civil engineering research no. 23 (2010)

RENEWABLE RESOURCE TECHNOLOGY

INTRODUCTION

Today, environmental concerns are everyone’s responsibility. Recycling, re-generating and renewing used or waste products into something useful are green initiatives that will contribute toward maintaining and improving our environment. CEE places great importance in pursuing research in this area. The Residues and Resource Reclamation Centre (R3C) was set up this year for this purpose. Other ongoing related research includes the development of biocement as a new construction material, and the recycling of used aggregates for new construction.

RESIDUES AND RESOURCE RECLAMATION CENTRE (R3C) The Residues and Resource Reclamation Centre (R3C) has been established by the Nanyang Technological University (NTU) to provide a platform for research and development in waste-management, especially for resource recovery and remediation. R3C, which is part of NTU’s Nanyang Environment and Water Research Institute

(NEWRI) ecosystem, aims to better support Singapore’s environmental and water technology (EWT) industry by developing novel and appropriate technologies for the local and regional markets on sustainable urban waste management. Presently, there are no comparable centres in Singapore which focuses primarily on resource recovery and remediation of contaminated land.

In resonance with the Singapore Green Plan (SGP) 2012, R3C will play a major role in achieving SGP 2012’s key targets of sustainable waste management. R3C will focus on three research themes: (1) waste to materials, (2) waste to energy, and (3) contaminated site remediation. R3C’s goal is to develop home-grown technologies that help to increase the recycling rate to at least 60% by 2012 and, eventually, 70% by 2030. This can result in potential savings of $70-80 million each year. In turn, the reduction in waste would help reduce the demand for new waste disposal facilities and their associated expenditures.

Equally important, waste minimization helps to conserve fi nite natural resources, expand the lifespan of landfi lls, and help Singapore move one step closer to sustainable waste

MESSAGE FROM THE CHAIR

This is the fi rst Message from the Chair to be included in our CEE

Research Bulletin and I am indeed setting somewhat of a precedent here. However, I feel it is important that I, as Chair, take every opportunity to connect with our readers who include

the larger CEE community comprising faculty, staff, students and alumni as well as colleagues, friends and visitors from outside NTU.

Singapore has been constrained in natural resources, particularly in land, water and energy. Over the years, CEE has been playing a key role in education and research to help Singapore overcome such constraints and develop sustainably. This effort has now been given greater emphasis with sustainability, environment and water issues made more urgent by the rapid urbanization seen in many Asian cities and compounded by the

www.ntu.edu.sg/cee/research/bulletin/index.asp

CIVIL ENGINEERINGCIVIL ENGINEERINGResearch

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ResearchISSN 0219-0370 No. 23 / 2010

Cont’d on Pg 2

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Civil Engineering Research • January 20102

IN FOCUS

management and zero landfi ll. A signifi cant reduction of greenhouse gases emission will also be achieved along the way.

In addition to performing cutting-edge research, the centre will also work closely with government agencies and industry in the capacity of a think tank to identify future R3 research and development directions as well as support Singapore’s EWT companies in addressing local and regional waste management issues. Additionally, it will train the manpower needed to support these EWT companies.

Vision of R3C: To become pre-eminent and industry preferred centre of competence for use-inspired residues and

resource reclamation research and translation in Singapore and the Asia and Pacifi c region.

The missions of R3C are (i) to be the focal point for R3 research and translation in the nation and region; (ii) to be the R3 resource and technology transfer centre; and (iii) to educate and train R3 professionals.

The S$25million-budgeted R3C will work with Singapore government agencies and industries starting from May 2009 and will train 32 researchers and PhD students in the next 5 years. The R3C was offi cially launched on 5 October 2009 by Mr Tan Yong Soon, Permanent Secretary, Ministry of the Environment and Water Resources and Dr Su Guaning, NTU President. The other two NEWRI research centres,

threat of impending climate change and sea level rise. CEE intends to be a leading School in addressing such issues and in 2009 adopted a new vision, that of being a “Leading School in Sustainable Built Environment”. Along with this, we have updated our mission statement and adopted the theme of urban systems as a new core theme that draws upon the diverse CEE faculty’s strength, complemented by expertise from other NTU schools. You will, therefore, fi nd in the feature article of this issue of CEE Research Bulletin the description of CEE’s research efforts in Renewable Resource Technology as well as the recent formation of a new research centre, the Residues and Resource Reclamation Centre (R3C) dedicated to research in this area. R3C is headed by Co-Directors Associate Professor Wang Jing-Yuan and Visiting Professor Rainer Stegmann from the Technical University of Hamburg.

I take pride in noting that the formation of R3C is the third of such research centres under NTU’s Nanyang Environment and Water Research Institute (NEWRI) with CEE being the key School in driving NEWRI. CEE Professor Ng Wun Jern who is also the current Tan Chin Tuan Centennial Professor in Engineering leads NEWRI as its founding Executive Director. Indeed together with the fi rst two such NEWRI centres, the Singapore Membrane Technology Centre and the DHI-NTU Research Centre on urban environmental issues and now the third centre R3C, CEE is poised to reach deeper into R&D as well as in technology creation for the environmental and water domains.

Besides environment and water, CEE is continuing with its research thrusts in urban systems covering protective, fi re and seismic resiliency, and underground space development. Furthermore, increasing efforts are

being made in the transportation, maritime and coastal domains. The curriculum is also being revised to align with recent recommendations from NTU’s Blue Ribbon Commission on curriculum and to have a deepened focus in sustainability. I hope to report these initiatives in the near future.

NTU has started a process of faculty renewal and indeed a number of highly talented assistant faculty members have joined bringing its full time faculty body to the current 58. Since January 2009, we have recruited 6 new faculty members. They are Assistant Professors Huang Yin-Nan (Structures, PhD SUNY Buffalo, 2008), Jasmine Lam (Maritime Economics, PhD University of Antwerp, 2008), Vinh Thai (Maritime Studies, PhD University of Tasmania, 2006), David Qin (Water Resources, PhD Regina University, 2008), David Wang (Transportation, PhD HKUST, 2008) and Louis Wong (Rock Mechanics, PhD MIT, 2007). We warmly welcome them to the CEE family.

On a personal front, the end of 2009 will mark my fi rst 18 months as Chair of CEE. It has been a most challenging period with the early months focused on charting, along with my faculty colleagues, the educational and research directions of CEE. Going forward we need to ensure that CEE academic goals continue to be highly relevant to the university and indeed to society at large. It is equally important that we effectively communicate these goals to our CEE community, both internally and externally, so as to receive their continued support. This is an on-going complex task and I look forward to your continued trust and support in the years ahead.

Associate Professor Edmond Lo

Message from the Chair (Cont’d from Pg 1)

Renewable Resource Technology (Cont’d from Pg 1)

Civil Engineering Research • January 2010 3

IN FOCUS

Figure 1. R3C’s Food Waste to Biogas Demonstration Plant on NTU Campus

i.e., Singapore Membrane Technology Centre (SMTC) and DHI-NTU Water and Environment Research Centre and Education Hub (DHI-NTU), were also launched at the same time as R3C. Figure 1 shows a photo of R3C’s food waste to biogas demonstration plant on NTU campus.

The Centre Director is Professor Rainer Stegmann and Co-director is Assoc Professor Wang Jing-Yuan.

BIOCEMENT - A NEW SUSTAINABLE AND ENERGY SAVING MATERIAL FOR CONSTRUCTION AND WASTE TREATMENT

Cement has been the most commonly used construction material for treating soils and wastes for civil and environmental engineering applications. The use of cement for soil improvement or waste treatment is ineffi cient in terms of both cost and energy consumption. With the development of microbial biotechnology, it has become possible to develop a new type of construction material, biocement, as an alternative to cement. Biocement is made by microorganisms at ambient temperature and thus requires much less energy to produce. It is a sustainable material as microorganisms can reproduce themselves at very low cost. The microorganisms that are suitable for making biocement are non-pathogenic and environmentally friendly. Furthermore, unlike the use of cement, soils or contaminated land can even be treated or improved without disturbing the ground or environment as microbial cells of small size can penetrate and reproduce themselves in soil. The development of biocement as a new construction material may result in an entirely new approach to geotechnical or environmental engineering problems and bring in enormous economic benefi t to construction industries. The use of biocement will also simplify some of the existing

construction processes and revolutionize the ways soils and wastes are treated. The main objectives of this proposed inter-discipline study are as follows:

1. To develop a new and economical construction material, biocement, using microbial biotechnologies.

2. To develop cost-effective and environmentally friendly micro-biological methods for using biocement to solve geotechnical or environmental engineering problems. These include constructions of roads, tunnels, land reclamation, slope stabilization, shore protection, and solid waste utilization.

3. To study the fundamental principles, microbiological and biochemical mechanisms that govern the formation of biocement by micro-organisms.

The scope of works includes mainly laboratory studies to investigate the formation of biocement as a new material and fi eld trials to study its practical applications as a new product to replace cement. A systematic screening involving different groups of heterotrophic and lithotrophic bacteria will be adopted. Suitable microorganisms and nutrients for making different types of biocements will be identifi ed. The properties of soil and waste before and after treatment using biocement will be studied.

The project intends to achieve the following two deliverables: (i) to create biocement as a new, environmentally friendly, and much less energy consuming construction material to replace cement; (ii) to develop the biocement materials into commercial products for construction and environmental industries.

So far, a critical review of the latest development in the proposed area has been carried out (Ivanov and Chu, 2008). A comparison of various mechanical, chemical and possible microbial soil stabilization methods has been made. An approach to screen the groups of bacteria for soil bio-clogging and bio-cementation has been proposed (Ivanov and Chu, 2008). By adopting this approach, the microorganisms that can be used effectively to modify or improve the properties of geomaterials may be studied and identified systematically. A preliminary study on the selection of bacteria for making biocement has been conducted in NTU and has demonstrated that several groups of microorganisms can be used for the biocementation of sandy soil:

• Enrichment culture of iron-reducing bacteria produced on iron ore particles;

• Enrichment culture of nitrifying bacteria;


IN FOCUS

• Enrichment culture of oligotrophic bacteria producing polysacchar ides wi th s t rong adherence.

The formation of microbial slime between sand grains (Figure 2(a)) or binding of sand particles by iron-reducing bacteria forming iron hydroxides and carbonates (Figure 2(b)) using renewable resources such as cellulose-containing wastes and organic compounds of wastewater treatment plants are just a few examples of biocementation mechanisms studied in NTU.

This project is undertaken by Assoc Professor Chu Jian and Dr Volodymyr Ivanov in collaboration with Professor J. Carlos Santamarina of Georgia Institute of Technology, USA and Mr John Tan Cheng Soon of JTC Corporation, Singapore.

MATERIAL PROPERTIES OF RECYCLED AGGREGATE CONCRETE FOR STRUCTURAL APPLICATIONS

In the last two decades there has been growing concern regarding the footprint of human activities on our planet. The future of mankind lies with the implementation of sustainable development. This includes the study of the impact of the use of non-renewable resources such as aggregates for concrete. For example, a number of South East Asian countries have banned their exports of aggregates to Singapore due to environmental concerns. One way to reduce the quantity of aggregate used for constructions is to recycle it. The use of Recycled Aggregate Concrete (RAC) for construction is in line with Singapore’s objective to serve as a model for sustainable development.

Singapore is experiencing fast growth in the construction industry due to mega-projects (for example, the integrated

Figure 2. Effect of Biocementation: (a) Formation of Slime bonding; (b) Cementation Effect.

(b)(a)

resort) and modernisation of its building infrastructures. These activities generate a large amount of concrete waste that needs to be disposed of properly. It is becoming increasingly attractive, at least from the environmental viewpoint, to use recycled aggregates for new construction.

This research project is a joint collaboration between Nanyang Technological University, Singapore and The University of Newcastle, Australia for a total budget of S$474,278. Its main aims are to investigate the material properties of Recycled Aggregate Concrete at room temperature, to confi rm that RAC can be used safely in building construction and that RAC satisfi es building design requirements. To achieve these goals the research project is divided into four parts:

1. Experiments to establish the material properties of RAC using different percentages of recycled aggregates

2. Experimental testing of RAC beam specimens to investigate their structural behaviour under monotonic loading

3. Documentation of the propagation of cracks in the tension zone

4. Study of the infl uence of ageing of the concrete on the mechanical properties.

Six different mixes will be investigated to establish the stress-strain relationship of normal strength concrete and to assess the infl uence of the percentage of recycled aggregates used on the performance of RAC. One set of specimens (cubes and beams) will be cast without recycled aggregate as reference specimens. The other sets will be cast using 20%, 40%, 60%, 80%, and 100% of recycled aggregate. The specimens will be tested when aged between 28 days and 2 years to assess the effect of aging on the mechanical properties of the concrete. It is expected that the optimum percentage of recycled aggregate that can be used in fresh concrete will be identifi ed, and that guidelines be established for the design of structural elements so that the RAC can be used safely in Singapore.

This project is undertaken by Assoc Professor Tan Kang Hai and Professor Didier Talamona of the University of Newcastle, Australia. Financial support for the project is from the Building Construction Authority (BCA), Singapore, the University of Newcastle, Australia and Nanyang Technological University.


IN FOCUS

Figure 3 shows a photograph of virgin versus recycled aggregates. The recycled aggregates appear more rounded.

Figure 3. Shows a photograph of virgin versus recycled aggregates. The recycled aggregates appear more rounded.


CEE VISION & MISSION

CEE VISION AND MISSION

A leading school for sustainable built

environment.

Our Vision

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

practice of civil and environmental engineering

and maritime professions.

Our Mission



STATISTICS

Publications, Patents and Research Grant

Year 2005 2006 2007 2008 2009

Journal 129 145 167 151 144papers

Conference 89 76 120 91 54papers

Patents 1 1 3 3 –

Research 5.077 9.644 9.912 13.549 36.383Grant ($mil)

Students Enrolment

Programme/ Under- MEng PhD PhD MSc MSc MSc MSc Academic Year graduate (SSP) (Civil Eng) (Env Eng) (ICM) (MS)

AY2005-06 1092 36 143 2 254 60 107 152

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 15* 171 6 106* 42* 50* 121*

*Semester 1 only

Faculty & Staff (as of 1 March 2010)

STATISTICS


BACHELOR OF ENGINEERING (CIVIL)

The Civil Engineering programme is structured on a fl exible 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 fi nal 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.

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 fi elds 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 fl exible 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 fi nal 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 fl uid 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. 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.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

BACHELOR DEGREE PROGRAMMES

UNDERGRADUATE PROGRAMMES


pursue their own fi elds 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. 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 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 fi rst 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 fl exible 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, fi nancial 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.

UNDERGRADUATE PROGRAMMES


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 post-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.

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.

BY RESEARCH

Students can choose to pursue Master of Engineering or Doctor of Philosophy degree in one of the following disciplines:

Construction Technology and Management Construction Technology Construction 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

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

Transportation Engineering Transport Modelling and Traffi c Management

GRADUATE STUDIES

GRADUATE PROGRAMMES


ACHIEVEMENTS AND COMMENDATIONS


AWARDS

Professor Henry Fan was conferred the inaugural title SAA Fellow by the Civil Aviation Authority of Singapore for distinguished contribution to civil aviation. He is one of three persons from the international aviation community honored with this title by CAAS.

