Engineering (CEE) and supported by six
other NTU faculty members as Co-PIs. The programme
also partner with three government agencies, two industrial
companies, and two overseas universities.
OBJECTIVES
The main objective of this research programme is to
develop sustainable urban waste management solutions for
2020. Research outcomes are expected to bring long term
environmental, economical and social benefits to Singapore
and eventually the rest of the world. To achieve the main
objective, the following three research subprogramme were
proposed:
• Subprogramme A: Communities as renewable resource
recovery centres
• Subprogramme B: Wastewater treatment plants as urban
eco power stations
• Subprogramme C: Rapid land reclamation of closed
dumping grounds
RESEARCH OUTCOME
Various technologies will be developed, tested, and
demonstrated for all the subprogrammes.
Subprogramme A
IN FOCUS
•
A technology for phosphorous - and nitrogen-recovery
from yellow water
KEY MEMBERS OF PROGRAM TEAM:
•
A technology for odour removal from household source
separation system
Principal Investigator:
•
Assoc Prof J-Y Wang (CEE, NTU)
•
A two-phase anaerobic digestion (AD) system for codigestion of black water and food waste
•
An integrated thermophilic co-digestion (CoD) and cocomposting (CoC) system
•
Prof W.J. Ng (CEE, NTU): PI on co-digestion of
sludge and community organic waste
•
An integrated solid oxide fuel cell (SOFC) + microbial
electrolysis cell (MEC) + proton exchange membrane
fuel cell (PEMFC) system
•
Prof R. Harianto (CEE, NTU): Co-PI on capillary
capping development using recycled materials
•
Assoc Prof X. Wang (CBE, NTU): Co-PI on
integrated SOFC + MEC + PEMFC system
•
Assoc Prof J. Chu: Co-PI on non-invasive site
characterization technique development
•
Asst Prof Victor Chang: Co-PI on nutrient recovery
and odor removal
•
Asst Prof C.S. Lee: Co-PI on co-digestion of black
water and food waste
•
Mr S.H. Lim (National Environment Agency):
Partner on the whole programme
•
Ms Cherlyn Leong (Jurong Town Corporation):
Partner on subprogrammes A and C
•
Ms P.S. Teh (Housing Development Board): Partner
on subprogramme A
•
Mr William Phay (Keppel Pte Ltd): Partner on
subprogramme B
•
Mr S.O. Goh (SembCorp Pte Ltd): Partner on
subprogramme C
Local Collaborators:
Subprogramme B
•
An efficient sludge + organic waste co-digestion (single
stage + thermophilic ) system
•
Other developments: A two-phase AD for sludge +
organic waste co-digestion
Subprogramme C
A technology for non-invasive geophysical site
investigation
•
Landfill mining technologies including waste
characterization and separation
•
Remediation technologies including electrokinetic, soil
washing, bioremediation, etc.
•
Resource recovery technology, e.g., fast pyrolysis
•
Evapotranspiration-based (capillary) capping technology
•
Prof Rainer Stegmann (Technical University of Hamburg
and Harburg, Germany): Collaborator on integrated codigestion and co-composting system
•
Prof J.S. Chang (National Cheng-Kung University
(NCKU), Taiwan): Collaborator on co-digestion of black
water and food waste and landfill remediation
•
Prof S.S. Cheng (NCKU, Taiwan): Collaborator on
bioenergy development
•
Overseas Collaborators:
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CEE VISION AND MISSION
CEE VISION & MISSION
Our Vision
A leading school for sustainable built
environment.
Our Mission
To nurture students to be responsible leaders
capable of realising their maximum potential
in their profession and community. To provide
a collegiate environment for faculty to excel
in education and research for sustainable
development. To advance knowledge for the
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practice of civil and environmental engineering
and maritime professions.
STATISTICS
STATISTICS
Faculty & Staff (as of 1 December 2010)
Publications, Patents and Research Grant
Year
2006
2007
2008
2009
2010
Journal
papers
145
167
151
202
79
Conference
papers
76
120
91
90
45
Patents
1
3
3
2
2
9.6
9.9
13.5
36.4
30.0*
Research
Grant ($mil)
*Partial figure only
Students Enrolment
Programme/
Academic Year
MEng
PhD
PhD
(SSP)
MSc
(Civil Eng)
MSc
(Env Eng)
MSc
(ICM)
MSc
(MS)
AY2006-07
1364
36
145
3
254
102
79
175
AY2007-08
1290
37
150
6
228
107
102
201
AY2008-09
1210
29
163
6
216
93
98
256
AY2009-10
1148
5
169
7
38
14
25
22
AY2010-11*
1149
5
206
7
54
31
45
49
*Semester 1 only
Undergraduate
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UNDERGRADUATE PROGRAMMES
BACHELOR DEGREE PROGRAMMES
BACHELOR OF ENGINEERING (CIVIL)
The Civil Engineering programme is structured on a flexible
and diverse system that allows students to choose from a
broad range of courses to receive a well-rounded education
while maintaining high academic standards. In the final year
of study, students are given the opportunity to specialize in
particular areas of civil engineering by selecting the relevant
elective courses. Furthermore, though students typically
complete the degree course in four years, they may study
at their own pace and complete their studies within the
time frame of three-and-half to seven years.
In the first year of study, students take the common
engineering course which deals with basic concepts
in mathematics, science and fundamental engineering
principles. The curriculum also includes a course in
communication skills and two courses of laboratory
experiments.
In the second year, students are required to take fundamental
courses in the civil engineering discipline, such as basic
theory of structures, geotechnical engineering, water
resources engineering, engineering drawing & measurement.
Second-year students also take additional courses in
mathematics, two courses of laboratory experiments and
a technical communication skills course. In the second
semester of the second year, students study “Engineering
Innovation and Design”, a course in which students work
in groups on a given open-ended project to learn the
practical and innovative problem-solving skills required
of engineers.
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In the third year of their studies, students are offered a
balanced mix of core courses comprising structural analysis,
design in concrete and steel structures, and specialized
courses in foundation, transportation and environmental
engineering. After students attaining the requisite academic
units for promotion to third year, the students can, if they
wish, register for a 22-week Industrial Attachment (IA)
in a private company or public organization, where they
learn to practise civil engineering under the guidance of
experienced engineers and managers.
In the final year, the Civil Engineering programme
concentrates on training students in professional civil
engineering practice as well as managerial and entrepreneurial
skills. Students are given the choice to pursue their own
fields of interest in a particular area of specialization by
selecting from a group of optional elective courses offered
by the School. Each student is also required to complete
a two-semester duration research project in any of the
specializations in civil engineering. In Integrated Design,
students will be involved in team effort to confront and solve
real-life open-ended civil and environmental engineering
problems.
BACHELOR OF ENGINEERING
(ENVIRONMENTAL)
The Environmental Engineering programme is structured on
a flexible and diverse system that allows students to choose
from a broad range of courses to receive a well-rounded
education while maintaining high academic standards. In
the final year of study, students are given the opportunity to
specialize in particular areas of environmental engineering
by selecting the relevant elective courses. Furthermore,
though students typically complete the degree course in
four years, they may study at their own pace and complete
their studies within the time frame of three-and-half to
seven years.
In the first year of study, students take the common
engineering course which deals with basic concepts
in mathematics, science and fundamental engineering
principles. The curriculum also includes a course in
communication skills and two courses of laboratory
experiments.
In the second year, students are required to take fundamental
courses in the environmental engineering discipline, such
as fluid mechanics, hydrology, environmental chemistry,
environmental processes, and environmental microbiology.
Students are given foundational training in sustainable
infrastructure by taking some courses in basic theory of
structures and engineering drawing & measurement. Secondyear students also take additional courses in mathematics,
two courses of laboratory experiments and a technical
communication skills course. In the second semester of
the second year, students study “Engineering Innovation
and Design”, a course in which students work in groups
on a given open-ended project to learn the practical and
innovative problem-solving skills required of engineers.
In the third year of their studies, students are offered
a balanced mix of core courses comprising water
supply engineering, wastewater engineering, solid waste
engineering, geo-environmental engineering, hydraulics and
basic structural design. After attaining the requisite academic
units for promotion to third year, the students can, if they
wish, register for a 22-week Industrial Attachment (IA)
in a private company or public organization, where they
learn to practise the environmental engineering under the
guidance of experienced engineers and managers.
In the final year, the Environmental Engineering
programme concentrates on training students in professional
environmental engineering practice as well as managerial
and entrepreneurial skills. Students are given the choice to
pursue their own fields of interest in a particular area of
specialization by selecting from a group of optional elective
courses offered by the School. Each student is also required
to complete a two-semester duration research project in any
of the specializations in environmental engineering.
BACHELOR OF SCIENCE (MARITIME
STUDIES)
The Maritime Studies programme focuses primarily on
tertiary education in shipping, business, management, and
maritime science and technology, to build up the expertise
of the local shipping industry as well as working towards
establishing Singapore as a centre of excellence for shipping
business, research and development. The programme is
conducted jointly by NTU and the Norwegian School of
Management (BI), Norway, supported by the Maritime and
Port Authority of Singapore (MPA).
With the support from the College of Engineering,
Nanyang Business School and School of Humanities
and Social Sciences, students enrolled in the Maritime
Studies programme will learn from academics from various
disciplines, thereby developing different skills in a holistic
and comprehensive learning environment. The Norwegian
School of Management (BI) is Norway’s second largest
educational institution, and one of the largest business
schools in Europe. BI is the first Norwegian educational
and research institution to achieve international accreditation
establishing BI as one of Europe’s leading business
schools.
The Maritime and Port Authority of Singapore (MPA) and
the shipping industry have recognised that the shipping
practice and business in Singapore need to be further
elevated in order to enter into the regional and global
arenas. The BSc (Maritime Studies) degree is a strategic
development that would provide high-level and high-value
education for professionals in shipping and related business,
elevating them from local business management to one of
international business standing. The BSc (Maritime Studies)
with Business Major degree aims to produce graduates
well versed with the maritime industry and strong business
knowledge so that they will be the future business leaders
in the global maritime industry. MPA and the industry are
fully supportive of the Maritime Studies degree programmes
and MPA also provides an endowed Professorship (Shipping
Management) in NTU.
The BSc (Maritime Studies) curriculum aims to provide
students with both depth and breadth. The course structure
is flexible and broad base. Students will be required to
complete:
• Foundation courses including mathematics, social
sciences, business and technology
• Shipping specialist courses including organization
and management of shipping companies, international
shipping logistics, maritime law, marine insurance,
shipping strategy, and a research project
• Prescribed electives for specialisation in the
programme, and General Education Requirement
courses for broadening the learning experience
In addition to the above, the more rigorous BSc (Maritime
Studies) with Business Major curriculum includes core
business courses in accounting, business law, company
law, principles of taxation, business environment, financial
analysis & reporting, marketing, and organisation behaviour
& design.
Students will complete a semester of their studies at BI,
Norway, in their third year of studies. The curriculum
also includes an Industrial Immersion - ten weeks for BSc
(Maritime Studies) and twelve weeks for BSc (Maritime
Studies) with Business Major - where students will be
attached to organizations in the shipping and related
industry.
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GRADUATE PROGRAMMES
GRADUATE STUDIES
BY COURSEWORK
Master of Science (Civil Engineering)
The programme equips students with the latest advancements
in knowledge and technology in modern civil engineering
practice. Students will also have the opportunity to acquire
knowledge in several civil engineering disciplines by
selecting appropriate courses.
Master of Science (Environmental
Engineering)
The programme equips graduate engineers and other related
professionals with advanced skills and expertise in a wide
variety of environmental disciplines. The programme
offers a comprehensive range of subjects on advanced
water and wastewater treatment, air and land pollution
as well as broader aspects of environmental management
and planning.
Master of Science (International Construction
Management)
The programme enables graduate engineers, architects and
other related professionals to expand their decision-making
horizons given the kind of parameters and risks which
international construction managers encounter. The main
objective of the programme is to develop competent and
well rounded construction managers who have the skills
to source, secure and effectively manage projects in the
domestic and international construction market.
Master of Science (Maritime Studies)
The programme provides graduate level and high-value
education for professionals in shipping and related business;
elevating them from local business management to one of
the international and global business settings. The foremost
intention is for young graduates and middle-management
executives working in shipping related areas an avenue
for higher education. The programme will also be suitable
for graduates who wish to be involved in the maritime
profession.
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Master of Science (Environmental Science and
Engineering)
The NEWRI Environmental Master of Science (NEMS)
programme is offered by NTU’s School of Civil and
Environmental Engineering with a Summer attachment
at Stanford University, and the Nanyang Environment
and Water Research Institute (NEWRI) on the research
project component. The programme is designed to prepare
students to be at the forefront of Environmental Engineering
with a combination of coursework and project/research
components. It aims to produce high calibre environmental
engineers equipped with both fundamental understanding
and practical skills.
Master of Science (Infrastructure Engineering
and Management)
The programme is a joint Degree Programme between the
School of Civil & Environmental Engineering, Nanyang
Technological University, Singapore and the Department
of Civil Engineering, Indian Institute of Technology
Bombay, India. The programme provides holistic training
in infrastructure engineering and management covering
conceptual and physical planning, design, and operational
aspects of infrastructure systems. Such systems are in great
demand in rapidly developing regions such as in China,
India, ASEAN and the Middle East and include air, sea
and land transport networks, water supply and wastewater
systems and power distribution networks.
RESEARCH
Students can choose to pursue Doctor of Philosophy degree
in one of the following disciplines:
Construction Technology and Management
Construction Technology and Management
Risk and Project Financing
Facility and Infrastructure Management
Structures and Mechanics
Computational Mechanics
Earthquake Engineering and Structural Dynamics
Protective Technology
Fire Engineering
Concrete and Steel Technology
Geotechnical Engineering
Foundations of High-Rise Buildings
Land Reclamation
Underground Space Development
Tropical Soil Engineering
Rock Mechanics and Engineering Geology
Environmental and Water Resources
Membrane Technology in Environmental Engineering
Water Reclamation Technologies
Waste Reuse and Resource Recovery
Environmental Biotechnology
Integrated Urban Water Management
Environmental Fluid Mechanics
Sediment Transport
Coastal Management
Maritime Studies
Maritime Logistics
Port Economics and Management
Maritime Strategy and Risk Management
Strategic and Quality Management in Shipping
Supply Chain Management
Transportation Engineering
Transport Modelling and Traffic Management
Transport Planning
Congestion Pricing
Road Safety Engineering
ACHIEVEMENTS AND COMMENDATIONS
ACHIEVEMENTS AND
COMMENDATIONS
AWARDS
Professor Chiew Yee Meng was awarded the Distinguished
Contribution to Sediment Research in 2010 by World
Association for Sedimentation and Erosion Research
(WASER) for the publication of an outstanding research
paper in International Journal of Sediment Research entitled
“Scour Protection around Bridge Piers with Tetrahedron
Frames”.
Associate Professor Darren Sun’s past research has yielded
major achievements in the development of mesoporous
nanostructured Titanium Dioxide microspheres and the
free-standing, flexible and multifunctional Titanium
Dioxide nanofiber/tube filtration membrane. These new
generation membranes will be able to produce high quality
drinking water and concurrently generate electricity, thus
eliminating the cost of water production and chemical usage
together with waste minimization. His innovation has a
major impact in membrane technology and many venture
capitalists have shown keen interest to commercialize his
innovation. Associate Professor Sun has 5 patents on
Titanium Dioxide membrane field. Since 2006, he has
attracted research grants totaling S$17.6 million. He has
won several prestigious awards in the past including the
International Water Association Innovation Award 2008,
the IES Prestigious Engineering Achievement Award 2008,
and the Enterprise Challenge Award 2006.
(2) Dr Sun was interviewed by Sandra Upson, Associate
Editor, IEE Spectrum on Water and Energy issue related
to research. IEEE Spectrum, June 2010, Page 56.
Singapore’s Water Cycle Wizardry: Singapore’s
toilet-to-top technology has saved the country from
shortages-and a large electricity bill.
(4) “Water and Industrial 2009 Conference”, Palmerston
North New Zealand, 30 November to 2 December 2009.
http://seat.massey.ac.nz/conferences/water09/#.
Dr Darren Sun was a Co-Chair for this conference
Associate Professor Leong Eng Choon was awarded
the Singapore Accreditation Council Assessor Award
(Distinguished) and SPRING Singapore Merit Award in
2010.
Assistant Professor Tang Chuyang received the 2010
Fellowship Award from the International Desalination
Association (IDA) for his work on membrane technology
for water reuse and desalination.
Assistant Professor Yang Yaowen received the 2009
Teacher of the Year Award at the Nanyang Awards 2009.
PATENTS
Sun, Darren Delai, Yinjie Wang, Liu Jincheng and Xiwang
Zhang (2009). “Concurrent electricity and clean water
production module made by dye sensitized titanium dioxide
nanostructures”. Ref No TECH/080/09, TD/080/09.
(1) Professor Sun’s Research on TiO2 solar cell was
reported by The Straits Times on 18 April 2009.
(3) Dr Sun was interviewed by NanoGlobe
“Nanostructured Photocatalytic Materials Enable
Capturing Solar Energy and Simultaneously Powering
Water Purification” - An interview of Associate
Professor Darren Delai SUN, Nanyang Technological
University, Singapore
http://www.nanotech-now.com/columns/?article=474.
11
INVITED LECTURES
•
Invited Lecture: “Recent development in the
construction of coastal structures” at the Kyoto
Seminar 2010 on Geotechnics/Earthquake
Geotechnics towards Global Sustainability, January
12-14, 2010, Kyoto, Japan.
•
Invited Lecture: “Strain softening and instability of
sand and practical application” at the 2010 Huang
Wenxi Lecture, Chinese Institution of Geotechnical
Engineering, 11 April 2010, Nanjing, China.
•
Invited Lecture: “Improvement of ultra soft soil for
the reclamation of a slurry pond in Singapore” at
the Symposium on New Techniques for Design and
Construction in Soft Clays, 22 and 23 May 2010,
Brazil.
•
Keynote Lecture: “Land reclamation and related soil
improvement methods in Singapore” at the Australia
Geomechanics Society Ground Improvement
Workshop, 11-12 June 2010, Perth, Australia.
•
Professor Harianto Rahardjo and Associate Professor
Leong Eng Choon were invited to deliver a keynote lecture
entitled “Laboratory characterisation of unsaturated soil for
slope stability studies” at the 4th Asia-Pacific Conference on
Unsaturated Soils, Newcastle, Australia, 23-25 November
2009, pp. 565-578.
Keynote Lecture: “Recent development in ground
improvement methods” at the 7th International
Conference on Ground Improvement Techniques,
23-25 June 2010, Seoul, Korea.
•
Associate Professor Darren Sun was invited as a speaker
for the following International Conferences
Keynote Lecture: “Methods for construction of
coastal protection structures” at the Conference
on Natural Hazards and Countermeasures in
Geotechnical Engineering, 4-5 November 2010,
Dhaka, Bangladesh.
•
Keynote Lecture: “Methods for the improvement of
high water content soft clay and sewage sludge”
at the International Symposium, Exhibition, and
Short Course on Geotechnical and Geosynthetics
Engineering: Challenges and Opportunities on
Climate Change, 7-9 December 2010, Bangkok,
Thailand.
Professor Pan Tso-Chien was invited as a speaker for the
following conferences:
•
Keynote Paper: “An overview of the current
research programmes in Protective Technology
Research Centre at NTU.” Proceedings of the 3rd
International Conference on Design and Analysis
of Protective Structures 2010 (DAPS-2010), 10-12
May 2010, Singapore, pp. K25-K39.
•
Keynote Speech: “Developing technology for
protection.” Inaugural Workshop on Building
Infrastructure Protection for Homeland Security,
13 May 2010, Singapore.
•
Keynote Lecture: “Seismic hazard of low/moderate
seismicity regions – Singapore’s perspective.” The
10th International ROSE School Seminar, 20-21 May
2010, EUCentre, Collegio Cardinale Riboldi, Pavia,
Italy.
•
Special Invited Speaker: “TiO2 Nanofiber/tube
Membrane Powering the Water and Energy
Productions” at IWA Leading Edge Technology
Conference at Singapore International Water Week,
June 2009.
•
Invited Keynote Speaker: “Smart Multi functional
TiO2 nanotube membrane for Water and Energy
Production” at IWA Water and Industry 2009, New
Zealand, 30 November to 2 December 2009.
Associate Professor Chu Jian was invited to deliver
lectures at the following international conferences:
•
12
Keynote Lecture: “Innovative dike construction
methods” at International Symposium on Geotechnical
Engineering, Ground Improvement & Geosynthetics
for Sustainable Mitigation and Adaptation to Climate
Change including Global Warming, 3-4 December
2009, Bangkok, Thailand.
RESEARCH CENTRES
Activities of Centre for Infrastructure Systems (CIS)
from August 2009 to July 2010
(A) Centre Activities
Speakers:
•
Assistant Professor Jasmine Lam
•
Mr Gunasagaran, PSA
•
Dr W. Y. Yap, ITMMA
Seminars, Short Courses & Symposium
1.
BI and NTU Joint Programme –
An Intensive 5-Day Short Course on “Key Elements
of Shipping”
CIS and BI jointly organized a five-day intensive short
course on “Key Elements of Shipping” from 9–13
March 2010. It was attended by 25 participants from
government agencies and the maritime industry, such
as professionals from the Maritime and Port Authority
of Singapore (MPA), Mediterranean Shipping Company
(MSC), I.M. Skaugen and J.B. Ugland Shipping.
Public Seminar on “Bearing Capacity of Uplift
Piles Under Deep Excavation”
A public seminar on “Bearing Capacity of Uplift Piles
Under Deep Excavation” was held on 8 December
2009. Professor Maosong Huang from the Department
of Geotechnical Engineering at Tongji University,
Shanghai, China, was the speaker of the seminar.
His general research interests are focused on strain
localization and progressive failure in soils, strength
and deformation characteristics of soft clays, trafficload-induced permanent deformation, constitutive
modeling of soils, pile-supported earth platform,
centrifuge modeling, stability analysis of soil structures,
and pile foundations in soft clays.
4.
Invited Public Lecture on “Reinforced Soil System:
Bring Research to Applications”
Associate Professor Robert Lo from the University
of New South Wales, Australia is the invited speaker
of CIS on 17 May 2010 who delivered a public
lecture on “Reinforced Soil System: Bring Research
to Applications”. He was awarded the Thomas Telford
Prize for his paper on the topic of partial factors
in geotechnical design and was a member of TC-9
(reinforced soil) and a core member of TC-39 (coastal
disaster mitigation). Professor Lo has published over
140 research articles in soil behaviour, liquefaction,
soft clay engineering, reliability analysis and limit
state design, pavement geotechnics, and reinforced
soil technology.
Speakers:
•
Assistant Professor Jasmine Lam
•
Cathrine Bjune, BI Norwegian School of
Management
•
Captain Robert Gordon, Seasia P&I Services
•
Professor Barry Dubner, Barry University
Andreas
•
Lasse Rochstad Lim, Tuffchem Shipping Ltd.
•
Stephen Fordham, Wikborg Rein
•
Mike Pollen, K&L Gates
•
Lewis Hart, Willis
•
Dag Olav Halle, DNV
2.
Executive Programme on “Port Management and
Finance Programme”
CIS organized a two-day short Executive Programme on
Port Management and Finance from 29–30 July 2010.
It was attended by 28 participants from government
agencies and the port and maritime industry, such as
professionals from the Maritime and Port Authority
of Singapore (MPA), Jurong Port and V Ships.
3.
13
RESEARCH CENTRES
5.
Joint Public Seminar on “Improving the Productivity
and Peformance of Social Infrastructure Project
Delivery” and Public Private Partnership (PPP)
Success Stories
To develop a new and economical construction material,
biocement, using the latest microbial biotechnologies; 2)
To develop cost-effective and environmentally friendly
microbiological methods to use biocement for geotechnical
or environmental engineering problems. These include
constructions for roads, tunnels, land reclamation, slope
stabilization, shore protection, and waste treatment; and
3) To study the fundamental principles, microbiological
and biochemical mechanisms that govern the formation
of biocement by microorganisms. So far, suitable
microorganisms and nutrients that could be used for making
different types of biocements were identified. The properties
of soil and waste before and after the treatment using
biocement were studied. Some patents applications have
also been reviewed. Methods for creating water pond in
sand and for the mitigation of liquefaction potential have
been developed.
The afternoon of 15 July 2010 witnessed the
presentation of Infrastructure Projects and PublicPrivate-Partnership, by two professors from Curtin
University of Technology, Australia and Nanyang
Technological University, Singapore which was held at
the Singapore campus of Curtin University, located in
Jalan Rajah. Professor Love is from the School of Built
Environment, Art and Design, Faculty of Humanities
at Curtin University in Perth, Western Australia. He
delivered a topic on “Improving the Productivity and
Performance of Social Infrastructure Project Delivery”
and discussed three social infrastructure projects
in Western Australia, which included a hospital, a
school and a prison. The second presentation was
by Associate Professor Robert Tiong, School of
Civil & Environmental Engineering and Deputy
Director, Centre for Infrastructure Systems, Nanyang
Technological University, Singapore. Associate
Professor Robert Tiong focused on success stories
of Public-Private Partnerships (PPP) in this region,
with a key focus on China, India, Korea, Thailand,
Taiwan, Singapore, Malaysia and the Philippines. He
also elaborated on typical causes of PPP failures.
Research Project on Planning and Management of
Infrastructure Systems Phase I: Studies on Mega
Projects in Singapore
The project is focusing on the planning and management
issues related to implementation of mega infrastructures
in Singapore. It researches into Lifecycle Management
and consists of coordinating planning, designing, building,
operation and maintenance of facilities to achieve
management competitiveness. The project objectives
are to create a systems-level approach in building and
managing a single portfolio of systems in Singapore, to
create an infrastructure database and lay the foundation
for further studies on the lifecycle management of these
mega projects. It uses the system dynamics methodology
to propose a strategy of operational & economic success
of these mega infrastructures. The project is currently at
its stage I phase where it is focusing on MRT as the pilot
infrastructure project to be studied. Initial data collection
on its planning & design, construction, extension projects
and future project has been done. Going forward, the
challenges in this research would be in data collection and
obtaining more information from government and agencies
that are involved in the mega infrastructure projects in
Singapore.
(B) Research and Development
14
CRP Grant on Underwater Infrastructures and
Underwater City of the Future
Centre Director, Associate Professor Chu Jian, together with
Associate Professor Susanto Teng, Associate Professor Tan
Soon Keat and Centre Deputy Director Associate Professor
Robert Tiong, are awarded a $10M grant by the National
Research Foundation (NRF) for the above project.
Research Projects
Research on Biocement – A new sustainable and energy
saving material for construction and waste treatment
The main objectives of this inter-discipline study are 1)
Research Project on Study of Transport Energy
Efficiency, Methodology, Practice and Policy Effect
This 2-year research project, which is undertaken by NTUCIS in collaboration with the Land Transport Authority,
started in September 2010. The aim is to study the issue
of road transport energy efficiency (EE) in Singapore.
The project investigators are Assistant Professor Chang
Wei-Chung Victor, Associate Professor Gopinath Menon,
Associate Professor Wong Yiik Diew, Project Officer Ms
Lu Ping, PhD Candidates Ms Ho Sze Hwee and Mr Ho
Sijie. The project encompasses literature survey of EE best
practices and estimation models, assembly of databases
related to fuel efficiency based on indigenous data from
stake-holder agencies and field surveys, and development of
fuel consumption models for road vehicles. The study will
also look into fuel management practices of fleet operators
as well as conducting possible field trials.
RESEARCH CENTRES
Research Project on Mobility of Visually-Handicapped
Pedestrians – Crossing Behaviour and Assistive Design/
Technologies at Signalised Pedestrian Crossings
Mitsui Sumitomo Insurance Welfare Foundation (MSIWF)
awarded a research grant to Associate Professor Wong Yiik
Diew, Associate Professor Gopinath Menon, and doctoral
student Ms Koh Puay Ping to research into traffic safety
of visually-handicapped pedestrians (VHPs) at signalised
pedestrian crossings. The 12-month project is aimed at
developing a better understanding of VHP’s crossing
behaviour at signalised pedestrian crossing facility, and
studying ‘best practices’ in the provision of assistive
design/technologies. The study shall contribute towards
enhancing the mobility of VHPs on the roads.
3)
2010 Huang Wenxi Lecture, annual lecture series
organised by the Chinese Institution of Geotechnical
Engineering, 11 April 2010, Nanjing, China.
Associate Professor Chu Jian was invited to this event
to deliver an Invited Lecture.
4)
1st GlobalTech Workshop on Sustainable Urban
Solutions organized by Shanghai Jiao Tong University
and the Global Alliance of Technological Universities,
3-4 May 2010, Shanghai, China.
Associate Professor Chu Jian attended this workshop
as a delegate from NTU and delivered a lecture.
5)
Symposium on New Techniques for Design and
Construction in Soft Clays, Brazil, 22-23 May 2010.
Associate Professor Chu Jian was invited to this
conference to deliver an Invited Lecture.
6)
AGS Ground Improvement Workshop organised by
the Australia Geomechanics Society, 11-12 June 2010,
Perth, Australia.
Associate Professor Chu Jian was invited to this event
to deliver a Keynote Lecture.
International Conference Participation
1)
International Symposium on Geotechnical Engineering,
Ground Improvement & Geosynthetics for Sustainable
Mitigation and Adaptation to Climate Change including
Global Warming, 3-4 December 2009, Bangkok,
Thailand.
conference to deliver a Keynote Lecture.
2)
Kyoto Seminar 2010 on Geotechnics/Earthquake
Geotechnics towards Global Sustainability, 12-14
January 2010, Kyoto, Japan, organized by Kyoto
Sustainability Initiative (KSI), Kyoto University.
conference to deliver an Invited Lecture.
15
RESEARCH CENTRES
Activities of DHI-NTU Centre in 2010
RESEARCH FOCUS/RESEARCH
HIGHLIGHTS
The DHI-NTU Centre is a joint collaborative effort between
NTU and DHI, Denmark (previously known as Danish
Hydraulic Institute). The Centre initiated operation in
October 2007 with funding support from the Environment
and Water Industry Development Council (EWI), Singapore
National Research Foundation. It is an integral part of the
ecosystem of the Nanyang Environment and Water Research
Institute (NEWRI) in NTU. The mission of the Centre is
to advance research in the following areas:
(a) Urban Planning and Water Management
(b) Industrial Water Management
(c) Solid Waste Management
(d) Environmental Impact Assessment
(e) Decision Support System Tools and Technologies
universities worldwide has been actively pursued, and joint
projects has been initiated together with local governmental
agencies or industry as described in the following. A
highlighted event was that in September 2010, NEWRI
signed a MoU with NPark on promoting research and
development, and together the Centre also signed a project
agreement with NPark on the development of a modular
bio-retention system for urban storm water management.
In June 2010, Assoc Professor Adrian Wing-Keung Law
was appointed as co-Director of the Centre (taken over
from Assoc Professor Tan Soon Keat who had assumed
the role of Deputy Director, NEWRI), together with Dr
Ole Larson, the co-Director from DHI.
RESEARCH OUTPUT
1)
Research Publications in Year 2010
In Year 2010, the Centre had accelerated the development
of research projects in the above areas. Cooperation with
a)
Refereed Journals
Title of paper
16
Author name(s)
Journal title, Vol. no.
Date
A comparison of municipal solid waste
Gersberg, management in Berlin and
Singapore
Zhang, D.Q., Tan, S.K., R.M.
Waste Management, 30, 921-933
2010
Urban solid waste management in
China: status, problems and challenges
Zhang D.Q., Tan, S.K.,
Gersberg, R.M.
Journal of Environmental
Management, Vol. 91, Issue 8,
1623-1633
2010
Extreme Air-gap Response below Deck
of Floating Structures.
Li, J., Huang, Z. and Tan, S.K.
International Journal of Ocean
and Climate Systems, 1(1): 15-26
2010
Lagrangian Modeling of Tidal Bores
Passing Through Bridge Piers
Jing LI, Huaxing LIU and
Soon Keat Tan
Journal of Hydrodynamics, 20(5),
supplement: 513-519
2010
Turbulent velocity profiles: a new law
for narrow channels
Pu J.H., Bonakdari H.,
Lassabatere L., Joannis C. and
Larrarte F.
La Houille Blanche International
Journal, Vol. 3, pp. 65-70
(DOI : 10.1051/lhb/2010036)
2010
Google Earth as a tool in 2-D
hydrodynamic modeling
Nguyen Quang Chien and
Tan Soon Keat
Computers & Geosciences; online
2010
A novel application of a
neuro-computational technique in
event-based rainfall-runoff modeling
Amin Talei, Lloyd H.C. Chua
and Chai Quek
Expert Systems With Applications,
Vol: 37 (2010) 7456-7468
2010
Evaluation of rainfall and discharge
inputs used by Adaptive
Network-based Fuzzy Inference Systems
(ANFIS) in rainfall-runoff modelling
and Tommy S.W. Wong
Journal of Hydrology, Vol: 391
(2010) 248-262
2010
Experimental and numerical study on
flow behavior behind two unequal
circular cylinders in tandem arrangement
Gao Y.-Y., Etienne S.,
Yu D.-Y., Tan S.K., Wang X.K
and Hao Z.
Fluid Dynamics Research, Vol. 42,
doi:10.1088/0169-5983/42/5/055509
2010
RESEARCH CENTRES
b)
Conferences
Title of paper
Gray water treatment in an Urban Area
of Beijing, China
Author name(s)
Zhang D.Q., Tan, S.K. and
Gersberg, R.M.
A case study of silt screen performance
Vu T.T., Tan S.K. and
Doorn-Groen S.
Dong X., Du P.F. and
Zeng S.Y.
Rehabilitating Urban Water System for
the Inner City of Beijing: Status and
Challenges
Modelling of flow in Everglades
National Park, Florida, USA using a
quadtree grid
Tan Soon Keat
Tan Soon Keat
Wang X.K., Hao Z. and
Tan S.K.
Environmental fluid dynamics – jet flow
Wang X.K. and Tan S.K.
Laboratory investigation of hydraulic
performance of silt screen
Vu T.T. and Tan S.K.
Three dimensional Simulation of Bore
Flow using SPH.
Liu, H. and Tan S.K., Li, J.
Experimental studies of vortex structures
in the wake of a cylinder with helical
strakes
Hao Z., Zhou T., Wang X.K.
and Tan S.K.
Flow around a pipeline near a smooth
bed in steady current
Wang X.K., Hao Z. and
Tan S.K.
Flow behaviour behind two side-by-side
circular cylinders with unequal diameters
Gao Y.-Y., Yu D.-Y., Tan S.K.,
Wang X.K. and Hao Z.
Quantification of viable Enterococcus
faecalis in recreational water by propidium
monoazide quantitative PCR
The use of Adaptive Network-based
Fuzzy inference System (ANFIS) in
event-based rainfall-runoff modeling
Velocity profiles for shallow, vegetated
open channel flows
Goh, S.G. and Gin, K.Y.H.
and Chai Quek
Nguyen Hoai Thanh
Three-Dimensional Scour at Submarine
Pipelines in Unidirectional Steady Current
Wu, Y. and Chiew, Y. M.
Effect of Seepage on River Bank Stability
Chiew, Y. M., Narasimhan, N.
and Chu, J.
Lateral dispersion of granular flows down
a rough plane
Cheng Nian Sheng
Date
2010
Proceeding, 9th International
Conference on Hydroinformatics,
Tianjin, China
Proceeding, International
Conference on Fluvial Hydraulics,
Germany
Conference on Scour and Erosion,
7-10 November, San Francisco,
USA, Geotechnical Special
Publication No. 210, ASCE.
Conference on Scour and Erosion,
7-10 November, San Francisco,
USA, Geotechnical Special
Publication No. 210, ASCE.
2010 International Debris Flow
Workshop, Chengdu, China
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
2010
Near field mixing process of multi-port
diffusers: numerical modelling with
quadtree grids
Hydrodynamics of trapezoidal
embankment weirs
Journal title, Vol. no.
Conference on Bioinformatics
and Biomedical Engineering,
Vol. 6 Water Quality &
Public Health – Treatment,
Disposal and Discharge of
Wastewater, Chengdu, China
Proceeding, 19th World Dredging
Congress, Beijing, China
Proceeding, Conference in Urban
Environment Pollution, Boston,
USA
Proceeding, 17th Asian Pacific
Division Congress, International
Association of Hydro-Environment
Engineering and Research,
Auckland, New Zealand
Symposium Environmental
Hydraulics, Athens, Greece
Conference on Hydrodynamics,
Shanghai, China
Shanghai, China
Shanghai, China
Conference on Ocean, Offshore
and Arctic Engineering, Shanghai,
China
China
China
China
Biotechnology Symposium, Italy
17
RESEARCH CENTRES
COLLABORATIONS AND
PARTNERSHIPS
c)
1)
d)
2)
18
Collaboration with universities:
a) Asia Pacific: Ocean University (China), Tsinghua
University (China), Changsha University of Science
and Technology (China), Sichuan University
(China), University of Peradeniya (Sri Lanka),
University of Wollongong (Australia), University
of Western Australia – to initiate projects on water
quality and watershed management.
b) US: San Diego State University – to conduct
experiments on constructed wetland for
pharmaceutical wastewater.
c) UK: University of Bradford, University of
Birmingham – to apply modelling on urban storm
water management.
Projects with local government agencies and
industry:
a) Maritime and Port Authority of Singapore (MPA):
on sediment transport in the presence of silt
screen.
b) Land Transport Innovation Fund (LTIF): on
assessing environmental risk of CNG vehicle.
e)
f)
National Research Fund (NRF): on hydraulics
calculation and environmental assessment of
underwater city structure.
Temasek Defence Systems Institute (TDSI):
on study of integrating flexible dye sensitized
solar cells into flexible sheets for environmental
applications.
National Parks Board (NParks): on developing
a modular bio-retention system for urban storm
water management.
SembCorp Utilities: on studying a virtual brain
system for treatment processes and performance
forecasting of an anaerobic biological treatment
system.
EVENTS, CONFERENCES &
SYMPOSIA
The Centre assisted in the organization of the International
Conference on Vision and Roadmap for R&D Priorities in
Maritime Environment, Technology, Business, Policy and
Security by NTU in June 2010.
RESEARCH CENTRES
Activities of Maritime Research Centre (MRC)
from 2009 to 2010
Maritime Research Centre (MRC) has established itself
successfully as the bridge between the maritime community
and the research community in NTU. MRC has strengthened
the link with the Maritime and Port Authority of Singapore
(MPA) and Economic Development Board (EDB), IE
Singapore, and has established new and strong working
relationship with the American Bureau of Shipping (ABS),
Sembcorp, Keppel and other offshore engineering companies
such as Acergy. The centre is active in outreach activities
and establishes contact with local and regional institutes
and companies.
simulations”. The 5th International Conference on
Asian and Pacific Coasts, Singapore, 14-16 October.
4.
Wang, X.K. and Tan, S.K., 2009. “Experimental
study of flow about a square cylinder placed on a
wall”. Proceedings of the 8th International Symposium
on Particle Image Velocimetry – PIV09, Melbourne,
Victoria, Australia, 25-28 August.
5.
Wang, X.K., Hao, Z. and Tan, S.K., 2009. “Wavelet
Analysis of Flow Images Obtained by PIV (Particle
Image Velocimetry)”. Civil Engineering Research,
Vol. 22, pp. 43-46.
6.
Kurniawan, A. and Ma, G.W., 2009. “Optimization
of ballast plan in launch jacket load-out”. Structural
and Multidisciplinary Optimization, Vol. 38, pp. 267288.
7.
Lie, S.T., Yang, Z.M. and Gho, W.M., 2009. “Validation
of BS7910:2005 Failure Assessment Diagram for
Cracked Square Hollow Section T-, Y- and K-joints”.
International Journal of Pressure Vessels and Piping,
Vol. 86, No. 5, pp. 291-344.
Academic Staff Exchange Programme
(2009-2010)
8.
1.
2.
3.
4.
Lie, S.T. and Yang, Z.M., 2009. “Fracture Assessment
of Damaged Square Hollow Section (SHS) Kjoint Using BS7910:2005”. Engineering Fracture
Mechanics, Vol. 76, No. 9, pp. 1303-1319.
9.
Lie, S.T. and Yang, Z.M., 2009. “Safety Assessment
Procedure for a Cracked Square Hollow Section
(SHS) Y-joint”. International Journal of Advances in
Structural Engineering, Vol. 12, No. 3, pp. 359-372.
New Projects (2009-2010)
1.
Sediment transport in the vicinity of Silt-screen
2.
Development of portable on-site sulphur detection
device for bunker
3.
Development of an innovative gangway for vessel-toplatform operation.
Shanghai Maritime University
Sichuan University
China Ocean University
Shanghai Jiao Tong University
Selected publications (2009-2010)
1.
3.
Jing Li, Soon Keat Tan, Zhenhua Huang and Adi
Kurniawan, 2009. “Wave Amplification and Air-gap
Response under a Multi-column Platform”. Conference
of Coastal Dynamics 2009, Tokyo, Japan, 7-11
September.
Huang, Z.H., Liu, C.R., Kurniawan, A., Tan, S.K.
and Nah, E., 2009. “Responses of a free-floating
rectangular caisson to regular waves: Comparisons of
measurements with time-domain and frequency-domain
11. Lie, S.T. and Zhang, B.F., 2010. “Plastic collapse load
investigation for safety assessment of cracked square
hollow section (SHS) T-, Y- and K-joints”. OMAE
2010, Shanghai, OMAE2010-20324.
12. Low, Y.M. and Grime, A.J., 2010. “Extreme
response analysis of floating structures using coupled
frequency domain analysis”. OMAE 2010, Shanghai,
OMAE2010-20033.
13. Li, F.Z. and Low, Y.M., 2010. “Sensitivity study
of critical parameters influencing the uncertainty of
fatigue damage in steel catenary risers”. OMAE 2010,
Shanghai, OMAE2010-20045.
2.
Kurniawan A., Huang Zhenhua, Li Jing, Liu C.,
Wang X., Hao Z., Tan S.K. and Edwin N., 2009. “A
numerical analysis of the response and air gap Demand
for Semi-submersibles”. Proceedings of the 29th
International Conference on Offshore Mechanics and
Arctic Engineering (OMAE2009), Honolulu, Hawaii,
USA, 31 May-5 June.
10. Lie ,S.T. and Yang, Z.M., 2009. “Static Ultimate
Strength of Cracked Square Hollow Section Y-joint”.
Civil Engineering Research Bulletin, School of Civil
& Environmental Engineering, Nanyang Technological
University, Singapore, pp. 94-96.
19
RESEARCH CENTRES
14. He, J.W. and Low, Y.M., 2010. “Probabilistic
assessment of the clashing between flexible marine
risers”. OMAE 2010, Shanghai, OMAE2010-20046.
15. Wang, X.K., Hao, Z. and Tan, S.K., 2010. “Flow
around a pipeline near a smooth bed in steady current”.
Proceedings of the 29th International Conference on
Ocean, Offshore and Arctic Engineering (OMAE2010),
6-11 June, Shanghai, China, OMAE2010-20749.
Public Seminar on “Regional Environmental Simulator
(RES) and its applications”, 6 February 2009.
2.
Training course: “In-house Training Course for HDB
- Land Reclamation and Coastal Protection Work Design and Analysis”, February-March 2009.
3.
Public Seminar on “Important role of R&D in offshore
EPCI contract”, 27 May 2009, NTU
4.
Public Seminar on “Panama Canal Third-lane Locks
and Access Channel Expansion Program”, 8 June 2009,
NTU
5.
5th International Conference on Asian and Pacific
Coasts (APAC2009), 13-16 October 2009, NTU
(Singapore)
6.
NTU – SJTU International Workshop on R & D in
Civil and Environmental Engineering. 12 October 2009
(Singapore)
19. Chunrong Liu, Zhenhua Huang, Adrian Law Wing
Keung and Nan Geng, 2010. “A Numerical Study of
Wave Energy Converter in the Form of an Oscillating
Water Column Device Based on a Mixed EulerianLagrangian Formation”. Proceedings of the 29th
International Conference on Ocean, Offshore and
Arctic Engineering (OMAE2010), 6-11 June, Shanghai,
China, OMAE2010-21056.
7.
Training Course for BCA - An Introductory Course
on Coastal Engineering, Analysis-Design-Application,
July-August, 2009 (Singapore).
8.
Vision and Roadmap for R&D Priorities in Maritime
Environment, Technology, Business, Policy and
Security, 29-30 April, 2010 Hilton Singapore,
Singapore.
20. Nguyen Quang Chien and Tan Soon Keat, 2010. “Near
field mixing process of multi-port diffusers: numerical
modelling with quadtree grids”. Proceedings of the
International Symposium on Environmental Hydraulics,
Athens (in press)
9.
NTU-SMU International Workshop on Offshore
Engineering, June 2010, Shanghai China.
21. Wang, X.K., Hao, Z. and Tan, S.K., 2010.
“Hydrodynamics of trapezoidal embankment weirs”.
Hydrodynamics (ICHD – 2010), 11-15 October 2010,
Shanghai, China, pp. 386-390.
11. Professional Training Course for HDB on the
Design of Container Bund, October-November, 2010
(Singapore).
17. Gao, Y.-Y., Yu, D.-Y., Tan, S.K., Wang, X.K. and
Hao, Z., 2010. “Flow behaviour behind two sideby-side circular cylinders with unequal diameters”.
Ocean, Offshore and Arctic Engineering (OMAE2010),
18. Huaxing Liu, Soon Keat Tan, Jing Li and Xikun Wang,
2010. “Three dimensional simulation of bore flow
using SPH”. Proceedings of the 29th International
Conference on Offshore Mechanics and Arctic
Engineering (OMAE2010), Shanghai, OMAE 201021090.
Workshops-seminars-conference (2009-2010)
1.
16. Hao, Z., Zhou, T., Wang, X.K. and Tan, S.K., 2010.
“Experimental studies of vortex structures in the wake
of a cylinder with helical strakes”. Proceedings of the
29th International Conference on Ocean, Offshore and
Arctic Engineering (OMAE2010), 6-11 June, Shanghai,
China, OMAE2010-20181.
20
23. Jing LI, Huaxing LIU and Soon Keat Tan, 2010,
Lagrangian modelling of tidal bores passing through
bridge piers, Proceedings of the 9th International
Conference on Hydrodynamics (ICHD – 2010), 11-15
October 2010, Shanghai, China, pp. 513-519.
22. Wang, X.K. and Tan, S.K., 2010. “Environmental
fluid dynamics – jet flow”. Proceedings of the 9th
International Conference on Hydrodynamics (ICHD
– 2010), 11-15 October 2010, Shanghai, China, pp.
1009-1014.
10. In-house Training Course for Marine Contractor, July
2010, Singapore.
12. Training Course for LTA - Interpretation of Geotechnical
Design Parameters to Geotechnical Design Parameters
and Laboratory Testing, November 2009, Singapore.
RESEARCH CENTRES
Activities of Protective Technology Research Centre
(PTRC) from November 2009 to September 2010
OUTREACH PROGRAMMES
moderated strain rates before and beyond damage with
non-linear equation of state properties for strong shock
waves. The model is readily available to all users of the
commercial hydrocode AUTODYN and continuously
supported since the year 2000. Over the last decade it
has found numerous worldwide applications reflected in
publications. They deal with dynamic load cases such
as projectile and shaped charge penetration, contact
detonation, internal and external blast loading.
The outreach programmes provide a platform for knowledge
transfer and they also help PTRC to establish collaborations
with local and foreign agencies in the area of protective
technology and homeland security. There are 5 public
seminars, 1 international conference and 1 workshop
organized by PTRC which are summarized as follows:-
Public Seminars
1.
Large Scale Blast Simulator Based
Explosive Gas Loading Methods for
Structures and Recent Advances in
HIT BRPE Lab, 28 April 2010
Speaker:
Professor Zhang Chunwei, Associate
Professor, School of Civil Engineering,
Harbin Institute of Technology; Visiting
Research Fellow, School of Civil and
Resource Engineering, The University
of Western Australia
PI (Initiator): Associate Professor Ma Guowei
Professor Zhang Chunwei met Associate Professor
Ma Guowei’s UTRE group to share about impact
and blast tests, especially on the large scale blast
simulator based explosive gas loading methods for
structures, as well as the recent advances in Harbin
Institute of Technology Blast Resistance and Protective
Engineering Laboratory.
4.
Title:
Title:
Title:
A Review of Concrete Modeling and
Hydrocode Applications, 11 February
2010
Speaker:
Dr Werner Riedel, Deputy Head of
Department “Safety Tech. and Protective
Structures” at the German Fraunhofer
Society, Ernst-Mach-Institute
PI (Initiator): Professor Fan Sau Cheong
The RHT concrete model was developed at ErnstMach-Institut (EMI) in German 10 years ago. It
combines detailed tri-axial strength descriptions at
Title:
Tunnel Fires and Related Concrete
Technological Issues, 24 June 2010
Speaker:
Dr. – Ing. Frank Dehn, Executive
Director, MFPA Leipzig GmbH, Leipzig
Institute for Materials Research and
Testing
PI (Initiator): Associate Professor Tan Kang Hai
A number of devastating fires in tunnels has put the
subject of concrete spalling back to many research
agendas. The sensitivity of concrete towards spalling
has shown to be responsible for severe damages of
concrete linings inside rock-drilled tunnels and/or
shield driven soft-soil tunnels. Many trial tests - mostly
mechanically unloaded and on lab-scale - have been
conducted in order to discover the mechanisms that
are responsible for this specific “thermo-physicalmechanical-chemical phenomenon”. Up till now, the
mechanisms of spalling are still rather unknown.
Currently used measures, such as an addition of
synthetic fibres, turned out to be most effective in
reducing the spalling and heat ingress to a tolerable
limit so that the structural integrity of concrete tunnel
construction can be still guaranteed. However, to verify
a more realistic material and structural behaviour tests
in full scale - which are (simultaneously) mechanically
2.
Liquefaction of Sand in Plane-Strain,
18 December 2009
Speaker:
Dr. Dariusz Wanatowski, MSc, PhD,
MSEAGS, MASCE, Nottingham Centre
for Geomechanics, University of
Nottingham, United Kingdom
PI (Initiator): Associate Professor Chu Jian
Liquefaction of granular soils is one of the most
rapid and thus one of the most dangerous initiation
mechanisms of landslides. Therefore, it requires the
special attention from civil engineers and researchers.
The majority of experimental studies on static
liquefaction and instability of sand have been carried
out under axisymmetric conditions. However, most
geotechnical structures such as slopes, embankments,
and retaining walls are not axisymmetric problems and
can only be simplified into plane-strain conditions. A
comprehensive experimental study on the liquefaction
of a granular soil under plane-strain conditions is
presented in this talk. Undrained tests on very loose
sand under both plane-strain and axisymmetric
conditions were conducted and compared. Instability
behaviour of very loose sand under drained conditions
is also discussed. Based on the testing data, a unique
relationship between the stress ratio of the instability
line and the state parameter is established to enable the
triaxial results to be used for plane-strain conditions.
The experimental data presented in this talk shed new
light on static liquefaction and instability phenomena of
granular soils, and should be of interest to academics,
researchers, and engineers, or anyone else who may
be interested in experimental soil mechanics.
3.
21
RESEARCH CENTRES
and thermally loaded - are an appropriate measure.
Such an approach has been successfully used for
several tunnel projects all over Europe (Sweden, The
Netherlands, Belgium, Germany and Spain) and in
Oceania (Australia).
The speaker shared with the participants the gained
experiences out of these tunnel projects, gave some
remarks concerning concrete mix design, mode of
testing, interpretation of test results and concluded
with recommendations for the construction of - more
or less - fire proof concrete tunnels.
UTRE seminars are one of the regular research
activities of the programme. Research progress of the
UTRE programme is reviewed on a half-yearly basis
during the seminars. During this seminar, discussions
and information on the development of different
projects were exchanged.
Project
Speaker
Topic
A1
Mr Fan Lifeng
Rock dynamic testing
B3
Ms An Xinmei
Development on 2D
numerical manifold method
(NMM)
A2
Mr Muley Pravin
Sudhakar
Continuous structural health
monitoring system-BOTDR
B1
Mr Bao Huirong
Implementation of coupled
FEM and DDA approach in
rock modelling
C
Associate Professor
Tor Yam Khoon
The Digital Rock
Engineering System based
on 3DGIS Technology
D
Associate Professor
Tan Kang Hai
Survival condition in
underground fire
Conference
Seminar on Tunnel Fires and Related Concrete Technological
Issues (Associate Professor Tan Kang Hai presenting a token
of appreciation to Dr.-Ing. Frank Dehn.)
5.
22
Title:
Underground Technology & Rock
Engineering (UTRE) Phase II
Programme, 9 July 2010
PI (Initiator): Associate Professor Zhao Zhiye
The UTRE is a joint R&D programme between DSTA
and PTRC. Phase II of UTRE is a continuation of
the first five-year research efforts contributing to 4
research areas related to underground technology and
rock engineering. Phase II has a duration of 4 years
from 2009 to 2013. There are 8 research projects with
9 faculty members focusing in different areas.
A1: Protection of Underground Structure
A2: Development of a continuous and distributed
monitoring system for underground applications
A3: Risk assessment and management system for
underground rock cavern projects
B1: DDA modelling and advanced analysis and design
system
B2: Probabilistic stability assessment of rock
caverns
B3: 2D/3D manifold method modelling for jointed
rock mass
C: GIS-based digital rock engineering
D: Tunnel fire safety assessment and evacuation
tool
The Third International Conference on Design and
Analysis of Protective Structures in 2010 (DAPS2010),
10 – 12 May 2010
PTRC and DSTA have jointly organized the Third
International Conference on Design and Analysis of
Protective Structures (DAPS) 2010. The DAPS Conference
has been well received with a total attendance of around
280 delegates with 34 foreign delegates representing 18
various countries (as compared to 150 in DAPS 2003 and
250 in DAPS 2006). In total, 43 technical papers were
presented during the 3-day conference at Novotel Clarke
Quay Singapore. Mr Quek Tong Boon, Chief Defence
Scientist and Chief Research & Technology Officer from
the Ministry of Defence, Singapore delivered the opening
keynote speech as the Guest of Honour, while Mr Soh Koh
Pheng (CE DSTA) hosted the conference dinner.
The conference was jointly organised by Associate Professor
Tan Kang Hai from PTRC side, and Mr Chua Hian Koon
from DSTA side.
The other 4 keynote addresses were presented by Professor
Ted Krauthammer (University of Florida, USA), Professor
Magnus Langseth (Norwegian University of Science and
Technology, Norway), Professor Pan Tso-Chien (Dean,
College of Engineering & Director, PTRC, NTU) and
Associate Professor Tan Kang Hai (Deputy Director,
PTRC, NTU).
RESEARCH CENTRES
Visit by Dr Lim Chee Onn, NTU Board of
Trustees, Chairman of Singbridge International
Singapore Pte Ltd, 24 May 2010
Third International Conference on Design and Analysis of
Protective Structures (DAPS) 2010
(Mr Quek Tong Boon, Chief Defence Scientist and Chief
Research & Technology Officer from the Ministry of Defence,
Singapore delivering the Opening Keynote Speech
as the Guest of Honour.)
Visit by Dr Lim Chee Onn
Visit by Delegates from Ministry of Home
Affairs, 29 June 2010
Workshop
Building Infrastructure Protection for Homeland
Security, 13 May 2010
In conjunction with the DAPS2010 Conference, DSTA
and NTU organized a half-day workshop “Building
Infrastructure Protection for Homeland Security” on 13
May 2010 at Novotel Clarke Quay. The workshop brought
together interest groups from the respective Ministries
and government agencies to share experiences and create
better awareness on how Singapore may move forward in
developing national capability in protective technology.
Around 75 delegates attended the workshop.
* The delegation was led by Mr Eric Yap, Senior Director,
Homefront Security Division, MHA.
INTERNATIONAL AND LOCAL
VISITORS
PTRC has received 5 delegations (around 70 visitors) during
the reporting period. The visitors whom we have received
include the following:-
Visit by Delegates from MHA
Visit by Delegates from the MINDEF, 26 April
2010
Visit by Delegates from MINDEF
* The delegation was led by BG(NS) Ravinder Singh,
DS(T), MHQ.
23
RESEARCH CENTRES
On-going Projects
The table below shows the current projects.
No
Project Title
1
Development of Analytical
Tools for Progressive Collapse
due to Terrorist Bombing
Dynamic Properties of
Singapore Soils
Underground Technology and
Rock Engineering (UTRE)
Programme, Phase II
2
3
4
5
6
24
An Integrated Multiple-Hazards
Research Programme for
Resilient Structures
Project 1
Effects of Catenary and
Membrane Actions on the
Collapse Mechanisms of RC
Buildings – Behaviours of
Structural Elements
Project 2
The Influence of Floor Slabs
and Transverse Beams on the
Behaviour of RC Beam-Column
Joints under Loss of Column
Scenarios
Project on Underground Target
Detection using Ground Tremor
Analysis
Prediction of Explosion
Hazards from Earth Covered
Magazines
External
Funds (S$)
Collaborating
Partners
Tan Kang Hai (CEE)
Li Bing (CEE)
Lee Chi King (CEE)
Leong Eng Choon (CEE)
1,260,000
164,800
Defence Science and
Technology Agency
(DSTA)
DSTA
A/Prof Ma Guowei (CEE)
A/Prof Zhao Zhiye (CEE)
A/Prof Yang Yaowen (CEE)
A/Prof Tor Yam Khoon (CEE)
A/Prof Tan Kang Hai (CEE)
A/Prof Chu Jian (CEE)
A/Prof Goh Teck Chee, Anthony
(CEE)
A/Prof Tiong Lee Kong, Robert
(CEE)
Asst/P Wong Ngai Yuen, Louis
(CEE)
Programme Coordinator:
Prof Pan Tso-Chien (CEE)
3,850,000
DSTA
Principal Investigator (s)
A/Prof
A/Prof
A/Prof
A/Prof
DSTA
PIs:
A/Prof Tan Kang Hai (CEE)
A/Prof Lee Chi King (CEE)
732,930
PI:
A/Prof Li Bing (CEE)
523,600
A/Prof Leong Eng Choon (CEE)
271,200
DSTA
1,564,000
DSTA
Prof Fan Sau Cheong (CEE) +
Collaborators from other Schools in
College of Engineering
RESEARCH CENTRES
Residues and Resource Reclamation Centre (R3C)
The Residues and Resource Reclamation Centre (R3C)
was established on 1 May 2009 as a platform for waste
management research, especially on resource recovery and
remediation under the Nanyang Environment and Water
Research Institute (NEWRI) of the Nanyang Technological
University (NTU) in Singapore. The main objective is
on conducting cutting edge research and strengthening
Singapore environmental industry‘s capability in the area
of waste resource management.
Contaminated Site Remediation
Developing solutions and technologies for remediating
contaminated sites (e.g. landfill mining, contaminants
removal from soils and ground water, bio-remediation and
utilisation, etc.)
RESEARCH AREAS
Waste to Materials
Converting wastes into new and useful materials (e.g. plastic
waste into biodegradable PHA polymer, incineration bottom
ash into carbonated ash product for high value usage,
nutrient recovery, high quality compost production, etc.)
MISSIONS
R3 Research and Translation in Singapore
and the region
•
•
•
Waste to Energy
Harnessing energy from urban biomass, sewage sludge,
agricultural residues, micro-algae (e.g. food waste converted
to hydrogen and methane, bio-ethanol produced from
agricultural and horticultural waste, microbial full cell,
etc.)
Acting as a think tank to identify R3 research needs
Cutting edge interdisciplinary research within NEWRI
and NTU
Benchmarking with international leading research
institutes
R3 Resource and Technology Transfer
Centre
•
•
•
Research partner of the R3 industry and the public
sector
Practical application of research outcome
Monitoring and upgrading existing R3 plants
•
•
•
Providing research scholarships for PhD programme
Inviting and working with renowned visiting professors
and scientists
Organising international workshops, symposia and
conferences
Education and Training for R3 Professionals
25
RESEARCH CENTRES
CENTRE ACTIVITIES
•
Site selection for sanitary landfill using GIS
Professor Anil Dikshit
Centre for Environmental Science & Engineering
(CESE) Indian Institute of Technology Bombay, Powai
Mumbai 400076 India
25 Jun 2010
•
Minimizing environmental impacts of a petroleum
refinery: LCA approach
(CESE) Indian Institute of Technology Bombay, Powai
Mumbai 400076 India
2 July 2010
•
Recycling science
Dr Peter Rem
Separation Technology Materials & Environment Delft
University of Technology The Netherlands
13 July 2010
•
Planning, design and implementation of a solid
waste managment plan for an urban area
(CESE) Indian Institute of Technology
Bombay, Powai Mumbai 400076 India
2 July 2010
Seminars
•
•
26
Rehabilitation and remediation of NeiHu landfill
in Taipei city
Professor Cheng Sheng-Shung
National Cheng Kung University (NCKU) Taiwan
24 Jun 2009
Issues, challenges, and opportunities for municipal
solid waste management in Shanghai;
Application of aged refuse from landfill mining for
leachate and feedlot wastewater treatment;
Biogas production from food waste and cassava
stillage
Assoc Professor NIU Dongjie
UNEP-TONGJI Institute of Environment for
Sustainable Development (UNEP-IESD)
Tonggji University, Shanghai, China
8 and 15 Jan 2010
•
Greenhouse gas and carbon quantification of algal
biodiesel
Dr Tom Beer
Transport Technologies and Sustainable Fuels Energy
Transformed Flagship, CSIRO Australia
1 Apr 2010
•
Production of biofuels and biochemicals from
renewable resources
Dr Wu Jinchuan
Institute of Chemical and Engineering Sciences
Singapore
9 Apr 2010
•
Sustainable and CO2-free bioenergy production
system using lignocellulosic and microalgal
feedstock
Dr Jo-Shu Chang
Centre for Bioscience and Biotechnology,
Department of Chemical Engineering,
National Cheng Kung University, Taiwan
26 May 2010
•
Use of molecular tools for quantifying slowly
growing microbial biomass in environmental bioprocesses
Dr Seokhwan Hwang
School of Environmental Science & Engineering,
Pohang University of Science and Technology
(POSTECH) South Korea
16 Jun 2010
•
Arsenic decontamination of groundwater
( C E S E ) I n d i a n I n s t i t u t e o f Te c h n o l o g y
B o m b a y, P o w a i M u m b a i 4 0 0 0 7 6 I n d i a
18 Jun 2010
Colloquium
•
Joint colloquium with National Cheng Kung
University (NCKU) of Taiwan
16 August 2010
A delegate of 6 members consisting of professors
and researchers visited R3C and shared their research
interests and findings with R3C researchers.
RESEARCH CENTRES
Workshop
News Updates
•
•
R3C official launch
5 October 2009
•
R3C awarded NRF’s competitive research
programme (CRP) Grant
28 January 2010
•
R3C awarded Environment Technology and
Research Programme (ETRP) Grant
8 February 2010
•
For more information, please refer to:
http://www.ntu.edu.sg/r3c
Joint ETO/R3C workshop on urban waste
management
14 September 2010
It was jointly organized by R3C and Environment
Technology Office, National Environment Agency
(ETO, NEA). Eighty participants from government
agencies, industries and research institutes attended
this workshop. This workshop successfully provided
a platform for industries, government agencies, and
research institutes to exchange ideas and eventually
delineated a waste management research road map
for Singapore.
27
ENVIRONMENTAL AND WATER RESOURCES ENGINEERING
A LABORATORY STUDY OF
WAVE-INDUCED SETUP OVER CORAL
REEFS WITH AN IDEALIZED RIDGE
Yu Yao (yaoyu@pmail.ntu.edu.sg)
Zhenhua Huang (zhhuang@ntu.edu.sg)
Edmond Lo Yat-Man (cymlo@ntu.edu.sg)
S.G. Monismith (monismith@stanford.edu)
ABSTRACT: We report a laboratory study of wave-induced setup over an idealized coral reef that includes a ridge at the seaward
edge -- a geometrical feature commonly found in nature. To understand the role of the ridge in wave-transformation mechanism and
wave-induced setup over the reef, laboratory experiments on a range of water depths and wave conditions were carried out. The focus
of this study is a comparison of wave-induced set-ups obtained with and without the idealized rectangular ridges.
INTRODUCTION
The wave-induced setup due to wave breaking is one
of the important factors to consider in determining both
water level and mass transport above a reef-top, which
has ecological as well as engineering significance. It has
been observed that a ridge (reef crest) may be present at
the reef edge (Gourlay 1996b, Hench et al. 2008). When
a ridge exists, the strong nonlinear wave-ridge interactions
make the problem much more complicated for analytical
analysis. Therefore, a series of experiments were carried
out in a wave flume with idealized reef-ridge models being
installed at the reef edge to simulate fringing reefs with
rectangle ridges. Based on our experiments, we will discuss
wave breaking mechanics, the variation of wave-induced
setup, etc.. The comparison between the results with and
without ridge models is made to highlight the effects of
the ridge on the wave dynamics over coral reefs.
INSTRUMENT AND EXPERIMENTAL
SETTINGS
28
The laboratory experiments were conducted in a glasswalled wave flume with 36m long, 0.55m wide and
0.60m deep, which is located in the Hydraulic Modeling
Laboratory at Nanyang Technological University, Singapore.
A piston type wave-maker was placed at one end of the
flume to generate the designed waves. At the other end, a
beach with a mild slope was covered with porous material
to reduce wave reflections. To construct an idealized 2D
fringing reef model, a plane slope of approximate 1:6 was
built with PVC plates at the mid-section 16.35m from the
wave-maker and joined with a horizontal platform which
was 0.35m above the flume bottom. The horizontal platform
was 7m long with its width matching the inner width of
the flume. A rectangular box 55cm long, 50cm wide and
5cm high was placed at the edge of the platform to model
a ridge. Over the reef profile, a total of twelve wave gages
were used to measure the water surface elevations. The
detailed arrangement is shown in Figure 1. The wave
gages have an accuracy of 0.1mm. All the wave gauges
were sampled at 50Hz by a personal computer through a
data acquisition system.
The design regular and irregular incident wave conditions
were selected from a combination of wave heights, wave
periods and water depths (see Table 1 for details). The
irregular waves were generated according to JONSWAP
spectra with peak enhancement factor γ = 3.3. During
the experiments, each wave condition was repeated three
times to check the repeatability. After the wave-maker
was started, a steady wave condition was assured before
starting data acquisition. Between two subsequent tests,
several minutes were allowed to elapse so that the water
surface could become calm and the effects of residual
currents were minimal.
Table 1. Test wave conditions
Type
Range
Without ridge
With ridge
Water level (m)
0.35,0.4,0.45
0.4,0.42,0.45
Offshore regular wave height: (m)
0.046-0.131
0.035-0.135
Offshore regular wave period: (s)
0.83-1.67
0.83-1.67
Offshore significant wave height: (m)
0.033-0.091
0.032-0.087
Offshore peak wave period (s):
1.00-1.67
1.00-1.67
Figure 1. Sketch of the experimental arrangement
RESULTS
Wave Transformation over Reef Crest and Wave
Reflection
Videos of the wave breaking area were taken after the wave
field had reached a steady state. Plunging breakers were
observed in most of experiments; spilling breakers were
also observed in some of the experiments with water depth
h=0.45m. The breaking point moves from the fore-reef
slope onto the reef-top as water depth increases. Figure 2
shows the representative features of wave transformation
and breaking over the reef crest in the presence /absence
of the ridge for incident regular waves of deep water wave
height Ho=0.095m and wave period T=1.25s in water of
depth h=0.45m. Four different phases are shown in Figure
2, starting from the moment when the lip of breaker hit the
water surface (t/T=0). For the reef without ridge, waves
plunged on the reef flat at t/T=0, while at t/T=1/4, the
splash-up jet due to plunging breaker hit the water ahead
of it, producing an air-water mixture of foam, bubbles and
some subsequent white-capping. After one half wave period
(t/T=1/2), the broken waves propagated across the surf-zone
in the form of fully turbulent bores with a turbulent roller in
the front. For the last phase (t/T=3/4), the bore was mostly
dissipated and a transmitted wave was reformed on the reef
flat. A strong reverse flow could be observed during this
period before the next incoming wave arrived.
Reflection coefficients for regular waves, which were
determined using a two-probe method (Goda 2000), ranged
from 2% to 25% in the absence of the ridge and from 6%
to 55% in the presence of the ridge. For irregular waves,
reflection coefficients ranged from 9% to 37% in the absence
of the ridge and from 20% to 66 % in the presence of
the ridge. Irregular waves have larger values of reflection
coefficients than comparable regular waves because the low
Figure 2. Snapshots of regular wave transformation over reef
crest at difference phases (Ho=0.095m,T=1.25s,h=0.45m).
Mean Water Level (MWL) across the Reef platform
Twelve wave gages (G1 to G12) were used in our
experiments, enabling us to construct reasonably detailed
setup/set-down profiles across the reef models by a linear
interpolation. Two cases representing regular and irregular
wave conditions are illustrated in Figure 3. As we may
expect, for both types of waves, set-down occurred for
gages located at the seaward side of the surf-zone. Within
the surf-zone, there is a monotonic increase of MWL (setup)
due to the wave attenuation through wave breaking. The
maximum setup always appears at G9; after that point, the
setup first decreases slightly and then become more or less
constant. Under the same wave condition, the magnitude of
the setup measured in the presence of ridge is significantly
larger than that seen in the absence of the ridge. Moreover,
the ridge also caused the lowest point of MWL and the
point where the waves broke to shift seaward.
When a ridge was present at the reef crest, the breaking
point shifted seaward, the breaking waves strike the front
side or the edge of the ridge, and then plunged onto the
ridge-top, resulting in stronger wave reflections and air
entrainment. However, the whole transformation process
is otherwise identical to the reef without ridge.
frequency portion of wave spectra reflects more efficiently.
The effects of the ridge on the wave reflection are more
evident for waves of small wave slope. The enhanced wave
reflection is expected since the ridge structure functions like
a submerged breakwater, which is widely used to reflect
the wave energy (Yao et al. 2009).
29
Under similar wave conditions, the ridge causes a noticeable
increase in the wave setup on the reef-top, particularly
for the cases of longer wave periods. In some cases, the
wave-induced setup is as much as doubled by the ridge.
The wave-induced setup on the reef flat increases almost
linearly with increasing Ho for all cases with and without
a ridge. The relationship between and T is less obvious.
However, by comparing the setup with similar Ho, it is found
that in general increases with increasing T, which agrees
with the observations of Gourlay (1996a). Meanwhile,
the setups for regular waves (Figures 4(a) and 4(b)) are
remarkably larger than those for irregular waves (Figures
4(c) and 4(d)) if we use the offshore significant wave
height (Hso) instead of Ho and offshore peak wave period
(Tp) instead of T to characterize spectral waves.