EDITORSHIP

Professor Henry Fan was appointed as:

• Member of the LTA Academy Advisory Board by the Land Transport Authority.

• an Associate Editor of the International Journal of Applied Logistics. Other Editorial Board memberships: (1) IES journals and (2) Journal of Aviation Management.

• Scientifi c Advisory Board member and a Panelist of a plenary discussion session at the Mobil.TUM 2009: ITS for Larger Cities Conference, Munich, Germany, May 2009.

• Honorary Guest and served as Chairman of a technical session of the International Forum on Shipping, Ports and Airports 2009, Hong Kong SAR, May 2009.

Associate Professor Robert Tiong has been appointed as:

• Regional Editor (Outside of China: Asia) of the Journal of Chinese Management Studies published by Emerald Publishers, UK.

• Editorial Board member of the Journal of Public Works Management & Policy, University of Southern California, The Keston Institute for Public Finance and Infrastructure Policy, California, USA.

Associate Professor Tommy Wong has been appointed the Founding Editor of the Hydrological Science and Engineering book series published by Nova Science Publishers.

PATENTS

1. Fane, A.G., Phattaranawik, J. and Wong, F.S. (Patent). “Contaminated Infl ow Treatment with Membrane Distillation Bioreactor”. WO/2006/137808: PCT/SG2006/000165.

2. Phattaranawik, J., Fane, A.G. and Wong, F.S. (Patent). “Detection Apparatus and Method Utilizing Membranes and Ratio of Transmembrane Pressures”. WO/2007/129994: PCT/SG2007/000130.

3. Sun, Darren Delai; Hay Choon Teck; Khor, Swee Loong and James Leckie (W/O/2008/066497). “Water Reclamation without Biosludge Production”. PCT/SG2007/000410.

4. Sun, Darren Delai; Lee Pei Fung and Leckie, O. James (WO/2008/076082). “Microspheric TiO2 Photocatalyst”. PCT/SG2007/000436.

5. Sun, Darren Delai; Xiwang Zhang; Alan Jianghong Du; and Leckie, O. James (2008). “Membrane Made of A Nanostructured Material”. PCT/SG2008/000101

6. Tay J.-H., Tay S.T.-L., Ivanov V., Stabnikova O., Wang J.-Y. (2008). “Compositions and methods for the treatment of wastewater and other waste”. US Patent: 7,393,452. Date of grant: July 1, 2008. Date of fi ling 1 April 11, 2003.

INVITED LECTURES

Professor Henry Fan was invited to deliver a Lecture entitled ‘Challenges in Transport Planning and Congestion Management’ as well as served as a member of the Best Student Paper Award Subcommittee at the 13th International Conference of the Hong Kong Society for Transportation Studies, Hong Kong SAR, December 2008.

Professor Pan Tso-Chien was invited to deliver lectures at the following conferences:

• Invited Paper: “Effect of Long-Distance Sumatra Earthquakes on High-Rise Buildings in Singapore.” Proceedings of the 5th International Conference on Urban Earthquake Engineering, 4 to 5 March 2008, Tokyo, Japan.

• Invited Paper: “Micro-Insurance for Natural Disasters Concepts, Present and Future Outlook.” Proceedings of the 14th World Conference on Earthquake Engineering (14WCEE), 12 to 17 October 2008, Beijing, China.

• Keynote Paper: “Seismic risk of the region surrounding Singapore.” Proceedings of the 11th East Asia-Pacifi c Conference on Structural Engineering and Construction (EASEC-11), 19 to 21 November 2008, Taipei, Taiwan.



Professor Harianto Rahardjo was invited to deliver lectures at the following conferences:

• Keynote Lecture: “Mechanism of Rainfall-induced Slope Failures in Tropical Regions”. Proceedings of the First Italian Workshop on Landslides (IWL): “Rainfall-induced Landslides: Mechanisms, Monitoring Techniques and Nowcasting Models for Early Warning Systems”, Departimento Di Ingegneria Civile, Seconda Universita di Napoli, Naples, Italy, 8 to 10 June 2009.

• Invited Speaker: “Slope Stability against Rainfall and Preventive Measures.” Proceedings of BCA Seminar 2009 – Structural Inspection and Maintenance of Building Safety. Singapore, 23 October 2009.

• Principal Speaker: “Unsaturated Soil Mechanics for Solving Geotechnical Problems.” Proceedings of the 1st International Conference on Sustainable Infrastructure and Built Environment in Developing Countries (SIBE 2009). Institut Teknologi Bandung (ITB), Bandung, Indonesia, 2 to 3 November 2009.

Associate Professor Chu Jian was invited to deliver lectures at the following conferences:

• Invited Lectures: on “Use of Geofabric for Reclamation Projects” at the 2nd Conference on Geoenvironmental Engineering and Geosynthetics Technology, Changsha, China, 14 to 15 November 2008.

• State-of-the-Art Lecture: on “Construction Processes” at the 17th International Conference on Soil Mechanics and Geotechnical Engineering. Alexandria, Egypt, 5 to 9 October 2009.

• Keynote Lecture: on “Innovative Dike Construction Methods” at the International Symposium on Geotechnical Engineering, Ground Improvement & Geosynthetics for Sustainable Mitigation and Adaptation to Climate Change including Global Warming, Bangkok, Thailand, 3 to 4 December 2009.

Associate Professor Lie Seng Thjen was invited to deliver lectures at the following conferences:

• Invited Lectures: to deliver a series of fi ve lectures on the Design of Steel Structures Using BS5950: 2000 at School of Civil Engineering, Yantai University, Yantai City, China, 8 to 12 June 2009.

• Invited Lecture: Plastic collapse loads Pc of damaged square hollow section (SHS) T-, Y- and K-joints, 4 November 2009, Faculty of Engineering, National University of Singapore.

• Invited Public Lecture: the Center for Offshore Research and Engineering, CORE and Department of Civil Engineering, National University of Singapore.


RESEARCH CENTRES

Activities of Centre for Infrastructure Systems (CIS) from July 2008 to June 2009

CENTRE ACTIVITIES

Seminars, Short Courses & Symposium

1. 2nd International Symposium on Advances in Steel & Composite Structures (2ISASCS)

More than 150 practicing engineers attended the International Symposium on Advances in Steel and Composite Structures on 1 August 2008. Organised by CIS, this 2nd international symposium is a sequel to the inaugural symposium on the same theme which was held successfully back in May 2006. Following renowned academics and researchers were invited to speak in the full-day symposium:

• Professor Kim Sang-Hyo, Yonsei University, Korea

• Professor Chung Kwok-Fai, Hong Kong Polytechnic University

• Professor Chan Chun-Man, Hong Kong University of Science and Technology

• Professor Stephen Quach, University of Macau

• Professor Tao Zhong, Fuzhou University, China

• Professor Richard Liew, National University of Singapore

• Assoc Professor Chiew Sing Ping, NTU

• Assoc Professor Lee Chi King, NTU

2. The RSA International Symposium on Innovations in Structural Steel

CIS organized The Regency Steel Asia International Symposium which attracted close to 150 participants on 1 December 2008. Several international experts in structural steel were invited to share their experiences. They are:

• Dr Yoshimitsu Murahashi and Mr Masakazu Sugimoto, Nippon Steel Corporation, Japan & Singapore

• Professor Frans Bijlaard, Delft University of Technology, The Netherlands

• Professor Reidar Bjorhovde, The Bjorhovde Group, Tucson, USA

• Assoc Professor Chiew Sing-Ping, Nanyang Technological University, Singapore

• Professor Mark Bradford, The University of New South Wales, Australia

• Professor Chen Yi-Yi, Tongji University, China

• Professor Chan Siu-Lai, The Hong Kong Polytechnic University, Hong Kong

• Professor Richard Liew, National University of Singapore, Singapore

• Professor Dennis Lam, University of Leeds, United Kingdom

• Assoc Professor Ben Young, The University of Hong Kong, Hong Kong

3. Short Course on Urban Traffi c Management and Impact

CIS organized a three-day customized short course on Urban Transport Management and Impact for offi cers of the Land Transport Authority of Singapore (LTA) from 4 – 6 March 2009. It was attended by 15 offi cers from the ITS Centre at River Valley Road and from Traffi c Management Offi ce at Hampshire Road. The instructors for the course were Assoc Professor Lum Kit Meng, Assoc Professor Wong Yiik Diew from the School of CEE and Assoc Professor Tan Yan Weng from SIM University.

4. Seminar on Infrastructure Monitoring for Improved Security and Operations

A public seminar on Infrastructure Monitoring for Improved Security and Operations was held on 15 April 2009. Dr Sean A. McKenna, a Distinguished Member of the Technical Staff at Sandia National Laboratories in Albuquerque, New Mexico was the speaker of the seminar.

International Conference Participation

The 13th International Conference of the Hong Kong Society of Transportation Studies, Hong Kong SAR, 13 – 15 December 2008

Professor Henry Fan was an invited Plenary Session speaker. He presented a paper titled “Challenges in Transport Planning and Congestion Management” at the conference. He was also a member of the “Best Student Paper Award” committee.

Mobil.TUM2009, International Scientifi c Conference on Mobility and Transport -- ITS for larger Cities, Munich, Germany, 12 – 13 May 2009

Professor Henry Fan was a member of the Scientifi c Advisory Board and an invited panelist in the discussion session at the conference. He also reviewed some papers and chaired a session at the conference.


RESEARCH CENTRES

International Forum on Shipping, Ports and Airports (IFSPA) 2009, Hong Kong SAR, 24 – 27 May 2009

Professor Henry Fan was an invited Honorary Guest speaker. He reviewed some papers and chaired a session at the conference.

The 3rd International Conference on Construction Engineering and Management/ 6th International Conference on Construction Project Management (ICCEM/ICCPM 2009)

CIS was the co-organiser of the conference which was held in Jeju, South Korea from 27 – 30 May 2009.

Research Project

Research on Performance Approach to Recycled Aggregates Classifi cation

In April 2009, CIS collaborated with NUS and the BCA Academy to develop a method of classifying recycled aggregates for use in concrete by performance and to develop recycled aggregate specifi cations for appropriate concrete applications. Assoc Professor Ting Seng Kiong is the Principal Investigator for this project.

Research Project on Planning and Management of Infrastructure Systems: Studies on Mega Projects in Singapore

The objective of the research is to study the critical factors for the successful planning and management of mega projects in Singapore. The design, planning, construction, operation, maintenance and management strategies will be studied. The aim is to develop a systematic and practical lifecycle management scheme for the planning and management of future mega projects in Singapore and the region. The faculty members involved in this research are Asst Professor Chen Po-Han and Assoc Professor Robert Tiong.


RESEARCH CENTRES

Activities of DHI-NTU Centre from 2008 to 2009

RESEARCH FOCUS/RESEARCH HIGHLIGHTS

In 2009, the Centre focused on water quality management, carbon and related issues, and eco-friendly technology for water quality control. A number of research projects have been initiated, and they are aimed at improving the clarity of water in the coastal areas of Singapore, and to apply new technologies such as TiO2 membrane in water treatment.

An international symposium was convened in June. The symposium served as a forum for scientists to exchange experience on carbon credit, fi nancing and marketing, including carbon issues in wastewater treatment industry. On energy effi ciency for wastewater treatment plants, our researchers are also conducting a worldwide survey and collaborate with other wastewater treatment plant operators/planners to solicit information and scan for innovative technologies in wastewater treatment. The Centre is also working towards developing new eco-friendly technologies to improve water quality, and these technologies should be of low investment cost and relatively maintenance free , for example, constructed wetland, green roof, fl oating vegetation mat, etc.

The Centre is also focusing on coastal hydrodynamics. By using SPH (Smoothed Particle Hydrodynamics, a mesh free numerical method), the researchers have modelled propagation of storm surges and tidal bore running up a river, and have subsequently extended the development to include debris fl ow in coastal fl ooding processes. The Lagrangian nature of SPH allows the modeling of wave breaking, splash-up, and the subsequent fl uid turbulence. To make the computation more effi cient, we are developing a parallel version of the computer codes as well. We have simulated 6-DOF motion of boats and structures interacting with ocean waves. A typical case is modeling a fl ap motion in a wave generator project.

RESEARCH OUTPUT

Research Publications • Adi Kurniawan, Zhenhua Huang, Chunrong Liu, Jing

Li, Xikun Wang, Zhiyong Hao and Soon Keat Tan, 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, Honolulu, Hawaii, USA, 31 May - 5 June 2009.

• Chunrong Liu, Zhenhua Huang, Adi Kurniawan, Xikun Wang, Nguyen Anh Tuan, Zhiyong Hao and Soon Keat Tan, 2009. “Responses of Deep Draft Floating Barges to Surface Waves in Shallow Water”. ISOPE, Osaka, Japan, 21-26 June 2009.

• Yushi Wu and Yee-Meng Chiew, 2009. “Experimental Study on 3-Dimensional Scour at Submarine Pipelines”. 33rd IAHR 2009 Congress – Water Engineering for a Sustainable Environment, Vancouver, Canada. Paper ID: 10371, 9-14 August 2009.

• Dongqing Zhang, Richard M. Gersberg and Soon Keat Tan, 2009. “Constructed Wetland in China”. Ecological Engineering, Vol. 35, pp. 1367-1378.

• Jing Li, Soon Keat Tan, Zhenhua Huang and Adi Kurniawan, 2009. “Wave Amplifi cation and Air-Gap Response under a Multi-Column Platform”. 6th International Conference on Coastal Dynamics, Tokyo, Japan. Paper No. 381507, 7-11 September 2009.

• Chunrong Liu, Zhenhua Huang and Soon Keat Tan, 2009. “Nonlinear Scattering of Non-Breaking Waves By a Submerged Horizontal Plate: Experiments and Simulations”. Ocean Engineering (Available online at Science Direct), September 2009.

• Nguyen Quang Chien and Soon Keat Tan, 2009. “Simulation of Storm Surge and Inundation in the United States due to Hurricanes using AnuGA Modelling Tool”. The 3rd International Conference on Estuaries and Coasts (ICEC 2009), 14-16 September 2009.

• Dongqing Zhang, Richard M. Gersberg, Christian Wilhelm and Manfred Voigt, 2009. “Decentralized Water Management: Rainwater Harvesting and Greywater Reuse in an Urban Area of Beijing, China”. Urban Water Journal, Vol. 6, No. 5, pp. 375-385.

• Hoang-Ha Nguyen and Lloyd H.C. Chua, 2009. “Modelling the Physical Properties of Fine Suspended Sediments”. The 5th International Conference on Asian Pacifi c Coasts (APAC2009), 13-16 October 2009, Vol 1, pp 337-342.

• Vu Thu Trang and Soon Keat Tan, 2009. “A Review of the Current State-of-the-arts on the Application of Silt Screens as Sediment Control Equipment in Open Water”. The 5th International Conference on Asian Pacifi c Coasts (APAC2009), 13-16 October 2009, Vol. 2, pp. 60-66.

• Nguyen Quang Chien and Soon Keat Tan, 2009. “Quadtree Mesh for Combined Hydrodynamic and Water Quality Modelling”. The 5th International Conference on Asian Pacifi c Coasts (APAC2009), 13-16 October 2009, Vol. 2, pp. 246-251.


RESEARCH CENTRES

• Nguyen Ba Tuyen and Ho Viet Hung, 2009. “An Experimental Study on Wave Reduction Effi ciency of Mangrove Forests”. The 5th International Conference on Asian Pacifi c Coasts (APAC2009), 13-16 October 2009, Vol. 4, pp. 336-343.

Collaborations and Partnerships

• Housing and Development Board (HDB): DHI-NTU Centre conducted training course on “Design of Marine Coastal Structure”.

• Global Water Research Coalition (GWRC) and PUB: ongoing research project on energy effi ciency recovery in domestic wastewater treatment plant.

• JTC Corporation and Menard Geosystems Singapore Pte Ltd: ongoing research project of feasibility study on the application of soft materials for reclamation fi ll using vacuum consolidation.

• Environment and Water Industry Development Council (EWI): on two projects: High Performance Computational Simulations of Multi-Scale and Multiphase Flows in Membrane Filtration and MBR Process Modeling and Optimization: Case Study of Ulu Pandan Water Reclamation Plant with Future Scale-Up Considerations:

- Building and Construction Authority (BCA): DHI-NTU conducted training course on “Marine – Coastal Structure”;

- National Parks Board: collaboration on two projects - Improving Water Clarity within large Bodies of Water in coastal Areas of Singapore; Green Roof and Bioinfiltration in Nanyang Lake.

AWARDS AND RECOGNITIONS • 5 EWT PhD scholarships were awarded: Mr Ng JiaWei,

Mr Wang YinJie and Ms Liu Lei. They are working on projects on developing TiO2 membrane for water treatment and water and energy production. Ms Le Song Ha works on urban hydrology and Ms Vu Thu Trang conducts research on sediment transport studies in the coastal environment.

• 4 DHI-NTU scholarship holders enrolled in the PhD programme in August 2009.

EVENTS, CONFERENCES & SYMPOSIA

• International Symposium on Global Carbon Finance and Market (24–26 June): the symposium provided a platform for industry professionals, government offi cials and multilateral agency representatives to present the latest developments on carbon emission reduction project as well as risk transfer, fi nancing and management mechanisms.

• NTU & SJTU Inter-Research Group Workshop Discussion on Hydrodynamics, Sedimentation and Water Quality in the Estuary and Coastal Environment (13 October): the workshop provided an opportunity to explore further R&D collaboration between the Centre and Shanghai Jiaotong University in hydrodynamics, sedimentation and water quality in the estuary and coastal environment.

• The 5th International Conference on Asian Pacifi c Coasts (13–16 October): This conference was attended by 250 delegates from more than 20 countries. The conference succeeded in promoting technological progress and activities, knowledge exchange and cooperation.

ANOTHER MATTER THAT THE CENTRE WOULD LIKE TO HIGHLIGHT

DHI-NTU Centre was launched together with SMTC and R3C as member centres of NEWRI on 5 October 2009.


RESEARCH CENTRES

Activities of Maritime Research Centre (MRC) from 2008 to 2009

Maritime Research Centre (MRC) has established itself successfully as the bridge between the maritime community and the research community in NTU. MRC has strengthened her link among the Maritime and Port Authority of Singapore (MPA), Economic Development Board (EDB), and International Enterprise (IE) Singapore. MRC has also established new and strong working relationship with American Bureau of Shipping (ABS), Sembawang Corporation group of companies, Singapore Technologies (ST), Keppel and offshore engineering companies such as Acergy.

The Centre is active in outreach activities and has established contact with more than 40 companies. The Centre also works closely with a local university (NUS – CORE), A*STAR Institutions (IHPC and SIMTECH), polytechnics and particularly R&D centres such as the Centre of Innovation at Ngee Ann Polytechnic, the Singapore Maritime Academy located at Singapore Polytechnic.

The Centre has developed and established the following R&D projects during the period of 2004 – 2008:

* 2008: No. of projects: ~ 6 Project costs: ~ $1.2M Workshop and seminars: ~ 4

Projects in Progress (9)

1. Developing a Maritime Piracy Detection System Using Microwave Radar Sensor. Saman S. Abeysekera and Toh Hock Lye (EEE), and {ST Electronics}

2. Experimental Study of the Turbulent Wake Flow Generated by Two Side-by-Side Circular Cylinders. Zhou Tongmin {UWA, Australia}, Cheng Nian Sheng (CEE) and {ABS}

3. Modelling of Wave Run-up, Air-gap and Hydrodynamic Loads of Semisubmersible Structures. Huang Zhenhua (CEE), {DTG} and {ABS}

4. Structural Health Monitoring System for Shipyard and Offshore Heavy Cranes. Ma Guowei (CEE)

5. Remote Stress Monitoring System (RSMS) for Safe Storage of CNG Tank Cylinders under High Pressure. Lie Seng Tjhen (CEE)

6. Fracture Capacity Investigation of Pipeline Girth Welds During Installation and Operation. Xiao Zhongmin (MAE)

7. Real-Time Quality Monitoring of Arc Welding Processes. Ling Shih Fu (MAE)

8. Novel Bending Stiffeners for Easy Transportation and Installation in Flexible Risers of Offshore Floating Structures. Low Ying Min (CEE)

9. Development of Active Oxygen Processing System for Freight Decontamination. Tan Soon Keat and Dai Ying (CEE)

Support for Postgraduate Students

1. Supported 9 visiting students on short-term attachment

2. Supported 3 local s tudents on short - term employment

3. Supported 2 Vietnamese MSc students on part-time employment in 2008

Support for Academic Staff Exchange Programme

1. Shanghai Maritime University – Professors Zhang Weiguo, Zhao Ning, Chang Daofang, Xi Qing, Yang Dagang

2. Dalian University of Technology – Professor Teng Bin

3. Hong Kong UST - Professor Liu Hongwei

4. Shanghai Jiao Tong University – Professor Zhang Jingxin

Support for Student Assistants in Part-Time Duties

1. MSc student Nguyen Manh Tuan participated in the research projects “Active oxygen as an alternative oil dispersant and oil spill combat agent” and “Development of active oxygen processing system for freight decontamination” in 2008.


RESEARCH CENTRES

2. MSc student Nguyen Xuan Lan participated in the research project “Active oxygen as an alternative oil dispersant and oil spill combat agent” in 2008.

3. PhD student Ding Li is helping with the preparation of the “International Symposium on Global Carbon Finance and Market” from 2009 to the present.

4. MSc student Zhao Qian is helping with the preparation of the “International Symposium on Global Carbon Finance and Market” from 2009 to the present.

5. PhD student Li Yuanyuan helped with the preparation of the “5th International Conference on Asian and Pacifi c Coasts” in 2009.

6. Undergraduate student Zhao Kuifeng helped with the preparation of the “5th International Conference on Asian and Pacifi c Coasts” in 2009.

PUBLICATIONS

1. Hao, Z., Zhou, T., Chua, L.P. and Yu, S.C.M., 2008. “Approximations to energy and temperature dissipation rates in the far fi eld of a cylinder wake“. Experimental Thermal and Fluid Science, Vol. 32, pp. 791-799.

2. Hao, Z., Zhou, T., Zhou, Y. and Mi, J., 2008. “Dependence on Reynolds number of the inertial range scaling of energy dissipation rate and enstrophy in a cylinder wake”. Experiments in Fluids, Vol. 44, pp. 279-289.

3. Cheng, N.S., Hao, Z. and Tan, S.K., 2008. “Comparison of quadratic and power law for nonlinear fl ow through porous media”. Experimental Thermal and Fluid Science, Vol. 32, pp. 1538-1547.

4. Kusnowidjaja Megawati, Zhenhua Huang, Felicia Shaw, Wu, T.R., Yunong Lin, Tan Soon Keat and Pan, T.C., 2008. “Tsunami hazard from the subduction megathrust of the South China Sea: Part I - Source characterisation and the resulting tsunami”. Special issue on South China Sea tsunami, Journal of Asian Earth Sciences (in press).

5. Zhenhua Huang, Wu, T.R., Tan Soon Keat, Kusnowidjaja Megawati, Felicia Shaw, Liu Xiaozhen and Pan, T.C., 2008. “Tsunami hazard from the subduction megathrust of the South China Sea: Part II - Hydrodynamic modelling and possible impact on Singapore”. Special issue on South China Sea tsunami, Journal of Asian Earth Sciences (in press).

6. Wang, X.K. and Tan, S.K., 2008. “Comparison of fl ow patterns in the near wake of a circular cylinder and a square cylinder placed near a plane wall”. Ocean Engineering, Vol. 35, pp. 458-472.

7. Wang, X.K. and Tan, S.K., 2008. “Near-wake fl ow characteristics of a circular cylinder close to a wall”. Journal of Fluids and Structures, Vol. 24, No. 5, pp. 605-627.

8. Hao, Z., Cheng, N.S. and Tan, S.K., 2008. “Investigation of inertial effect in simplifi ed porous media fl ow”. Proceedings of the 16th Congress of Asia and Pacifi c Division of International Association of Hydraulic Engineering and Research (16th IAHR-APD), Nanjing, China, 20-23 October 2008.

9. Wang, X.K., Hao, Z. and Tan, S.K., 2008. “Visualization of the vortical structures behind a normal plate near a plane wall”. Proceedings of the 13th International Symposium on Flow Visualization (ISFV13), Nice, France, July 1-4, 2008.

10. Shuqing Yang and Soon Keat Tan, 2008. “Flow resistance model of an alluvial channel”. Journal of Hydraulic Engineering, ASCE, July, Vol. 134, No. 7, pp. 937–947.

11. Wang, Z.Q., Tan, S.K. and Cheng, N.S., 2008. “Design of headland control, beach protection scheme”. Proceedings of the 16th Congress of Asia and Pacifi c Division of International Association of Hydraulic Engineering and Research (16th IAHR-APD), Nanjing, China, 20-23 October.

12. Hao, Z., Cheng, N.S. and Tan, S.K., 2008. “Investigation of inertial effect in simplifi ed porous media fl ow”. Proceedings of the 16th Congress of Asia and Pacifi c Division of International Association of Hydraulic Engineering and Research (16th IAHR-APD), Nanjing, China, 20-23 October.

13. Wang, Z.Q., Tan, S.K., Cheng, N.S. and Goh, K.W., 2008. “A simple relationship for crenulate-shaped bay in static equilibrium”. Coastal Engineering, Vol. 55, No. 1, pp. 73-78.

14. Wang, Z.Q. and Cheng, N.S., 2008. “Infl uence of secondary fl ows on distribution of suspended sediment concentration”. Journal of Hydraulic Research, Vol. 46, No. 4, pp. 548-552.

15. Qu Shuying, Zhang Baofeng, Zhang Guodong and Shao Yongbo, 2008. “Experimental study of the stress concentration factor for completely overlapped K-joints under axial load and bending load”. Mechanical Science and Technology for Aerospace Engineering, Vol. 27, No. 7, pp. 909-913.

16. Lie, S.T. and Zhang, B.F., 2008. “Failure assessment of cracked circular hollow section (CHS) welded joints using BS7910: 2005”. The 12th International Symposium on Tubular Structures, Shanghai, China, pp. 367-373.

17. Huang, Z.H. and Liu, C.R., 2008. “A linear theory for wave scattering by double slotted barrier in weak steady currents”. Chinese Ocean Engineering, Vol. 22, No. 2, pp. 215-226.

18. Liu, C.R., Deng, L.Y., Huang, Z.H. and Huhe, A.D., 2008. “An experimental study of sediment incipience under complex flows”. Transactions of Tianjin University, Vol. 14, pp. 300-306.


RESEARCH CENTRES

19. Liu, C.R., Huang, Z.H. and Tan, S.K., 2008. “Study of nonlinear wave scattering by a submerged step in a fully nonlinear DBIEM numerical wave tank”. The Eighth Pacifi c Asia Offshore Mechanics Symposium, Bangkok, Thailand, 10-13 November.

20. S.-K. Tan, J.-Y. Wang, T. Nakajima, W.-C. Chang, T. Oki, J. Dahe, P.V. Tan, X. Wang, D. Yang, M. Iyngararasan, S. Devotta, A.K. Gosain, M.R. Rahman, P.H. Viet, M. Rupakheti and J. Kim, 2008. “Impacts of atmospheric brown clouds on water”. Report submitted to United Nations Environment Programme (UNEP), Regional Resource Centre for Asia and the Pacifi c (RRC.AP), webpage: http://www.rrcap.unep.org/abc/impact/water.cfm.

21. Lie, S.T., Yang, Z.M. and Gho, W.M., 2008. “Infl uence of residual stresses on the failure assessment diagrams of a cracked square hollow sections T-joint”. Civil Engineering Research Bulletin, School of Civil & Environmental Engineering, Nanyang Technological University. Singapore, pp. 67-70.

22. 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 - 5June.

23. Jing Li, Soon Keat Tan, Zhenhua Huang and Adi Kurniawan, 2009. “Wave amplifi cation and air-gap response under a multi-column platform”. Conference of Coastal Dynamics 2009, Tokyo, Japan, 7-11 September.

24. Huang, Z.H., Liu, C.R., Kurniawan, A., Tan, S.K. and Nah, E., 2009. “Responses of a free-fl oating rectangular caisson to regular waves: Comparisons of measurements with time-domain and frequency-domain simulations”. The 5th International Conference on Asian and Pacifi c Coasts, Singapore, 14-16 October.

25. Wang, X.K. and Tan, S.K., 2009. “Experimental study of fl ow 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.

26. Wang, X.K., Hao, Z. and Tan, S.K., 2009. “Wavelet analysis of fl ow images obtained by PIV (Particle Image Velocimetry)”. Civil Engineering Research, Vol. 22, pp. 43-46.

27. Kurniawan, A. and Ma, G.W., 2009. “Optimization of ballast plan in launch jacket load-out”. Structural and Multidisciplinary Optimization, Vol. 38, pp. 267-288.

28. 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.

29. 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.

30. 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.

31. Lie, S.T. and Yang, Z.M., 2009. “Static ultimate strength of cracked square hollow section Y-joint”. Civil Engineering Research, Vol. 22, pp. 94-96.

WORKSHOPS/SEMINARS

1. Public Seminar on “Introduction to Current Research on Hydrology and Water Resources in Tsinghua University”, 24 January 2008, NTU.

2. Public Seminar on SCIC Meeting to Introduce DHI-NTU Centre, 30 January 2008, NTU.

3. International Symposium on Fatigue and Fracture of Steel Structures, 4 December 2007, NTU.

4. Community Involvement: Special Interest Lecture at Nanyang Girls’ High School, 15 April 2008, Nanyang Girls’ High School.

5. Public Seminar on “Overview of Tsunami Session of AOGS 2008”, 3 July 2008, NTU.

6. Public Seminar on “Engineering Aspects of Hydrodynamic Modelling with Examples from Simulation of Tsunamis and Cooling Water Emissions”. 2 October 2008, NTU.

7. Public Seminar on “Regional Environmental Simulator (RES) and Its Applications”, 6 February 2009, NTU.

8. Training Course: “In-house Training Course for HDB - Land Reclamation and Coastal Protection Work - Design and Analysis”, February - March 2009, One-North, Singapore.

9. Public Seminar on “Important Role of R&D in Offshore EPCI Contract”, 27 May 2009, NTU.

10. Public Seminar on “Panama Canal Third-lane Locks and Access Channel Expansion Program”, 8 June 2009, NTU.

11. 5th International Conference on Asian and Pacifi c Coasts (APAC2009), 13-16 October 2009, NTU.