Figure 3. Mean water level (MWL) offshore and across the
reef profile under different wave conditions: (a) regular waves;
(b) irregular waves. Open circles denote the locations of wave
gages, dash lines indicate reef profile without ridge, and
solid lines indicate reef profile with ridge.
Wave Setup as a Function of Offshore Wave Height
The above analysis shows that the MWL always reaches
maximum around G9 on the reef platform; thus, the setup at
G9 is a good measure of the maximum setup ( ). Figure 4
shows this wave-induced setup as a function of deep water
wave height (Ho), for different wave periods (T) and two
water depths of h=0.40m and 0.45m. The cases with and
without a ridge are also compared in the figure.
CONCLUSIONS
A series of experiments have been carried out to study the
effects of idealized ridge on the wave-induced setup over
a two dimensional horizontal, impermeable reef-top. It is
found that the behaviors of the wave transformation in the
presence of a ridge are significantly different from those
in the absence of the ridge. In particular, the location of
the breaker point can be moved toward deep water side
and the reflection coefficients of the reef model were
dramatically increased. Furthermore, the ridge near the
reef edge causes a considerable increase in the setup over
the reef platform under both regular and irregular wave
conditions. Finally, it is found that the wave-induced setup
increases with increasing deep-water wave height and wave
period. Analytical and numerical studies will be carried out
to further analyze our experimental data.
REFERENCES
[1] Goda, Y., 2000. “Techniques of Irregular Wave Analysis in
Random Seas and Design of Maritime Structures”. World Sci.
Press, Singapore.
30
Figure 4. Maximum wave setup on reef flat as a function of
deep water wave height for different wave periods, still water
depths, and incident wave conditions. Open markers indicate
reef profile without ridge, and solid markers indicate
reef profile with ridge.
[2] Gourlay, M.R., 1996a. “Wave set-up on coral reefs. 1.
Set-up and wave –generated flow on an idealized two
dimensional reef”. Journal of Coastal Engineering,
27:161-193.
[3] Gourlay, M.R., 1996b. “Wave set-up on coral reefs. 2.
Wave set-up on reefs with various profiles”. Journal of
Coastal Engineering, 28: 17-55.
[4] Hench, J.L., Leichter, J.J. and Monismith, S.G.,
2008. “Episodic circulation and exchange in a wavedriven coral reef and lagoon system”. Limnology and
Oceanography, 53(6): 2681-2694.
[5] Yao, Y., Lo, E.Y.M., Huang, Z.H. and Monismith, S.G.,
2009. “An Experimental Study of Wave-induced Set-up
over a Horizontal Reef with an Idealized Ridge” paper
presented at 28th International Conference on Offshore
Mechanics and Artic Engineering, ASME, Hawaii,
USA.
ADOPTION AND ACCEPTANCE OF
CNG VEHICLES ON THE URBAN
ENVIRONMENT
Isaac Sadikin (isadikin@ntu.edu.sg)
Lie Seng Tjhen (cstlie@ntu.edu.sg)
ABSTRACT: This study addressed the issue of society perception of CNG as an alternative fuel in a motor-vehicle. The impact of the
adoption of CNG includes environmental impact with respects to fueling station (risk of leakage, stock-pile, increased traffic emission
and noise), incidents of leakages, sudden explosion. The deliverables of the study includes the appropriate measure to address citizens’
concern of close vicinity to stock-pile of CNG in the residential neighborhood, sudden release of CNG to the environment and risk, and
suggested appropriate counter measures.
INTRODUCTION
CNG is an alternative fuel for motor-vehicles besides
using conventional fuel such as petrol, diesel and LPG.
This alternative fuel had been implemented worldwide
for the cars, truck, school buses, and trains. The study on
the environmental impact, incidents and sudden explosion
of CNG cylinder and refueling station will be discussed
in this article.
CNG PROPERTIES & EMISSIONS
CNG or compressed natural gas is a domestically available,
economical, clean burning, alternative fuel source for
vehicles. Rather than burn gasoline or diesel fuel, a
consumer would fuel their vehicle with natural gas. In
order to provide enough range, the gas is compressed and
stored on the vehicle in pressurized tanks. CNG tanks can
hold up to 3,600 psi. The fact is that natural gas is a much
safer fuel than gasoline.
The number of CNG vehicles and refueling stations
are growing from year to year even as ongoing efforts
Table 1. Adoption of CNG in world wide as of 2008
CNG (as of 2008)
Country
Number of Vehicles
Refueling
Stations
Argentina &
Brazil
> 3 million
3352
US
110,000
1,100
Colombia
257,468
378
Egypt
63,000
95
Iran
1.3 million
750
Italy
The 4th country in the world
for number of CNG-powered
vehicles
800
Sweden
14,500
90
Singapore
5000
5
INCIDENT
There are a few incidents occurred in several countries
due to cylinder ruptures, tank fires or fire exposure, illegal
use of the cylinder. Most of the incidents did not result in
human casualties.
In Singapore, there is only one incident to date which
occurred on a bus in August 2010. The investigation of
the incident is ongoing (see Figure 1 for a media report
of the incident).
SAFETY & RISK
Consequence analysis was done by considering accident
locations and computing the physiological damage and
lethality effects of heat fluxes generated from fires. The
CNG also produces significantly lesser emissions of
pollutants such as carbon dioxide (CO2), hydrocarbons
(UHC), carbon monoxide (CO), nitrogen oxides (NOx),
sulfur oxides (SOx) and particulate matter (PM), as compared
to petrol. For example, an engine running on petrol for 100
km emits 22,000 grams of CO2, while covering the same
distance on CNG emits only 16,275 grams of CO2. The
corresponding figures are 78 and 25.8 grams respectively,
for nitrogen oxides. Carbon monoxide emissions are
reduced even further. Due to lower carbon dioxide and
nitrogen oxides emissions, switching to CNG can help
mitigate greenhouse gas emissions. The ability of CNG to
reduce greenhouse gas emissions over the entire fuel life
cycles will depend on the source of the natural gas and
the fuel it is replacing.
in minimizing pollution from the transportation sector
intensifies.
31
total risk was determined by summing the risk associated
with each fire/accident scenario.
The projected fatality resulting from an unconstrained fire
is 2.2E-5/bus/year. For the 8500 CNG buses in operation
in year 2001 in the United States, this would translate to
approximately 0.19 deaths/year or a mean time to occurrence
of a fatality of 5.4 years/fatality.
If all of the present school buses in the United States are
converted to CNG type, then the projected mean fatality
would be 9.9/year or a mean time to occurrence of a
fire related fatality of 1.2 months/fatality. Accordingly,
catastrophic bus-related failure event leading to a fire is
certainly a major safety issue in CNG powered buses. The
table below summarizes major results of this study.
Comparing the estimated results for CNG buses with those
of historical diesel school experience, one may conclude
that CNG buses are on the average 2.5 times more prone to
fire fatality risk than diesel buses. While these comparative
values are based on best estimate averages, the worst
case fire scenarios for CNG buses are expected to lead to
higher fatalities as compared to worst case fire scenarios
of diesel buses.
32
The Straits Times, Saturday, 14 August 2010
Figure 1. First CNG Accident in Singapore.
used to describe how the material was dispersed to some
concentration levels. Then, fire and explosion models
converted the source model information on the release into
hazard potentials such as thermal radiation and explosion
overpressures [2, 3, 4]. All of the mentioned steps were
modeled using PHAST 6.5 software package developed by
DNV. Finally, effect models converted results obtained by
software into effects on people represented by probability
of death. Probit equations are commonly used to quantify
the expected rate of fatalities for the exposed population.
Finally, risks of non-fatal fire scenarios (those primarily
leading to injuries) should also be estimated.
All of the selected scenarios had been investigated in two
different atmospheric conditions corresponding to day and
night as detailed in Table 2.
CASE STUDY IN IRAN – RISK ASSESSMENT
OF SITING THE CNG REFUELLING STATION
(Sharif University of Technology)
Table 2. Atmospheric conditions responding to day and night
Sharif University of Technology has been conducting the
study of the application of quantitative risk assessment
(QRA) on the sitting of compressed natural gas (CNG)
stations and determining nearby land use limitations [1].
The most important consideration is to be assured that the
proposed site would not be incompatible with existing land
uses in the vicinity. It is possible by the categorization
of the estimated levels of individual risk (IR) which the
proposed site would impose upon them. An analysis of the
consequences and likelihood of credible accident scenarios
coupled with acceptable risk criteria is then undertaken.
The study would determine the safe distance from CNG
station borders and how dense the population of the
proposed/existing CNG station.
Typical incidents are identified into a few class of risk
happening at the CNG station. In Tehran (Iran), they chose
one of the largest CNG stations as their case study to obtain
required information. Low frequency and low consequence
scenarios were determined to identify the risk estimation.
Once the scenario was defined, source models were selected
to describe how materials are discharged. The source model
provides a description of the discharge rate and the total
quantity discharged. A dispersion model was subsequently
Parameters
Day
Night
Wind velocity (m/s)
2.5
2.1
Atmospheric stability
A
D
Ambient temperature (oC)
27
3
35%
70%
Humidity
Frequency estimation
Frequency estimation is the methodology used to estimate
the number of occurrences of a scenario through a year.
Estimates may be obtained from historical incident data on
failure frequencies or from failure sequence models, such
as FTA [5]. Depending on scenario type both techniques
were used to estimate scenario frequencies as listed in
Table 3.
Table 3. Estimated frequencies of credible scenarios
Scenario
No.
01
Scenario description
Rupture in dryer pipeline
Estimated
Frequency
7.5E-5
02, 03
5mm and 25 mm hole
diameter in cylinders
3.8E-5 and 1.0E-7
04, 05
5mm hole diameter and
rupture in dispenser pipes
0.8E-2 and 1.7E-2
Risk estimation
One popular measure to risk monitoring is IR usually shown
on a risk contour plot. The IR is defined as the probability
of death at any particular location due to all undesired
events. The following figure presents the IR contours of
the selected CNG station.
In our present case study, sensitive locations such as
houses, recreational places and high traffic roads are
located exactly adjacent to CNG station borders which
are absolutely advised against and these areas must be out
of the Outer zone characterizing by more than 82 m as
a safe distance. Shopping places are also located in close
CNG station neighborhood which are advised against too
and they must be out of the Middle zone characterized by
more than 30m as a safe distance.
There are such calculated distances between CNG station
and general acceptable risk borders that usually are not
followed (e.g. present case study), these distances usually
are not intended more important in comparison with other
aspects to determine proper distances such as site area
value and accessibility for vehicles.
IR contonurs for selected CNG Station
Figure 2. IR Contours for selected CNG Station.
Table 4. Safe and real distances from CNG station
borders for each zone
Safe distance from
station border (m)
Real distance from
station border (m)
Inner zone (18)
-*
Middle zone (30)
12
Outer zone (82)
0
*No industrial development is available.
CONCLUSIONS & RECOMMENDATIONS
(a) Regular check on the both CNG vehicle and refueling
station must be carried out to meet the standard as
stipulated by the National Fire Protection Association
or NFPA.
(b) Training on the mitigation measure to deal with
explosion due to CNG tank or refueling station must
be conducted. In Singapore, Singapore Civil Defense
Force (SCDF) issues the regulations and mitigation
measures in the contingency of accident related to
flammable materials under the Fire Safety Act Chapter
109A.
(c) Different type or material of cylinder of CNG will
affect the safety of the incident rate. The latest material
used for the CNG tank (Type 4) and the safest to date
is fiber glass hence the cost is expensive.
(d) CNG can help to reduce the reduce greenhouse
gas emissions compare to normal fuel engine system
or diesel.
When considering proposals to site a process industry or
any development in its neighborhood, four general categories
of development are distinguished: industrial, shopping,
housing and sensitive. Within the Inner zone (where the
IR is greater than 1.0E-5 yr-1) UK HSE normally advises
against all developments other than small or moderate
industrial developments and limited numbers of other
small developments. Within the Outer zone (where the
IR is between 1.0E-6 yr-1 and 3.0E-7 yr-1) only sensitive
developments are advised against. Across the Middle zone
(1.0E-5 yr-1 to 1.0E-6 yr-1) and where developments
straddle zone boundaries, each development proposal is
considered on its own merits [6, 7]. By comparing these
general criteria with numerical results extracted from
Figure 2, safe distances from CNG station borders can be
determined for each zone as shown in Table 4.
Obtained results obviously introduce many limitations to site
CNG station toward following all acceptable risk criteria
for all construction developments, these limitations show
that a large number of parameters should be considered
to select optimal site for a CNG station in a populated
city. This undesirable outcome is almost always present;
to ignore these criteria means imposing unacceptable
risk on people living and working in the neighborhood.
The number of CNG stations and their close vicinity to
populated areas, residential and office buildings and other
reasons, especially in Iran, prove that enough studies have
not been done in this field. Although CNG stations have
an important role to play in the country’s economy and
environment, they are hazardous sources; the risks posed
by CNG stations are poorly evaluated. Further studies on
defining acceptable risk evaluation criteria for different
societies are necessary.
33
(e) Choosing the site for CNG station needs to consider all
the risk criteria to minimize the undesirable outcome.
The considerations to site the CNG station to the close
vicinity are populated areas, residential and office
buildings. These are highly populated areas where the
mortal risk is very high.
REFERENCES
[1] Badri, N., Nourai, F. and Rashtchian, D., 2009. “Quantitative
Risk Assessment to Site CNG Refueling stations”. Sharif
University of Technology, Iran.
[2] CCPS, 2000. “Guidelines for Chemical Process Quantitative
Risk Analysis”. 2nd Edition, AIChE, New York, USA.
34
[3] CCPS, 2003. “Guidelines for Facility Sitting and Layout”.
AICHE, New York, USA.
[4] CCPS, 2007. “Guidelines for Hazard Evaluation Procedures”.
3rd Edition, AIChE, New York, USA.
[5] Harvard Paper Quoted by International at Left, 2003, National
Highway Traffic Safety Administration (DOT) FARS Data
Run for Natural Gas Vehicle Coalition in 2003, USA.
[6] Rosli, A.B., Mohamad F.O. and Semin, A.R.I., 2008. “The
Compressed Natural Gas (CNG) Cylinder Pressure Storage
Technology” in Natural Gas Vehicles (NGV) Research Trends,
USA.
[7] SAE Paper 2001-01-1343, 2001, “Well-To-Wheel Energy
Use and Greenhouse Gas Emissions for Various Vehicle
Technologies”. J.J.J. Louis, Shell Global Solutions, USA.
ADSORPTION THERMODYNAMICS
OF ANTIBIOTICS BY GAC
Shen Liang (shen0042@e.ntu.edu.sg)
Liu Yu (cyliu@ntu.edu.sg)
ABSTRACT: This study investigates the adsorption thermodynamics of three representative β-lactam antibiotics (penicillin G, PCG;
ampicillin, AMP and cephalosporin C, CPC) by GAC. A series of adsorption experiments were carried out at different temperatures.
Results showed that GAC has a substantial adsorptive capacity for the antibiotics studied. Negative ∆G° value suggests that the antibiotic
adsorption by GAC would be spontaneous. ∆H° was estimated as 64.8, 64.4 and 60.3 kJ/mol for PCG, AMP and CPC, respectively,
indicating that the adsorption of three antibiotics by GAC would be endothermic and chemisorption-predominant. FTIR spectra of
antibiotic-loaded GAC further confirmed that antibiotics were adsorbed by GAC through chemical bindings.
INTRODUCTION
Nowadays, antibiotics have emerged in various water bodies
due to their expanding production and application in the
world. Antibiotic resistance would thereafter evolve and
spread in ecosystem, which poses a serious risk for human
health (Kümmerer 2004). Adsorption has been shown to
be effective in removing various soluble organics from
water. Therefore, this study investigates the adsorption
thermodynamics of antibiotic adsorption by granular
activated carbon (GAC).
MATERIALS AND METHODS
RESULTS AND DISCUSSION
Adsorption isotherm
In this study, the equilibrium data were fitted to the following
isotherm equations,
qe = qm
KLCe
KLCe + 1
… (1)
Freundlich isotherm:
qe = KFC1/n
e
… (2)
in which KL is the Langmuir equilibrium constant (L/mg);
qe and qm are the equilibrium and maximum adsorption
capacity, respectively (mg/g); KF is the Freundlich constant;
and n is the heterogeneity factor. Table 1 shows that the
Langmuir isotherm can provide a better description for
adsorption data of PCG, AMP and CPC than the Freundlich
isotherm at all the temperatures studied. The values of
qm from the Langmuir isotherm indicate that GAC has a
substantial adsorption capacity for three β-lactam antibiotics
studied, and the adsorption capacity of antibiotics by GAC
is in the order of PCG>AMP>CPC.
Table 1. Equilibrium constants for the adsorption of
antibiotics by GAC.
Name T/K
Freundlich isotherm
n
Langmuir isotherm
R
qm
KL
R2
PCG 303 261.5 4.44
0.8334
460.2
0.061
0.9711
PCG 308 288.2 4.77
0.7681
485.6
0.081
0.9355
KF
2
PCG 313 309.0 4.93
0.6920
502.7
0.102
0.9856
AMP 298 65.49 2.24
0.9680
164.2
0.023
0.9981
AMP 303 92.32 3.01
0.8777
177.1
0.033
0.9831
AMP 308 100.7 3.16
0.8320
178.0
0.045
0.9205
AMP 313 117.4
3.72
0.8410
179.0
0.082
0.9875
CPC 298 33.07 3.28
0.7851
33.67
0.46
0.8543
CPC 303 53.62 3.64
0.7996
50.90
0.49
0.9584
CPC 308 59.14 3.86
0.8460
63.20
0.75
0.9929
CPC 313 67.46 4.03
0.9032
71.9
1.46
0.9879
GAC from Calgon Carbon Corporation, USA, was used
as the adsorbent with a mean size of 2.8 mm, an apparent
density of 450 kg/m3 and a particle density of 650 kg/m3.
The GAC was carefully rinsed with distilled water and
dried at 103ºC overnight before use. Three representative
β-lactam antibiotics, namely penicillin G (PCG), ampicillin
(AMP) and cephalosporin C (CPC) from Sigma-Aldrich
Pte Ltd, Singapore, were used as the model antibiotics.
Equilibrium experiments were performed with 1.0 to 10.0
grams of GAC in 250 mL of the antibiotic solutions with
various concentrations in a temperature controlled shaking
thermostat (298, 303, 308 and 313K). Concentrations of
antibiotics were determined by high-performance liquid
chromatography (HPLC, Perkin Elmer Series 200, USA)
with a UV detector at 220 nm. Fourier transform infrared
(FTIR) spectra of antibiotic-loaded GAC were obtained
from the BioRad Excalibur Series FTS 3000 spectrometer
(USA).
Langmuir isotherm:
35
The Gibbs free energy indicates the degree of spontaneity
of an adsorption process. The Gibbs free energy change
(∆G°) of adsorption can be determined as follows:
∆G° = -RTlnKL
… (3)
∆G° is also related to the change in entropy, ∆S° and the
heat of adsorption, ∆H° at a given temperature in a way
such that:
∆G° = ∆H° - T∆S°
… (4)
Combining Eqs. 3 and 4 yields,
In KL = – ∆H° + ∆S°
RT
R
… (5)
Thus, ∆H° and ∆S° can be determined from the slope
and the intercept of the linear Van’t Hoff plot, i.e. ln KL
versus 1/T.
The Langmuir equilibrium constants obtained at 298, 303,
308 and 313K were used to calculate ∆G°, ∆H° and ∆S° for
adsorption of PCG, AMP and CPC by GAC, respectively
(Table 2).
Table 2. Thermodynamic parameters for the adsorption
of antibiotics by GAC.
Name
36
∆H°
∆S°
kJ/mol
J/mol K
∆G° (kJ/mol)
298K
303K
308K
313K
PCG
64.8
295.3
-22.8
-25.2
-26.3
-27.3
AMP
64.4
290.8
-22.4
-23.7
-24.9
-26.9
CPC
60.3
301.9
-30.1
-30.8
-32.4
-34.7
Table 2 shows that ∆H° and ∆S° have positive values,
while negative values for and ∆G°. The positive ∆H°
implies that the adsorption of three antibiotics by GAC
is endothermic. In addition, the value of qm in Table
1 increased with the increase in temperature, which
confirms the endothermic nature of the adsorption of three
antibiotics by GAC. Basically, the heat evolved during the
physical adsorption is of the same order of magnitude as
the heat of condensation, i.e., 10 to 20 kJ/mol, whereas
the heat of chemisorption generally falls into the range
of 40 to 400 kJ/mol (Bansal and Goyal 2005). Therefore,
it appears that chemisorption would be the predominant
mechanism of these three antibiotics adsorption by GAC.
The positive ∆S° suggests the increased randomness at the
solid-solution interface with some structural changes in the
adsorbate/adsorbent and antibiotic affinity to GAC. In fact,
the positive ∆S° is often referred to as an increase in the
degree of freedom of the adsorbed species. The negative
∆G° indicates the degree of spontaneity of the adsorption
process, i.e. the higher negative value of ∆G°, the more
energetically favorable adsorption was. It seems that the
three antibiotics adsorption by GAC would be spontaneous
in the nature (Table 2).
The ∆H° for PCG, AMP and CPC suggests that adsorption
of PCG, AMP and CPC by GAC was a chemicaldominant process. However, it should be pointed out that
the thermodynamic mechanisms of adsorption would be
dependent on the chemical structures of various antibiotics.
For example, ∆H° values reported in the adsorption of
7-aminocephalosporanic acid, cephalexin, cefadroxyl and
6-aminopenillanic acid by activated carbon ranged from
17 to 46 kJ/mol (Dutta et al. 1999), implying a physicalchemical mixed mechanism.
FTIR spectrum
The FTIR spectra can be used to identify the functional
groups capable of adsorbing organic compounds. Figure 1
shows the FTIR spectra of GAC before and after adsorption
of antibiotics at 298 K. The common structure of PCG,
AMP and CPC is the four-membered (β) lactam ring fused
to another thiazole ring. Therefore, in FTIR spectra of the
used GAC, the peak at around 1700 cm-1 represents the
C=O stretching vibration of the β-lactam ring; the peak at
around 3480 cm-1 represents the N-H stretching vibration
of the β-lactam ring. Furthermore, the peak at around 650
cm-1 in the spectra of PCG-loaded GAC and AMP-loaded
GAC suggests the C-H bending vibration of the benzene
ring. Meanwhile, this peak did not appear in the spectrum
of CPC-loaded GAC due to the absence of the benzene ring
in the CPC molecular structure. The intermediate portion of
the spectrum of 1300-900 cm-1 is often referred to as the
“fingerprint” region. The absorption pattern in this region
is rather complex because the stretching vibration of all
single bonds and vibration of molecular skeleton would
take place. Compared to the spectrum of virgin GAC,
absorbance in the spectra of the antibiotic-loaded GAC
became more intense, showing adsorption of antibiotics
by GAC through chemical bonds.
3488
d.CPC-loaded GAC
1718
3480
c.AMP-loaded GAC 1718
Absorbance
Thermodynamics of adsorption
659
3476
b.PCG-loaded GAC
1684
647
a. GAC blank
4000
3000
2000
-1
Wavenumber (cm )
1000
Figure 1. FTIR spectra of antibiotic-loaded GAC at 298 K.
CONCLUSIONS
REFERENCES
This study demonstrated that β-lactam antibiotics, such as
PCG, AMP and CPC, can be effectively removed by GAC
adsorption. The equilibrium data can be best described
by the Langmuir isotherm. The positive enthalpy value
indicates the endothermic nature of the adsorption process,
whereas the magnitude of enthalpy suggests that the
adsorption of these antibiotics by GAC was chemisorptionpredominant. The FTIR analysis further confirmed that the
β-lactam ring of these three antibiotics could form the
strong chemical bonds (e.g. C=O and N-H) with GAC’s
functional groups.
[1] Bansal, R.C. and Goyal, M., 2005. Activated Carbon
Adsorption. London: Taylor & Francis.
[2] Dutta, M., Dutta, N.N. and Bhattacharya, K.G., 1999.
“Aqueous phase adsorption of certain beta-lactam antibiotics
onto polymeric resins and activated carbon”. Separation and
Purification Technology, 16(3): 213-224.
[3] Kümmerer, K., 2004. Pharmaceuticals in the environment:
sources, fate, effects and risks. New York: Springer.
37
AN INTERVAL APPROACH FOR
SUPPORTING URBAN WATER
SUPPLY ANALYSIS
X. S. Qin (xsqin@ntu.edu.sg)
Y. Xu (xuye@ntu.edu.sg)
ABSTRACT: An interval-parameter chance-constrained programming (IPSCCP) model is proposed for supporting urban water supply
management under uncertainty. Through incorporating chance-constrained programming (CCP) into an interval linear programming
(ILP) framework, the model effectively deals with uncertainties expressed as not only probability distributions but also as discrete
intervals, and incorporate pre-defined acceptable levels of constraints satisfaction directly into the optimization process. An interactive
two-step sub-modeling method could be used for model solution. The obtained results would be useful for decision makers to gain
an insight into the tradeoffs between environmental and economic objectives and between increased certainties and decreased safeties
(or increased system-failure risks). The study is a new endeavor in advancing an integrated uncertainly-analysis tool for urban water
supply management; the approach could also be applicable to many other water resources management problems.
INTRODUCTION
The shortage of urban water resources has become a major
obstacle for sustainable socio-economic development of
the cities and has aroused much attention over decades.
Integrated Urban Water Supply Management (IUWSM)
focuses on the integrated management of technical aspects
of water services and is effective in relieving the shortage
problems of water resources. However, IUWSM systems
are often complicated with uncertainties. During the past
decades, many inexact optimization techniques were
developed to describe and handle imprecise and uncertain
elements presented in real-world problems. The purpose
of this study is to develop an interval-parameter stochastic
chance-constrained programming (IPSCCP) model and
apply it to IUWSM system under uncertainties.
URBAN WATER SUPPLY SYSTEM
38
In this study, an IUWSM system will be used for
demonstrating the applicability of proposed method. This
case was adapted from a real case provided by Fattahi &
Fayyaz (2010). For many urban areas, it is necessary to
develop effective tools for assisting in urban water service
providers and government agencies to generate rational
water resources management scheme. An integrated IUWSM
system, which incorporated water demand management
and water supply system into a general framework, is
very important for relieving water shortage problems
and realizing balance between water demand and supply.
Figure 1 shows the structure and components of IUWSM
system. The time periods of IUWSM system operation are
considered as one year (it has a time interval of month).
Table 1 shows the related parameters within IUWSM
system, which are assumed as random variables in normal
distributions and interval numbers, respectively.
Figure 1. Urban water supply management system.
Table 1. Parameters related to the water supply system
Information of
water sources
Dam
Well
Information of
treatment plants
Treatment plant 1
Treatment plant 2
Treatment plant 3
Treatment plant 4
Information of
reservoirs
Reservoir 1
Reservoir 2
Reservoir 3
Reservoir 4
Reservoir 5
Reservoir 6
Reservoir 7
Beginning inventory Maximum capacities
(×103 m3)
(×103 m3)
*
[15000, 19000]
(4600, 480) *
[2050, 2950]
(3800, 365)
(×103 m3)
(×103 m3)
[5, 7.5]
(1900, 220)
[10, 13]
(3400, 245)
0
+∞
0
+∞
(×103 m3)
(×103 m3)
[16, 26]
(4500, 420)
[6.5, 13.5]
(720, 60)
[1, 3.5]
(230, 15)
[6.5, 13.5]
(440, 35)
[2, 4.5]
(230, 15)
[22, 38]
(700, 50)
[4, 6.5]
(440, 35)
Note: [a1, a2] * represents an interval number where a1 and a2 are
the lower and upper bounds, respectively; (m1, d1)** represents a
random variable where m1 and d1 are the mean values and standard
deviation, respectively.
MODEL FORMULATION
For the studied urban water supply system, an intervalparameter stochastic chance-constrained programming
model can be formulated as follows (Fattahi & Fayyaz
2010):
…(1)
Subject to:
…(2)
…(3)
…(4)
…(5)
…(6)
…(7)
…(8)
…(9)
…(10)
…(11)
…(12)
…(14)
…(15)
…(16)
The solutions at a number of acceptable probability levels
(i.e. 0.9, 0.95 and 0.99) are obtained through solving the
IPSCCP model. The results indicate that the water supply
patterns based on the demand amounts would be affected
by multiple factors. Firstly, the objective function value and
part of the decision variables from IPSCCP would present
as discrete intervals rather than fixed values. For example,
at a significance level of 0.9, the objective function value
(i.e. total system cost) would range from 38.68 to 74.26
…(13)
where f is the net system cost ($); k (k = 1, 2, …, K)
is the index of time periods and K is number of time
periods; j, t, r and z (j = 1, 2, ..., J; t = 1, 2, …, T; r =
1, 2, …, R; z = 1, 2, …, Z) are indexes of specific water
sources, treatment plants, reservoirs and consuming zones,
respectively; J, T, R and Z are numbers of water sources,
treatment plants, reservoirs and consuming zones; BJjk is the
recovered water for each water resource j in each month k
(×103 m3); CJTjt, CTRtr and CRZrz are the transferred costs
of water in network, from water sources j to treatments t,
treatments t to reservoirs r and reservoirs r to consuming
zone z, respectively ($); Dzk is the amount of water required
for consuming zone z in month k (×103 m3); IROr, ITOt
and IJOj are the inventories of each reservoir r, treatment
t and water resource j at the first of the planning horizon,
respectively (×103 m3); IRrk, ITtk and IJjk are the inventories
of each reservoir r, treatment t and water resource j at
end of each month k, respectively (×103 m3); LXJjt, LXTtr
and LXZrz are the leakage rates of water in network, from
water sources j to treatments t, treatments t to reservoirs
r and reservoirs r to consuming zone z, respectively (%);
MJjk is the maximum amount of water that can be exited
from water sources j at each month k (×103 m3); PRjk is
the purchasing cost of water from water sources j at each
month k ($); qz is the acceptable level of constraintssatisfaction. TL is the allowed maximum leakage amounts
(×103 m3); VRrk and VTtk are the capacities of reservoirs r
and treatment t at each month k (×103 m3); XJTjtk, XTRtrk
and XRZrzk are decision variables, representing the amount
of water transferred from water sources j to treatments
t, from treatments t to reservoirs r and from reservoirs
r to consuming zones z at each month k, respectively
(×103 m3); ZRZrz, ZJTjt and ZTRtr are binary variables (i.e.
expressed as 1 or 0, representing yes or no answers) used
to define paths in the network, respectively. Referring
to the proposed model, the constraints with interval and
random coefficients (i.e. constraints 2, 7, 11 and 14) can
be transformed to their respective crisp equivalent (Charnes
et al. 1972; Huang et al. 1992; Qin et al. 2007). Referring
to the proposed model, the transformed ILP models can be
formulated and solved, such that the objective values and
decision variables expressed as discrete intervals at various
constraints-violation levels can be obtained.
39
(×106) dollars. The lower bound of the objective function
represents an optimal decision scheme with the lowest cost;
correspondingly, the obtained decision variables would reach
their lower bounds. Conversely, the solution corresponding
to the higher bound of system cost is of conservative
consideration. Based on the obtained interval solutions, a
variety of alternatives can be generated through adjusting
within their solution intervals.
Figure 2 indicates that the variations in the acceptable
levels would result in changes of water supply patterns.
For example, in the entire planning period, the total water
amounts transferred from water sources to treatment
plants at significance levels of 0.99, 0.95 and 0.99 would
be [38,287.11, 52,396.04], [38,900.23, 53,224.34] and
[40,050.34, 54,778.08] (×103 m3), respectively. The amounts
from reservoirs to consuming zones are [37,305.83,
48,760.20], [37,895.13, 49,511.91] and [39,000.55,
50,922.00] (×103 m3), respectively. The reason is that, as
the increases of the acceptable levels, the constraints would
become stricter.
40
Figure 3 presents the variation of system cost at various
acceptable levels. Generally, the system cost would increase
as the increase of acceptable levels. For example, at different
significance levels (from 0.90 to 0.99), the system costs are
[38.68, 74.26], [39.19, 75.27] and [40.15, 77.17] (×106 $),
respectively. This is because, as the acceptable level goes
higher, the constraints would become stricter. To compare the
proposed IPSCCP model with other alternatives, a general
SCCP model is formulated for the same problem where
the deterministic parameters are derived by averaging the
upper and lower bounds of intervals from IPSCCP model.
As shown in Figure 2, the total water amounts transferred
from water sources to treatment plants at significance levels
of 0.99, 0.95 and 0.99 would be 44,308.26, 45,013.78
and 46,337.20 (×103 m3), respectively. The amounts from
reservoirs to consuming zones are 42,198.95, 42,858.26 and
44,095.02 (×103 m3), respectively. In reference to Figure
3, the total cost at different significance levels are 70.88,
71.88 and 73.76 (×106 $), respectively. In such a case, the
decision alternative would be restricted to a single solution,
which may limit its application in real-world systems.
Figure 2. Total water amounts transferred in the network.
Figure 3. Comparison of solutions between
IPSCCP and SCCP models.
CONCLUSIONS
An interval-parameter stochastic chance-constrained
programming (IPSCCP) model was proposed for urban
water supply management. IPSCCP could effectively deal
with uncertainties expressed as both discrete intervals and
random variables. It was also capable of incorporating a set
of pre-defined acceptable levels of constraint satisfaction into
optimization process, allowing model solutions to achieve
higher system costs at allowable violation probabilities. The
results indicate that IPSCCP could help decision makers
gain in-depth insights into the trade-offs between increased
system benefits and decreased safeties, and establish rational
water supply patterns under complex uncertainties for
meeting the city’s water demand. The method could also
be applicable to many other environmental problems.
REFERENCES
[1] Charnes, A., Cooper, W.W. and Kirby, P., 1972. “Chance
constrained programming: An extension of statistical method”.
New York: Optimizing Methods in Statistics, Academic
Press.
[2] Fattahi, P. and Fayyaz, S., 2010. “A compromise programming
model to integrated urban water management”. Water
Resources Management, 24: 1211-1227.
[3] Huang, G.H., Baetz B.W. and Patry, G.G., 1992. “A grey linear
programming approach for municipal solid waste management
planning under uncertainty”. Civil Engineering Systems, 9:
319-335.
[4] Qin, X.S., Huang, G.H., Zeng, G.M., Chakma, A. and
Huang, Y.F., 2007. “An interval-parameter fuzzy nonlinear
optimization model for stream water quality management
under uncertainty”. European Journal of Operational Research,
180(3): 1331-1357.
ANAEROBIC HYDROLYSIS OF
PARTICULATES IN SEWAGE
Teo Chee Wee (teoc0044@ntu.edu.sg)
Philip Wong (pcywong@ntu.edu.sg)
ABSTRACT: Anaerobic hydrolysis of particulates presents both a challenge and an opportunity for the treatment of dilute wastewaters such
as sewage. A significant portion of the total chemical oxygen demand of raw sewage is in the form of particulates. These particulates have
to be hydrolyzed prior to assimilation by the anaerobic consortia. Through enhancing hydrolysis kinetics, the overall biotransformation
rate can be increased, chemical energy in the organic solids can be efficiently tapped, and solids accumulation can be better managed.
This study investigates the optimum conditions for anaerobic hydrolysis of particulates in sewage treatment, with a focus on enzyme
augmentation with hydrolases. The operating conditions investigated were pH, temperature and enzymes dosage. Experimental results
showed a higher degree of hydrolysis at pH 5.0 showed higher degree of hydrolysis compared to those at pH 9.0. In addition, control
experiments revealed considerable degradation of enzymes in the batch reactors, which may be attributed to proteolysis of amylases
and autolysis of proteases.
INTRODUCTION
Hydrolysis in anaerobic sewage treatment
One feature of anaerobic digestion in organic waste
stabilization is the concomitant production of energy in the
form of methane and hydrogen gas. This technology can
potentially be exploited to recover valuable energy directly
from raw sewage. In anaerobic digestion, hydrolysis of
suspended solids tends to be rate limiting especially for
substrates with high solids content. This is also the case for
treatment of domestic wastewater (Seghezzo et al., 2005).
Hydrolysis is also vital for the degradation of dissolved
macromolecules and soluble microbial products (SMPs)
that are prevalent in wastewater.
Complex wastewater such as sewage contains carbohydrates,
lipids and proteins. Carbohydrates are known to be
hydrolyzed rapidly to simple sugars (Zeeman & Sanders,
2001). Domestic wastewater typically comprises of 40-60
percent of proteins, 25-50 percent of carbohydrates and 8-12
percent of oil and fats (Asano et al., 2007). Additionally,
urea and some synthetic organic chemicals may also be
present. Proteins are hydrolyzed into amino acids, lipids are
hydrolyzed into long chain fatty acids (LCFAs) and glycerol,
and carbohydrates are hydrolyzed into simple sugars.
Anaerobic hydrolysis of complex substrates can proceed in
a number of ways (Angelidaki et al., 2004). For instance,
the hydrolytic bacteria can secrete exo-enzymes into the
bulk solution to hydrolyze the complex substrate. Hydrolytic
bacteria can also attach itself to the particulate and excrete
exo-enzymes to degrade it. Finally, the hydrolytic bacteria
can adsorb to the particulate surface and utilize their attached
enzymes (ectoenzymes) to initiate hydrolysis.
Enhancing hydrolysis of particulates
Hydrolysis of particulate macromolecules
Hydrolysis is a reaction in which the chemical bonds
in polymers are cleaved by the introduction of water
molecules. H+ ion is added to a fragment of the polymer
whereas OH- ion is added to the other fragment from the
same polymer. From a biochemical perspective, hydrolytic
Several pretreatment techniques had previously been
investigated. Tanaka et al. (1997) studied the effect of
thermochemical pretreatment on the anaerobic digestion
of waste activated sludge. The pretreatment solubilized the
volatile suspended solids (VSS) by 40-50% and increased
methane production by more than 200% relative to the
Domestic wastewater contains approximately 500-800mg/l
of total solids with a suspended solids concentration of
approximately 155-330mg/l (US EPA, 2008). In terms
of chemical oxygen demand (COD), suspended solids
represent up to 85% of the total COD (Tarek et al., 2001).
Hence, hydrolysis of organic solids in sewage represents
an important step in reducing the effluent COD as well
as to improve overall treatment efficiency. Hydrolysis of
organic solids also produces short chain fatty acids that
can be utilized for downstream biological nutrient removal
(Feng et al., 2009).
bacteria produce exo-enzymes which break up polymers
forming short chain dimers and monomers, which are in
turn further degraded by other microbes for catabolism and
anabolism. The polymers have to be hydrolyzed to low
molecular weight monomers (≤ 1000 Dalton) before they
can be assimilated into cells (Burgess et al., 2008).
41
control without pretreatment. Neis et al. (2000) studied
the enhancement of sludge hydrolysis by ultrasonic
pretreatment. The process improved sludge degradation rate
by 30% at a solids residence time (SRT) of 16 days.
Enzymatic hydrolysis as pretreatment of lipids-rich
wastewater using low cost lipase prepared from porcine
pancreas was investigated by Adriano et al. (2006). The
wastewater was hydrolyzed prior to addition into the
bioreactor. Higher COD removal (69-80%) and biogas
production (10-12ml/g COD) compared to the control
without enzymatic pretreatment (COD removal of 40%
and biogas production of 6ml/g COD). Moreover, it was
found that direct addition of enzymes into the bioreactor is
viable and attractive, with high COD removal of 76.4%. The
feasibility of enzymatic hydrolysis was also demonstrated
by others authors (Leal et al., 2006; Rosa et al., 2009;
Lee et al., 2008).
The exogenous enzymes added were liquid enzymes blend
(BioCat Microbials Pte Ltd, USA) containing proteases,
lipases and amylases. The blend was purified in laboratory
using a stirred cell with 10kDa ultrafiltration membrane
disc (Amicon PM 10, Millipore Co., USA) to remove
the low molecular weight propylene glycol before each
experiment.
Erlenmeyer flasks (0.5L) with rubber stoppers were used
as batch reactors. The headspace of the flasks was flushed
with nitrogen gas before sealing with rubber stoppers.
A water bath shaker was used to provide the necessary
temperature and agitation. pHs were adjusted daily with
6N HCl and 6N NaOH.
Hydrolysis of particulates can be enhanced by operating at
the optimal pH and temperature. The rate is higher under
thermophilic condition compared to mesophilic condition.
Within each range, hydrolysis rate proceeds faster at higher
temperatures. In general, the optimum pH is at near neutral
(Rollon, 1999), although Isaacson (1990) pointed out that,
neutral pH commonly operated in anaerobic digesters aims
to maximize the rate of methanogenesis; hydrolysis may
have a different optimum. For example, the optimum pH
of holocellulytic bacteria is species dependent and can
range from 3 to 11. The optimum pH for hydrolysis and
acidification is 5.6-6.0 whereas that for methanogenesis is
6.8-7.2 (Riva, 1992). Therefore it can be inferred that the
optimum pH for hydrolysis varies according to the substrate
composition and the hydrolytic species present.
TSS, VSS and sCOD were quantified according to the
Standard Methods (APHA, 1998). DOC was analyzed with
the TOC ASI-V (Shimadzu Co., Japan) TOC analyzer.
Samples for sCOD and DOC assays were filtered with
0.45μm syringe filters. Protease assay was performed
using Sigma Aldrich assay kit with casein as the substrate
(substrate product no.: C7078). α-amylase assay was
performed using the dinitrosalicylic acid method (Bernfeld,
1955). Biogas production rate was measured by the syringe
displacement method (Owen et al., 1979). One unit of
protease activity is defined as the amount of enzyme that
hydrolyzes casein to produce 1.0μmol of tyrosine per minute
at pH 7.5 and 35oC. One unit of amylase activity is defined
as the amount of enzyme that hydrolyzes starch to liberate
1mg of maltose in 3 minutes at pH 7 and 25oC.
The objective of this research is to investigate the optimum
conditions for the anaerobic hydrolysis of particulates in
sewage including a preliminary study on the feasibility of
enzyme augmentation.
The experiments were performed in batches of 20 days.
The degree of hydrolysis of particulates was calculated
from the following equation by analyzing the period where
hydrolysis predominates:
42
Seed sludge was obtained from the anaerobic digester at
Ulu Pandan Water Reclamation Plant, Singapore. The seed
sludge was washed twice with phosphate buffered saline
(PBS) to remove residual soluble COD. Sludge was added
to the batch reactors such that the starting concentration
was 8000mg MLSS/l (5000mg MLVS/l).
The synthetic wastewater used in the experiments was
prepared to simulate raw municipal wastewater with
suspended solids. The soluble constituents of the wastewater
were prepared according to the OECD guideline for synthetic
sewage (OECD 303A). The twice diluted composition gives
a COD of 150mg/l. Suspended solids in wastewater are
simulated by 250mg/l of dry dog food with a COD of
400±50mg/l (ALPO, Purina Co., USA). ALPO dog food
was selected because it has similar organic composition
with primary sludge (Kim et al., 2003). This gave a total
COD of 550±50mg/l.
Degree of hydrolysis = [(∆sCOD + ∆CODH2 + ∆CODCH4)
/ (Initial particulate COD)]
(1)
where ∆CODH2 is the sCOD converted into biogas as H2
(8g COD/g H2); ∆CODCH4 is the sCOD converted into
biogas as CH4 (4g COD/g CH4). Hence, the degree of
hydrolysis is expressed in grams of COD hydrolyzed per
gram of particulate COD.
Temperature and pH were investigated in the range of 2535oC and pH 5.0-9.0 respectively. Enzymes were augmented
at the concentration of 0-0.7% (w/v).
Degree of hydrolysis
The degree of hydrolysis is calculated from the period where
hydrolysis predominates, as indicated by rising sCOD. The
calculated degree of hydrolysis at these periods (indicated in
parentheses in days) and the total degree of hydrolysis for
the respective batch experiments are shown in Table 1.
Complete degradation of initial sCOD by Day 1 is assumed
as it is easily degradable and low in concentration (COD of
100mg/l). For computation that includes Day 0-1, 100mg/l
is deducted from the COD balance to ensure accountability.
At pH 5.0 and 9.0, COD removal due to biogas production
is assumed to be negligible as methane and hydrogen
production is low at these pH [Lay et al., 1997; Wang
et al., 2007; Lin et al., 2006]. The majority of the COD
remains in the aqueous phase as soluble compounds like
volatile fatty acids (VFAs), long chain fatty acids (LCFAs)
and alcohols.
Table 1: Degree of hydrolysis at different conditions
Conditions
Period 1
Period 2
Period 3
Total
pH 9, 35 C,
0.7% (w/v)
0.415
(3-9)
0.1725
(15-20)
-
0.5875
pH 9, 25oC,
0.7% (w/v)
0.2775
(2-6)
0.0325
(8-10)
0.145
(16-20)
0.455
pH 5, 25oC,
0.7% (w/v)
0.2025
(0-1)
0.105
(7-9)
0.35
(10-13)
0.6575
pH 5, 35oC,
0.7% (w/v)
0.9425
(0-1)
0.18
(7-8)
0.225
(15-17)
>1
o
In the context of enzyme augmentation, it is possible for the
calculated degree of hydrolysis to exceed 1 as the enzymes
can exert COD. From the experimental results, it can be
deduced that lower pH enhances the rate of anaerobic
hydrolysis of particulates in municipal wastewater. Other
authors reported an optimum pH of 5.5 for hydrolysis of
diary wastewater (Yu et al., 2002), 6.5 for hydrolysis of
synthetic PS (Kim et al., 2003) and 7.0 for hydrolysis of
kitchen waste (Zhang et al., 2005).
Figure 1: Control experiment.
low precision of VSS test as no replicates are performed.
Subsequently, there is a decrease in sCOD of 170mg/l
from Day 1-7, suggesting the consumption of enzymes as
substrate by the biomass. One possible mechanism is the
proteolysis of lipases and amylases as well as the autolysis
of proteases into monomers that can be consumed by
the microorganisms. In addition, hydrolytic bacteria may
secrete hydrolases to degrade the enzymes. There is a rise
in sCOD from Day 7 to 13 (69 to 143mg/l), suggesting
the production of SMPs due to cell death and lysis. The
fall in MLVSS from 4850 to 4350mg/l in the same period
indicates that the microorganisms are probably undergoing
endogenous respiration.
Control without the addition of biomass was performed in a
sterilized 250ml Duran bottle for a period of 4 days. Gradual
decline in enzymatic activity was observed throughout
the experimental period, suggesting the occurrence of
proteolysis and autolysis. Protease activity fell from
1.05U/ml to 0.22U/ml whereas amylase activity fell from
2.15U/ml to 0.079U/ml during the same period.
CONCLUSIONS
Control with enzymes
A control was performed with only enzymes and no
substrate added. Tap water was added as the source of
micronutrients in place of synthetic feed. The result of the
control is illustrated in Figure 1.
The data points are connected with straight lines for better
visualization. There is a rise in sCOD of 31mg/l from
Day 0-1, suggesting the hydrolysis of biomass. This may
be corroborated by MLVSS, which falls from 5150 to
5000mg/l. The low COD per unit of VSS may be due to the
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43
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swine wastewater”. Water Science and Technology, Vol. 58,
No. 7, pp. 1529-1534.
DATA-DRIVEN APPROACH FOR MULTISTEP AHEAD FLOOD FORECASTING FOR
THE LOWER MEKONG
Nguyen Khac-Tien Phuoc (nguy0077@ntu.edu.sg)
Chua Hock-Chye Lloyd (chcchua@ntu.edu.sg)
ABSTRACT: Accurate flood forecasts are essential for an early flood warning system to issue reliable flood warnings in order that proper
emergency actions be taken to mitigate flood damages. This study proposes a data-driven approach based on the Adaptive-NetworkBased Fuzzy Inference System (ANFIS) to forecast the water level for the Lower Mekong River at Pakse in Laos for lead-times from 1
to 5 days. In addition, the present study used an output updating scheme which is based on a recursive autoregressive (RAR) model to
enhance the accuracy of multi-step ahead forecasts. The results of the present study show that: (i) ANFIS model performed well for 1-,
2- and 3-days ahead forecasts when compared to the performance of a physically based model which is currently adopted for operational
forecasts; and (ii) the output updating technique significantly enhances 4- and 5-days ahead forecasts.
INTRODUCTION
The Mekong River with a length of approximately 4,800
km has its source in China’s Yunnan province and flows
through Myanmar, Thailand, Laos, Cambodia and Vietnam
and discharges into the South China Sea. It drains an area
of approximately 795,000 km2 and has a yearly average
flow rate of 15,000 m3/s (MRC, 2005). The wet season in
the Mekong occurs from the months of June to October
every year. Floods may occur during this time when
typhoons from the South China Sea cause heavy rains over
the basin. In order to deal with flood management and
mitigation in this region, an effective flood early warning
system is essential.
This study demonstrates the use of ANFIS incorporating
a recursive autoregressive or RAR based output updating
technique for multi-step flood forecasting for a reach of
the Lower Mekong River. The performance of the ANFIS
model was compared with the benchmark used by the
MRC to evaluate forecast accuracy and a Naïve model
which is the simplest forecast model that is often used as
base line to evaluate models. Finally, ANFIS model results
were also compared with results obtained from the URBS
model for 2009 forecasts.
METHODS
Adaptive-Network-Based Fuzzy Inference System
(ANFIS)
A neuro-fuzzy system is a hybrid system combining the
concepts of Fuzzy Inference System (FIS) and Artificial
Neural Network (ANN). A common framework of a
neuro-fuzzy system is to represent the FIS in an ANN
architecture and utilize the learning capability of ANN to
optimize the FIS parameters. The Adaptive Network-based
Fuzzy Inference System (ANFIS) proposed by Jang (1993)
is a well-know approach for neuro-fuzzy systems. ANFIS
is based on the Tagaki-Sugeno-Kang (Takagi and Sugeno,
Before 2009, flood forecasting for the Lower Mekong was
managed by a system that utilized models and concepts
developed during the 1970s (Apirumanekul, 2006). The
Streamflow Synthesis and Reservoir Regulation model
(SSARR), developed by the US Corps of Engineers was
used to model the rainfall-runoff process for the upper
reaches from Chiang Saen to Pakse, while regression
models were used to model the flows downstream from
Pakse. A new flood forecasting system has recently been
developed and put into operation at the Regional Flood
Management and Mitigation Centre of the Mekong River
Commission (RFMMC-MRC). This system was developed
in 2007 in order to improve short and especially medium
term forecasts. The rainfall-runoff processes for the upper
reach from Chiang Saen to Pakse is now modeled by the
Unified Run-off Basin Simulation (URBS) hydrological
model, and the flow routing downstream from Pakse is
modeled by the ISIS hydrodynamic model. The system was
operated in “test mode” during the 2008 flood season, and
has been in operational mode since 2009 (MRC, 2009).
An alternative flood forecasting tool, based on the datadriven approach, which utilizes the Adaptive-NetworkBased Fuzzy Inference System or ANFIS (Jang, 1993) was
developed for this study. ANFIS focuses on constructing
an input-output mapping based on the measured time
series data. Studies where ANFIS has been used in flood
forecasting include Nayak et al. (2005) and Chen et al.
(2006).
45
1985) fuzzy inference system embedded within the structure
of the ANN. Figure 1 shows a schematic of ANFIS with 2
rules for a system consisting of 2 inputs and 1 output.
Figure 1. Schematic of ANFIS architecture (Jang, 1993).
The function of each layer in ANFIS is briefly described
as follows:
Layer 1 - input nodes: each node generates membership
grades to which inputs at the inputs nodes are assigned, from
fuzzy sets based on the membership functions used. In our
study the Gaussian membership function was applied.
Layer 2 - rule nodes: in this layer, the AND or the OR
operator is applied to obtain one output that represents
the result of the antecedent for that rule, i.e. the firing
strength.
Layer 3 - average nodes: in this layer, the main objective
is to calculate the ratio of the ith rule’s firing strength to
the sum of all rules’ firing strength.
Layer 4 - consequent nodes: in this layer, the first-order
Sugeno fuzzy model is adopted. The fourth layer computes
the contribution of each rule towards the total output.
Layer 5 - output nodes: the single node computes the overall
output by summing all the incoming signals according to
the defuzzification process, where each rule’s fuzzy results
are transformed into a crisp output.
46
The learning algorithm in ANFIS optimizes the ANFIS
parameters that include the premise parameters, which
describe the shape of the membership function, and the
consequent parameters, which describe the overall output
of the system. The algorithm used is a hybrid learning
algorithm consisting of the gradient descent and leastsquares methods. The gradient descent method is employed
to tune the premise parameters, whereas the least-squares
method is used to identify the consequent parameters. The
present study used ANFIS implemented in the Fuzzy Logic
Toolbox of MATLAB (MATLAB, 2008) to forecast water
level of the Lower Mekong at Pakse in Laos.
Recursive Autoregressive Model
In order to improve the forecast accuracy, the present
study modelled the time-series of water level forecast
errors. Once the forecast error was estimated, it could then
update the forecast from the ANFIS model. Auto-regressive
(AR) model is a stochastic model that is typically used
for this purpose (Serban and Askew, 1991; WMO, 1992).
However, this is a non-adaptive model since its parameters
are fixed after calibration. Therefore it is not able to adapt
to changes once the model is calibrated. The recursive
autoregressive (RAR) model is an adaptive version of the
linear autoregressive model. Its parameters can be adjusted
by a recursive estimation algorithm using the most recent
error. Hence, the RAR model is more suitable compared
to the AR model in online applications. The present study
used an RAR model with a recursive estimation algorithm
(Ljung, 1999) implemented in the System Identification
Toolbox of MATLAB (MATLAB, 2008).
CASE STUDY
The most upstream station of the Lower Mekong is at
Chiang Saen in Laos and the most downstream station
is at Chau Doc in Vietnam. The upstream reach of the
Lower Mekong from Chiang Sean to Pakse is characterized
by steeper gradients compared to the lower reach where
gradients are generally flatter. The URBS model, which is
a physically-based lumped parameter model, is currently
used to model the flow upstream of Pakse. Because of the
flatter terrain, a 1-D hydrodynamic model (ISIS) is used
to model the flow downstream of Pakse. Thus, Pakse is
the boundary between the URBS and ISIS models and the
forecast at Pakse is used as input or upstream boundary
condition for ISIS. Therefore, the accuracy of forecasts
at Pakse is important as it can significantly influence the
accuracy of downstream forecasts.
ANFIS MODEL DEVELOPMENT
Data division
The water level of the Mekong at Pakse and upstream
stations in the wet seasons from 1993 to 1998 were used
for training, while data from 1999 to 2000 were used for
testing, and data from 2001 to 2003 and 2009 were used
for validation. ANFIS model results are compared to the
URBS results for the wet season in 2009 only, since URBS
model results are available only for that year. Table 1 shows
some pertinent information of water levels at Pakse in the
three data subsets.
Table 1. Statistical properties of training, test,
and validation data sets.
Mean
(m)
Duration
(days)
Min
(m)
Max
(m)
Training
(1993-1998)
5.98
1,134
1.36
13.01
Test
(1999-2000)
7.12
380
2.56
13.34
Validation
(2001-2003 and
2009)
6.88
693
1.45
12.7
Input-output selection
ANFIS is a Multi-Input-Single-Output (MISO) system.
Each ANFIS model has only one output. Therefore, five
ANFIS models providing outputs of L-days (L = 1, 2, …
, 5 days) ahead forecasts of the water level at Pakse were
developed. This study employed a statistical approach
suggested by Sudheer et al. (2002) to identify the appropriate
input vector. The method is based on the heuristic that the
potential influencing variables corresponding to different
time lags can be identified through statistical analysis of
the data series using cross correlation, autocorrelation, and
partial autocorrelation between the variables in question.
Correlation analyses showed that the water level at Pakse
at L-days ahead is most related to three recent water levels
at Pakse, then followed by the three recent water levels at
Savanakhet, which is situated 240 km upstream of Pakse.
Thus, the general form of the relationship between the
water level at Pakse at step t+L and water levels at Pakse
and Savannakhet can be expressed as follows:
a membership function (e.g., Gaussian, Triangular) is defined
with the center located at the center of the class. There
are two methods to generate an initial model for ANFIS
training which are based on two partitioning techniques
on the data: grid partition and subtractive clustering. It
is not advisable to use grid partitioning in ANFIS when
the input dimension is more than five or six (Nayak et
al., 2005) due to excessive propagation of the number of
rules (curse of dimensionality). The present study used
the subtractive clustering technique to generate the initial
model for ANFIS training. A proper number of membership
functions applied to each input was identified by trial-anderror. The number of membership functions was increased
from three to twenty. It was found that when the number
of membership functions increased from three to ten the
performance of the model was more or less the same on
the test data set, and when the number of rules was greater
than ten, model performance deteriorated. The number of
membership functions used was thus three. This would
imply that the range of water level can be divided into
three main regions: low, medium and high.
OUTPUT UPDATING
Five independent ANFIS models were developed to
provide multi-step ahead water level forecasts at Pakse.
The Lth (L = 1, 2, … , 5 days) ANFIS model is denoted
by ANFISL. Its output predicted at time t is denoted by
(L). This is the forecast made at time t for the water
level at the lead time t+L. The difference between the
actual measurement Ht+L, to be measured at time t+L, and
(L) is the output error of the ANFISL model predicted at
time t. This error can be stated as:
et(L) = Ht+L –
This means that each ANFIS model has as output, the
L-days ahead forecast of the water level at Pakse and the
three most recent water levels at Pakse and Savanakhet
as inputs.
Model evaluation
Model structure selection and model calibration
In ANFIS, each input variable is clustered into several class
values in layer 1 to build up the fuzzy rules. In each class,
At time t, et(L) is unknown since Ht+L is unknown. An
output updating procedure is implemented which attempts
to approximate the value of et(L) denoted by
. Once
is determined, the predicted error can then be added
to the original output (L) in order to obtain the updated
output,
, as follows:
=
(L) +
An incremental updating procedure was used in the present
study that utilised output of ANFIS1 to update the output
of ANFIS2, the outputs of ANFIS1 and ANFIS2 to update
the output of ANFIS3 and so on. Figure 2 shows that the
difference between output of ANFISL at time step t and the
output of the ANFISL+1 at time step t-1 is used to estimate
error of the ANFISL+1 output at time step t-1. This estimated
error is applied to an RAR model to obtain the estimated
error of the ANFISL+1 output at time step t. This error is
then added to the original ANFISL+1 output to obtain the
updated forecast.
The coefficient of efficiency (COE) was used to assess the
overall goodness of fit. The mean absolute error (MAE),
mean percentage absolute error (MPAE), and root mean
square error (RMSE) were adopted as absolute error
measures. In addition, the mean absolute error of forecasts
for water levels higher than the alarm water level (MAEhigh
= 11 m) at Pakse was used to assess model performance
at high river stages.
(L)
47
1.25
Benchmark
Naïve
ANFIS
MAE (m)
1.00
0.75
0.50
0.25
0.00
(a)
1
2
3
4
5
4
5
Lead-time (day)
1.25
Benchmark
Naïve
ANFIS
MAE high (m)
1.00
0.75
0.50
0.25
Figure 2. Incremental output updating procedure
based on the I-RAR algorithm.
0.00
(b)
1
2
3
Lead-time (day)
RESULTS AND DISCUSSIONS
Verification of output updating procedure
The comparison of MAE for different forecast lead times
is shown in Figure 3(a) and Figure 4(a) for the entire
training and validation data sets, and for high water levels
(> 11 m) in Figures 3(b) and 4(b). The ANFIS models
show good overall performance as shown in Figures 3(a)
and 4(a), since the MAE of the ANFIS model results are
significantly less than that for the benchmark and Naïve
models for all lead times. However, if only high water
levels are considered, MAE is less than the benchmark at
only 1- and 2- lead-day forecasts, approximately equal to
the benchmark at 3- and 4-days forecasts, and higher than
the benchmark at 5-days forecast. In the model validation
phase, the ANFIS model gives MAE similar to the Naïve
model at 4- and 5-days forecast for high water levels.
Figure 4. MAE calculated on the validation dataset by ANFIS
(without updating) model for 1 to 5 day forecasts for:
(a) entire wet seasons, (b) high water levels.
The incremental updating procedure proposed in the present
study significantly improved the accuracy of multi-stepahead forecasts as shown in Figure 5 and by the time series
plot in Figure 6. The MAE computed on the entire the
wet seasons (Figure 5a) shows only a slight improvement.
However, for high water levels (Figure 5b), the improvement
is more significant, especially for 5-days forecast. The time
series in Figure 6 shows that although there is still a lagtime error, the amplitude error of ANFIS output updated by
I-RAR procedure (ANFIS+I-RAR) is lesser, in comparison
to the original ANFIS model output.
1.25
Benchmark
Naïve
ANFIS
ANFIS+ I-RAR
1.00
1.25
Benchmark
Naïve
ANFIS
MAE (m)
MAE (m)
1.00
0.75
0.50
0.75
0.50
0.25
0.25
0.00
(a)
48
(a)
1
2
3
4
1.00
Benchmark
Naïve
ANFIS
0.50
4
5
0.75
Benchmark
Naïve
ANFIS
ANFIS+ I-RAR
0.50
0.25
0.25
0.00
0.00
1
(b)
3
1.25
MAEhigh (m)
0.75
2
Lead-time (day)
Lead-time (day)
1.00
1
5
1.25
MAEhigh (m)
0.00
2
3
4
5
Lead-time (day)
Figure 3. MAE calculated on the training dataset by ANFIS
(without updating) model for 1 to 5 day forecasts for:
(a) entire wet seasons, (b) high water levels.
(b)
1
2
3
4
5
Lead-time (day)
Figure 5. MAE calculated for 1 to 5 lead time steps on
validation data with output updating: (a) entire wet seasons,
(b) high water levels
CONCLUSIONS
Figure 6. Measured and computed (ANFIS and ANFIS+I-RAR)
time series of 5-lead day forecasts (at the high river stages
in 2000 and 2001).
Comparison of ANFIS and URBS models
100
100
80
80
COE (%)
Successful Forecast Percentage
(%)
ANFIS+I-RAR and URBS model results are compared for
the 2009 wet season in Figure 7. The Naïve model is used
as a baseline for comparison. All error indexes show that the
ANFIS+I-RAR model have significantly better performance
than that of the URBS model at 1- to 3-lead-day forecasts.
However, ANFIS+I-RAR achieves only slight improvement
in comparison with URBS model at 4- and 5-days forecast.
The ANFIS model is able to associate the water levels
at Savanakhet and Pakse well for a few days due to the
high correlation of water levels at Savanakhet and Pakse
from 1 to 3 lags. This also implies that the performance
of the ANFIS model will deteriorate when this correlation
decreases as is the case when L > 3 days. It is expected
that ANFIS model results can be further improved by the
inclusion of rainfall as an additional input, to improve 4and 5-days forecasts. This is left as future work.
60
40
40
20
0
0
1
2
3
4
1
5
3
4
5
RMSE (m)
2
3
4
0.8
[5] Jang, J.S.R., 1993. “ANFIS: adaptive-network-based fuzzy
inference system”. IEEE Transactions on Systems, Man and
Cybernetics, 23(3), 665-685.
0.4
1
5
2
3
4
Number of Lead Days
Number of Lead Days
5
[6] Ljung, L., 1999. “System Identification: Theory for the User”.
Prentice Hall PTR, Upper Saddle River, NJ.
[7] Mekong River Commission (MRC), 2005. “Overview of the
Hydrology of the Mekong Basin”. Mekong River Commission,
Vientiane, 73 p.
15
10
5
0
1
[1] A pirumanekul, C., 2006. “Flood forecasting in the Mekong
River Basin: an improvement plan for the flood forecasting
system”. International Conference on Mekong Research for
the people of the Mekong, 18-21 October 2006, Chiang Rai,
Thailand.
2
3
4
5
Number of Lead Days
Figure 7. Comparison of performance between URBS,
ANFIS+I-RAR and Naïve models
[8] Mekong River Commission (MRC), 2009. “System
Performance Evaluation Report, The MRC Technical Task
Group for verification of the new MRC Mekong Flood
Forecasting System (FEWS-URBS-ISIS)”. Mekong River
Commission Regional Flood Management and Mitigation
Centre, Phnom Penh, Cambodia, October 2009.
[9] MATLAB, 2008. “User guide for release R2008b”. The
MathWorks, Inc.
1
REFERENCES
[4] Goswami, M., O’Connor, K.M., Bhattarai, K.P. and Shamsedin,
A.Y., 2005. “Assessing the performance of eight real-time
updating models and procedures for the Brosna River”.
Hydrology & Earth System Sciences, 9(4), 394-411.
0.0
0.0
MPAE (%)
MAE (m)
2
1.2
0.5
We wish to thank the Regional Flood Management and
Mitigation Center - Mekong River Commission for
providing the measured data and results from the URBS
model.
[3] Chen, S.H., Lin, Y.H., Chang, L.C. and Chang, F.J., 2006.
“The strategy of building a flood forecast model by neurofuzzy network”. Hydrological Processes, 20: 1525-1540.
Number of Lead Days
Number of Lead Days
1.0
ACKNOWLEDGMENTS
[2] Box, G.E.P. and Jenkins, G.M., 1976. “Time Series Analysis:
Forecasting and Control”. Holden-Day: Oakland, CA.
60
20
The following can be concluded from this study:
1. The ANFIS model is able to provide accurate forecasts
within the benchmark level, for up to 5 -days forecast
for the entire flood season. For the high water forecasts,
ANFIS is accurate only up to 4 lead-days.
2. Significant improvements to 4- and 5-day forecasts
were obtained when ANFIS model results were updated
with the I-RAR output update algorithm.
3. Comparing between ANFIS+I-RAR and URBS model
results for 2009, the ANFIS+I-RAR model produced
significantly better results compared to the URBS
model for 1- to 3-days forecasts. However, ANFIS+IRAR achieved only slight improvement in comparison
with URBS model for 4- and 5-days forecast.
49
[10] Nayak, P.C., Sudheer, K.P., Rangan, D.M. and Ramasastri,
K.S., 2005. “Short-term flood forecasting with a neuro-fuzzy
model”. Water Resources Research, 41: 1-16
[11] Serban, P. and Askew, A.J., 1991. “Hydrological forecasting
and updating procedures”. IAHS (International Association
of Hydrological Sciences) Publication, Vienna, Austria.
50
[12] Takagi, T. and Sugeno, M., 1985. “Fuzzy identification of
systems and its applications to modeling and control”. IEEE
Transactions on Systems, Man and Cybernetics, 15(1), 116132.
[13] WMO, 1992. “Simulated Real-time Inter-comparison of
Hydrological Models”. World Meteorological Organization,
Operational Hydrology Report No. 38. WMO-No. 779.
Geneva Switzerland.
DESIGN OF BRINE OUTFALL FOR
SEA WATER REVERSE OSMOSIS (SWRO)
DESALINATION PLANTS
Adrian Law Wing-Keung (cwklaw@ntu.edu.sg)
Shao Dongdong (SHAO0004@ntu.edu.sg)
ABSTRACT: The design of brine outfall for SWRO desalination plants is a complex engineering task. In this paper, three different
design aspects which the authors have conducted recent research are discussed. They are (a) minimizing the recirculation between the
sea water intake and brine outfall, (b) predicting the mixing of brine discharges in coastal waters, and (c) avoiding the Coanda effect at
the discharge point with sufficient clearance from the bottom.
INTRODUCTION
Sea water desalination with Reverse Osmosis (SWRO)
is an increasingly viable option to supplement the water
supply for many coastal cities. Significant advancements
have been made in recent years in membrane technology,
process control and brine management, and together they
have led to a considerable reduction in the water production
cost. The output capacity of SWRO plants is also increasing
rapidly to achieve an economy of scale, and the brine flow
rate to the sea has increased correspondingly. This brings
to focus the need to design properly the brine outfall from
the SWRO plant so that the impact to the environment
can be minimized.
The design of brine outfall for SWRO desalination plants
is a complex engineering task. It involves the necessary
considerations to determine the discharge location (and
thus the length of the outfall pipe), the geometrical layout
and arrangement (incorporating the bottom bathymetry and
the characteristics of tidal hydrodynamics in the coastal
waters), the type of outfalls (single ports, or multi-ports
diffuser), and the range of design flow rates. In what follows,
three aspects that we have conducted recent research are
described.
The brine discharge from the outfall can potentially lead
to an increase in the salinity of the ambient water at the
sea water intake location due to recirculation. Law (2011)
performed a quantitative analysis to show that the effect
of recirculation to desalination plants is of high concern,
since the increase in ambient salinity near the intake has
a direct impact on the operating cost of the desalting
process. Thus, it is important to minimise the recirculation
for desalination plants, and the potentially higher initial
capital cost required can be compensated by corresponding
savings in the operation cost in the long run.
Far-field recirculation refers to the residual salinity increase
in the ambient waters due to the long term buildup of
salinity by the desalting operation. The magnitude of farfield recirculation depends on the various local ambient
characteristics, including the amount of tidal flushing in the
area, the seabed bathymetry and the shoreline geometry.
Shao et al. (2008) and Shao and Law (2009) presented
analysis to illustrate that the distance between the outfall and
intake is the key factor controlling the amount of far-field
recirculation for a uniform water depth. With a complex
bathymetry, however, the situation is more complicated and
the residual salinity can be accumulated in pockets of low
lying seabed undulations. A good far-field simulation using
a comprehensive numerical model would then be essential
for analysis (Bleninger et al., 2010).
PREDICTING THE MIXING OF BRINE
DISCHARGES
The near-field mixing of the brine discharges is the major
design consideration as far as the structure of the outfall
is concerned. Figure 1 shows that the typically near-field
mixing of a single port brine discharge. The ideal would
be for the brine plume to mix effectively with the ambient
water, to have a maximum rise below the water surface,
MINIMIZING RECIRCULATION BETWEEN
SEA WATER INTAKE AND BRINE OUTFALL
The build-up of ambient salinity near the intake can be
attributed to two effects that occur simultaneously, namely
near-field and far-field. Near-field recirculation refers to
the active mixing whereby the brine plume spreads and
propagates in the ambient coastal waters due to the initial
momentum and buoyancy fluxes, in such a manner that
leads to a direct and immediate re-entrainment of portion
of the brine by the intake. Adverse near-field recirculation
can normally be avoided by properly selecting the outfall
geometry, so that sufficient near-field dilution can occur
in the immediate vicinity of the outfall and the ambient
standard can be met within a prescribed mixing zone. A
good description on the near-field processes can be found
in CORMIX (Doneker and Girka, 2001).
51
and later to impact the seabed at sloping bathymetries that
direct the heavier plume towards the open sea.