RESEARCH CENTRES

Activities of Protective Technology Research Centre (PTRC) from July 2008 to November 2009

OUTREACH PROGRAMMES

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. The public seminars, short courses, workshops and forums organized by PTRC in the reporting period are as follows:-

Public Seminars

1. Structural Aspects of Severe Fires in Tunnels

Professor Chung Kwok Fai, Professor, The Hong Kong Polytechnic University; Deputy Director, Research Centre for Advanced Technology in Structural Engineering; Vice President, The Hong Kong Institute of Steel Construction, 6 August 2008

Professor Chung’s seminar touched on recent studies on explosive concrete spalling in reinforced concrete structures. The conventional fi re-resisting construction in reinforced concrete members under standard fi re tests was reviewed. It was considered insuffi cient to merely specify concrete cover with suffi cient thickness when designing structures that will withstand a fi re attack. In general, concrete spalling always occurs in both building and tunnel structures, particularly under severe fi res, i.e. fi res with extremely high heat-release rates. Recent disastrous fi res in tunnels reported in several European countries reveal that multi-layered explosive concrete spalling can be extensive in tunnels where there are severe fi res. Hence, both localised damage in concrete linings and overall structural failure of tunnel sections should be prevented in order to facilitate safe evacuation and effective rescue of tunnel users, as well as quick reinstatement of tunnel structures after a fi re event.

2. Recent Developments on Rock Joint Roughness, Rock Joint, Rock Mass Strength and Deformability

Professor Pinnaduwa Kulatilake, University of Arizona, Professor of Geological / Geotechnical Engineering, 5 August 2009

The seminar covered the following topics:a) Natural rock joint roughness quantification

through fractal techniques

b) A new rock mass strength criterion for biaxial loading conditions

c) Estimation of rock mass strength and deformability in 3D for a 30m cube at a depth of 485m at Äspö Hard Rock Laboratory, Sweden

d) Development of a new peak shear strength criterion for anisotropic rock joints

e) Models for normal fracture deformation under compressive loading

3. The Art of Structural Design

Er. Patrick Choy Wai Meng, Senior Executive Engineer, Building Engineering Division, Bridges & Structural Steel Dept, Building & Construction Authority, 25 September 2009

The seminar highlighted the following:

Structural design involves a process and commences with conceptualising the structural arrangement with clear load path in determining a good frame design system. The next stage is structural analysis which investigates the effects resulting from actions imposed upon or anticipated throughout the intended life of structures. The seminar also touched on the connection design based on realistic assumptions of distribution of internal forces.

Ease of fabrication, handling, transport and erection are essential during the design process so that maximum structural effi ciency and economy are attained. Good engineering practice also takes into consideration such needs as future maintenance, fi nal demolition, recycling and reuse of materials.

4. Decision Aids for Tunnelling

Mr Jean-Paul Dudt, Rock Mechanics Laboratory,Swiss Federal Institute of Technology, Lausanne (LMR-EPFL), Switzerland, 5 – 9 October 2009

Mr Jean-Paul Dudt graduated from the «Ecole Nationale Supérieure des Mines de Paris» in 1974. He

Recent Developments on Rock Joint Roughness, Rock Joint, Rock Mass Strength and Deformability,

Professor Pinnaduwa Kulatilake


RESEARCH CENTRES

works as a senior researcher and teacher at the Rock Mechanics Laboratory of the Swiss Federal Institute of Technology, Lausanne, Switzerland (LMR-EPFL). His area of specialization is in numerical modeling and in probabilistic approaches. He has worked closely with Professor Herbert H. Einstein since 1990 in the development of the “Decision Aids for Tunneling” and has used the model in several projects, such as the Gothard and Lötschberg base tunnels in Switzerland.

5. Impact on Thin-Walled Spheres & a Series of Seminars on Discontinuous Deformation Analysis

Professor Xu Tong-Xi, Hong Kong University of Science and Technology & UTRE Researchers (Xinmei AN, Lifeng FAN, Wei WU, Lei HE, Liqing JIAO and Youjun NING), 20 November 2009

The Series of Seminars on Discontinuous Deformation Analysis includes the following:

a) A comparison between the XFEM and the NMM for discontinuity modeling by Xinmei AN

b) An equivalent medium model for p-wave propagation through rock mass with parallel joints by Lifeng FAN

c) Discrete modeling of fluid flow in fractured sedimentary rocks by Wei WU

d) The development on 3D numerical manifold method by Lei HE

e) The support design for slope and tunnel engineering based on block theory by Liqing JIAO

f) Development of the NMM for rock failure simulation by Youjun NING

Short Courses

1. Rock Mechanics and Tunnelling

Professor Zhao Jian, Chair Professor and Director, Rock Mechanics Laboratory (LMR), EPFL, Switzerland, 09 & 10 February 2009

In recent years, with continuing economic and social development in Singapore, urban underground space has been developed rapidly to overcome the limitation of land space. It is important for regulators, planners, developers, engineers and contractors to have a more comprehensive understanding of rock mechanics and rock engineering. Professor Zhao Jian delivered a systematic short course and shared his expertise and research experience in this area. Geotechnical and geological characteristics of Singapore were also presented and discussed.

2. Blast Response of Structures

Dr Dan Pope, Principal Scientist, United Kingdom Government;

Dr Andrew Tyas, Senior Lecturer, Department of Civil and Structural Engineering, University of Sheffi eld, UK, 23-24 March 2009

The course was aimed at graduate and professional engineers who have an interest in developing their understanding of both the effects of blast loading on structures, and the analytical and design methods available to consultant engineers. Day 1 of the course focused on helping the audience develop understanding of key features of blast loading and effects as well as presented some necessary background theory. Day 2 included simple analytical techniques for predicting structural response and an introduction to current numerical modelling techniques. Dr Pope and Dr Tyas concluded the course by presenting several illustrative examples of the use of different analyses and design techniques for a variety of scenarios.

Workshops

1. A General Introduction and Discussion on Singapore Geology and Bedrocks

Professor Zhao Jian, Chair Professor and Director, Rock Mechanics Laboratory (LMR), EPFL, Switzerland, 22 January 2009

A General Introduction and Discussion on Singapore Geology and Bedrocks, Professor Zhao Jian

2. Underground Technology and Rock Engineering (UTRE) Workshop 2009, Novotel Clarke Quay Singapore, 23-24 November 2009

The Guest of Honour at the opening session was Mr Quek Tong Boon, Chief Defence Scientist and Chief Research & Technology Offi cer from the Ministry of Defence, Singapore. Jointly organised by the Defence Science and Technology Agency (DSTA) and NTU, the workshop provided an excellent opportunity for the exchange and sharing of knowledge about underground technology and rock engineering as well as an opportunity for the UTRE international network of collaborators to renew their ties. Over 100 participants from all over the world attended this workshop, with renowned speakers from the UTRE team, as well as noted researchers from overseas sharing their leading-edge research.


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ASEAN Forum on Natural Catastrophe Exposures in ASEAN

Visit by Delegates from the Defense Threat Reduction Agency (DTRA), USA

Underground Technology and Rock Engineering (UTRE) Workshop 2009

Forums

1. Micro-insurance Round Table Forum, Nanyang Executive Centre, 3-4 April 2009

PTRC, together with Risk Management Solutions, Inc., California, USA, organized the 3rd Micro-insurance Round Table (MiRT) Forum on 3rd and 4th April, 2009. The Singapore-NTU Alliance for Micro-Insurance was set up after the Forum. The alliance is made up of individuals and organization partners who have the knowledge of and interest in furthering the concept of using micro-insurance to assist those who need help after major man-made or natural disasters.

2. ASEAN Forum on Natural Catastrophe Exposures in ASEAN – Understanding, Preparing, Protecting, Hotel Grand Park City Hall Singapore, 16-17 July 2009

The Guest of Honour was Dr Syamsul Maarif, Head of the Indonesian National Disaster Management Agency (BNPB). Mr Ng Nam Sin, Executive Director, Financial Centre Development Department, Monetary Authority of Singapore, gave the special guest address. The objective of the Forum was to provide a platform for academics and university students, insurance industry professionals, industry regulators and representatives from the relevant government agencies, as well as other interested private and public sector organisations from the ASEAN region to share and exchange information on the latest scientifi c research and developments relating to natural disasters (including earthquakes, fl oods and typhoons). Thus public awareness and understanding of the risks and potential impact of natural disasters would be raised. Another objective was to initiate action required for effective catastrophe risk management of natural disasters.

INTERNATIONAL AND LOCAL VISITORS

PTRC received a total of 11 delegations with a total of about 150 visitors during the reporting period. Some of the visitors whom we received include the following:-

Visit by Delegates from the Defense Threat Reduction Agency (DTRA), USA, 21 July 2008

* The delegation was led by Mr G. Pete Nanos, Associate Director for Research and Development, DTRA, USA

Visit by Delegates from the Swedish Defence Research Agency (FOI), 17 October 2008

* The delegation was led by Ms Madelene Sandstrom, Director General, Swedish Defence Research Agency (FOI)


RESEARCH CENTRES

Visit by Delegates from the Swedish Defence Research Agency (FOI)

Visit by Delegates from US Dept of Energy

Visit by Participants from the Forum on Natural Catastrophe Exposures in ASEAN

Visit by Offi ce of Chief Science and Technology Offi cer (OCSTO), Ministry of Home Affairs

Visit by participants of the Ministry of Home Affairs (MHA) Basic Building Security Course

Visit by Delegates from US Dept of Energy, Infrastructure Security and Energy Restoration Division, Offi ce of Electricity Delivery and Energy Reliability (OE), 5 February 2009

* The delegation was led by Mr William Bryan, Deputy Assistant Secretary, US Dept of Energy

Visit by Participants from the Forum on Natural Catastrophe Exposures in ASEAN, 16 July 2009

* About 70 participants from the Forum on Natural Catastrophe Exposures in ASEAN visited the Protective Engineering Laboratory as part of the Forum programme.

Visit by Offi ce of Chief Science and Technology Offi cer (OCSTO), Ministry of Home Affairs, 1 October 2009

* The delegation was led by Dr Lee Fook Kay, Chief Science and Technology Officer (CSTO), Ministry of Home Affairs

Visit by participants of the Ministry of Home Affairs (MHA) Basic Building Security Course

Assoc Professor Tan Kang Hai, Deputy Director of PTRC, and Mr Chelladurai Subasanran, Laboratory Manager, hosted the visit by the participants of the MHA Basic Building Security Course (BBSC) which was held on 26 March 2009 and 20 August 2009. The participants of the 4th and 5th run of the BBSC visited the Protective Engineering and Construction Laboratories.


RESEARCH CENTRES

No Project Title Principal Investigator (s) External Collaborating Funds (S$) Partners

1 Dynamic Properties of Assoc Prof Leong Eng Choon 164,800 Defence Science Singapore Soils and Technology Agency (DSTA)

2 Development of Analytical Assoc Prof Li Bing 1,260,000 DSTA Tools for Progressive Collapse Assoc Prof Tan Kang Hai due to Terrorist Bombing

3 Underground Technology and Assoc Prof Ma Guowei 3,850,000 DSTA Rock Engineering (UTRE) Assoc Prof Zhao Zhiye Programme, Phase II Asst Prof Yang Yaowen Assoc Prof Tor Yam Khoon Assoc Prof Tan Kang Hai Assoc Prof Tiong Lee Kong, Robert Assoc Goh Teck Chee, Anthony Assoc Prof Chu Jian

4 Effects of Catenary and Assoc Prof Tan Kang Hai 732,930 DSTA Membrane Actions on the Assoc Prof Lee Chi King Collapse Mechanisms of RC Buildings – Behaviors of Structural Elements

5 The Infl uence of Floor Slabs Assoc Prof Li Bing 523,600 DSTA and Transverse Beams on the Behavior of RC Beam – Column Joint under Loss of Column Scenarios

No Project Title Principal Investigator (s) External Collaborating Funds (S$) Partners

1 Underground Technology and Assoc Prof Ma Guowei 2,398,000 DSTA Rock Engineering (UTRE) Assoc Prof Zhao Zhiye Programme, Phase I Asst Prof Yang Yaowen Assoc Prof Tor Yam Khoon Assoc Prof Tan Kang Hai Assoc Prof Tiong Lee Kong, Robert

2 Study on Debris Modelling Prof Fan Sau Cheong 764,500 DSTA and Prediction II

3 Integrated Explosion Modelling Assoc Prof Ma Guowei 398,750 DSTA

4 Research and Development of Asst Prof Kusnowidjaja Megawati 447,352 National Operational Tsunami Prediction Environment and Assessment System Agency (NEA)

On-going Projects

The table below shows the current projects.

Completed Projects

The table below shows the completed projects from July 2008 to November 2009.


ENVIRONMENTAL AND WATER RESOURCES ENGINEERING

INTRODUCTION

Water clarity in the natural marine environment around Singapore in recent years is generally low, caused chiefl y by the high loads of suspended solids (SS) and sedimentation in the water column. The visibility has been reduced from 10m in the 1960s[1] to less than 2m currently[2]. This problem is the result of various coastal developments and human activities, such as land reclamation, shipping, recreation and tourism, dumping of solid waste, and land-based wastes [3]. The increase of sediment loads not only poses a threat to marine biodiversity, but has undesirable effects on desalination processes, the cooling capacity of offshore and coastal facilities, as well as aquaculture. Therefore, this increase needs to be addressed.

In order to explore the possible solutions to the problem of increased sediment and its damage to the marine environment, DHI-NTU Center has engaged in a collaborative research project with NParks. This research project identifi es corals (phylum Cnidaria) as the key organism, since coral reef environments are known to be much more sensitive to the increase of sediment loadings. This study reviews the impact of sediments on corals as well as scan for viable technologies to remove sediments in the marine environment.

IMPACT OF SUSPENDED SOLIDS

Impact Mechanisms

Coral reefs are impacted by sediment through two major mechanisms, namely, suspension in the water column and settling/deposition. The former increases water turbidity and block the sunlight, and the latter causes excessive deposition of sediment on coral reefs.

Turbidity refers to the amount of dissolved and particulate matter suspended in the water column. The presence of

A REVIEW: IMPACT OF SUSPENDED SOLIDS ON CORALS AND

TREATMENT TECHNOLOGIESDai Ying, NTU ([email protected])Dong Xin, NTU ([email protected])

Le Tuyet Minh, NTU ([email protected]) Zhang Dongqing, NTU ([email protected])

Cheng Nian Sheng, NTU ([email protected])Tan Soon Keat, NTU ([email protected])Nigel Goh, NParks ([email protected])

Jacqueline Lau, NParks ([email protected])

turbidity leads to light attenuation. Since the growth of corals depends on symbiotic photosynthesis process of algae, corals become highly sensitive to increased turbidity and associated reduction of light penetration[4]. Aside from the reduction of photosynthesis, increased turbidity also affects the reproduction and recruitment of corals by reducing larval survival and coral polyp activity.