Integral analysis has been widely used to predict the near
field mixing. In this approach, the governing equations are
first established in terms of continuity, Navier-Stokes and
scalar advection-diffusion equations. To solve the system of
equations numerically, another closure equation is required
and the entrainment hypothesis is often adopted. In the
literature, distinctly different values of the entrainment
coefficient had been reported for buoyant plumes that are
along or against the direction of gravity. This poses difficulty
to the analysis as the brine plume would experience both
regimes through the rising and then falling stage. Shao et
al. (2010) developed a new integral model with a unified
entrainment function for arbitrary buoyancy that is able
to resolve the entrainment non-uniformity in a continuous
manner. Based on extensive comparison with available
data, the new model is shown to be able to be able to
reasonably predict the behavior for the brine discharges
at various inclinations.
In the literature, a 60° inclined single port outfall had
been recommended for desalination plants to achieve a
maximum mixing efficiency. However, the terminal rise
associated with 60° is relatively high, and thus a smaller
inclination is often more desirable for shallow coastal
waters. At the same time, with the smaller inclinations, a
port that is placed at close proximity to the bottom may
suffer from the Coanda effect that reduces the amount of
mixing compared to an unbounded environment.
Shao and Law (2010) investigated experimentally the
mixing behavior of brine discharges at smaller angles of
30° and 45° in a stationary ambient. Based on the results,
the characteristic geometrical features of the inclined dense
jets are quantified. The mixing and diluting behaviors are
also revealed through the analysis of the velocity and
concentration profiles. The study also examined the effect
of proximity of the discharge port to the bed. For 30°, it
was found that the bed influence became significant when
CONCLUSIONS
This bulletin article describes the recent research conducted
by the authors towards the design of brine outfalls for
SWRO desalination plants. Further studies are ongoing to
address other design issues that may affect the operational
performance of the outfall. (The first author is currently
a member of the Joint IAHR/IWA Committee on Marine
Outfalls as well as the Task Group Leader on Brine
Outfalls).
REFERENCES
[1] Bleninger, T., Niepelt, A., Jirka, G.H., Lattemann, S., Purnama
A., Al-Barwani, H.H. and Doneker, R.L., 2010. “Environmental
hydraulics framework of the design of discharges from
desalination plants”. Proceedings of the 6th Int. Sym. Env.
Hyd., Athens, Greece.
AVOIDING COANDA EFFECT AT THE
DISCHARGE PORT
52
z0/LM < 0.2, where z0 is the centre height of the port, and
LM is a discharge momentum length scale. For 45°, the
boundary effect was considerably weaker and did not seem
to affect significantly even for z0/LM down to the smallest
tested value of 0.05.
[2] Doneker, R.L. and Jirka, G.H., 2001. “CORMIX-GI systems
for mixing zone analysis of brine and wastewater disposal”.
Desalination, 139: 263-274.
[3] Law, A.W.K., 2011. “Recirculation between intakes and
outfalls of desalination plants”. To presents in the Qingdao
International Desalination Conference.
[4] Shao, D.D. and Law, A.W.K., 2009. “Salinity build-up due to
brine discharges into shallow coastal waters”. Modern Physics
Letters B, 23(3): 541-544.
[5] Shao, D.D. and Law, A.W.K., 2010. “Mixing and Boundary
interactions of 30 and 40 degree inclined dense jets”. Journal
of Environmental Fluid Mechanics, 10(5): 521-553.
[6] Shao, D.D., Law, A.W.K. and Adams, E.E., 2010. “Integral
modelling of inclined round turbulent jets with arbitrary
buoyancy”. Journal of Fluid Mechanics, currently under
review.
[7] Shao, D.D., Law, A.W.K. and Li, H.Y., 2008. “Brine discharges
into shallow coastal waters with mean and oscillatory tidal
currents”. Journal of Hydro-environment Research, 2(2): 9197.
x/D
Figure 1. Typical pattern of the mixing of a brine discharge from an inclined port.
FOULING BEHAVIOR OF FORWARD
OSMOSIS MEMBRANES
She Qianhong (QHSHE@ntu.edu.sg)
Gu Yangshuo (YGU4@e.ntu.edu.sg)
Tang Chuyang (CYTang@ntu.edu.sg)
ABSTRACT: Forward Osmosis (FO), an emerging separation technology, has potential applications in water and wastewater treatment as
well as desalination. Internal concentration polarization (ICP) and membrane fouling have been found to adversely affect its performance.
This research aims to study the fouling behavior of FO membranes using humic acid as a model foulant. By performing batch cross flow
fouling experiments, the effect of FO membrane orientation and draw solution concentration on the fouling behavior were investigated.
Compared to the active layer facing draw solution (AL-facing-DS) orientation, flux was remarkable stable for the active layer facing
feed solution (AL-facing-FS) orientation due to the ICP self-compensation effect. FO suffered greater flux loss in AL-facing-DS, which
was likely due to the internal clogging of the porous structure and the resulting enhanced ICP in the support layer.
INTRODUCTION
Forward osmosis (FO), which uses osmotic pressure
difference across a selective membrane as the driven force,
has gained growing interests in both research and application
in recent years (Cath, Childress et al. 2006; Tang, She et al.
2010; Wang, Shi et al. 2010; Xu, Peng et al. 2010). Due
to its prominent advantages of low energy consumption
and high solute rejection, FO has been applied in the
water and wastewater treatment and seawater or brackish
water desalination (Cath, Childress et al. 2006). In the
FO process, internal concentration polarization (ICP) has
been identified to be a major obstacle of the FO membrane
performance in previous studies (Mehta and Loeb 1978;
Lee, Baker et al. 1981; McCutcheon and Elimelech 2006;
Tang, She et al. 2010). The water flux Jv in a different
membrane orientation due to the ICP effect can be modeled
by the Eq. (1) and Eq. (2) (Tang, She et al. 2010).
Jv = Kmln
( AπAπ + J+ +B B) (AL-facing-FS)
(1)
Jv = Kmln
(AπAπ – J+ B+ B) (AL-facing-DS)
(2)
draw
feed
draw
v
v
This study aims to systematically investigate fouling
behavior in the FO process and further explore the potential
mechanisms inherent in the FO process.
In the current research, the FO membrane was derived
from the commercial Hydrowell filter which was purchased
from Hydration Technology Inc. (HTI). The purified
Aldrich humic acid (PAHA) was used as a model foulant.
The schematic diagram of the FO membrane filtration
bench-scale experimental system is shown in Figure 1.
The system was comprised of two loops of solutions (i.e.,
feed solution and draw solution) which were separated by
the FO membrane in the cross flow membrane filtration
cell. The water flux of the FO process was gained by
measuring the weight changes of the feed solution in the
fixed duration. Unless otherwise specified, the following
conditions were used as the reference conditions: 10 mM
NaCl and 10 mg/L humic acid in FS, crossflow velocity
23.2 cm/s, temperature 22-24oC.
feed
Km =
D
D
=
l
S
τ. ε
(3)
Where D is the solute diffusion coefficient, τ is the tortuosity
of the support layer, l is the length of the support layer, ε
is the porosity of the support layer, and S is the membrane
structure parameter.
Fouling is another important drawback limiting the flux
level of the FO process (Mi and Elimelech 2008; Lay,
Chong et al. 2010; Tang, She et al. 2010). However, few
publications have systematically studied the mechanisms of
FO membrane fouling so far (Mi and Elimelech 2008).
Figure 1. Schematic diagram of the FO membrane
filtration system.
where A and B are the respective transport coefficients for
water and solute, πfeed and πdraw are the respective osmotic
pressure of the feed solution and draw solution, Km is the
solute mass transfer coefficient, which is given by
53
50
35
30
AL facing FS
Fouling test
AL facing DS
Fouling test
35
Baseline
Baseline
30
25
20
15
25
2
Flux (L/m hr)
Flux(g/10 min)
40
AL f acing
draw solution
AL f acing
f eed solution
45
40
10
5
0
0
200
400
00
ti
600
( iin))6
tim e(m
800
Figure 2. Flux behavior in the baseline flux tests.
Effect of FO membrane orientation
5
0
60
120
180
240
300
360
420
480
Time (min)
Figure 3. Effect of the membrane orientation on the fouling
behavior of FO membrane (cited from reference
(Tang, She et al. 2010)).
conducted in the AL facing DS configuration. Clearly,
greater baseline flux level was obtained at higher draw
solution concentration as a result of the increased osmotic
pressure difference at higher draw solution concentration.
For the fouling tests, the flux level exhibited nearly identical
trend with the baseline flux at 0.5 M and 1 M draw solution
concentration (low initial flux level), while significant flux
loss was observed when the draw solution concentration
was 2 M and 4 M (initial flux was above 40 L/m2h).
The phenomenon of severe fouling behavior at high draw
solution concentration (thus high driven force) in the FO
process was similar to that in the pressure-driven membrane
process. This is attributed to the greater hydrodynamic
drag force for promoting foulant deposition.
Baseline, 4 M
Baseline, 2 M
Baseline, 1 M
Baseline, 0.5 M
60
55
Fouling, 4 M
Fouling, 2 M
Fouling, 1 M
Fouling, 0.5 M
50
45
40
35
2
Figure 3 illustrates the FO fouling behavior under the two
different membrane orientations. The experiments at the
two different membrane orientations were conducted under
the same initial flux (~30L/m2.hr). As shown in Figure
3, little flux reduction was observed for the AL-facing-FS
configuration, while the flux decreased significantly for the
AL-facing-DS configuration. When the membrane rejection
layer faced the feed solution, humic acid had lower tendency
to deposit on the smooth surface, which was verified by
the minimal measured humic acid deposition. As a result,
no significant flux reduction occurred. In addition, the ICP
self-compensation effect is another plausible explanation for
the flux stability under the AL-facing-FS configuration.
15
10
Flux (L/m hr)
During the whole test, the DS was diluted and the FS was
concentrated as the water was transported from the FS to
the DS. Therefore, prior to each fouling experiment, the
baseline test which has an identical condition except without
adding foulant in the FS was performed to identify the
flux loss due to membrane fouling. Figure 2 presents a
group of baseline fluxes under the two types of membrane
orientation using 2 M NaCl as draw solution. Due to the
severe ICP in the AL-facing-FS, the flux in the AL-facingFS was much lower than that in the AL-facing-DS.
20
54
For the AL-facing-DS configuration, the porous support
layer was exposed to the feed solution, humic acid had
greater tendency to enter the porous support layer and was
retained inside the support by the active layer, inducing
severe internal pore clogging. This effect significantly
increased the structure parameter (S value) and thus reduced
mass transfer coefficient Km. As the ICP is exponentially
dependent on the mass transfer coefficient, the observed
flux decreased significantly.
Effect of the draw solution concentration
The effect of draw solution on FO fouling behavior is
shown in Figure 4. The baseline and fouling tests were
30
25
20
15
10
5
0
60
120
180
240
300
360
420
480
Time (min)
Figure 4. Effect of the draw solution concentration on the
fouling behavior of FO membrane (cited from reference
(Tang, She et al. 2010)).
CONCLUSIONS
The fouling behavior in the FO process was systematically
investigated. In the AL-facing-FS orientation, the flux
exibted inherently stability. Any attempt to decrease the
flux level was compensated by the reduced level of ICP.
In contrast, in the orientation of AL-facing-DS, the flux
was subject to large loss under the fouling conditions due
to the pore clogging enhanced ICP as well as the reduced
membrane permeability. The enhanced ICP effect was
more dominant at higher flux levels.
REFERENCES
[1] Cath, T.Y., A.E. Childress, et al. (2006). "Forward osmosis:
Principles, applications, and recent developments." Journal
of Membrane Science, 281(1-2): 70-87.
[2] Lay, W.C.L., T.H. Chong, et al. (2010). “Fouling propensity
of forward osmosis: Investigation of the slower flux decline
phenomenon.” Water Science and Technology, 61: 927-936.
[4] McCutcheon, J.R. and M. Elimelech (2006). “Influence of
concentrative and dilutive internal concentration polarization
on flux behavior in forward osmosis.” Journal of Membrane
Science, 284(1-2): 237-247.
[5] Mehta, G.D. and S. Loeb (1978). “Internal polarization in
the porous substructure of a semipermeable membrane under
pressure retarded osmosis.” Journal of Membrane Science,
4(2): 261-265.
[6] Mi, B. and M. Elimelech (2008). “Chemical and physical
aspects of organic fouling of forward osmosis membranes.”
Journal of Membrane Science, 320(1-2): 292-302.
[7] Tang, C.Y., Q. She, et al. (2010). “Coupled effects of internal
concentration polarization and fouling on flux behavior of
forward osmosis membranes during humic acid filtration.”
Journal of Membrane Science, 354(1-2): 123-133.
[8] Wang, R., L. Shi, et al. (2010). “Characterization of novel
forward osmosis hollow fiber membranes.” Journal of
Membrane Science, 355(1-2): 158-167.
[9] Xu, Y., X. Peng, et al. (2010). “Effect of draw solution
concentration and operating conditions on forward osmosis
and pressure retarded osmosis performance in a spiral wound
module.” Journal of Membrane Science, 348(1-2): 298-309.
[3] Lee, K.L., R.W. Baker, et al. (1981). “Membranes for
power generation by pressure-retarded osmosis.” Journal of
Membrane Science, 8(2): 141-171.
55
ESTIMATE OF RESISTANCE INDUCED
BY SIMULATED EMERGENT VEGETATION
IN OPEN CHANNEL FLOWS
Nian-Sheng Cheng (cnscheng@ntu.edu.sg)
Hoai Thanh Nguyen (c070041@ntu.edu.sg)
INSTRUCTION
The vegetation drag and its relevant Reynolds number have
been defined diversely in the literature and some definitions
are even misleading because of improper use of length
and velocity scales. As a result, a general formula similar
to Manning equation developed for regular open channel
flows is not available at present for evaluating resistance
to vegetated open channel flows, even for the emergent
case that is relatively simple.
Table 1 compares rv with other hydraulic radii. Using rv, the
Colebrook-type resistance relation for open channel flows
subject to emergent vegetation is proposed here,
fv = f (Rev)
where fv =
…(3)
4V r
8grvS
and Rev = νv v .
2
Vv
In this study, a vegetation-related hydraulic radius is
proposed and applied to redefine the Reynolds number
and friction factor for vegetated open channel flows. All
considerations are limited to the case of emergent rigid
vegetation simulated with circular cylinders.
VEGETATION-RELATED HYDRAULIC
RADIUS
(a) Plan view
As shown in Fig. 1, we consider emergent vegetation
simulated with staggered rigid cylinders. In this case, the
effective vegetation height is the same as the flow depth h,
and the configuration of vegetation is solely governed by
the stem diameter d and density λ defined as the average
volume fraction occupied by stems.
56
For vegetated flows without sidewall and bed effects, we
consider a 3D domain that measures ∆x × ∆y × 1, in the
streamwise, lateral and vertical direction, respectively.
Similar to the regular hydraulic radius, the hydraulic radius
in the 3D domain is defined as the ratio of the volume
occupied by water to the wetted surface area,
…(1)
Note that in the above definition, the total wetted surface
area is used. For vegetation-induced form drag, we only
need to consider the frontal area of the stem. This yields
an effective wetted area equal to Nd in the 3D domain, and
then the vegetation-related hydraulic radius is given by
…(2)
(b) Side view
Figure 1. Emergent vegetation simulated with
circular cylindrical rods.
Table 1. Length scales for characterizing flow geometry.
Flow geometry
Geometrical
dimension
Hydraulic radius
D
4
-1
Rectangular
channel width, B 1
1
+
open channel
flow depth, h
h 0.5B
Porous media
grain size, d50
11–λ
d50
comprising grains pore size
6 λ
Vegetated channel
stem diameter, d π 1 – λ
d
without channel
stem spacing, s
4 λ
boundary effects
Circular pipe
pipe diameter, D
Open channel
with emergent
vegetation
channel width, B
flow depth, h
stem diameter, d
stem spacing, s
§
¨1
¨h
¨
©
-1
·
1
1
+ π 1 – λ ¸¸
+
0.5B
d¸
4 λ
¹
DRAG COEFFICIENT
i.e.
For each cylindrical stem, the drag force in the streamwise
direction is
FD = CDvρhd
Vv2
2
…(4)
n=
Bh
S1/2
V B + 2h
2/3
…(11)
Obviously, the n-values so obtained would generally depend
on vegetation configuration for vegetated open channel
flows. From Eq. (7),
where CDv is the drag coefficient. The total drag per unit
bed area is
2
NFD =
2
Vv
2λρhVv
4λ
C ρhd
= CDv
πd
2
πd2 Dv
…(5)
which is equivalent to the streamwise component of the
gravitational force,
CDv
2λρhVv2
= (1 – λ)ρghS
πd
…(6)
CDv
Here, the shear forces induced by sidewalls and bed
are considered negligible. Otherwise, sidewall and bed
corrections are applied. From Eq. (6),
CDv =
gr S
1–λ
gSπd = 2 v2
Vv
2λV2v
…(7)
Furthermore, by comparing Eq. (7) with the definition of
fv, one gets
CDv =
1
f
4 v
Figure. 2. Variation of CDv with Rev.
From Eq. (7),
DEPENDENCE OF CDV ON REV
To empirically describe the relationship of CDv and Rev, a
best-fit function is proposed here
…(9)
MANNING COEFFICIENT
The Manning coefficient can be determined experimentally
from the bulk flow velocity V [= Q/(Bh)], regular open
channel hydraulic radius Bh/(B+2h), and energy slope S,
√S
CDv
=
V
2grvε2
√
…(12)
Substituting Eq. (12) into (11), we get
n=
CDv
Bh
2grv(1 – λ)2 B + 2h
√
2/3
…(13)
Fig. 3 shows that the Manning coefficients predicted using
Eq. (13), where CDv is estimated using Eq. (9), agree
reasonably with the measurements, i.e. those determined
using Eq. (11) with the data provided by Ishikawa et al.
[3], James et al. [4], and those collected in this study.
CONCLUSIONS
This study demonstrates that the concept of hydraulic radius
is useful to unify experimental data of resistance to vegetated
open channel flows, which have been collected for various
bed and vegetation configurations. The hydraulic radius
is redefined by taking into account effects of vegetation
size and density, and channel geometry. It serves as a good
length scale in the definition of drag coefficient, friction
factor and Reynolds number for open channel flows subject
to emergent vegetation.
The analysis was performed with the data collected in this
study and also those available in several other studies. Fig.
2 plots all data in the form of CDv against Rev, from which
the following observations could be made. First, though
scattered to some extent, all data points generally follow
the same monotonic decreasing trend of CDv with increasing
Rev. Second, for Rev > 7000, CDv fluctuates within a limited
range, and could be taken to be constant, i.e. CDv ≈ 1.3.
Third, it seems that CDv dips in the range of Rev = 7 ×
103 – 6 × 104. This could be related to possible difference
that may exist between the channel configured with the
randomly distributed stems (only related to Tanino and
Nepf’s data[1]) and that with staggered stems. Otherwise,
it could be explained by vortex shedding and surface waves
that take place in vegetated channel flows [2].
Rev
CDv = 500.43 + 0.7 1 – exp –
15000
Rev
Rev
…(8)
57
REFERENCES
[1] James, C.S., Birkhead, A.L., Jordanova, A.A. and O’Sullivan,
J.J., 2004. “Flow resistance of emergent vegetation”. Journal
of Hydraulic Research, Journal of Forest Research, 2004;
42(4): 390-8.
[2] Ishikawa, Y., Mizuhara, K. and Ashida, S., 2000. “Effect of
density of trees on drag exerted on trees in river channels”.
Journal of Forest Research, 2000; 5(4): 271-9.
[3] Tanino, Y. and Nepf, H.M., 2008. “Laboratory investigation
of mean drag in a random array of rigid, emergent cylinders”.
Journal of Hydraulic Engineering-ASCE. 2008 Jan; 134(1):
34-41.
[4] Zima, L. and Ackermann, N.L., 2002. “Wave generation in
open channels by vortex shedding from channel obstructions”.
Journal of Hydraulic Engineering-ASCE. 2002 Jun; 128(6):
596-603.
Figure. 3. Comparison of predicted and measured
Manning coefficients.
58
LIFE CYCLE ANALYSIS OF
OFFSHORE GANGWAY
Nguyen Anh Tuan (atnguyen@ntu.edu.sg)
Cao Thi Viet Phuong (CVPhuong@ntu.edu.sg)
Wang Xikun (CXKWang@ntu.edu.sg)
Dai Ying (DaiYing@ntu.edu.sg)
Gho Wie Min (CWMGho@ntu.edu.sg)
Tan Soon Keat (CTANSK@ntu.edu.sg)
ABSTRACT: The life cycle analysis of an offshore gangway as a means of embarkation and disembarkation for personnel access between
the two vessels or between a work boat and an offshore platform was carried out. The strength integrity of the gangway was first reviewed
to validate its geometrical configuration from the requirement of Health and Safety Executive (2002). Key factors that significant influence
to the environmental impact, including production, processing, operation and activities of the gangway are highlighted.
INTRODUCTION
Gangway is widely used in the offshore and marine industry
as a specialized equipment to facilitate safe transportation
of goods and personnel between offshore supply vessels and
platform/vessel. It is a type of bridge structures specially
designed with heave compensation system at supports to
minimize the effect due to sea motion. Gangway can be
constructed from steel or aluminium or a combination of
both to offer a lightweight structure while not comprising
its high strength and stiffness. It can be designed with
sufficient width to accomodate one- or two-way traffic
movements to suit onsite requirements.
Scopes of study
The life cycle evaluation of an offshore steel gangway for
means of embarkation and disembarkation for personnel
access between the two vessels or between a work
boat and an offshore platform is carried out. Extensive
reference to the published data and information is drawn.
The strength integrity of the gangway is first reviewed
with the application of finite element analysis to validate
Objective of study
The objective of the assessment is to determine the
key factors suitable for the LCA of steel gangway and
associated environmental impact. Parameters considered
include carbon (CO2), sulfur oxide (SOx) and nitrogen
oxides (NOx) emission to air and water and the amount
of energy consumed.
MODEL SOLUTIONS METHODOLOGY
The model solution methodology for the gangway is based
on the LCA to assess the potential environmental impacts
associated with the production, processing and activities
throughout its entire life cycle. This method analyses the
impact of a product over a lifetime from the process of
extraction of raw materials, manufacturing through to the
waste disposal of its various components for recycling or end
of its service life. The factors relevant to the entire life cycle
of the gangway system are compiled to create a scenario
to show the extent of impact to the environment.
The LCA is conducted based on the guidelines provided in
the International Organization for Standardization (ISO14040
1996, ISO14041 1998, ISO14042 2000, ISO14043 2000
and ISO14044 2006). The procedure includes the data
Life cycle analysis (LCA) is a method for analysing and
assessing the environmental impact of a material, product
or service throughout its entire life cycle, usually from
the acquisition of raw materials to final decommissioning
and disposal. For the LCA of the gangway, its production,
manufacturing process, transportation, installation,
operation, application, disposal and recycle after use are
briefly discussed. The environmental factors that contribute
to the greenhouse effect include the effect of emissions
to the atmosphere and water as well as the amount of
energy consumed. These factors can be incorporated in the
analytical tools based on the life cycle assessment approach
to determine the impact of this gangway structure on the
environment.
its geometrical configuration from the requirement of
Health and Safety Executive (HSE 2002). The key factors
that contribute to the greenhouse effects as well as the
environmental impact with respect to material production,
processing and activities related to the fabrication and
operation of the gangway are highlighted. A scenario is
hence developed by integrating these factors to emulate the
actual condition, which would be useful for manufacturers
and users to evaluate the life cycle of a gangway and its
operation in the marine environment.
59
collection and evaluation and the interpretation of results
after analysis. In this evaluation of the life cycle of the
steel gangway, the approach is to firstly gather data and
information through the literature review of previous
publications of steel structures based on LCA methodology.
The process flow chart of the major life cycle of gangway
product is summarized as shown in Figure 1. Generally,
the process flow chart for typical gangway comprises five
(5) main stages which can be used as a framework for
inventory analysis. Each stage will contain unit processes
with elementary inputs and outputs represented as building
blocks for data collection.
used as part of a reference to further investigate in greater
details the life cycle of various types of offshore gangway
used in the marine industry.
Figure 2. Emission to the atmosphere (kg).
Figure 1. Process flow chart with data of gangway system.
LIFE CYCLE ANALYSIS OF GANGWAY
Based on the major process flow stages of the gangway
products as shown in Figure 1, all the unit processes within
each of these stages are considered within the system
boundary, and also include all elementary flows that relate
to the environmental impacts. The inputs are the energy
consumption and the natural resources such as water. The
elementary flow outputs in the system boundary are the
waste removal and the harmful air emissions specifically
for those that have significant influence on global warming.
Air emissions that relate to toxicity and acidification are
considered as primary effects.
60
Figure 3. Discharge to recipient water (kg).
Data for each stage is collected from two main sources.
The first source can be found in the database established by
the Swiss Centre for Life Cycle Inventories which provides
thousands of process flows across the entire spectrum of
manufacture industries (Ecolnvent, 2010). The second is
the industry reports and publications including material
specific journals, reports and websites.
RESULTS
The results of the LCA calculation based on a typical
gangway available in the market in such aspects as emissions
to atmosphere, water and the energy consumptions per unit
weight of 100kg of the product are presented in Figures
2, 3 and 4, respectively. This set of information can be
Figure 4. Energy consumption (MJ).
CONCLUDING REMARKS
REFERENCES
In this study, the geometrical configuration and the strength
integrity of the offshore gangway has been verified against
the requirement of Health and Safety Executive. This
preliminary study was based on extensive reference to
the published data and information and was conducted to
determine important factors that would have contributed
significant impact to the environment. The results of the
sulfur oxide, nitrogen oxides and carbon emission to the
atmosphere, recipient water and the energy consumption
from the process of gangway manufacture and production
are presented.
[1] Ecolnvent database 2010. http://www.pre.nl/ecoinvent/, The
Netherlands.
[2] HSE 2002. Health and Safety Executive, Decks, stairways,
gangways and their associated handrails, Offshore technology
report 2001/69, Bomel Ltd, UK.
[3] SO 14040 2006. International Organization for Standardization,
Environmental management, Life cycle assessment, Principles
and framework, Switzerland.
[4] ISO 14041 1998. International Organization for Standardization,
Environmental management, Life cycle assessment, Goal and
scope definition and inventory analysis, Switzerland.
Environmental management, Life cycle assessment, Life cycle
impact assessment, Switzerland.
Environmental management, Life cycle assessment, Life cycle
interpretation, Switzerland.
Environmental management, Life cycle assessment,
Requirements and guidelines, Switzerland.
61
DAM-BREAK FLOW SIMULATION WITH
SEDIMENT TRANSPORT
Pu Jaan Hui (jhpu@ntu.edu.sg)
Shao Songdong (s.shao@bradford.ac.uk)
Tan Soon Keat (CTANSK@ntu.edu.sg)
ABSTRACT: In this study, 2D shallow water equations together with a sediment continuity-concentration (SCC) model were applied to
flow with mobile sediment boundaries. The SCC model could reproduce the information for both bed and suspended loads. A combination
of the shallow water and the sediment transport models was constructed using the fully conservative law to preserve the integrity of
their governing equations, and the proposed computation model was based on the Finite Volume (FV) method. The Monotone Upwind
Scheme of Conservative Laws (MUSCL)-Hancock scheme was used with the Harten Lax van Leer (HLL) approximate Riemann solver
to discretize the FV model.
INTRODUCTION
A variety of numerical schemes have been used and
proposed to simulate the sediment laden flows. The sediment
continuity model is one of the most basic sediment transport
models to simulate sediment transport in flow. However,
since this model only considers the bed load sediment
transport, it could not be used to accurately represent
sediment transport flow with rapid suspended concentration
change, such as debris or dam-break flow.
show the two-dimensional fully conservative shallow water
and sediment continuity-concentration equations [Valiani
and Caleffi (2001), Cao et al. (2004), and Wu and Wang
(2008)]
…(1)
…(2)
Realising the shortcomings of the earlier sediment continuity
model, Armanini and Di Silvio (1988) suggested a set
of sediment continuity-concentration (SCC) equations to
improve the sediment transport representation by including
the exchange effect of the bed and suspended loads. Their
model was solved in a 1D domain but with consideration
of the non-equilibrium lag of sediment transport. These
equations were further tested by Valiani and Caleffi (2001),
and Wu and Wang (2008) for the case of turbulent dambreak sediment transport flow, and good correspondence
between the numerical simulation and the experimental
data were observed.
…(3)
…(4)
…(5)
62
Most of the previous sediment laden flow models were
constructed based on the sediment bed load assumption
using a 1D flow continuity-momentum approach. In this
paper, the combination of 2D shallow water and SCC
models were used to simulate the bed and suspended
loads movement in a 2D depth averaged flow. The
proposed combined model was used to predict a highly
discontinuous dam-break sediment transport flow. The
experimental measurements from the literature were also
used for validation.
GOVERNING EQUATIONS
The proposed model described in this paper was built using
the sediment continuity-concentration model combined
with the shallow water flow equations. Equations (1) - (5)
The variable φ refers to geopotential, and is given by
φ = g • h ; where h is the water depth; g is the gravitational
acceleration. u and v are the depth averaged flow velocities
in streamwise and lateral directions respectively; ρs and ρw
are density of sediment and water respectively; C is the
flux-averaged volumetric sediment concentration; λ is the
sediment bed porosity; and zb is the bed elevation. es and ds
are sediment erosion and deposition rates respectively. x, y
and t denote the spatial-longitudinal, spatial-transverse and
time domains respectively. Sox and Soy in equations (2) – (3)
are the bed slopes in the streamwise and lateral-directions
respectively; and the friction slope of the channel, Sf, are
given by
, and
where, n in the Manning friction coefficient.
…(6)
NUMERICAL SCHEME
There are different discretization techniques that can be
used to discretize a Shallow Water model, namely Finite
Difference (FD), Finite Element (FE) and Finite Volume
(FV) methods. In this study, FV method was chosen for
its robust nature in simulating high dimensional shockcapturing flow profiles accurately (Mingham and Causon,
2000).
In the inviscid flux modelling of the proposed FV model, the
Godunov-type Hancock scheme was used with a two-stage
predictor-corrector temporal discretization. The Godunovtype Hancock scheme was coupled with Harten Lax van
Leer (HLL) approximate Riemann solver for upwinding
volumetric discretization. The slope limiter method was
used in the HLL solver to ensure the spatial discretization
scheme satisfies flux-limiting property (Mingham and
Causon, 2000). MUSCL (Monotone Upwind Scheme
for Conservation Laws) scheme was used to update the
variables spatial wise. The MUSCL and Hancock schemes
keep the proposed FV model at a second order of accuracy
in spatial and temporal domains respectively. The overall
inviscid solution is indicated by
…(7)
For time stepping, the Courant-Friedrichs-Lewy criterion
was followed to ensure the utilised time step does not
exceed its maximum allowable limit. In the numerical source
term, a first order derivative was used for its discretization.
No complex discretization method is needed as HLL-type
scheme is having competence to capture source term solution
accurately (Hu et al., 2006).
A dam-break flow is a well-known and rapidly varying flow
event with a highly unpredictable nature. The effect of a
dam-break flow on a mobile sediment bed was investigated
by Capart and Young (1998) experimentally using a channel
equipped with a rapidly opened sluice-gate. This experiment
was simulated using the proposed model and the results
are reported herein.
A rectangular channel with dimensions of 12.0m length
and 0.2m width was used for Capart and Young (1998)
experimental test case. The sediment used in the test
has a size of 6.1mm, a density of 1048kg/m3, and a fall
velocity of 0.076m/s. The flow was initially at rest, where
it had an initial water depth of 10cm at the upstream and
dry water depth at the downstream with a layer of 6cm
sediment at the bed throughout the channel from upstream to
downstream. The sluice gate, which was originally situated
at 4m location from upstream, was opened instantaneously
at the start of the flow. The results of the water surface
and bed load elevation profiles around the dam breaking
point are shown in Figure 1. The time-distribution of the
Figure 1. Water surface and bed elevation profiles comparison for different models
63
flow profiles are shown for every 0.1s interval over 0.5s
to capture the transient changes in the water flow and bed
change conditions. The proposed model results are plotted
against the experimental measurements of Capart and Young
(1998). The sediment continuity modelling results from
Capart and Young (1998), and the sediment continuityconcentration modelling results from Wu and Wang (2007)
are also plotted in the same figure for comparison.
Both crucial dam break flow characteristics of water wave
front and bed scour hole size are well-predicted using
the proposed model compared to the other computational
models. Numerically, the behaviour of the suspended load
in the proposed model is simulated using the sediment
concentration partial differential equations. This improved
feature simulates the suspended sediment information at
the water wave front, hence giving a consistent prediction
to the measured water wave front.
CONCLUSIONS
A 2D shallow water Finite Volume (FV) numerical model
was developed to analyse shallow flow with sediment
transport. The proposed model was applied to a dam-break
flow test over movable bed in this paper. The proposed
model simulation was compared to the experimental
measurements in literature, and the comparison shows
good corresponding results at its water and bed elevation
predictions. The above-mentioned statements are clearly
demonstrated by the water wave front and the bed scour
hole size predictions of the proposed model, which are
not predicted so accurately by the other models proposed
in the literature.
64
REFERENCES
[1] Armanini, A., and Di Silvio, G., 1988. “A One-dimensional
model for the transport of sediment mixture in non-equilibrium
conditions”. Journal of Hydraulic Research, 26(3): pp. 275292.
[2] Cao, Z., Pender, G., Wallis, S. and Carling, P., 2004.
“Computational dam-break hydraulics over erodible sediment
bed.” Journal of Hydraulic Engineering, 130(7): pp. 689703.
[3] Capart, H. and Young, D.L., 1998. “Formation of a jump by
the dam-break wave over a granular bed”. Journal of Fluid
Mechanics, 372: pp. 165-187.
[4] Hu, K., Mingham, C.G. and Causon, D.M., 2006. “A mesh
patching method for finite volume modelling of shallow water
flow”. International Journal for Numerical Methods in Fluids,
50: pp. 1381-1404.
[5] Mingham, C.G. and Causon D.M., 2000. “Calculation of
unsteady bore diffraction using a high resolution finite volume
method”. Journal of Hydraulic Research, 38(1): pp. 49-56.
[6] Valiani, A. and Caleffi, V., 2001. “Dam break modeling for
sediment laden flows”. Proceedings of the 2001 International
Symposium on Environmental Hydraulics, Arizona, USA,
pp.1-6.
[7] Wu, W. and Wang, S.S.Y., 2007. “One-dimensional modeling
of dam-break flow over movable beds”. Journal of Hydraulic
Engineering, 133(1): pp. 48-58.
[8] Wu, W. and Wang, S.S.Y., 2008. “One-dimensional explicit
finite-volume model for sediment transport with transient
flows over movable beds”. Journal of Hydraulic Research,
46(1): pp. 87-98.
NUMERICAL SIMULATION OF
WEDGE WATER ENTRY BASED ON
TWO-PHASE SPH MODEL
GONG Kai (gongkai@ntu.edu.sg)
LIU Hua (hliu@sjtu.edu.cn)
TAN Soon Keat (ctansk@ntu.edu.sg)
ABSTRACT: The hydrodynamic problem of two-dimensional wedge entering water was studied based on two-phase SPH model. A
non-reflection boundary treatment for SPH method was proposed to reduce the size of computational domain. The details of water entry
and enclosing were simulated using multi phase SPH model. Numerical simulations verified our experimental observations.
GENERAL INSTRUCTIONS
Since the first studies by von Karman, lots of works have
been carried out in water entry problems. Water entry of
a solid through the free surface is still a current focus of
the researches in hydrodynamics. The water entry problem
is part of the general fluid-structure impact problem. The
first complete solution was obtained by Dobrovol’skaya
(1969) for a two-dimensional wedge based on velocity
potential theory. Zhao and Faltinsen (1993) studied the
same problem using a refined procedure with a more
advanced computer.
The SPH method has extraordinary potential for problem
solving in areas where traditional techniques have been
unsuccessful. The method has the advantage of conceptual
simplicity, ease of implementing new physics, natural
treatment of void regions, ease of simulating threedimensional problems and ease of handle large deformations
of the free surface. SPH method is attractive on simulating
the violent wave impact problems, e.g. Oger et al (2006).
For water entry problems, the air cavity enclosed by the
water may significantly affect the local free surface profile
and flow field, and then the hydrodynamics loads. Correctly
NUMERICAL MODELING
The momentum and kinematics equations for fluid particles
in SPH method are
…(1)
…(2)
where a represents the reference particle; b represents the
neighboring particles of a; Wab = W(|ra – rb|, h) is kernel
function defined by
…(3)
For weak compressible method, the pressure was
calculated by state equation that was first used by
Monaghan (1994) and based on Batchelor’s (1974) equation,
P = P0 (ρ – ρ0)γ – 1 , where γ = 7 and ρ0 = 1000 for water.
The parameter P0 was chosen to have maximum density
oscillations of order of O(1%) around the reference density
ρ0. In practice, the constant P0 refers to the sound speed
Smoothed Particle Hydrodynamics (SPH) is a meshfree
method that offers substantial potential in many classes
of problems especially those characterized by large
deformations. It was originally developed for astrophysical
computations (Gingold and Monaghan 1977, Lucy 1977)
and has later been extended to model a wide range of
problems including multi-phase flow (Monaghan and
Kocharyan 1995), impact and fracture problem (Randles et
al. 1995). It is a pure Lagrangian, particle method. Unlike
the Particle In Cell method (PIC), SPH method does not
need a grid to calculate spatial derivatives. Instead, it is
based on analytical differentiation of interpolation function.
The continuum equation and the momentum conservation
equations are reduced to sets of ordinary differential
equations. The particle positions and attributes are computed
using standard numerical integration methods in time
domain such as leap-frog scheme.
simulating the multiphase flows may improve the force
prediction.
65
c02 = dP / dρ which is ten times or larger than the highest
fluid velocity expected in the physical problem, that is
P0 = ρ0 c02 / γ. For weak compressible flows, the density
was calculated by integrating:
dρa
= – ρa∇ua =
dt
∑ mb (ua – ua)∇aWab
…(4)
b
The two-phase SPH model given by Colagrossi and Landrini
(2003) was adopted.
Non-absorbing boundary
Absorbing boundary
Figure 2. Pressure distribution of the whole flow field.
CODE VERIFICATIONS
Verification was conducted to verify the weak compressible
SPH code and various boundary implementations. A twodimensional wedge vertical impacting the free surface is
simulated. The boundary pressure was obtained using an
improved coupling boundary treatment approach. Three
snapshots of pressure distribution during water entry are
illustrated in Figure 1. Computational results were compared
with the experimental and analytical results given by Zhao
& Faltinsen (1993). The pressure distribution fits well with
the analytical results.
SIMULATION OF CAVITY ENCLOSING
In some circumstances, the single phase model could not
predict the physical process after enclosing, wherein the
pressure is zero even in the enclosed cavity. However, with
two phase SPH model, the flows of entrapped air could be
well simulated after enclosing of the cavity. A comparison
between numerical results and physical experiments shows
a good agreement, as shown in the particles distribution in
Figure 3. Only water particles are shown in the figure.
To save computational efforts, absorbing boundary was
implemented to remove the sound disturbance from the
computational domain, details in Gong et al (2009). By
this approach, the computational time can be extended
without the limitation of sound wave’s reflection from
solid boundaries, which is a common drawback of weak
compressible SPH method. Figure 2 shows the effects of
absorbing boundary. The sound wave’s reflection from solid
boundaries is obviously reduced.
66
Figure 3. Comparison between experimental results and
computed results of water phase.
The flow field and pressure is shown in Figure 4. The
pressure of vented cavity equals the atmosphere pressure,
shown in relative value. After enclosing, the pressure in the
sealed cavity increases rapidly and equals to the surrounding
water’s pressure. Note the re-entrant jet is formed after the
deep enclosure.
Figure 1. Distribution of pressure for water entry of wedge in
the case of free moving. (top: t = 0.00438s;
middle: t = 0.0158s, bottom: t = 0.0202s).
REFERENCES
[1] Batchelor, G.K., 1974. “Introduction to Fluid Dynamics”.
Cam. Univ. Press, Cambridge, U.K.
[2] Colagrossi, A. and Landrini, M., 2003. “Numerical Simulation
of Interfacial Flows by Smoothed Particle Hydrodynamics”.
J. Comput. Phys., 191: 448-475.
[3] Dobrovol’skaya, Z.N., 1969. “On some problems of similarity
flow of fluid with a free surface”. J. Fluid Mech., 36: 805829.
Figure 4. Pressure (in colour) and velocity vector
distribution before and after cavity closure.
CONCLUSIONS
To simulate the enclosing process after water entry, a
two-phase SPH method was applied. With fine particle
distribution, details of water entry, including surface
profile, pressure distribution and total force etc, could
be well predicted. The enclosing of water entry was
successfully simulated with proposed SPH model, providing
a powerful Lagrangian approach for violent free surface
flow calculation.
[4] Gingold, R.A. and Monaghan, J.J., 1977. “Smoothed particle
hydrodynamics: Theory and application to non-spherical
stars”. Mon. Not. R. Astron. Soc., 181: 375-389.
[5] Gong, K., Liu, H. and Wang, B.L., 2009. “Water Entry of a
Wedge Based on SPH Model with an Improved Boundary
Treatment”. Journal of Hydrodynamics, 21(6): 750-757.
[6] Lucy, L.B., 1977. “A numerical approach to the testing of
the fission hypothesis”. Astron. J., 82(12): 1013-1024.
[7] Monaghan, J.J., 1994. “Simulating Free Surface Flows with
SPH”. J. Comput. Phys., 110(2): 399-406.
[8] Monaghan, J.J. & Kocharyan, A., 1995. “SPH simulation of
multi-phase flow”. Computer Physics Communication, 87:
225-235.
[9] Oger, G., Doring, M., Alessandrini, B. and Ferrant, P., 2006.
“Two-dimensional SPH simulations of wedge water entry”.
J. Comp. Phys., 213: 803.
[10] Randles, P.W., Carney, T.C., Libersky, L.D., Renick, J.R.
and Petschek, A.G., 1995. “Calculation of oblique impact
and fracture of tungsten cubes using smoothed particle
hydrodynamics”. International Journal of Impact Engineering,
17: 661-672.
[11] Zhao, R. and Faltinsen, O., 1993. “Water entry of twodimensional bodies”. J. Fluid Mech., 246: 593-612.
67
OPTIMIZATION AND ENHANCEMENT
OF MICROBIAL HYDROLYSIS OF
LIGNOCELLULOSIC WASTE TO
REDUCING SUGARS
Bernard Ng Jia Han (bernhan@ntu.edu.sg)
Wang Jing-Yuan (jywang@ntu.edu.sg)
Qi Wei (qiwe0001@ntu.edu.sg)
Chen Chia Lung (clchen@ntu.edu.sg)
ABSTRACT: Nineteen pure strains of lignocelluloses-converting microorganisms were successfully isolated in this study. The best
combination of pure culture of Microbacterium sp. F28, Tsukamurella sp. C35, Pseudallescheria sp. D42 and Bacillus sp. F4 showed
the maximum reducing sugars yield of 1,653 mg/L, which is ten times higher than the original consortia. The maximum reducing sugars
production yield of 173 mg reducing sugars/g lignocellulose was obtained under the optimum conditions at temperature 56.9 ºC, pH 5.8
and with initial lignocellulose concentration at 28.9 g/L after orgnosolv pretreatment.
INTRODUCTION
68
The world’s energy crisis has exacerbated in recent years.
Alternative non-fossil fuel energy sources are in urgent
demand. Bioethanol is such an alternative fuel which has
low carbon content and environmentally friendly. However,
current food-based feedstock for bioethanol production may
not be practical since it may cause competition between
food and energy crops for land use. A potential source of
low-cost ethanol production is to utilize lignocellulosic
waste, viz crop residues, grasses, sawdust, wood chips and
solid animal waste, which represents one of the foreseeable
sustainable sources in nature because of its relatively low
cost and plentiful supply [1]. Hydrolysis of lignocellulosic
waste to reducing sugars is one of the key steps during
bio ethanol production. The main drawbacks of traditional
hydrolysis methods (viz enzymatic and acidic treatments)
are their high operation costs, generation of secondary
pollution and their under optimized and underdeveloped
technologies. Thus, in this study, microbial hydrolysis of
lignocellulosic waste to reducing sugars was employed. 1year old compost, 4-month old compost, aerated activated
sludge, garden soil and yellow mealworm guts were selected
as inoculate sources to isolate lignocellulose-converting
microorganisms. Enhancement of microbial hydrolysis of
lignocellulosic waste to reducing sugars was investigated
by the combination of pure strains and optimization of
environmental conditions to further improve reducing
sugars yield.
soil (GS). Samples were taken from the four sources in
sterilized sample bags and stored at 4 ºC until cultivation of
microorganisms was performed. The inoculated flasks were
fed with lignocellulose as the sole carbon source with the
following basic nutrient: (NH4)2SO4 2 g L-1, CaCl2 0.1 g·L-1,
KH2PO4 0.5 g·L-1, K2HPO4 2.0 g·L-1, MgSO4·7H2O 0.1 g·L-1,
NaCl 6.0 g·L-1, Yeast extract 1.0 g·L-1 and lignocellulose 10
g·L-1. Tenebrio Molitor Linnaeus (yellow mealworm) was
provided. Every 8 mealworms were disrupted by passing
through a syringe needle for each medium. The disrupted
gut debris were suspended in 200 ml medium 1 [2]. Medium
1 and Medium 2 were supplemented with carboxymethyl
cellulose (CMC; 10 g L-1; 21900; Fluka, Buchs, Switzerland;
degree of substitution 0.70-0.85; medium 1a), filter paper
strips (10 g L-1, brand; medium 1b), and lignocellulose waste
powder (10 g L-1; with a size of less than 1 mm; medium
1c), respectively. The flasks were placed in a reciprocal
incubation shaker (Grant, OLS 200, Grant Instruments,
UK) at 30±2°C and at a horizontal rotational speed of 150
rpm. Samples in the cultivated flasks were analyzed every
24 hours in the cultivated flasks and measurements were
recorded. pH was measured with a pH meter (CyberScan
PCD 6500 pH meter, Germany). A phenol-sulfuric acid
method was used to quantify polysaccharides [3], with
glucose as the standard. Monosaccharides were measured
by DNS method with glucose as the standard [4]. Each
sample was measured in triplicates.
The inoculums originated from four specifically selected
natural sources, i.e., 1-year compost (C1), 4-month compost
(C4), aerated activated sludge seed (AAS) and garden
Nineteen dominant microbes were successfully isolated
and characterized from microbial communities of the
four natural sources and mealworm guts. Cellulomonas
and Pseudomonas were the most abundant phylum in all
isolates. The Pseudomonas group, were reported as strict
aerobes and are known for the presence of a variety of
metabolic pathways that are capable of degrading complex
organic compounds including xenobiotics [5]. The genera
of Bacilli were ubiquitous among the mixture of microbial
community. In Bacillus sp., xylanase is induced by xylose,
but is repressed in the presence of glucose [6]. Three
fungi isolates from the microbial community in this study
are assigned to Pseudallescheria sp. which is known as a
potential animal pathogen and can degrade a wide range
of organic waste [7].
method is orgnosolv pretreatment, and the liquid hot water
pretreatment is slightly better than diluted sulfuric acid
pretreatment for reducing sugars production. The reducing
sugars yield produced after optimization is much higher
than those of enzymatic hydrolysis in reported in prior
literature [8] [9].
Figure 2. Reducing sugars yield by the best
microbial “cocktail”.
Figure 1. The gram staining pictures of the players
of the best combination.
Optimization experiments were conducted to investigate
the effects of substrate concentration, pH and temperature
under three types of pretreatment methods by the defined
microbial “cocktail” selected in above section. The
maximum reducing sugars production yield of 173 mg
reducing sugars/g lignocellulose was estimated at the
optimum conditions of temperature 56.9 ºC, pH 5.8, and
lignocellulose concentration 28.9 g/L under orgnosolv
pretreatment (Figure 3). The important degree of three
variables on reducing sugars yield is: pH > temperature
> lignocellulose concentration. The best pretreatment
Figure 3. Comparison of reducing sugars yield under three
different pretreatment methods at 56.9 ºC, pH5.8, 28.9g initial
lignocellulosic waste (From left to right). 1. diluted acid
pretreatment, 2. liquid hot water pretreatment,
3. orgnosolv pretreatment.
CONCLUSIONS
The results of this study indicated that microbial hydrolysis
can effectively convert lignocellulosic waste to reducing
sugars and it is an alternative hydrolysis method for fuel
ethanol production.
REFERENCES
[1] Mabee, W.E. and J.N. Saddler, 2010. “Bioethanol from
lignocellulosics: Status and perspectives in Canada”.
Bioresource Technology, 101(13): pp. 4806-4813.
[2] Wenzel, M., et al., 2002. “Aerobic and facultatively anaerobic
cellulolytic bacteria from the gut of the termite Zootermopsis
To enhance reducing sugars yield, seven pure microbial
strains consisting of Microbacterium sp. F28 (M1),
Cellulosimicrobium sp. C10 (M2), Tsukamurella sp. C35
(M3), Pseudallescheria sp. D42 (M4), Bacillus sp. F4 (M5),
Strenotrophomonas sp. B15b (M6) and Pseudomonas sp.E8
(M7) were combined to investigate the best defined microbial
combination. The best defined microbial combination was
selected, which was the combination of Microbacterium sp.
F28, Tsukamurella sp. C35, Pseudallescheria sp. D42, and
Bacillus sp. F4 (Figure 1). The maximum reducing sugars
yield was 1,653 mg/L (Figure 2), which is ten times more
than the original consortia. Bacillus sp. F4 is a critical
factor. Pseudallescheria sp. D42, which is the only fungus
in the combination, was the second most important factor
to obtaining more reducing sugars.
69
angusticollis”. Journal of Applied Microbiology, 92(1): pp.
32-40.
[3] DuBois, M., et al., 1956. “Colorimetric method for
determination of sugars and related substances”. Analytical
Chemistry, 28(3): pp. 350-356.
[4] Miller, G.L., 1959. “Use of dinitrosalicylic acid reagent for
determination of reducing sugar”. Analytical Chemistry, 31(3):
pp. 426-428.
[5] Landy, E.T., et al., 2008. “Bacterial diversity associated with
archaeological waterlogged wood: Ribosomal RNA clone
libraries and denaturing gradient gel electrophoresis (DGGE)”.
International Biodeterioration & Biodegradation, 61(1): pp.
106-116.
70
[6] Beg, Q.K., et al., 2001. “Microbial xylanases and their
industrial applications: a review”. Applied Microbiology and
Biotechnology, 56(3): pp. 326-338.
[7] Anastasi, A., G.C. Varese, and F.M. Valeria, 2005. “Isolation
and identification of fungal communities in compost and
vermicompost”. Mycologia, 97(1): pp. 33-44.
[8] Saha, B.C. and M.A. Cotta, 2008. “Lime pretreatment,
enzymatic saccharification and fermentation of rice hulls to
ethanol”. Biomass and Bioenergy, 32(10): pp. 971-977.
[9] Jensen, J.R., et al., 2010. “Effects of dilute acid pretreatment
conditions on enzymatic hydrolysis monomer and oligomer
sugar yields for aspen, balsam, and switchgrass”. Bioresource
Technology, 101(7): pp. 2317-2325.
REMOVAL OF PHARMACEUTICAL
COMPOUNDS IN TROPICAL
CONSTRUCTED WETLANDS
Dongqing Zhang (dqzhang@ntu.edu.sg)
Sara Sadreddini (S.Sadreddini@ntu.edu.sg)
Junfei Zhu (JFZhu@ntu.edu.sg)
Nguyen Anh Tuan (ATNGUYEN@ntu.edu.sg)
Richard. M. Gersberg (rgersbe@mail.sdsu.edu)
Soon Keat Tan (ctansk@ntu.edu.sg)
ABSTRACT: The ability of a tropical horizontal subsurface constructed wetlands (HSSF CWs) planted with Typha Angustifolia to remove
four widely used pharmaceutical compounds (carbamazepine, declofenac, ibuprofen and naproxen) at the relatively short hydraulic residence
time of 2 to 4 days was documented. For both ibuprofen and naproxen, pharmaceutical compounds with low Kow values, the planted
beds showed significant (p<0.05) enhancement of removal efficiencies (80% and 91%, respectively at the 4 day HRT) as compared to
unplanted beds (60% and 52%, respectively). The presence of plants resulted in the removal of these pharmaceutical compounds from
artificial wastewater. Carbamazepine, considered as one of the most recalcitrant pharmaceuticals, and declofenac, showed low removal
efficiencies in our CW, and is attributable to their higher hydrophobicity. The fact that the removal of these compounds could be explained
by the sorption onto the available organic surfaces, explains why there was no significant difference (p>0.05) in their removal efficiencies
between planted as compared to unplanted beds. No statistical significant differences (p>0.05) were observed for the removal efficiencies
of any of the pharmaceuticals tested for the 2-day HRT as compared to that corresponding to 4-day HRT. The rather efficient removal
shown by the tropical wetlands with HRTs of 2 to 4 days indicates the possibility of using such a CW system (with less land/footprint
requirements) for removing certain pharmaceutical compounds from drinking water reservoirs.
INTRODUCTION
Many pharmaceutical compounds are now considered as
emerging contaminants of environmental concern because of
their widespread use, continuous release, their persistence,
and increasing evidence of their ecotoxicological (if not
human health) effects (Buser et al., 1999). Since some
pharmaceutical compounds are not completely removed
by conventional wastewater treatment, they are ubiquitous
and persistent pollutants in receiving waters worldwide,
especially where municipal wastewaters are discharged
into waterways (Ellis et al., 2006).
In this paper, we focused on the removal efficiency of four
pharmaceuticals: carbamazepine, declofenac, ibuprofen and
naproxen, in a HSSF CWs in a tropical environment. These
pharmaceuticals were chosen because they were widely
used and reportedly present in the effluents of wastewater
treatment plant (WWTP) effluents. The objectives of
this study were to (i) compare the removal efficiency of
selected pharmaceuticals in a HSSF CWs planted with
Typha Angustifolia and in unplanted bed (sand filter); (ii)
compare the removal efficiency of selected pharmaceuticals
at relatively low hydraulic residence time (2 and 4 days),
and (iii) determine quantitatively the role of aquatic plant
plays in removal of the selected pharmaceuticals in a
tropical CW.
METHODS AND MATERIAL
Description of constructed wetlands
The wetland beds were 120 cm long, 60 cm wide and 60
cm deep. Thickness of gravel bed was 0.30m with 4-10 mm
gravel (D60=3.5mm). The porosity was 0.45. Three HSSF
CWs were planted with cattail (Typha Angustifolia) at a
density of 9-10 plant/m2, and 3 beds without plant were
used as “unplanted” control beds. All the containers had
a flat bottom and a horizontal drainage pipe 0.4 m long
Technologies do exist which can lower the level of
pharmaceuticals discharged into receiving waters (e.g.,
ozonation, reverse osmosis, and advanced oxidation
processes, see Ternes et al., 2002). Such treatment is
extremely expensive (Heberer, 2002). Therefore use of
constructed wetlands (CWs) is growing in popularity as
a low impact and economical alternative for purifying
contaminated waters. Wetlands ecosystems contain a rich
biological diversity and contribute great benefits to society
by recharging aquifer, retaining sediments and nutrients,
controlling floods and microclimate stabilization (Mitsch
et al., 2008). The complexity of such processes makes it
difficult to ascertain the primary removal mechanism for
each class of contaminants. While there were extensive
research on CWs removal of organic matters (Mitsch et
al., 2005), relatively few work has been conducted to
evaluate pharmaceutical removal efficiencies (Llorens et
al., 2009) in engineered low impact systems such as CWs
(Matamoros et al., 2005).
71
and 50 mm in diameter located at the lower edge of the
containers. Water depth was maintained at 5 cm below gravel
surface and the hydraulic loading rate was maintained at
2.96 cm/day. Different from a conventional continuous flow
wetland, our design was a batch-flow constructed wetland.
Artificial wastewater enriched with selected pharmaceutical
compounds was rapidly filled in each bed and then drained
completely every 2 or 4 days.
General parameter detection
This experiment was carried out in April 2010. During
the experiments, all the beds were fed with synthetic
wastewater with the same organic load. Effluent samples
were collected from each bed every two and four days in
a 1-L amber glass bottles. The samples were immediately
analyzed to determine the reduction in concentration of
the general parameters, i.e., COD, ammonia-N (NH4N), nitrate (NO3) and total phosphorus (TP). General
parameters were analyzed by using spectrophotometer
(HACH-DR3800, USA) in accordance with the conventional
methods (Standard Methods for Examination of Water and
Wastewater - APHA, 1989). Total organic carbon (TOC) was
conducted by using Total Organic Carbon Analyzer (TOCVcsh, Shimadzu, Japan). Dissolved oxygen (DO), pH value
and conductivity were measured by using Multi-Parameter
Digital Meter (HACH – HQ40d, USA) directly.
Injection of pharmaceutical products and chemical for
pharmaceutical dectection
72
HPLC-grade acetonitrile, methanol, Hexane and ethyl
acetate (both HPLC grade) were obtained from Fisher
(USA). Ultrapure water was obtained from Milli-Q
water purification system (Millipore, Bedford, USA).
Carbamazepine, declofenac, ibuprofen, and naproxen (97100% purity) were obtained from Sigma-Aldrich. The
microfiters of solid phase extraction (SPE) cartridges,
packed with GracePureTM C18 – Max SPE column 500
mg, 6 mg, were purchased from Belgium. The 0.45 um
glass fiber filters of 47 mm (Whatman) were purchased
from Schleicher & Schuell (Germany). Stock solution of
500 μg/ml was prepared in methanol and stored at 4 °C.
Working solutions were prepared by diluting the stock
standard solution with methanol.
With respect to the pharmaceutical injection, 50 L of
synthetic wastewater were spiked with 1.25 mg of each
pharmaceutical compound to obtain a final concentration
of 25μg L-1. The injection experiment lasted 60 days.
Solid phase extraction (SPE)
All the effluent samples were kept refrigerated at 4°C and
analyzed within 24 hours. Prior to extraction, 500 ml of
effluent wastewater were filtered through a 0.45 μm glass
fibre membrane filter (Millipore, USA) and then acidified
to pH 2 with hydrochloric acid. The SPE cartridges were
conditioned using 5 ml n-hexane, 5ml ethyl acetate, 10 ml
methanol and 10 ml of Milli-Q water (pH=2) at a flowrate of approximate 3 ml/min. Samples were percolated to
the SPE cartridges through a Teflon tube at a flow-rate of
approximate 10 ml/min. The cartridge filter was then rinsed
with methanol: milli-Q water (pH=2) = 10:90, followed by
20 ml of Milli-Q water (pH=2). Thereafter, the cartridges
were allowed to dry for 30 min and then eluted with 5
ml ethyl acetate with elution solutions collected in 15 ml
calibrated centrifuge tubes. The extracted solution was then
concentrated to ca. 400 μl under a gentle nitrogen stream
and was then reconstituted to 500 μl with methanol.
HPLC Liquid chromatography analysis for
pharmaceutical
Chromatographic analysis was performed on a Shimadzu
Ultra Fast Liquid Chromatograph (UFLC) (Shimadzu,
Japan) equipped with a quaternary LC-20AD pump, a
CTO-20A oven, and a SPD-M20A Diode Array Detector
(DAD). The injector was SIL-20A HT fitted to a Shimadzu
autosampler with a 20 μl sample loop. Chromatographic
separation were carried out using a GracePureTM SPE C18Max (4.6*150 mm, 5 μm) cartridge column protected by
a ODS-3 (C18) (4.6*50 mm., 5 μm) guard column (Alpha
Analytical). The system was controlled using an interface
module and a personal computer. Chromatograms were
processed using a “Shimadzu LCSolution program”.
RESULTS AND DISSCUSSION
Results
Table 1 presents the mean levels of pharmaceutical
compounds, and their removal efficiencies in the CWs.
Table 1. Mean levels of pharmaceutical compounds, and
their removal efficiencies in the CWs
Cabamaze
pine
(μg1–1)
2-day HRT
HFCW
Removal
SF
Removal
4-day HRT
HFCW
Removal
Removal
Naproxen
(μg1–1)
17.9±2.5
4.3±1.8
28.4±10.38 2.8±7.1*
17.8±2.8
13.1±3.7
28.8±11.3 49.5±13.0*
17.0±4.7
17.9±2.0
28.3±8.1
Diclofenac
(μg1–1)
Ibuprofen
(μg1–1)
12.8±2.8
47.5±8.1
14.2±3.8
46.7±12.3
7.3±3.4
71.0±15.5
11.9±6.6
56.6±24.6
2.6±2.4
11.3±2.8
4.3±2.1
12.0±4.2
14.6±2.8
10.1±5.7
52.0±17.3* 41.1±11.3* 59.8±22.7*
The removal efficiency of ibuprofen in our experiment
was higher in the planted beds (71.0% for 2-day HRT and
79.7% for 4-day HRT) than that for the unplanted beds
(56.7% for 2-day HRT and 60.0% for 4-day HRT), but
the enhancement by plants was only significant (p<0.05)
at the 4-day HRT.
A significant difference (p<0.05) was observed for naproxen
removal efficiency between the planted HSSF beds (82.8%
for 2-day HRT and 91.3% for 4-day HRT) and the unplanted
beds (49.5% for 2-day HRT and 51.8% for 4-day HRT) at
both HRTs (Table 1).
As for carbamazepine, no significant differences in
carbamazepine removal efficiency between planted beds
(28.4% for 2-day HRT and 26.7% for 4-day HRT) and
unplanted beds (28.8% for 2-day and 28.3% for 4-day
HRT) were observed in our study. Another pharmaceutical
compound, diclofenac has also been reported as a recalcitrant
compound in microcosm experiments, membrane bioreactor
systems, and activated sludge STP (Hebere, 2002), and
in our study the removal efficiency of diclofenac in the
planted beds ranged from 47.5 to 55.4%, compared to that
of unplanted bed of 41.1% to 46.7% (Table 1).
3.2 Discussion
In our present study, ibuprofen and naproxen, both
pharmaceutical compounds with low Kow values, showed
significantly (p<0.05) higher removal efficiencies in the
planted beds as compared to that in the unplanted beds
(Figure 2). This finding is also consistent with those
reported by other researchers, which indicated the removal
efficiency for ibuprofen in planted HSSF (with sand depth
of 0.27 m) ranged from 71-80% and 80-90% for naproxen
(Matamoros and Bayona, 2006), but only 49-90% for
ibuprofen and 66-80% for naproxen in unplanted beds
(Matamoros et al, 2007). This may be well attributed to
the rhizosphere effect, since it has been extensively shown
that rhizosphere aeration plays an important role part in
the establishment of an oxidizing environment to support
high microbial activity (Reddy et al., 1989).
The removal of ibuprofen and naproxen that were observed
in planted beds was also reported by Hijosa-Valsero et al
(2010). The author also indicates that ibuprofen does not to
bind significantly to organic matter retained in the gravel
beds or pond sediment, and an HFCW planted with T.
latifolia played a significant role in the removal of ibuprofen.
This is attributed to the effect of rhizosphere aeration and
more oxidized conditions in these shallow subsurface of
Carbamazepine is considered to be one of the most
recalcitrant pharmaceuticals and the removal behavior of
such compounds is completely different from the others
above. The recalcitrant nature of this substance has also
been previously reported at other WWTPS. Its low removal
efficiency can be attributed to its higher hydrophobicity,
and the major fraction of removal of this compound could
be explained by the sorption onto the available organic
surfaces (Matamoros et al., 2005). Surprisingly, comparing
with other unplanted beds, HSSF CWs, VSSF CWs, or
even WWTPs, the removal efficiencies of cabamazepine in
our study shows much better outcome. However, HijosaValsero et al (2010) reported that carbamazepine removal
was favored by plant presence, which is not consistent
with our results.
As for diclofenac removal, the sorption of these compounds
onto organic matter retained in the gravel bed is an
important removal mechanism due to their hydrophobic
structure, which could be ascribed to specific structural
characteristics. Surprisingly, a significant difference between
planted and unplanted bed was observed for planted beds as
compared to the unplanted beds but only at a 4-day HRT
(Table 1). Further investigation of its removal pathway
and mechanisms is needed to be carried out in future
experiments.
CONCLUSIONS
This study demonstrated that CWs can be cost-effective
and sustainable alternative for removing selected emerging
contaminants. The key results can be drawn as follows:
CWs can offer comparable or even better pharmaceutical
removal efficiencies as compared to conventional WWTPs.
Both ibuprofen and naproxen, pharmaceutical compounds
both with low Kow values showed significant (p<0.05)
enhancement of removal in planted beds as compared to
unplanted ones. The presence of plants seems to favor
the removal of certain pharmaceuticals from wastewater.
Rhizosphere aeration plays an important role part in the
establishment of an oxidizing environment, and the more
Surprisingly in our CW system, levels of DO, COD and
TOC in the planted beds as compared to those in the
unplanted beds were found to be not statistically different
(p>0.05). Since the levels of the pharmaceutical compounds
enriched into our wetlands were in the μg/L range (as
opposed to COD levels in the tens to hundreds of mg/L
range), we would have expected that the oxygen demand
to satisfy the requirements for pharmaceutical removal,
would be relatively small. Therefore, our results indicate
the possibility of some rhizosphere effect, aside from
rhizosphere aeration alone, as playing a significant role
in the efficient pharmaceutical removal in tropical CWs
we observed.
plated CWs, which can promote aerobic reactions leading
to higher removal efficiency. It is also known that root
exudates released by the plant in the rhizosphere, are
known to result in intense microbial activity in the vicinity
of roots (Brimecombe et al., 2001). The establishment of
large numbers of metabolically active populations of soil
microbes in the rhizosphere is certainly important (Brix,
1997), as the microbial population found in the soil is
associated with the plant roots, which can reach up to
109 to 1012 per gram of soil (Whipps, 1990). In addition,
the possibility that root exudates also may play a role in
induction of specific metabolic activities conferring the
ability to degrade certain pharmaceuticals, or increase
bioavailability of pharmaceuticals by acting as surfactants
or transporters, should not be overlooked.
73
oxidized condition in the planted beds can promote aerobic
reactions to support high microbial activity, leading to higher
degree of biodegradation and removal efficiency.
Carbamazepine, considered as the most recalcitrant
pharmaceuticals, and declofenac showed low removal
efficiencies in our CW, attributed to their higher
hydrophobicity. The fact that the removal of these
compounds could be explained by the sorption onto the
available organic surfaces, explains why there was no
significant difference (p>0.05) in their removal efficiencies
between planted and unplanted beds.
No statistical significant differences (p>0.05) were observed
for the removal efficiencies of any of the pharmaceuticals
tested for a 2-day HRT as compared to a 4-day HRT.
However, the rather efficient removal shown by the tropical
wetlands with HRTs of 2 to 4 days indicates the possibility
of using such a CW system (with less land requirements)
for removing certain pharmaceuticals from drinking water
reservoirs in Singapore or other tropical regions.
REFERENCES
[1] Brimecombe, M.J., Leij, F. A.A.M. and Lynch, J.M., 2001.
“Rhizodeposition and microbial populations”. In: The
rhizosphere: biochemistry and organic substances at the
soil-plant interface, Pinton, R.,Varanini, Z., Nannipieri, P.,
Eds., Marcel Dekker, New York, 2001, pp. 74-98.
[2] Brix, H., 1997. “Do macrophytes play a role in constructed
treatment wetlands?” Wat. Sci. Tech., Vol. 35, No. 5, pp 1117.
[3] Buser, H., Poiger, T. and Mueller, M. D., 1999. “Occurrence
and environmental behaviour of the chiral pharmaceutical drug
ibuprofen in surface waters and in wastewater”. Environ. Sci.
Technol. 1999, 33, 2529-2535.
[4] Ellis, J. B., 2006. “Pharmaceutical and personal care products
(PPCPs) in urban receiving waters”. Environ. Pollut. 144,
184-189.
74
[5] Heberer, T., 2002. “Occurrence, fate and removal of
pharmaceutical residues in the aquatic environment: a review
of recent research data”. Toxico. Lett. 2002, 31, 5-17.
[6] Hijosa-Valsero, M., Matamoros, V., Sidrach-Cardona, R.,
Martín-Villacorta, J., Bécares, E. and Bayona, J.M., 2010.
“Comprehensive assessment of the design configuration of
constructed wetlands for the removal of pharmaceuticals and
personal care products from urban wastewaters”. Water Res.
44 (2010) 3669-3678.
[7] Llorens, E., Matamoros, V., Domingo, V., Bayona, J.M.
and García, J., 2009. “Water quality improvement in a fullscale tertiary constructed wetland: Effects on conventional
and specific organic contaminants”. Science of the Total
Environment, 407 (2009) 2517-2524.
[8] Matamoros, V., García, J. and Bayona, J.M., 2005. “Behavior
of selected pharmaceuticals in subsurface flow constructed
wetlands: a pilot-scale study”. Environ. Sci. Technol. 2005,
39, 5449-5454.
[9] Matamoros, V. and Bayona, J.M., 2006. “Elimination of
pharmaceuticals and personal care products in subsurface
flow constructed wetlands”. Environ. Sci. Technol. 2006, 40,
5811-5816.
[10] Matamoros, V., Arias, C., Brix, H. and Bayona, J. M., 2007.
“Removal of pharmaceuticals and personal care products
(PPCPs) from urban wastewater in a pilot vertical flow
constructed wetland and a sand filter”. Environ. Sci. Technol.
2007, 41 8171-8177.
[11] Mitsch, W. J., Day, J. W., Zhang, J. L. and Lane, R., 2005.
“Nitrate-nitrogen retention by wetlands in the Mississippi
River Basin”. Ecological Engineering, 24: 267-278.
[12] Mitsch, W.J., Tejada, J., Nahlik, A., Kohlmann, B., Bernal,
B. and Hernández, C.E., 2008. “Tropical wetlands for climate
change research, water quality management and conservation
education on a university campus in Gosta Rita”. Ecological
Engineering, 34 (2008) 276-288
[13] Ternes, T.A., Stüber, J., Herrmann, N., McDowell, D., Ried,
A. and Kampmann, M., 2003. “Ozonation: a tool for removal
of pharmaceuticals, contrast media and musk fragrances from
wastewater?” Water Res 2003, 37(8): 1976-82.
[14] Whipps, J.M., 1990. “Carbon economy”. In J.M., Lynch, ed,
The Rhizosphere. Wiley, New York, pp 59-97.
RESPONSES OF FLOATING BREAKWATER
TO REGULAR WAVES
Wenbin Zhang (wbzhang@ntu.edu.sg)
INTRODUCTION
With the development of a large number of small marinas
and recreational harbors, many new types of breakwaters
have been proposed to reduce the energy transmitted into the
harbors. However, in deep waters, traditional bottom-fixed
breakwaters may lead to more expensive construction costs.
Recently, floating breakwaters are considered as an efficient
alternative approach to protecting marinas and harbors
from coastal waves. In this report, an experimental study
on motion responses and wave scattering of pontoon-type
floating breakwater is reported, aiming at collecting a set
of reliable experimental data under various wave conditions
for future theoretical and numerical studies.
Figure 1. A view of the breakwater model in the wave flume.
A mooring cable with the anchor is shown in the left panel
of Figure 2.
EXPERIMENTAL SETUP
The experiments were conducted in a water flume located
in the Hydraulics Laboratory at Nanyang Technological
University (NTU), Singapore. The concrete-walled wave
flume used in the experiments is about 45 meters in total
length, 1.55m in width and 1.55m in depth. At one end of
the flume, there is an adjustable slope beach covered with
several porous pads to minimize wave reflections.
A piston-type wave generator is equipped with a system
so-called Active Wave Absorption Control System
(AWACS), which was developed by Danish Hydraulic
Institute (DHI). The principle used in the AWACS is to
measure the (reflected) waves on the wave paddle, and
by means of digital filters and the servo system, to isolate
the reflected part and then impose an opposite movement
of the wave paddle, which results in the desired incident
wave conditions.
The mooring system consists of 2 components: mooring
cables and anchors. It should be noted that the anchors
need proper weights and volumes so that they can provide
sufficient tensional forces for the mooring cables, but do
not disturb the water waves significantly. Stainless steel
chains were used as they are strong enough and do not
rust when being placed in the wave tank for a long time.
In order to reduce the potential risk of damaging the model
and two walls of wave flume and maintain a two dimensional
motion, ball bearing structures were designed and fixed at
the two sides of the floating breakwater. The ball bearings
can prevent the floating structure from colliding with the
walls of the wave flume when the floating breakwater
responses to the regular waves. The ball bearing structure
is shown in the middle panel of Figure 2.
The responses of the floating breakwater model to waves
were recorded by an Inertia Measurement Unit (IMU), which
can measure the accelerations of three translational motions
and angular velocities of the three rotational motions. The
IMU was mounted at one corner on the top plate of the
model, referring to the right panel of Figure 2. The IMU
sampling frequency used in this study was 200Hz.
The experimental configuration of floating breakwater is
illustrated in Figure 3. A total of 5 wave gauges were
used for recording wave elevations. There were three wave
probes placed in front of the model to separate the incident
waves from reflected waves. The other two probes were
placed after the model to record the transmitted waves.
The distances between the three wave probes in front of
The breakwater model used in this study is 1.420m long,
0.75m wide and 0.410m high. The total weight of the
breakwater reaches 230kg. The draft was set at 0.217m in
our experiments. The normalized natural frequencies of three
modes were found to be 0.89. A view of the breakwater
model installed in the wave flume is shown in Figure 1.
Figure 2. Anchor with mooring cable, ball-bearing
structure, and mounted IMU.
75
the model were chosen based on the requirement of the
two-point wave separation method (C.R. Liu, et al. 2009;
Goda, Y. 2000). On each testing day, pre-calibration and
post-calibration were performed to ensure the accuracy of
the experimental results.
Figure 3. Experimental configuration of breakwater.
Figure 5. Measured RAOs for pitch, surge &
heave of the floating breakwater.
Figure 4 shows the variation of measured reflection
coefficients and transmission coefficients with normalized
wave frequency parameter, i.e. ω2B/2g, where ω is circular
frequency of the incident waves, and B is the breadth of
floating breakwater.
CONCLUSIONS
A series of experiments have been conducted to investigate
the wave scattering and motion responses of a 2-dimensional
floating breakwater under regular waves. The influences of
wave period (ranging from 0.8s to1.6s) on the reflection
coefficient and transmission coefficient were studied. The
RAOs were thoroughly analyzed. Our experimental results
agree with the existing results found in the literature
(Sannasiraj, S.A et al. 1998; Yamamoto, T. 1981), indicating
that our data are reliable. These data obtained are intended
for verifying theoretical and numerical models in future
studies. It is also our motivation that the results presented
here will be a foundation for our further study on the effects
of different damping devices on the responses of floating
breakwaters to regular and irregular waves.
REFERENCES
76
Figure 4. Measured reflection coefficient (Cr) & transmission
coefficient (Ct) of the floating breakwater.
[1] C.R. Liu, Z.H. Huang, and S.K. Tan, 2009. “Nonlinear
scattering of non-breaking waves by a submerged horizontal
plate Experiments and simulations”. Ocean Engineering, 36
(2009) 1332-1345.
The measured Response Amplitude Operators (RAOs) for
pitch, surge and heave responses are shown in Figure 5 as
functions of the normalized wave frequency parameter. It
can be found that the maximum values of RAOs for three
modes of motion occur when the incident wave frequency
equals to the natural frequencies of the breakwater model.
This can be attributed to the resonance phenomena of the
floating breakwater.
[2] Goda, Y., 2000. “Random Seas and Design of Maritime
Structures”. 2nd Edition, World Scientific, Singapore.
[3] Sannasiraj, S.A., Sundar, V. and Sundaravadivelu, R., 1998.
“Mooring forces and motion response of pontoon-type floating
breakwaters”. Ocean Engineering, 25(1): 27-48.
[4] Yamamoto, T., 1981. “Moored floating breakwater response
to regular and irregular waves”. Applied Ocean Research, 3,
114-123.
SOLITARY WAVE INTERACTION WITH A
SLOTTED BARRIER: WAVE SCATTERING
AND HYDRODYNAMIC FORCES
Zhida Yuan (yuan0025@ntu.edu.sg)
ABSTRACT: Slotted barrier are low cost structures that can be very effective in reducing the transmitted energy of long waves. In this
study, the transmission and reflection of tsunami waves, with the leading wave being modelled by a solitary wave, through slotted barriers
in the form of a row of circular cylinders were studied experimentally. The results were also analyzed by a method based on long wave
approximations. It is found that the spacing between two adjacent cylinders is one of the main factors that control the transmission of
solitary waves through slotted barriers. Hydrodynamic forces induced by solitary wave were measured and drag force coefficients of
the slotted barrier are discussed in this paper.
INTRODUCTION
EXPERIMENTAL SET-UP
Tsunami waves generated by mighty underwater earthquakes/
landslides, which can occur at any time, can strike in
minutes, and cause damages to coastal areas. Active
protective measures such as breakwaters are also necessary
to prevent ships from breaking mooring lines and hitting
the port facilities because of the tsunami-induced current.
Pile or slotted breakwaters are low cost breakwaters (see
Mani & Jayakumar (1995) for cost estimation for pipe/
slotted breakwaters) that can be very effective in reducing
the transmitted energy of long waves (see Mei et al.
(1974)). Figure 1 shows a section of pile breakwater along
Singapore coast. A lot of research has been carried out on
the interactions of regular waves with slotted barriers in the
absence of currents (e.g. Kakuno & Liu (1993); Isaacson et
al. (1998); Huang (2007)). Recently, the effects of currents
on the scattering of regular waves by slotted barriers were
examined by Huang (2006) and Huang & Ghidaoui (2007).
However, few studies about tsunami wave interaction with
slotted barriers are reported.
In laboratory simulation, the first peak of tsunami waves
is normally modeled by a solitary wave in view of
the extremely long length of such waves. A series of
experiments were conducted in a wave flume located at
the Hydraulics Laboratory, NTU, Singapore, to study the
transmission/reflection and wave forces of solitary waves
through pile/slotted breakwaters consisting of an array of
circular cylinders of diameter D = 3 cm. Two wave probes
were used to measure the surface elevations at location G1
and G2, and the middle cylinder was instrumented with
a 3-D force transducer at its top end to measure the total
wave forces acting on it. Figure 2 shows a view of the
pile breakwater used in our experiments. The wave flume
was 32 m long and 54 cm wide. Installed at one end of
the wave flume was a piston- type wave generator (HR
Wallingford), which was used to generate the solitary waves.
Figure 3 shows the experimental setup, where the wave
probe G1 was used to measure the incident and reflected
waves while the wave probe G2 was used to measure the
transmitted wave.
Figure 1. A segment of pile breakwater found in a section of
the Singapore coast.
The main objective of this study is to examine experimentally
the transmission and reflection of tsunami waves (solitary
waves) through pile breakwaters; moreover, wave forces
were measured and hydrodynamic coefficients were
investigated and compared.
Figure 3. Sketch of experimental setup showing the relative
locations of the slotted barrier and the two wave probes.
Figure 2. A view of the slotted barrier installed
in the wave flume.
77
To study the effects of water depth and incident wave
height, five wave heights varying from 4 cm to 8 cm were
examined for h = 15 cm and six wave heights varying
from 5 cm to 10 cm were examined for h = 20cm. Three
different slotted barriers were used in the experiments,
with the center to-center distance between two adjacent
cylinders (spacing) being S = 4.5 cm, S = 4.2 cm, S =
3.64 cm, respectively. As the diameter of the cylinder was
3 cm, the spacing-to-diameter ratio S/D ranged from 1.50
to 1.21 in this study.
We can define the reflection (CR) and transmission (CT)
coefficients by
CR =
HR
H
, CT = T
HI
HI
…(1)
where HR, HT and HI are the heights of reflected, transmitted
and incident solitary waves, respectively. These coefficients
are determined both experimentally and by using the
theory developed for long waves interacting with a slotted
barrier in the presence of a uniform current (Huang &
Ghidaoui (2007)).In our experiments, two water depths
were examined with D/h = 1/5 and D/h = 3/20, respectively.
After analyzing our experimental data, it was found that
the measured reflection and transmission coefficients are
nearly independent of D/h. Figures 4~6 show the measured
reflection and transmission coefficients, together with those
predicted by long wave theory of Huang & Ghidaoui
(2007), for spacing-to-diameter ratio S/D = 1.21, 1.40,
and 1.50, respectively. Here, f is an equivalent quadratic
loss coefficient to be determined from the experiments.
For a given S/D, the measured transmission coefficient
decreases with increasing HI/h, while the measured reflection
coefficient is insensitive to the change in HI/h. These trends
are similar to those found in long waves scattered by a
slotted barrier in the presence of a uniform current (Huang
& Ghidaoui (2007)).
78
For a given incident wave height HI/h, the measured
transmission coefficient increases with increasing spacingto diameter ratio S/D, while the reflection coefficient
decreases with increasing S/D. These trends agree with
the following theoretical observations: in the limit of
S / D → ∞, theoretically CT → 1 and CR → 0; in the
limit of S / D → 0, theoretically CT → 0 and CR → 1.
The transmission coefficients are calculated by long wave
theory by Huang & Ghidaoui (2007) for a given barrier
and incident wave conditions. Numerical experiments
show that the following values of f can produce the best
fits to the measured transmission coefficients for the three
barriers: f =3 for S/D =1.5, f =6 for S/D =1.4 and f = 18
for S/D = 1.21. Figures 4~6 show the comparison between
the predicted and measured transmission coefficients for all
three barriers studied in the experiments. It can be seen that
the long wave approximation can predict the transmission
coefficient satisfactorily.
Figure 4. Comparison between the measured and predicted
hydrodynamic coefficients for S/D=1.21. Solid lines (f =18),
chains (f=14.4), and dashed lines (f =21.6).
(See Huang & Yuan 2010).
hydrodynamic coefficients for S/D = 1.40. Solid lines (f = 6),
chains (f =4.8), and dashed lines (f =7.2).
The predicted reflection coefficients are also shown in
Figures 4~6. The long wave approximation can still provide
reasonable prediction of the reflection coefficients for
relatively small HI/h, i.e., the nonlinearity is weak. For large
HI/h, long wave approximation over-predicts the reflection
coefficients for all three barriers. It is expected that the
nonlinear interaction between the incident and reflected
solitary waves cannot be handled by long wave theory of
Huang & Ghidaoui (2007).
hydrodynamic coefficients for S/D = 1.50. Solid lines (f = 3),
chains (f = 2.4), and dashed lines (f = 3.6).
Figure 7 shows the experimentally obtained drag force
coefficients It can be seen that the drag coefficients are
remarkably dependent on cylinder spacing. The mean
coefficients curves show that coefficient values for S / D
= 1.21 are very close to those for S / D = 1.14 within the
present test range. The mean curve for S / D = 1.5 clearly
lies below those of S / D = 1.21 and S / D = 1.14.
REFERENCES
[1] Huang, Z. and Ghidaoui, M.S., 2007. “A model for the
scattering of long waves by slotted breakwaters in the presence
of currents”. Acta Mechanica Sinica, 23:1-9.
[2] Huang, Z. and Yuan, Z., 2010. “Transmission of solitary waves
through slotted barriers: A laboratory study with analysis by
a long wave approximation”. Journal of Hydro-environment
Research, 3: 179-185.
[3] Huang, Z., 2006. “An experimental study of wave scattering
by a vertical slotted barrier in the presence of a current”.
Ocean Engineering, 24:717-723.
[4] Huang, Z., 2007. “Wave interaction with one or two rows of
closely-spaced rectangular cylinders”. Ocean Engineering, 34:
1584-1591.
[5] Isaacson, M., Premasirl, S. and Yang, G., 1998. “Wave
interaction with vertical slotted barrier”. Journal of Waterway,
Port, Coastal and Ocean Engineering, 124 (3): 118-126.
[6] Kakuno, S. and Liu, P.L.F., 1993. “Scattering of water waves
by vertical cylinders”. Journal of Waterway, Port, Coastal
and Ocean Engineering, 119 (3):302-322.
Figure 7. General tendency of drag coefficients versus
dimensionless incident wave heights.
CONCLUDING REMARKS
In this study, the transmission, reflection and drag force
of solitary wave through pile breakwaters were studied
experimentally, and the measured transmission coefficients
agree well with those calculated by using long wave
approximation. The transmission coefficient decreases
slightly with increasing HI/h, while the reflection coefficient
is not sensitive to the change of HI/h; the drag force
coefficient decreases slightly with increasing HI/h. The
spacing between the adjacent cylinders has significant
influence on the transmission, reflection and drag force
coefficient; reducing the barrier spacing would remarkably
reduce/increase the transmission/reflection and drag force
coefficient.
[7] Mani, J.S. and Jayakumar, S., 1995. “Wave transmission by
suspended pipe breakwater”. Journal of Waterway, Harbor,
Coastal and Ocean Engineering, 121 (6): 335-338.
[8] Mei, C.C., Liu, P.L.-F. and Ippen, A.T., 1974. “Quadratic
head loss and scattering of long waves”. Journal of Waterway,
Harbor and Coastal Engineering Division, 99: 209-229.
[9] Titov, V.V., Rabinovich, A.B., Mofjeld, H.O., Thomson, R.E.
and Gonzalez, F.I., 2005. “The global reach of the 26 December
2004 Sumatra tsunami”. Science, 309: 2045-2048.
79
TECHNOLOGIES FOR WATER
SOFTENING: A REVIEW
Fang Wangxi (WXFang@ntu.edu.sg)
Wang Rong (RWang@ntu.edu.sg)
INTRODUCTION
The term, “hard water”, refers to water with a high mineral
content that primarily consists of calcium and magnesium
cations and other divalent or multivalent metal ions.
Hard water is undesirable as the minerals can produce an
unpleasant taste, react with soap anions to decrease the
cleaning efficiency, induce scaling and corrosion problems
and cause serious failures in pipelines of boilers, heat
exchangers and electrical appliances, etc. [1]. Figure 1
shows the examples of scaling in a faucet and a pipe.
(a)
exchange easily with divalent calcium and magnesium ions
in the water. As the water passes through the column, the
hardness ions replace the hydrogen, sodium or potassium
ions which are released into the water, thus the softer
water is achieved. When the resins become saturated with
hardness cations, they gradually lose their effectiveness
and must be regenerated. The regeneration is normally
implemented by passing a concentrated brine solution such
as sodium chloride or potassium chloride through them [4].
Figure 2 illustrates the reaction occurred during a typical
ion exchange resin treatment and regeneration process.
Due to greater affinity of the resin for larger multivalent
cations, the reaction shifts from left to right when the hard
water passes though the resins, while in the regeneration
process, the sodium concentration in the brine solution is
so high that the equilibrium of the reaction shifts toward
left, leading to the replacement of the calcium ions on the
resin with sodium ions.
(b)
Figure 1. (a) Drop coming out of a faucet coated with calcium
from the hard water; (b) Scale reducing the size
of pipework [2].
80
Water softening is a water treatment process that serves
the removal of dissolved minerals in hard water. Various
methods have been applied to remove hard water minerals
from natural, industrial or domestic water sources, which
include the applications of ion exchange, demineralization,
chemical precipitation, distillation and membrane separation
[3]. Currently, with the financial support from EWI,
Singapore Membrane Technology Center (SMTC) is
collaborating with Siemens Water Technologies to develop
low-pressure hollow fiber membranes for water softening.
This study reviews three major treatment technologies
that are currently used in domestic and industrial water
softening applications.
ION EXCHANGE
Water softening by ion exchange resins
In an ion exchange process, hard water passes through
a column of polymer resins. The polymer resins possess
negatively charged functional groups, which can adsorb
and bind metal cations. The univalent hydrogen, sodium or
potassium ions initially contained in the resins are able to
Figure 2. Schematic of typical cation exchange reactions.
An advantage of the cation exchange treatment process is
that it does not change the pH or alkalinity of the water.
Other advantages include excellent process reliability,
chemical safety and process stability for long-time
performance. That is why water softening by ion exchange
has been used worldwide, especially in household and
industrial water treatments. However, this process has
several major drawbacks. Firstly, total dissolved solids
(TDS) in the treated water do not decrease significantly due
to the release of sodium or potassium. Secondly, the excess
brine solution produced during the regeneration process
may be difficult to treat with. In addition, the resins may
be fouled by some metal cations like oxidation by ferric
ions and thus lose the treatment efficiency.
Alternatively, a class of minerals called zeolites also
exhibits good ion exchange properties. In fact, zeolites
were widely used in earlier water softening [5], and later
replaced by synthetic ion exchange resins. Compared
with natural zeolites, ion exchange resins are artificially
synthesized to achieve better treatment efficiency and
regeneration ability.
to 10.6 to achieve efficient precipitation [7]. If the raw
water contains a high amount of magnesium, excess lime
must be introduced to raise pH above 11 in order to help
precipitating magnesium hydroxide.
Demineralization
Table 1. Lime softening reactions
If the water needs to have the mineral content entirely
removed, it is passed through a cation exchange column in
the hydrogen ion form (H+), followed by an anion exchange
column in the hydroxide form (OH-) to replace all the
cations and anions, respectively. The two-step ion exchange
process is called demineralization [6]. The regeneration
process involves the recharging of both hydrogen with a
strong acid (usually HCl) and hydroxide ions with a strong
base (usually NaOH) for the two columns of resins.
Water demineralization is also widely used for the
production of high purity water. However, compared with
the ordinary ion exchange resin process, additional hazards
are introduced due to the involvement of strong acid and
base. That is the main reason why this technology is less
commonly applied in household use.
Hardness
Lime
Precipitate
CO2’
+
Ca(OH)2
→
CaCO3 + H2O
Ca(HCO3)2
+
Ca(OH)2
→
2CaCO3 + 2H2O
Mg(HCO3)2
+
Ca(OH)2
→
CaCO3 + MgCO3 + 2H2O
MgCO3
+
Ca(OH)2
→
Mg(OH)2 + CaCO3
If non-carbonate hardness is involved, soda ash addition
is needed. Table 2 shows the additional reactions involved
for lime-soda ash softening. The raw water is assumed to
contain SO42- in addition to bicarbonate ions.
Table 2. Additional reactions for lime-soda softening.
Hardness
Lime/soda ash
Precipitate
MgSO4
+
Ca(OH)2
→
Mg(OH)2 + CaSO4
CaSO4
+
Na2CO3
→
CaCO3 + Na2SO4
CHEMICAL PRECIPITATION
Evaluation of lime softening technology
Water softening by chemical precipitation
A key feature of lime softening is that both the calcium in
the raw water as well as the calcium added with the lime
are precipitated. As a result, the total dissolved solids (TDS)
decrease after the treatment. This is in contrast to the ion
exchange softening where sodium is exchanged for calcium
and magnesium ions, and no significant change occurs in
the level of TDS. The cost-effectiveness in treating large
quantities of surface water also makes lime softening be
a major water softening technology in water treatment
plant-scale applications [8].
Water softening by chemical precipitation has been applied
commonly for large-scale industrial and potable water
production. There are two major types of precipitation
reactions involved in water softening, which include
precipitation by the addition of lime (calcium hydroxide,
Ca(OH)2) or soda ash (sodium carbonate, Na2CO3). Lime
is used to remove chemicals that cause carbonate hardness,
while soda ash is introduced to remove chemicals that
cause non-carbonate hardness. Other chemicals applied
for precipitation treatment include quicklime (CaO) and
caustic soda (NaOH).
Working principles of lime and lime-soda ash
treatments
MEMBRANE FILTRAION
Water softening by pressure-driven membrane
processes
With rapid development of membrane technology in recent
years, conventional water softening methods involving
ion exchange resin, zeolites, and lime or lime-soda
ash treatments are being replaced by membrane-based
approaches. Compared with conventional methods, water
softening through membrane filtration does not involve large
quantities of chemicals such as lime and sodium chloride
During lime softening process, the addition of lime leads
to the increase of raw water pH and the shift of the
equilibrium of the carbonate species in the water. When pH
gets above 9.5, most of the dissolved carbon dioxide and
bicarbonate convert into carbonate so that it becomes the
dominant species in the carbonate system. Then calcium
carbonate begins to precipitate because the concentrations
of the two ions exceed solubility limit of calcium
carbonate. Additionally, magnesium can be precipitated
as magnesium hydroxide if excess lime is added into the
system and pH exceeds 11. Table 1 shows the chemical
reactions occurred during lime softening process. For raw
water containing minimal magnesium ions, only calcium
needs to be removed. No excess lime needs to be added,
and system pH can be maintained in a range from 10.3
However, several problems are encountered during the
application of this technology. Water after lime treatment
has a high pH, which needs an additional stage of pH
neutralization process. The treatment and disposal of large
amount of high pH sludge is also a problem. Moreover,
continuous removal of the calcium carbonate scale on rapid
mixers and flocculation basin equipment brings additional
operating and maintenance costs.
81
as well as other potentially hazardous chemicals, which
can reduce significantly the TDS of raw water. Therefore,
hardness removal through membrane processes has the
potential to offer lower operating and by-product disposal
costs, increased operation safety and relatively lower energy
consumption [9].
Membrane filtration is a separation process with the input
of energy, which serves as a driving force to separate a
mixture. For the application of water softening, reverse
osmosis (RO) or nanofiltration (NF) membranes are utilized
to physically remove the hard water minerals from the
raw water source. The type of membrane determines the
degree of treatment.
Reverse osmosis
RO has been widely used from household drinking water
purification and industrial water purification to large-scale
water production, seawater desalination and wastewater
treatment. Forward osmosis is the automatic net flow of
water through a semi-permeable membrane from a dilute
solution to a concentrated solution due to the osmotic
pressure difference across the membrane. In contrast, RO
is a pressure-driven membrane process which allows water
in the concentrated solution to pass through the membrane
and flow into the dilute solution under an external hydraulic
pressure to overcome the osmotic pressure difference. In this
case, the concentrated solution gets even more concentrated
while more diluted solution i.e. purified water is produced.
Figure 3 shows a schematic diagram of reverse osmosis
process.
82
Figure 3. Schematic of reverse osmosis process.
RO membranes are able to reject almost all solutes existing
in the water such as bacteria, natural organic matters,
heavy metal ions and multivalent, divalent and univalent
ions. Thus, when using as a means of water softening,
RO process does not only remove hard water minerals,
but also purifies the raw water to a higher degree than the
requirement of water softening. This characteristic is not
always an advantage. A higher degree of water treatment
would produce highly concentrated brine that needs to be
handled properly. The RO membrane also faces serious
scaling and fouling problems and loses performance during
the treatment process [10]. Anti-fouling or pretreatment of
raw water is therefore required, which reduces the efficiency
of the overall treatment processes. In addition, the high
operating pressure causes high energy consumption. In fact,
the operating and maintenance costs are a few of the major
drawbacks of RO process in large-scale applications.
Nanofiltration membranes
In order to overcome the problems of high energy
consumption and membrane scaling and fouling, NF
membranes are being employed to replace the RO
membranes for certain applications. Since NF membranes
have a less dense structure than RO membranes, a lower
applied pressure is required for NF membranes to achieve a
similar water permeation flux as RO membranes. However,
NF membranes have a nominal pore size in nanometer
scale and thus present poorer rejection for univalent ion
species like sodium chloride. Nevertheless, NF membranes
still remain high rejection to divalent and multivalent ions
such as calcium and magnesium ions, which makes it more
suitable for water softening.
NF membranes are often charged to enhance removal of
hard water divalent ions from raw water. The separation
mechanisms in this case involve an electrostatic effect
named Donnan exclusion and size exclusion. For example,
the surface of the NF membrane can carry positive charges.
The divalent ions like Ca2+ and Mg2+ in the feed water
will be electrostatically excluded from getting closed to
and passing through the membrane. In order to keep the
neutrality of the feed water, the anions like Cl- and SO42have to be retained in the solution- thus only water can
pass through the membrane. The Donnan exclusion is less
efficient for the rejection of univalent cations because the
charge density on the univalent ions is smaller than divalent
and multivalent ions [11].
Although the required trans-membrane pressure for
nanofiltration is lower as compared with RO process, the
operating pressure for conventional NF membranes is still
relatively high in order to achieve productive permeation
flux. For water softening application, it is a challenge to
develop NF membranes that remain capable permeation
flux at a low operating pressure so as to reduce energy
consumption and membrane fouling tendency. In addition,
NF membranes are mainly in the configurations of flat
sheet and tubular membranes. It is desirable to utilize
hollow fiber membranes for large scale water softening
processes, as hollow fiber membranes offer better packing
density, higher surface area to volume ratio and self-support
capability. To address these challenges, the Singapore
Membrane Technology Centre at NTU is currently
conducting research in collaboration with Siemens Water
Technologies. The project aims to fabricate novel NF hollow
fiber membranes with high water permeation flux and high
rejection of divalent ions at a low operating pressure for
water softening.
SUMMARY
Three technologies of ion exchange, chemical precipitation
and membrane filtration, which are widely used for water
softening, are reviewed. The pros and cons of each
technology are discussed. Ion exchange resin and zeolites
treatment are mainly applied in household and industrial
water softening, but the excess brine solution produced
during the regeneration process is difficult to handle if the
technology is applied in a large-scale. Lime softening and
lime-soda ash treatments are more suitable for large-scale
municipal or industrial water production, while facing
problems involving post-treatment for pH neutralization of
softened water and disposal of large amount of high pH
sludge. These two conventional water softening methods are
being replaced by advanced membrane filtration technology,
due to its potential to offer lower operating and by-product
disposal costs, and relatively low energy consumption.
Nanofiltration is found to be the most suitable membrane
process for water softening, but extensive R&D is needed
to develop high performance NF hollow fiber membranes
for this application.
REFERENCES
[1
C. Gabrielli, G. Maurin, H. Francy-Chausson, P. Thery, T.T. M.
Tran and M. Tlili, Electrochemical water softening: principle
and application. Desalination (2006) 201, 150–163.
[2] Hustvedt, Drop coming out of a faucet coated with calcium
from the hard water. Retrieved October 21, 2010, from
http://upload.wikimedia.org/wikipedia/commons/b/bb/Hard_
water_and_drop.jpg
[3] A.P. Sincero and G.A. Sincero, Physical-chemical treatment of
water and waste water. IWA Publishing: CRC Press; 2003.
[4] W. Wist, J.H. Lehr and R. McEachern, Water softening
with potassium chloride: process, health, and environmental
benefits. J. Wiley; 2009.
[5] G.F. Hodkinson, Zeolite water softener, US Patent 1,763,783,
1930.
[6] C.E. Harland, Ion exchange: theory and practice, Royal
Society of Chemistry; 1994
[7] S. Kawamura, Integrated Design and Operation of Water
Treatment Facilities, 2nd ed., J. Wiley; 2000
[8] American Water Works Association, American Society of Civil
Engineers, Water treatment plant design, 3rd ed., McGrawHill; 1998.
[9] F.E. Duran and G.W. Dunkelberger, A comparison of
membrane softening on three South Florida groundwaters,
Desalination (1995) 102, 27-34.
[10] E.M. Vrijenhoek, S. Hong and M. Elimelech, 2001. “Influence
of membrane surface properties on initial rate of colloidal
fouling of reverse osmosis and nanofiltration membranes”.
Journal of Membrane Science, 188, 115-128.
[11] Yaroshchuk, A.E., 2001. “Non-steric mechanisms of
nanofiltration: superposition of Donnan and dielectric
exclusion”. Separation and Purification Technology, 22-23,
143-158.
83
TIME-SEQUENCE ANALYSIS OF
JET-FLIPPING OF LOCALIZED SCOUR
BY 2-D WALL JETS
Lim Siow Yong (csylim@ntu.edu.sg),
Xie Chen (xiec0001@ntu.edu.sg)
INTRODUCTION
Severe localized scour downstream of 2-D wall jets may
cause stability problem to the hydraulic structure—it is one
of the major factors to consider when engineers design the
required erosion protection measures. Researchers working
on this issue focused mainly on finding and predicting the
maximum scour depth and other related scour geometries
at the equilibrium condition (Lim and Yu 2002). However,
under certain flow conditions for 2-D jet scour, there would
be jet-flipping, which is a phenomenon where the jet action
would suddenly flip from the bed to the water surface and
vice versa. It would result in a pseudo equilibrium condition.
Video recording of the scouring process showed a scour
hole being developed with time when the jet action was
digging as a bed-jet. A deep scour hole was formed with
a distinct downstream ridge. This was the digging phase
by the bed-jet. After the hole attained a certain maximum
depth, the jet would suddenly flip to the surface as a
surface-jet. Sand particles on the ridge were seen rolling
down its slope and filling the hole. This is the filling
phase by the surface-jet. The hole became shallower with
time under this filling phase. The digging-filling process is
cyclical. In this study, we will present preliminary results
on the cyclical time-sequence of the jet-flipping due to a
submerged horizontal jet issuing from a sluice gate.
EXPERIMENTAL SETUP AND
MEASUREMENTS
84
The experiments were conducted in a 8m long, 0.3m wide,
0.6m deep glass-walled flume (Fig. 1) in the Hydraulics
Laboratory at NTU. A solid Perspex platform was
constructed to simulate a rigid apron over which a vertical
sluice gate was fixed. The sluice gate can be installed at
any location on the apron. This arrangement facilitates
the study of the effect of apron length on the jet-flipping
phenomenon downstream of the gate. Uniform sand with
median grain diameter (d50) of 0.73 mm was used and
the geometric standard deviation (σg) was 1.12. All the
experiments ran for 7 days and were set with the same
tailwater depth (Ht = 12.7cm), sluice gate opening (d0 =
10mm), discharge (Q = 2.128L/s), velocity (u0 = 0.71m/s),
Froude number (Fr = 2.267), while only the apron length
(L) was changed. We used a video to record the scouring
process. From the recording, the duration of the digging
and filling phases was noted. The end of digging or
Figure 1 Layout of experimental set-up.
Table 1 Summary of experimental data.
No.
L
(cm)
t0
(min)
dse-dig
(cm)
dse-fill
(cm)
d
(%)
Run16
0
None
14.7
--
--
Run15
15
937
8.1
5.1
37
Run13
21
258
6.5
4.6
29
Run14
30
24
3.9
2.8
28
the start of filling phase corresponded to when the water
surface suddenly transformed from calm to wavy. When
the water surface changed from wavy to calm again, this
moment was recorded as the end of filling or the start
of digging phase. Table 1 summarizes the test conditions
for the 4 runs, where dse-dig is the maximum depth of
scour recorded during the digging phase, dse-fill is the
minimum depth of scour recorded during the filling phase,
and d is the % scour depth difference defined as
(dse-dig - dse-fill)/dse-dig, t0 is the average time to complete one
cycle of digging-filling phase, expressed as follows:
n
fi + tdi)
t0 = ∑(t
i=1
n
where n = number of digging-filling cycles, tfi and tdi are
the filling and digging time in the ith cycle, respectively.
Time sequence analysis
Under normal circumstances for a typical jet scour
experiment, the scour hole will increase with time, and
eventually it will attain an equilibrium state after a long
scouring time. For the hydraulic conditions used in the
present study, at the initial stage the jet would dive and
start to dig at the sediment bed. Soon scour hole of a
Figure 2. (a) Bed profile during digging phase by bed-jet with calm water surface (b) Bed profile during filling phase
with wavy water surface by surface-jet. (Arrow shows direction of jet action).
Figure 3. The time-sequence of each digging and filling phase for different apron lengths.
vigorously as the surface-jet is again transformed into a
bed-jet. Hence, the process is cyclical with bed-jet scouring
the bed during the digging phase and then transforms to a
surface-jet where the hole is back-filled during the filling
phase, and vice versa. For a run time of 7 days, we have
extracted from the video recording the number of cycles
and their durations for each digging and filling phases (Fig.
3). Usually, the scour depth reached a maximum in the first
few digging phases and the maximum depth in each digging
phase was almost the same. And the minimum depth in
each filling phase was also almost the same.
Figure 3 shows that, for each run, the filling time is much
longer than the digging time. The filling time becomes
increasingly longer, while the digging time becomes shorter
with small scale oscillation over the recording period. For
comparison, a dimensionless time is used (Fig. 4). The
lines of digging for L = 21cm and 30cm are quite similar.
However, the lines for L = 15cm is very short for the
certain depth with a corresponding ridge was formed. The
hole continued to deepen as the scour progressed with time
until a stage was reached whence there was no significant
change in the scour depth, which looked like the equilibrium
state was reached. This period is called the digging phase
of the scour development, and the jet action was generally
along the bed and the water surface was calm (Fig. 2a).
However, a short while later, the sediment was observed to
suddenly roll down from the ridge region and back-filling
into the scour hole. The water surface also became rough
and wavy. This was caused by the sudden change of the
jet action from a bed-jet to a surface-jet (Fig. 2b). In the
filling phase, the rate at the initial stage of filling was rapid
and the scour hole was almost leveled and the ridge was
flattened in the process. For quite a long period during this
filling phase, it seemed an equilibrium state was reached
as there was no significant depth change in the filled scour
hole. The filling phase usually lasts very long, at the end
of which the jet would suddenly begin to scour the bed
85
Figure 4. Dimensionless time analysis for three runs with different apron length.
reason that the average time t0 for a shorter apron is much
longer, about 937 mins. Although all the experiments ran
for 7 days, it is not long enough for Run 15 but too long
for Run 14. But the trend can be found that the lines for
Run 15 are quite similar to Run 13 and Run 14. That is,
if Run 15 is allowed to run for more days, its trend seems
to have a similar pattern as Run 13 and Run 14. In Table
1, Run 16 has no apron (i.e. L = 0) and the jet-flipping
phenomenon did not occur. It seems to indicate that the
apron plays an important role for jet-flipping to occur. The
results in Table 1 show that the average time t0 increases
exponentially as the apron length decreases.
Fig. 5 shows 3 photos at different stages of the scouring
process for Run 13. It can be seen that the maximum
scour depth did not change, but the ridge height decreases
over the many flipping cycles between Fig. 5a (24/8/10,
05:33) to Fig. 5c (30/8/10 16:25). The ridge profiles in
Figs. 5b and 5c can be seen being flattened compared to
Fig. 5a, resulting in a reduced ridge height. Fig. 5c shows
that the shaded ridge material has been deposited further
downstream, giving an elongated and flattened bed profile
downstream of the crest after about 6.5 days of scouring
action.
As scouring time increases and as more digging-filling
cycles occurred, more particles ‘escaped’ and there are
relatively less particles in the hole-ridge region compared
to earlier cycles. The net effect is that back-filling of
sediments from the ridge to the scour hole takes a longer
time to fill the hole to a level for the next digging action
to be triggered. The digging time remains more or less the
same, and the jet digs to a depth that is required to trigger
the next filling phase. This explains why the maximum
scour depth remains almost constant but the filling time
is increasingly longer as scour progresses.
CONCLUSIONS
86
Figure 5. Transition of the scour profile.
The present study mainly observed the jet-flipping
phenomenon. Some conclusions can be drawn from the
study:
(1) Under certain hydraulic conditions, jet-flipping is
observed in localized scour due to a 2-D wall jet.
(2) There are two phases. A digging phase where the jet
behaves as a bed-jet and a scour hole is formed. The
water surface is calm during this phase. After the
scour depth reaches a certain maximum value, the jet
flips from the bed towards the water surface causing
it to become rough and choppy and the filling phase
commences. During this phase, the sediments on the
ridge roll back to fill up the hole until it reaches a
certain minimum scour depth whence the digging
phase would resume. The digging-filling processes are
cyclical.
(3) It was observed that as scouring progresses, the
duration of filling phase increases, while the digging
time remains relatively unchanged. The duration for the
filling phase is much longer compared to the digging
phase. The loss of sediment materials on the ridge
as scouring progresses is the main reason for filling
becoming increasing longer.
(4) The apron plays an important role in the process of
jet-flipping. The average time t0 which is the time
from the start of a filling phase to the next start of
a filling phase, increases exponentially as the apron
length decreases.
REFERENCES
[1] Lim, S.Y. and Yu, G., 2002. “Scouring downstream of Sluice
Gate”. Proceedings of First International Conference on Scour
of Foundations, Texas, USA, 17-20 November 2002, Vol. 1,
pp. 395-409.
87
INFRASTRUCTURE SYSTEMS AND MARITIME STUDIES
A DECISION SUPPORT SYSTEM FOR
PORT SELECTION
Jasmine Siu Lee LAM (sllam@ntu.edu.sg)
ABSTRACT: The paper presents a web-based decision support system (DSS) for port selection using analytical hierarchy process
(AHP) methodology. AHP is able to assist managers in obtaining a detailed understanding of the criteria and address the port selection
problem utilising multi-criteria analysis. It shows how technology advancement can bring positive effects on strategic planning of
shipping firms.
INTRODUCTION
Users
In liner shipping, service network planning is an important
activity. Selecting the candidate calling ports is the first
step in service network planning. In practice, the current
mode of planning is still to a large extent manual, where
considerable professional knowledge and experience is the
key driver. This may not be an ideal method when time is
of essence and rapid decision making is required to respond
to a dynamic market. Therefore, a DSS that can carry out
the process more efficiently is of utmost importance.
♦
User Interface (Visual Basic)
Port Selection Module (AHP)
SYSTEM ARCHITECTURE
In this paper, we integrate AHP with a DSS using
optimisation system development. To the best of our
knowledge, our work is the first attempt of such an
approach. AHP is a multi-objective, multi-criteria theory of
measurement. Once the method is integrated with a DSS,
it can help players in liner shipping industry to shorten
the time needed for making decisions on port selection in
service planning by a more robust approach.
88
Difficulties in obtaining data could be a major reason for
hindering the application of choice theories (AHP) on
port selection. However, the proposed DSS is web-based;
therefore it can be accessed by more users and data
collection can be carried out faster. Figure 1 shows the
proposed overall structure. Being a web-based system, the
DSS includes three tiers. The first tier is the interface that
interacts with the user. The second layer is the mechanism
which handles all the calculations and optimisations.
The last tier is the database that stores all the necessary
information for processing. VB.net is used to develop the
front end of the system, whereas in the second layer, Visual
Basic is employed to develop mechanisms to perform
simple manipulations of the records and interact with the
database, as well as with the optimisation and financial
analysis modules. The database, on the other hand, is mainly
handled by Microsoft software. We use Access and Excel
to maintain all the necessary data.
Optimisation
Database server
Databases (Access, Excel)
Figure 1. Decision support system architecture.
MODEL AND CASE ILLUSTRATION
This section illustrates the port selection procedure inside
the DSS. The step-by-step procedure is as follows:
1.
Select the regions (or markets) to be covered in the
service network.
2.
Determine the total number of ports to be visited and
the number of ports to be visited in region i (xi).
3.
Select the port criteria (j = 1, 2,….N) to be considered
and determine the weight of each criterion (wj); the
sum of all selected criteria weights must be equal to
1. If the user cannot determine the criteria weights
directly, the weights are calculated using pair-wise
comparison (from AHP using a nine-scale scoring).
In pair-wise comparisons, inconsistency may occur.
Therefore, the consistency ratio (CR) is calculated and
if CR is greater than 0.1, the pair-wise comparison
matrix is revised.
4.
Retrieve scores to all ports in selected regions and
criteria from the ports’ database. The score of port k
under criterion j is Skj.
5.
The total score of port k (TSk) is the weighted sum
of the port’s scores in all criteria.
TSk = ∑wjSkj
6.
For each region choose xi ports with the highest
score.
7.
Perform sensitivity analysis if the decision maker
wants to know the effects of changing his preference
for port criteria, due to, for example, a change in port
situation.
The second interface is the comparison and prioritization
module. The module allows the decision maker to make
pair-wise comparisons of the selected criteria, and reports
the weight of each criterion and the consistency ratio
(CR) using AHP. In this case, the decision maker focuses
more on container transhipment and its costs than on port
infrastructure. Based on criteria weight calculation in this
case, the weight for port infrastructure, port charge and
container traffic is 0.2, 0.4 and 0.4 respectively. CR is 0.00,
which is less than 0.1 and thus the pair-wise comparison is
consistent. Same as criteria selection, different users have
different preferences, and thus the other decision makers
can change the “Input” data (pair-wise comparisons of
the selected criteria) in the module to get the new criteria
weights automatically.
Case study
The system has been tested and validated with an anonymous
liner shipping company in real operation mode to ensure
that it is suitable for practical operations. The company is
an international liner operator with a wide liner service
network. In our DSS, there are ten proposed regions: North
Asia, East Asia, South East Asia, South Asia, Australia,
New Zealand and Pacific, Africa, Europe, Middle East,
North America and Latin America. These regions depend
on the applicable shipping line network. According to the
literature review and interviews with the managers in the
company, the following six criteria are included for the port
selection analysis: location, port charge, port infrastructure,
ship calls, container traffic, and water depth.
Selection of the port region, the number of ports visited
and the subject criteria to be analyzed is done by the first
interface of the system. Through this interface, the decision
maker selects the port regions to be served in the liner
network analysis by adding a new port region or removing
any port region from the port regions list. After selecting
port regions to be served, the decision maker chooses the
number of ports to be visited in the responding port region
and the subjective criteria to be considered for the liner
network within these selected port regions.
CONCLUSIONS
In this system, the most valuable trait is that the user
himself can select the port criteria he wants and change the
preference of each criterion according to the real situation
and company policy.
Due to the flexibility of the system, the decision maker
in the company can change his preferences case by case,
which helps to enhance the service quality of the liner
shipping company and get a more competitive position in the
dynamic shipping market. The paper shows how technology
advancement like utilising DSS can bring positive effects
on strategic planning of shipping companies.
The work to develop the DSS can be enhanced in future
research. Port criteria are essential to select ports and
represent an important linkage in the DSS. Marketing theory
has pointed out that a customer’s perception of a particular
situation is often different from that of another customer.
Therefore, future work includes surveying the perspective
of the shippers in various port regions, and modifying the
system according to the new port criteria in order to give
the user more precise choices on port criteria.
In this case, the user of the system needs to choose 3
ports in South Asia and 2 ports in Middle East to serve a
liner network. A liner network planning manager (decision
maker) in the company bases on company policy and/or his
experience and selects three criteria – port infrastructure,
port charge and container traffic - to evaluate the ports. Since
the criteria selection is based on company’s/ management’s
preference, other users can choose different criteria for port
evaluation to get different results.
In the third interface, port data are retrieved from the
database. Thereafter, the ports with the highest overall
score in each region are selected. In this case, there are
five ports in each region, South Asia and Middle East,
respectively. According to the requirement for the number
of ports selected in each region, which has been mentioned
above, Karachi, Mundra and Nhava Sheeva in South Asia
and Aden and Jeddah in Middle East having the highest
scores are selected.
89
DANGEROUS GOODS REGULATING
SYSTEM IN SINGAPORE
Cui Yifang (cuiy0003@ntu.edu.sg)
Wong Yiik Diew (cydwong@ntu.edu.sg)
ABSTRACT: Dangerous Goods (DG) can lead to serious consequences if improperly managed. Hence, a sound regulating system is
needed to safeguard the handling of DG. In Singapore, many international and national regulations have been implemented. Supportive
initiatives have also been launched by DG agencies to improve the regulation system.
Our research study shows that there are incongruous opinions between industry and regulating agencies concerning Singapore’s DG
regulation system. While industry companies aspire for a unified system with one DG agency in charge to reduce confusions existing in
the current system, the regulatory bodies have their reasons to retain the multi-agency system as they continue to improve and delegate
responsibilities clearly among DG agencies.
A common response from the industry interviewees is that there is room to improve the effectiveness of communication between industry
and regulating agencies. The agencies shall endeavour to timely inform companies about DG developments.
INTRODUCTION
Dangerous goods (DG) are radioactive, flammable, explosive
or toxic substances and organisms in solid, liquid or gas
forms that can cause danger to the public, property and the
environment (UOW 2007). As a result, there are a number
of regulations covering safe transportation, storage and
packaging of DG such as International Maritime Dangerous
Goods (IMDG) Code and Maritime and Port Authority of
Singapore (Dangerous Goods, Petroleum and Explosives)
Regulations.
Globally, DG is heavily regulated especially in Europe as
it concerns the health and safety of the population as well
as being environmental hazards. Moreover, DG can also
become terrorist weapons which could cause potentially
dangerous situations with disastrous consequences.
90
In Singapore, DG carriers can be seen frequently on the
roads with special signs indicating the specific class of
DG on board. Since there is limited geographical space in
Singapore, even approved DG vehicles transportation routes
cannot avoid the closeness to the residential and central
district areas. Furthermore, research shows an increase
in frequency of accident occurrences in transportation of
DG in Europe and North America regions ever since the
beginning of 20th century to 2004 (Planas et al. 2008).
Singapore is also exposed to similar hazards from frequent
DG transportation and storage given its small land space.
The hub-and-spoke system that the port of Singapore has
adopted requires an enduring, safe and secure transition of
cargoes including DG which is a competitive advantage of
Singapore port compared with the others. Therefore, the
importance of a well-managed DG system is enormous.
In order to safeguard the process of transport, storage and
carriage of DG, several governmental agencies in Singapore
have launched initiatives including various regulations
and applied technologies to help the industry to build up
a strong DG logistics chain. At the same time, the DG
industry is also paying good attention to the handling
process of DG.
The objectives of this study are to identify critical
issues for DG regulating system in Singapore through a
thorough literature review, and to gauge the usefulness
and compliance status of DG regulations by assessing the
logistics industry’s perceptions on the current regulation
system for DG transport in Singapore.
The research is within the context of Singapore with focus
on transportation and logistics of DG. Relevant regulations
and supporting activities are reviewed and profiled; the
compliance status and usefulness of regulations, as well
as the future trends, are obtained from interviews and
survey.
METHODOLOGY
Primary data for this study were collected through interviews
and surveys. Logistics companies in Singapore which are
involved in DG transportation or handling were contacted.
Interviews were conducted with DG professionals in the
logistics companies and DG agencies. Survey questionnaires
were posted to DG logistics companies in Singapore. Survey
questions were designed in accordance to the objectives
of this study. Online survey was also administered on the
survey targets.
Secondary data collection covered literature reviews
of various resources such as databases, journals, books
and internet. Secondary data are important to generate
supportive evidence and comparative references for this
research study.
LITERATURE AND INTERVIEW FINDINGS
Primary activities and supporting activities
Several prior studies were assessed in order to understand
DG regulating system in Singapore, and thus to identify
the critical issues inherent in the system.
Primary activities refer to the international and national
regulations while supporting activities serve to strengthen
implementation of the regulations. The main supporting
activities discussed in this study are technology applications
such as vehicle tracking devices and web portals, while
other supportive initiatives are conferences and responsible
care held and promoted by Singapore Chemical Industry
Council (SCIC). The characteristics of the primary and
secondary activities can be categorised as follows:
• General rules and regulations
• Classification and labelling of DG
• Declaration of DG
• Emergency Management
• Licensing Control
• Health and safety of personnel
General system
Having adopted a number of international DG rules and
regulations, Singapore has steadily improved its DG
regulating system and is catching up on European countries.
Mr. Jacobsen from Leschaco Pte Ltd observed, during an
interview, that Singapore has made considerable progress
in the past decade especially in the aspect of warehousing
for DG.
In general, Singapore has established a relatively sound
DG regulating system based on the various regulations
and supportive activities promoted by several DG agencies.
These regulations cover different aspects of DG transport
and logistics which safeguard the DG transport chain within
Singapore in air, land and ocean freight. As Mr. Foong from
DHL has mentioned, Singapore enjoys a good international
reputation with good ratings for quality, technology and
extremely low corruption as well as good transportation
infrastructure. These performance indicators are important
considerations in the management of DG because it gives
confidence to customers that DGs are managed in an
efficient and effective manner with full compliance to
international DG regulations.
DG incidents in Singapore
A strong emergency response programme is considered
as critical for dealing with DG incidents. In Singapore,
according to Mr. Kwok of SCDF, there are 4 Hazmat
stations located at Alexandra, Jurong Island, Tuas and
Tampines. The Hazmat stations together with fire fighting
stations and Company Emergency Response Team (CERT)
form a strong emergency response team.
DG agencies in Singapore
The Singapore’s DG regulation system encompasses
a multiplicity of agencies (Table 1) which can cause
inconvenience for DG handling parties such as manufacturers,
carriers and storage providers. Although each agency has
clearly-defined roles and responsibilities, there are grey
areas in the regulating system due to the complexities of
DG properties that result in different standards.
Table 1. DG agencies in Singapore.
Main DG agencies
Singapore Civil Defence Force (SCDF)
National Environmental Agency (NEA)
Singapore Police Force (SPF)
Other DG agencies
Ministry of Manpower (MOM)
Maritime and Port Authority of Singapore (MPA)
Health Science Authority (HAS)
Singapore Customs (SC)
Land Transport Authority (LTA)
SPRING Singapore
PSA
SUMMARY OF SURVEY AND INTERVIEW
RESULTS
The perspectives of the industry towards the inconvenience
inherent in multi-agency regulation system were garnered
from the survey. The scope of a compromise between the
agencies and the industry towards enhancing the efficiency
of Singapore’s DG regulation system was explored.
Internationally, DG accidents occur most frequently in
developed countries, especially on highways. The Major
Accident Hazards Bureau (MAHB) in Europe was
established for reporting and analysing DG accidents. In
Singapore, as noted by several interviewees, the accident
rate is low compared with other developed countries.
This may be due to two reasons-one being Singapore’s
limited landscape but more importantly, implementation
of prevention measures and a well-established regulation
framework such that possibility of accident occurrence is
minimised. However, without an established accidents
reporting system, accurate accident data are not available
for analysis. Mr. Tang from DGM Pte Ltd said that the
scale of DG incidents in Singapore was usually small and
Mr. Heng of SCDF ascribed the principal cause of incidents
to human negligence.
These categories of initiatives were surveyed by compliance
status and usefulness, and the results are presented in the
following Survey and Interview Results section.
91
continue strengthening the structure, and improving
clarity of each agency’s roles and responsibilities.
Survey results
Most participating companies in the survey are involved
in ocean freight, transportation and logistics and almost
half of the respondents are handling all 9 classes of DG.
The most commonly handled class of DG is class 3 which
is flammable liquids. The survey obtained the following
observations:
a.
Most respondents agreed that the numbers of
regulations, regulatory agencies and web portals in
Singapore are adequate.
b.
There was contention regarding coverage of the
regulations. One in four respondents perceived that the
regulations do not fully cover all applicable DG issues;
42% of the respondents considered comprehensive
coverage while the remaining 33% of the respondents
felt that there were duplications in some areas.
c.
d.
e.
Half of the participants rated the regulations as being
somewhat useful while the other half rated very useful.
Most participants viewed web portals and the vehicle
tracking devices as being somewhat useful.
Whereas an early study in 2006 indicated deployment
level being lower than perceived usefulness level in
various categories of activities launched by relevant DG
agencies, the present study revealed comparable levels
between deployment and usefulness levels, thereby
suggesting improvements in the activities of the DG
system in Singapore over the past few years.
All the R&D needs proposed to the respondents were
viewed as important and urgent. These R&D needs
included integrated DG regulation system, regulations
for post-accident environmental protection, strong
accident-reporting system and communication channel
between regulatory bodies and industry for relevant DG
information updates. In the 2006 study, multiple DG
agencies and weak communication in disseminating
DG regulation updates were also rated as important
weaknesses existing in Singapore.
Interview results
The interview results further complement the survey results
from industry and regulatory agencies.
92
a.
Interviewees expressed a multitude of opinions
regarding the multi-agency issue in Singapore.
Interviewees who considered the number of agencies
as being too many were principally concerned that
there would be some repetition in the works to be
done such as when applying for licences, submission
of DG manifest, etc. Interviewees who considered the
number of agencies as adequate held the view that
principal DG regulating agencies, namely the SCDF,
NEA and SPF, should not thus pose any big problem.
On the other hand, the agencies did not foresee any
major change to the current framework, and they would
b.
Interviewees had different perspectives regarding
coverage of regulations. Some perceived grey areas
that warranted further clarification by the agencies;
some felt that there were duplications in coverage of
regulations as well as responsibilities of the agencies.
Moreover, as Mr. Jacobsen mentioned, in comparison
with Europe, Singapore still needs to establish more
regulations, especially certain in-house practices. He
suggested that Singapore should introduce a mandatory
appointment of a Dangerous Goods Safety Advisor,
who is trained and certified based on the local and
international rules and regulations, similar to the EU
practice.
c.
Interviewees suggested that more educative information
could be included in web portals for amateur to learn
about DG on-line. Moreover, vehicle tracking devices
are only installed on vehicles licensed to carry DG, and
non-licensed DG carriers continue to pose threats.
d.
There was general agreement about the lack of
effective communication channel in the DG system.
The industry may not have timely awareness of new
updates in regulations or functions on the web portals,
as a result, some inconvenience would arise.
e.
The cost associated with compliance of regulations
and deployment of technologies was considered
relatively high by the interviewees, for example,
the infrastructure cost and training cost. However,
effectiveness, usefulness and safety considerations
seemed more important than cost. Nevertheless, more
cost-effective measures should be developed by the
agencies for the benefit of the industry.
CONCLUSIONS AND RECOMMENDATIONS
The major findings from this study on Singapore’s DG
regulating system are summarised as follows.
First of all, Singapore has an established DG regulation
system encompassing different initiatives and agencies.
However, in comparison with the European system, there
is still space for Singapore to improve further. One major
finding is the industry’s claims of multiple DG agencies in
Singapore to regulate the system which lead to confusions
and time consumption. The industry aspired for an integrated
system to make transactions more effective and efficient
such as when applying for various licences. Moreover, this
can also help companies to reduce consultation times with
different agencies when enquiring on DG issues. Contrarily,
DG agencies stated that they had recognised the benefit of
such system to industry and had discussions on this issue for
the past few years. The agencies have decided to maintain
a multi-agency framework whereby each agency has DG
professionals to deal with specific kind of DG matters.
Furthermore, there are only three major DG agencies namely
SCDF, NEA and SPF, and they constantly endeavour to
define division of roles among each agency clearly for the
benefits of industry. The multi-agency approach involving
each agency exercising responsibilities for specific DG
issues shall be maintained in the foreseeable future.
Secondly, one important and urgent demand from the
industry is effective communication with the authorities.
Updates on the web portals or regulations may not be
timely communicated to the industry thereby causing
inconvenience and delay. Previously, it was SCIC playing
the bridging role in bringing industry and agency personnel
together to share opinions and suggestions several times
each year. One key initiative should be to promote and
enhance connection between the industry and the regulatory
bodies to facilitate the process of exchanging information
and points of views.
Thirdly, by comparing the findings of this study with the
2006 study by Mr. Rajkumar on DG logistics system in
Singapore (Rajkuma 2006), there has been better industry
compliance with agencies’ initiatives as resulting from the
continuous efforts put in by both the companies and the
agencies to improve DG system in Singapore.
As for further R&D, one potential area is the harmonisation
of DG classification system at an international level. As
there are two sets of chemical classification systems defined
by United Nations Recommendations on the Transport of
Dangerous Goods (UNRTDG) and United Nations Globally
Harmonised System of Classification and Labelling of
Chemicals (GHS), international organisations do aspire and
have intention to unify the classifications system so that
there is less confusion. This intended action would affect
the national standards as many countries are complying
with both UNRTDG and GHS. Moreover, Singapore port’s
indigenous classification of DG, i.e. the PSA Classes 1,
2 and 3, which only apply in Singapore port may cause
misunderstanding by shipper and carriers of DG, especially
if they are unfamiliar with the system.
This research study has mainly focused on the internal
factors, specific to Singapore’s context. Future research
studies on DG regulating system should include more
external factors such as comparisons with other countries’
DG systems. The advantages and disadvantages of each
country’s DG framework can be examined to find the gaps.
By analysing both internal and external environments, the
structure and content of Singapore’s DG regulating system
can be further improved to achieve an even safer and more
effective DG regulating system in Singapore.
REFERENCES
[1] Planas, E., Pastor, E., Presutto, F. and Tixier, J., 2008. “Results
of the MITRA project: Monitoring and intervention for the
transportation of dangerous goods”. Journal of Hazardous
Materials, 152(2), 516-526.
[2] Rajkumar, T.V., 2006. Analysis of Dangerous Goods Logistics
in Singapore. Master of Science (Logistics) dissertation,
Singapore: Nanyang Technological University, retrieved
September 2009.
[3] University of Wollongong, 2007. Dangerous Goods, School
of Chemistry, Australia: University of Wollongong, retrieved
November 2010.
93
DETERMINATION OF COEFFICIENT OF
CONSOLIDATION BY ROWE CELL
Budi Wibawa (cwibawa@ntu.edu.sg)
Liyenita Widjaja (liye0002@ntu.edu.sg)
ABSTRACT: Structures built on clay layers will cause consolidation settlement. There are two aspects of consolidation settlement,
i.e. the magnitude of settlement that is related to compression index and the rate of settlement corresponding to the coefficient of
consolidation. A Rowe cell was used to determine the coefficient of consolidation for both vertical and horizontal flow directions with
various drainage conditions.
INTRODUCTION
Structures which are built over soil layers will experience
settlements. One of the settlements, consolidation settlement,
will mainly occur if the structures rest on saturated clay
layers. Consolidation settlement is related to consolidation
- a process of reduction of volume due to dissipation of porewater pressure in the clay layers due to induced compression.
There are two aspects of the consolidation settlement - the
magnitude and rate of settlement. The magnitude of the
consolidation settlement is related to compression index,
whereas the rate of settlement corresponds to coefficient of
consolidation. The coefficient of consolidation is a measure
of the rate of consolidation or the rate of water flow inside
the soil, which is used to determine consolidation time. In
this article, our focus will be on the determination of the
coefficient of consolidation of saturated clay.
94
Terzaghi et al (1967) indicated that both permeability (k)
and coefficient of compressibility (mv) decrease rapidly
with decreasing void ratio so that the ratio (k/mv) tends
to be constant; hence, the coefficient of consolidation in
vertical flow direction (cv) is fairly constant over a wide
range of effective vertical consolidation pressures. However,
based on a study conducted by Robinson & Allam (1998)
on the effect of clay mineralogy on the coefficient of
consolidation, it was found that cv is not constant, but
varies with consolidation pressures. It was also found
that the compressibility of clays is influenced by both
mechanical and physicochemical effects (Mesri & Olson,
1970), depending on the type of mineral, saturating cation
and the pore fluid. Sridharan et al. (2004) observed that soil
with lesser shrinkage index or plasticity index shows an
increasing trend of cv versus vertical effective stress (σv’),
but for higher shrinkage index or plasticity index, there is
a decreasing trend of cv versus σv’ for soils of nearly the
same liquid limit.
In a saturated clay layer, water may flow in both horizontal
and vertical directions during consolidation process. The
rate of flow of water in vertical and horizontal directions
contributes to the overall rate of consolidation indicating
the need of the determination of both coefficients of
consolidation, cv and ch. While cv is usually determined by a
conventional oedometer test, ch cannot be done by this test;
therefore a Rowe Consolidation Cell (Rowe and Barden,
1966) was used instead of the oedometer, to determine the
coefficient of consolidation. Hence, the objective of this
article is to determine the coefficients of consolidation of
clay in both vertical and horizontal directions using the
Rowe cell for various drainage conditions.
EXPERIMENTS AND DISCUSSION
Material
Kaolin was used for the experiments. Tests on basic
properties of soil were done in accordance to BS: 1377
– Part 2. The soil properties are Specific gravity (2.65),
Liquid Limit (76.5%) and Plasticity Index (27.3%).
Three tests to determine coefficient of consolidation were
conducted, i.e. single drainage, double drainage and radial
drainage conditions.
Single drainage
The values of cv are found to be in the range of 8.05×10-7 to
4.33×10-6 m2/s. Although Terzaghi assumed the permeability
(k) and the coefficient of volume compressibility (mv) to
be constant, during consolidation process, as water is being
squeezed out from the soil, the permeability of the soil
will decrease, as well as the coefficient of compressibility.
However, the rate of decrease of permeability and
compressibility may not be the same (Robinson & Allam,
1998), and the difference in the rate affects the trend of
cv. In this experiment, the trend of cv tends to increase in
the early stage of the consolidation up to a certain value,
and then decrease. This may be due to a larger rate of
decrease of permeability as compared to the decrease of
compressibility. When this trend occurs, even if there is a
decrease in both permeability and compressibility, the ratio
of the rate may give an increase to the cv.
Double drainage
CONCLUSIONS
For double drainage tests, the trend of cv is found to have
nearly the same trend as that of single drainage, but it has
a slightly lower value. The values of cv are in the range of
5.19×10-7 to 1.65×10-6 m2/s. During consolidation process,
both permeability and compressibility reduce with increasing
effective consolidation pressure. The reason for this trend
may be due to the significant difference between the rates
of decrease of permeability as compared to the rate of
decrease of the coefficient of compressibility. In the early
stage of consolidation, the rate where permeability decreases
is larger than the rate of decrease of the compressibility.
When the rate is almost the same, the ratio is constant and
it will cause the cv to decrease with increasing effective
pressure. The soil properties as compared to the specimen
of Sridharan (2004) are similar. As the soil specimen has a
higher liquidity index (IL) when cv is directly proportional
to IL, consequently, the calculated values of cv in this
experiment are higher than that of Sridharan (2004).
In this study, Rowe consolidation cell was used to overcome
the major disadvantages of conventional oedometer test.
Rowe cell allows a larger sample size, which is very
advantageous in the case of testing a non-uniform soil
sample. On top of that, the application of load is simpler,
and it allows a control of drainage.
The coefficient of consolidation in the vertical flow direction
range is to be from 8.05×10-7 to 4.33×10-6 m2/s in the single
drainage condition and from 5.09×10-7 to 1.65×10-6 m2/s
in the double drainage condition.
Radial drainage
[1] Chu, J., Myint, W.B., Chang, M.F. and Choa, V., 2002.
“Consolidation and permeability properties of Singapore
marine clay”. Journal of Geotechnical and Geoenvironmental
Engineering, Vol. 128, No. 9, pp. 724-732.
The coefficient of consolidation in the horizontal flow
direction (ch) has a range between 4.29×10-7 and 7.85×10-7
m2/s. It was found that ch shows a decreasing trend with
increasing effective consolidation pressure, and generally
lower value than that of cv. The decrease is noted to be more
visible in low pressure range, whereas in high pressure, it
tends to increase. As compared to the research on Singapore
marine clay done by Chu et al. (2002), the values of ch of
kaolin in this study are found to be higher than Singapore
marine clay. However, the trend of ch with respect to
effective consolidation pressure is in a good agreement with
previous findings. As the effective consolidation pressure
increases, both permeability and compressibility will also
decrease. In this case, it is probable that the rate of decrease
of permeability and compressibility are relatively the same,
which leads to a decrease in coefficient of consolidation.
The different value may be due to the difference in the
nature of the soil.
In addition, the coefficient of consolidation in the horizontal
flow direction is found to be from 4.29×10-7 to 7.85×10-7
m2/s in the radial drainage condition.
REFERENCES
[2] Mesri, G. and Olson, R., 1970. “Mechanisms Controlling the
Compressibility of Clays”. Journal of American Society of
Civil Engineers, Vol. 96, pp. 1853-1878.
[3] Robinson, R. and Allam, M., 1998. “Effect of clay mineralogy
on coefficient of consolidation”. Clays and Clay Minerals,
Vol. 46, No. 5, pp. 596-600.
[4] Rowe, P. and Barden, L., 1966. “A new consolidation cell”.
Géotechnique, Vol. 16, No. 2, pp. 162-169.
[5] Sridharan, A. and Nagaraj, H., 2004. “Coefficient of
consolidation and its correlation with index properties of
remolded soils”. Geotechnical Testing Journal, Vol. 27, No.
5, pp. 469-474.
[6] Terzaghi, K., Peck, R.B. and Mesri, G., 1996. Soil Mechanics
in Engineering Practice. New York: Jon Wiley & Sons,
Inc.
95
EFFECTS OF ELECTRIC VEHICLES ON
CLIMATE GOALS – SINGAPORE AND
GERMANY IN COMPARISON
Rainer WITZIG (rainer.witzig@tum.de)
WONG Yiik Diew (cydwong@ntu.edu.sg)
CHANG Wei-Chung Victor (WCChang@ntu.edu.sg)
ABSTRACT: We create a model to simulate the effects of a large number of electric vehicles (EVs) on energy demand and CO2-emissions.
The model reflects the impacts on electricity demand, the structure of power plants, electricity price, and the price elasticity of cars. We
compared the reduction potential of energy demand and emission in Germany and Singapore.
The simulations show a greater potential to reduce energy demand by using EVs in Singapore than in Germany. The main reason for
this is the higher specific energy demand of conventional cars for solely urban use in Singapore. However, introducing emission-free
power plants in Singapore could improve the CO2-balance further.
INTRODUCTION
The intensifying climate change comes along with the
need to reduce greenhouse gas emissions significantly. The
transport sector’s substantial role in this context leads to the
imperative to decrease the energy demand in transportation
considerably. The changeover from cars with combustion
engines to electric vehicles (EVs) is currently strongly
supported by politics in many countries, and justified with
the positive effects on climate goals that would come with
it (GEA 2009). This raises high expectations of EVs’ green
benefits in media, industries, societies and lobby groups. We
analysed EVs’ actual impact on climate goals, as well as
its side effects, comparing different scenarios in Singapore
and Germany.
THE EVICE MODEL
96
An argument for the proliferation of electric vehicles in
replacement of fossil fuel-driven vehicles is the comparably
low energy demand for the end user and the theoretical
option to operate EVs independently of fossil fuels. Also,
due to the current electricity price, operational costs driving
an EV would be much cheaper compared to a conventional
car. However, this could also result in an increasing vehicle
mileage. The future structure of power plants which would
be necessary to meet the increasing demand of electricity
is another important variable to be analysed. In turn, these
factors would counterbalance today’s linear estimations
regarding CO2-emissions, electricity price and demand of
fossil fuels.
We developed the EVICE model (electric vehicles’
impact on climate change and energy demand) for further
inspections. This model contains the feedback of electricity
demand, electricity price, price elasticity of mobility and
the changing mileage. The model allows simulations up
to the year 2020. A basic scheme of the EVICE model is
shown in Figure 1.
Firstly, we estimate the mileage of private car traffic in
Singapore and Germany for the next 10 years. In different
scenarios we assume different numbers of EV entering the
market. These substitute conventional cars with a given
share of urban /interurban use. Based on these parameters,
we compute the electricity demand which is necessary to
meet the energy demand for EVs. The model also computes
the costs to produce electricity, which is one of the two
main parameters to calculate the operating costs of EVs
(Roth 2009).
Since the travel costs driving an EV will differ significantly
to travel costs with a conventional car, the driving
performance will alter. We model this effect using a given
price elasticity for fuel price. The new mileage EVs results
in an electricity demand different to our first assumption.
Feeding in the new data of electricity demand, we start an
iteration of the steps as shown in Figure 1. After obtaining
equilibrium we are able to compute final results for CO2emissions, energy demand, mileage and travel cost for EVs
and conventional cars, respectively.
SCENARIOS
In a reference scenario, we assume no EV in Germany or
Singapore in the next 10 years. This allows us to compare
the results of different settings. In different scenarios we
simulate a substitution of 10% or 100% of conventional
cars by EVs. Whereas the first case seems to be realistic,
the last scenario is not lifelike. However, this scenario helps
to illustrate the maximum potential of EV’s use.
Figure 1. Scheme of the EVICE model.
We also assume a yearly increase of gasoline price by
6% according to estimations of the German Institute
for Economic Research (Hunsicker andSommer 2008).
However, we also simulate scenarios with different rates and
elasticities. Further parameters taken into account include
today’s and future battery costs, average fuel consumption
of Germany’s car fleet, share of EVs’ urban/interurban use,
timeslots for charging, durability of batteries, as well as
additional taxes for fuel or electricity. The importance of
these parameters will be discussed in a following sensitivity
analysis.
mileage. In the scenario with 100% replacement of cars, it
would increase by 9% - 27%, depending on the fuel price
elasticity. However, in the more realistic scenario with a
10%-replacement, the increase in mileage is between 1%
and 7% in both countries (see Figure 2).
Singapore
13.5
13.0
mileage [billion vkm]
One important input parameter is the fuel price elasticity
for car use. We assume this value to be -0.05, according
to over 100 empirical estimations (Forschung-InformationsSystem 2009).
12.5
12.0
0%
11.5
10%
11.0
100%
10.5
10.0
9.5
2010
2011
2012
2013
2014
2015
year
2016
2017
2018
2019
2020
Germany
700
RESULTS AND ANALYSIS
First results of the EVICE simulation show that in both
countries the low electricity price would lead to increasing
660
640
0%
620
10%
600
100%
580
560
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
year
Figure 2. Mileage in Singapore and Germany.
The potential savings in energy demand in the 10%-scenario
are marginal in Germany. In Singapore on the other side,
where the average fuel consumption of cars is higher, the
savings would be 6%, and even 57% in case of a total
substitution by EVs. In Germany, the according values are
0.5% and 32% (see Figure 3).
In different scenarios we simulate the impact of a
substitution of 10% and 100% of conventional cars by
EVs in Singapore and Germany. Germany’s composition of
power plants today consists of nearly 20% renewable energy
resources, which makes the use of EVs environmentally
friendlier. In Singapore on the other hand, the main benefit
of EVs is the fact that the average fuel consumption of
conventional cars is significantly higher than in Germany.
The reason for this disparity is not the quality of the car
fleet, but the solely urban use of cars, which comes along
with higher specific energy demand.
mileage [billion vkm]
680
97
SENSITIVITIES OF UNKNOWN
PARAMETERS
Figure 3. Primary Energy Demand for motorized vehicles
in Singapore and Germany.