Sedimentation refers to deposition of sedimentary material onto coral reefs and the substrata. It is considered a stress to coral because prolonged accumulation of sediments on coral tissue leads to necrosis and partial mortality. As a result, corals must invest extra energy in sediment rejections by reducing photosynthetic nutrition, increasing ciliary and polyp activity, increasing respiration, and producing mucous[5]. If sedimentation exceeds the corals’ ability of removal, it may lead to expulsion of zooxanthellae and may cause bleaching. If sediment accumulated on tissues cannot be removed, necrosis and partial mortality occurs[6]. The reproduction and recruitment processes are affected by sedimentation too, especially during larvae settlement and juvenile survival. In high sedimentation cases, larval settlement is restricted to downward-facing surfaces with little sunlight, and this negatively affects larvae survival.

(b) Mucous production and sediment removal

Figure 1. Sediment and the impact on corals

(a) Turbidity generated from marine works



Singapore Situation

Surveys of live coral coverage in Singapore were conducted for the fi rst time in 1980s. Because of economic growth, population increase, coastal development and modifi cation, the visibility of the water column has been reduced signifi cantly. As a result, corals generally do not exist beyond 6m water depth, and coral diversity has been declining in many locations.

Figure 3. Status of coral reefs in Singapore and SEA (Wilkinson, 2008)

Figure 2. Relationship of sediment stress and its impact to corals (Gilmour et al., 2006)

In 2008, the Global Coral Reef Management Network (GCRMN)[8] presented the latest coral reef conditions in Singapore. Compared with the 1990s, coral reefs in “very good” condition have disappeared. 70% of coral reefs fall into the “poor” category where less than 25% space is covered by live corals. According to this report, the current

reef area in Singapore is less than 5km2, almost 10% of which are under immediate threat of loss and 25% are under long-term threat of loss. Compared to reef area 100 years ago, about 60% of the reefs have been lost.

TREATMENT TECHNOLOGIES

Several experiments adopting different technologies for SS removal in marine water have been reported. These technologies range from fi ltration to air-fl oatation, coagulation, and biological removal. The results of these experiments are reviewed below.

Filtration systems

An experiment was conducted at Kasaoka Bay in Japan in 2002[9], in which a double step fi ltration was used for SS removal.

Rapid and slow fi ltration techniques were applied to achieve the sediment removal target. The difference between the two stages was determined by the rate of dC/dt and dC’/dt, where C and C’ are the pollutant concentrations before and after treatment, respectively. Hazardous and nutrient contents were reduced to the allowable level during the “rapid removal” stage, which took place close to the seashore. Mechanical treatment system was introduced at this stage to reduce the level of pollutants. In the “slow removal” stage, the concentration of pollutants was quite stable. Therefore, a fi ltering technique was adopted with the intention of reducing impacts on the environment. This method provided high effi ciency of particle removal, but the energy cost was high.

Figure 4. Concept of the 2-step fi ltration system (Masaharu et al., 2006)

Threshold of Critical Impacts

Reported studies[7] suggest that the load and duration of turbidity and sedimentation stress, and their relationship have adverse impacts on corals. The results show that long-term stress of turbidity and sedimentation injure the coral and the injury easily leads to mortality. The curves in Figure 2 apply to “tolerant” species, which means more severe impacts are expected on sensitive species. Also it should be noted that the curve is for sediment with “average” grain size. For fi ne grain sizes and sediment with high organic content, the same load and duration would result in more severe consequences.



Coagulation – Flocculation

Coagulation & fl occulation processes involve the use of chemicals to fl occulate the suspended solids, and letting the fl ocs settle by gravity. In 1985, an experiment was carried out at the University of Jerusalem, using seawater with turbidity of 1.0–17.5 NTU, TSS of 7.6–35.4mg/l. The typical particle size was in the range of 4-300 um. The treated water then served as the infl ow of reverse osmosis (RO) membrane system. The authors reported reduced level of sediment after the treatment. However, some organic matters attached to the surface of particles negatively impacted the effects of fl occulation. Generally, coagulants and fl occulants were allowed to be used in drinking water. But the toxicity of alum is still under debate, which stopped this method from full-scale application in the marine environment. Organic polymers, such as Chitosan, have surfaced recently as a potential candidate to replace inorganic polymers. Studies have been conducted to demonstrate and prove the effi ciency of chitosan as a biofl occulant, especially in aquaculture environment and brackish waters[11].

Dissolved air fl oatation

Johnson and his research group in Dalhousie University conducted a lab-scale experiment, combining fl occulation with air fl oatation processes[12].

The experiment was carried out in a column 200cm long and with a diameter of 10cm. Aerobic conditions were maintained. Bacterial and particle counts were performed using microscopy. Dissolved air was introduced into the tank under pressure through nozzle (diameter less than 200 μm). Air pressure was reduced to atmospheric pressure gradually as the bubbles rose from the bottom to the surface of the water. Dissolved air turned into bubbles to which colloidal and particles adhered. At the air–water interface, the particles were aggregated and collected in jet drops. For easier aggregation of the particles, fl occulants could be added to the water before being introduced into the dissolved air fl otation tank.

The study suggested that the initial particle size was a critical factor affecting the process because of its impact on effi ciency of bubble collection. The method is, as a result, applicable for particle size ranging from 0.2-1.2 μm.

Biological Removal with Bacteria

Biological removal of suspended solids using bacteria can be applied to biodegradable suspended solids. Eco-Biological Block (EBB), produced by a Japanese company, is one example.

EBB is a porous block media that contains effective bacteria (Bacillius subtilis natto), which doubles in population every 30min. The bacteria are aerobic and are viable in both air and water. When the block is dipped into the water, the bacteria will start propagating and disperse through the water with the fl ow of the current. Bio-oxidation and nitrifi cation take place to oxidise organic matter as well as to change ammonium and nitrite to nitrate. Because of the reproduction of bacteria, the block can remain effective for a substantially long period. The outcome of this process is the reduction of colour, turbidity and organic matters in water. However, the feasibility of these bio-products in large water body still needs further investigation.

DISCUSSION

The review fi nds that the most popular method applied to suspended solid removal in marine water is fi ltration. Coagulation and flocculation may also result in high removal effi ciency, but it is diffi cult to carry out full scale application due to potential risks of the chemicals. Both the mechanical system and biological-based system could achieve high removal effi ciency that ranges from 70–90%. However, selection of the method is strongly dependent on the environment (current, tide, wave) and sediment on site, the culture/activities of the surrounding areas, and also the geotechnical conditions at the site. It is possible, and recommended, that a complementary selection of mechanical and biological methods be used simultaneously.

REFERENCES

[1] Chua CYY and Chou LM (1992). Coral Reef Conservation in Singapore: a Case Study for costal Area Management. In: Chou LM and Wilkinson CR (ed.) 3rd ASEAN Science & Technology Week Conference Proceedings Vol. 6, 437-446.

[2] Chou LM (2002). Singapore Reefs Report. Report of the Global Coral Reef Monitoring Network (GCRMN) Regional Workshop for the East Asian Seas, pp. 85-95.

[3] Dikou A and van Woesik R (2006). Survival under Chronic Stress from Sediment Load: Spatial Patterns of hard Coral Communities in the southern Islands of Singapore. Marine Pollution Bulletin, (52), pp. 1340-1354.

[4] Falkowski PG et al (1984). Light and the Bioenergetics of a Symbiotic Coral. Bioscience 34, pp. 705-709.

Figure 5. Dissolved air fl oatation system (Johnson et al., 1986)



[5] Stafford-Smith MG (1993). Sediment-rejection Effi ciency of 22 Species of Australian Scleractinian Corals. Marine Biology, (115), pp. 229-243.

[6] Gilmour JP (2002). Acute Sedimentation Causes Size-specifi c Mortality and Asexual Budding in the Mushroom Coral, Fungia Fungites. Marine and Freshwater Research, (53), pp. 805-812

[7] Gilmour JP et al (2006). Early Warning Indicators of Change in the Condition of Corals and Coral Communities in Response to Key Anthropogenic Stressors in the Pilbara. Australian Institute of Marine Science, Technical Report.

[8] Wilkinson C (2008). Status of Coral Reefs of the World: 2008. Global Coral Reef Monitoring Network and Reef and Rainforest Research Center, Australia.

[9] Masaharu F et al (2006). Development of Filtration System for Removal of Contaminated Suspended Solids in an Enclosed Sea Area. Journal of ASTM International, 3(6), pp. 320-329.

[10] Adin A and Klein-Bany C (1986). Pretreatment of Sea Water by Flocculation and Settling for Particulars Removal. Desalination, 58, pp. 227-241.

[11] Renault F, Sancey B, Badot M, Crini G (2009). Chitosan for Coagulation/ Flocculation Processes – An Eco-Friendly Approach. European Polymer Journal, 45, pp. 1337-1348

[12] Johnson BD, Zhou XL, Wangersky PJ (1986). Surface Coagulation in Sea Water. Netherlands Journal of Sea Research, 20(2/3), pp. 201-210.



INTRODUCTION

A large number of bridge failures due to abutment scour which occurred during fl ood events have been recorded and this is of great concern to engineers and scientists (Yu and Lim 2002). This paper presents a semi-empirical model to predict the maximum scour depth around a bankline abutment, which is a unique case of abutment scour where the structure spans the entire width of the fl oodplain in a 2-stage channel. Figure 1 shows a defi nition sketch of a bankline abutment, and it can be seen that the localized scour occurs in the main channel. The model is based on the premise that at equilibrium scouring conditions, the bed shear stress in the scour hole would be equal to the critical Shields stress on the sloping bed. Once the bed shear is known, the bed profi le can be determined in accordance with the balance of forces exerted on the sediment particles. Finally, the fl ow depth, inclusive of the scour depth, may be calculated for a given fl ow discharge.

Figure 1. Defi nition sketch of scouring around a bankline abutment.

SEMI-EMPIRICAL ANALYSIS

Prior to the construction of the abutment, the total discharge, Q, in the two stage channel can be written as

Q = Bf hfp Ufp + Bm hmp Ump (1)

where the subscript p refers to the original conditions before the abutment is built, Bf and Bm = fl oodplain and

main channel width, respectively; hfp and Ufp = fl ow depth and mean velocity in the fl oodplain, respectively; hmp and Ump = fl ow depth and mean velocity in the main channel, respectively. As shown in Figure 1, the fl ow area above the lateral cross section at the deepest scour location may be divided into three sub-fl ow sections. The fi rst is in the scour hole with a width = XL, measured from the abutment tip to the maximum scour point (hsm). The second is XR wide, between the maximum scour location to point j on the original bed level. The third refers to the un-scoured portion, from j to the sidewall of the main channel. At the equilibrium clear-water scour conditions, the bed shear stress at any location on the scour hole would be equal to the critical value for sediment initiation on sloping surface, while on the un-scoured bed it would be lower or equal to the critical Shields shear parameter on fl at bed (Yu and Lim, 2002), which can be expressed as

τcd = θc (ρs – ρ)gd* (2)

where τcd = critical shear stress, θc = Shields parameter, ρs = sediment density, ρ = fl uid density, g = gravitational acceleration, and d* = representative sediment size (= d95 for sediment mixture, d95 is the sediment size of which 95% is fi ner, and for uniform sediment, the median sediment size, d50 is used). Experimental results show that the lateral scoured bed profi les can be described by a parabolic function (see Figure 1),

y = kx2 (3) where the origin of the curve is at the deepest scouring location, y = height above the deepest point, and k = constant related to the sediment size and fl ow conditions. Referring to Figure 1, suppose the bed slope at point

j is = β, and assuming β to be equal to tan α,

where α = the angle of repose of the sediment, then differentiating (3) and substituting x = XR at point j yields

k = (4)

Substituting the coordinates of point j, (XR, hsm) into (3), we get hsm = kX (5)

A STUDY OF BANKLINE ABUTMENT SCOUR

Lim Siow Yong ([email protected])Yu Guoliang ([email protected])

2XR

β

R2

dydx



Using (4) and (5), k = β2/4hsm, and substituting into (3), the lateral bed profi le of the scour hole can be written as

y = x2 (6)

Based on the results of the present experiments, it was found that XL ≈ XR/3. Therefore, using (3), (4) and (5), the width of the scour hole can be expressed as

XL + XR = (7)

Referring to Figure 1, the fl ow depth, h in the scour hole can be written as

(8)

where .

For fl ow in a wide alluvial channel, the depth-averaged velocity at any arbitrary lateral location in the scour hole may be approximated by the power-law

U = Cθmhn (9)

and (10)

where U = depth-averaged velocity, u* = shear velocity, h = normal fl ow depth, ks = equivalent sand roughness, (=2d50), m and n = coeffi cient and exponent, respectively.

It is known that the fl ow will be diverted towards the main channel as it approaches the abutment tip and fl ow separation occurs at the lee side of the abutment (Yu and Lim, 2002)). As a result, the yaw of the fl ow affects the fl ow conveyance and a correction factor, CQ is needed, which is assumed to be proportional to the ratio of the unblocked main channel discharge to total discharge, i.e.

(11)

where CR = flow correction coefficient and M* =

discharge contraction ratio = . Hence, the

discharge through the scour hole section, Qss may be calculated as follows:

Qss = CQ Cθmhn ∫ hdx (12)

Substituting h from (8) and CQ from (11) into (12), it can be shown that

Qss = Cθ m (hmp + hsm)1 + n

(13)

QUmp hmp Bm

The discharge in the un-scoured section, Qus, can be calculated as

Qus = Ump hmp Bm – (14)

From continuity, the total fl ow discharge through the abutment section is,

Q = Qss + Qus (15)

The maximum scour depth, hsm is implicit in (15) and can be easily obtained by solving equations (10), (18), (19) and (20) using an Excel spread sheet.

Verifi cation and Sample Calculation

We conducted 12 sets of experiments in a 19 m, 1.6 m wide and 0.75 m high two-stage channel in the Hydraulics Laboratory. Two types of sand were used: a sediment mixture with d50 = 1.14 mm and a geometric sediment gradation, σg = 3.6, and uniform sand with d50 = 0.93 mm and σg = 1.17. In addition, we also used 3 bankline abutment data points from Cardoso and Bettess (1999) to verify the model.

A sample calculation for Run 1 from the present study is shown here and this run has the following fl ow conditions: Q = 0.0425 m3/s, d50 = 0.93 mm, ρs = 2640 kg/m3, α = 33° and β = 0.65. θc = 0.031, hmp = 0.209m, hfp = 0.059 m, Ump = 0.249 m/s and Ufp = 0.195 m/s. We used m = 7.66 and n = 1/6, i.e., equivalent to the Manning-Strickler formula, and ks = 2d50 = 1.86 mm. Hence, the coeffi cient Cθ = 0.0615 using (10). The fl ow ratio, M* = 0.731. Using an Excel spreadsheet, the maximum scour depth can be calculated by trial and error using (18), (19) and (20). We found CR = 1.12 giving the best estimate for all the data tested here.

For Run 1, we start the calculation by assuming a value of hsm. Suppose the fi rst estimate is hsm = 0.083m. Then use (18) and (19), Qss = 0.0290 m3/s and Qus = 0.0135 m3/s, respectively. Next, use (20), and Q = 0.0425 m3/s, which is equal to the measured Q. Hence, continuity is conserved and this hsm would be the best estimate for this run, and this agrees well with the measured value of hsm = 0.079m. The iteration will be repeated, i.e., using a new estimate of hsm, if Q from (20) does not equal the measured Q value. Figure 2 shows a comparison between the measured and calculated hsm and it can be seen that the agreement is good for most of the data, including those from Cardoso and Bettess (1999).