The CO2 emissions of EV depend on the type of power
plant which is used to generate the electricity. The
environmental friendly mix in Germany cannot come up
for a 100% replacement of cars by EVs. In consequence,
new coal fuelled power plants would have to be built. This
shortcoming limits the maximum potential of emission
savings to 37%. In the Singapore case, the CO2 savings
potential behaves almost linear to the energy demand – its
maximum potential is around 62%. This can be achieved by
continuously using oil and gas fuelled plants. Introducing
emission free power plants, this value could even be higher
(see Figure 4).
EVICE uses many input parameters which are afflicted with
uncertainty. These include the future fuel price, battery costs,
fuel consumption of the car fleet, timeslots for charging,
restrictions of CO2-emissions for Germany’s power plants,
durability of batteries, as well as additional taxes for fuel
or electricity. We want to analyze the importance of these
variables to the final result. Therefore we run several
simulations, consecutively changing single parameters and
calculate each parameter’s sensitivity. In these simulations,
the reference scenario will be the 10%-replacement of cars
by EVs. The final result which we take for comparison is
the primary energy demand in private transport in 2020.
We compute the sensitivities η using the mean arc elasticity
function:
Q2 – Q1
(Q2 + Q1)/2
ηQ,P =
P2 – P1
(P2 + P1)/2
ηQ,P :
Q1 :
Q2 :
P1 :
P2 :
elasticity of changing parameter
primary energy demand in10%-scenario
primary energy demand with parameter P2
parameter in 10%-scenario
new parameter
We observe a high relevance of the annual rise in fuel
price, fuel consumption of the conventional car fleet and
the fuel price elasticity. The other parameters mentioned
above play an insignificant role in the overall outcome.
CONCLUSIONS
We created the EVICE model in order to simulate the
change of all relevant variables when using a large number
of EVs in Singapore and Germany. This includes electricity
demand, the structure of power plants, electricity price, price
elasticity of car use and others. In iterations we calculated
the change of each parameter and its impact on the others,
until equilibrium is reached.
98
Figure 4. CO2-emission of motorized vehicles
in Singapore and Germany.
The simulations show a greater potential to reduce energy
demand by using EVs in Singapore than in Germany.
The main reason for this disparity is the higher specific
energy demand of conventional cars in the solely urban
use in Singapore. We also observe a greater potential in
Singapore to reduce CO2-emissions compared to Germany.
The environmental friendly power plants in Germany have
reached the limits of their capacities since not many more
wind, water and solar power plants can be built in the future.
In Singapore, on the other hand, introducing emission free
power plants could improve the CO2-balance even more.
The sensitivity analysis showed that the parameters with
the biggest impact in this model are the annual rise in fuel
price, the fuel consumption of the conventional car fleet
and the fuel price elasticity. Further research is needed to
understand the exact reaction of passengers to fuel price
changes.
REFERENCES
[1] Forschung-Informations-System. Elastizitäten der
Kraftstoffpreise. http://www.forschungsinformationssystem.
de/. 03.06.2009
[2] GEA (2009). Electric Vehicles and CO2 Emissions.
[3] Hunsicker, F. and Sommer, C. (2008). “Welche Zukunft darf’s
denn sein?” Internationales Verkehrswesen Nr. 9, 334-335.
[4] Roth, H. (2009). “Optimierung der Kraftwerkparkentwicklung”.
Lehrstuhl für Energiewirtschaft und Anwendungstechnik, TU
München.
99
MARITIME STUDIES DEGREE
PROGRAMMES IN SHIPPING
MANAGEMENT -AN INTERNATIONAL COMPARISON
Gou Xueni (goux0001@ntu.edu.sg)
Wong Yiik Diew (cydwong@ntu.edu.sg)
ABSTRACT: World GDP is increasing and international seaborne trade is expanding momentously. Shipping, shipping education and
training have evolved into global and sophisticated businesses. Several maritime degree programmes are offered by universities around
the world for training shipping management personnel who are knowledgeable in both vessel operations and shore-side business. This
study reviews 22 relevant shipping management bachelor degree programmes around the world. The interactive factors include maritime
heritage, economic development, seaborne trade and maritime business. The educational structures and overall academic disciplines of
an institution also have impact on the academic content of these programmes.
100
INTERNATIONAL ECONOMIC GROWTH
AND MARITIME BUSINESS
MARITIME BUSINESS AND SHIPPING
MANAGEMENT DEGREE PROGRAMMES
Trade and shipping businesses have always been important
enablers of wealth and growth. International trade has
expanded by more than 1,700% over the second half of the
20th century in volume terms (WTO, 2010). Although world
GDP experienced a steady growth over time, international
merchandise trade has roughly tripled in importance
compared with the economy as a whole (The World Bank,
2010). It is generally accepted that more than 90% of global
trade is carried by sea. Seaborne trade worldwide has been
growing very rapidly in recent 55 years from 500 million
tonnes in 1950 to 7 billion tonnes in 2005 (UN, 2008).
Many academies have existed for a long time in training
mariners. As the maritime business evolves, some of
these mariners make career transitions from the sea to
the shore to helm shore-side shipping businesses. In
light of highly integrated shipping industry, a number of
academic programmes have flourished to train shipping
management personnel. This is evidenced by the existence
and development of maritime degree programmes in
shipping management in various universities and institutes
throughout the world.
Maritime trade is dominated by three economic centres,
viz Europe, North America and Asia, strung out along a
“Westline”. It is the line along which the commercial centre
of maritime trade has moved west over the last century
of maritime business. The recent fast growth in seaborne
trade stems especially from Asian countries. Although
European countries keep a large share of seaborne trade,
the growth rate is relatively slow and sea trade volume
has remained static.
In terms of fleet tonnage, based on total deadweight ton
(DWT) controlled as a percentage of world fleet by parent
companies located in different countries and territories, the
top 35 countries control 94.0% and 95.6% of world fleet
as end of 1998 and 2008, respectively. The ship owning
business tends to converge within a small number of
countries, among which Asian countries take an increasing
share from 38.6% to 44.8% (UNCTAD, 2009).
In order to have a detailed understanding of the shipping
management programmes, a sample of 22 programmes is
selected for a substantial analysis, taking into consideration
a combination of factors such as the national economies,
maritime heritage, and institutions’ academic disciplines
and curriculum structures.
ANALYSIS
Shipping management programmes and maritime
tradition, economic growth, merchandise trade
Tradition plays a major part in most European maritime
nations. Germany stands out as it experiences fast GDP
growth over the last decade and its merchandise trade
as a percentage of GDP is also increasing. Additionally,
based on World Bank Logistics Performance Index 2009,
Germany has replaced Singapore ranking as world No. 1
(The World Bank LPI, 2009).
Table 1. Institutions and degree programmes selected for analysis.
No.
Country/Institute/Degree Programme
No.
Country/Institute/Degree Programme
1
Greece/
University of Piraeus/
Maritime Studies (4 years)
12
Philippines/
Asian Institute of Maritime Studies/
Maritime Business (4 years)
2
Cyprus/
Frederick Institute of Technology/
13
Taiwan/
National Taiwan Ocean University/
Shipping & Transportation Management (4 years)
3
UK/
University of Plymouth/
Maritime Business & Logistics (3 years)
14
PRC/
Shanghai Maritime University/
Shipping Management (4 years)
4
Germany/
University of Applied Science OOW/
Maritime Economics & Port Management (4 years)
15
Thailand/
Burapha University/
Maritime Management
5
UK/
Southampton Solent University/
Maritime Business (3 years)
16
Japan/
Kobe University/
Maritime Logistics
6
UK/
Liverpool John Moores University/
Maritime Business & Management (3 years)
17
PRC-HK/
Hong Kong Polytechnic University/
International Shipping & Transport Logistics (3 years)
7
USA/
State University of New York/
18
Taiwan/
Kainan University/
Logistics & Shipping Management (4 years)
8
USA/
California Maritime Academy/
International Business & Logistics (4 years)
19
Singapore/
Nanyang Technological University/
9
USA/
Massachusetts Maritime Academy/
International Maritime Business (4 years)
20
Singapore/
Nanyang Technological University/
Maritime Studies with Business Major (4 years)
10
USA/
Texas A&M University at Galveston/
Maritime Administration (4 years)
21
Australia/
University of Tasmania/
Maritime & Logistics Management (3 years)
11
Canada/
Memorial University of Newfoundland/
Maritime Studies (diploma+1 year)
22
Egypt/
Arab Academy of Science, Technology & Maritime
Transport/
Management of Trade Logistics & International
Transport (4 years)
Japan outstands in Asia with very high GDP. It gained
maritime power at almost the same time as the West.
Economic independence after WWII has necessitated the
rapid advancement and expansion of the sea transportation
industry in Japan. It ranks No. 1 as of end of 2008
controlling the largest merchant fleet in the world. Taiwan,
Hong Kong and Singapore are Newly Industrialising
Economies (NIE) in Asia. They are all surrounded by
sea and control a large fleet by DWT. For Hong Kong
and Singapore, there is a huge amount of merchandise
trade as a percentage of GDP. Because of their strategic
positions, they are striving to become the regional as well as
international maritime centre. China has indeed a very long
maritime history. Compounded by its rapid growth in GDP
and international merchandise trade since joining WTO in
2001, China is emerging as a major maritime nation. Over
90% of its foreign trade volume is transported by sea and
shipping on sea and on river also plays an important role
for domestic traffic. Its merchant fleet also ranks among
one of the world’s largest five.
Among all the countries where the selected programmes
are offered, the US has the highest GDP but the lowest
merchandise trade as a percentage of GDP. Despite the
small percentage, the absolute amount of merchandise trade,
or more specifically seaborne trade, is not little at all. Of
US foreign trade, waterborne trade as a percentage of all
modes trade has increased steadily from 2003 to 2008 in
value terms. Domestic waterborne trade is comparable to its
international trade (U.S. Department of Transportation). As
perceived by Texas A&M University at Galveston, “activity
in American ports is expected to more than double in the
next 20 years, and some ports in the Gulf of Mexico are
expected to see a tripling of port activity”. In addition,
the next 40 years will see greatly expanded oil and gas
production in the deep waters of the western Gulf of Mexico
(Texas A&M University at Galveston).
101
Course categorisation
Analysis in groups
The courses within each programme are categorised
into maritime-technology, business-management, hybrid
and general. Maritime Technology (M-T) courses are
courses which are specific to those in shipping and
would not normally be offered in other programmes, e.g.
Ship Technology, Maritime Transportation, etc. Business
Management (B-M) courses are courses that are typically
found in business and management programmes, e.g.
Accounting, Economics, etc. Hybrid courses are those
courses that have elements of both M-T and B-M contents,
e.g. Shipping Economics, Maritime Law, etc. General
courses refer to courses that are not specific to any degree
programmes whereby the basic premise is for education
broadening, e.g. Physics, Chemistry, etc. All the figures
are expressed percentagewise below. The academic units
for each course are directly available according to the
course content descriptions. Academic units for each type
of courses are then summed and shown as a percentage
of the total academic units required for the corresponding
programme, as illustrated in Figure 1.
The selected programmes are classified into three groups
(Figure 1). Group A (No. 8-10, 12-14, 22) includes
programmes which are offered in independent maritime
institutes, Group B (No. 5-7, 11, 15, 21) consists of
programmes that are offered by maritime colleges or
academies within comprehensive universities, and Group C
(No. 1-4, 16-20) comprises programmes in comprehensive
universities which do not have any specific maritime
college or academy (with one exception: No. 1 is offered
by a university as a principally business discipline). As
an overview, B-M and Hybrid courses are the dominant
course types.
B-M courses dominate in Group A; while B-M and Hybrid
courses dominate in Groups B and C. Group C has more
M-T courses as compared with the other two groups. The
universities/institutes without much maritime background
may place more focus on shipping knowledge as compared
to the traditional maritime academies. While, with plenty of
expertise in the technical aspects of shipping, it seems more
meaningful for the maritime academies or colleges to put
in more efforts on the business areas. For the independent
maritime institutes (Group A), even the Hybrid category is
emphasized to a lesser extent.
A notable feature of Group A is that General courses have
taken a fairly large weightage. These include 3 programmes
(No. 8-10) selected from the USA and 1 each from China
and Philippines. This is mainly due to the educational
systems in the respective countries which give much focus
on the general tertiary education. This is evidenced by
No. 7 programme under Group B which is offered in the
USA by SUNY Maritime College, part of a comprehensive
university now, and it has heavy General course content as
well. Meanwhile, this programme has clearly more General
courses and Hybrid courses but fewer B-M courses when
compared with the other 3 USA programmes. Drawing from
this case, it is perceived that the composite and organisation
of the education systems certainly have some impact on
the structures of various shipping programmes.
102
As for the extraordinariness of programme No. 16, it is
worthwhile to point out more background information.
Although Kobe University is considered as a comprehensive
university with no specific maritime college or academy, the
Faculty of Maritime Science (established in 2003) indeed
can be traced back to 1917 with its origin as Kawasaki
Merchant Marine School. It was nationalised in 1920 as
Kobe Nautical College and later united with other two
nautical colleges in Tokyo and Shimizu to become as
Kobe National College (Kobe University). In this sense,
the Kobe University should have plenty of expertise and
resources in M-T education which they exploit to the extent
that they outstand in M-T courses weightage among other
comprehensive universities.
Figure 1. Course content by groups.
To further gauge the breadth and depth of maritime and
business knowledge in different shipping management
Figure 2. Comparison of M-T content and B-M content.
programmes, comparison is made on the basis of a
conceptual framework as developed by Leong, Wong &
Williams (2009). Academic units for Hybrid courses are
divided equally between the M-T and B-M categories
while general courses are excluded in this comparison.
The percentages are calculated and shown in Figure 2.
Generally speaking, B-M content is being given more
attention than M-T content.
CONCLUSIONS
[1] Kobe University. Retrieved on 12 May, 2010 from http://www.
maritime.kobe-u.ac.jp/maritime_e/history.html
[2] Leong, E.C., Wong, Y.D. and Williams, E.C., 2009. Conceptual
Framework for Comparing University Baccalaureate
Programmes in Shipping Management. WMU Journal of
Maritime Affairs 8(1): 47-58.
[3] Texas A&M University at Galveston. Retrieved on 31 May,
2010 from http://www.tamug.edu/mara/academic%20 program.
htm
[4] The World Bank Statistics, 2010. Retrieved on 26 June, 2010
from http://databank.worldbank.org/ddp/home.do?Step=12
andid= 4&CNO=2
[5] UNCTAD Review of Maritime Transport, 2009. Retrieved
on 26 June, 2010 from www.unctad.org/en/docs/rmt2009_
en.pdf
[6] United Nations Statistical Yearbook, 2008. 52nd Issue. United
Nations: New York.
[7] U.S. Department of Transportation Maritime Administration,
2009. U.S. Water Transportation Statistical Snapshot. Retrieved
on 20 May, 2010 from http://www.marad. dot.gov/documents/
US_Water_Transportation_Statistical_snapshot.pdf
[8] The World Bank Logistics Performance Index, 2009. Retrieved
on 26 June, 2010 from http://info.worldbank.org/etools/
tradesurvey/mode1b.asp#ranking
[9] WTO Statistics, 2010. Retrieved on 26 June, 2010 from http://
www.wto.org/english/res_e/statis_e/its2010_e/its2010_e.pdf
There are strong interdependent links between economic
growth, global trade, seaborne trade and maritime transport
service. With transformation of the management structures
in the shipping industry, the education system for training
shipping management personnel has evolved and will
continue to evolve. The westerly shift of maritime power
has prompted the establishment of various shipping
management programmes in Europe, North America, Asia
and elsewhere. They are offered in maritime academies as
well as universities and institutes. A substantial sample of
22 shipping management bachelor degree programmes is
selected for an international comparison. The interactive
factors include maritime heritage, economic development,
seaborne trade and maritime business. Business content
is paid greater attention, and Hybrid courses provide an
integrated means to bridge the general business and maritime
business. In essence, the academic content of the different
shipping management programmes varies depending on
the respective educational structures and overall academic
disciplines of an institution.
REFERENCES
103
P-WAVE VELOCITY MEASUREMENTS
IN SEDIMENTARY ROCKS
Wong Ngai Yuen Louis (LNYWong@ntu.edu.sg)
Zhang Xiaoping (ZhangX.P@ntu.edu.sg)
ABSTRACT: We investigated the P-wave velocity of sedimentary rocks, including sandstone and siltstone, in natural water content and
saturated conditions. The P-wave velocity measurements indicated that the anisotropic characteristics of siltstone were more significant
than that of sandstone. The correlation between P-wave velocity and uniaxial compressive strength (UCS) was also studied.
INTRODUCTION
As part of the on-going experimental studies to characterize
the mechanical behavior of the sedimentary rocks in
Singapore, P-wave velocity tests were conducted. This
non-destructive geophysical testing method offers a reliable
means to reveal the anisotropic nature in the rocks. It
also has a promising potential to serve as a quick means
to correlate the strength of the rocks with the measured
P-wave velocity.
Two major rock types, siltstone and sandstone, were tested.
To help reveal rock anisotropy characteristics, P-wave
velocity tests were conducted in a direction generally
parallel to the sedimentary plane (θ=0°) and perpendicular
to the sedimentary plane (θ=90°). The definition of θ is
shown in Fig. 1.
Receiver
Specimen
Transmiter
©
Se
dim
ent
ar y
p la
ne
Figure. 1 Schematic illustration of P-wave velocity test.
METHODOLOGY
104
Principle
Ultrasonic techniques are widely used in geotechnical and
rock mechanics applications as they are non-destructive
and easy to apply in both site and laboratory conditions.
The sound velocity of a rock mass is closely related to
the intact rock properties. Measuring the velocity in rock
masses can interrogate the rock structure and texture. The
important influencing factors are rock type, mineralogical
composition, rock texture and structure, grain size and
shape, density, porosity, anisotropy, porewater, weathering
and alteration, bedding planes, joint properties (roughness,
filling material, water, dip and strike, etc.), in addition to
confining pressure and temperature.
Except in the immediate vicinity of the seismic source, i.e.
transmitter, the strains associated with the passage of seismic
pulse are minute and may be assumed to be elastic. Based
on this assumption, the propagation velocities of seismic
pulse are determined by the elastic moduli and densities
of the materials through which they pass. The velocity of
propagation of a compressional body wave, i.e. P-wave
(Vp) in any material is given by
E
Vp = √ p
…(1)
where E is the Young’s modulus and ρ is density of material.
The velocity of a shear body wave (Vs), which involves a
pure shear strain, is given by
Vp = √ G
p
…(2)
where G is the shear modulus. Since the first transmitted
arrival wave is the P-wave, its detection is relatively easy.
The shear-wave arrival, however, may be obscured by
vibrations due to ringing of the transducers and reflections
of the compression wave. Therefore P-wave (compression
wave) is more favorably used in laboratory rock testing.
A number of studies have found that P-wave velocity and
rock properties are closely related. From testing of nineteen
different rock types, Kýlýç and Teymen (2008) obtained
the correlation between P-wave velocity and mechanical
properties, which includes UCS (Fig. 2a), indirect tensile
strength (Fig. 2b) and loss of volume (Fig. 2c). The latter
is a measure of abrasion resistance. Kahraman and Yeken
(2008) also identified strong correlations between P-wave
velocity and physical properties of rock, which includes
density, porosity, void ratio, water absorption by weight
based on fourteen different carbonate rocks.
Methodology
The instrument used for the present P-wave velocity
measurement was the CNS Farnell Pundit Plus (Model
PC1006), as shown in Figure 3. CNS Farness ultrasound
couplant was applied at the end faces to facilitate the
coupling effect between the rock core and the sensors.
Figure 3. Experimental set-up for P-wave
velocity measurement.
(a)
measurements were conducted in 92 specimens, in which
47 of them can be classified as siltstone (or siltstone with
occasional beds of sandstone), while 45 of them can be
classified as sandstone. The specimens are either of natural
water content (considered to be in dry condition) or in wet
condition. The wet specimens had been immersed in water
under a vacuum condition for 26 days before the P-wave
velocity measurement was performed.
(b)
P-wave velocity measurements
The test results of the P-wave velocity measurements
are summarized in Table 1. In general, the average Pwave velocity values in sandstone are higher than those
in siltstone, in orientation both along and normal to the
sedimentary planes.
(c)
Figure 2. Empirical relationships between direct P-wave
velocity and (a) uniaxial compressive strength (UCS),
(b) indirect tensile strength and (c) loss of volume (Kýlýç
and Teymen, 2008).
The P-wave velocity was calculated from the following
equation:
Vp = d/tp
…(3)
where Vp is the P-wave velocity, d is the length of the
specimen and tp is the time taken by the P-wave to travel
across the specimen from transmitter to receiver. The
Correlation with rock strength
Correlations of the P-wave velocity with the strength values
of the rock specimen were also attempted in the present
study. The first correlation was based on the empirical
relationships of equations (4) and (5) provided by Kýlýç
and Teymen (2008), as shown in Fig. 2, for the prediction
of the uniaxial compression strength (σc) and the tensile
strength (σt). The results are listed in Table 2.
The testing procedures were in general accordance with
the first method contained in the “Suggested Methods
for Determining Sound Velocity” of Ulusay and Hudson
(2007).
For siltstone of natural water content, along the sedimentary
plane (θ=0°), the average velocity is 5679.3 m/s, which
is higher than that of normal condition (θ=90°) – 5405.6
m/s. For sandstone of natural water content, the velocities
in both directions are close to each other, 5838.5 m/s and
5829.9 m/s respectively. The relatively larger difference
of P-wave velocity in the two measured orientations of
siltstone compared to that in sandstone may be attributed
to the stronger degree of anisotropy in siltstone than
in sandstone. In soaked condition, the average P-wave
velocities of siltstone & sandstone in orientation both along
and perpendicular to the sedimentary plane all increased
as compared to the dry condition. The Vps/Vpd ratio is also
computed for reference (Table 1).
105
Table 1. P-wave velocities in siltstone and sandstone.
P-wave velocities (m/s)
θ
Natural water content (Vpd)
Soaked (Vps)
5687.6
5520.9
Maximum
90°
Siltstone
0°
90°
Sandstone
0°
Minimum
5126.0
5259.6
Average
5405.6 (16)
5426.0 (12)
Maximum
5869.0
5986.2
Minimum
5571.0
5575.7
Average
5679.3 (11)
5732.8 (8)
Maximum
6030.5
5878.5
5585.6
5796.1
Average
5829.9 (16)
5845.6 (12)
Maximum
5995.8
6070.9
5611.2
5757.1
Average
5838.5 (9)
5921.8 (8)
1.004
1.009
Minimum
Minimum
Vps / Vpd
1.003
1.014
Note: the number in parenthesis after each average velocity value indicates the number of specimens
measured in each group.
σc = 2.304Vp2.4315 (R2=0.94)
…(4)
σt = 0.49 Vp1.8723 (R2=0.92)
…(5)
The average UCS values of siltstone obtained from
correlation are 139.4 MPa and 157.2 MPa for θ=90o and 0o
respectively. For sandstone, the correlated UCS values are
167.6 MPa and 168.2 MPa for θ=90o and 0o respectively.
For both siltstone and sandstone, the UCS values obtained
based on the correlation appear to be lower than those
obtained from the previous UCS experiments performed
on similar rock types (Ma et al., 2010). A major reason
is that the empirical relations, which serve as a basis for
the above prediction (Table 2), is derived from a data set
consisting of nineteen different rock types, instead of the
sedimentary rock types specifically tested in this project.
Table 2. Estimated UCS and σt based on average
P-wave velocity measurements.
Siltstone
106
Sandstone
θ
P-wave
velocity (m/s)
Estimated
UCS (MPa)
Estimated
σt (MPa)
90°
5405.6
139.4
11.5
0°
5679.3
157.2
12.7
90°
5829.9
167.6
13.3
0°
5838.6
168.2
13.3
A second approach of correlation, which was based on
the experimental results previously obtained by NTU (Ma
et al., 2010), was also attempted. In this previous study,
twenty specimens equally divided into four groups were
tested, which included dry siltstone, saturated siltstone, dry
sandstone and saturated sandstone. The P-wave velocity
measurements and UCS values are reproduced in Table 3
and table 4 respectively.
Note: Three specimens failing at a very low load level due
to the presence of pre-existing fractures were not included
in the present analysis. Because of the lack of sandstone
Table 3. Test results of P-wave velocity (Ma et al., 2010).
Siltstone
Sandstone
Specimen
number
Saturated
condition
Dry condition
1
5000
4761
2
5263
5000
3
5263
5000
4
5000
4761
5
5882
5555
Ave
5282
5015
1
5555
5263
2
5263
5000
3
5882
5555
4
5263
5000
5
5555
5263
Ave
5504
5216
specimens in this batch, three specimens, A3, A4 and A5
tested in the previous phase were included in the present
analysis.
The UCS (MPa) data and the P-wave velocity (m/s) data
are plotted in Figures 4 and 5. Due to the substantial degree
of scattering, and most importantly very small sample size
(only 5 in each group), a statistically significant correlation
cannot be derived with confidence. To obtain an acceptable
correlation the sample size has to be increased, which will
be the scope of work in the near future.
CONCLUSIONS
The P-wave velocity tests were conducted on 92 specimens,
in which 47 of them can be classified as siltstone (or
siltstone with occasional beds of sandstone), while 45 of
them can be classified as sandstone. Specimens of either
natural water content (dry condition) or in wet condition
were tested.
Table 4. Test results of uniaxial compressive strength (UCS) for siltstone and sandstone (Ma et al., 2010).
Sandstone
Siltstone
No.
Stress (MPa)
Strain (%)
Young’s Modules
(GPa)
No.
Stress (MPa)
Strain (%)
Young’s Modules
(GPa)
I*
171.09
0.28
65.41
AI*
293.17
0.38
79.97
I2
164.83
0.30
57.51
A2
341.90
0.44
80.73
I3
204.67
0.34
64.75
A3
298.90
0.41
73.56
223.34
0.38
71.60
I4
180.23
0.31
60.64
A4
I5
219.25
0.38
58.41
A5
192.31
0.26
75.04
Ave
188.01
0.32
61.34
Ave
269.92
0.37
76.18
SI1**
123.02
0.23
59.54
SA1**
232.02
0.23
76.18
SI2
138.45
0.28
61.13
SA2
241.19
0.37
75.31
SI3
128.67
0.28
61.81
SA3
298.43
0.43
76.79
SI4
127.01
0.24
56.04
SA4
231.67
0.35
75.77
SI5
125.89
0.26
62.29
SA5
271.47
0.41
74.83
Ave
128.61
0.26
50.16
Ave
254.96
0.38
75.74
*Dry condition
**Saturated condition
*Dry condition
**Saturated condition
The P-wave velocity measurements indicate that the Pwave velocity in sandstone is generally higher than that
in siltstone. Based on the previous correlation by Kýlýç
and Teymen (2008) and other similar studies, the uniaxial
compressive strength is expected to increase with the Pwave velocity measurement, i.e. sandstone is stronger than
siltstone. This finding agrees with our previous experimental
findings from UCS tests (Ma et al., 2010).
Figure 4. UCS and P-wave velocity data of siltstone.
Secondly, the difference of P-wave velocity measurements in
the two measured orientations of siltstone, i.e. along bedding
planes and normal to bedding planes, is much larger than
that in sandstone. It indicates that the anisotropic nature
associated with the bedding in siltstone is more significant
than in sandstone.
In order to establish a more significant statistical relationship
between the P-wave velocity measurement and the UCS
of rock cores, additional tests involving a bigger sample
size should be performed. This will become the scope of
the upcoming experimental study.
REFERENCES
[2] Kahraman, S. and Yeken T., 2008. “Determination of physical
properties of carbonate rocks from P-wave velocity”. Bulletin
of Engineering Geology and the Environment, 67(2), 277281.
Figure 5. UCS and P-wave velocity data of sandstone.
[3] Ma, G.W. and Wu, W., 2010. “Water saturation effects on
sedimentary rocks”. Civil Engineering Research (NTU), 23,
129-131.
[4] Ulusay, R. and Hudson, J.A., 2007. “The complete ISRM
suggested methods for rock characterization, testing and
monitoring”. 1974-2006.
[1] Kýlýç, A. and Teymen A., 2008. “Determination of mechanical
properties of rocks using simple methods”. Bulletin of
Engineering Geology and the Environment, 67(2), 237-244.
107
ROLE OF FILLER IN MACRO STRUCTURE
OF ASPHALT MIXTURE AND ITS BINDING
CHARACTERISTIC WITH ASPHALT
Anggraini ZULKATI (angg0007@e.ntu.edu.sg)
WONG Yiik Diew (cydwong@ntu.edu.sg)
Darren SUN Delai (ddsun@ntu.edu.sg)
ABSTRACT: The role of filler in macro structure of asphalt mixture and micro interaction between filler and asphalt was investigated.
Preliminary results revealed that changing the amount of filler would affect aggregate packing structure, asphalt content and its properties,
and also workability during mixing and compaction, thus affecting asphalt mixture performance. Interaction of asphalt-filler mastic was
also examined using three types of fillers (granite, hydrated lime, kaolin) which revealed that the presence of filler in asphalt increased
the softening point and viscosity of asphalt. High-definition images of the morphology of the mastic were scrutinized that showed
evidences of “compatibility’ between asphalt and filler that could be attributed different affinity between filler and asphalt, or simply
micro voids around the filler from incomplete mixing process. It is conjectured that the presence of filler may cause stretching of atomic
bonds in the asphalt matrix, which either can enhance asphalt strength or possibly break the atomic bonds of asphalt matrix, leading to
undesired properties of mastic.
INTRODUCTION
Asphalt mixture used in the surface layer of flexible
pavement road is formed from asphalt, coarse and fine
aggregates and filler. Aggregates are expected to provide
a strong stone skeleton to resist the repeated traffic load
applications. Asphalt provides adhesive action among
aggregate particles. The mixture derives its strength from
the interlocking and frictional resistance of aggregates,
cohesion strength of the asphalt and adhesion binding
between asphalt and aggregates
Filler is the fraction of the mineral aggregate which mostly
passes the 75 μm sieve. Fillers fill voids between larger
aggregates in the mixture. A good packing of coarse, fine
and filler shall provide a strong backbone for the mixture
(Vavrik et al. 2002, Alshamsi 2006, Qiu 2006, Rivera 2008).
Filler may also alter properties of the asphalt, because the
filler can act as an integral part of the asphalt mastic which
is the combination of asphalt and filler.
108
Even though fillers act as a ‘filler of voids’ or ‘asphalt
extender’, it is well documented that they play an important
role in providing strength stiffness and durability of asphalt
mixture (Kandhal et al.1998, Menglan and Chaofan 2008).
The presence of filler in the asphalt mixture is even more
important because of their large surface area. Having
larger surface area, filler may absorb more asphalt and its
interaction with asphalt may lead to different performances
of asphalt mixture (Kavussi and Hicks 1997, Taylor 2007,
Liao 2007, Lesueur 2009).
It is noted that despite the vast number of studies conducted
to design a good aggregate gradation, none attempted to
comprehensively identify and investigate the role of filler in
gradation design. Furthermore, interactions between asphalt
and filler which, jointly, may generate certain properties of
the mastic. Different types of filler have different properties,
may interact differently with asphalt, and hence create ‘new’
properties in the asphalt-filler mastic. The interaction should
be dependent on physical and chemical properties of filler
as well as asphalt properties. As loading and temperature
regime for asphalt pavement may vary, the micro interaction
between asphalt and filler should behave and perform
differently at that variably condition. Thus, there is a need
to further examine the interaction between asphalt and filler
in micro level under different conditions.
The on-going research was undertaken to investigate the
role of filler in the macro structure of asphalt mixture. It
also investigated micro interaction among the constituent
materials in asphalt mixture. Some preliminary findings
are reported in this paper.
MATERIALS AND METHOD
Experimental set up
The first task was focused on examining the filler effect with
respect to overall packing structure in aggregate gradation,
its interdependence with other sizes of fine aggregate and
its effect on workability during mixing and compaction.
Six different gradations which vary in filler content were
designed. Marshall samples were fabricated and tested for
mixture performance.
The second task was to study the interaction of asphalt and
filler in mastic and the resultant properties. Three different
types of fillers were selected to assess the effect of filler
in asphalt mastic.
Materials
The type of aggregate used is Indonesian granite. Three
fillers: granite, hydrated lime and kaolin were supplied by
local chemical company. Sufficient quantity of aggregates
and filler was produced using a crusher and milling
machine. Asphalt Pen 60/70 supplied by Shell Bitumen
(Singapore) was used for asphalt mastic and asphalt
concrete mixture.
Gradation design
Mid value of Singapore’s standard W3B gradation and five
other gradations were designed as shown in Table 1.
Table 1. Gradation design.
Gradation
Gradation type
Coarse to fine
proportion (%)
% filler by
total mass
W3B
C-G
55:45
6
W3B-1
C-G
55:45
0
W3C-1
C-G
55:45
8
W3C-2
C-G
69:31
6
W3D-1
F-G
40:60
4
W3D-2
F-G
40:60
6
C-G: coarse graded
F-G: fine graded
W3B-1 is W3B gradation with exclusion of filler passing
75 μm sieve. W3C and W3D gradations are coarse and
fine-graded gradations respectively. Bailey method for
aggregate packing (Vavrik et al. 2002) was adopted
for designing these gradations. The method considers
the individual characteristics of aggregate properties. It
allows the adjustment of the aggregate voids by changing
the packing of the coarse and fine aggregates and filler.
Aggregate packing ratios for each gradation were also
calculated to examine the packing structure of aggregates.
The aggregate ratios for all gradations were evaluated based
on Bailey packing ratios (Vavrik et al. 2002).
The Marshall stability tests were conducted according to
ASTM D6927-06 (ASTM, 2006). As for evaluating the
material stiffness properties, the 5-pulse indirect tensile
test as described in the Australian Standard Method 13.1
(AS, 1995) was performed with the following conditions:
temperature at 25OC, peak loading force at 2kN, loading
period at 0.1 s, rest period at 0.9 s.
Asphalt-filler mastic preparation and test
Asphalt-filler mastic samples were prepared to investigate
the property changes of asphalt in presence of filler. Filler
was put into a 1000C oven for 24 hours to ensure moisturefree particle surfaces. The asphalt-filler mastics were
produced by adding the correct mass of filler to the heated
asphalt at a temperature of 150oC until a homogeneous
mastic was obtained. The mixing time was restricted to a
maximum of 15 minutes. The mastic was then transferred
to make samples for further testing. Asphalt-filler mastic
properties were then characterised based on the established
standard.
It is known that the specific gravity of three fillers is
different. The equivalent volume ratio was adopted for
calculating the concentration of different filler in asphalt.
The filler-asphalt ratios by volume equivalent are 0.06, 0.12,
0.18, and 0.24. The filler-asphalt ratio was determined by
dividing respective filler volume with asphalt volume.
Role of filler in macro structure
The volumetric properties of each designed gradation
are presented in Table 2. Table 3 presents the Marshall
stability and resilient modulus test results. The use of the
Marshall stability and resilient modulus provides a basis
for comparison of changes in material bearing capacity and
stiffness respectively for different mixture types.
Table 2. Volumetric properties of samples at 5% binder content.
Asphalt mixture preparation
After a 24-hour curing period for all Marshall specimens,
volumetric measurement for all specimens was conducted.
Density
(g/cm3)
VMA
(%)
VTM
(%)
VFA
(%)
W3B
2.34
13.92
3.47
75.08
W3B-1
2.29
15.20
5.20
66.85
W3C-1
2.32
14.95
4.31
70.61
W3C-2
2.34
13.72
3.22
76.40
W3D-1
2.24
15.95
6.34
60.27
W3D-2
2.32
14.22
4.40
69.05
VMA: voids in mineral aggregate
VTM: voids in the mix
VFA: voids filled by the asphalt
Asphalt concrete mixture specimens were manufactured
using Marshall hammer compaction at 75 blows. The
Marshall specimens were fabricated with asphalt content
of 5.0% based on the optimum asphalt content for W3B
gradation. The 5.0% asphalt content may not be the
optimum asphalt content for other gradations due to inherent
differences in terms of aggregate proportion. However, it
was chosen in order to analyse the volumetric properties
and mechanical performance of the mixture under the same
amount of asphalt.
Gradation
109
Table 3. Stability and resilient modulus at 5% binder content.
Gradation
% filler by
total mas
Marshall stability
(kN)
Resilient
modulus
(MPa)
W3B
6
14.00
3,000
W3B-1
0
12.00
2,160
W3C-1
8
12.70
2,850
W3C-2
6
16.50
2,990
W3D-1
4
11.70
1,800
W3D-2
6
19.00
3,800
W3B-1 was simply designed by removing the filler
passing 0.075 mm in W3B gradation and replacing the
corresponding amount with particles at size 0.3-0.075 mm.
It can be seen that, although fillers are very tiny particle,
their presence affected the volumetric properties of the
mixture. At certain amount, filler shall contribute to a
better packing for the mixture by filling the voids created
by larger fine aggregates. The removal of that filler and
replacement with other larger fine particles would cause
‘overfilling’ of certain sizes, resulting in more voids (higher
VMA and VTM) and lesser density being created. With
higher voids, VFA of that unbalanced mix would be lesser
than that of other mixes with better proportion of coarse,
fine and filler.
With such filler-deficient volumetric structure, the stability
and stiffness of the mix were lower as compared with
other mixes with filler. Although the voids can be filled
by adding more asphalt binder, however, the aggregate
structure would not be well-packing. In addition, with poor
packing, having more asphalt can contribute to a lesser
shear and deformation resistance of the mix, particularly
at high temperature.
The presence of filler in asphalt matrix may also affect
the workability during mixing and compaction. In simple
mechanistic view, filler can perform as ‘a tiny roller
effect’ during mixing and compaction process (Figure 1).
This ‘tiny roller effect’, at certain filler asphalt ratio, shall
correspond to a lesser friction, resulting in slightly faster
and smoother re-orientation movement of larger aggregates
during mixing, thereby facilitating a tighter packing when
compaction load is applied.
110
As part of continuous size of gradation, filler content shall
relate to the proportion of other aggregates in gradation.
Once gradation of design is selected, the proportion of coarse
and fine is then defined, and changing of the filler content
shall affect the proportion of aggregates in the fine fraction
only. Fines are small in size, but they have large surface
area, thereby playing an important role in determining the
asphalt content and the resultant mixture performances. As
seen in Tables 2 and 3, in comparing W3C-1 and W3C-2
properties or W3D-1 and W3D-2 properties, it was found
that changing a little amount of filler and the other fine
aggregates proportion impinged on all volumetric properties
and mechanical performance as well.
Role of filler in asphalt mastic
The properties of three fillers are shown in Table 4. The
finest size is that for kaolin fillers, while granite filler is
the coarsest among the other two fillers. Hydrated lime has
larger surface area, while granite has the lowest among the
other two fillers.
Table 4. Filler properties.
Fillers
Apparent specific
gravity (g/cm3)
Specific surface
area (m2/g)
Granite
2.56
0.758
hydrated lime
2.20
1.210
kaolin
2.48
1.110
Particle shape and morphology of the filler were examined
using scanning electron microscopy (SEM). It was found
that the quartz in granite filler had largest and angular
particles, hydrated lime had angular particles but they were
rather smaller than quartz, and kaolin particles were more
flaky with high aspect ratio.
Softening point and viscosity of asphalt-filler mastic at
different filler-asphalt ratios are shown in Figures 2 and
3. It can be seen that at equivalent volume ratio, kaolin
filler provided highest effect in increasing the softening
point and viscosity of the mastic. It was found that the
stiffening effect of the filler in asphalt is dependent on
filler size and surface area of filler. For industrial practice,
these mastic properties should be more appropriate for
batching design purpose. These properties may also more
appropriate in terms of establishing a correlation with the
resultant performance of asphalt concrete mixture.
As seen in Figures 4, 5 and 6, scanning electron microscopic
(SEM) images were used to examine the surface morphology
of the asphalt-filler mastic. The micro morphology was
used to approximately determine the compatibility of the
asphalt-filler mastic.
Figure 1. Roller effect of filler.
It was found that for the granite mastic, ‘white shadow’
which covers the granite filler in asphalt matrix always
appear in the images. This shadow may indicate the
incompatibility between asphalt and filler which possibly
Figure 2. Softening point of asphalt-filler mastic.
Figure 5. SEM micrograph of hydrated lime mastic.
Figure 3. Viscosity at 135OC of asphalt-filler mastic.
occurs due to the different affinity of filler and asphalt or
simply indicative of small voids around the filler. Physically,
the presence of filler, especially at larger size, may cause
the stretching of atomic bonds of asphalt matrix, which
either can enhance asphalt strength or possibly break the
atomic bonds of asphalt matrix
For lime and kaolin mastic, the white shadow was not
found. It can be due to the finesses of these two materials.
However, it was observed that some of lime and kaolin
fillers were not covered by asphalt. Incomplete mixing
process might be one possible reason. The other reason
can be due to the very fine size of these fillers, hence bulk
asphalt may not ‘touch’ and desorbs into the filler.
CONCLUSIONS AND FUTURE RESEARCH
WORKS
The experimental results demonstrated that filler contributed
to the aggregate packing structure, and together with asphalt,
jointly affected the workability, enhanced asphalt volume
and provided stiffening effect to the mastic.
It is emphasised that filler content should be designed to
consider the corresponding changes to other aggregate
proportion in the fine fraction. It leads to a reverse gradation
design, that is, once the optimum filler content is defined,
the proportion of other larger aggregates in the fine fraction
can then be designed. A well-balanced proportion of coarse,
fine and filler allows better packing with sufficient voids and
optimum asphalt needed, and provides desired performance
of the mixture in terms of strength, stiffness and durability.
It is noted that the properties of the asphalt-filler mastic
are also determined by interfacial bonding between the
bulk asphalt and filler. Such compatibility may result in an
undesirable balance of properties under different thermal
or load states.
With the benefits of preliminary findings, future tasks
shall focus on: (i) investigating the role of filler in the
Figure 4. SEM micrograph of granite filler mastic.
Figure 6. SEM micrograph of kaolin mastic.
111
macro structure of asphalt mixture; (ii) examining asphaltmastic characteristic at surface interaction level; and (iii)
reengineering selected fillers, all with the aim of enhancing
the mastic and asphalt mixture performance.
REFERENCES
[1] Alshamsi, K.S., 2006. “Development of a mix design
methodology for asphalt mixtures with analytically
formulated aggregate structures”. PhD thesis, Louisiana State
University.
[2] AS 1995. Method 13.1: Determination of the resilient
modulus of asphalt – Indirect tensile test, Australian standard
AS 2891.12.1. Methods of sampling and testing asphalt.
Australia.
[3] ASTM 2006. D1559-89: Standard test method for resistance
to plastic flow of bituminous mixtures using Marshall
apparatus. Annual books of ASTM standard, 04.03: 11031187. Philadelphia.
[4] Kandhal, P.S., Lynn, C.Y. and Parker, F., 1998. “Characterization
tests for mineral fillers related to performance of asphalt
paving mixtures”. NCAT report 98(2).
[5] Kavussi A. and Hicks, R.G., 1997. “Properties of bituminous
mixtures containing different filler”. Proceedings of the
association of asphalt paving technologists, 66: 153-186.
112
[6] Lesueur, D., 2009. “The colloidal structure of bitumen:
consequences on the rheology and on the mechanisms of
bitumen modification”. Advances in colloid and interface
science, 145: 42-82.
[7] Liao, M., 2007. “Small and large strain rheological and
fatigue characterisation of bitumen-filler mastics”. PhD thesis,
University of Nottingham: UK.
[8] Menglan, Z. and Chaofan, W., 2008. “Effects of type and
content of mineral filler on viscosity of asphalt mastic and
mixing and compaction temperatures of asphalt mixture”.
Transportation research record, 2051: 31-40.
[9] Qiu, Y., 2006. “Design and performance of stone mastic
asphalt in Singapore conditions”. PhD thesis, Nanyang
Technological University: Singapore.
[10] Rivera, F.A., 2008. “Evaluation of the Bailey method as a
tool for improving the rutting resistance of mix designs using
New Hampshire aggregate”. MSc thesis, University of New
Hampshire.
[11] Taylor, R., 2007. “Surface interactions between bitumen and
mineral fillers and their effects on the rheology of bitumenfiller mastics”. PhD thesis, University of Nottingham: UK.
[12] Vavrik, W.R., Pine, W.J., Carpenter, S.H. and Bailey, R., 2002.
“Bailey method for gradation selection in hot-mix asphalt
mixture design”. Transportation research board, Washington
D.C.
STRUCTURES AND MECHANICS
A CO-ROTATIONAL SHELL ELEMENT
WITH MATERIAL NONLINEARITIES
Xu Jin (xu0003in@e.ntu.edu.sg)
Tan Kang Hai (ckhtan@ntu.edu.sg)
Lee Chi King (ccklee@ntu.edu.sg)
ABSTRACT: This paper shows a 6-node curved nonlinear co-rotational shell element with nonlinear models. Vectorial rotational variables
are used in this co-rotational element, so that a symmetric stiffness matrix can be obtained and the updating procedure is simplified. In
order to investigate the behaviour of structures with nonlinear material constitutive relationships, a layered model is adopted so that material
properties varying along the thickness of shell structures can be simulated independently. Since the co-rotational approach is adopted,
the material constitutive model based on stress-strain relationship can be used directly in each elemental local coordinate system.
INTRODUCTION
Co-rotational (CR) approach is an efficient method to solve
geometrical nonlinearity, which finds its origin in the paper
of Wempner (Wempner 1969). The popularity of the CR
formulation is largely due to the decomposition of a large
displacement into rigid body motion and deformational
displacement. In this way, a geometrically-nonlinear problem
is transferred to be a small strain problem and different
material nonlinearities are easier to be implemented in the
CR formulation, compared with Total Lagrangian (TL)
formulation or Updated Lagrangian (UL) formulation.
CO-ROTATIONAL FORMULATION
Coordinate Systems
Three coordinate systems are defined in the present CR
elements: 1) the global system, 2) local systems and
3) natural systems. The global system OXYZ is defined
during the modelling stage by users. Each element has
its own local system. The local system is fixed on the
element and co-rotates with the element. The rotation and
translation of a local system represents the rigid body
rotation and rigid body translation of its corresponding
element, respectively.
node i: ngi = [pi,X, pi,Y, pi,Z], whose modulus are the two
smaller ones.
Figure 1. The global and the local coordinate system.
The relationship between the nodal variables in the global
and the local systems is given by Equation (1) and (2).
ti = R(Xi – X1) – R0(Xi0 – X10)
(1)
ri0 = Rh0ngi0, ri = Ringi
(2)
where R and Rh are the rotation matrices for translational
and rotational displacements, respectively; ngi (i = 1, 2, …,
6) is the normal vector for node i; the subscript 0 refers
to coordinates or normal vectors that are in the initial
configuration.
Kinematics of the Shell Element
In the present shell element, there are five degrees of
freedom for each node, namely, three translational variables
and two rotational variables. The three translational variables
include diT = [Ui, Vi, Wi] for node i in the global system
and tiT = [ui, vi, wi] for node i in the local system, while
the two rotational ones are vectorial rotational variables
(Li & Izzuddin et al. 2008; Xu & Tan et al. 2010), which
are piT = [pi,mi, pi,ni] for node i in the global system and
riT = [ri,x, ri,y] for node i in the local coordinate system.
pi,mi and pi,ni are the components of the normal vector at
The in-plane strain ε and the shear strain γ for shallow
curved shell element are given in Equation (3) and (4),
respectively.
ε = εm + zχ
(3)
(4)
where εm is the in-plane strain of the reference surface
(the mid-surface of the shell structure), which is given by
Nodal Degree of Freedom
113
Equation (5); χ is the curvature of the element, which is
given by Equation (6); z is the z-coordinate of the point
of interest in the local system; the nabla symbol ∇ refers
to the gradient of a scalar function.
Stiffness Matrix and Internal Force Vector
The strain energy of an element is given by Equation
(8).
(8)
(5)
(6)
where Vj is the volume of the jth layer; V is the volume of the
whole element; We is the work done by the external force;
D1 (size: 3×3) is the material constitutive matrix for in-plane
stress-strain and D2 (size: 2×2) the material constitutive
matrix for shear stress-strain. For linear elastic material, D1
and D2 is given by Equation (9); for elasto-plastic material,
D1 is modified by elasto-plastic modulus Dep.
The derivative ∇f (x, y, z) = J-1∇f (ξ, η, ζ), where J is the
Jacobian matrix [∂x/∂ξ], is applied in Equation (4) ~ (6).
,
Layered Model
(9)
In order to incorporate material nonlinearity, a layered model
is adopted in the present shell element so that material
constitutive relationships can be modelled in each layer.
The layers are numbered sequentially, starting from the
bottom surface of the element and each layer may have
different thicknesses, as shown in Figure 2.
where E is the Young’s modulus; μ is the Poisson’s ratio;
k is the shear correction parameter, k = 5 / 6.
The stiffness matrix kTL (size: 30×30) and the internal
force vector fLT (size: 30×1) of the element are the Hessian
matrix and Jacobian matrix of strain energy.
The internal force vector in the global system fG is given
by Equation and the stiffness matrix in the global system
kTG is given by Equation (11).
fG = TTfL
(10)
(11)
where T is the transformation matrix: T = [∂uL / ∂uGT].
Figure 2. Layered model.
The in-plane strain εj at the mid-surface of the jth layer is
given by Equation
εj = εm + zjχ
114
(7)
where zj is the distance from the mid-surface of the element
to the mid-surface of the jth layer. It should be noted that
the in-plane strain εm may not be the pure membrane strain
for material nonlinear cases.
The shear strain is assumed to be uniformly distributed
along the thickness direction of the element, which means
that the shear strain of each layer is the same and is given
by Equation (4).
MATERIAL NONLINEARITY
Elasto-plastic Constitution
Since the layered model is adopted, the modification for
material nonlinear analyses is focused on the material
constitutive matrix. In the present element, only in-plane
stress components are taken into account when dealing
with elasto-plastic material.
The incremental stress is given by Equation (12)
(12)
where H is the hardening parameter and vector a is the
first derivative of effective stress with respective to the
stress components.
Reinforced Concrete Model
The reinforced concrete model employed in the present shell
element is proposed by Owen and Figueiras (1984).
NUMERICAL EXAMPLES
Figure 4. The computational model of the flat plate.
Roll-up of a Clamped Beam
An initially flat shell is fully fixed at one end and is acted by
a bending moment at the other end. The analytical solution
for this example is governed by the classical formula:
(13)
where M is the bending moment applied on the beam
and ρ is the curvature of the beam. For M = 2π EI / L,
where L is the length of the beam, the beam rolls up into
a complete circle.
Figure 5. The equilibrium path of the flat plate.
area to the loading point, the more refined is the mesh. For
both meshes, 5 layers for each element are used.
A Reinforced Concrete Slab
Figure 3. The process of rolling-up for the beam.
A corner supported square plate is loaded by a concentrated
force at the centre, as shown in Figure 6.
Table 1. The rotation angle for the cross-section at the free end.
λ
0
0.1
0.2
0.3
0.4
0.5
θ(rad)
0.000
0.692
1.226
1.803
2.415
2.982
λ
0.6
0.7
0.8
0.9
1.0
θ(rad)
3.572
4.213
4.864
5.620
6.336
The geometric and material properties for the beam are
chosen as L = 12, I = bd3 / 12 = 1 / 12, E = 2.40 × 105,
μ = 0.3. A total of 20 elements (1 × 10 × 2) is used for
this example.
A perfectly elasto-plastic analysis of a simply supported
square flat plate is conducted in this example (Figure 4).
The geometric and material properties for the computational
model are chosen as: the length L = 16 m, thickness t =
0.5 m, Young’s modulus: E = 7.05 × 106 N/mm2, yielding
stress: σ0 = 2.44 × 102 N/mm2. The computational model is
meshed by 200 elements (10 × 10 × 2) and 800 elements
(20 × 20 × 2). For the case of 200 elements, the closer the
Three cases (S1, S2, S3) are tested with different amounts
of reinforcement in each direction, but with the total amount
of reinforcement in the plates kept constant. The ratio of
the amounts of reinforcement in the two direction (ρX : ρY)
is shown in Table 2.
Table 2. The reinforcement for the three cases in the RC slab.
slabs
S1
S2
S3
ρx : ρ Y
1:1
1:1.89
1:2.75
The geometrical properties of the computational model and
the mesh used are shown in Figure 6. The configuration
A Steel Plate Applied by a Point Load
Figure 6. The computational model of the RC slab.
115
CONCLUSIONS
Figure 7. The concrete layers and reinforcement layers
along the thickness direction.
of the cross-section is shown in Figure 7. The material
properties for concrete and reinforcement are listed in
Table 3.
Table 3. Material properties for RC slab (kN, cm).
A 6-node curved co-rotational shell element with layered
model is presented. The present element has several
features: 1) the rotational variables are commutative as
the translational variables, so that the stiffness matrix of
this element is symmetric; 2) the updating of the rotational
variables are simplified, because the spin matrix for the
updating of the convention rotational variables is not
needed; 3) layered model is employed in this element
so that it can be used in material nonlinear analyses, for
example: reinforced concrete structures, elasto-plastic
materials and so on.
Concrete
Young’s modulus
Ec = 1640
Poisson’s ratio
μ = 0.0
Ult. Comp. Strs.
fc’ = 4.30
Ult. Ten. Strs.
ft = 0.3
Ult. Comp. Strn.
εu = 0.0035
α = 0.7
εm = 0.0035
Ten. Stiff. Coeff.
Ten. Stiff. Coeff.
Reinforcement
Young’s modulus
Es = 20100
Young’s modulus
ET = 700
Poisson’s ratio
μ = 0.0
Yield stress
σu = 60.0
σu = 70.0
Ult. Stress.
The results are plotted in Figure 8 together with the results
from numerical analysis (Owen & Figueiras 1984) and
experiment (Duddeck & Griebenow et al. 1978).
Figure 8. The equilibrium path of the RC slab.
116
REFERENCES
[1] Wempner, G. 1969. Finite elements, finite rotations and small
strains of flexible shells. International Journal of Solids and
Structures 5(2): 117-153.
[2] Li, Z.X., Izzuddin, B.A., et al. 2008. A 9-node co-rotational
quadrilateral shell element Computational Mechanics 42(6):
873-884.
[3] Xu, J., Tan, K.H., et al. 2010. A Co-Rotation Shell Element
with Material Nonlinearities. In B. H. V. Topping, J. M.
Adam, F. J. Pallarés, R. Bru and M. L. Romero (ed.), The
Tenth International Conference on Computational Structures
Technology, Valencia, Spain, Stirlingshire, Scotland: CivilComp Press.
[4] Owen, D.R.J. and Figueiras, J.A. (ed.) 1984. Finite element
software for plates and shells. Swansea, United Kingdom,
Pineridge Press.
[5] Duddeck, H., Griebenow, G., et al. 1978. Material and time
dependent nonlinear behaviour of cracked reinforced concrete
slabs. G. Mehlhorn, H. Ruhle and W. Zerna. Darmstadt, West
Germany.
COLLISION ANALYSIS OF OFFSHORE
FLEXIBLE RISERS
Jian Wen He (heji0006@e.ntu.edu.sg)
Ying Min Low (ymlow@e.ntu.edu.sg)
ABSTRACT: Flexible marine risers are compliant to external forces from waves, current and platform motions, and clashing between
risers is an important concern. In deepwater developments where the number of connected risers is large, it is not economical to space
them too far apart. In this regard, it is necessary to establish the probability of riser clashing throughout the service life; however, at
present there appears to be no systematic procedure for assessing this risk. This article presents a novel procedure for estimating the
probability of riser clashing based on post-processing results obtained from time domain simulations of flexible risers subjected to
random wave loads.
INTRODUCTION
As the emphasis of the oil and gas industry shifts towards
greater water depths, deepwater marine risers play an
indispensable role in the production of hydrocarbons.
Several major types of deepwater risers are Flexibles,
Hybrid Riser Towers (HRTs) and Steel Catenary Risers
(SCRs); Top Tensioned Risers (TTRs) and umbilicals are
also widely in use. Among the types mentioned above,
flexible risers seem to be popular around the world, and
they dominate the oil and gas production in Brazil. In
Europe, the UK section of the North Sea alone has more
than 1000 flexible risers.
In view of current gaps, the motivation of this study is to
establish a probabilistic approach to assess the reliability
of riser systems in which riser clashing rarely occurs.
Uncoupled time domain analysis of the riser will be
performed as a first step. It is sensible to exclude VIV
and wake effects at this preliminary stage. For simplicity,
current will not be included in the analysis.
PREDICTION OF EXTREME RESPONSE
General
Marine risers are usually analyzed as line elements using
a numerical model such as the popular finite element
method. In this article, the commercial software is used
which performs the time domain analysis using the lumped
mass approach. The time history of the nodal positions is
extracted directly from the simulation results. It is worth
noting that the approach in this article can be applied to any
other numerical model provided that all the nodal positions
are available at all time steps. Here, time history X(t) is
recommended to be the maximum normalized clearance
between two risers. The generation of X(t) is discussed at
length by He and Low (2010).
In this approach, it is assumed that the critical condition
will occur during a typical storm according to a 100-year
return period, and the sea state is stationary for typically
three hours. A wave spectrum is chosen to express features
of short-term conditions.
Crossing rate analysis is the method adopted in this article.
In time domain simulation for a stationary sea state, the
In deepwater fields where the number of connected risers
tends to be large, designers generally prefer compact riser
systems for economical reasons. However, the compliancy
of flexible risers means that close riser spacing will increase
the risk of mutual contact and collision. The two conflicting
design requirements bring about the need for an optimized
riser layout design, which should have certain reliability
against riser clashing. In fact, riser clashing is a complicated
problem, because both static contact and dynamic clashing
can cause the risers to have fatigue or coating damage, and
the latter may even lead to loss of integrity. To address this
concern, DNV code (Det Norske Veritas, 2009) recommends
that the minimum clearance between two risers be the
sum of their diameters without considering safe factors.
Nevertheless, when optimization is of concern, engineers
prefer to know the reliability of a particular system rather
than being given inflexible criteria. Riser dynamics is so
varied and complex that recommendations based on past
experience may not be suitable for a particular problem.
For one thing, nonlinearity of line structure evidently
complicates the prediction of its response. For another
thing, vortex-induced vibrations (VIV) and wake effects
between two close risers are still too intricate to be fully
understood. Such effects are significant; for example, VIV
is able to cause large deflection in the risers to the extent
of one diameter.
Riser clashing is usually controlled within a low level, for
example, less than 10-4 during field life. It is not appropriate
to use experimental methodology for assessment, and
simulation is a better alternative. However, in literature,
there is no approach to offer a quantitative conclusion to
show the reliability of a riser system.
117
crossing rates are commonly extracted from the time history
X(t). If the total simulated duration is T0, which usually
includes a number of independent simulations with duration
T, and the associated number of up-crossings exceeding
threshold z within [0, T0] is
, then the mean upcrossing rate is
vz+ (0; T0) =
nz+ (0; T0)
m
…(1)
The probability of crossing a given threshold within a
certain time range can be estimated as
Pf = 1 – exp (–vz T)
…(2)
Here, Pf represents the probability for X(t) to exceed
threshold z in duration T and Eq. (2) is a good approximation
if the crossing level z is sufficiently high.
Figure 1. Riser model.
Naess method
Naess et al. (2008) gave an empirical formula of the
crossing rate
vz = q(z)exp{[–a(z – b)]c}
…(3)
where a, b and c are constant parameters, and q(z) can
also be regarded as constant when z is in a high level. q
is recommended to be estimated by the average of
for the largest values of z, where fz is the response pdf. b
is determined empirically, it should not be larger than the
smallest z for the fitting and the choice of b must optimize
the curve fitting (Naess et al., 2008). It is the first time
to apply this method to a riser system. Eq. (3) can be
rearranged to give
v
1n (–1n( zz )) = 1n(a) + c(1n(z – b))
…(4)
In Eq. (4), the left side is treated as the dependent variable,
1n(z – b) and c are regarded as independent variable and its
gradient. Because 1n(a) is a constant, q and b are estimated
beforehand. The art of linear fitting can be directly applied
to achieve parameters a and c. The desired crossing rate
obtained from Eq. (3) can be put back to Eq. (2) to attain
the corresponding Pf.
118
MODEL AND NUMERICAL RESULTS
Model
A simple model, which comprises two flexible risers
following the Lazy Wave configuration, is set up in the
commercial software Orcaflex in Fig. 1. The two ends of
a riser are attached to the floater and seafloor with pinned
joints respectively. To alleviate the heavy burdens of
calculation, only around 60% of the length (95 elements) is
contained in the analysis. A severe condition is elaborated
by allowing the wave direction to be perpendicular to the
symmetrical plane of two risers (i.e. in the y-direction) and
assigning a small top end clearance (0.6 D) and a small
separation angle (0.5 degrees). The significant waveheight
Hs and mean zero crossing period T0 are 15.7 m and 13.5
s separately for a severe JONSWAP sea state. All the
properties and structural details are reported in Tables
1-2.
A wave time history derived from a certain number of
wave components is synthesized. The wave spectrum is
divided into 250 components with equal frequency interval
approach from 0.07 Hz to 0.239 Hz. To improve the quality
of prediction, thirty independent random number sets are
employed to simulate 30 one-hour storms. To make the
computational intensity remain in an acceptable level, it
is sensible to simplify the environmental loadings. Thus,
only the first-order wave forces are considered in the model
and the current, VIV and wake effects are neglected at this
incipient stage.
Table 1. Structure of risers.
Line Type
Section
Length (m)
Descriptions
Flexible (upper section)
605
Included in analysis
Flexible with buoyancy
80
Not included in
analysis
Flexible (lower section)
341
Not included in
analysis
Total
1026
Table 2. Properties of risers.
Riser Types
Flexible
Outside Diameter (mm)
478.4
Flexible with
Buoyancy
873.0
Wall Thickness (mm)
133.1
330.4
Mass (kg/m)
200.0
431.1
Area (cm2)
1443.9
5632.1
EI (kN×m2)
153
153
1.200
0.979
Hang-off Angle (°)
10
N.A.
Content Density (kg/m3)
500
500
Cd (~)
Numerical results
The up-crossing rates are directly extracted from a 30-hour
simulation time history. Insufficient exceedances of certain
critical values will produce unrealistic crossing rate. In
Fig. 2, the unsteady pattern at the tail is mainly due to
lack of data.
Figure 3. Crossing rate extrapolation by Naess method;
1n(–1n((vz+)/q)) is plotted against 1n(z – b); q=0.36, b=-0.05,
a=14.14, c=1.097; range of value from z = 0.15 to 0.35;
CONCLUSIONS
Currently, the focus on ultra-deep water field operation
and compact riser designs makes riser collision a topic of
concern. As a safety precaution, a riser system is always
designed in a conservative way to avoid riser clashing.
This article has proposed an effective approach to assess
the low probability riser clashing. Such an approach is
based on the existing nodal positions obtained from a
time domain simulation and does not require extra work.
For the riser system in which no collision is allowed, the
proposed approach can directly calculate the probability of
failure in terms of riser clashing.
REFERENCES
[1] Det Norske Veritas, 2009, Offshore Standard DNV-RP-F203:
Riser Interference.
Figure 2. Crossing rate.
[3] Naess, A., Gaidai, O. and Teigen, P.S., 2008. “Extreme response
prediction for nonlinear floating offshore structures by Monte
Carlo simulation”. Appl. Ocean Res., 29, pp. 221-230.
Naess method is robust and gives a practical guide for the
extrapolation. It is worth noting that, to achieve an accurate
extreme value distribution, the up-crossing events of the
high response levels must be statistically independent.
This requirement is usually satisfied provided that the total
damping of a system is small such as, typically, a riser
system. It is shown in Fig. 3, Pf = 0.13% at the desired
threshold z=1. The crossing rate is extrapolated from
=2.4E-3 to the expected value about 1E-7 which is
expensive in CPU time with direct simulations.
[2] He J.W. and Low, Y.M., 2010. “Probabilistic Assessment of
the Clashing between Flexible Marine Risers”. Proc. OMAE,
Paper No. 20046, Shanghai.
119
EFFECTS OF ANISOTROPIC
PERMEABILITY OF FRACTURED ROCK
MASSES ON ROCK CAVERNS
Sun Jianping (sunjp@ntu.edu.sg)
Zhao Zhiye (czzhao@ntu.edu.sg)
ABSTRACT: An isotropic assumption is often applied to analyze in-situ permeability tests of fractured rock masses, and the isotropic
hydraulic conductivities are then used directly in the seepage analysis. However, the hydraulic conductivities are normally anisotropic
in fractured rock masses and the effects of the anisotropic permeability should be taken into account in rock engineering analysis,
especially for seepage analysis of underground oil storage caverns. In this study, an underground oil storage cavern project is analyzed
and the Oda’s method is used to determine the anisotropy in permeability. The anisotropy in permeability is determined using the fracture
orientation and the in-situ stress information from the field survey. A typical cavern unit is numerically modeled using the computer
code FLAC. The effects of anisotropic permeability on water pressure and critical gas pressure are studied. The results indicate that the
calculated results based on the in-situ hydraulic tests with isotropic permeability assumption can be used safely in the underground oil
storage cavern project.
INTRODUCTION
The basic principle of oil storage in unlined underground
caverns is that the hydraulic potential in the rock mass
around the caverns should be higher than the potential
on the perimeter of the storage caverns. The groundwater
flow through fractured rocks should be analyzed carefully
for underground storage cavern, so as to make sure no
leakage under various operating conditions. For analyzing
the groundwater flow correctly, some borehole hydraulic
tests were performed around the project site. Based on the
isotropic assumptions, the hydraulic conductivities were
obtained from the correlation curve of the injected tests.
However, hydraulic conductivities are usually anisotropic
in fractured rock masses, so the question of whether
the analysis results based on in-situ hydraulic tests with
an isotropic assumption can be used in the preliminary
design of underground oil storage cavern projects should
be addressed.
ANALYSIS OF ANISOTROPIC PERMEABILITY
BASED ON IN-SITU DATA
120
Theoretical model
If a fractured rock mass block can be treated as a
homogeneous, anisotropic and porous medium, it would
obey Darcy’s law. In order to obtain the components
of the hydraulic conductivity in fractured rock masses,
the following assumptions are made: (i) each fracture is
idealized by a set of parallel plates with a uniform aperture
t; (ii) the solid matrix is impermeable; (iii) the hydraulic
gradient is uniformly distributed over the whole body; (iv)
seepage flow through a fracture can be treated as a laminar
flow between parallel plates with a uniform aperture; and
(v) there is no head loss at intersections between fractures.
Based on these assumptions, Oda (1985) proposed hydraulic
conductivity components as follows:
kij = λg(Pkkδij – Pij) / μ
…(1)
Where
πρ ∞ ∞
Pij = 4 ∫0 ∫0 ∫Ω r 2 t 3 n i n i E(n,r,t)dΩdrdt
…(2)
Pkk = P11 + P22 + P33
…(3)
and
where g (LT-2) is the gravitational acceleration; μ(L2T-1)
is the kinematic viscosity; λ is a nondimensional scalar
dependent on the connectivity among joints, and can be
set to 1/12 for practical applications; δij is the Kronecker
delta; ρ is the number of joints per unit volume; ni is the
component of n projected on the orthogonal reference
axis system (xi =1,2,3); n is the fracture orientation; r
is the fracture length; and t is the fracture aperture. If
the unit vectors n normal to the fractures are orientated
inside a small solid angle dΩ around n and the diameters
and the apertures range from r to r + dr and from t to t
+ dt, respectively, E(n,r,t)dΩdrdt is then given as the
probability of the unit normal of (n,r,t) fractures.
Site investigation data
As part of the site investigation program, six vertical
boreholes are drilled to investigate rock hydraulic properties.
The locations of six vertical boreholes, B1, B2, B3, B4, B5
and B6, are shown in Fig. 1. The fracture orientation data
and dip/dip angle are obtained from the borehole survey.
S h, S H and S v (MPa)
80
0
2
4
6
8
10
100
Depth (m ACD)
120
Sh
140
SH
Sv
160
180
200
Figure 3. Stress’s profile for borehole B5.
In-situ anisotropic permeability analysis
Figure 1. Schematic map of locations of vertical boreholes
for the underground cavern.
In total, 72 hydraulic conductivity measurements were
conducted in the six boreholes, by the injection tests. Fig.
2 presents the measured hydraulic conductivity data at the
six boreholes at the depth between -40 mACD and -200
mACD, which ACD is the abbreviation of “Admiralty Chart
Datum”. The results show that the hydraulic conductivity
varies between 10-11 m/s and 10-4 m/s. It should be noted that
the hydraulic conductivities obtained from the correlation
curve of injected water pressure and flow quantity of the
injected water are based on the assumptions that the fracture
rock is homogeneous, isotopic and porous media and the
flow geometry is cylindrical, which do not reflect the
anisotropic property of fractured rock. In order to derive
the local stress regime at the proposed development area
for the oil storage cavern, a total of 10 hydraulic and
hydrofrac/hydraulic injection tests were conducted in the
uncased section of borehole B5 between -96 mACD and
-181.4 mACD (Fig. 3).
Hydraulic conductivity (m/s)
-13
10
10
-11
10
-9
10
-7
10
-5
10
-3
Depth (m ACD)
-80
-120
-160
-200
-240
B1
B2
B3
B4
B5
B6
Figure 2. Hydraulic conductivity with increasing depth
at six boreholes.
Based on Oda’s theoretical model and in-situ investigation
data, the ratio of anisotropy in permeability defined as
k1 / k3 and k1 / k2 can be determined, in which k1 , k2 and k3
are the principal hydraulic conductivities. Fig. 4 shows the
calculated results of the ratios of anisotropy in permeability
for six vertical boreholes between -80 mACD and -180
mACD depth. It can be seen from Fig. 4 that the ratio of
anisotropy in permeability decreases with increased depth,
due to the effect of geostatic stress. In borehole B1, the ratio
of k1 / k3 decreases from 1.91 to 1.65 with the increased
depth. In borehole B2, the ratio of k1 / k3 decreases from
2.50 to 2.09 with the increased depth. The ratios at the
other boreholes are between the ratios at B1 and B2. The
results also show that the ratios k1 / k2 for all the boreholes
are close to 1. The calculated results illustrate that k1 and
k2 are almost in horizontal directions and k3 is close to
vertical direction. Hydraulic conductivities obtained from
the correlation curve of the injected water pressure and flow
quantity of the injected water are based on the assumptions
that the fracture rock is homogeneous, isotropic and porous
media and the flow geometry is cylindrical. As k1 and k2
are almost the same and along the horizontal direction, the
hydraulic conductivity measured from the injection test
(Fig. 2) can be considered as the average value of k1 and
k2, and k3 can be estimated by the ratio of k1 / k3 (Fig. 4)
from the Oda’s method.
-40
In additional to the geostatic stress and fracture orientation
information, fracture length and aperture information should
be known in order to obtain the hydraulic conductivities.
But the site investigation does not provide such information,
so some assumptions are needed. Let us assume that the
statistical variables n and r are mutually independent. A
lognormal distribution function is used for the distributed
forms of fracture length.
121
-80
Depth (m ACD)
conductivity obtained from the injection test (Fig. 2) is used
as the horizontal hydraulic conductivity kH. The vertical
hydraulic conductivity kV is estimated based on Oda’s model
in Section 2. The ratios of kH / kV equal to 1.0, 1.5, 2.0 and
2.5, respectively, will be used in the following analyses
to study the effects of anisotropic permeability on the
storage caverns.
B1
B2
B3
B4
B5
B6
-60
-100
-120
-140
-160
-180
1.4
1.6
1.8
2
2.2
K 1/K 3
2.4
2.6
Figure 4. The ratios of anisotropic permeability
for six vertical boreholes.
NUMERICAL MODELING OF UNDERGROUND
OIL STORAGE CAVERNS
A typical oil storage cavern unit is modeled as a 2D
model. The computer code FLAC is adopted to model
the groundwater flow into the caverns. The crowns of
caverns are located at -119 mACD. The shape of the
cavern is horseshoe, with the height = 26m and the width
= 20m. The vertical water curtain is installed between the
contiguous storage units and connects with water gallery.
The modeling area is 140m wide and 165m deep. The mesh
size is 2.5m×2.5m. The distance between the two caverns
is 40m. The representative cross section for the model is
shown in Fig. 5. Regarding rock mass characteristics, the
four main hydrogeological classes have been taken into
account along the vertical direction: the recent sediment/
landfill class, the weathered zone class, the low confined
zone class and the confined bedrock class.
JOB TITLE :
(*10^2)
FLAC (Version 5.00)
LEGEND
-0.200
7-Aug-09 12:51
step
0
-1.100E+02 <x< 1.100E+02
-2.075E+02 <y< 1.250E+01
Permeability
7.136E-12
4.077E-10
5.097E-09
1.019E-07
Grid plot
0
-0.600
water
gallery
water
gallery
-1.000
5E 1
water
curtain
water
curtain
-1.400
122
-1.800
-0.800
-0.400
0.000
(*10^2)
0.400
0.800
Figure 5. A numerical model for the rock cavern unit.
The rock classes of landfill/recent sediment, the weathered
rock and the low confined zone are assumed to be isotropic
due to their adequate weathering. Anisotropic permeability
is considered for the confined bedrock class only. Because
k1 and k2 are almost the same and in the horizontal direction
in the confined bedrock, the geometric average hydraulic
The groundwater flow is assumed to be steady in this study.
Constant pressure which is equal to 15m water column
is used on the upper boundary to simulate the effect of
sea water pressure. Constant head boundaries at the water
curtains are assigned with the fixed hydraulic potential H
equals to 0 mACD. Two different phases, construction phase
and operation phase, are considered. The main differences
between the two cases are related to the pressure inside
the cavern and water gallery condition. In the construction
phase, the caverns and water galleries are filled by air with
the atmosphere pressure of 0 MPa. In the operation phase,
the water galleries are filled by water and the fixed hydraulic
potential H which is equal to 0 mACD is applied as the
boundary condition; the caverns are filled with oil in density
= 900 kg/m3 and the distribution of hydraulic pressure at
the wall of the cavern equals to the oil pressure.
INFLUENCES OF ANISOTROPIC
PERMEABILITY ON UNDERGROUND
STORAGE CAVERNS
Influences on water pressure distributions
The calculated results show that the water pressure between
the two caverns decreases as the ratio of kH / kV increases.
During the construction phase, the maximum water pressure
changes from 148kPa to 75.1kPa as the ratio of kH / kV
increases from 1.0 to 2.5. During the operation phase,
the maximum water pressure changes from 257.13kPa to
185.30kPa as the ratio of kH / kV increases from 1.0 to 2.5.
Hence, a conservative result will be obtained by using
isotropic assumption to assess the rock stability between
the caverns, as a higher water pressure will reduce joint
strength, and reduce the rock mass strength.
The results also show that the water pressure distribution
between the vertical water curtain and the cavern has little
variation as the ration of kH / kV increases. This means that
the anisotropic permeability has little influence on the rock
stability between the vertical water curtain and the cavern.
The vertical water pressure distribution above the cavern
crown is studied. As depth changes from -15 mACD to
-119 mACD, the water pressure increases first and then
decreases. It can be seen that an increase of water pressure
above the cavern crown will happen as the ratio of kH / kV
increases. During the construction phase, the water pressure
at -108 mACD increases from 289.73kPa to 316.00kPa
as the ratio of kH / kV increases from 1.0 to 2.5. During
the operation phase, the water pressure at -108 mACD
increases from 344.30kPa to 423.38kPa as the ratio of
kH / kV increases from 1.0 to 2.5. This implies that the rock
stability around the cavern crown decreases as the ratio of
kH / kV increases.
and the in-situ stress obtained from field survey. The results
show that the ratio of k1 / k3 varies from 1.65 to 2.50, and
k1 and k2 are almost in the horizontal direction and k3 is
close to vertical direction in this site.
Influences on critical gas pressure
A typical cavern unit is numerically modeled using the
computer code FLAC. The geometric average hydraulic
conductivities obtained from the injection test are used as
the horizontal hydraulic conductivity kH and kH / kV equal to
1.0, 1.5, 2.0 and 2.5, respectively, are used in this numerical
model. The effects of anisotropic permeability on water
pressure and critical gas pressure are studied carefully.
The results show that most calculated results which are
based on in-situ hydraulic tests with isotropic permeability
assumption can be used safely in the underground oil
storage cavern project.
The gas tightness of rock caverns should also be considered.
Goodall et al. (1988) recommended a practical design
criterion that no gas will leak as long as the water pressure
increases along all possible gas leakage paths away from
the caverns. According to Goodall’s criterion, at the critical
gas pressure, the groundwater pressure in the vicinity of
the cavern is equal to the gas pressure at some point on
the boundary of cavern, i.e., ∂p / ∂n = 0, where p is the
groundwater pressure and n is the unit normal vector at
this point. Liang and Lindblom (1994) suggested the “critical
gas pressure” as the maximum tolerable gas pressure for
a given storage system at no gas leakage conditions. In
this study, the Goodall’s criterion is used to determine
the critical gas pressure and the influence of anisotropic
permeability on critical gas pressure is investigated. The
calculated results show that an increase of the ratio of
kH / kV can linearly increase the critical gas pressure. The
critical gas pressure is 0.846 MPa and 0.890 MPa for
kH / kV = 1.0 and kH / kV = 2.5, respectively. Using the
isotropic assumption, a safe critical gas pressure is obtained
and can be used to design the engineering project.
Only the anisotropy induced by fracture orientation and
in-situ stress are considered in this paper. The influences of
bolting, shotcreting and redistributed stress after excavating
on anisotropy in permeability and heterogeneous property
of fractured rock mass are not studied. Further studies
that consider these influences will be carried out in our
future work.
REFERENCES
[1] Oda, M., 1985. “Permeability tensor for discontinuous rock
masses”. Geotechnique, 35(4), 483-495.
CONCLUSIONS
In this study, Oda’s method for determining the anisotropic
permeability, which is difficult to achieve from the in-situ
tests, is used for the seepage analysis of an underground oil
storage cavern. In this method, anisotropic permeability of a
site is determined from the fracture orientation distribution
[2] Goodall, D.C., Aberg, B. and Brekke, T.L., 1988. “Fundamental
of gas containment in unlined rock caverns”. Rock Mechanics
and Rock Engineering, 21, 235-258.
[3] Liang, J. and Lindblom, U., 1994. “Analyses of gas storage
capacity in unlined rock caverns”. Rock Mechanics and Rock
Engineering, 27(3), 115-133.
123
ENTROPY BASED ENSEMBLE NEURAL
NETWORK DESIGN
Zhang Yun (zhangyun@ntu.edu.sg)
Zhao Zhiye (czzhao@ntu.edu.sg)
ABSTRACT: Ensemble neural networks (ENNs) are commonly used networks in many engineering applications due to their better
generalization properties. An ENN usually includes several component networks in its structure, and the component networks commonly
use a single feed-forward network trained with the back-propagation learning rule. In this paper, an ENN, which combines the component
networks by using the entropy theory, is proposed. The entropy based ENN searches the best structure of each component network first,
and employs the entropy as an automating design tool to search the best combining weights of the ENN. An analytical function, namely
Friedman function, is used to assess the accuracy of the proposed ensemble approach. The computational experiment verified that the
proposed entropy based ENN outperforms the simple averaging ENN and the stand alone neural network.
ENSEMBLE NEURAL NETWORKS
The artificial neural network (NN) (McCulloch & Pitts 1943)
is a mathematical or computational model for information
processing based on the biological neural networks. An
ensemble neural network (ENN) is a collection of a finite
number of NNs that are trained for the same task. Usually
the networks in an ensemble are trained independently
and then their predictions are combined (Sollich & Krogh
1996). In other words, any one of the component networks
in the ENN could provide a solution or a predictor to the
task by itself, but better results might be obtained by an
ENN by combining the solutions that are achieved by the
component networks. The architecture of a typical ENN
is shown in Figure 1. The two main steps to construct an
ENN are creating component networks and combining these
component networks.
The resulting maximum entropy probability distribution
corresponds to a distribution which is consistent with the
given partial information but has maximum uncertainty or
entropy associated with it.
To illustrate Jaynes’ principle, we consider a discrete random
variable X. To obtain the ‘most objective’ probability
distribution of X, the maximum entropy principle can be
used in the following procedure:
max
…(1)
subject to
…(2)
and
, j=1,2,…,m
…(3)
where fj (x) is a given function of x. Using the method of
Lagrange’s multipliers, the resulting distribution is λi (x) =
e–α0 –α1 f1 (xi) –α2 f2 (xi) –…–αm fm (xi), i = 1,2,…,n, where α0, α1, …, αm
are the Lagrangian multipliers which are determined from
the (m+1) constraints in Equations (2) and (3).
124
Figure 1. Architecture of a typical ENN.
ENTROPY
The entropy was introduced in the context of efficiency of
heat engines in early 19th century. According to the second
law of thermodynamics, the entropy never decreases in
a closed system, and it is a measure of the disorder or
complexity of a system. The maximum entropy formalism
published by Jaynes (1957) is a fundamental concept in
the information theory. The maximum entropy formalism
is used to determine the probabilities underlying a random
process from any available statistical data about the process.
DESIGN ENSEMBLE NEURAL NETWORKS
USING ENTROPY CONCEPT
The entropy based ENN can reduce over-fitting in the ENN.
The major steps of the entropy based ENN are shown in
Figure 2, which are explained further as follows.
Creation of the component network can be divided into two
steps. The first step is to generate the training data and test
data sets, and the second step is to create the component
networks. In Step 1, some common ratios of the training
data to the test data will be used in the analyses. The data
used for training each component network are the same.
In Step 2, each component network is created several
times, but the best structure will be used in the ENN.
The criterion to choose the best component network is to
subject to
Start
, Pi > 0
…(6)
where S(P) is the entropy value of the combining weights of
the whole ENN; Pi is the ith component network’s weight
of the ENN; m is the number of the component networks;
μT and μENN are the mean values of the target and the ENN
output, respectively; σT and σENN are the standard deviations
of the target and the ENN output, respectively.
Create an ENN,
determine the no. of the component
networks and no. of the hidden nodes
in each component network.
The Lagrangian multipliers can be solved as follows:
Max
For each component NN, randomly
run several times, then choose the
best structure, which has the
minimum training-MSE.
…(7)
where λ0, λ1 and λ2 are the Lagrangian multipliers.
Calculate the solution of entropy
equations to determine the
weights of each component NN.
Let
, i=1,2,…,m, the solution of this problem
is Pi = e–1–λ0 –λ1 • μi–λ2 • σi . Let A = e1+λ0, B = e–λ1, C = e–λ2, and
,
Use test data to calulate
the test-MSE.
the
solution
of
this
problem
becomes
. And Newton’s method is used to solve
the above equations, so to obtain weights of the component
networks.
end
Figure 2. Flowchart of entropy based ENN.
select the one with the smallest training mean-squared-error
(MSE). Since good regression ensemble members must be
both accurate and diverse, the training of each component
network should also have the high accuracy and diversity.
Thus, different numbers of hidden nodes would be used
in different component networks. The procedure to define
the number of hidden nodes in each component network
is similar to Zhao’s method (Zhao et al. 2008), but the
difference is that choosing the best performance component
networks are based on the component network with the
smallest training MSE.
Problem max
…(4)
min
…(5)
Friedman #1 is a nonlinear prediction problem which
was used by Friedman (1991) in his work on multivariate
adaptive regression splines (MARS). It has 5 independent
predictor variables that are uniform in [0, 1]. The following
Friedman #1 with normally distributed noise (mean 0,
variance 1) is used to test the entropy based ENN.
Y = 10sin(πx1x2) + 20(x3 – 0.5)2 + 10x4 + 5x5
…(8)
Firstly, 5×5×5×5×5 evenly distributed data along both the
five x-axis and the y-axis are selected from the domain [0, 1]
as the training data for the simulation. Another 4×4×4×4×4
evenly distributed points from the same domain are used
as the test data. The maximum training epoch of each
component network is set to 30. There are 3125 examples
in the training data set, and 1024 examples in the test data
set. The 3 kinds of NNs used for the example are: (1) single
NN, (2) ENN with simple averaging combined method, and
(3) ENN with entropy based combined method.
The number of the input nodes is 5, and the number of the
output nodes is 1. The single NNs use 4, 6, 8, 10 hidden
nodes in their hidden layer, respectively. The single NNs
are trained 4 times randomly to find the best results for
To use the entropy concept to obtain the unbiased ENN,
three parts of the problem should be optimized at the same
time: to maximize the entropy of the combining weights of
the whole ENN; to minimize the error between the mean
output of the ENN and the mean target value; to minimize
the difference of the standard deviation of the output of
the ENN and the standard deviation of the target value.
This will be benefiting the whole ENN. The three part
optimizing problem can be formulated as follows:
A VERIFICATION EXAMPLE
125
comparison. In the other two ENNs, there are 4 component
networks. The numbers of hidden nodes in the component
networks are 4, 6, 8 and 10, respectively. After choosing
the best weight configuration of each component network
from 4 random runs, the output of the ensemble networks is
combined with the simple averaging method (noted as AveENN) for the simple averaging ENN, and the entropy based
ensemble method (noted as EN-ENN) uses the modified
entropy value to determine the networks’ weights.
Table 1 shows the corresponding MSE values of the test
data and the training data with 20 runs during training.
From Table 1, it can be observed that the EN-ENN provides
the best generalization in terms of the mean value and
the S.D. for the 20 runs. The relative small SD for both
ENNs indicates the main advantage of the ENN, i.e. the
consistency of the NN simulation. The comparison between
the actual and predicted test results of EN-ENN is shown
in Figure 3. It is noted that all the data points are within
a narrow band of the 45o line.
Test-MSE
Train-MSE
Single
Ave-ENN
EN-ENN
1.052
1.410
1.285
Mean
2.889
1.948
1.862
S.D.
1.679
0.455
0.437
Minimum
0.041
0.481
0.181
Mean
0.357
0.963
0.584
S.D.
0.383
0.358
0.296
[4] Sollich, P. and Krogh, A., 1996. “Learning with ensembles:
How over-fitting can be useful” in: Touretzky, D.S., Mozer,
M.C., Hasselmo, M.E. (Eds.), Advances in Neural Information
Processing Systems 8, Denver, CO, MIT press, Cambridge,
MA, p. 190-196.
[5] Zhao, Z.Y., Zhang, Y. and Liao, H.J., 2008. “Design of
ensemble neural network using the Akaike information
criterion”. Eng Appl Artif Intel, 21: 1182-1188.
20
Predicted Value
[1] Friedman, J.H., 1991. “Multivariate adaptive regression
splines”. Ann Statist, 19(1): 1-82.
[3] McCulloch, W.S. and Pitts, W., 1943. “A logical calculus
of the ideas immanent in nervous activity”. Bulletin of
Mathematical Biophysics, 5: 115-133.
25
15
10
5
The Friedman function is used to verify the performance
of the proposed ENN. From the comparison study, which
include the single NN, the simple averaging ENN and the
entropy based weighted ENN, it is found that the proposed
entropy based ENN outperforms other methods. These
results also showed the potential of the proposed ENN to
be applied to other kinds of problems.
[2] Jaynes, E.T., 1957. “Information theory and Statistical
Mechanics I”. Phys Rev, 106: 620-630.
30
126
This paper aims to improve the ENN in two aspects: 1)
instead of using component NN directly, a preliminary
selecting process is used to get the best component
NN; 2) the entropy is used to determine the weights of
the component NNs in the ENN. Using the entropy to
combine these best component networks can improve the
performance of the ENN by balancing the contribution of
each component network.
REFERENCES
Table 1. Results of twenty runs on Friedman #1 function
with 4 component networks.
Minimum
CONCLUSIONS
0
0
5
10
15
20
25
Actual Value
Figure 3. Comparison between the actual and predicted
Friedman #1 function test results of EN-ENN.
30
BURST STRENGTH ESTIMATION OF A
CRACKED COMPRESSED NATURAL GAS
(CNG) TANK CYLINDER
Lie Seng Tjhen (cstlie@ntu.edu.sg)
Zhang Baofeng (bfzhang@ntu.edu.sg)
ABSTRACT: In this study, the fracture behavior of a 30-liter cracked compressed natural gas (CNG) cylinder was investigated numerically.
A series of experimental tests was conducted to study the material property of a typical steel CNG cylinder as well as the true profile of
the cylindrical structure. Then, fracture assessment of the cracked steel cylinder was carried out to predict its burst pressure. The approach
adopted in the present analysis was based on the Failure Assessment Diagram (FAD) given by BS 7910 and API 579. Finally, a comparison
was made between the theoretical burst pressure and the ones predicted by both codes of practice.
INTRODUCTION
Fracture failure
This study described the structural integrity of a 30-liter
CNG cylinder having a wide range of internal surface cracks.
The approach adopted in present analysis was based on the
FAD given by BS 7910 [2] and API 579 [3]. The standard
Level 2A FAD curve, which is identical to the Level 2
assessment in API 579, was used to estimate the burst
strength of a typical cracked CNG cylinder specimen.
FAILURE ASSESSMENT DIAGRAM (FAD)
In the standards, the general FAD Level 2A assessment
curve is given by
Kr = (1 – 0.14L2r)[0.3 + 0.7 exp(–0.65L6r)]
…(1)
Loading path
Service point
Critical point
Unsafe Plastic collapse
failure
Safe
Lr =Applied load/plastic collapse load
1.0
Figure 1. Failure assessment diagram (FAD) for
flawed structures.
The load ratio Lr for pressure vessels is provided as
…(2)
where σref is the reference stress and σy is the yield strength
of the material.
It is essential to recognize that the Kr parameter uses the
linear elastic stress intensity factor with no allowance for
the effect of plasticity on the crack tip driving force. As
Lr increases, plasticity also increases the effective crack
tip driving force [4].
CNG CYLINDER SPECIMEN
Cylinder geometry
A 30-liter steel cylinder was cut open to reveal the internal
structure as shown in Figure 2. The measured dimensions
are external diameter D = 230 mm, side wall thickness t
= 6.4 mm and overall length l = 670 mm.
The usage of the FAD for the assessment of flawed structure
is illustrated in Figure 1. This method adopts the assessment
curve which uses the ratio of the stress intensity factor
to the fracture toughness, Kr, as the vertical axis and the
ratio of the applied load to the plastic collapse load, Lr,
as the abscissa axis. If the service point falls inside the
assessment curve, the structure is considered safe, otherwise,
the structure is deemed unsafe.
Applied load or crack size
Failure assessment curve
rdrpVr
In order to determine the critical crack size with which the
crack becomes unstable and causes the CNG cylinder to
fail, the damaged structure should be assessed according to
the knowledge of the service stresses and the knowledge
of the fracture properties of the material. The fitness for
service is an important procedure used to indicate the right
level of material and fabrication quality for application
with regard to the risks and consequences of failure [1].
Fitness for service assessment procedures for evaluating
crack-like flaws in pressure vessels are based on the failure
assessment diagram (FAD) method, which has evolved as
the most widely accepted methodology for the analysis of
components containing a crack-like flaw.
1.0
127
Table 2. Material properties.
Yield
Tensile Young’s Critical Charpy Estimated
strength modulus CTOD V-notch
Kmat
stress
σy (MPa) σu (MPa) (GPa) δIC (mm) Energy (N/mm3/2)
(Joules)
868.8
968.6
204.5
0.07
101
3464
Table 3a. Assessment results of burst strength (BS 7910).
BS 7910 (2005)
Figure 2. 3D model of the 30-liter CNG cylinder.
a
Table 1. Principal dimensions of the surface cracks.
Crack depth a
(mm)
Half crack length c
(mm)
a/t
1.28
6.40
3.20
2.13
1.60
1.28
0.2
1.92
9.60
4.80
3.20
2.40
1.92
0.3
2.56
12.80
6.40
4.27
3.20
2.56
0.4
3.20
16.00
8.00
5.33
4.00
3.20
0.5
3.84
19.20
9.60
6.40
4.80
3.84
0.6
4.48
22.40
11.20
7.47
5.60
4.48
0.7
5.12
25.60
12.80
8.53
6.40
5.12
0.8
For a high pressure compressed natural gas (CNG) tank
cylinder, a surface crack is often initiated from the internal
wall thickness and rapidly grows into an approximately
semi-elliptical in shape [5]. Thus, a semi-elliptical internal
surface crack was assumed at the side wall of the specimen
as shown in Figure 3. The assumed surface cracks covers
a wide range of crack profiles as listed in Table 1, where
the ratio of crack depth to wall thickness a/t ranged from
0.2 to 0.8 with an interval of 0.1; the ratio of crack depth
to crack length a/c ranged from 0.2 to 1 with an interval
of 0.2.
σh,u (δ route)
(MPa)
c
σh,u (K route)
(MPa)
deepest
crack tip
deepest
crack tip
1.92
9.60
695.33
819.40
681.97
807.72
1.92
3.20
778.92
803.04
766.78
791.19
1.92
1.92
830.48
807.97
818.61
796.10
3.20
16.00
514.05
633.22
498.62
622.78
3.20
5.33
698.20
714.93
684.64
701.97
3.20
3.20
771.74
739.23
759.65
726.34
4.48
22.40
293.43
388.11
280.42
379.04
4.48
7.47
586.81
590.07
572.48
575.89
4.48
4.48
706.56
658.11
694.04
643.73
Table 3b. Assessment results of burst strength (API RP579).
API RP579 (2007)
a
c
σh,u (K route)
(MPa)
deepest
crack tip
1.92
9.60
756.46
913.30
1.92
3.20
871.18
879.30
1.92
1.92
930.98
889.40
3.20
16.00
597.58
762.66
3.20
5.33
784.40
777.98
3.20
3.20
863.43
805.41
4.48
22.40
464.12
611.25
4.48
7.47
707.55
679.06
4.48
4.48
811.49
729.554
FAILURE ASSESSMENT OF CRACKED CNG
CYLINDER
128
Figure 3. Mesh of CNG cylinder model with a surface crack.
Material properties
The material properties of the CNG cylinder were obtained
through tensile coupon test, CTOD test and Charpy impact
test, and they are summarized and tabulated in Table 2.
The safety of this CNG cylinder containing internal surface
crack under a working pressure was assessed according to
BS 7910 [2] Level 2A and API 579 [3] Level 2 respectively.
Both stress intensity factor, K, and CTOD, δ, assessment
routes were employed in the evaluation of the burst strength
of the cracked CNG cylinder. The residual stresses were
set as zero because it was a seamless type CNG tank
cylinder, i.e. there were no continuous longitudinal girt
welds. The selected assessment results of the burst strength
are tabulated in Table 3.
CONCLUSIONS
REFERENCES
In this study, a 30-liter CNG cylinder with a wide range
of semi-elliptical internal surface cracks was assessed to
predict its burst strength.
[1] Wells, A.A., 1981. “The meaning of fitness for purpose and
the concept of defect tolerance”. International Conference
of Fitness for Purpose Validation of Welded Constructions.
London, UK: The Welding Institute, Paper 33.
Based on the tensile strength and fracture properties
obtained, the prediction was performed using BS 7910 [2]
and API 579 [3] approaches respectively. Fracture toughness
in terms of critical CTOD value obtained from the CTOD
test and critical stress intensity factor KIC estimated from the
Charpy impact test data were applied in the prediction.
[2] BS 7910, 2005. “Guide on Methods for Assessing the
Acceptability of Flaws in Fusion Welded Structures”. British
Standards Institution, London, UK.
From the prediction results for the cracked CNG cylinder,
it can be concluded that the fracture toughness estimated
from Charpy impact test data can be used in the fracture
strength prediction for the cracked CNG cylinder. BS 7910
[2] approach produces more conservative predictions of
the fracture strength compared to that the API 579 [3]
standard. When the ratio a/c increases, the weakest point
of the crack is expected to shift from the deepest point to
the crack tip.
[3] API RP579-1/ASME FFS-1, 2007. “Fitness-for-Service”.
American Society of Mechanical Engineers, New York,
USA.
[4] Ainsworth, R.A., 1984. “The assessment of defects in
structures of strain hardening materials”. Engineering Fracture
Mechanics, 19(4), 633–642.
[5] Lin, X.B. and Smith, R.A., 1998. “Fatigue Growth Prediction
of Internal Surface Cracks in Pressure Vessels”. Journal of
Pressure Vessel Technology, 120(1), 17-23.
129
EXPERIMENTAL STUDY AND NUMERICAL
MODELING OF STRESS CONCENTRATION
FACTOR OF HIGH STRENGTH STEEL
PLATE-TO-PLATE Y JOINTS
Chiew Sing Ping (cspchiew@ntu.edu.sg)
Jiang Jin (jian0048@e.ntu.edu.sg)
Yu Yi (yuyi@.ntu.edu.sg)
ABSTRACT: In this study, the stress concentration factor (SCF) distribution of a set of plate-to-plate Y joints made from high strength
steel plates (with yield stress equal to 690MPa) under the action of static axial tensile loading applied on the brace were studied. The
detailed SCF distributions were analyzed via finite element modelling and empirically tested using small scale specimens (with plate
dimensions of 450mm×150mm). Two groups of specimens with different welding procedures are studied: The first group consists of
joints with welding completed at ambient temperature while the second group consists of joints with welding completed at a per-heated
temperature of 100°C. Comparison study is then carried out for the stress concentration factor of high strength steel joint in different
fabrication environments and geometries.
INTRODUCTION
Currently, most steel structures are made of mild steel for
its satisfactory mechanical property and availability. In the
existing codes and standards, mild steel is well specified
for application. However, there has been an increasing
interest in the use of high strength steels, which generally
have yield strengths larger than 460MPa, for recognizing
the benefits from an increase in the strength to weight ratio
and savings in the cost of materials. This is particularly
applicable to offshore structures to reduce weight which can
lead to achievement of considerable saving in supporting
substructures. Compared with mild steel, high strength steel
has merits in economy, architecture and safety.
On the other hand, fatigue is one of the major problems
causing the degradation of offshore structures in long term
integrity. Therefore, stress concentration factor, which is
the ratio between the hot spot stress, caused by structural
discontinuities or welding, and the nominal member stress,
is of significant meanings.
130
Eqn. 1
Figure 2 illustrates geometry profile for the joints whose
angle is ranging from 60° to 90. In this case, the end of
attachment plate in the welding part is cut into shape with
30° to satisfy welding requirement. Assuming the coordinate
of point H and G are (l1/2, t1) and (l1/2, t1+R) respectively,
the coordinate of C, D, E, and F can be expressed as:
GEOMETRICAL AND NUMERICAL
MODELLINGS
A systematic geometrical modelling procedure for a general
high strength steel plate-to-plate Y joint without cracks was
proposed in this study. The global coordinate system (x-y)
of the joint is defined with the original O locates at one end
point of the plate. The geometry profile for the 45°joints
angle is shown in Figure 1. Assuming that the coordinate
of point C is ((l1+t2)/2, t1), the coordinate of point D can
be written as ((l1+t2)/2, t1+R). Furthermore, the coordinates
of points E, F and G can be expressed as:
Eqn. 2
During numerical modelling using ABAQUS, by using
the importing modulus in ABAQUS and using variable
values of l1, l2 t1, t2 and θ, it was easy to change the
plate size and welding parameters. Load was applied on
the surface of EF, as shown in Figure 1 and Figure 2, by
a point-surface coupling. Five monitoring points, a, b, c,
d and e, whose z coordinates are 15mm, 45mm, 75mm,
105mm and 135mm respectively, were set for results
analysis in each case (Figure 3) after the modelling were
completed. Linear interpolation was used to get the stress
in monitoring points after the hot spot stresses at element
nodes were obtained.
t2
F
y
l2
E
ș
H
G
o
tw
R
D
C
B
x
t1
A
l
Figure 1. Welding Profile for 45° joints.
l2
R
I
D ș
G
H
x
C
o
l
l1
d
z b
a
5
Minimum
Yield Strength
(MPa)
Tensile
Strength
(MPa)
Minimum
Average
Impact Energy
RQT701
690
790~930
27J@ -45°C
LB-70L
685
755
108J@-60°C
t1
20
x
Figure 3. Measuring points in the specimen.
Two series of specimens were included to compare the
influence of welding condition on stress concentration factor
distribution near the weld toe. One group was fabricated in
ambient temperature while the other group was pre-heated
to 100°C before welding. There were 6 different geometries,
consisting of 3 different parent steel plates thicknesses and
2 welding connection angles of each group were employed
to explore the variation of the residual stress near the weld
toe. During the welding, full penetration welding for tubular
joint was used by following the standard AWS D1.1-2008.
For the 45° joints, the welding profile shown in Figure 1.
Figure 2 shows the welding profile for the 60° joints.
To fix the specimen in the grip of testing machine, a set of
supporting joints, made of mild steel S355 with thickness
of 55mm, was designed. It was designed in such a way that
have nearly triple thickness when comparing with specimens
to make sure the failure will turn out in specimens rather
than the supporting joints. The specimen and supporting
joint are connected by 12 high strength hexagon bolts of
grade 10.9HR. In each end of connection, 6 bolts were
positioned in two lines. Figure 4 shows the profile of the
specimen and supporting joint after assembly.
The Instron Model 8506 Dynamic Materials Testing System
was introduced when tensile loading was to be applied in
the specimen. With maximum tensile loading capability of
2000KN, it is an advanced multiprocessor-based control
y
e
B
A
c
Items
t2
E
y
In the present experimental investigation, a number of
plate-to-plate T/Y joints, made of high strength steel with
minimum yielding stress of 690MPa, were fabricated by
welding. This high strength steel, RQT701, which was
supplied by Corus Group, was quenched and tempered
structural steel with improved forming and welding
performance by substituting some alloying element with
carbon. In the process of welding, great precautions were
needed to ensure that welding qualification is satisfactory.
Electrodes and fluxes with very low hydrogen content must
be used in order to prevent hydrogen cracking. Hence, an
ultra low hydrogen and moisture resistant type covered
electrode for 690MPa high tensile strength steel for low
temperature service, LB-70L, which is equivalent to the
class ASME/AWS A5.5 E10016-G and supplied by Kobelco
of Japan, was employed [1]. The welding procedure was
carried out according to the AWS D1.1 2008 [2]. Other
standards also were referenced [3-4]. Table 1 gives the
mechanical properties of the RQT701 plate and LB-70L
electrode.
Table 1. Mechanical properties of RQT701 steel plate
and LB-70L electrode.
l1
F
EXPERIMENTAL INVESTIGATION
131
console which provides full digital control of a testing
system. It consists of a closed load and four columns frame
with movable crosshead, a hydraulic actuator to apply a
force, gripping mechanisms to hold the mechanical test
specimen, and a load cell to measure the force. The position
of the actuator, under closed loop control by controlling the
hydraulic fluid flowing through a servo-valve supplying the
actuator, is measured by a displacement transducer.
FLA-2 of TML strain gauge, which has only one grid, was
adhered on the surface of the specimen. Six strain gauges
were used and installed in the position as Figure 4 shown.
In the direction of specimen length, the strain gauges
positioned in two lines, which were away from weld toe
5mm and 20mm respectively, were applied.
5
Weld Toe
25
C
B
A
C1
B1
A1
50
50
Figure 5. The distribution of SCF in monitoring points
of 8mm–45° joints.
20
25
Figure 4. Plane view of scheme of strain gauges
for static testing.
RESULTS ANALYSIS
132
Figure 5 illustrates the distributions of SCF both by
modelling and test for the 8mm-45° joints, where line
A denotes the specimen in ambient temperature and line
B refers to the specimen fabricated with preheating. The
modelling result agrees well with test outcomes. In this
case, the maximum SCF locates at the middle of plate
width. The SCF in joint welded at ambient temperature is
slightly higher than in pre-heating joint. Figure 6 depicts
the modelling and test results for the 8mm-60° joints. In
this case, two SCF values in the middle of plate width
deviate much from modelling results and another two
values from test. However, the values in both two ends
agree well. It is the existence of small notch near weld
toe that make two values in the middle of plate width
deviate from the modelling result and the other two values
derived by test.
Figure 7 shows comparison between modelling and test
results for the 12mm-45° joints. The numerical results
corroborate the test results. However, in Figure 8, where the
distribution of SCF for the 12mm-60° joints is illustrated,
the values at both ends appear to diverge. At one end of
the plate width, the SCF at joint with welding at ambient
temperature is 0.80 while at the other end point in joint
with welding at pre-heating temperature is 2.12. This
phenomenon may be due to the uneven distortion of plate
during welding and the asymmetrical applied stress caused
by the tensile machine. However, in the middle of plate
width, the test results are close to modelling value. Figure
9 and Figure 10 give the results for the 16mm-45° joints
and the 16mm-60° joints, respectively. In these two cases,
the modelling results corresponds with test values well.
CONCLUSIONS
Based on numerical analysis and test results, several
conclusions are obtained as follow:
(1) In most cases, the SCF values obtained by modelling
have good consistence with test results. The numerical
analysis by using python through ABAQUS is
efficient.
(2) The notch near the weld toe has significant influence
on SCF values and it is necessary to avoid producing
such flaws in process of welding. Additionally, the
distortion due to welding may also be an effect of the
distribution of SCF.
(3) In most of the 45° and 60° high strength steel joints,
the SCF locates in the range from 1.4 to 2.3. Several
aberrant values may turn out in the test due to limitation
of the specimens and test setup.
(4) The welding conditions including ambient temperature
and pre-heating temperature do not exert much influence
on SCF.
REFERENCE
[1] AWS. ANSI/AWS A5.5. “Specification for Low-Alloy Steel
Electrodes for Shield Metal Arc Welding”. American Welding
Society, Miami, USA. 2006.
[2] AWS.ANSI/AWS D1.1. “Structural Welding Code-Steel”.
American Welding Society, Miami, USA. 2008.
[3] AS/NZS. “Structural steel welding part 4: Welding of high
strength quenched and tempered steels”. Australia/New
Zealand Standard AS/NZS 1554.4, 2004.
[4] BSI. “Eurocode3 -- Design of steel structures. Part1-12:
Additional rules for the extension of EN 1993 up to steel
grades S700”. British Standards Institute, London, UK.
2007.
133
EXPERIMENTAL TESTS OF DIFFERENT
TYPES OF STEEL BEAM-COLUMN JOINTS
SUBJECTED TO CATENARY ACTION
Yang Bo (yang0206@e.ntu.edu.sg)
ABSTRACT: Several structural collapse incidents indicate that failure usually starts from the beam-column joints when exposed to
abnormal loads, especially for steel and composite structures. If the connections are sufficiently robust and there is adequate axial restraint
from adjoining structures, catenary action forms in the beams and slabs. This gives rise to alternate load paths when affected columns
are severely damaged, resulting in large deformations in the beams and slabs. This paper presents experimental results of steel beamcolumn joints subjected to catenary action. Two groups of connections (viz. simple and semi-rigid) were studied under column removal
scenarios. Seven experimental tests were conducted. The experimental results demonstrated that web cleat, flush end plate and top and
seat with web angles connections had better performance under extreme loading conditions compared with other types of joints.
INTRODUCTION
The alternate load path method, an important design
approach to mitigate progressive collapse, has been included
by a number of design codes including GSA [1] and DOD
[2]. It is an approach that allows local failure to occur when
subjected to an extreme load, but seeks to provide alternate
load paths so that the initial damage can be contained and
major collapse can be averted. A typical example is shown
in Figure 1 under the scenario when an interior column has
been removed by a blast and an alternate load path can
take place through adjacent structural assemblage including
beams, columns and joints. One of the key mechanisms in
mitigating the spread of “domino” effect is to redistribute
applied loading on damaged members through catenary
action. As shown in Figure 1, the term “catenary action”
refers to the ability of beams to resist vertical loads through
the formation of a net-like mechanism.
134
It is noteworthy that beam-column joints are critical
elements of any building structures and they usually
control the extent of catenary action because of the limited
resistance and rotation capacity of joints. So far, only
very limited research works have been conducted on the
performance of bare steel connections subjected to catenary
action. Most of the reported works focused on welded
moment connections [3, 4]. However, in Europe, bolted
steel connections such as fin plate, flush end plate, web
cleat and extended end plate, are very popular and the
evaluation of these kinds of joints subjected to catenary
action is important and timely.
A structure research group at Nanyang Technological
University, Singapore, is conducting a research programme
to investigate the stiffness, strength and ductility of bolted
steel connections subjected to catenary action under the
column-removal scenario. This project involves a series of
experimental tests on conventional bolted steel connections,
finite element (FE) investigation of connection behaviour,
Figure 1. Typical example of alternate load path.
and development of mechanical models for analysis and
design purpose. This paper focuses on the experimental
tests of different types of steel beam-column joints under
catenary action.
In total, 7 experimental tests were carried out on different
types of steel beam-column joints, including simple and
semi-rigid connections. The experimental tests were
carried out in the Protective Engineering Laboratory of
Nanyang Technological University. In the group of simple
connections, web cleat, top and seat angle, top and seat
with web angles (TSWA) (8mm thickness angles) and fin
plate connections were investigated while in the group of
semi-rigid connections, flush end plate, extended end plate
and TSWA (12mm thickness angles) were studied. The
principal aim of this paper is to provide the experimental
results of steel beam-column joint behaviour, including
failure modes, development of forces and deflections in
the beams.
TEST SET-UP AND SPECIMENS
Test set-up
The beam-column joint considered for experimental tests
was located above the storey where an internal perimeter
column had been removed. To simplify the tests, an
inflection point was assumed at the middle of the beam
span. Thus, only half of the beam span was used with pin
conditions, as shown in Figure 2. This simplification was
admissible since the focus was on the central connection
above the removed column. With the possible exception
of the floor immediately above the blast, the simplified
specimen was representative of any other upper floors
above the zone of damage since all the joints experienced
a downward rigid body displacement.
(a) Aerial view
Figure 2. Prototype beam-column joint.
The test set-up is shown in Figure 3. Compared with other
joint tests under normal loading conditions, additional
horizontal restraints were provided by an A-frame and
a strong reaction wall to consider the restraint from
surrounding structural elements. In order to consider the
rotational restraint from the continuous column to beamcolumn joints, a rotational restraint system was adopted,
as shown in Fig. 3. In addition, the beams were restrained
from lateral movement. A displacement-controlled point load
was applied to the middle column using an actuator.
Test specimens
In total, seven tests were carried out. Table 1 summaries
the test specimens. In all these seven tests, M20 8.8 bolts
were used.
(b) Front view
Figure 3. The test set-up.
TEST RESULTS
Simple connections
Before the test was started, the specimen was held at the
horizontal position. A vertical load was then applied to
the middle column gradually until fracture occurred in the
connection part.
In the test of web cleat, the specimen reached the largest
loading point with fracture of the web cleat close to the
heel, shown in Figure 4.
Table 1. Summary of the test specimens.
Connection type
Simple
connections
Top and seat
angle
Fin plate
TSWA
Semi-rigid
connections
Extended end
plate
Extended end
plate
TSWA
End
plate/angle
305×165×40
UB S355
305×165×40
UB S355
305×165×40
UB S355
305×165×40
UB S355
254×146×37
UB S355
254×146×37
UB S355
254×146×37
UB S355
L90×8
S275
L90×8
S275
100×8
S275
L90×8
S275
200×12
S275
200×12
S275
L150×100×12
S275
Figure 4. Failure mode of web cleat.
A ductile failure mode was observed in this test and due
to the high rotation capacity, catenary action could develop
well.
Web cleat
Beam
section
135
In the test of the top and seat connection, high flexural
action was observed and the failure mode was similar with
the test of web cleat, as shown in Figure 5. However, due
to this high flexural action, catenary action could not form
until the bottom angle fractured.
Figure 6. Failure mode of top and seat with web angles.
Figure 5. Failure mode of top and seat.
In the test of TSWA, the same angle fracture phenomenon
was observed, as shown in Figure 6.
In the test of the fin plate connection, bolts fractured in
shear were observed, as shown in Figure 7.
Figure 7. Failure mode of fin plate.
Figure 8 shows the load-displacement curves for different
types of connections tested in this group. The results from
the experimental tests demonstrated that simple beamcolumn joints could provide fairly significant gravity load
carrying capacity under column removal scenarios. The
achievement of these capacities lies with the ability of these
types of connections to accomodate large rotations. If large
rotations can be reached, axial tension stiffness (catenary
action) will overcome moment stiffness as the dominating
mechanism to resisting gravity loading.
The web cleat and TSWA connections exhibited good axial
tension and rotation capacities to develop catenary action. In
contrast, the fin plate and top and seat connections exhibited
only very limited axial tension and rotation capacities.
Figure 8. Load-displacement curves for different types
of connections (simple connections).
136
Semi-rigid connections
The same loading procedure was used in this group of
tests. Figures 9, 10 and 11 show the failure modes of these
three semi-rigid connection tests.
Figure 6. Failure mode of top and seat with web angles.
Figure 12 shows the load-displacement curves for different
types of connections tested in this group. The results from
the experimental tests demonstrated that flush end plate and
TSWA connections could perform well to develop catenary
action under column removal scenarios due to their large
rotation capacities.
CONCLUSIONS
Figure 9. Failure mode of flush end plate.
In this study, experimental tests were conducted to
investigate the behaviour of bolted steel beam-column
joints subjected to catenary action. Simple and semi-rigid
connections were studied. The test results demonstrated
the ductility and load capacity of the six connection types
in catenary mode. Among the simple connections in this
study, the web cleat connection had the best combination
of desirable features: ability to develop catenary action
and extremely high ductility (rotational capacity) through
deformation of the web angles. The flush end plate and
TSWA connections had a similar performance with regard to
catenary action in the group of semi-rigid connections.
REFERENCES
[1] General Services Administration (GSA), “Progressive Collapse
Analysis and Design Guidelines for New Federal Office
Buildings and Major Modernization Projects”. 2003.
[2] Department of Defense (DOD), 2005. “Design of Buildings
to Resist Progressive Collapse”. Unified Facilities Criteria,
4-023-03,
Figure 10. Failure mode of extended end plate.
[3] European committee for standardization, Eurocode 3: Design
of steel structures—Part 1-8: Design of joints, BS EN 19931-8: 2005, British Standards Institution, UK, 2005.
[4] Khandelwal, K. and El-Tawil, S., 2007. “Collapse behaviour
of steel special moment resisting frame connections”. Journal
of Structural Engineering-ASCE, 133(5), 646-655.
Figure 11. Failure mode of TSWA.
Figure 12. Load-displacement curves for different types
of connections (semi-rigid connections).
137
MODELING OF PIEZOELECTRIC
ENERGY HARVESTERS
Yang Yaowen (cywyang@ntu.edu.sg)
Tang Lihua (c070073@ntu.edu.sg)
INTRODUCTION
Uncoupled circuit model
To date, wireless sensor networks have been widely
employed for civil structure health monitoring. One
challenge in their applications is the limited lifespan of
the embedded batteries. For the sensor nodes deployed at
inaccessible locations, battery replacement could be tedious
and expensive. Hence, harvesting ambient vibration energy
as sensor’s power supply has aroused an intensive research
interest in the past few years [1].
Regarding the term at the right hand side of Eqn. (1b)
as a current source i, this equation actually satisfies the
Kirchoff’s current law. Under uncoupled assumption, the
coupling term χrV in Eqn. (1a) can be dropped. Hence,
the vibration of the PEH ηr and in turn the current source
i in Eqn. (1b) are independent of the electrical load (or
the energy harvesting process). For open circuit condition,
Eqn. (1b) is rewritten as
Among all transduction mechanisms, piezoelectric energy
harvesting is enthusiastically pursued in the literature for
its high power density [2]. Analytical or numerical models
can be established to predict the optimal power from
piezoelectric energy harvesters (PEHs) by considering a pure
resistive load. However, for a practical energy storage circuit,
these approaches are not applicable due to the intrinsic
complexity of storage circuit. One effective approach to
address this problem is to derive the circuit model of a
PEH, such that the entire system can be simulated. In this
article, we first derive an accurate circuit model for the
fabricated PEH prototype. Subsequently, the entire circuit of
the energy harvesting system is established and simulated in
an electronic simulator. Finally, experiments are carried out
on the fabricated PEH. The experiment results, including
the frequency responses of the open circuit voltage, short
circuit current, the power delivered on various resistors as
well as the results of charging various capacitors, validate
the prediction of circuit simulation.
…(2)
CIRCUIT MODELING
138
From the beam vibration theory and constitutive equations
of piezoelectricity, the modal electromechanical governing
equations for a cantilevered PEH can be described as [3]
…(1a)
…(1b)
where the subscript ( )r represents the r-th vibration mode;
ηr, ωr,
and χr are the modal coordinate, natural frequency,
damping ratio and modal electromechanical coupling
coefficient, respectively; – früg is the excitation force due
to the base acceleration üg; V and I are the voltage across
the PEH and current output from the PEH, respectively;
and CS is the clamped internal capacitance of the PEH.
which represents a circuit composed of an ideal current
source placed in parallel with the internal capacitance of the
PEH CS. This uncoupled model (Fig. 1(a)) or its equivalent
model, i.e., an ideal voltage source placed in series with
CS (Fig. 1(b)) is usually utilized as the circuit model of
a PEH [4]. However, such models fail to account for the
resonance frequency shift for different circuit conditions.
In addition, the prediction of optimal load and power under
uncoupled consumption is inaccurate if electromechanical
coupling is not negligible [5].
(a)
(b)
Figure 1. Uncoupled circuit models of PEHs.
In fact, if we move χrV in Eqn. (1a) to the righ hand side
as shown in Eqn. (3), χrV obviously plays the role as an
additional excitation force imposed on the beam.
…(3)
When the excitation frequency approaches one resonance
frequency, the magnitude of V will significantly increase
and the term χrV cannot be neglected especially when the
coupling χr is strong. Hence, ηr in Eqn. (3) and the current
source i in Eqn. (2) are dependent on the electrical load.
Accurate circuit model
To derive the accurate circuit model of PEH, the
electromechanical coupling term χrV should remain in
Eqn. (1a). The derivation of the circuit model starts from
this equation.
Analogizing the displacement ηr as charge qr, the excitation
force – früg as a voltage source vr, and the coefficients, 1,
2 ωr, ωr2 and χr of each term at the left hand side as
an inductor Lr, a resistor Rr, the reciprocal of a capacitor
Cr and a transformer with turn ratio Nr, Eqn. (1a) can be
rewritten as
…(4)
Eqn. (4) represents the constitutive equation of an LCR
circuit and satisfies Kirchoff’s voltage law. This circuit is
actually the r-th branch of the accurate circuit model and
represents the r-th vibration mode of a PEH. Considering
multiple modes, the accurate circuit model of a PEH is
comprised of an LCR circuit network (Fig. 2).
(a)
(b)
Figure 3. r-th branch of the circuit model
when the PEH works in actuator mode.
When the excitation frequency approaches r-th natural
frequency, Y can be approximated as
…(7)
in which, Yd and Ymot are termed damped and motional
admittance, respectively [3], i.e.,
…(8a)
…(8b)
From (8b), the locus of Ymot in the complex plane near r-th
mode is an approximate circle, i.e.,
…(9)
Figure 2. Accurate multi-mode circuit model of a PEH.
Using FEA, we can obtain Ymot near each mode. Drawing
the locus of Ymot, we can obtain the parameters Lmr, Rmr,
Cmr and Nmr by
For a PEH with a regular profile, the parameters Lr, Rr,
Cr, Nr and vr can be easily determined by analogizing Eqns
(1a) and (4) after analytical modal analysis. However, for
a PEH with an irregular and complicated profile, these
parameters should be identified by finite element analysis
(FEA) [3]. The procedure of this approach will be briefly
introduced below.
…(10)
For parameter Lr, Rr, Cr, Nr
Finally, by Eqn. (6), Lr, Rr, Cr and Nr can be determined.
These parameters should be derived from the admittance
of the PEH. The admittance of the PEH is defined by
In FEA, applying the voltage on the PEH, we obtain the
charge or current response, and subsequently the admittance
Y by applying Eqn. (5). The PEH in this case works in
actuator mode. Hence, the r-th branch of circuit model
(Fig. (3a)) can be converted to Fig. (3b) according to the
properties of an ideal transformer, i.e.,
…(6)
For parameter vr
The last undetermined parameter is the magnitude of the
voltage source vr for r-th mode. Under a unit excitation
acceleration, vr is related to the charge response exactly at
r-th natural frequency by the following equation [3],
…(11)
Hence, after we obtain the charge response Q(jωr) by FEA,
vr can be determined by Eqn. (11).
…(5)
139
SIMULATION AND VALIDATION
Fig. 4 shows the prototype of a fabricated PEH and the
experimental apparatus. Two piezoelectric transducers,
electrically connected in parallel, are bonded on each
side of an aluminum substrate and a steel proof mass is
attached at the beam tip. The beam is clamped on a shaker.
An accelerometer is attached on the shaker to monitor the
acceleration of the base excitation. Table 1 lists all the
parameters of the PEH prototype. These parameters are
required in FEA to derive the parameters of the circuit
model of the PEH.
resonance frequencies as observed in experiment, which
is one prominent characteristic of the electromechanical
coupling effect. Additionally, the magnitudes of Voc and Isc
from simulation agree well with those from the experiment.
Besides, it should be mentioned that the frequency response
curves in experiment are slightly bent to left (softening
stiffness), which results from the unavoidable imperfect
clamping condition [1].
Figure 5. Overall diagram of the energy harvesting system.
Figure 4. PEH prototype and experimental apparatus.
By applying the approach introduced in the previous section,
we derive the circuit model of the fabricated PEH, as
shown in the dashed box in Fig. 5. Two vibration modes
are considered to increase the accuracy. Fig. 5 also shows
the standard energy storage circuit (full-wave rectifier D +
storage capacitor Cstorage). The overall circuit of the system
is established in the SPICE software (NI Multisim 10.0
student version). In the following subsections, we report
the simulation that was conducted and compared with the
experimental results.
(a)
Open circuit and short circuit responses
140
The frequency responses of Voc and Isc from simulation
and experiment in the range dominated by the 1st mode
are compared in Fig. 6. The responses are all normalized
by the root mean square (RMS) input acceleration for
fair comparison. It is noted that the derived model can
predict the shift between the open circuit and short circuit
(b)
Figure 6. Open circuit volt age and short circuit current
responses: (a) simulation and (b) experiment.
Table 1. Properties of the PEH.
Item
Piezoelectric Transducer
Epoxy Layer
Substrate
Proof Mass
Dimensions (mm×mm×mm)
85×28×0.2 (active volume)
85×28×0.1
178×32×1.5
18.5×32×14
Density (kg/m3)
7750
2200
2700
7850
Modulus (GPa)
E11=60.98
E=0.1
E=70
E=200
Poisson’s ratio
0.35
0.38
0.35
0.29
Dielectric constant
ε33 /ε0=830
–
–
–
Piezoelectric constant (10-12m/V)
d31= -185
–
–
–
Rayleigh damping coefficients
S
α=1.7, β=2.25×10-5
(calculated by experimentally measured 1st and 2nd damping ratio ζ1=0.011, ζ2=0.0114 )
Optimal power delivered on various resistors
To evaluate the optimal power and corresponding optimal
load, various resistors are directly attached to the PEH. Fig.
7 shows the frequency responses of the power for different
resistive loads. Although the power magnitudes from
experiment and simulation are not exactly the same, their
trends with resistance increase are similar. Both experiment
and simulation results show that the maximum delivered
power first increases and then decreases with the resistance.
The optimal resistance is around 40KΩ. Furthermore, the
frequency to achieve the maximum power (or the peak)
shifts to right when the resistance increases. These results
are reasonable since the increase of resistance corresponds
to the circuit condition shifts from short-circuit to opencircuit. The simulation captures these phenomena as the
experiment, validating the circuit model that we derived.
(a)
There is a minor discrepancy in this frequency between
the experiment measurement and simulation prediction due
to the imperfect clamping in the experiment, as mentioned
in previous section.
Fig. 8 shows the voltage waveforms across the five
capacitors in time domain when the energy harvesting
process starts. It is noted that small capacitors are quickly
charged to saturation, which means that they are preferable
when instant power supply is required. Additionally, good
consistency is observed between the experiment and
simulation results. Hence, with the help of the derived
circuit model, it is convenient to predict the performance of
a piezoelectric energy harvesting system by circuit modeling
and simulation, avoiding the tedious experimental work.
Figure 8. Simulation and experiment results for the
PEH charging various capacitors.
CONCLUSIONS
(b)
Figure 7. Power delivered on various resistors:
(a) simulation (b) experiment.
Charging various storage capacitors
A standard energy storage circuit and the overall system
diagram are shown in Fig. 5. We consider five different
capacitors. In both experiment and simulation, the PEH
is tuned to vibrate at open circuit resonance frequency.
REFERENCES
[1] Yang, Y.W., Tang, L.H. and Li, H.Y., 2009. Smart Mater.
Struct., 18:115025.
[2] Roundy, S., Wright, P.K. and Rabaey, J., 2003. Computer
Communications, 26:1131-1144.
[3] Yang, Y.W. and Tang, L.H., 2009. J. Intell. Mater. Syst. Struct.,
20:2223-2235.
[4] Ottman, G.K., Hofmann, H.F., Bhatt, A.C. and Lesieutre,
G.A., 2002. IEEE Transactions on Power Electronics, 17:669676.
[5] Erturk, A. and Inman, D.J., 2008. Smart Mater. Struct.,
17:065016.
For a pure resistive load, analytical model or finite
element method can also be used to evaluate the system
performance. However, in practice, the AC voltage from
the PEH should be first rectified to DC voltage and then
the harvested energy can be consumed by a load or stored
in a capacitor. Hence, we further conduct the simulation
and experiment to evaluate the circuit model when the
PEH charges various capacitors.
In this article, an accurate circuit model for a PEH has been
derived. The entire circuit of the energy harvesting system
was established and simulated in an electronic simulator.
Experiments were also carried out on the fabricated PEH.
For the open circuit voltage, short circuit current and the
power harvested for various resistors, consistent trends
of these frequency responses were observed in both
experiment and simulation. The experimental results of
charging various storage capacitors further validated the
prediction from the circuit modelling and simulation. Hence,
the proposed circuit model of PEHs provides an effective
approach to evaluate the performance of a piezoelectric
energy harvesting system.
141
NUMERICAL SIMULATION OF STEEL
BOLTED BEAM-COLUMN CONNECTIONS
SUBJECTED TO DYNAMIC LOADING
Liu Chang (Liuc0014@ntu.edu.sg)
Andrew Tyas (a.tyas@sheffield.ac.uk)
Fung Tat Ching (CTCFUNG@ntu.edu.sg)
Tan Kang Hai (CKHTAN@ntu.edu.sg)
ABSTRACT: This study presents the development of a finite element model with the ability to simulate and analyse the response of
steel bolted end-plate connections subjected to extremely rapid rates of applied loading. The effect of material strain-rate sensitivity
was taken into account and a shear failure criterion was adopted to predict the failure of the connections. By comparing the simulation
results with experimental observed response, it is found that the numerical techniques and the material model used in this study can
predict the structural behaviour of connections subjected to dynamic loading reasonably well.
INTRODUCTION
Progressive collapse is one of the most under-researched
areas in structural engineering, and yet it holds the key
to the survival of a structure after a blast event. It is well
known that progressive collapse is a dynamic process
because it happens in a matter of seconds. The importance
of steel connections to resist progressive collapse has been
emphasized by many studies over the years. Most of them
focused on investigation of catenary action of the steel
and concrete connections under quasi-static loading [1,
2]. Little test data has been published to demonstrate the
performance of steel connections subjected to rapid rates
of loading. Recently, Tyas’s research team has conducted
a series of experimental works to determine the response
of typical semi-rigid steel beam-column connections when
loaded rapidly to failure. This experimental programme is
still ongoing and only some initial test results are published
[3]. The results show that significant differences appeared
between the behaviour of connections under dynamic and
static loads.
142
It is acknowledged that the experimental work under
dynamic conditions is much more complicated than the
static one. Safety issues have to be considered for dynamic
testing. Recording the response of structural elements over
time accurately is also quite difficult. Therefore, numerical
simulations become an attractive option for investigating the
behaviour of connections subjected to dynamic loading.
The main purpose of this study is to develop a finite
element model with the ability to simulate and analyse the
response of the steel bolted end-plate connections subjected
to extremely rapid rates of applied loading. The explicit
module of commercial finite element software ABAQUS
is used to form the detailed three-dimensional modelling.
The simulation results can provide some additional useful
information which is difficult to be measured during the
testing, such as the energy absorption, the distribution
of stress in each component of the connections and the
ductility of the connections.
Figure 1. The general layout of the testing and
the geometric details of the connection (unit mm).
FINITE ELEMENT ANALYSIS
Description of the dynamic testing
The finite element modelling was based on the experimental
work conducted by Tyas[3], in which both dynamic and
static responses of the flexible end plate beam-column
connetions were investigated. The connection performance
was characterized by a connection tension load vs rotation
relationship. Fig. 1 shows the general layout of testing and
the geometric details of the connection. An 8mm thick
flexible end plate was welded to the beam web by 6mm
welding and bolted to the column flange using M20 Grade
8.8 bolts. In the tests, the dynamic loads were applied from
zero to the peak in 50-60ms.
Finite element model
The testing were modelled using the explicit module of
commercial finite element code ABAQUS. Information from
previous studies conducted by Krauthammer [4] indicated
that, for high rate dynamic loads, ABAQUS has very good
simulation capabilities. Due to small time durations and
high applied loads required for the current study, the finite
element model was created using 8-noded continuum (brick)
elements with reduced integration (C3D8R). The model
considered contact conditions between the bolts/nuts head
and the end plate/column, the bolt shanks and the holes, the
end plate and the column, respectively. The fixed boundary
condition was applied at the bottom of the beam.
been found to be in good agreement with some reported
test results, these values were selected here to model the
material strain rate of the beam and the end plate.
In order to simplify the model and minimise computational
time, the column was modelled as a rigid plate. This is
because the deformation of the column, either globally under
bending or locally at the connection, can be ignored during
the tests. Moreover, only 200mm length of the beam, which
was sufficient to show local deformations of the connection,
rather than the full length, was modelled. An overview of
the finite element model is shown in Fig. 2.
Figure 3. The influence of strain rate sensitivity.
However, there were very limited research the information
on the influence of strain rate on bolts and welds. Therefore,
dynamic increase factors (DIF) of 1.1 developed by
Department of the US Army Corps of Engineers were taken
into account for strain-rate effects of the bolts and welds
when connections were applied at high rate of loading.
Thus the dynamic stress can be determined as:
σd = 1.1σ0
…(2)
Failure criterion
Figure 2. An overview of the finite element model.
Material model
The material model adopted Young’s modulus of 205 GPa
and Poisson’s ratio of 0.3 for all of the steel components.
It should be noted that the densities of the beam and the
column were adjusted to make sure their masses were the
same in actual test. Plastic stress-stain curves based on
true stress-strain relationship were defined in this study.
Von Mises yield criterion was used to simulate plastic
deformations of the connection.
σd = σ0 | 1 + ( D ) |
δ
q
…(1)
where D and q are the material parameters, which were
determined from experimental results.Various values of
the constants D and q have been reported in the literature
for mild steel. Some of the most representative values for
the strain rate sensitivity of mild steel are shown in Fig.
3. Since the values suggested by Marais et al. [5] have
ANALYSIS RESULTS
First, the validation of three-dimensional finite element
models was preceded by comparing their predictions against
static test data using ABAQUS. As described in the test
report [3], a static load was applied on the right side of the
column with a pivot, as shown in Fig. 1. In this test, the
connection was not highly deformed due to the limitation of
the loading system. The relationship between the connection
The effects of the material rate sensitivity are very important
in the high-strain-rate analysis. In this study, the strain rate
effects were introduced into the material model by the
widely-used Cowper-Symonds equation as follows:
As strain-based failure model controls the brittleness/
ductility of the material, a shear failure criterion where
equivalent plastic strain as the failure measure was applied
to simulate the cracking of the connections (elements that
are heavily deformed and satisfy the criterion during loading
are automatically deleted from the mesh). Unlike turning
simulations where a predefined fracture line exists, this
damage parameter was activated across the whole analysis.
It should be noted that this failure model is only suitable
for high-strain-rate dynamic problems. The research work
conducted by Hyun Chang Yim et al. [6] suggested the
equivalent plastic strain values of base metal and welds
is 0.2 for base metal and 0.1 for welds. These values are
obtained by comparison with the dissipated energy values
of welds and base metal in the Charpy-V Notch test.
143
tension load and the connection rotation from experimental
tests and computer simulations are compared in Fig. 4. As
shown in Fig. 4, results from the simulation and that from
the experiment corresponded very well. It was demonstrated
that the FE model including the definition of materials and
the contact conditions is shown to be, reliable for quasistatic connection behaviour.
Based on the validated FE model, the analysis of the
connection under rapidly applied loading was conducted,
with strain rate sensitivity and the failure criterion. Fig.
5 shows a comparison between the simulation result and
the test one. Reasonable agreement is also achieved on the
connection load versus rotation curve. The existence of
discrepancy may be due to the simplified loading method
defined as the load reaches the peak in 0.05ms followed
by a constant force during the rest of analysis in the
numerical simulation.
Comparisons of the final deformed configuration of the
connection and the failure mode between FEA and test
results are shown in Fig. 6. It can be seen that the numerical
model can successfully predict the failure mode of the
connection which involves cracking along the fillet weld
between the end plate and the beam web. From the test
result, we can see that cracking usually starts on one side.
The simulation result can also predict this phenomenon.
However, it should be noted that the prediction of which
side of connection crack first is somehow arbitrary.
Figure 6. Final deformed connections and the failure mode.
Figure 4. Load vs. Rotation for flexible endplate
connection under static loading.
144
Figure 7. The development of cracking at T=30ms.
Figure 5. Load vs. Rotation for flexible endplate
connection under rapidly applied loading.
The numerical model was validated against the experimental
results conducted at the University of Sheffield, UK (A.
Tyas et al. 2010), in which a series of partial depth endplate connections have been tested under both static and
dynamic loading, respectively. The finite element method
allows for further parametric analyses of steel beam-column
connections to provide some comprehensive results which
can be used to form the simplified analytical model for
design, such as the component-based joint model.
REFERENCES
[1] Demonceau, J.F., 2008. “Steel and composite frames: sway
response under conventional loading and development of
membrane effects in beams further to an exceptional action”.
Doctor of Philosophy thesis, Civil and Environmental
Engineering, University of Liège, 2008.
Figure 8. The development of cracking at T=50ms.
CONCLUSIONS
In this study, a finite element numerical model was
developed to simulate the response of steel bolted endplate connections subjected to extremely rapid rates of
applied loading.
The explicit module of commercial finite element software
ABAQUS is used to form the detailed three-dimensional
modelling. The effect of material strain-rate sensitivity
is taken into account using the Cowper and Symonds
formulation and a dynamic shear failure model was adopted
to simulate the development of cracking during the applied
loading.
[2] Yang, B. and Tan, K.H., 2009. “Numerical analyses of beamcolumn joints subjected to catenary action under in-plane
loading”. Proceedings of the 7th International Conference
on Tall Building, Hong Kong.
[3] Tyas, A. et al, 2011. “Dynamic testing of semi-rigid steel
beam-column connections”. Proceeding of the COST C26
International Conference.
[4] Krauthammer, T., Lim, J. and Oh, G.J., 2000. “Findings from
three computer code validations with precision impact test
data”. Proceedings of the 29th Department of Defense Explosive
Safety Seminar, New Orleans, LA; 2000, p. 18–20.
[5] Marais, S.T., Tait, R.B., Cloete, T.J. and Nurick, G.N., 2004.
“Material testing at high strain rate using the split-Hopkinson
pressure bar”. Latin American Journal of Solids and Structures
2004; 1(1): 319–39.
[6] Yim, H.C. and Krauthammer, T., 2009. “Load–impulse
characterization for steel connection”. International Journal
of Impact Engineering, 36 (2009), 737–745.
145
EXPERIMENT INVESTIGATION ON
RESIDUAL STRESS DISTRIBUTIONS OF
HIGH STRENGTH STEEL
PLATE-TO-PLATE Y JOINTS
Chiew Sing Ping (cspchiew@ntu.edu.sg)
Jiang Jin (jian0048@e.ntu.edu.sg)
Yu Yi (yuyi@ntu.edu.sg)
ABSTRACT: In this study, an investigation of the residual stress distribution near the weld toe of a set of plate-to-plate Y joins made
from high strength steel with yield stress equal 690MPa are carried out. The hole-drilling method is applied to measure the residual stress
distribution near the weld toe of the joints. Special template and accessories are manufactured to ensure that precise drilling could be
conducted close to the weld toe. The characteristics of the residual stress are discussed and its relationship with the joint geometry and
the welding profile is summarized.
F
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Two series of specimens were included to compare the
influence of welding condition on residual stress distribution
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SPECIMEN DETAILS
In the present experimental investigation, a number of
plate-to-plate Y joints, made of high strength steel with
minimum yielding stress of 690MPa, were fabricated
by welding. This high strength steel, RQT701, which
is supplied by Corus Group, is quenched and tempered
structural steel with improved forming and welding
performance by substitute some alloying element with
carbon. In the process of welding, greater precautions are
needed to ensure that welding qualification is satisfactory.
Electrodes and fluxes with very low hydrogen content must
be used in order to prevent hydrogen cracking. Hence, an
ultra low hydrogen and moisture resistant type covered
electrode for 690MPa high tensile strength steel for low
temperature service, LB-70L, which is equivalent to the class
ASME/AWS A5.5 E10016-G and supplied by Kobelco of
Japan, was employed[1]. The welding procedure is carried
out according to AWS D1.1 2008[2]. Other standards also
are referenced [3-5].
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When comparing with mild steel, high strength steel (HSS)
shows relatively poor ductility and therefore the residual
stress engendered in the process of welding may have
significant influence on the fatigue performance of HSS
joints. Residual stress not only affects the initiation and
onset of the propagation of surface cracks but also changes
the path of a crack as it grows below the surface. The effect
of residual welding stresses on the performance of welded
structure is particularly significant when low stresses are
applied. Therefore, for high strength steel structures, it is
significant to investigate the distribution of residual stress
due to welding in joints. In this research, hole-drilling
method is applied for checking the residual stress caused
by welding.
near the weld toe. One group is fabricated in ambient
temperature while the other group is pre-heated to 100°C
before welding. There are 6 different geometries, consisting
of 3 different parent steel plates thicknesses and 2 welding
connection angles of each group, employed to explore the
variation of the residual stress near the weld toe. During the
welding, full penetration welding for tubular joint is used
by following the standard AWS D1.1-2008. The welding
profiles of 45° and 60° joints are shown in Figures 1 and
2, respectively.
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INTRODUCTION
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TEST SETUP
5
Weld Toe
The RS-200 Milling Guide is a high-precision instrument
for analyzing residual stress by the hole-drilling method
through positioning and drilling of a hole in the center of
a special strain gauge rosette. Its ruggedness and flexibility
make it equally suitable for laboratory or field application.
Since positioning precision of the milling guide has great
influence on the accuracy of measurement, the RS-200
milling guide with a microscope installed was applied
and secured to samples with quick-setting and frangible
adhesive to bond its foot pads. The milling cutter was
guided carefully to make the cutter progress in a straight
line devoid of side pressure on the hole and friction at the
non-cutting edge. A high-speed air turbine was employed
to form good hole shape and adaptability to incremental
drilling as shown in Figure 3. To make the measured points
close to the weld toe of the joint, a special supporting set
was designed.
C
B
A
15
25
B1
B2
25
50
50
25
Figure 5. Plane view of scheme of strain gauges.
100°C
25°C
Figure 3. RS-200 High speed drilling setup.
Figure 6. Comparison of stresses in points A, B and C in y
direction of specimens with 45° and 12mm.
STRAIN GAUGE LOCATIONS
z
5 15 25
x
50
25
25
y
50
Figure 4. Strain gauges scheme for residual
stresses measurement.
Generally, several steps were followed orderly when the
hole-drilling method was applied. Firstly, a special strain
gauge rosette with three grids was bonded at the point
where the residual stresses were to be determined as shown
in Figure 5 and Figure 6. Then the RS-200 Milling Guide
was attached to the test part and centered over the rosette.
Afterwards a precision hole was introduced at the center
of the rosette and readings of the relaxed strains were
recorded. Finally, residual stresses were computed.
CALIBRATION TEST
Two calibration coefficients denoted as
and
were
determined firstly to calculate the stress from relieved
strains. It was accomplished by installing the residual
strain rosette, FRAS-2, on a uniaxially stressed tensile
specimen, whose size is 200mm × 70mm. It was made of
the steel plate used to fabricate the specimens. The plate
was oriented in such a way that grid 1 is parallel to the
loading direction (y), placing grid 3 along the transverse
axis (x) of specimen when this specimen is fixed in grip
of tensile machine.
Before drilling, a small loading P, which does not beyond
half of the yield stress of the specimen, was applied to
the specimen to develop the desired calibration stress σc
In the measurement of residual stress, a special type of strain
rosette, FRAS-2, which was designed by TML to facilitate
positioning three grids on one side of the measurement point,
was used to measure the released strain of the specimen
during drilling. In the transverse direction (labeled with y
in Figure 4), the shortest distance between the weld toe
and the strain rosette is 5mm. The further one is 15mm
away from the weld toe while the furthest strain rosette
has a spacing of 25mm from weld toe. In the longitudinal
direction (labeled with x in Figure 5), three strain rosettes
were fixed with distance of 25mm, 75mm and 125mm
away from the edge. It is positioned such that grid 1 is
parallel with direction of applied loading. Figure 5 shows
the plane view of the strain gauges scheme applied to the
specimens.