CONCLUSIONS

A semi-empirical model has been proposed to predict the maximum equilibrium scour depth for bankline abutment in 2-stage channels. The approach is promising and future

4hsm

β2

8hsm 3β

Ch = hmp + hsm

14hsm

β2

Cθ = θC – 1 gd* [ ρsρ

1/2 n

ks

1 [

CQ α = CRM* QUmp hmp Bm

XR

-XL

CR M* hsm

β

[ 8hsm 3β [



works would include applying the model to abutment scour in rectangular channels, setback abutments on fl oodplain and abutments which extend into the main channel of 2-stage channels.

REFERENCES

[1] Cardoso, A.H. and Bettess, R. (1999). “Effects of time channel geometry on scour at bridge abutments.” J. Hydr. Engrg., ASCE, 125(4), 388-399.

[2] Yu, G. and Lim, S.Y. (2002). “Flow and scouring in main channel due to abutments.” 1st Int. Conf. on Scour of Foundations, Texas, USA, 17-20 Nov., 785-794.

Figure 2. Comparison of calculated and experimental scour depths



INTRODUCTION

Membrane technology is an emerging technology and has become increasingly important in our life. After nearly 50 years of rapid advancement, membrane-based processes today enjoy numerous industrial applications. These cover water and dairy purifi cation, sea and brackish water desalination, wastewater reclamation, food and beverage production, gas and vapor separation, energy conversion and storage, air pollution control and hazardous industrial waste treatment, hemodialysis, protein and microorganism separation, etc.

DEVELOPMENT OF NOVEL MEMBRANES FOR WATER AND

ENVIRONMENTAL APPLICATIONSWang Rong ([email protected])

Tang Chuyang ([email protected]) Tony Fane ([email protected])

ABSTRACT: The Singapore Membrane Technology Centre (SMTC) at Nanyang Technological University is currently striving to develop novel membranes for water and environmental applications. The main projects related to novel membrane development at SMTC are highlighted. The success of these projects will have direct benefi ts for the water industry with regard to cost effective water reuse, reclamation, desalination, and/or energy recovery.

Figure 1. Custom designed membrane fabrication facilities in the SMTC lab.

The effi ciency of existing membrane technology is being continuously improved and the scope of the applications of membrane technology is still expanding, stimulated by the development of novel or improved membrane materials and membranes with better chemical, thermal and mechanical properties or better permeability and selectivity characteristics, as well as by the decrease of capital and operation costs. The Singapore Membrane Technology Centre (SMTC) at Nanyang Technological University is currently striving to develop novel membranes for water

and environmental applications. Figure 1 shows custom designed membrane fabrication facilities in the SMTC lab. The main projects related to novel membrane development are highlighted below. All of the projects described are based in CEE, with collaboration from other specialists at NTU and overseas.

MAIN PROJECTS

Forward osmosis (FO) hollow fi bre membranes for water reuse and reclamation

Forward osmosis (FO) is an osmotically-driven membrane process which utilizes the osmotic pressure difference across a selectively permeable membrane as the driving force for the transport of water through the membrane. Compared with pressure-driven membrane processes, the FO process exhibits unparalleled advantages - it operates at low or no hydraulic pressures, it has nearly complete rejection of a wide range of contaminants, and it may have lower membrane fouling propensity. As a result, FO has been intensively studied recently for a range of applications, which include wastewater treatment, water purifi cation and seawater desalination.

However, there exist a number of technical barriers that impede FO’s industrial applications. One of the major challenges to be overcome is the lack of an ideal membrane that can produce a high fl ux comparable to commercial RO membranes. Currently, with the fi nancial support from the Environmental and Water Industry Development Council (EWI) of Singapore, the SMTC team is developing novel FO membranes, as shown in Figure 2. Preliminary results show that in-house made FO hollow fi bre membranes possess promising performance in terms of water permeability and salt rejection. Further characterization and evaluation against available commercial FO fl at sheet membranes are showing good progress.



Figure 2. In-house made FO hollow fi bre membranes at SMTC.

Aquaporin based biomimetic membranes for water reuse and desalination

Nature has developed a most effi cient way for water transport across an osmotic pressure gradient via aquaporin (AQP) proteins. The aquaporins or water channel proteins, typically bound in phospholipid cellular membranes, are highly permeable to water but highly retentive to solutes. This makes water delivery across a cell possible at an energy cost closer to the thermodynamic minimum. This project is based on the concept that an artifi cial membrane may be developed to mimic the natural cellular membranes by incorporating aquaporins into an ultrathin amphiphilic block copolymer film. With a robust and carefully engineered microporous support structure, the composite aquaporin biomimetic membrane can be applied for water reuse and seawater desalination at low cost. A conceptual AQP biomimetic membrane is shown schematically in Figure 3. Compared to the conventional reverse osmosis membranes, the proposed biomimetic membrane promises important advantages including potentially better selectivity,

improved water permeability, reduced energy consumption, and improved product water quality. The SMTC is working on this project with a multidisciplinary NTU team and in collaboration with DHI-NTU Centre and Aquaporin A/S (Denmark). This newly funded project by EWI commenced in June 2009 and aims to develop mechanically and thermodynamically stable aquaporin biomimetic membranes suitable for cost effective water reuse and desalination. The tasks of the project include: (1) aquaporin selection, expression, purification and characterization; (2) preparation and optimization of support structure; (3) incorporation of aquaporins to form a rejection fi lm and optimizing its interface with the support structure; (4) membrane characterization and performance/stability testing; (5) molecular dynamic simulation and process modeling; and (6) evaluation of scale up issues.

Highly hydrophobic membranes for brine processing by membrane distillation crystallization

Desalination of seawater has been extensively used to solve the problems of water supply world-wide. While enjoying the benefits brought by the advanced water treatment technique, we are facing the challenges imposed by seawater desalination, as discharge of brine concentrate to the ocean has a potentially signifi cant impact on the environment such as marine life.

Conventional brine discharge methods are limited by many factors such as cost, energy consumption, and/or adverse ecological effects. The ideal brine treatment process would help to maximise water production, provide an option for solids recovery, have modest energy demand and impose minimal impact on the environment. Membrane Distillation (MD) of the feed stream coupled with crystallization to allow removal of solids and enhance water production has the potential to satisfy these challenging specifi cations. This integration is referred to as membrane distillation crystallization (MDC). SMTC has recently been awarded funding for MDC development by the EWI.

The MD operation is realized by means of a micro-porous hydrophobic membrane which acts as a physical barrier separating a warm aqueous solution from a cooler chamber, and through which only water vapor molecules

Figure 3. A conceptual AQP biomimetic membrane.



are transported. However, since the membranes currently available for the MD process were fabricated initially for other processes such as microfi ltration, they can suffer some drawbacks. These include high cost or a pore size distribution with some larger pore sizes, which can cause membrane wetting and performance deterioration.

The SMTC is approaching membrane development in two ways: (i) collaborating with our commercial partner, Siemens Water Technology; and (ii) using in-house developed membranes. Siemens Water Technology is developing a range of hydrophobic fl uoropolymer hollow fi bres that are suitable for MD. In-house we are fabricating highly hydrophobic mircoporous membranes with controlled pore structure. In addition, we aim to tailor membrane surface chemistry and pore structure through different surface modifi cation techniques to minimize membrane wetting.

CO2 separation membranes for biogas upgrading

Biogas, which is produced in an anaerobic bioreactor treating sewage, is mainly composed of methane (~60%) and carbon dioxide (~40% CO2) with other trace gases. Removal of CO2 from biogas can improve the heating value of biogas, and make biogas utilization more effective for various applications such as power generation, vehicle fuel or as compressed gas.

However, there are relatively few processes in the world that can achieve economically viable biomethane commercialization. The problem with all the existing technologies is their cost, and the most expensive part of the treatment is the removal of carbon dioxide. The conventional methods require signifi cant capital investment, huge size equipment, or intensive energy consumption. Therefore, in most small and medium-sized anaerobic municipal treatment plants, biogas produced tends to be fl ared. Anaerobic sewage treatment is not considered as an energy producer due to economic reasons.

The membrane contactor, which operates at low pressure, is expected to have the potential to overcome the disadvantages of conventional equipment when combined with acid gas absorption processes. However, no commercial CO2 removal process using membrane contactor technology is presently in operation. The main technical barrier is membrane wetting, which results in poor performance of the system.

With recently announced support from the EWI we seek development of two novel membranes – a highly hydrophobic microporous hollow fi bre membrane and a CO2-selective facilitated transport non-porous membrane used as contactors for CO2 absorption, as aqueous absorbent solutions tend to be repelled at the pore openings of hollow fi bre membranes made of hydrophobic materials. Utilization of nonporous membranes can also provide solutions to prevent membrane wetting. In addition, this type of membrane is based on the reversible reaction of the targeted gas (CO2) with the reactive carrier (amine), which is contained inside the membrane to facilitate the transportation of CO2. Professor Winston Ho from the Ohio State University is the international collaborator in the project.

SUMMARY

The success of the ongoing novel membrane development projects in SMTC will have direct benefits for the water industry with regard to cost effective water reuse, reclamation, desalination, and/or energy recovery. It will also provide strategic benefi ts for Singapore by meeting the national goals of sustainability through water reclamation. Through R&D and manpower training, these projects will provide skilled professionals for the Singapore water industry.



INTRODUCTION

The wake fl ow behaviors behind two side-by-side circular cylinders have been reported in many studies. For the gap ratio T/D = 1.2 – 2.0 (where T is the spacing between the cylinder axes, and D is diameter of cylindergap fl ow defl ection concerning the double wake has been investigated by many researchers ([1]-[6]). However, there are still many reports about the failures to observe the so-called bistable behavior in experiments. Peschard & Le Gal [4] failed to observe the bistable behavior in their low-Reynolds-number water-tunnel experiments. They suggested that it may be caused by the turbulent perturbations in the incoming fl ow. Sumner et al. [6] suggested that the bistable characteristic is not caused by misalignment of the cylinders or other extraneous infl uences, but is an intrinsic property of the fl ow. Moreover, they put foward three possible reasons why the bistable behavior was not observed in the water tunnel experiments: namely, a small degree of misalignment of the cylinders, experimental effects such as aspect ratios and blockage, and experimenting in different fl uid mediums - wind tunnel or water tunnel. The understanding of the coupled wakes appears incomplete and the mechanism for the biased nature of the asymmetric fl ow regime is not well-understood.

In this study, dynamic characteristics of fl ow past two circular cylinders of different diameters arranged in a side-by-side confi guration were investigated using the technique of particle image velocimetry (PIV) in a re-circulating open channel. The center-to-center pitch ratio T/D and the Reynolds number Re were 1.2 and 1200, respectively. The biased fl ow behavior was studied based on the instantaneous and average patterns of velocity, vorticity and Reynolds stress contours.

EXPERIMENTAL STUDY ON BIASED FLOW BEHAVIOR BEHIND

TWO SIDE-BY-SIDE CIRCULAR CYLINDERS WITH UNEQUAL DIAMETERS

Gao Yangyang ([email protected])Tan Soon Keat ([email protected]) Wang Xikun ([email protected])

Hao Zhiyong ([email protected])

EXPERIMENT SET-UP

Experiments were conducted in a 6m long, re-circulating open channel at Maritime Research Center, Nanyang Technological University. The test section has a rectangular cross-section of 0.3m x 0.4m (W x H). A simple schematic sketch of the experimental setup is shown in Figure 1. The coordinates x, y and z denote the streamwise, transverse, and spanwise directions, respectively. Two steel cylinders with different diameters of 12mm and 8mm were vertically mounted in the y – z plane (x = 0), perpendicular to the oncoming fl ow in the x direction. To ensure smooth entrance of the fl ow into the test section, the stilling chamber upstream of the contraction was fi tted with perforated steel plates and honeycomb-screen. The streamwise turbulence intensity in the free stream was about 2%.

A PIV system (Lavision model) was used to measure the fl ow fi eld. Based on a compromise between the requirements of recording a large fi eld of view and resolving detailed fl ow structures, the viewing area was chosen to be about 125mm x 95mm. A Quantel System double cavity Nd: YAG laser (power~120Mj per pulse, duration~5ns) was used to illuminate the fl ow fi eld. The particle images were recorded using a 12-bit charge-coupled device (CCD) camera, which has a resolution of 1.6K x 1.2K pixels and a frame rate of 15Hz. Considerable care was taken to ensure the high quality of the images. The particle displacement was calculated using the cross correlation algorithm with the standard Gaussian sub-pixel fi t structured as an iterative multi-grid method. The processing procedure included two passes, starting with a grid size of 64 x 64 pixels, stepping down to 32 x 32 pixels overlapping by 50%. Therefore, the spatial resolution for this experimental set-up was about 1.25mm x 1.25mm. For each experiment condition, a set of 1050 frames of the instantaneous fl ow fi elds were acquired at the frequency of 15Hz (i.e. 70s recordings), in order to achieve a reasonable converge of the turbulent quantities.



Figure 1. Schematic of the experimental system.

The PIV recording parameters, including the particle image size (about 3 pixels) and seeding densities (about 10~30 particles per mm2), were optimized to ensure valid detection of the correlation peak. Hollow glass beads with diameter of 10 ~ 15μm and specifi c density of 1.05-1.15 were seeded in the fl ow as the tracer particles. The time delay between double pulses was set at 500μs, corresponding to the fl ow velocity u = 0.1m/s. The blockage ratio was about 6.67%, suggesting that the blockage effect due to the side walls was negligible.

RESULTS AND DISCUSSION

The patterns of time-averaged velocity, streamlines, vorticityand normalized Reynolds stress for two side-by-

Figure 2. Time-averaged velocity vector (a), streamline (b), vorticity contours (c) and normalized Reynolds stress fi eld (d) for two side-by-side cylinders with unequal diameters in the steady cross-fl ow. Solid lines represent positive, dashed lines represent negative. Incremental value of vorticity is 0.2. Reynold stress contour interval is 0.005°

side circular cylinders at gap ratio T/d=1.2 and Reynolds number Re=1200 are presented in Figure 2. Solid lines and dashed lines represent positive and negative values, respectively. Incremental value of the vorticity is 0.2. Contour interval for the normalized Reynolds stress is 0.005. It can be seen from these fi gures that there is a “blank out” region behind the cylinders due to the shadow cast by the stainless-steel cylinders in the laser light sheet.

Biased fl ow is observed in this study. It can be seen from Figure 2 that the gap fl ow is defl ected to one side. A narrow near-wake and a wide near-wake occur downstream of the smaller-diameter upper cylinder and the larger-diameter lower cylinder, respectively. This observation is in agreement with previous studies which found that the fl ow past two side-by-side cylinders is biased (or asymmetric) for intermediate cylinder spacing 1.2 < T/D < 2.0. The biased fl ow patterns can be elucidated by the time-averaged velocity vector fi eld, streamlines topologies and vorticity contours, as shown in Figure 2. Figure 2(b) shows that at this fl ow condition, only one foci point in the streamline patterns can be seen behind the large cylinder, and there is no foci point behind the upper, small-diameter cylinder.