147
and the values of ε1’ and ε3’ were recorded. It is required
that the tensile stress be uniform over the cross section of
the specimen. Then the loading was released and the plate
was removed out form tensile machine. A standardized
dimension hole, whose dimension is the same as in objective
joints, was drilled. The specimen was replaced in the
tensile machine and applied the exactly same loading P as
before drilling and recorded another group strains ε1’ and
ε3’. To make the results more reliable, 8 groups reading
are recorded in different depths ranging from 0 to 2mm
with 0.25mm gap.
TEST RESULTS
It can be seen that, in Figure 6, for the 45° joints, preheating
can effectively reduce the magnitude of residual stress at
points A, B, C. At point C where x coordinate is 125mm,
the residual stress is compressive for preheating case while
it is tensile for welding in ambient. At point B which is
located at the middle of the plate, the residual stress is
also slightly reduced for preheating case. For 60° joints,
the magnitude of residual stress also can be reduced by
preheating as shown in Figure 7.
In Figure 8, it can be seen that, at points A and B, the
magnitude of stress in the specimens of 60° is higher than
45°, and at point C, the stress in the specimen of 45° is
slightly higher. In Figure 9, the magnitude of stress in the
specimens of 60° is also higher than 45° at points B and
C. It seems that in the middle of plate, the magnitude of
residual stress in 60° joints is higher than 45°one.
45°
148
60° (2)
Figure 8. Comparison of stress in points A, B and C in y
direction of specimen with preheating and 8mm.
45°
60° (1)
60° (2)
Figure 9. Comparison of stress in points A, B and C in y
direction with specimen of roomtemp and 12mm.
It is illustrated in Figure 10 for stresses at points B, B1,
and B2. It can be seen that the magnitude of residual
stress becomes smaller when the distance from weld toe
gets further. But this variation is not linear. The stress is
reduced quickly when the distance goes from 5mm to 15
mm. However, the stress rises slightly from point B1 to
B2. But for the specimens with preheating, the variation
seems somewhat scattered.
100°C (1)
25°C (1)
60° (1)
100°C (1)
25°C (1)
100°C (2)
25°C (2)
100°C (2)
25°C (2)
Figure 10. Comparison of stresses in points B, B1 and B2
in y direction of specimens with 60° and 8mm.
CONCLUSIONS
Figure 7. Comparison of stresses in points A, B and C in y
direction of specimens with 60° and 12mm.
(1) Frequently, the maximum tensile residual stress
perpendicular to weld toe appears in the middle of
plate. In the ends of the plate, either compressive
residual stress or tensile stress may exist.
(2) The magnitude of residual stress reduces greatly
from point B to point B1 for most cases. However, it
may increase in a smaller magnitude from B1 to B2.
It means that the relationship between the change of
residual stress and the distance away from weld toe
is non-linear.
(3) Preheating can effectively reduce the magnitude of
residual stress of 45° joints. For 60° joints, preheating
can also reduce the residual stress in some cases.
However, it also can increase the residual stress.
Therefore, it is pertinent that evenly high-quality
preheating of the steel plate should be applied during
the welding of high strength steel joints.
(4) Regarding the effect of welding angle for preheating
specimens, the maximum residual stress seems higher
in 60° joints than 45° joints in most cases. In the room
temperature welding specimens, the angle effect is not
quite obvious.
(5) For the specimens test in this study with plate thickness
from 8mm to 16mm, the plate thickness only has
slight influence on the magnitude of residual stress.
However, it should be noted that for thicker plate, it
could be possible that the plate thickness may have
more significant effect on residual stress.
(6) In general, the magnitude of residual stress in x
direction is much higher than the residual stress in the
y direction. In particular, for one joint, the maximum
residual stress in x direction is located in the middle
of the plate. The principle stress can be beyond the
yielding stress in some cases.
REFERENCES
[1]. AWS. ANSI/AWS A5.5. Specification for Low-Alloy Steel
Electrodes for Shield Mtetal Arc Welding. American Welding
Society, Miami, USA. 2006.
[2]. AWS.ANSI/AWS D1.1. Structural Welding Code-Steel.
American Welding Society, Miami, USA. 2008.
[3]. AS/NZS. Structural steel welding part 4: Welding of high
strength quenched and tempered steels, Australia/ New Zealand
Standard AS/NZS 1554.4, 2004.
[4]. BSI. Eurocode3---Design of steel structures. Part1-12:
Additional rules for the extension of EN 1993 up to steel
grades S700. British Standards Institute, London, UK. 2007
[5]. API.Recommended Practice for Planning, Designing and
Constructing Fixed Offshore Platforms, API-RP2A. American
Petroleum Institute, Washington, DC, USA. 1993.
149
ROBUSTNESS OF STEEL ANGLE
BEAM-COLUMN JOINTS UNDER
COLUMN REMOVAL SCENARIOS
Yang Bo (yang0206@e.ntu.edu.sg)
ABSTRACT: Following the World Trade Centre disaster, some researchers have identified joint integrity as a key parameter to maintaining
structural integrity under catenary action and have conducted extensive research works. This paper presents experimental results of
steel angle beam-column joints subjected to catenary action. Three types of angle connections were studied under column removal
scenarios. Nine experimental tests were conducted. The experimental results demonstrate the ductility and load capacities of these three
connection types with different angle thicknesses in catenary mode.
INTRODUCTION
After the partial collapse of the Ronan Point apartment
tower in 1968, engineers began to realise the importance
of structural resistance to progressive collapse. Further
research and design efforts have been directed to this
area, especially after the World Trade Centre disaster on
11 September 2001. The alternate load path method, an
important design approach to mitigate progressive collapse,
has been included by a number of design codes including
GSA [1] and DOD [2]. It is an approach that allows local
failure to occur when subjected to an extreme load, but seeks
to provide alternate load paths so that the initial damage
can be contained and major collapse can be averted. One
of the key mechanisms to mitigate the spread of “domino”
effect is to redistribute applied loading on damaged members
through catenary action. The term “catenary action” refers
to the ability of beams to resist vertical loads through the
formation of a net-like mechanism.
150
Following the World Trade Centre disaster, some researchers
have identified joint integrity as a key parameter to
maintaining structural integrity under catenary action and
have conducted extensive research works. Khandelwal and
EI-Tawil [3] used structural simulation to investigate a
number of key design variables that influence the formation
of catenary action in special steel moment resisting frame
sub-assemblages. Welded joints with and without reduced
steel beam sections were considered. Fahim et al. [4]
conducted an experimental and analytical assessment of
the performance of steel beam-column assemblies with
two types of moment-resisting connections similar to the
ones investigated by Khandelwal and EI-Tawil [3] under
the column-removal scenario. As a follow-up work, this
paper investigated the behaviour and failure modes of
typical steel connections subjected to catenary action under
the condition of in-plane loading. In 2009, Karns et al. [5]
conducted a test programme consisting of a steel frame
subjected to a blast. The behaviour of different beam-column
joints subjected to blast was evaluated experimentally and
numerically. Conventional welded moment and side-plate
moment connections were investigated. Demonceau [6]
conducted a substructure experimental test and five beamcolumn joint tests in order to observe the development
of catenary action and its effect on the joint behaviour.
The M-N interaction curves of composite joints (under
hogging and sagging moments) were included in his
work [6]. Most of the reported works focused on welded
moment connections [4, 5]. However, in Europe, bolted
steel connections such as fin plate, flush end plate, web
cleat and extended end plate, are very popular and the
evaluation of these kinds of joints subjected to catenary
action is important and timely.
A structures research group at Nanyang Technological
University, Singapore, is conducting a research programme
to investigate the stiffness, strength and ductility of bolted
steel connections subjected to catenary action under the
column-removal scenario. This paper focuses on the
experimental tests of steel angle beam-column joints under
catenary action.
In total, 9 experimental tests were carried out on different
types of steel angle beam-column joints. Three types of
connections, including web cleat, top and seat, and top and
seat with web angles (TSWA) connections were investigated
while three thicknesses (8mm, 10mm and 12mm) of angles
were tested. The principal aim of this paper is to provide
experimental results of steel angle beam-column joint
behaviour, including failure modes, development of forces
and deflections in the beams.
TEST SET-UP AND SPECIMENS
A detailed description of the test set-up was given in a
previous paper [7], so only the specimen details are given
here.
In total, nine tests were carried out. Table 1 summarises
the test specimens. In all these nine tests, M20 8.8 bolts
were used.
Table 1. Summary of the test specimens.
Connection
type
Web cleat
Top and
seat angle
TSWA
Angle
thickness
Beam
section
End plate/
angle
8mm
254×146×37
UB S355
L90×8
S275
10mm
254×146×37
UB S355
L90×10
S275
12mm
254×146×37
UB S355
L150×100×12
S275
8mm
254×146×37
UB S355
L90×8
S275
10mm
254×146×37
UB S355
L90×10
S275
12mm
254×146×37
UB S355
L150×100×12
S275
8mm
254×146×37
UB S355
L90×8
S275
10mm
254×146×37
UB S355
L90×10
S275
12mm
254×146×37
UB S355
L150×100×12
S275
Figure 2. Failure mode of web cleat (10mm angle thickness).
TEST RESULTS
Web cleat
The failure mode was observed to change with angle
thickness. When the angle thickness is 8mm, the failure
mode is shown in Figure 1. Failure was caused by the
fracture of the web cleat close to the heel. This fracture
happened at a very high rotation. The two cleats had
undergone a significant amount of deformation at that
stage. All the bolts remained undamaged.
Figure 4 shows the load-displacement curves of web cleat
connections using different angle thicknesses. When the
angle thickness increases, failure mode also changes from
angle fracture to bolt fracture. However, from the loaddisplacement curves shown in Figure 4, no significant
change of the load-carrying capacity was observed. This is
due to the failure mode of angle fracture having a higher
deformation capacity.
When the angle thickness is 10mm, the failure mode is
shown in Figure 2. Similar with the previous test, failure
of this test was controlled by the fracture of the web cleat
close to the heel. Nevertheless different from the first test,
the bottom bolt in the test deformed significantly.
When the angle thickness is 12mm, no web cleat fracture
was observed. The connection failed by the bolt fracture,
as shown in Figure 3.
Figure 4. Load-displacement curves of web cleat connections.
151
Top and seat angle
TSWA
Figure 5 shows the failure modes of the top and seat angle
tests. The same failure modes with web cleat tests were
observed.
Figure 7 shows the failure modes of TSWA tests. The same
failure modes with web cleat tests were observed.
(a) 8mm thickness
152
(b) 10 mm thickness
(a) 8mm thickness
(b) 10 mm thickness
(c) 12mm thickness
(c) 12mm thickness
Figure 5. Failure mode of top and seat angle.
Figure 7. Failure mode of TSWA.
Figure 6 shows the load-displacement curves of top and
seat angle connections using different angle thicknesses.
Higher flexural action and load-carrying capacity were
observed when angle thickness increased. However, catenary
action could not contribute significantly to the load-carrying
capacities even when the angle thickness was increased.
Figure 8 shows the load-displacement curves of TSWA
connections using different angle thicknesses. Higher
flexural action and load-carrying capacity were observed
when angle thickness increases. With regard to the stage
of large deformation, all these three connections could
develop catenary action well.
Figure 6. Load-displacement curves of top and
seat angle connections.
Figure 8. Load-displacement curves of TSWA.
CONCLUSIONS
In this study, experimental tests were conducted to
investigate the behaviour of steel angle beam-column joints
subjected to catenary action. Three types of connections
were studied. The test results demonstrated the ductility
and load-carrying capacity of these three connection types
with different thicknesses in catenary mode. Among the
web cleat connections in this study, angle thickness has a
limited influence to load-carrying capacities. In the tests of
TSWA connections, the experimental results indicate that
when angle thickness increases, higher flexural action and
load-carrying capacity are obtained.
[3] Khandelwal, K. and El-Tawil, S., 2007. “Collapse behaviour
of steel special moment resisting frame connections”. Journal
of Structural Engineering-ASCE, 133(5), 646-655.
[4] Fahim, S., Joseph, A.M., Lew, H.S., Robert, S.D. and
Chiarito, V., 2009. “Testing and analysis of steel beam-column
assemblies under column removal scenarios”. Proceedings of
the 2009 Structures Congress, USA.
[5] Karns, J.E., Houghton, D.L., Hong, J.K. and Kim, J., 2009.
“Behaviour of varied steel frame connection types subjected to
air blast, debris impact, and/or post-blast progressive collapse
load conditions”. Proceedings of the 2009 Structures Congress,
USA.
REFERENCES
[6] Demonceau, J.F., 2008. “Steel and Composite Frames: Sway
Response under Conventional Loading and Development
of Membrane Effects in Beams further to an Exceptional
Action”. Doctor of Philosophy thesis, Civil and Environmental
Engineering, University of Liège.
[1] General Services Administration (GSA), 2003. “Progressive
Collapse Analysis and Design Guidelines for New Federal
Office Buildings and Major Modernization Projects”.
[7] Yang, B. and Tan, K.H., 2011. “Experimental tests of different
types of steel beam-column joints subjected to catenary
action”. CEE Research Bulletin 24, Nanyang Technological
University.
[2] Department of Defense (DOD), 2005. “Design of Buildings
to Resist Progressive Collapse”. Unified Facilities Criteria,
4-023-03.
153
SEISMIC RESPONSES OF REINFORCED
CONCRETE BUILDINGS WITH
WALL-LIKE COLUMNS
Sahil Bansal (sahi0004@e.ntu.edu.sg)
Huang Yin Nan (ynhuang@ntu.edu.sg)
ABSTRACT: The objective of this study is to investigate the structural response of a typical reinforced concrete building in Singapore,
subjected to a scenario earthquake with a mean annual frequency of exceedance of 2% in 50 years. Two-dimensional finite element
models of a sample 10-storey building with complete infill wall and with no infill in the first storey are analyzed. The results of non
linear analysis show that the latter case has a high value of storey drift ratio at the first storey that may result in significant damage to
the building.
Singapore is situated in relatively low seismicity region
therefore current design procedures for buildings do not
include any specific provision for seismic loading. Most
buildings are lightly reinforced concrete (RC) structures
designed for gravity and wind loads. Among the RC
buildings, a commonly used structural system is the
buildings consisting of wall-like columns, which are used
to minimize the protrusions of columns into otherwise
usable space (Lim et al. 2009).
Studies by Megawati and Pan (2002, 2009) show that
medium and high rise buildings in Singapore might be at
risk in case of a Magnitude-9+ earthquake in the Sumatran
subduction zone. This study investigates seismic response
of reinforced concrete buildings with wall-like columns
subjected to ground motions associated with a mean annual
frequency of exceedance of 2% in 50 years on a soft soil
site in Singapore. Two-dimensional finite element models of
a sample 10-storey building found in general in Singapore
are developed and analyzed. The impact of infill wall on
modeling and structural performance is discussed.
in Figure 2. According to the plan of Figure 2, geometric
symmetry is apparent.
30
20
Concrete Stress, f
INTRODUCTION
10
E
Esec
0
0
0.002
Concrete Strain
0.004
0.006
Figure 1. FEDEAS Concrete Material Model.
MODELING
154
For the analysis part, numerical models of the sample
building have been created using nonlinear analysis program
OpenSees developed by the Pacific Earthquake Engineering
Research (PEER) Center in UC Berkeley. All beam and
column sections are modeled using the fiber element and
rigid floor assumption has been made. Concrete and steel
material models from FEDEAS structure library have
been implemented to represent the non linear behavior of
material. Figure 1 presents the compression envelop and
material parameters for the concrete model. Masonry infill
wall has been replaced by an equivalent diagonal strut
model proposed by Madan et al. (1997) using two-nodded
truss elements. General layout of the building is shown
Figure 2. First Storey Layout.
AMBIENT VIBRATION TEST (AVT)
To validate the numerical building models, the microvibration response of the sample building subjected to
wind and ground ambient vibration was measured using
tri-directional velocity-meters sampling at 100 Hz. This
test provides information about the modal parameters of
a structure, namely, natural frequency, mode shape and
damping. The technique used in this study to estimate
the modal parameters of the sample building is Frequency
Domain Decomposition (Beincker et al. 2001). It consists
of decomposition of power spectral density matrix into
single degree of freedom systems using singular value
decomposition. The first decomposed singular value
represents contribution of the dominating mode at that
particular frequency and the corresponding singular vector
is the mode shape. The remaining represents the lower
modes or the noise component.
To characterize the first two translational frequencies,
measurements have been performed on the 2nd, 9th and
10th floors of the sample building. Figure 3 shows the
SVD values plotted against frequency in the X direction
and the first two modes can be identified at frequencies
of 1.97 Hz and 4.85 Hz.
Table 1. Natural Frequency Comparison.
Without Infill
With Infill
AVT
X-Direction
Mode 1(Hz)
0.46
1.95
1.97
Mode 2(Hz)
1.38
5.61
4.85
Y-Direction
Mode 1(Hz)
0.65
2.06
2.17
Mode 2(Hz)
1.78
6.09
ND
RESPONSE-HISTORY ANALYSIS
Ground Motions
Megawati and Pan (2002) studied scenario earthquakes
possible for Singapore and proposed uniform hazard
spectra for different return periods. Figure 4 presents the
spectral acceleration of 10 ground motions generated by
Megawati for this study such that their average matches a
uniform hazard spectrum associated with a mean annual
frequency of exceedance of 2% in 50 years on a soft soil
site in Singapore.
Figure 3. Singular Values vs. Frequency.
The model without infill wall significantly underestimates
the frequencies of the sample building identified from the
AVT data and the frequencies of the model with infill have
a good agreement with the results of the AVT data. The
contribution of infill wall should not be ignored in the
modeling and analysis of the sample building.
Figure 4. Acceleration Response Spectra.
Response-History Analysis
Nonlinear response-history analyses were performed to
investigate the structural response of the sample building
subjected to the spectrally-matched acceleration time series
of Figure 4. Only the result for one of the time series of
Figure 4 is presented herein. Maximum inter-storey drift
ratio is chosen to represent the building performance. Some
cases of buildings, where the first floor is used as common
space, do not include wall in the first storey. Analysis for
such cases is done using the same model but by removing
the wall in the first storey. Figure 5 compares the peak
storey drift of the sample building in the X and Y directions
1) with complete infill wall and 2) with no infill in the first
Table 1 reports the natural frequencies of the sample
building determined using AVT and eignvalue analysis of
the numerical models. To study the impact of infill wall on
frequencies of structures, the frequencies of the numerical
models for the sample building without and will infill wall
are presented in columns 2 and 3 of Table 1, respectively.
A Young’s modulus of 28000 N/mm2 for concrete is used
for eignvalue analysis to determine the frequencies of
the sample building. The value is corresponding to the
initial tangent modulus E, rather than Esec, of Figure 1: a
reasonable assumption for low strain values resulting from
ambient vibration.
155
storey. Drift ratio is less than 0.5% for the case with infill
wall throughout the height of the building thus implying that
the damage of the sample building is insignificant. For the
case without infill wall at storey one, the distribution of the
drift ratio indicates a soft storey with a drift ratio of 3% at
storey one in the X direction of the sample building. This
drift ratio will result in significant damage in the beams,
columns and walls of that storey.
The response-history analysis for the sample building
with regular infill shows that the maximum drift ratio is
less than 0.5% and that for the building with an irregular
distribution of wall indicates a maximum drift ratio of 3%
for the first storey in the X direction.
In this study, the beam-column joints of the sample building
are assumed rigid, which might underestimate the drift ratio
if the demand of joints exceeds their elastic capacity. More
research is needed to study the impact of the nonlinear
behavior of beam-column joints on the performance of
the sample building.
REFERENCES
[1] Beincker, R., Zhang, L. and Andersen, P., 2001. “Model
identification of output-only systems using frequency domain
decomposition.” Smart Material and Structures, 10, 441445.
[2] Chopra, A.K. (1995). Dynamics of structures: Theory and
applications to earthquake engineering. Prentice-Hall, N.J.
[3] Lim, C.L., Li, B. and Pan, T.-C., 2009. “Seismic performances
of reinforced concrete frames with wall-like columns.” The
IES Journal Part A: Civil & Structural Engineering, 2(2),
126-142.
Figure 5. Storey Drift.
CLOSING REMARKS
Natural period determined using model with infill is in good
agreement with the actual natural period of the building
identified from AVT data. The results clearly indicate
the importance of incorporating infill wall in numerical
modeling and its effect on the dynamic behavior of buildings
with wall-like columns.
156
[4] Madan, A., Reinhorn, A.M., Mander, J.B., and Valles, R.E.,
(1997). “Modeling of Masonry Infill Panels for Structural
Analysis.” Journal of Structural Engineering, 123(10), 12951302.
[5] Mazzoni, S., McKenna, F. and Fenves, G.L., 2005. “OpenSees
command language manual.” University of California, Pacific
Earthquake Engineering Center, Berkeley (CA).
[6] Megawati, K. and Pan, T-C., 2002. “Prediction of the maximum
credible ground motion in Singapore due to a great Sumatran
subduction earthquake: the worst-case scenario.” Earthquake
Engng. Struct. Dyn., 31, 1501-1523.
[7] Megawati, K. and Pan, T.-C., 2009. "Regional seismic hazard
posed by the Mentawai segment of the Sumatran megathrust.”
Bulletin of the Seismological Society of America, 99(2A),
566-584.
CONSISTENCY OF SHEAR-WAVE
VELOCITY STRUCTURES INFERRED
FROM MICROTREMOR OBSERVATIONS
Daniel Lukas Mulyawan Jap (Daniel.Mulyawan@arup.com)
Irana Pantow (IRAN0001@ntu.edu.sg)
Kusnowidjaja Megawati (kusno@ntu.edu.sg)
ABSTRACT: Shear-wave velocity structures at three locations in Singapore are investigated by the means of array measurement of
microtremor. The microtremor data was analyzed using spatial autocorrelation method and frequency-wave number method. The results
of this study indicate that the shear-wave velocity structures inferred from microtremor observation are consistent with those obtained
using crosshole PS logging. The study also shows that the velocity structure obtained from microtremor survey is independent of the
shape of the array and the time of the measurement. Microtremor survey method is not only applicable for investigating soft soil sites,
but it is also usable for weathered rock sites with thin soil deposits. This is a Final Year Project carried out by the first and second
authors under the supervision of the third author.
INTRODUCTION
Referring to Figure 1, the basic scheme and the procedure
of microtremor survey method consist of three steps:
Soft soil deposits are mostly found in Central and SouthEastern parts of Singapore, namely Kallang and East
Coast. These soil deposits are filled predominantly with
soft marine clay and alluvial sands. This type of soil
would amplify seismic ground motions from earthquakes
in Sumatra. To quantify the site response amplification, it is
necessary to construct a 3D velocity structure beneath this
area, which can be achieved through array measurement
of microtremors (Okada, 2003). Some of the advantages
using microtremor survey method over conventional drilling
method in subsurface structure investigation are lower cost
and less disturbing effect suffered by the residents due to
noise pollution and vibration.
1.
Observation by seismometer network (array) arranged
on the ground surface
2.
Estimation of dispersion of the surface wave (Rayleigh
wave) as a response to the subsurface structure directly
below the array
3.
Estimation of subsurface structure causing the
dispersion by means of inversion
STEP 1
STEP 2
Field observations were conducted in Katong Park (KAT),
Beatty Secondary School (BES) and Nanyang Technological
University (NTU). These three locations were chosen based
on consideration that Katong Park and Beatty Secondary
School lie on Kallang Formation (soft marine clay), while
NTU lies on Jurong Formation (weathered rock) and the
availability of bore log data at these three locations. Table
1 summarizes field observation details.
Field observations were carried out using 7 portable
microtremor recorder systems. Each set of recorder system
consists of a vertical geophone, a digital recorder and a
Global Positioning System (GPS) antenna, which is used
to identify the coordinates of the point of measurement
and to synchronize the clock of all recorders.
Figure 1. Basic Procedure of Microtremor Survey Method.
RESULTS
Several methods can be used to analyze microtremor data,
such as frequency-wave number (f-k) method, spatial
autocorrelation method (SPAC), or H/V spectral ratio. In
this research, only SPAC and f-k method were used for
data processing.
Influence of various array configurations on the
consistency of SPAC method
The objective of the investigation is to examine if the phase
velocity of the Rayleigh wave and the shear-wave velocity
STEP 3
FIELD OBSERVATION DETAILS AND DATA
PROCESSING
157
Table 1. Field Observations Summary.
Location
Katong Park
(KAT)
Beatty
Secondary
School
(BES)
Date
Array Configuration
1-10-08
Triangular (7.5 m, 30 m, 400 m
and 1200 m)
2-12-09
Triangular (7.5 m, 30 m, 200 m,
400 m, 600 m and 800 m)
21-01-10
Various Small Array
Configurations
6-02-10
and 400 m) and Line
(30 m road side and 60 m)
3-10-08
and 1200 m)
19-03-10
Triangular (10 m, 40 m, 200 m
and 400 m)
Nanyang
4-02-10
Technological
University
19-03-10
(NTU)
Triangular (7.5 m and 30 m)
Triangular (200 m and 400 m)
of the subsurface layers inferred from the microtremor
measurement is dependent on the configuration of the
array. Ideally, the shear-wave velocity profile should
be independent from the array configuration. Several
array configurations, as shown in Figure 2, were used to
investigate the subsurface structure at KAT.
Figure 3. Accuracy and consistency of various
array configurations.
Applicability of microtremor method in estimating
subsurface soil profile
The accuracy and consistency of microtremor survey
method were investigated using several field observations
mentioned previously. The Observations were conducted
using triangular array with increasing sizes to allow for
estimation of deeper soil layers. The records from small-size
array (7.5 m and 30 m) were analyzed using SPAC method
while the records for medium-size (200 m) and large-size
(400 m) array were analyzed using f-k method.
Figure 2. Sketch of various array configurations.
158
The shear-wave velocity profiles inferred from microtremor
measurements using different array configurations are
presented in Figure 3. This shows that the estimation
of the shear-wave velocity values of the topmost layer
obtained from different array configurations are consistent
and agreeable with the value obtained from crosshole PS
logging (reference value). The thickness of the topmost layer
ranges from 25 to 31 m among various array configurations,
and it is thinner than the 40-m thickness revealed by the
crosshole PS logging. It should be noted that microtremor
survey method is not able to capture the gradual increase
of shear-wave velocity from the depth of 33 to 45 m as
revealed by the crosshole PS logging.
SPAC method estimates the phase velocity based on the
length combinations of the array. Length combination is
the distance between one sensor to another in an array.
Hence, in a seven sensors triangular array, there exist
five length combinations with their corresponding phase
velocity value. Subsequently the average of the phase
velocity values was used for estimating the soil layer. On
the other hand, f-k method estimates the phase velocities by
searching for dominant wave within a wavenumber range
specified. Hence, a good range of wavenumber allow for
more accurate estimation of phase velocities.
Katong Park measurement
Theoretical soil layers constructed from the dispersion
curve estimated using SPAC and f-k method for the three
measurements in KAT are shown in Figure 4 below. The
comparison of the theoretical soil layers with conventional
bore log data is presented in Figure 5 below. It can be
seen that microtremor provides a reliable estimation for
subsurface soil structure.
Based on investigations using array of size larger than
600m, it was found that long-period Rayleigh wave did not
have enough energy to cause microtremor wave propagation
throughout the large array area. This finding implies that
KAT is a relatively calm area with low level of vibration
caused by long-period oceanic wave. Hence, large array
recordings were not used for further analysis of KAT.
Figure 4. (from top) Theoretical soil profile estimated from
1 October 2008, 2 December 2009, and 6 February 2010
measurements at Katong Park.
The theoretical soil layers constructed from BES
measurement are shown in Figure 6 below. Figure 7 shows
the comparison of soil profile estimated form microtremor
measurement and soil profile constructed from bore log data.
An observation using large array was also conducted and
it is concluded that similar to KAT, the area is relatively
calm with little long-period microtremors. The results from
both KAT and BES also showed that the recordings obtain
from the several observations conducted yield consistent
subsurface structures.
Figure 6. Theoretical soil profile estimated for BES area based
on 3rd October 2008 and 19th March 2010 observations.
Figure 7. Comparison of soil profile obtained from bore log
with profiles estimated from microtremor observations
for Beatty Secondary School.
Figure 5. Comparison of soil profile obtained from bore
log with profiles estimated from microtremor observations
for Katong Park.
Beatty Secondary School measurement
159
Nanyang Technological University (NTU)
CONCLUSIONS
This observation was done to assess the feasibility of
microtremor method applied in hard soil stratum. The
observation result with the estimated soil profile is shown
in Figure 8 below. The comparison of the estimated soil
profile with nearby bore log exploration result is presented
in Figure 9. The soil strength is represented by SPT N
values in the bore log data. The N value was then converted
into shear wave velocity value using formula extracted
from report by BCA (2006). The finding implies that
microtremor method could provide a reliable estimation
for hard soil layers.
Shear-wave velocity structures at three locations in
Singapore were investigated by the means of array
measurement of microtremor. The microtremor data
was analyzed using spatial autocorrelation method and
frequency-wave number method. The results of this study
indicated that the shear-wave velocity structures inferred
from microtremor observation are consistent with those
obtained using crosshole PS logging. The study also showed
that the velocity structure obtained from microtremor
survey is independent of the shape of the array (line,
square, rectangle, and equilateral triangle) and the time of
the measurement. Microtremor survey method is not only
applicable for investigating soft soil sites, but it is also
usable for weathered rock sites with thin soil deposits.
REFERENCES
[1] Building and Construction Authority, 2006. Evaluation of
Site Response in Singapore due to earthquake effects (part
ii). [unpublished].
Figure 8. Theoretical soil profile estimated for NTU area
based on February and March 2010 observations.
[2] Brigham, E.O., 1988. The Fast Fourier Transform and Its
Application. Prentice Hall.
[3] Capon, J., 1969. High-Resolution Frequency-Wavenumber
Spectrum Analysis. IEEE, (pp. 1408-18).
[4] Chavez-Garcia, F.J., Rodriguez, M. and Stephenson, W.R.,
2006. Subsoil Structure Using SPAC Measurements along a
Line. Bulletin of the Seismological Society of America, Vol.
96, No. 2, 729–736.
[5] Horike, M., 1985. Inversion of phase velocity of long-period
microtremors. J. Phys. Earth. 33, 59-96.
[6] Ohori, M., Nobata, A. and Wakamatsu, K., 2002. A Comparison
of ESAC and FK Methods of Estimating Phase Velocity
Using Arbitrarily Shaped Microtremor Arrays. Bulletin
of the Seismological Society of America, Vol. 92, No. 6,
2323–2332.
[7] Okada, H., 2003. The Microtremor Survey Method. Society
of Exploration Geophysicists.
[8] Toksöz, M.N., 1964. Microseisms and and attempted
application to exploration. Geophysicics, 29, 154-177.
160
Figure 9. Comparison of soil profile obtained from bore log
with profiles estimated from microtremor observations for NTU.
RESEARCH PROJECTS
ONGOING PROJECTS
A partial list of research projects is summarized below. Readers are welcome to email the respective investigators for more
information regarding their work.
PRINCIPAL INVESTIGATOR
Underwater Infrastructure and Underwater City of the Future
Chu Jian
cjchu@ntu.edu.sg,
Teng Susanto
csteng@ntu.edus.g,
Tan Soon Keat
ctansk@ntu.edu.sg
Sustainable Urban Waste Management for 2020
Wang Jing-Yuan,
jywang@ntu.edu.sg
Ng Wun Jern
wjng@ntu.edu.sg
Underground Technology and Rock Engineering (UTRE) Phase II
Ma Guowei
cgwma@ntu.edu.sg
Aquaporin Based Biomimetic Membranes For Water Reuse and Desalination
Anthony Gordon Fane
agfane@ntu.edu.sg
TEC Project. Nanostructures Photocatalyst for Membrane Fouling Control
Sun Delai, Darren
ddsun@ntu.edu.sg
Development of a GIS Based System for Earthquake Response Monitoring of
Buildings in Singapore
Kusnowidjaja Megawati
kusno@ntu.edu.sg
Enhanced Biological and Physical Stabilization in Landfills
Ng Wun Jern
wjng@ntu.edu.sg
Improving The Efficiency of Membranes in the Water Industry_Project 176:
Novel Technologies for Enhanced Control of Concentration Polarisation and
Fouling in Reverse Osmosis Membrane Processes
Tang Chuyang
cytang@ntu.edu.sg
Environmental Technology of Brine and Reject Streams_ Project 174:
Brine Processing By Membrane Distillation Crystallization
Anthony Gordon Fane
agfane@ntu.edu.sg,
Law Wing-Keung Adrian
cwklaw@ntu.edu.sg
Environmental Technology of Brine and Reject Streams_Project 173:
Novel Pressure Retarded Osmosis (PRO) Technology for Cost-Effective
and Environmentally Sustainable Desalination Brine Disposal and
Osmotic Power Harvesting
Tang Chuyang
cytang@ntu.edu.sg,
Law Wing-Keung Adrian
cwklaw@ntu.edu.sg
Novel high energy density vanadium redox flow cell for renewable
energy storage
Tuti Mariana Lim
tmlim@ntu.edu.sg
Prediction of Explosion Hazards from Earth Covered Magazine
Fan Sau Cheong
cfansc@ntu.edu.sg
Nitrogen-Doped TIO2-Activated Carbon (AC) Composite for Adsorptive
Photocatalytic Oxidation-Reduction of Refractory Organic Substances
Under Solar Irradiation in Water Purification
Lim Teik Thye
cttlim@ntu.edu.sg
PROJECT TITLE
161
RESEARCH PROJECTS
162
PROJECT TITLE
Structural Resilience Study of Concrete Precast and Composite Steel Joints
Subject to Missing Column Scenario
Tan Kang Hai
ckhtan@ntu.edu.sg
Development of Analytical Tools for Progressive Collapse Analysis due to
Terrorist Bombing
Tan Kang Hai
ckhtan@ntu.edu.sg
Novel Hydrodynamics for Low Pressure Membrane Processes
Law Wing-Keung, Adrian
cwklaw@ntu.edu.sg
Sand Accretion Study
Tan Soon Keat
ctansk@ntu.edu.sg
Assembling Of Multifunctional TIO2 Nanofiber Membrane For
Water Treatment (0802-IRIS-06)
Sun Delai, Darren
ddsun@ntu.edu.sg
Integration of Novel Forward Osmosis Membranes and Optimized
Bioprocess for Water Reclamation
Anthony Gordon Fane
agfane@ntu.edu.sg
Plane wave absorbers for wave power generation
Law Wing-Keung, Adrian
cwklaw@ntu.edu.sg
Sensors For Fouling Control in Reverse Osmosis Membrane Processes
Anthony Gordon Fane
agfane@ntu.edu.sg
Emerging Organic Contaminants in Catchment Surface Waters of the
Marina Bay
Chang Wei-Chung
wcchang@ntu.edu.sg
MBR Process Modeling And Optimization: Case Study of Ulu Pandan
Water Reclamation Plant With Future Scale-Up Considerations
Jim Chen Chin-Kuang
jimchen@ntu.edu.sg
MPA-NTU Joint Collaboration on Maritime Innovation and
Strategic Technology
Tan Soon Keat
ctansk@ntu.edu.sg
Explore Concept of Membrane Action in Slabs to Reduce Fire Protection
for Beams
Tan Kang Hai
ckhtan@ntu.edu.sg
Slope Instrumentation for the Study of Rainfall -Induced Slope Failures
in Singapore
Harianto Rahardjo
chrahardjo@ntu.edu.sg
Conversion of Municipal Plastic Waste into an Innovative
Polyhdroxyalkanoate (PHA) Material
Wang Jing-Yuan
jywang@ntu.edu.sg
Development of Novel Hollow Fiber Membranes Integrated with
Biological/Biomimetic sorption for CO2 separation from Biogas
Wang Rong
rwang@ntu.edu.sg
Energy efficiency and indoor air-quality control in air-conditioned buildings
Chang Wei-Chung
wcchang@ntu.edu.sg
The Jurong rock cavern project at Banyan Basin, Jurong Island
(JTC C05502007)
Low Bak Kong
bklow@ntu.edu.sg
Slope repair and technology in Singapore
Harianto Rahardjo
chrahardjo@ntu.edu.sg
Integration Development of Flexible DSSC for Commercial Application
Sun Delai, Darren
ddsun@ntu.edu.sg
RESEARCH PROJECTS
PROJECT TITLE
Development and Assembling of High Efficiency Dye Sensitized Solar Cells
and Water Cleavage-Hydrogen Production Reactor Using Novel Nano
Structured Ti)2 Fiber/Tube/Membrane
Sun Delai, Darren
ddsun@ntu.edu.sg
Biocement-A New Sustainable And Energy Saving Material For Construction
And Waste Treatment
Chu Jian
cjchu@ntu.edu.sg
Failure Modes and Ultimate Strength of Tubular Joints under Elevated
Temperatures
Tan Kang Hai
ckhtan@ntu.edu.sg
The Jurong rock cavern project at Banyan Basin, Jurong Island
(JTC C05502007)05
Low Bak Kong
bklow@ntu.edu.sg
The Influence of Floor Slabs and Transverse Beams on the Behavior of
RC Beam-Column Joints under Loss of Column Scenarios
Li Bing
cbli@ntu.edu.sg
Off-line Portable Damage Detection Devices for Compressed Natural
Gas (CNG) Cylinders Fitted in Vehicles
Lie Seng Tjhen
ctlie@ntu.edu.sg
163
RESEARCH PROJECTS
COMPLETED PROJECTS
Strengthening techniques to increase seismic
resistance in school building in Hebei &
Liao Ning, China
Principal Investigator: Li Bing
Report No.: CEE/2010/192
The project beneficiaries include 1,000 students who will
upon project completion benefit from a safer school building
being repaired and strengthened against earthquakes.
Through the training of the trainers, 10 master trainers and
40 local builders will also benefit.
Sichuan earthquake - a drop of Hope
Construction of Mobile Water Purification System (MWPS)
which is capable of producing an estimated output of 60
m3/day of drinking water (using reverse osmosis) and 180
m3/day for general usage (using ultra filtration).
Sichuan earthquake - New School New Hope
Seismic strengthening and repair of school building
against earthquakes using carbon fibre, steel angles and
wire mesh
Sichuan earthquake - New School New Hope
1.0 To study suitable location for sensors to be installed
in an estimated number of 6 buildings, where
extensive instrumentation with a minimum of six
tri-axial seismic sensors (or episensor force-balance
accelerometers) linked to a data logger shall be done
for each building.
2.0 To study suitable location for the sensors to be installed
for the remaining buildings, where a minimum of two
tri-axial seismic sensors (or episensor force-balance
accelerometers) linked to a data logger should be
placed in each building for monitoring purposes.
3.0 To perform computer modeling, structural analyses
and to give recommendations on the followings:
(a) Propose and use special purpose software to
develop detailed analytical models of 20 buildings
and then analyze the buildings using non-linear
static and dynamic analyses based on the latest
as-built structural drawings. The models shall
account for material and geometric non-linear
behavior, including strength/stiffness degradation,
ductility of structural elements and joints, second
order effects and also take into consideration
amplifications of seismic motion due to soil and
structural resonance.
(b) Determine structural responses and capacity curves
for the selected buildings under study in terms
of accelerations and lateral drifts at base, mid
height and roof levels of the building and base
shear through the analyses.
(c) Study the seismic performance of high-rise
buildings in Singapore.
The project beneficiaries include 1,000 students who will
upon project completion benefit from a safer school building
being repaired and strengthened against earthquakes.
Through the training of the trainers, 10 master trainers and
40 local builders will also benefit.
164
Consultation Study On The Tremor Monitoring
System (TMS) For 30 Buildings
Principal Investigator: Kusnowidjaja Megawati
NTU has recently been appointed as Tremor Assessment
Specialist (TAS) in a project commissioned by BCA to
instrument 30 high-rise buildings in Singapore. In this
project, NTU is partnering with Ryobi Geotechnique Pte
Ltd. Dr Zhang Qiwei, the proposed Research Fellow, is to
work on this project. The scopes of the work are:
Underground Technology and Rock Engineering
(UTRE) Program - Behaviour of Rock Cavern
Under Dynamic Loads
Principal Investigator: Zhao Zhiye
The study includes two parts: the behavior of rock caverns
under dynamic loads and the analysis of drill/blast operation
in rock excavation.
(1) Numerical simulations were conducted to investigate
the blast loading and blast induced damage into rock
mass and rock cavern based on continuous modelling.
The fully-coupled method was used to obtain the blast
load and the damage depth of rock mass. The PPV
damage criteria, taking into account of the influence of
RMR, were used as the damage criterion. The damage
depth into rock mass including the effect of loading
density, weight of charge and rock mass properties was
RESEARCH PROJECTS
obtained. The effects of rock bolts were also studied
based on the continuous model. The effects of standoff distance, rock bolts and joint orientation on the
dynamic response of rock cavern were investigated
based on discontinuous deformation analysis (DDA). It
can be concluded that the displacements and velocities
of a certain measure point near rock tunnels under blast
loading are highly dependent on the stand-off distance
from the charge hole, the overburden of the tunnel,
and joints orientation. The rock bolts can slightly
decrease the displacement and velocity of measure
points near it while its effects are insignificant.
Myanmar Cyclone - Wellspring of Hope
Providing safe drinking water by extracting ground water
(drilling tube-wells) or surface water (pumping river water)
complete with appropriate water treatment facilities (sand
filters with backwash and chlorine disinfectants), storage
tanks, diesel engine and compressors for the Cyclone Nargis
affected communities which are served by the Sun Quality
Health clinics at 20 locations in the Irrawaddy delta.
(2) Rock blasting is a rock excavation technique widely
used in the mining and construction industry due to its
reliability, economy and safety. The goal of blast design
is to attain the expected technical target (advance and
good contour) at an economical cost.
In addition, the vibration caused by rock blasting should
be taken into consideration, and be controlled under a
safe level to ensure the stability of adjacent structures.
An extensive literature review on the various drill/blast
methods was carried out, and the numerical modelling
using both the continuous and discontinuous methods
(LS-DYNA and DDA) was conducted to investigate
the influence by various design parameters. A case
study was included in the report.
Autonomous Verification and Validation for
Simulation Modeling
Principal Investigator: Yang Yaowen
Simulation models have been increasingly used in problem
solving and in decision making. The correctness of a
simulation model is addressed through model verification
and validation, which is a significant factor to determine
the accuracy and confidence level of the simulation
model. Unfortunately, there has been no set of tests that
can be easily applied to determine the correctness of the
model. Furthermore, no algorithm exists to determine
what techniques or procedures to use. The tool of model
validation and verification is thus highly desired in the
simulation industry, especially in the situation without
test data or with incomplete test data. Model validation
approaches to assess the quality of a simulation model
will be explored in this project. An effective model
validation method will be proposed to conduct model
validation with incomplete test data. It will cover data
validity, conceptual model validity, computerized model
verification, and operational validity. A process of model
validation will be proposed and implemented as part of
modelling environment.
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RESEARCH PROJECTS
PhD THESES
The Occurrence and Molecular
Characterization of Enteric Viruses in the
Tropical Aquatic Environment
Candidate: Aw Tiong Gim
Report No.: CEE/PhD/2010/211
Enteric viruses have emerged as important causes of
major waterborne disease outbreaks in recent years. The
occurrence of enteric viruses in aquatic environments
constitutes a major health hazard because of their low
infective dose and resistance to environmental breakdown.
Currently, our knowledge on the occurrence of enteric
viruses in tropical water environments is limited. This
thesis describes the first study of the prevalence and
molecular characterization of waterborne pathogenic viruses
in urban water catchments and community wastewaters in
Singapore. Noroviruses were determined to be the most
prevalent enteric viruses detected in both wastewater and
surface water samples. Molecular characterization revealed
the genetic diversity of astroviruses, enteroviruses and
noroviruses in water environments. The norovirus strains
detected in environmental samples are closely related to
the concurrently identified clinical strains in Singapore
during gastroenteritis outbreaks between August 2006 to
January 2007. Knowledge on the occurrence of human
enteric viruses in water environments contributes to the
understanding of the mechanisms of viral transmission
and the possible role played by water as a vehicle of
transmission.
Nodal-based Discontinuous Deformation
Analysis
Candidate: Bao Huirong
166
This thesis presents a nodal-based discontinuous deformation
analysis (NDDA) based on the coupling of the discontinuous
deformation analysis (DDA) and the finite element method
(FEM), for modeling blocky systems, especially for
simulating crack propagation in rock mass. The NDDA can
provide a more accurate stress and strain distribution in
each block and has a higher computational efficiency than
the standard DDA in dealing with continuum materials. As
an important ability of the NDDA, the fracturing capability
that allows for shear or tensile fracturing of intact blocks
has been provided based on the Mohr-Coulomb law. A
computer program called 2D-NDDA was developed to
handle the combination of continuous and discontinuous
large displacement problems, as well as large deformation
and failure analysis, under external loads and boundary
conditions.
After a brief introduction of the concept of the standard
DDA, detailed reviews of the validation and enhancement
of the DDA in the past decades were given. The formulae
of the NDDA for program were also presented as a main
work of this thesis. The analytical solutions for the inertia
matrix and contact matrices which control the stability of
the open-close iterations of block kinematics of the NDDA
were provided and discussed. The NDDA is not a simple
couple of the FEM and the DDA but a hybrid of them. It
can work at three states: pure FEM, pure DDA and mixed.
When the system is continuous, the NDDA works in the
pure FEM mode. When the system is totally discontinuous,
the NDDA works in the pure DDA mode. Otherwise, the
NDDA works in a mixed mode which retains the advantages
of both methods.
The idea of NDDA is easy and ready to be realized
since the FEM and the DDA are both derived from the
minimization of the total potential energy of the system.
An FEM code can be easily transformed into a DDA code
when the kinematics part is considered. The NDDA can
absorb both the advantages of the FEM and the DDA.
To transform an FEM algorithm into a DDA algorithm,
two steps are necessary: (1) scheme for the fracture of
the continuous material; (2) introducing of the inertia and
kinematics matrices.
Lastly, numerical simulations were performed to show the
improvement and flexibility of the NDDA over the standard
DDA. The simulation of stress wave propagating inside a
rock bar shows the ability of the NDDA in dealing with
wave problems and its fracturing ability when the stress
wave cause breakage. The simulation of rock specimen with
initial cracks under uniaxial forces shows the procedure of
crack propagation which agrees with empirical findings.
The simulations of Brazilian disc test series also agree well
with the experimental results. Indeed, the NDDA can be
applied to more engineering problems other than the crack
propagation problems if more mature FEM algorithms are
applied to them.
Sorption of Oxyanions on Nanocrystalline
Mg/Al Layered Double Hydroxides: Sorption
Characteristics, Mechanisms, and Matrix
Interferences
Candidate: Goh Kok Hui
Nanocrystalline Mg/Al layered double hydroxide (LDH)
with nitrate intercalation produced in this study exhibited
excellent affinity for polyvalent oxyanions, but comparatively
less affinity for monovalent oxyhalides. Nanocrystalline
LDH was prepared by a fast coprecipitation with
subsequent hydrothermal treatment method. The synthesized
nanocrystalline LDH possessed mesoporous characteristic
with a large surface area and comprised nanocrystalline
RESEARCH PROJECTS
grains. Interactions of oxyanions (i.e. arsenate, chromate, and
vanadate) and oxyhalide (i.e. bromate) with nanocrystalline
LDH were studied through stoichiometric calculations,
nitrate displacement investigations, comprehensive
sorption/desorption experiments, and analyses with several
microscopic techniques such as XPS, EXAFS, XRD, FTIR,
CHNS/O, and EDX. The influences of co-existing species
on the sorption of oxyanions by nanocrystalline LDH were
investigated by conducting experiment in the presence of
natural organic matter (NOM) and common anions such as
nitrate, silica, sulfate, carbonate, and phosphate. Arsenate
sorption performances of LDHs prepared by various
alternative synthetic routes were also explored and compared
with those of LDHs prepared by conventional routes.
Exhausted Carbon for the Removal of
Hydrogen Sulfide and Ammonia
Candidate: Jiang Xia
Effect of Seepage on Sediment Transport
Candidate: Liu Xiaoxie
This study presents the experimental results and theoretical
analyses of seepage effects on sediment transport. A total
of 529 experiments grouped under four different series of
tests were conducted in a laboratory flume with a permeable
sediment boundary to investigate the effect of seepage, the
Three dimensionless groups, viz. Einstein’s parameter
Φ, Shields’ parameter without seepage τ*o and modified
densimetric Froude number Ω are chosen to examine how
seepage affects bedload transport rate. Eleven undisturbed
flow conditions were tested, five under clear water and
six in live-bed condition. No bedforms with significant
height were observed during the experiments. The results
show that an increase in suction rate causes an increase in
shear velocity excess, which is defined as the difference
between the bed and critical shear velocities, leading to an
increase in bedload transport rate. The experimental data
also show that for the same undisturbed flow conditions,
the dimensionless bedload transport rate increases linearly
(in semi-logarithmic scale) with increasing suction rates.
The equations for predicting bedload transport rate under
suction are derived empirically; the predicted results using
these empirical equations compared well with measured
data, with an accuracy of ±20%. Published results from
other researchers are used to compare with results obtained
and inference drawn from the present study. The similarities
and differences of these studies are highlighted.
On the other hand, the experimental results show that
the sediment transport rate decreases with an increase
in injection velocity, but the magnitude of the reduction
is comparatively smaller than that of the increment with
suction. The equation for predicting bedload transport
rate with injection is also empirically determined by fitting
the ratio of Einstein’s parameter Φ with injection to that
without as a function of the ratio of modified densimetric
Froude number with injection to that without.
The effect of the length of the seepage zone on sediment
transport rate was investigated experimentally in this
study. Only suction effects were studied in this part of the
research. The results show that for the same undisturbed
flow conditions and suction rate, the bed load transport
rate, which is represented by Einstein’s dimensionless
parameter Φ, decreases with a reduction in suction zone
length. A slope modifier is introduced to account for the
length effect. The empirical equation for predicting the
slope modifier is obtained in terms of the Shields’ parameter
without seepage and the relative suction zone length, which
is defined as the ratio of the suction zone length to that
at 2-m length.
Finally, the experimental results also show that the bedload
transport rate in the presence of suction increases rapidly
with time until it reaches a peak, beyond which, the
transport rate decreases. The duration for the bedload
transport rate to reach the peak is shorter for flows with
higher sediment transport rates. With an increase in time,
the bedload transport rate reduces, and eventually reaches
a balance between the incoming and outgoing sediment
The main objective of this study is to develop a highly
efficient and economical biofiltration process for the
co-removal of H2S and NH3 using exhausted carbon
as packing material. Firstly, the feasibility of re-using
exhausted carbon in biofilters for the removal of H2S was
confirmed. The removal efficiency of H2S was almost
identical in the biofilters packed with exhausted carbon
and fresh carbon. Furthermore, a mathematical model was
developed to explore and explain the different mechanisms
of H2S removal in the two biofilters. The profiles of H2S
concentration along the biofilm thickness and carbon radius
were simulated using the proposed model system. The
ratios of the H2S removal by the mechanism of adsorption
and biodegradation in the biofilters were also simulated,
respectively. Thereafter, the effect of substrates acclimation
strategy on simultaneous biodegradation of NH3 and H2S
was evaluated. Different biodegradation capacities of
NH3 and H2S were observed under different substrates
acclimation strategies. Lastly, a horizontal biotrickling filter
(HBTF) packed with exhausted carbon for the co-removal
of H2S and NH3 was investigated. The results demonstrate
that it is highly efficient and effective for simultaneous
biodegradation of H2S and NH3 by the HBTF over 316
days of operation. The long-term high performance of
the HBTF is attributed to low accumulation of biomass
and products, stable carbon characteristics and microbial
communities.
length of the suction zone and time on bedload transport
rate. Two different types of cohesionless sand particles
with diameters = 0.9 mm and 0.48 mm were used in the
study.
167
RESEARCH PROJECTS
transport, called the equilibrium condition, i.e., the sediment
transport with no seepage condition.
The Role of Microbial Aggregation in Aerobic
Granulation
Candidate: Luo Yiqun
In the present study, dispersed aerobic granules bacteria
were subjected to selective hydraulic pressure by settling
time, resulting in the loose structured aggregates formed
by enrichment process, in which the coaggregating bacteria
with mild auto aggregating ability were observed as the
consequence. In comparison, strong auto aggregating
bacteria or co aggregating bacteria only occur in aerobic
granules sheltered by compact structure. The studies on
composition and diversity of aggregating microbes in
activated sludge, acetate-fed granule and phenol-degrading
granule showed that higher proportion of microbial
community members in aerobic granules was involved
in cell-cell aggregating interactions than that in activated
sludge. The fraction of co aggregating microbes can be
increased under the chemical and toxic shock. Granule
isolate S35 possessing both aggregating and autoaggregating
ability was demonstrated to accelerate the formation of
aerobic granule in 5 days. The feasibility of bioaugmentation
of aggregating mono culture to accelerate the granulation
process is supported. Bioaugmentation with granule isolate
S 15 was shown to significantly improve recovery extent of
disintegrated granular sludge. Reaggregated aerobic granules
appeared in Rl on day 5 and quickly grew to replace the
loose disintegrated granular sludge as a dominant form in
the biomass. The results suggest the microbial aggregation
might be an integral part for aerobic granulation, and the
presence of aggregating bacteria acted as a trigger to the
aerobic granulation.
Behavior of Comer Column-Slab Connections
in Irregular Flat Plate Floors under Gravity
and Bidirectional Lateral Loading
168
The objective of this study is to improve the analysis and
design of flat plate structure slab-column connections by
obtaining representative values of unbalanced moments. It
is achieved by proposing reduced slab stiffness model based
on the modified effective moment of inertia method. The
use of the effective moment of inertia method for cracked
flexural members ensures simplicity and, with appropriate
use of parameters, can lead to accurate prediction of
reduced stiffness of cracked flexural members. Unlike
currently available models that are only applicable for flat
plate structures with regular columns layouts, the proposed
model is also applicable for irregular columns layouts. The
proposed model has been verified using the experimental
data of unbalanced moment-lateral drift relationships from
both square column-slab connections from past research as
well as rectangular column-slab connections tested in this
experimental program. The accuracy of the proposed model
in modeling reduced slab stiffness has been shown much
better compared to applying uniform reduced slab stiffness,
which is commonly used in the available models such as
Effective Beam Width and Equivalent Frame Model. The
proposed model of reduced slab stiffness should be useful
for design engineers dealing with flat plate slab-column
connections to obtain accurate slab deflection, inelastic
lateral drift, and design value of transferred unbalanced
moment.
This study also investigates the behavior of flat plate
structure with irregular columns layout, which is currently
still unclear due to very limited experimental data. The
experimental program consists of five corner column-slab
connections and four slab-column connections with 135degree slabs with rectangular columns, which are often
found in modern flat plate structures. The specimens were
tested to investigate their behaviors in term of strength,
drift capacity, stiffness, ductility, and the effect of shear
reinforcement. The experimental results show the effects
of bidirectional lateral load, gravity load magnitude, and
the use of stud shear reinforcement (SSR).
Candidate: Soerya Widjaja
Estimation of foreign exchange exposure in
Public Private Partnership infrastructure
projects
The structural behaviors of rectangular column-slab
connections in modem flat plate structures are still unclear
due to currently limited experimental data. One of the
unclear aspects is the design value of transferred unbalanced
moments, which are critical contributor to the connection
shear stresses. More accurate values of unbalanced moments
can be obtained by modeling reduced slab stiffness due to
slab cracking more accurately. However, currently available
models such as Effective Beam Width, Equivalent Frame
Model, and simplified frame analysis, which are only
applicable for flat plate structures with regular columns
layouts, do not represent the actual behavior of the cracked
slab.
Economic foreign exchange (FX) exposure is an important
risk factor which affects Public-private partnership (PPP)
projects in developing countries. The risk exists because
PPP projects typically sell their outputs domestically and
generate revenues in local currency, while their financing
costs and operating and maintenance costs are often
denominated in hard currencies. Traditionally, FX risk is
tested through the use of risk factors on revenue and costs
or by adopting conservative assumptions in the cash flow.
While this method provides a range of a risk value based on
scenarios, it does not give the potential FX risk exposure.
Candidate: Matthias Ehrlich
RESEARCH PROJECTS
What constitutes minimum and maximum risk values is
often defined on the basis of subjective judgements.
This research contributes to the solution of this problem
with a methodology to quantify annual economic FX
exposure in project companies financed under project finance
modality. The application of the developed FX index to
describe the project feasibility on economic FX exposure
is superior as it is an extra tool which is linked to the
financial models without the ambiguities to incorporate
risk factors in the cash flow. It is a unique mathematical
process for dimensioning currency risk on a various set of
cash flow positions.
A first-order second-moment reliability method based on
the Hashofer-Lind reliability index beta was undertaken
to reflect the uncertainties of market risks with impact
on the cash flow of the PPP project. The FX index was
modelled via an expanding dispersion ellipsoid in the
original space of random variables. The input variables
in the proposed foreign exchange exposure (FEE) model
include inflation rates, interest rates and foreign exchange
rates. The variables form the ellipsoid of an n-dimensional
shape. It reflects not only the effect of the mean values but
also the covariances of the random variables influencing a
defined investability domain. The computation of the FX
index involved eigenvalues and eigenvectors, rotation of
the reference frame, and transformed space for the random
variables.
Additionally, a country reliability risk (CRR) index was
designed to evaluate risk mitigation instruments (RMIs).
FX risk exposure is often mitigated by RMIs. The value of
RMIs depends on the affordability and the willingness of
the government to compensate unforeseen FX fluctuation
in the project. Factors influencing country reliability can be
identified in the ability to repay debt obligations, liquidity
difficulties and political difficulties.
Candidate: Sopha Thong
In the current research, carefully planned experimental
studies were firstly carried out to investigate the SCF and the
HSS distributions along the joint intersection of three fullscale partially overlapped CHS K-joints. The experimental
results show that depends on the geometrical parameters of
the partially overlapped K-joints, the maximum SCF could
locate on either the brace side or the chord side of the joint.
The experimental results show that Efthymiou formulae are
conservative only when the partially overlapped K-joints
are subjected to IPB loading, but not for the case of AX
loading. In addition, it is observed that the S-N curves are
found to be on the conservative side of the test results. A
comparison between tests results with FE analyses shows
that reliable SCF and HSS values could be obtained.
After the experimental study, FE models were created to
simulate the test specimens. A total of 3500 FE models
with wide range of geometrical parameters of partially
overlapped K-joints were created. A set of parametric
equations was subsequently proposed for predicting the
SCF of partially overlapped CHS K-joints. However, as
part of an attempt to gain more an accurate prediction, a
new method is created for estimating the SCF and HSS
values of partially overlapped CHS K-joint. The assessment
confirms the efficiency and reliability of the new method for
predicting the SCF and HSS of partially overlapped CHS
K-joints under basic AX, IPB and combined loadings.
Finally, a comparison study between the gapped and the
partially overlapped CHS K-joints has been made. It is
observed from the comparison results that the partially
overlapped CHS K-joints are mainly in favour when they
are working under the AX load case, while the gapped
CHS K-joints are in favour on working under the IPB
loading.
Development of Neural Networks in Civil
Engineering Applications
Candidate: Zhang Yun
The architecture of neural networks (NNs) has a
significant impact on a network’s generalization ability.
Ensemble neural networks (ENNs) are commonly used
networks in many engineering applications due to their
better generalization properties. An ENN usually includes
several back-propagation networks in its structure, where
the back-propagation network is a single feed-forward
network trained with the back-propagation learning rule.
In this thesis, the Akaike information criterion (AIC) and
the entropy were used as the automating design tools for
Both methodologies the FX index and the CRR index
represent strategic components in the set of quantitative
tools. The models can be used as a monitoring tool for
performing FX exposure analysis. It is a forward looking
approach which indicates how prepared the project is in
absorbing economic FX exposure. The models can take
care of the different institutional arrangements and payment
structures because they are directly linked to the financial
models. The FX index reflects the annual life cycle costs
and revenue structures during the whole concession period.
The outcome illustrates to project sponsors and lenders the
critical variables that they need to control. The CRR index
provides the default probabilities on RMIs. Both models
can be applied to infrastructure projects such as power,
water supply, and transportation.
Stress Concentration Factor and Hot Spot
Stress Studies of Partially Overlapped
Circular Hollow Section K-Joint
169
RESEARCH PROJECTS
balancing the generalization against the parameters and
finding the best combining weights of the ENNs. Two
ENNs, namely, the AIC based ENN and the entropy based
ENN were developed first. Since the AIC and entropy have
their own merits for solving different problems, a new
AIC-entropy based ENN was developed. Two analytical
functions – the peak function and Friedman function were
used first to assess the accuracy of the proposed ensemble
approaches. The verified approaches were then applied to
the civil engineering applications.
Strut-and-Tie Modelling on Deep Beams
Candidate: Zhang Ning
A modified strut-and-tie model for deep beams was
developed. Several significant improvements were made and
gave rise to better prediction performance of deep beam
shear strength, evaluated by 233 test results. No empirical
stress limit was required and the concrete softening effect
was embedded in the model. The proposed model was further
extended to calculate continuous deep beams with rigid and
elastic supports, which was validated by 54 beams from
literature as well as the author’s experimental programme
on continuous deep beam subjected to differential support
settlement. The effects of support settlement were studied
and discussed through crack patterns, failure loads, steel
strains and load-deflection responses. The author further
developed the model into a generalised form, including
asymmetrical loading conditions and the capability of
predicting failure modes. Eight beams were tested and
conclusions were drawn on the effects of unsymmetrical
loadings on the beam behaviour. The strut-and-tie model
was also developed to account for size effect in deep beams,
followed by a test programme of eleven geometricallysimilar specimens with varied sizes. The proposed model
outperformed several other methods and is a promising
tool for engineers.
Desalination Discharges in Shallow Coastal
Waters
Candidate: Shao Dongdong
170
From an environmental viewpoint, the outfall of a
desalination plant needs to be properly designed to ensure
the discharged brine plume to be mixed rapidly with the
ambient coastal waters. In this study, I investigated the
behavior of submerged round brine discharges injecting
at 0°, 30° and 45° to stationary receiving water in the
laboratory. Advanced laser diagnostic method of combined
Particle Image Velocimetry (PIV) and Planar Laser Induced
Fluorescence (PLIF) was adopted to measure the velocity
and concentration fields, respectively. The experimental
results obtained provide regulatory references on the gross
geometrical characteristics of the smaller-angle discharges,
the resulting mixing behavior as well as the potential
influence of the close proximity of the seabed on the brine
plume, i.e., the Coanda effect. Assuming flat seabed and a
combination of mean and oscillatory tidal current, I further
developed a mathematical model to simulate the long-term
salinity build-up on the far field around the outfall due to
continuous brine discharge.
Numerical Simulation of Heterogeneous
Material Failure by using the Smoothed
Particle Hydrodynamics Method
Candidate: Wang Xuejun
In the thesis, a micromechanical approach based on the
Smoothed Particle Hydrodynamics method was developed
to simulate the heterogeneous material failure by capturing
the detailed occurring sequence of the microscopic cracks
as well as the macro mechanical response. The program
employs an elasto-plastic damage model and utilizes
the statistical approach to account for the heterogeneous
strength distribution in the material microstructure.
Besides, a polymineral method that is suitable to model
the microstructure of multiphase material with different
components was proposed and implemented in the program.
A series of 2-D and 3-D simulations on rock-like material
failures were performed. The effects of strain rate as well
as the material heterogeneity on the specimen fracture
process and its dynamic strength were investigated.
Comparisons with the experimental results demonstrate
good agreements qualitatively. Results also reveal that the
strain rate dependency of the dynamic strength might be
ascribed to the apparent confining pressure during the rapid
loading as well as the material heterogeneity.
PUBLICATIONS
PUBLICATIONS
Publications of academic staff in journals and conference proceedings during the period from 2009 to 2010.
Authors who are not members of the School are indicated by *.
“Protection of Structures against Hazards IV”, 2009 - Ed. Han Linhai* and Lok, T.S., CI-Premier, Beijing, P.R. China, 440
pages. (ISBN 978-981-08-3244-5).
“Shock and Impact Loads on Structures VIII”, 2009 - Ed. Wu, C.Q.* and Lok, T.S., CI-Premier, Adelaide, Australia, 791 pages.
(ISBN 978-981-08-3245-2).
Annamdas, V.G.M. and Soh, C.K., 2010. “Application of electromechanical impedance technique for engineering structures:
Review and future issues”. Journal of Intelligent Material Systems and Structures, Vol. 21, No. 1, pp. 41-59.
Bai, H.W., Shao, J.H., Zhang, X.W. and Sun, D.D., 2010. “Effect of TiO2 photocatalytic oxidation for control of membrane
fouling by humic acid in water”. Chinese Journal of Environmental Engineering, Vol. 4, No. 1, pp. 28.
Bao, H.R. and Zhao, Z.Y., 2009. “Indeterminacy of the vertex-vertax contact in 2D discontinuous deformation analysis.”
Proceedings of the 9th International Conference on Analysis of Discontinuous Deformations (ICADD-9), Singapore, pp. 99107.
Bao, H.R. and Zhao, Z.Y., 2009. “Modelling crack propagation with nodal-based discontinuous deformation analysis.” Proceedings
of the 9th International Conference on Analysis of Discontinuous Deformations (ICADD-9), Singapore, pp. 161-167.
Bao, H.R. and Zhao, Z.Y., 2010. “An alternative scheme for the corner-corner contact in the two dimensional discontinuous
deformation analysis.” Journal of Advances in Engineering Software, Vol. 41, No. 2, pp. 206-212.
Bao, X.L. and Li, B., 2010. “Residual strength of blast damaged reinforced concrete columns”. International Journal of
Impact Engineering, Vol. 37, pp. 295-308.
Beppu, M.*, Ohno, T.*, Ohkubo, K.*, Li, B. and Satoh, K.*, 2010. “Explosive-resistant performance of fiber sheet reinforced
concrete plates under contact explosion”. International Journal of Protective Structures, Vol. 1, No. 2, pp. 257-270.
Bo, M.W.,* Chu, J., Arulrajah, A.* and Fabius, M.*, 2009. “A case study on predicting primary consolidation settlement
applying small, large strain and stress path methods.” Proceedings of the 17th International Conference on Soil Mechanics and
Geotechnical Engineering, Alexandria, Egypt, 5-9 October.
Brownjohn, J.M.W.* and Pan, T.-C., 2010. “Vibration serviceability of tall buildings due to wind loads: prediction, measurement
and evaluation.” Proceedings of the Structures Congress 2010, 12-15 May 2010, Orlando, Florida, USA.
Chan, C.L. and Low, B.K., 2009. “Reliability analysis of laterally loaded piles involving nonlinear soil and pile behavior.”
Journal of Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 135, No. 3, pp. 431-443.
Cheng, N.S., 2009. “Comparison of formulas for drag coefficient and settling velocity of spherical particles.”
Powder
Cheng, N.S. and Nguyen, H.T., 2010. “Hydraulic radius for evaluating resistance induced by simulated emergent vegetation
in open channel flows.” Journal of Hydraulic Engineering, ASCE. doi:10.1061/(ASCE)HY.1943-7900.0000377.
Cheng, N.S., Nguyen, H.T., Zhao, K. and Tang, X.*, 2010. “Evaluation of flow resistance in smooth rectangular open-channels.”
Journal of Hydraulic Engineering, ASCE, doi: 10.1061/(ASCE)HY.1943-7900.0000322.
Chiang C. Mei*, Mikhael Krotov*, Zhenhua Huang and Aode Huhe*, 2010. “Short and long waves over a muddy seabed”.
Journal of Fluid Mechanics, Vol. 643, pp. 33-58.
Chiew, S.P. and Beh, C.T.*, 2010. “Use of alternative steel in building steelwork design to BS5950”. International Journal
of Advances in Structural Engineering, Vol. 13, No. 3, pp. 431-439.
Cheng, N.S., 2009. “Application of incomplete similarity theory for predicting bed-material load discharge.” Journal of
Hydraulic Engineering, ASCE. doi:10.1061/(ASCE)HY.1943-7900.0000375.
171
PUBLICATIONS
Chiew, S.P., Lee C.K., Lie, S.T. and Nguyen, T.B.N.*, 2009. “Fatigue study of partially overlapped circular hollow section
K-Joints”. Proceedings of the 6th International Symposium on Advances in Steel Structures, ICASS-09, Hong Kong, 16-18
December, Vol. I, pp. 602-619.
Chiew, S.P., Lee, C.K. and Lie, S.T., 2009. “Research on tubular joints at Nanyang Technological University”. The IES Journal
Part A – Civil and Structural Engineering, Vol. 2, No. 1, pp. 68-84.
Chiew, S.P., Lee, C.K., Lie, S.T. and Nguyen, T.B.N.*, 2009. “Fatigue study of partially overlapped CHS K-Joints. Part II:
Experimental study and validation of numerical models”. International Journal of Engineering Fracture Mechanics, Vol. 76,
No. 15, pp. 2408-2428.
Chiew, S.P. and Wada, Y.*, 2009. “Corrosion control for building structural steelworks”. Proceedings of the International
Symposium on Advances in corrosion Protection to Steel Members in Building Construction, Hong Kong, 2 November, pp.
103-137.
Chiew, S.P. and Yu, Yi, 2009. “Debonding Behavior of CFRP Strengthened Steel Beams under Static and Cyclic Loads”.
Proceedings of the 6th International Symposium on Advances in Steel Structures, ICASS-09, Hong Kong, 16-18 December,
Vol. I, pp. 285-292.
Chin, K.B., Leong, E.C. and Rahardjo, H., 2009. “Cyclic behaviour of unsaturated silt in suction-controlled simple shear”.
Proceedings of the 4th Asia-Pacific Conference on Unsaturated Soils, Newcastle, Australia, 23-25 November, pp. 65-70.
Chin, K.B., Leong, E.C. and Rahardjo, H., 2010.
Geotechnical Journal (accepted for publication).
“A simplified method to estimate soil-water characteristic curve”. Canadian
Chou, S., Shi, L.*, Wang, R., Tang, C.Y., Qiu, C. and Fane, A.G., 2010. “Characteristics and potential applications of a novel
forward osmosis hollow fiber membrane”. Desalination, Vol. 261, pp. 365-372.
Chu, J., Ivanov, V., Lee, M.F., Oh, X.M. and He, J., 2009. “Soil and waste treatment using biocement”. Proceedings of the
International Symposium on Ground Improvement Technologies and Case Histories, 9-11 December, Singapore, Eds, Leung,
C.F., Chu, J., and Shen, R.F., Research Publishing, pp. 160-166.
Chu, J., Varaksin, S.*, Klotz, U.* and Mengé, P.*, 2009. “Construction processes.” State-of-the-Art-Lecture, Proceedings of
the 17th International Conference on Soil Mechanics and Geotechnical Engineering, Alexandria, Egypt, 5-9 October, Vol. 4,
pp. 3006-3135.