Time-averaged vorticity contours ω* are shown in Figures 2(c). It can be seen distinctly that there is a wide wake behind the large cylinder and a narrow wake behind the small one. At fl ow condition, it can be seen from Figure



2(c) that the two rows of vortices in the narrow wake are different both in vorticity strength and size. The peak value for the outer (negative) vortices ω* in the narrow wake is about 3.8, higher than that of 3.0 for the inner (positive) vortices. Moreover, the size of the outer wake is larger than that of the inner wake in the narrow wake generated behind the small cylinder. In the wide wake region, the peak value of the normalized vorticity ω* (positive and negative) is identical to that in narrow wake, and the size of the outer wake is also larger than that of the inner one. At about x/D = 3, the negative vortices behind the two cylinders start to merge into one. This may be due to the strong interactions between the two rows of vortices in the wide and narrow wakes.

CONCLUSIONS

The characteristics of fl ow past two circular cylinders with unequal diameters at gap ratio T/d=1.2 and Reynolds number Re=1200 were investigated using PIV technique. Average patterns of velocity, streamline topologies, vorticity and Reynolds stress contours were presented, indicating that the phenomenon of asymmetric biased fl ow occurred under this fl ow condition. Further investigation will be conducted to reveal the mechanism associated with this phenomenon.

REFERENCES

[1] Williamson, C. H. K., 1985. “Evolution of a single wake behind a pair of bluff bodies”. Journal of Fluid Mechanics, Vol. 159, pp. 1-18.

[2] Zdravkovich, M. M., 1968. “Smoke observation of the wake of a group of three cylinders in various arrangements”. Journal of Fluid Mechanics, Vol. 32, pp. 339-351.

[3] Kim, H. J. and Durbin, P. A., 1988. “Investigation of the fl ow between a pair of circular cylinders in the fl opping regime”. Journal of Fluid Mechanics, Vol. 196, pp. 431- 448.

[4] Peschard, I. and Le Gal, P., 1996. “Coupled wakes of cylinders”. Physical Review Letters, Vol. 77, pp. 3122-3125.

[5] Le Gal, P., Peschard I., Chauve, M. P. and Takeda, Y., 1996. Collective behavior of wakes downstream of row of cylinders”. Phys. Fluids, Vol. 8, pp. 2097-2106.

[6] Sumner, D., Wong, S.S.T., Price, S.J. and Paisoussis, M.P., 1999. “Flow behavior of side-by-side circular cylinders in steady cross-fl ow”. Journal of Fluids and Structures, Vol. 13, pp. 309-338.

[7] Akilli, H., Akar, A, Karakus, C., 2004. “Flow characteristics of circular cylinders arranged side-by-side in shallow water”. Flow Measurement and Instrumentation, Vol. 15, pp. 187-197.



INTRODUCTION

The microbial fuel cell (MFC) is a fast developing technology for waste degradation and renewable energy. MFC directly unleashes chemical energy bound in waste biomass as electrical power, and thus attains higher energy conversion effi ciency. One major hurdle to be overcome for the MFC technique is to enhance its power density, which is currently well below 1 mW/cm2. A number of factors limit the power density of fuel cells, but for MFCs, the sluggish electron transfer (ET) between microbes and electrodes is an outstanding issue.

Several studies have demonstrated that, redox mediators immobilized at the anode surface can effectively enhance the current delivered by microorganisms (Adachi et al. 2008; Lowy et al. 2006; Park and Zeikus 2003; Tanisho et al. 1989). The mediators are highly electroactive chemicals. When used at the MFC anode, they can be steadily reduced by bacterial cell surface redox elements, while the kinetics between anode and mediator is very fast. In addition, the organic dyes, a common class of redox mediators, possess abundant –NH2 groups. It has been shown that functionalization of the electrode with –NH2 groups resulted in better and faster formation of biofi lms (Cheng and Logan 2007).

Thereafter, immobilization of organic dyes onto the anode might be a promising approach to enhance MFC performance. Previously described methods for such immobilization included physical adsorption (Lowy et al. 2006) and covalent binding (Adachi et al. 2008). Simple adsorption suffers from a quick desorption of dye molecules (Lowy and Tender 2008), while covalent binding involves chemical syntheses which are diffi cult to handle for engineering researchers. The carbon nanotube (CNT) is an intensively studied nanomaterial. The surface

EXPLORING DYE-CNT NANOCOMPOSITE AS ANODE MATERIAL

FOR MICROBIAL FUEL CELLSLuo Peng ([email protected])

Shi-Jie You ([email protected])Jing-Yuan Wang ([email protected])

ABSTRACT: The study investigated the feasibility to optimize microbial fuel cell (MFC) anode process with dye-carbon nanotube (CNT) adduct. The dye-CNT nanocomposite was fabricated by soaking CNT modifi ed electrode in aquatic dye solutions. Due to π-π stacking between dye molecules and CNT surface, the nanocomposite showed excellent stability. When stored in de-ionized water overnight, no desorption of dyes was observed. Used as electrode modifi er, this nanocomposite signifi cantly enhanced catalytic current generated by Shewanella oneidensis. The methylene blue-CNT adduct outperformed toluidine blue-CNT and neutral red-CNT in term of current generation. The dyes adsorbed on CNTs might improved electron transfer rate from bacteria to electrode, it could also promoted formation of S. oneidensis biofi lm, both could enhance biofuel cell performance. But further study is needed to justify which mechanism is dominant.

of CNT consists of benzene-like structures, and dyes are aromatic hydrocarbons, a π-π stacking between CNT and dye maintains a stable dye-CNT nanocomposite (Yan et al. 2005). This feature affords an opportunity to develop a facile approach to immobilize dyes. Furthermore, heterogeneous ET kinetics of dyes are often reported as promoted with the presence of CNTs (Yan et al. 2005).

In this study, we explore the effect of mediators immobilized on CNTs towards biological current generation.

MATERIALS & METHOD

A 3 mm diameter glassy carbon electrode (GCE) was used as a working electrode. Prior to use, the GCE was polished sequentially with 1 μm and 50 nm alumina paste, followed by ultrasonic cleaning in de-ionized water for 5 minutes. Multi-walled CNTs (MWNTs, 95% in purity, 8 nm diameter) were purchased from Chengdu Organic Chemicals Co. LTD. (Chengdu, China). 1 mg of MWNTs was dispersed in 1 ml of 2% (w/w) sodium dodecyl sulfate (SDS) solution with the aid of an ultrasonic homogenizer. 4 μl of the obtained dispersion was dropped to a glassy carbon plate and allowed to dry in air. To remove the SDS adsorbed on CNTs, the GCE coated with MWNTs were soaked in acetone for 2 hours (Puchades et al. 1999). The obtained electrode was designated as MWNT/GCE.

The organic dyes investigated in our experiments included methylene blue (MB), toluidine blue (TB) and neutral red (NR). To further functionalize the electrode with mediators (dyes), the MWNT/GCE was soaked in a dye solution for 3 hours and then thoroughly rinsed to remove non-adsorbed materials. The obtained electrodes were referred as



MB/MWNT/GCE, TB/MWNT/GCE and NR/MWNT/GCE respectively.

For electrochemical tests, a platinum plate counter electrode and a saturated calomel reference electrode (SCE) were employed. A 15 ml capacity plastic cylinder mounted with a silicone elastomer cap served as an electrochemical cell. All electrochemical tests were conducted at room temperature of 25°C (±1°C). For cyclic voltammetries, the scan rate was 5 mV/s.

Shewanella oneidensis was used as a biocatalyst. S. oneidensis was cultivated in a shaking fl ask (150 rpm) from frozen stock, until optical density (OD600) reached 2.00. 200 μl of bacterial culture was inoculated into 9.8 ml of fresh Luria-Bertani (LB) broth (Difco Laboratories, MI, USA) prepared in a 50 mM sodium phosphate buffer (pH 7.4).

RESULTS & DISCUSSION

The stability of the dye-CNT nanocomposite was monitored by a daily registration of cyclic voltammograms (CV) of GCE modifi ed with a nanocomposite. Compared with the freshly prepared electrode, the MB/MWNT/GCE stored in DI water for 24 hours showed quite a similar voltammogram (Figure 1). The anodic peak current was virtually unchanged overnight, while the cathodic peak current remained at over 95% of the original value. This observation indicated that the MB largely remained bound with MWNT; thus the nanocomposite showed excellent stability. Other dyes demonstrated such stability with MWNT as well (data not shown).

Figure 1. CV of MB/MWNT/GCE in 0.1 M sodium phosphate buffer (pH = 7.0).

To evaluate whether the dye-CNT adducts could enhance current generation under MFC conditions, the functionalized electrodes were subjected to chronoamperometries with the presence of fuel and biocatalysts. For this, the working

electrode was poised at 0 V after the inoculated medium had been aseptically purged with nitrogen gas.

When the working electrode was polarized, the oxidative current grew readily, showing that bacteria began to attach to and proliferate on the electrode (Figure 2). For MWNT/GCE, the electrode was not modifi ed with any organic dye and thus acted as a control. It reached about 0.2 μA after 10 hours of incubation, and stayed almost stagnant thereafter. The MB modifi ed electrode showed rapid growth since the beginning of chronoamperometry, quickly reaching an output current as high as 0.8 μA in 5 hours. The current growth slowed down afterwards, but the growing trend lasted until the end of chronoamperometry. Comparing the current level attained by MB/MWNT/GCE and MWNT/GCE after 20 hours of polarization, the MB/MWNT/GCE achieved an enhancement of about 5 fold. The result indicated that dye-CNT adduct could successfully elevate current density in MFCs. The TB/MWNT/GCE and NR/MWNT/GCE also increased the current level, by 4 and 2.5 times respectively. Current was still growing at the end of chronoamperometry for all dye modifi ed electrodes.

Figure 2. Chronoamperometric plot of TB/MWNT/GCE, MB/MWNT/GCE, NR/MWNT/GCE and MWNT/GCE poised at 0 V.

The exact mechanism of how immobilized dyes enhanced current generation under our experimental conditions is currently not clearly understood. It is widely believed that those dyes may act as mediators and increase the ET rate. However, this is questioned in our study. Since the NR has a very negative redox potential, which is close to or even lower than the standard potential of fuels in our study, it is unlikely to be mediating electrons from bacteria to electrodes. MB and TB have redox potentials more negative than those of the outer membrane c-type cytochromes of S. oneidensis as well. Therefore, the dyes might promote biological current by stimulating faster and better formation of biofi lms. This is to be confi rmed by further studies.



CONCLUSIONS

The organic dyes can form stable adducts with CNTs, and are immobilized to electrodes in this way. The dye-CNT nanocomposite notably enhanced current generation through biocatalysts. Among the tested dyes, MB outperformed other dyes. The observed enhancement is likely due to optimized accumulation of electroactive bacteria at the electrode surface, but more studies are required to clarify the underlying mechanism.

REFERENCES

[1] Adachi, M., Shimomura, T., Komatsu, M., Yakuwa, H., and Miya, A., 2008. A novel mediator-polymer-modifi ed anode for microbial fuel cells. Chem. Commun., pp. 2055-2057.

[2] Cheng, S. and Logan, B.E., 2007. Ammonia treatment of carbon cloth anodes to enhance power generation of microbial fuel cells. Electrochem. Commun., Vol. 9, pp. 492-496.

[3] Lowy, D.A. and Tender, L.M., 2008. Harvesting energy from the marine sediment-water interface. III. Kinetic activity of quinone- and antimony-based anode materials. J. Power Sources, Vol. 185, pp. 70-75.

[4] Lowy, D.A., Tender, L.M., Zeikus, J.G., Park, D.H., and Lovley, D.R., 2006. Harvesting energy from the marine sediment-water interface II. Kinetic activity of anode materials. Biosens. Bioelectron., Vol. 21, pp. 2058-2063.

[5] Park, D.H. and Zeikus, J.G., 2003. Improved fuel cell and electrode designs for producing electricity from microbial degradation. Biotechnol. Bioeng., Vol. 81, pp. 348-355.

[6] Puchades, M., Westman, A., Blennow, K., and Davidsson, P., 1999. Removal of sodium dodecyl sulfate from protein samples prior to matrix-assisted laser desorption/ionization mass spectrometry. Rapid Commun. Mass Spectr., Vol. 13, pp. 344-349.

[7] Yan, Y., Zhang, M., Gong, K., Su, L., Guo, Z., and Mao, L., 2005. Adsorption of methylene blue dye onto carbon nanotubes: A route to an electrochemically functional nanostructure and its layer-by-layer assembled nanocomposite. Chem. Mater., Vol. 17, pp. 3457-3463.



INTRODUCTION

The interaction of a turbulent surface jet with a free-surface is an important topic, but relatively few works are focused on the effects of Froude number on the turbulent structure in free-surface jet fl ows. This paper is an attempt to fi ll this gap.

Measurements of a developing planar surface jet were made by [1], and the authors found a distinct decrease in vertical velocity fl uctuations near the free surface. An investigation by [2] showed that instabilities in the near-fi eld region of a round jet are strongly infl uenced by the presence of a free surface, and that the jet fl ow fi eld is altered through changes in the entrainment fi eld near the free surface. Based on the fi ndings from experiments with depths corresponding to h/d =1, 1.5, 2.5, 3.5 (where h, and d were defi ned as the jet depth, and the jet exit diameter respectively) using Hot-fi lm velocity measurements, [3] showed that the decay of the mean centerline velocity is slower in the free-surface jet than that in the free jet. Experiments by [4] using laser Doppler velocimetry (LDV) measurements demonstrated that the velocity fl uctuations normal to the free surface were reduced nearer to the surface while the tangential velocity components were enhanced. The effects of Reynolds and Froude numbers on the turbulence structure of round jets issuing beneath a free surface were examined using LDV measurements [5] who also provided a comprehensive review on this topic. The researchers [5] showed that at high Froude number, reduction in the interaction of the tangential vorticity with its image was observed and near the free surface the tangential velocity fl uctuations were enhanced while the surface normal fl uctuations were reduced.

In this study, PIV technique is used as the tool to obtain the complete velocity fi eld in the near fi eld of the fl ow (0 < x/d < 16). The purpose of the investigation is to examine the effects of Froude number on the vertical mean velocity distributions within the development zone of the free-surface jets.

HYDRAULIC CHARACTERISTICS OF JET-INDUCED INTERNAL CIRCULATION

IN A WATER COLUMN Manh-Tuan Nguyen ([email protected])

Soon Keat Tan ([email protected])

ABSTRACT: Particle Image Velocimetry (PIV) technique was used to study certain hydraulic characteristics of the turbulent jets and demonstrated the effects of Froude number on the vertical mean velocity distributions in the fl ow development region. The results show that an increase in Froude number results in the reduction in maximum velocity decay in the downstream direction. The fi ndings also revealed a distinct phenomenon termed as “dead” jet.

EXPERIMENTAL SETUP

A series of experiments were carried out in a 5 m long, re-circulating open water channel with a rectangular cross section of 0.3 m wide × 0.45 m height. A number of experiments were conducted at a jet exit velocity of 1 m/s and jet diameter of 1cm (Re=9960) for depths corresponding to h/d = 0.25, 0.62, and 1.87. The corresponding values of , where Ue is the jet exit velocity, for the free surface jet cases are 20.39, 10.19, and 2.55. The coordinates (x, y, and z) denote the streamwise, lateral, and vertical directions, respectively. The origin is located at the jet exit as shown in Figure 1.