Chu, J., Yan, S.W.* and Guo, W., 2009. “Innovative dike construction methods.” Keynote Lecture, International Symposium
on Geotechnical Engineering, Ground Improvement & Geosynthetics for Sustainable Mitigation and Adaptation to Climate
Change including Global Warming, 3-4 December, Bangkok, Thailand.
Chua, H.C., Goh, A.T.C. and Zhao, Z.Y., 2009. “Distinct element analysis of stage constructed underground cavern in the
vicinity of a fault.” Proceedings of the 9th International Conference on Analysis of Discontinuous Deformation (ICADD-9),
Singapore, pp. 429-435.
Chua, L.H.C., Leong, M.C.M., Lo, E.Y.M., Reinhard, M., Robertson, A.P.*, Lim, T.T., Shuy, E.B. and Tan, S.K., 2009. “Controlled
field studies on artificial recharge by surface infiltration in a sandfill”. Water Science and Technology, IWA publishing, Vol.
60, No. 5, pp. 1283-1293.
172
Chua, H.C.L., Lo, Y.M.E., Shuy, E.B. and Tan, B.K.S., 2009. “Nutrients and suspended solids in storm runoff from catchments
with various proportions of rural and urban land use in Kranji catchment, Singapore”. Journal of Environmental Management,
Vol. 90, pp. 3635-3642.
Chua, L.H.C., Lo, E.Y.M., Lim, T.T., Robertson, A.P.*, Shuy, E.B. and Tan, S.K., 2009. “Geochemical changes during recharge
with tertiary-treated wastewater at a coastal sandfill”. Water Science and Technology, IWA Publishing, Vol. 60, No. 5, pp.
1273-1281.
Chua, L.H.C. and Wong, T.S.W., 2010. “Improving event-based rainfall-runoff modelling using a combined artificial neural
network-kinematic wave approach”. Journal of Hydrology, Vol. 390, pp. 92-107.
Chua, L.H.C., Lo, E.Y.M., Shuy, E.B., Robertson, A.P.*, Lim, T.T. and Tan, S.K., 2010. “DOC and UVA attenuation with
soil aquifer treatment in the saturated zone of an artificial coastal sandfill”. Water Science and Technology, Vol. 62, No. 3,
pp. 491-500.
PUBLICATIONS
Chua, L.H.C., Wong, T.S.W. and Wang, X.H., 2010. “Determination of the constant loss rate and other physical parameters
in event-based rainfall-runoff modelling using linear artificial neural networks”. Applied Soft Computing, Vol. 11, No. 1, pp.
373-381.
Dao, M.H., Tkalich, P.*, Chan, E.S. and Megawati, K., 2009. “Tsunami propagation scenarios in the South China Sea.” Journal
of Asian Earth Sciences, Vol. 36, pp. 67-73.
Ding, H.-B., Tan, G.-Y. Amy, and Wang, J.-Y., 2010. “Caproate formation in mixed-culture fermentative hydrogen production”.
Bioresource Technology (Doi: 10.1016/j.biotech. 2010.07.056).
Feng, C.S.*, Wang, R., Wu, Y.* and Li, G.*, 2010. “Preliminary analysis of a linear pore pattern formed on poly (vinylidene
fluoride-co-hexafluoro propylene) porous membrane surfaces”. Journal of Membrane Science, Vol. 352, pp. 255-261.
Feng, C.S.*, Wang, R., Zhang, H.Y.* and Shi, L.*, 2010. “Diverse morphologies of PVDF hollow fibre membranes and their
performance analysis as gas/liquid contactors”. Journal of Applied Polymer Science, in press.
Foreman, J.*, Gallien, J.*, Alspaugh, J.*, Lopez, F.*, Bhatnagar, R.*, Teo, C.C. and Dubois, C.* 2010. “Implementing supplyrouting optimization in a make-to-order manufacturing network.” Manufacturing and Service Operations Management, Vol.
12, pp. 547-568.
Fujikake, K.*, Li, B. and Soeun, S.*, 2009. “Impact response of reinforced concrete beam and its analytical evaluation”. ASCE
Journal of Structural Engineering, August, Vol. 135, No. 8, pp. 938-950.
Gao, Y.Y.*, Yu, D.Y.*, Tan, S.K., Wang, X.K. and Hao, Z.Y., 2010. “Experimental study on the near wake behind two sideby-side cylinders of unequal diameters”. Fluid Dynamic Research, 42 055509.
Gao, Y.Y., Stephane Etienne,* Yu, D.Y.* and Tan, S.K., 2010. “Flow characteristics behind two unequal circular cylinders
in tandem arrangement”. ISOPE-2010 ¾ The 20th International Offshore and Polar Engineering Conference, Beijing, China,
20-26 June 2010.
Gao, Y.-Y.*, Yu, D.-Y.*, Tan, S.K., Wang, X.K. and Hao, Z., 2010. “Flow behaviour behind two side-by-side circular cylinders
with unequal diameters”. Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering
(OMAE2010), 6-11 June, Shanghai, China, OMAE2010-20217.
Gensheimer, R.J.*, Wang R.Q.*, Adams, E.E.*, Daichin*, Shao, D., Zhao, B., Huang, Z. and Law, A.W.K., 2010. “Dynamics
of particle clouds with application to open water sediment disposal.” Proceedings of the 6th International Symposium on
Environmental Hydraulics, 23-25 June, Athens, Greece.
Giannis, A.*, Pentari, D.*, Wang, J.Y. and Gidarakos, E.*, 2010. “Application of sequential extraction analysis to electrokinetic
remediation of cadmium, nickel and zinc from contaminated soils”. Journal of Hazardous Materials, Vol. 184, pp. 547-554.
Goh, A.T.C. and Hefney, A.M.*, 2010. “Reliability assessment of EPB tunnel-related settlement.” International Journal
Geomechanics and Engineering, Vol. 2, No. 1, pp. 57-69.
Goh, S.G., Rahardjo, H. and Leong, E.C., 2009. “Evaluation of shear strength equations for unsaturated soil”. Proceedings
of the 4th Asia-Pacific Conference on Unsaturated Soils, Newcastle, Australia, 23-25 November, pp. 753-758.
Goh, S.G., Rahardjo, H. and Leong, E.C., 2010. “Shear strength equations for unsaturated soil under drying and wetting”.
ASCE Journal of Geotechnical and Geoenvironmental Engineering, April, Vol. 136, No. 4, pp. 594-606.
Guo, W., Chu, J. and Yan, S.W.*, 2009. “Classification of geotubes and related analysis methods”. Proceedings of the
International Symposium on Ground Improvement Technologies and Case Histories, Eds, Leung, C.F., Chu, J. and Shen, R.F.,
Research Publishing, pp. 263-274.
Hao, Z., Zhou, T., Wang, X.K. and Tan, S.K., 2010. “Experimental studies of vortex structures in the wake of a cylinder with
helical strakes”. Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2010),
Hay, C.T., Khor, S.L., Sun, D.D. and Leckie, J.O.*, 2009. “Influence of a prolonged solid retention time environment on
nitrification/denitrification and sludge production in a submerged membrane bioreactor”. Desalination, Vol. 245, pp. 28-43.
(IF: 1.155).
Gu, J. and Zhao, Z.Y., 2009. “Considerations of the discontinuous deformation analysis on wave propagation problems.”
International Journal of Numerical and Analytical Methods in Geomechanics, Vol. 33, No. 12, pp. 1449-1465.
173
PUBLICATIONS
He, J.W. and Low, Y.M., 2010. “Probabilistic assessment of the clashing between flexible marine risers”. Proceedings of the
International Conference on Ocean, Offshore and Arctic Engineering, Shanghai, China.
He, L.*, Huang, G.H.* and Qin, X.S., 2010. “An integrated distributed-hydrologic and watershed-management model: A case
study in the Heshui River Watershed of Southern China.” Proceedings of the 4th International Yellow River Forum (IYRF) on
Ecological Civilization and River Ethics, Zhengzhou, China, October 20-23, 2009, Vol. 1, pp. 197-205.
Hota, G.*, Sundarrajan, S.*, Ramakrishna, S.* and Ng, W.J., 2009. “One step fabrication of MgO solid and hollow submicrometer
fibers via electrospinning method”. J. Am. Ceram. Soc., Vol. 92, No. 10, pp. 2429-2433.
Huang, G. and Law, A.W.K., 2009. “Taylor dispersion under random waves.” Proceedings of the 5th International Conference
on. Asian and Pacific Coasts (APAC2009), 13-16 October, Singapore.
Huang, G., Law, A.W.K. and Huang, Z., 2010. “Experimental study on wave-induced drift of small floating.” Proceedings of
the 9th International Conference on Hydro-Science and Engineering, 2-5 August, Chennai, India.
Huang, G.H.*, Sun, W.*, Nie, X.H.*, Qin, X.S. and Zhang, X.D.*, 2010. “Development of a decision support system for
rural eco-environmental management in Yongxin County, Jiangxi Province, China.” Environmental Modelling and Software,
Vol. 25, No. 1, pp. 25-42.
Huang, Z., Wu, T.-R., Tan, S.K., Megawati, K., Shaw, F., Liu, X. and Pan, T.-C., 2009. “Tsunami hazard from the subduction
megathrust of the South China Sea: Part II. Hydrodynamic modelling and possible impact on Singapore.” Journal of Asian
Earth Sciences, Vol. 36, pp. 93-97.
Huang, Z.H. and Aode, H., 2009. “A laboratory study of rheological properties of mudflows in Hangzhou Bay, China”.
International Journal of Sediment Research, Vol. 24, pp. 409-423.
Huang, Z.H., Liu, C.R., Adi, K., Tan, S.K. and Nah, E., 2009. “Responses of a floating rectangular caisson to regular waves:
A comparison of measurements with time-domain and frequency-domain simulations”. Proceedings of the 5th International
Conference on Asian and Pacific Coasts (Paper No. 200-206). Singapore: World Scientific Publishing.
Huang, Z.H., 2010. “A note on tsunami hazard mitigation by mangrove forests”. Proceedings of the 9th International Conference
on Hydroinformatics (Paper No. HICA00455-00733), China: Chemical Industry Press.
Huang, Z.H. and Yuan, Z.D., 2010. “Transmission of solitary waves through slotted barriers: A laboratory study with analysis
by a long wave approximation”. Journal of Hydro-Environment Research, Vol. 3, No. 4, pp. 179-185.
Huang, Z.H. and Zhang, W.B., 2010. “A laboratory study of dynamic responses of a moored rectangular floating breakwater
to regular waves” (7 pages). The International Symposium on Hydraulic Physical Modeling and Field Investigation. 13-15
September 2010, Nanjing, China.
Indrawan, I.G.B. and Rahardjo, H., 2010. “Water infiltration through capillary barrier models.” Proceedings of the Symposium
on “Protecting Life from Geo-Disaster and Environmental Hazards”, Department of Geological Engineering, Gadjah Mada
University and AUN/SEED-Net JICA, Bali, Indonesia, 25-26 February, pp. 439-446 (D14-(1-8).
Jia, Y., Wang, R. and Fane, A.G., 2009. “Hybrid PAC-submerged membrane system for trace organics removal I. Adsorption
kinetics study of PAC in a bubbled solution”. Chemical Engineering Journal, Vol. 155, pp. 155-160.
174
Jia, Y., Wang, R. and Fane, A.G., 2009. “Hybrid PAC-submerged membrane system for trace organics removal II: System
simulation and application study”. Chemical Engineering Journal, Vol. 149, pp. 42-49.
Jiang, B. and Liu, Y., 2010. “Energy uncoupling inhibits aerobic granulation”. Applied Microbiology and Biotechnology, Vol.
85, No. 3 pp. 589-595.
Jiang, H.-L., Maszenan, A.M., Zhao, Z.-W. and Tay, J.-H., 2010. “Properties of phenol-removal aerobic granules during normal
operation and shock loading”. Journal of Industrial Microbiology & Biotechnology, Vol. 37, pp. 253-262.
Jiang, X., Zhou, Y.* and Ng, W.J. 2010. “Acidogenic removal of monochlorophenols”. Proceedings of the 12th World Congress
on Anaerobic Digestion, 31 October – 4 November 2010, Guadalajara, Mexico.
Jinadasa, K.B.S.N.*, Sasikala, S.*, Tanaka, N.*, Mowjood, M.I. M.* and Ng, W.J., 2009. “Effect of pulsing application on
performance of tropical constructed wetland treating domestic waste”. International Symposium on Southeast Asian Water
Environment, Vol. 7, pp. 435-442.
PUBLICATIONS
Kim, W.*, Lee, S.*, Shin, S.G.*, Lee, C., Hwang, K.* and Hwang, S.*, 2010. “Monitoring methanogenic community changes
in duplicate anaerobic batch digesters treating swine wastewater”. Water Research, Vol. 44, pp. 4900-4907.
Krauthammer, T.*, Langseth, M.*, Ohno, T.*, Thoma, K.*, Pan, T.-C., and Lim, C.H., 2010. “Design and analysis of protective
structures – advances in protective technology”. Proceedings of the 3rd International Conference on Design and Analysis of
Protective Structures 2010 (DAPS-2010), Defence Science & Technology Agency, Singapore, 10-12 May 2010, Singapore.
Krisdani, H., Rahardjo, H. and Leong, E.C., 2010. “Application of geosynthetic material as a coarse-grained layer in capillary
barriers”. Special Issue on Unsaturated Geosynthetics, Geosynthetics International Journal, Vol. 17, No. 5, pp. 323-331.
Krisdani, H., Rahardjo, H. and Leong, E.C., 2010. Response to Discussion by Mbonimpa, M., Aubertin, M. and Bussiere, B.
on “Effects of different drying rates on shrinkage characteristics of a residual soil and soil mixtures”. Journal of Engineering
Geology, Vol. 107, No. 3-4, pp. 172-173 (2009). Published in Journal of Engineering Geology, Vol. 110, No. 1-2, pp. 3031.
Kulkarni, S.A. and Li, B., 2009. “Investigations on seismic behaviour of hybrid-steel concrete connections”. Journal of
Precast/Prestressed Concrete Institute (PCI), Winter, Vol. 54, pp. 67-87.
Kulkarni, S.A. and Li, B., 2009. “Seismic behaviour of reinforced concrete interior wide beam-column joints”. Journal of
Earthquake Engineering, January, Vol. 13, Issue 1, pp. 80-99.
Kumara, C.K.*, Ng, W.J., Bandara, A.* and Weerasooriya, R.*, 2010. “Nanogibbsite: Synthesis and characterization”. Journal
of Colloid and Interface Science, Vol. 352, pp. 252-258.
Kuniawan, A., Huang, Z.H., Li, J., Liu, C.R.*, Wang, X.K., Hao, Z.Y., Tan, S.K. and Nah, E.*, 2009. “A numerical analysis
of the response and air gap demand for semi-submersibles”. Proceedings of the 28th International Conference on Ocean,
Offshore and Arctic Engineering, OMAE2009, 31 May - 5 June 2009, Honolulu, Hawaii, USA, OMAE2009-79163.
Law, A.W.K., Au, S.* and Song, J., 2010. “Stochastic diffusion by progressive waves in turbulence.” Proceedings of the 9th
International Conference on Hydrodynamics, 11-15 October, Shanghai, China.
Lay, W.C.L., Chong, T.H., Tang, C.Y., Fane, A.G., Zhang, J. and Liu, Y., 2010. “Fouling propensity of forward osmosis:
investigation of the slower flux decline phenomenon.” Water Science and Technology, Vol. 61, No. 4, pp. 927-936.
Lay, W.C.L., Liu, Y. and Fane, A.G., 2010. “Impacts of salinity on the performance of high retention membrane bioreactors
for water reclamation: A review”. Water Research, Vol. 44, No. 1, pp. 21-40.
Lee, C., Kim, J.*, Chinalia, F.A.*, Shin, S.G.* and Hwang, S.*, 2009. “Unusual bacterial populations observed in a full-scale
municipal sludge digester affected by intermittent seawater inputs”. Journal of Industrial Microbiology and Biotechnology,
Vol. 36, pp. 769-773.
Lee, C., Kim, J.*, Hwang, K.* and Hwang, S.*, 2009. “Fermentation and growth kinetic study of Aeromonas caviae under
anaerobic conditions”. Applied Microbiology and Biotechnology, Vol. 83, pp. 767-773.
Lee, C., Kim, J.*, Hwang, K.*, O’Flaherty, V.* and Hwang, S.*, 2009. “Quantitative analysis of methanogenic community
dynamics in three anaerobic batch digesters treating different wastewaters”. Water Research, Vol. 43, pp. 157-165.
Lee, C.K., Chiew, S.P., Lie, S.T. and Nguyen, T.B.N.*, 2009. “Fatigue study of partially overlapped circular hallow sectionjoints, Part I: Geometrical models and mesh generation.” Engineering Fracture Mechanics, Vol. 76, No. 16, pp. 2445-2463.
Lee, C.K., Chiew, S.P., Lie, S.T. and Nguyen, T.B.N.*, 2010. “Adaptive mesh generation procedures for thin-walled tubular
structures.” Finite Element in Analysis and Design, Vol. 46, No.1-2, pp. 114-131.
Lee, C.K., Chiew, S.P., Lie, S.T., Sopha, T.* and Nguyen, T.B.N.*, 2009. “Experimental studies on stress concentration factors
for partially overlapped circular hollow section K-Joints”. International Journal of Advanced Steel Construction, Vol. 5, No.
4, pp. 481-499.
Lei, L., Bai, H.W., Liu, Z.Y. and Sun, D.D., 2010. “Hierarchical Ag/TiO2 nanofiber membrane for water purification”. IWA
LET Conference, Phoenix, USA, 3 June 2010.
Lee, C., Kim, J.*, Shin, S.G.*, O’Flaherty, V.* and Hwang, S.*, 2010. “Quantitative and qualitative transitions of methanogen
community structure during the batch anaerobic digestion of cheese-processing wastewater”. Applied Microbiology and
Biotechnology, Vol. 87, pp. 1963-1973.
175
PUBLICATIONS
Leong, E.C., He, L.C. and Rahardjo, H., 2009. Discussion on “Assessment of the use of the vapour equilibrium technique
in controlled-suction tests” by Pintado, X., Lloret, A. and Romero, E., (2009). Canadian Geotechnical Journal, Vol. 46, pp.
411-423. Published in Canadian Geotechnical Journal, Vol. 46, pp. 1482-1484.
Leong, E.C., Rahardjo, H. and He, L.C., 2010. Discussion on “Calibrations of a high-suction tensiometer” by Laurenco, S.D.N.,
Gallipoli, D., Toll, D.G., Augarde, C.E., Evans, F.D. and Medero, G.M. (2008), Geotechnique, Vol. 58, No. 8, pp. 659-668.
Published in Geotechnique, Vol. 60, No. 3, pp. 233-234.
Leung, C.F.*, Chu, J. and Shen, R.F.*, (Editors) 2009. “Ground improvement technologies and case histories”. Research
Publishing, ISBN: 981-08-3124-2.
Li, B. and Chen, Q., “Stiffness of reinforced concrete structural walls with irregular openings”.
Engineering & Structural Dynamics, Vol. 39, Issue 4, pp. 397-417.
Journal of Earthquake
Li, B. and Chua, G.H.Y., 2009. “Seismic performance of strengthened reinforced concrete beam-column joints using FRP
composites”. ASCE Journal of Structural Engineering, Vol. 135, No. 10, pp. 1177-1190.
Li, B., Kulkarni, S.A. and Leong, C.L., 2009. “Seismic performance of precast hybrid-steel concrete connections”. Journal
of Earthquake Engineering, June, Vol. 13, Issue 5, pp. 667-689. (First-Tier).
Li, B., Pan, T.-C. and Nair, A., 2009. “A case study of the effect of cladding panels on the response of reinforced concrete
frames subjected to distant blast loadings”. Nuclear Engineering and Design, March, Vol. 239, Issue 3, pp. 455-469.
Li, B., Pan, T.-C. and Tran, C.T.N. 2009. “Effect of axial compression load on seismic behaviour of non-seismically detailed
interior beam-wide column joints”. ACI Structural Journal, September-October, Vol. 106, No. 5, pp. 591-599.
Li, B., Pan, T.-C. and Tran, C.T.N., 2009. “Effects of axial compression load and eccentricity on seismic behaviour of nonseismically detailed interior beam-wide column joints”. ASCE Journal of Structural Engineering, July, Vol. 135, No. 7, pp.
774-784.
Li, B., Pan, T.-C. and Tran, C.T.N., 2009. “Seismic behavior of nonseismically detailed interior beam-wide column and beamwall connections”. Structural Journal, American Concrete Institute, Vol. 106, No. 5, pp. 591-599.
Li, B. and Tran, C.T.N., 2009. “Seismic behaviour of reinforced concrete beam-column joints with vertical distributed
reinforcement”. ACI Structural Journal, November-December, Vol. 106, No. 6, pp. 790-799.
Li, B., Tran, C.T.N. and Pan, T.C., 2009. “Experimental and numerical investigations on the seismic performance of lightly
reinforced concrete joints”. ASCE Journal of Structural Engineering, Vol. 135, No. 9, pp. 1007-1018.
Li, B., Huang, Z.W. and Lim, C.L., 2010. “The verification of non-dimensional energy spectrum based blast design for reinforced
concrete members through actual blast tests”. ASCE Journal of Structural Engineering, June, Vol. 136, No. 6, pp. 627-636.
Li, B. and Kulkarni, S.A., 2010. “Seismic behaviour of reinforced concrete exterior wide beam-column joints”. ASCE Journal
of Structural Engineering, Vol. 136, No. 1, pp. 26-36.
Li, B. and Lim, C.L., 2010. “Tests on seismically damaged reinforced concrete structural walls repaired using fiber-reinforced
polymers”. ASCE Journal of Composites for Construction, No. 10.
176
Li, B., Pan, T.-C., and Nair, A. “A case study of the local and global structural responses of a tall building in Singapore subjected
to close-in detonations”. The Structural Design of Tall and Special Buildings, John Wiley & Sons, Ltd, UK (to appear).
Li, F.Z. and Low, Y.M., 2010. “Sensitivity study of critical parameters influencing the uncertainty of fatigue damage in steel
catenary risers”. Proceedings of the International Conference on Ocean, Offshore and Arctic Engineering, Shanghai, China.
Li, H.Z.* and Low, B.K., 2010. “Reliability analysis of circular tunnel under hydrostatic stress field.”
Geotechnics, Vol. 37, Issue 1-2, pp. 50-58.
Computers and
Li, J., Tan, S.K., Huang, Z.H. and Kurniawan, A., 2009. “Wave amplification and air-gap response under a multi-column
platform”. Coastal Dynamics 2009, 7-11 September 2009, Tokyo, Japan.
Li, J., Huang, Z.H. and Tan, S.K., 2010. “Extreme air-gap response below deck of floating structures”. The International
Journal of Ocean and Climate Systems, Multi-Science Publishing, March, Vol. 1, No. 1, pp. 15-26.
PUBLICATIONS
Li, J., Liu, H.X. and Tan, S.K., 2010. “Lagrangian modelling of tidal bores passing through bridge piers”. Proceedings of
the 9th International Conference on Hydrodynamics (ICHD2010) (in press).
Liang, D.W.*, Shayegan, S.S.*, Ng, W.J. and He, J.Z.*, 2010. “Development and characteristics of rapidly formed hydrogenproducing granules in an acidic anaerobic sequencing batch reactor (AnSBR)”. Biochemical Engineering Journal, Vol. 49,
pp. 119-125.
Lv, L.*, Lu, Y.Q.*, Ng, W.J. and Zhao, X.S.*, 2009. “Bactericidal activity of silver nanoparticles supported on microporous
titanosilicate ETS-10”. Microporous and Mesoporous Materials, Vol. 120, No. 3, pp. 304-309.
Lie, S.T. and Yang, Z.M., 2009. “BS7910: 2005 Failure assessment diagram (FAD) on cracked circular hollow section (CHS)
Welded Joints”. International Journal of Advanced Steel Construction, Vol. 5, No. 4, pp. 385-393.
Lie, S.T. and Yang, Z.M., 2009. “Fracture assessment of damaged square hollow section (SHS) K-joint using BS7910:2005”.
Engineering Fracture Mechanics, Vol. 76, No. 9, pp. 1303-1319.
Lie, S.T. and Yang, Z.M., 2009. “Safety assessment procedure for a cracked square hollow section (SHS) Y-joint”. International
Journal of Advances in Structural Engineering, Vol. 12, No. 3, pp. 359-372.
Lie, S.T. and Yang, Z.M., 2009. “Validation of BS7910: 2005 Failure assessment diagram for cracked square hollow section
T-, Y- and K-joints”. International Journal of Pressure Vessels and Piping, Vol. 86, No. 5, pp. 291-344.
Lie, S.T. and Yang, Z.M., 2010. “Plastic collapse loads of cracked square hollow section (SHS) T-, Y- and K-joints”. Journal
of Offshore Mechanics and Arctic Engineering (OMAE), American Society of Mechanical Engineers (ASME), Vol. 132, No.
3, pp. 1-10.
Lie, S.T. and Zhang, B.F., 2010. “Plastic collapse load investigation for safety assessment of cracked square hollow section
(SHS) T-, Y- and K-joints”. Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering
(OMAE 2010), 6-11 June 2010, Shanghai, China, Paper OMAE2010-20324.
Lie, S.T., Zhang, B.F. and Yang, Z.M., 2010. “Numerical and experimental plastic collapse loads and CTODs of a cracked
square hollow section (SHS) K-joint”. Proceedings of the 13th International Symposium on Tubular Structures, 15-17 December
2010, Hong Kong, China.
Lim, C.L., Li, B. and Pan, T.-C., 2009. “Seismic performances of reinforced concrete frames with wall-like columns”. IES
Journal Part A: Civil and Structural Engineering, Vol. 2, No. 2, May, pp. 126-142.
Lim, Y.Y. and Soh, C.K., 2010. “Estimation of fatigue life using electromechanical impedance technique”. Proceedings of the
SPIE, March, San Diego, USA, Vol. 7647, p. 64722.
Lin, Q.G.*, Huang, G.H.*, Brad, B.*, Nie, X.H.*, Zhang, X.D.* and Qin, X.S., 2010. “EMDSS: An optimization-based decision
support system for energy systems management under changing climate conditions - an application to the Toronto-Niagara
Region, Canada”. Expert Systems with Applications, Vol. 37, No. 7, pp. 5040-5051.
Listiarini, K., Chan, W., Sun, D.D. and Leckie, J.O.*, 2009. “Fouling mechanism and resistance analyses of systems containing
sodium alginate, calcium, alum and their combinations in dead-end fouling of nanofiltration membranes”. Journal of Membrane
Science, Vol. 344, No. 1-2, pp. 244-251. (IF:3.247).
Liu, C., Huang, Z.H., and Tan, S.K., 2009. “Nonlinear scattering of non-breaking waves by a submerged horizontal plate:
Experiments and simulations”. Ocean Engineering, Vol. 36, pp. 1332-1345.
Liu, C., Qiu, Q. and Huang, Z.H., 2009. “Higher harmonic waves generated by a submerged horizontal thin plate: An experimental
study for breaking and non-breaking waves”. Proceedings of the 5th International Conference on Asian and Pacific Coasts,
Singapore, World Scientific Publishing, pp. 162-169.
Liu, C., Huang, Z.H., Law, A.W.K. and Geng, N., 2010. “A numerical study of wave energy converter in the form of an
oscillating water column based on a mixed Eulerian-Lagrangian formulation”. Proceedings of the 29th International Conference
on Ocean, Offshore and Arctic Engineering (Paper No. OMAE2010-21056). USA: ASME.
Listiarini, K., Sun, D.D. and Leckie, J.O., 2009. “Cake characterization of sodium alginate fouling of nanofiltration membranes
in the presence of calcium and alum”. IWA Water and Industry 2009, New Zealand, 30 November to 1 December 2009.
177
PUBLICATIONS
Liu, C.L.*, Li, G.Q.*, Sun, J.Y.* and Lok, T.S., 2009. “Design of planter-box as anti-ram barriers to resist vehicle bomb”.
Proceedings of the 4th International Conference on Protection of Structures against Hazards, Beijing, P.R. China, pp. 245253.
Liu, C.L.*, Palermo, D.*, Lok, T.S. and Chen X.L.*, 2009. “An analytical cost methodology in protective solution”. Proceedings
of the 8th International Conference on Shock and Impact Loads on Structures, Adelaide, Australia, pp. 379-388.
Liu, H.L.*, Chu, J. and Ren, Z.Y.*, 2009. “New methods for measuring the installation depth of prefabricated vertical drains.”
Geotextiles and Geomembranes, Vol. 29, No. 6, pp. 493-496.
Liu, H.W., Ghidaoui, M.S., Huang, Z.H. and Yuan, Z., 2009. “Numerical investigation of the interaction between solitary
waves and pile breakwaters”. Proceedings of the 5th International Conference on Asian and Pacific Coasts, Singapore, World
Scientific Publishing, pp. 163-169.
Liu, H.X., Li, J. and Tan, S.K., 2010. “Environmental fluid dynamics – jet flow”. Proceedings of the 9th International
Conference on Hydrodynamics (ICHD2010) (in press).
Liu, H.X., Tan, S.K., Li, J. and Wang, X.K., 2010. “Three dimensional simulation of bore flow using SPH”. Proceedings of the
29th International Conference on Offshore Mechanics and Arctic Engineering (OMAE2010), Shanghai, OMAE 2010-21090.
Liu, J.X., Zhao, Z.Y. and Liang, N.G.*, 2010. “Numerical and theoretical investigations of the tensile failure of shrunk
cement-based composites.” Chapter 2 of Computational Mechanics Research Trends, Editors: Hans P. Berger, Nova Science
Publishers, pp. 111-148.
Liu, J.X., Zhao, Z.Y., Deng, S.C.* and Liang, N.G.*, 2009. “A simple method to simulate shrinkage induced cracking in
cement-based composites by lattice-type modeling.” Computational Mechanics, Vol. 43, No. 4, pp. 477-492.
Liu, J.X., Zhao, Z.Y., Zhang, J.* and Liang, N.G.*, 2009. “Numerical investigation of crack growth in concrete subjected to
compression by the generalized beam lattice model.” Computational Mechanics, Vol. 43, No. 2, pp. 277-295.
Liu, Q.S.*, Liu, Y., Show, K.Y.* and Tay, J.H., 2009.
“Toxicity effect of phenol on aerobic granules”.
Environmental
Liu, S.S., Zhang, X.W., Sun, D.D. and Xu, Z.M., 2009. “Study on membrane fouling caused by activated sludge from a
membrane bioreactor with long solid retention time”. Chinese Journal of Environmental Engineering, Vol. 2, No. 10, pp.
1816-1820.
Liu, Y., 2009. “Is the free energy change of adsorption correctly calculated?” Journal of Chemical and Engineering Data,
Vol. 54, No. 7, pp. 1981-1985.
Liu, Y.J. and Sun, D.D., 2010. “Comparison of membrane fouling in dead-end microfiltration granular sludge suspension and
its supernatant”. Journal of Membrane Science, Vol. 352, No. 1-2, pp. 100-106. (IF:3.247).
Loh, C.-H.*, Mao, C.-H.*, Huang, J.-H.* and Pan, T.-C. “System identification and damage evaluation of degrading hysteresis
of reinforced concrete frames”. Journal of Earthquake Engineering and Structural Dynamics, International Association for
Earthquake Engineering (to appear).
Low, B.K., 2010. “Slope reliability analysis: some insights and guidance for practitioners.” Proceedings of the 17th Southeast
Asian Geotechnical Conference, Taipei, Taiwan, 10-13 May, Vol. 2, pp. 231-234.
178
Low, Y.M., 2009. “Frequency domain analysis of a tension leg platform with statistical linearization of the tendon restoring
forces”. Marine Structures, Vol. 22, No. 3, pp. 480-503.
Low, Y.M., 2009. “Efficient vector outcrossing analysis of the excursion of a moored vessel”. Probabilistic Engineering
Mechanics, Vol. 24, No. 4, pp. 565-576.
Low, Y.M., 2009. “Fatigue analysis of deepwater risers using a hybrid time/frequency domain method”. Proceedings of the
International Conference on Offshore and Polar Engineering, Osaka, Japan, Vol. 2, pp. 389-395.
Low, Y.M., 2010. “A method for accurate estimation of the fatigue damage induced by bimodal processes”. Probabilistic
Engineering Mechanics, Vol. 25, No. 1, pp. 75-85.
Low, Y.M., 2010. “Influence of the setdown of a tension leg platform on the extreme airgap response”. Applied Ocean
Research, Vol. 32, No. 1, pp. 11-19.
PUBLICATIONS
Low, Y.M., 2010. “A practical formulation for estimating the extreme vector excursion of a floating structure”.
Engineering, Vol. 37, No. 13, pp. 1159-1168.
Ocean
Low, Y.M. and Grime, A.J.*, 2010. “Extreme response analysis of floating structures using coupled frequency domain analysis”.
Journal of Offshore Mechanics and Arctic Engineering (accepted).
Low, Y.M. and Grime, A.J.*, 2010. “Extreme response analysis of floating structures using coupled frequency domain analysis”.
Proceedings of the International Conference on Ocean, Offshore and Arctic Engineering, Shanghai, China.
Luo, G., Xie, Li., Zhou, Z.H., Zhou, Q. and Wang, J.Y., 2010. “Fermentative hydrogen production from cassava stillage by
mixed anaerobic microflora: Effects of temperature and pH”. Journal of Applied Energy (accepted).
Ma, H.*, Yang, D.* and Tan, S.K., 2010. “Impacts of climate change and human activities on the flow discharge in the Miyun
Reservoir Catchment”. Journal of Hydrology (2010), doi:10.1016/j.jhydrol.2010.06.010.
McKeown, R.M.*, Scully, C.*, Enright, A.M.*, Chinalia, F.A.*, Lee, C., Mahony, T.*, Collins, G.* and O’Flaherty, V.*, 2009.
“Psychrophilic methanogenic community development during long-term cultivation of anaerobic granular biofilms”. The ISME
Journal, Vol. 3, pp. 1231-1242.
Megawati, K. and Pan, T.-C., 2009. “Regional seismic hazard posed by the Mentawai segment of the Sumatran megathrust.”
Bulletin of Seismological Society of America, Vol. 99, No. 2A, pp. 566-584.
Megawati, K. and Pan, T.-C. 2010. “Ground-motion attenuation relationship for Sumatran megathrust earthquakes”. Journal
of Earthquake Engineering and Structural Dynamics, International Association for Earthquake Engineering, Vol. 39, No. 8,
pp. 827-845.
Megawati, K. and Pan, T.C., 2010. “Development and validation of ground-motion attenuation relationship for large-magnitude
subduction earthquakes.” Proceedings of the 9th U.S. National and 10th Canadian Conference on Earthquake Engineering
(9USN/10CCEE), Toronto, Canada, 25-29 July 2010.
Megawati, K., Shaw, F., Sieh, K., Huang, Z., Wu, T.-R., Lin, Y., Tan, S.K. and Pan, T.-C., 2009. “Tsunami hazard from the
subduction megathrust of the South China Sea: Part I. Source characterization and the resulting tsunami.” Journal of Asian
Earth Sciences, Vol. 36, pp. 13-20.
Mun, C.H.*, He, J.Z.* and Ng, W.J., 2010. “Pentachlorophenol dechlorination by an acidogenic sludge”. Water Research,
Vol. 42, pp. 3789-3798.
Ng, C.A., Sun, D.D., Zhang, J., Wu, B. and Fane, A.G., 2010. “Mechanisms of fouling control in membrane bioreactors by
the addition of powdered activated carbon”. Separation Science and Technology, Vol. 45, No. 7, pp. 873-889. (IF:1.139).
Ng, J.W., Zhang, X.W., Zhang, T., Pan, J.-H., Du, A.J.-H. and Sun, D.D., 2009. “Construction of self-organized free-standard
TiO2 nanotube arrays for effective disinfection of drinking water”. Proceedings of the 2nd European Conference on Environmental
Applications of Advanced Oxidation Processes (EAAOP2), Cyprus, 9-11 September 2009.
Ng, J.W., Zhang, X.W., Zhang, T., Pan, J.-H., Du, A.J.-H. and Sun, D.D., 2010. “Construction of self-organized free-standard
TiO2 nanotube arrays for effective disinfection of drinking water”. Journal of Chemical Technology and Biotechnology, Vol.
85, pp. 1061. (IF:2.045); DOI: 10.1002/jctb.2395.
“Used-water treatment and Rethinking for the future”.
Hitachi Eco-Conference 2009, 16 March 2009,
Nguyen, Q.C. and Tan, S.K., 2009. “Quadtree mesh for combined hydrodynamic and water quality modelling”. Proceedings
of the 5th International Conference Asian and Pacific Coasts, Singapore, Vol. 2, pp. 246-251.
Nguyen, Q.C. and Tan, S.K., 2009. “Simulation of storm surge and inundation in the United States due to hurricanes using
AnuGA modelling tool”. Proceedings of the 3rd International Conference on Estuaries and Coasts, Sendai, pp. 604-609.
Nguyen, Q.C. and Tan, S.K., 2010. “Modelling of flow in Everglades National Park, Florida, USA using a quadtree grid.”
Proceedings of the 17th Congress of International Association of Hydraulics Engineering Research -- Asia Pacific Division,
Auckland, 7 pp.
Nguyen, Q.C. and Tan, S.K., 2010. “Near field mixing process of multi-port diffusers: numerical modelling with quadtree
grids”. International Symposium on Environmental Hydraulics, Athens (in press).
Ng, W.J., 2009.
Singapore.
179
PUBLICATIONS
Nguyen, T.H.N. and Qin, X.S., 2010. “Robust optimization for water quality management under uncertainty.” Proceedings of
the 2010 Young Water Talents Symposium, Suntec, Singapore, 28 June, pp. 43-48.
Nishimura, T.*, Rahardjo, H. and Koseki, J.*, 2010. “Direct shear strength of compacted bentonite under different suctions”.
Proceedings of the 5th International Conference on Unsaturated Soils, Barcelona, Spain, 6-8 September, Vol. 1, pp. 323-328.
Nyunt, T.T., Leong, E.C. and Rahardjo, H., 2009. “Effects of matric suction and loading rate on the stiffness-strain behaviour
of kaolin”. Proceedings of the 4th Asia-Pacific Conference on Unsaturated Soils, Newcastle, Australia, 23-25 November, pp.
15-19.
O’Reilly, J.*, Lee, C., Chinalia, F.A.*, Collins, G.*, Mahony, T.* and O’Flaherty, V.*, 2010. “Microbial community dynamics
associated with biomass granulation in low-temperature (15°C) anaerobic wastewater treatment bioreactors”. Bioresource
Technology, Vol. 101, pp. 6336-6344.
O’Reilly, J.*, Lee, C., Collins, G.*, Chinalia, F.A.*, Mahony, T.* and O’Flaherty, V.*, 2009. “Quantitative and qualitative
analysis of methanogenic communities in mesophilically and psychrophilically cultivated anaerobic granular biofilms”. Water
Research, Vol. 43, pp. 3365-3374.
Ong, S.L.*, Ng, W.J. and Lee, L.Y.*, 2009. “Nitrogen removal using an anoxic-oxic ultra-compact biofilm reactor”. International
Journal of Environmental Studies, Section B, Environmental Science and Technology.
Ow, L.F., Harnas, F.R., Indrawan, I.G.B., Sahadewa, A., Sim, E.K., Rahardjo, H., Leong, E.C., Fong, Y.K. and Tan, P.Y., 2010.
“Tree pulling experiment: An analysis into the mechanical stability of rain trees”. Trees – Structure & Function (available on
line and in print).
Pan, J.H., Sun, D.D., Lee, C.M., Kim, Y.J. and Lee, W.I., 2010. “Effect of calcination temperature on the textural properties
and photocatalytic activities of highly ordered cubic mesoporous WO3/TiO2 films”. Journal of Nanoscience and Nanotechnology,
Vol. 10, No. 7, pp. 4747-4751. (IF:1.987).
Pan, T.-C., 2010. “Developing technology for multiple-hazards protection”. Proceedings of the 9th International Symposium
on New Technologies for Urban Safety of Mega Cities in Asia, 13-14 October 2010, Kobe, Japan.
Pan, T.-C., 2010. “Developing technology for protection”. Keynote Speech, Inaugural Workshop on Building Infrastructure
Protection for Homeland Security, 13 May 2010, Singapore.
Pan, T.-C., 2010. “Seismic hazard of low/moderate seismicity regions – Singapore’s perspective.” Keynote Lecture, The 10th
International ROSE School Seminar, 20-21 May 2010, EUCentre, Collegio Cardinale Riboldi, Pavia, Italy.
Pan, T.-C., Leong, C.L., Karim, R.K., Shaw, F. and Tan, A.C.T., 2009. “Explosion induced ground motion monitoring.” Final
Report No.: MINDEF-NTU/JPP/05/01, Protective Technology Research Centre, Nanyang Technological University.
Pan, T.-C, Li, B., Lu, Y.* and Lim, C.L., 2009. “Response of buildings to external and internal blast loadings.” Home Team
Journal, Singapore, Issue No. 1, pp. 67-80.
Pan, T.-C., Tan, K.H., Li, B., Fan, S.C. and Ma, G.W., 2010. “An overview of the current research programmes in Protective
Technology Research Centre at NTU.” Keynote Paper, Proceedings of the 3rd International Conference on Design and Analysis
of Protective Structures 2010 (DAPS-2010), 10-12 May 2010, Singapore, pp. K25-K39.
180
Peng, L., You, S.-J. and Wang, J.-Y., 2010. “Carbon nanotubes as electrode modifier promoting direct electron transfer from
Shewanella oneidensis”. Biosensors and Bioelectronics, Vol. 25, pp. 1248-1251.
Peng, L., You, S.J. and Wang, J.Y., 2010. “Electrode potential regulates cytochrome accumulation on shewanella oneidensis
cell surface and the consequence to bioelectrocatalytic current generation”. Biosensors and Bioelectronics (DDI: 10.1016/
j.bios.2010.03.039).
Prochazka, P.*, Dolezel, V.* and Lok T.S., 2009. “Optimal shape design for minimum Lagrangian”. Engineering Analysis
with Boundary Elements, Elsevier Publishing, Vol. 33, No. 4, pp. 447-455.
Qi, W., Niu, D.J. and Wang, J.-Y., 2010. “Characterization of microbial communities during hydrolysis of lignocellulosic waste
to reducing sugars”. Journal of Biobased Materials and Bioenergy. (submitted and revised one time).
Qin, X.S., Huang, G.H.* and Yu, H.*, 2009. “Enhancing remediation of LNAPL recovery through a response-surface-based
optimization approach.” Journal of Environmental Engineering (ASCE), Vol. 135, No. 10, pp. 999-1008.
PUBLICATIONS
Qin, X.S., 2010. “Management of environmental pollution control problems under stochastic uncertainty.” Proceedings of the
5th IEEE International Conference on Management of Innovation and Technology, Singapore, June 2-5, 2010, pp. 366-371.
Qin, X.S., 2010. “Numerical simulation of DNAPL contaminant transport and remediation in a three-dimensional heterogeneous
subsurface.” Proceedings of the 9th International Conference on Hydroinformatics, Tianjin, China, 6-10 September, pp. 566573.
Qin, X.S., Huang, G.H.* and He, L.*, 2010. “Development of a cluster-analysis-based distributed hydrologic modeling system.”
Proceedings of the 4th International Yellow River Forum (IYRF) on Ecological Civilization and River Ethics, Zhengzhou, China,
October 20-23, 2009, Vol. 4, pp. 46-54.
Qin, X.S., Huang, G.H.* and Liu, L.*, 2010. “A genetic-algorithm-aided chance-constrained programming model for regional
air quality management under uncertainty.” Journal of the Air & Waste Management Association, Vol. 60, No. 1, pp. 63-71.
Qin, X.S. and Xu, Y., 2010. “River water quality modeling under dual-uncertainties: A fuzzy-parameterized stochastic simulation
method.” Proceedings of the 9th International Conference on Hydroinformatics, Tianjin, China, 6-10 September, pp. 21092116.
Rahardjo, H., Hua, C.J., Leong, E.C. and Santoso, V.A.*, 2010. “Performance of an Instrumented Slope under a Capillary
Barrier System”. Proceedings of the 5th International Conference on Unsaturated Soils, Barcelona, Spain, 6-8 September, Vol.
2, pp. 1279-1284.
Rahardjo, H., Leong, E.C. and Rezaur, R.B., 2009. “Laboratory characterisation of unsaturated soil for slope stability studies”.
Keynote Lecture, Proceedings of the 4th Asia-Pacific Conference on Unsaturated Soils, Newcastle, Australia, 23-25 November,
pp. 565-578.
Rahardjo, H., Ong, T.H., Rezaur, R.B., Leong, E.C. and Fredlund, D.G.*, 2010. “Response parameters for characterization of
infiltration”. Environmental Earth Sciences, Vol. 60, No. 7, pp. 1369-1380.
Rahardjo, H., Santoso, V.A.*, Leong, E.C., Ng, Y.S. and Tam, C.P.H., 2009. “Pore-water pressure characteristics of two
instrumented residual soil slopes”. Proceedings of the 4th Asia-Pacific Conference on Unsaturated Soils, Newcastle, Australia,
23-25 November, pp. 333-339.
Rahardjo, H., Satyanaga, A. Nio, Leong, E.C. and Ng, Y.S., 2010. “Effects of groundwater table position and soil properties
on stability of slope during rainfall”. ASCE Journal of Geotechnical and Geoenvironmental Engineering, November, Vol. 136,
No.11, pp. 1555-1564.
Rahardjo, H., Vilayvong, K. and Leong, E.C., 2010. “Water characteristic curves of recycled materials”. Geotechnical Testing
Journal, ASTM International, Vol. 34, No. 1, pp. 1-8 (available on line and in print).
Rahimi, A., Rahardjo, H. and Leong, E.C., 2010. “Effect of antecedent rainfall patterns on rainfall induced slope failure”.
ASCE Journal of Geotechnical and Geoenvironmental Engineering. (available on line and in print).
Rahimi, A., Rahardjo, H. and Leong, E.C., 2010. “Effect of hydraulic properties of soil on rainfall-induced slope failure”.
Journal of Engineering Geology, Vol. 114, pp. 135-143.
Reza Mohammadpour and Lim, S.Y., 2010. “Numerical modeling of three-dimensional flow around abutments in a compound
open channel”. Proceedings of 2010 International Conference on Environmental Science and Development, 26-28 February
2010, Singapore, pp. 328-332.
Schnellmann, R.*, Busslinger, M.*, Schneider, H.* and Rahardjo, H., 2010. “Effect of rising water table in an unsaturated
slope”. Journal of Engineering Geology, Vol. 114, pp. 71-83.
Shao, D.D. and Law, A.W.K. 2009. “Salinity build-up due to brine discharges into shallow coastal waters.” Modern Physics
Letters B, Vol. 23, No. 3, pp. 541-544.
Shao, D.D. and Law, A.W.K., 2009. “Turbulent mass and momentum transport of a circular offset dense jet.” Journal of
Turbulence, Vol. 11, Issue 40, pp. 1-24.
Shao, D.D. and Law, A.W.K., 2010. “Mixing and Boundary interactions of 30 and 40 degree inclined dense jets.” Journal
of Environmental Fluid Mechanics, Vol. 10, Issue 5, pp. 521-553.
Santoso, V.A.*, Rahardjo, H., Leong, E.C., Ng, Y.S. and Tam, C.P.H., 2009. “Horizontal drains in residual soil slopes”.
Proceedings of the 4th Asia-Pacific Conference on Unsaturated Soils, Newcastle, Australia, 23-25 November, pp. 325-332.
181
PUBLICATIONS
Shao, Y.B.*, Cai, Y.Q.* and Chiew, S.P., 2010. “Static strength of square tubular T-Joint under axial compression with collar
plate reinforcement”. Proceedings of the 4th International Conference on Steel and Composite Structures, Sydney, Australia,
21 – 23 July, pp. 415-421.
Shao, Y.B.*, Lie, S.T. and Chiew, S.P., 2010. “Static Strength of Tubular T-Joints with Reinforced Chord under Axial
Compression”. International Journal of Advances in Structural Engineering, Vol. 13, No. 2, pp. 369-377.
She, Q., Tang, C.Y., Wang, Y.N. and Zhang, Z., 2009. “The role of hydrodynamic conditions and solution chemistry on protein
fouling during ultrafiltration”. Desalination, Vol. 249, No. 3, pp. 1079-1087.
Shen, L. and Liu, Y., 2010. “Treatment of Ampicillin-loaded wastewater by combined adsorption and biodegradation”. Journal
of Chemical Technology and Biotechnology, Vol. 85, No. 6, pp. 814-820.
Shen, L., Liu, Y. and Paul, E.*, 2010. “A simple geometric approach for simplification of Langmuir kinetics for adsorption”.
Colloids and Surfaces A – Physical and Engineering Aspects, Vol. 349, No. 1-3, pp. 78-82.
Shi, L.*, Wang, R. and Cao, Y.*, 2009. “Effect of the rheology of poly (vinylidene fluoride-co-hexafluropropylene) (PVDF–HFP)
dope solutions on the formation of microporous hollow fibers used as membrane contactors”. Journal of Membrane Science,
Vol. 344, pp. 112-122.
Shin, S.G.*, Han, G.*, Lim, J.*, Lee, C. and Hwang, S.*, 2010. “A comprehensive microbial insight into two-stage anaerobic
digestion of food waste-recycling wastewater”. Water Research, Vol. 44, pp. 4838-4849.
Shin, S.G.*, Lee, S.*, Lee, C., Hwang, K.* and Hwang, S.*, 2010. “Qualitative and quantitative assessment of microbial
community in batch anaerobic digestion of secondary sludge”. Bioresource Technology, Vol. 101, pp. 9461-9470.
Soh, C.K. and Lim, Y.Y., 2009. “Detection and characterization of fatigue induced damage using electromechanical impedance
technique”. Multi-functional Materials and Structures II, Parts 1 & 2, Advanced Materials Research, Vol. 79-82, pp. 20312034.
Su, J.*, Huang, G.H.*, Xi, B.D.* and Qin, X.S. et al., 2010. “Long-term planning of waste diversion under interval and
probabilistic uncertainties”. Resources, Conservation and Recycling, Vol. 54, No. 7, pp. 449-461.
Su, J.*, Huang, G.H.*, Xi, B.D.*, Li, Y.P.*, Qin, X.S., Huo, S.L.* and Jiang, Y.H.*, 2009. “A hybrid inexact optimization
approach for solid waste management in the City of Foshan, China.” Journal of Environmental Management, Vol. 91, No. 2,
pp. 389-402.
Sun, D.D., 2009. “Membrane water reclamation: fouling and solution”. Challenges in Environmental Science & Engineering,
CESE-2009, 14-17 July 2009, Jupiters Hotel, Townsville Australia.
Sun, D.D. and Hay Choon Teck, 2009. “Prolonged sludge retention time for high strength wastewater treatment using submerged
membrane bioreactor”. IWA Water and Industry 2009, New Zealand, 30 November to 1 December 2009.
Sun, H.Y.*, Wong, L.N.Y., Shang, Y.Q.*, Lu, Q.* and Zhan, W.*, 2010. “Systematic monitoring of the performance of anchor
systems in fractured rock masses.” International Journal of Rock Mechanics and Mining Sciences, Vol. 47, pp. 1038-1045.
Sun, J.P. and Zhao, Z.Y., 2010. “Effects of anisotropic permeability of fractured rock masses on underground oil storage
caverns.” Journal of Tunnelling and Underground Space Technology, Vol. 25, No. 5, pp. 629-637.
182
Sun, J.P., Zhao, Z.Y. and Zhang, Y. “Determination of three dimensional hydraulic conductivities using a combined analytical/
neural network model.” Journal of Tunnelling and Underground Space Technology, accepted.
Sun, W.*, Huang, G.H.*, Zeng, G.M.*, Qin, X.S. and Sun, X.L.*, 2009. “A stepwise-cluster microbial biomass inference
model in food waste composting.” Waste Management, Vol. 29, No. 12, pp. 2956-2968.
Talei, A., Chua, L.H.C. and Quek, C., 2010. “A novel application of a neuro-computational technique in event-based rainfallrunoff modelling”. Expert Systems with Applications, Vol. 37, No. 12, pp. 7456-7468.
Talei, A., Chua, L.H.C. and Wong, T.S.W., 2010. “Evaluation of rainfall and discharge inputs used by Adaptive Network-Based
Fuzzy Inference Systems (ANFIS) in rainfall-runoff modelling”. Journal of Hydrology. (accepted).
Tan, C.H. (Grant), Koh, K.S.*, Rice, S.*, Zhou, Y.*, Ng, W.J. and Kjelleberg, S.*, 2010. “Concurrent quorum sensing and
quorum quenching in a simultaneous nitrification, denitrification & phosphorus removal (SNDPR) sludge community”. Biofilms4
International Conference, 1-3 September 2010, Winchester, UK.
PUBLICATIONS
Tan, S.B.K., Lo, E.Y.-M., Shuy, E.B., Chua, L.H.C. and Lim, W.H., 2009. “Generation of total runoff hydrographs using a
method derived from a digital filter algorithm”. Journal of Hydrologic Engineering, Vol. 14, No. 1, pp. 101-106.
Tan, S.B.K., Lo, E.Y.-M., Shuy, E.B., Chua, L.H.C. and Lim, W.H., 2009. “Hydrograph separation and development of empirical
relationships using single-parameter digital filters”. Journal of Hydrologic Engineering, Vol. 14, No. 2, pp. 271-279.
Tang, C.Y., Fu, Q.S., Gao, D., Criddle, C.S.* and Leckie, J.O.*, 2010. “Effect of solution chemistry on the adsorption of
perfluorooctane sulfonate onto mineral surfaces.” Water Research, Vol. 44, pp. 2654-2662.
Tang, C.Y., Kwon, Y.-N. and Leckie, J.O.*, 2009. “Effect of membrane chemistry and coating layer on physiochemical properties
of thin film composite polyamide RO and NF membranes. I. FTIR and XPS characterization of polyamide and coating layer
chemistry.” Desalination, Vol. 242, pp. 149-167.
Tang, C.Y., Kwon, Y.-N. and Leckie, J.O.*, 2009. “Effect of membrane chemistry and coating layer on physiochemical properties
of thin film composite polyamide RO and NF membranes. II. Membrane physiochemical properties and their dependence on
polyamide and coating layers.” Desalination, Vol. 242, pp. 168-182.
Tang, C.Y., Kwon, Y.-N. and Leckie, J.O.*, 2009. “The role of foulant-foulant electrostatic interaction on limiting flux for RO
and NF membranes during humic acid fouling-theoretical basis, experimental evidence, and AFM interaction force measurement.”
Journal of Membrane Science, Vol. 326, No. 2, pp. 526-532.
Tang, C.Y., She, Q., Lay, W.C.L., Wang, R. and Fane, A.G., 2010. “Coupled effects of internal concentration polarization and
fouling on flux behavior of forward osmosis membranes during humic acid filtration.” Journal of Membrane Science, Vol.
354, pp. 123-133.
Tang, H.W., Ding, B., Chiew, Y.M. and Fang, S.L., 2009. “Scour protection around bridge piers with tetrahedron frames”.
International Journal of Sediment Research, December, Vol. 24, No. 4, pp. 385-399.
Teo, C.C., Bhatnagar, R.* and Graves, S.C.* 2010. “Setting planned lead times for a make-to-order production system with
master schedule smoothing.” accepted for publication in IIE Transactions.
Thai, V.V., 2009. “Effective maritime security: conceptual model and empirical evidence.” Maritime Policy and Management,
Vol. 36, No. 2, pp. 147-163.
Thai, V.V., 2009. “Impact of increasing containership’s size on ports.” Proceedings of the 2nd International Symposium on
Marine Science and Technology, 2-3 November, Kaohsiung, Taiwan.
Thai, V.V., 2010. “Competency Requirements for Port Personnel in the New Era”. Proceedings of the 2010 International
Conference of Chinese Federation of Wharf Unions, 29 - 30 November, Kaohsiung, Taiwan.
Thai, V.V. and Latta, T.*, 2010. “Developing an employment brand strategy for the shortage of seafarers: The case in Australia.”
Proceedings of the 24th Australia-New Zealand Association of Management (ANZAM) Conference, 7-10 December, Adelaide,
Australia.
Thai, V.V. and Latta, T.*, 2010. “Employment brand strategy for the shortage of seafarers.” International Journal of Shipping
and Transport Logistics, Vol. 2, No. 4, pp. 411-428.
Tsai, T.T., Kao, C.M. and Wang, J.-Y., 2010. “Remediation of TCE-contaminated groundwater using Acid/BOF slag enhanced
in situ chemical oxidation”. Chemosphere (submitted).
Tunidau, J.* and Thai, V.V., 2010. “Critical factors for successful implementation of the ISM Code in some Pacific Islands
States.” WMU Journal of Maritime Affairs, Vol. 9, No. 1, pp. 63-80.
Vu, T.-T. and Tan, S.-K., 2009. “A review of the current state-of-the-arts on the application of silt screens as sediment control
equipment in open water”. Proceedings of the 5th International Conference on Asian and Pacific Coasts, Singapore, 13-16
October 2009, Vol. 2, pp. 60-66.
Vu, T.-T. and Tan, S.-K., 2010. “Laboratory investigation of hydraulic performance of silt screen”. Proceedings of the 9th
International Conference on Hydrodynamics, Shanghai, China, October 2010 (in press).
Thai, V.V., Cahoon, S.* and Tran, T.H.*, 2010. “Skill and knowledge requirements for logistics professionals in Australia.”
Proceedings of the 24th Australia-New Zealand Association of Management (ANZAM) Conference, 7-10 December, Adelaide,
Australia.
183
PUBLICATIONS
Vu, T.-T., Tan, S.-K., and Stéphanie Doorn-Groen, 2010. “A case study of silt screen deployment”. World Dredging Congress
XIX, Beijing, China, September 2010 (in press).
Vu, T.-T. and Tan, S.-K., 2010. “Laboratory investigation of hydraulic performance of silt screen”. Proceedings of the 9th
International Conference on Hydrodynamics, Shanghai, China, October 2010 (in press).
Vu, T.-T., Tan, S.-K., and Stéphanie Doorn-Groen, 2010. “A case study of silt screen deployment”. World Dredging Congress
XIX, Beijing, China, September 2010 (in press).
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Geomechanics and
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Journal, Vol. 47, No. 4, pp. 400-412.
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fiber membranes.” Journal of Membrane Science, Vol. 355, pp. 158-167.
Wang, R., Shi, L.*, Tang, C.Y., Chou, S., Qiu, C. and Fane, A.G., 2010. “Characterization of novel forward osmosis hollow
fiber membranes”. Journal of Membrane Science, Vol. 355, pp. 158-167.
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buoyant jet”. Proceedings of the 2nd International Symposium on Computational Mechanics (ISCM II) and 12th International
Conference on Enhancement and Promotion of Computational Methods in Engineering and Science (EPMESC XII), 30 November
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Wang, R.Q.*, Law, A.W.K., Adams, E.E.* and Fringer, O.B.*, 2009. “Large-eddy simulation of starting buoyant jets.”
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Wang, R.Q., Law, A.W.K., Adams, E.E.* and Fringer, O.B.*, 2009. “Buoyant formation number of a starting buoyant jet.”
Physics of Fluids, Vol. 21, Issue 12, Article No. 125114.
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of the 29th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2010), 6-11 June, Shanghai, China,
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treatment”. IWA LET Conference, USA, 3 June 2010.
Wei, X.Y., Zhao, Z.Y. and Gu, J., 2009. “Numerical simulations of rock mass damage induced by underground explosion.”
International Journal of Rock Mechanics and Mining Sciences, Vol. 46, No. 7, pp. 1206-1213.
Wicaksana, F., Fane, A.G.F. and Law, A.W.K., 2009. “The use of constant temperature anemometry for permeate flow distribution
measurement in a submerged hollow fibre system.” Journal of Membrane Science, Vol. 339, Issues 1-2, pp. 195-203.
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PUBLICATIONS
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Proceedings of the 9th International Conference on Analysis of Discontinuous Deformation - New Developments and Applications,
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Proceedings of the 44th U.S. Rock Mechanics Symposium and 5th U.S.-Canada Rock Mechanics Symposium, Salt Lake City,
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Xi, B.D.*, Su, J.*, Huang, G.H.* and Qin, X.S., et al. 2010. “An integrated optimization approach and multi-criteria decision
analysis for supporting the waste-management system of the City of Beijing, China.” Engineering Applications of Artificial
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Xiong, Y.H. and Liu, Y., 2010. “Involvement of ATP and Autoinducer-2 in Aerobic Granulation”.
Bioengineering, Vol. 105, No. 1, pp. 51-58.
Biotechnology and
Xiong, Y.H. and Liu, Y., 2010. “Biological control of microbial attachment: a promising alternative for mitigating membrane
biofouling”. Applied Microbiology and Biotechnology, Vol. 86, No. 3, pp. 825-837.
Xu, H.J. and Liu, Y., 2010. “Control of microbial attachment by inhibition of ATP and ATP-Mediated Autoinducer-2”.
Biotechnology and Bioengineering, Vol. 107, No. 1, pp. 31-36.
Xu, S.P. and Sun, D.D., 2009. “Significant improvement of hydrogen generation rate using TiO2 photocatalyst enhanced with
Cu”. International Journal of Hydrogen Energy, Vol. 34, Issue 15, pp. 6096-6104. (IF: 3.452).
Xu, S.P., Ng, J.W., Zhang, X.W., Bai, H.W. and Sun, D.D., 2010. “Fabrication and comparison of highly-efficient Cu incorporated
TiO2 photocatalyst for hydrogen generation from water”. International Journal of Hydrogen Energy, Vol. 35, pp. 5254-5261.
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Xu, S.P., Ng, J.W., Zhang, X.W., Bai, H.W. and Sun, D.D., 2010. “Adsorption and photocatalytic degradation of dye pollutants
over TiO2 nanotube photocatalyst”. Proceedings of the 6th International Conference on Interfaces Against Pollution, 16-19 May
2010, Beijing, China.
Xu, Y., Huang, G.H.* and Qin, X.S., 2009. “An inexact two-stage stochastic robust optimization model for water resources
management under uncertainty.” Environmental Engineering Science, Vol. 26, No. 12, pp. 1765-1767.
Xu, Y., Huang, G.H.* and Qin, X.S., 2010. “An inexact fuzzy-chance-constrained air quality management model.” Journal
of the Air and Waste Management Association, Vol. 60, No. 7, pp. 805-819.
Xu, Y., Huang, G.H.*, Qin, X.S. and Huang, Y., 2009. “SRFILP: A stochastic robust fuzzy interval linear programming model
for municipal solid waste management under uncertainty.” Journal of Environmental Informatics, Vol. 14, No. 2, pp. 1-9.
Xu, Y., Huang, G.H.*, Qin, X.S., Cao, M.F.* and Sun, Y.*, 2009. “An interval-parameter robust optimization model for
supporting municipal solid waste management under uncertainty.” Waste Management, Vol. 30, No. 2, pp. 316-327.
Xu, Y., Peng, X., Tang, C.Y., Fu, Q.S. and Nie, S., 2010. “Effect of draw solution concentration and operating conditions on
forward osmosis and pressure retarded osmosis performance in a spiral wound module.” Journal of Membrane Science, Vol.
348, No. 1-2, pp. 298-309.
Xu, Y., Huang, G.H.*, Qin, X.S. and Cao, M.F.*, 2009. “SRCCP: A stochastic robust chance-constrained programming model for
municipal solid waste management under uncertainty.” Resources, Conservation and Recycling, Vol. 53, No. 6, pp. 352-363.
185
PUBLICATIONS
Yan, S.W.* and Chu, J., 2010. “Construction of an offshore dike using slurry filled geotextile mats.”
Geomembranes (available online on 14 Feb 2010).
Geotextiles and
Yang, A.L.*, Huang, G.H.* and Qin, X.S., 2010. “An integrated simulation-assessment approach for evaluating health risks of
groundwater contamination under multiple uncertainties.” Water Resources Management, Vol. 24, No.13, pp. 3349-3369.
Yang, H., Rahardjo, H. and Xiao, D., 2010. “Rapid drawdown of water table in layered soil column.” ASCE Geotechnical
Special Publication No. 204, Geoenvironmental Engineering and Geotechnics, Proceedings of GeoShanghai International
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Yang, H.Y., Yu, S.F., Lau, S.P., Zhang, X., Sun, D.D. and Jun, G., 2009. “Direct growth of ZnO nanocrystals onto the surface
of porous TiO2 nanotube arrays for highly efficient and recyclable photocatalysts”. Small, Vol. 5, Issue 20, pp. 2260-2264.
(IF: 6.525).
Yoo, K.S. and Rahardjo, H., 2009. “Performance of modified volumetric pressure plate”. Proceedings of the 4th Asia-Pacific
Conference on Unsaturated Soils, Newcastle, Australia, 23-25 November, pp. 191-196.
Yoo, K.S. and Rahardjo, H., 2010. “Modification of volumetric pressure plate extractor“. Journal of ASTM International,
October 2010, Vol. 7, No. 9.
You, S.J., Ren, N.Q., Wang, J.Y., Zhao, Q.L., Yang, F.L., Zhang, J.N., Fu, L. and Luo, P., 2009. “Improving phosphate buffer
free cathode performance of microbial fuel cell based on biological nitrification”. Biosensors and Bioelectronics (accepted).
You, S.J., Ren, N.Q., Zhao, Q.L., Wang, J.Y. and Yang, F.L., 2009. “Power generation and electrochemical analysis of biocathode
microbial fuel cell using graphite fibre brush as cathode material”. Fuel Cells, Vol. 9, pp. 588-596.
You, S.J., Wang, J.Y., Ren, N.Q., Wang, X.H. and Zhang, J.N., 2010. “Sustainable conversion of glucose into hydrogen peroxide
in a solid polymer electrolyte microbial fuel cell”. ChemSusChem, Vol. 3, pp. 334-338.
You, S.J., Wang, X.H., Zhang, J.N., Wang, J.Y., Ren, N.Q. and Gong, X.B., 2010. “Fabrication of stainless steel mesh gas
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Yu Yao, Huang, Z.H., Lo, E.Y.M. and Monismith, S.G.*, 2009. “Wave-induced set-up over fringing coral reefs: A comparison
between smooth and porous reef flats”. Proceedings of the 5th International Conference on Asian and Pacific Coasts, Singapore,
World Scientific Publishing, pp. 236-244.
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187
CONTENTS
MESSAGE FROM CHAIR
1
SUSTAINABLE URBAN SYSTEMS
1
CEE VISION AND MISSION
6
STATISTICS
• Faculty & Staff
• Publications, patents and research grants
• Student Enrolment
7
7
7
7
8
GRADUATE PROGRAMMES
10
11
RESEARCH CENTRES
• Centre for Infrastructure Systems (CIS)
• DHI-NTU Centre
• Maritime Research Centre (MRC)
• Protective Technology Research Centre (PTRC)
• Residues and Resource Reclamation Centre (R3C)
ENVIRONMENTAL AND WATER RESOURCES
ENGINEERING
• A laboratory study of wave-induced setup over coral
reefs with an idealized ridge
• Adoption and acceptance of CNG vehicles on
the urban environment
• Adsorption thermodynamics of antibiotics by GAC
• An interval approach for supporting urban
water supply analysis
• Anaerobic hydrolysis of particulates in sewage
• Data-driven approach for multi-step ahead
flood forecasting for the Lower Mekong
• Design of brine outfall for seawater reverse
osmosis (SWRO) desalination plants
• Fouling behavior of forward osmosis membranes
• Estimate of resistance induced by simulated
emergent vegetation in open channel flows
• Life cycle analysis of offshore gangway
• Dam-break flow simulation with sediment transport
• Numerical simulation of wedge water entry based on
two-phase SPH model
• Optimization and enhancement of microbial hydrolysis
of lignocellulosic waste to reducing sugars
• Removal of pharmaceutical compounds in tropical
constructed wetlands
• Responses of floating breakwater to regular waves
• Solitary wave interaction with a slotted barrier:
wave scattering and hydrodynamic forces
13
16
19
21
25
28
31
35
38
41
45
51
53
56
59
62
65
68
71
75
77
•
•
Technologies for Water Softening: a review
Time-sequence analysis of jet-flipping of localized
scour by 2-D wall jets
INFRASTRUCTURE SYSTEMS AND MARITIME
STUDIES
• A decision support system for port selection
• Dangerous goods regulating system in Singapore
• Determination of Coefficient of Consolidation by
Rowe Cell
• Effects of electric vehicles on climate goals – Singapore
and Germany in comparison
• Maritime Studies Degree Programmes in Shipping
Management – An International Comparison
• P-wave velocity measurements in sedimentary rocks
• Role of filler in macro structure of asphalt mixture
and its binding characteristic with asphalt
• A co-rotational shell element with material
nonlinearities
• Collision analysis of offshore flexible risers
• Effects of anisotropic permeability of fractured rock
masses on rock caverns
• Entropy based ensemble neural network design
• Burst strength estimation of a cracked compressed
natural gas (CNG) tank cylinder
• Experimental Study and numerical modeling
of stress concentration factor in high strength steel
plate-to-plate Y joints
• Experimental tests of different types of steel
beam-column joints subjected to catenary action
• Modeling of piezoelectric energy harvester
• Numerical simulation of steel bolted beam-column
connections subjected to dynamic loading
• Experiment investigation on residual stress distributions
of high strength steel plate-to-plate Y joints
• Robustness of steel angle beam-column joints
under column removal scenarios
• Seismic responses of reinforced concrete buildings
with wall-like columns
• Consistency of shear-wave velocity structures
inferred from microtremor observations
88
90
94
96
100
104
108
113
117
120
124
127
130
134
138
142
146
150
154
157
161
164
166
PUBLICATIONS
171
EDITORIAL BOARD
ADDITIONAL COPIES AND ENQUIRIES
For general enquiries about this publication and
request for additional copies, please write to:
Jamillah Bte Sa’adon
84
RESEARCH PROJECTS
• Ongoing projects
• Completed projects
• PhD Theses
Leong Eng Choon – Chairman
Cheng Nian Sheng
Jim Chen
Low Ying Min
Teh Cee Ing
Tiong Lee Kong, Robert
EDITORIAL ASSISTANT
80
Chair
School of Civil and Environmental Engineering
Nanyang Technological University
50 Nanyang Avenue
Singapore 639798
Tel: 65-67905264
Fax: 65-67910676
Email: D-CEE@ntu.edu.sg
Published by School of Civil and Environmental Engineering, Nanyang Technological University, Singapore
Printed by PHOTOPLATES PTE LTD

- CEE - Nanyang Technological University

Transcription

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