PIV system (LaVision model) was used to obtain the results in the vertical plane of the jet (xz plane). The view of fi eld was 116 mm x 155 mm. A Litro System double cavity Nd:YAG laser was used to illuminate the fl ow fi eld. The particle images were recorded using a 12-bit charge-couple device (CCD) camera which had a resolution of 1600x1200 pixels and a frame rate of 15 Hz.

Figure 1. Sketch of experimental setup.

Ue/√gh



Our fi ndings show that as Froude number increases, the maximum mean velocity decay of the free-surface jets associated with h/d=0.28 and h/d=0.63 is slower than that of submerged jet (h/d=1.88) as shown in Figure 3. This means that the closer the jet is to the free-surface, the smaller is the decay in maximum velocity. This Phenomenon will be investigated further.

The trajectory of the mean maximum velocity associated with h/d=0.25 is signifi cantly different from those of the cases h/d =0.63 and h/d=1.88. In Figure 4 Zm/d is plotted as a function of x/d for various cases examined. Zm is defi ned as the distance from the location of the maximum mean velocity to the free surface. For h/d=1.87 and h/d=0.62 the location of the maximum mean velocity remains on the jet centre line plane; meanwhile that of h/d=0.25 moves downward beneath the jet centre line and fl uctuates along the downstream direction.

Figure 2. Vertical mean velocity profi les for free surface jets. Ue = 1.0 m/s, Reynolds number 9960. (a) h/d=0.25;

(b) h/d=0.62; (c) h/d=1.87. The fl ow is from right to left.

Figure 4. The maximum mean velocity locations along the streamwise coordinate. Ue = 1.0 m/s, Re= 9960. ®, h/d=0.25;

Ο, h/d=0.62; ∆, h/d=1.87.

A distinct feature of free-surface jet corresponding to the case of h/d=0.28 is the clear revelation of the “dead” zone, which corresponds to the part of water body enclosed by the locus of the max jet velocity when the maximum mean velocity decreases rapidly and signifi cantly from x/d=0 to x/d=6.09, and recovers from then till x/d=8.28 before decaying in the downstream direction. These phenomena may be caused by the sharp increase in pressure at the initial region at x/d<8.28.

Figure 3. Downstream evolution of the maximum mean velocity of the free surface jets. Ue = 1.0 m/s, Re= 9960. ®, h/d=0.25;

Ο, h/d=0.62; ∆, h/d=1.87.


Mean velocity profi les were plotted along the x-direction as shown in Figure 2 for depths corresponding to h/d=0.25, 0.62, and 1.87, respectively. In all cases the measured mean velocity profi les are normalized by the maximum velocity at the nozzle (Ue). Figure 2 (c) shows the velocity profi les measured at h/d=1.87 and various distance from the jet axial plane. Eventually the jet reaches the free surface resulting at a non-zero mean velocity at the surface. For x/d<8.28 the jet does not approach the free-surface and the velocity distributions are very similar to the free jet velocity profi les. Downstream of this location the normalized mean velocities at those points close to free-surface increase. However, at this depth and (0<x/d<16) the maximum mean velocity is always found at the centre line of the jet (Fig. 4). As the jet is located close to free-surface (h/d≤0.62) the interaction occurs immediately from the jet exit (nozzle) as clearly indicated in Figure 2 (a) and (b).



CONCLUSIONS

PIV measurement was used to investigate certain hydraulic characteristics of the turbulent jets and demonstrated the effects of Froude number on the vertical mean velocity profi les in the fl ow development region. It was shown that an increase in Froude number results in the reduction in maximum velocity decay in the downstream direction. The results also revealed a very interesting phenomenon termed as “dead” jet which might be caused by the increase in pressure along the jet centreline.

REFERENCES

[1] Swean, T.F., Ramberg, S.E., Plesniak, M.W. & Stewart, M.B., 1990. “Turbulent surface jet in channel of limited depth.” Journal of Hydraulic Engineering, Vol. 115(12), pp. 1587-1606.

[2] Liepmann, D., 1990. “The Near-field Dynamics and Entrainment Field of Submerged and Near-surface Jets.” PhD Thesis, University of California, San Diego.

[3] Madnia, C.K. and Bernal, L.P., 1994. “Interaction of a turbulent round jet with the free surface.” Journal of Fluid Mechanics, Vol. 261, pp. 305-322.

[4] Anthony, D.G. and Willmarth, W.W., 1992. “Turbulence measurements in a round jet beneath a free surface.” Journal of Fluid Mechanics, Vol. 243, pp. 699-720.

[5] Walker, D.T., C.Y. Chen, and Willmarth, W.W., 1995. “Turbulent structure in free-surface jet fl ows.” Journal of Fluid Mechanics, Vol. 291, pp. 223-261.



INTRODUCTION

Studies of fl ow over trapezoidal profi le weirs have a number of applications in many typical civil engineering structures, such as fl ood fl ow over highway and railway embankments. The fl ow characteristics over this type of weirs often provide important boundary conditions for the application of large 2-dimensional (2D) fl ow models. Most of the previous experimental works are concentrated on estimating the discharge coeffi cients to determine the overfl ow capacity under different submerged conditions [1]. It has been found that the trapezoidal weir, i.e. with sloping embankments, has a higher discharge capacity than a typical rectangular weir with vertical faces [2]. From geotechnical considerations, the embankment slope is normally 1:2 (V:H) due to bank stability and seepage control. However, the detailed fl ow information such as the velocity and vorticity distributions, in regions either upstream or downstream of the weir, have received little attention.

Tail-water protection, embankment erosion and storage consideration depend essentially on the fl ow characteristics. Currently, the fl ow around a weir cannot be simulated exactly, because it involves free surface and turbulence structure, either of which remains a great challenge for computational fl uid dynamics (CFD). Therefore, a robust experimental database is desirable and necessary to enhance the physical understanding of this fl ow confi guration in particular, and free surface turbulent fl ows in general, as well as to facilitate numerical code development to simulate such fl ows. Considering that the fl ow is highly complex and unsteady, the measurements were performed using particle image velocimetry (PIV), which has the advantage of capturing the whole-fi eld fl ow structure over conventional point-measurement techniques such as hot-fi lm anemometer or laser Doppler anemometer.

EXPERIMENTAL SETUP

Experiments were performed in a horizontal, re-circulating open-water channel at Maritime Research Centre, Nanyang Technological University. The test section had a total length of 5 m, a width of 300 mm and a height of 450 mm. Water was supplied to the head tank using a centrifugal pump with a variable speed controller in order to achieve desired fl ow rate (Q). To ensure that the approach fl ow is free of surface waves and large-scale vortices, the settling chamber upstream of the test section was fi tted with perforated steel

INVESTIGATION OF FLOW OVER A TRAPEZOIDAL WEIR

Wang Xikun ([email protected]) Tan Soon Keat ([email protected])

plates and honeycomb-screen arrangements. A trapezoidal weir, which was made of Perspex and whose span was equal to the width of the test section, was mounted fi rmly on the channel fl oor of the test section and perpendicular to the main stream. A schematic diagram of the confi gurations for the model and the fl ow geometry is given in Figure 1.

Figure 1. Flow schematic and nomenclature.

For the present study, the weir height (p) is 24 mm and the crest length (w) is 12 mm. The weir is symmetrical about the crest, with a slope of 1:2 for both upstream and downstream faces, and the aspect ratio (the ratio of the weir span to its height) is 12.5, which is considered large enough to ensure a 2D type of fl ow. All measurements were performed in the mid-plane of the channel. The coordinates x and y denote the streamwise and vertical directions, respectively.

Flow velocities were measured using a PIV system (LaVision model). A Litron double cavity Nd:YAG laser (power ~ 135 mJ per pulse, duration ~ 5 ns) was used to illuminate the fl ow fi eld. The particle images were recorded using a 12-bit charge-coupled device (CCD) camera, which had a resolution of 1.6K × 1.2K pixels and a frame rate of 15 Hz. The particle displacement was calculated using the cross-correlation algorithm with the standard Gaussian sub-pixel fi t structured as an iterative multi-grid method [3]. The processing procedure included two passes, starting with a grid size of 64 × 64 pixels, stepping down to 32 × 32 pixels overlapping by 50%. For each experimental condition, a set of 1050 instantaneous fl ow fi elds were acquired at the frequency of 15 Hz (i.e. 70s recordings), in order to achieve a reasonable converge of the turbulent quantities. The uncertainty in the instantaneous velocities (u and v) is estimated to be about 2.5%. A more detailed description of the PIV post-processing procedure and uncertainty analysis is given in [4].



During the experiments, the overflow depth (h) was maintained constant at 48 mm, which is measured at 3h in front of the weir’s upstream toe. The approach streamwise velocity (U) at this location is set at U = 0.18, 0.25, 0.29 and 0.39 m/s for various experiments. At these velocities, on the one hand, the Reynolds number is suffi ciently large to ensure that the fl ow is fully turbulent. On the other hand, various fl ow patterns would be generated depending on the value of the Froude number Fr = U/(gh)0.5, which is generally accepted as the key parameter in free surface fl ow. The total head upstream of the weir (Ht) is Ht = h + U2/2g. An overview of the parameters for the series of testing is given in Table 1. For Cases A, B and C, Fr is less than 1.0, indicating that the fl ow is subcritical. For case D, Fr is approximately 1.0, which means that the fl ow is nearly critical or so-called transcritical.

Table 1. Experimental conditions

Case No. U (m/s) Ht (m) Fr

A 0.18 0.050 0.41

B 0.25 0.051 0.53

C 0.29 0.052 0.63

D 0.39 0.055 0.84


The water surface profi le can be obtained by tracking the air–water interface in the PIV images. Figure 2 shows a representative (instantaneous) profi le for each of the 4 cases considered. The profi les, particularly those of the three subcritical cases (i.e., Cases A, B and C), are similar both upstream and over the crest of the weir but exhibit differences and especially so over the downstream face. In the case of the fl ow with the lowest Froude number (Case A), the fl ow is essentially steady and the water surface keeps nearly horizontal. With the increase in Fr (i.e., Cases B, C and D), there is an increasing reduction in water level near the downstream end of the crest to follow the downstream slope. Also, the profi les downstream of the weir become unstable, resulting in increasingly violent surface undulance as clearly depicted in the fi gure. Moreover, the effects of Froude number on the surface profi le upstream of the weir are also discernible: for subcritical fl ow (i.e., Cases A, B and C) the profi le stays essentially horizontal and steady, while in the case of transcritical fl ow (i.e., Case D) a slightly surging of the profi le is observable at the streamwise location of about 2–3h upstream of the weir.

Figure 2. Free-surface profi le.

The mean fl ow quantities were obtained by ensemble averaging the 1050 instantaneous velocity vector fi elds for each experimental condition. Figure 3 shows the mean velocity vector (U, V) plot upstream of the weir for Case B, in which streamlines are included to highlight the fl ow structure. The fl ow pattern for other cases is basically the same, and is thus not shown herein.

A general observation is that the flow is propagated smoothly forward (or downstream), although there is an upward tendency in regions near the upstream surface due to the slope. The corner vortex, which would otherwise be expected for the case of weirs with vertical upstream face due to accumulation of bulk fl uid and adverse pressure, does not exist. The reduction in fl ow separation could explain the previous fi nding that an improved discharge coeffi cient (approximately 10% higher according to the literature) can be achieved for trapezoidal weirs as compared to the standard, vertical-faced ones. Measurements were also conducted in regions downstream of the weir to obtain the velocity fi eld at the tail-water. Figures 4a–d show the mean velocity vector plots for Cases A–D, respectively.

These fi gures clearly show that the velocity distribution is highly dependent on the Froude number. In Case A or B, a recirculation region that rotates in clockwise direction can be identifi ed, inducing backward fl ow near the bed wall. The latter is entrapped by the shear layer separated from the downstream corner of the weir and the zone extends to the reattachment point on the bed wall (the point where the mean streamwise velocity is 0). The streamwise length of the recirculation region has a decreasing trend with the increase in Fr, which is about 5h in Case A, decreases to about 4h in Case B, and then disappears completely when Fr is further increased. In the transcritical case (i.e., Case D), the fl ow propagates smoothly along the downstream slope and adheres to the bed wall; in other words, no fl ow separation is observed from the solid surfaces of both the weir and the bed. However, in this case there exists a recirculation region near the free surface, and is anticlockwise in direction, as highlighted by the arrowed ellipse in Figure 4d. This recirculation region is in sharp contrast to that in Case A, which is clockwise in the rotational direction and located at the lower part of the fl ow regime (i.e., near the bed wall).

Figure 3. Mean velocity vector plot in the x-y plane upstream of the weir.



The measured velocity vector distribution can be used to calculate other hydraulic properties of the weir, such as the discharge coeffi cient CD as defi ned in Equation (1):

(1)

The fl ow rate Q can be obtained by the integration of the measured streamwise velocity along the vertical direction at a streamwise location upstream of the weir, namely:

(2)

In addition, it has been proposed by [2] that the experimental data on broad-crested weirs would collapse to a single curve defi ned by Equation (3), when CD is plotted against the relative crest length ε = Ht/(Ht + w), with 0 < ε < 1:

(3)

This correlation relates to fl ow over an embankment weir with both the upstream and downstream faces sloped at 1:2, which is exactly the same confi guration as that of the present study. The calculated discharge coeffi cients using Equations (1) and (2) are shown in Figure 5, and the curve as defi ned by Equation (3) is also plotted for comparison. It is shown that over the ε-range considered, the predicted

value is nearly constant, namely, CD ≈ 0.47 which agrees well with the measured value for Case D but is considerably higher than that for the three lower Fr cases (i.e., Cases A, B and C). The data scatter is mainly due to the difference in Fr between these two studies.

32 tD gHbCQ

dyyUbQ hp

0 )(

)]55.0(sin[06.043.0DC

Figure 5. Discharge coeffi cient.

Figure 4. Mean velocity vector plot in the x-y plane downstream of the weir for: (a) Case A; (b) Case B;

(c) Case C; and (d) Case D.

CONCLUSIONS

The fl ow characteristics over a trapezoidal embankment weir with the upstream and downstream faces sloped at 1:2 (V:H) have been investigated experimentally using PIV (Particle Image Velocimetry) technique. Three hydraulic properties, namely, the free surface profi le, the velocity field and the discharge coefficient, are discussed and analyzed. It is shown that the fl ow is highly dependent on the Froude number over the range from subcritical to transcritcial state.

REFERENCES

[1] Johnson, M.C., 2000. “Discharge coeffi cient analysis for fl at-topped and sharp-crested weirs.” Irrigation Science, Vol. 19 (3), pp. 133-137.

[2] Fritz, H.M. and Hager, W.H., 1998. “Hydraulics of embankment weirs.” Journal of Hydraulic Engineering, Vol. 124, pp. 963-971.

[3] Raffel, M., Willert, C.E. and Kompenhans, J., 1998. Particle Image Velocimetry: a practical guide, Springer, Berlin Heidelberg New York.

[4] Wang, X.K. and Tan, S.K., 2008. “Near-wake flow characteristics of a circular cylinder close to a wall.” Journal of Fluids and Structures, Vol. 24, pp. 605-627.



INTRODUCTION

The rapid detection of live bacterial cells is essential for many applications, from environmental study and water quality monitoring to the detection of biological weapons (Hughes et al. 2008). Disposable hand-held assay test kits and biosensors for the fast detection of indicator and pathogenic bacteria in water using lateral fl ow immunoassays are known. However, these test kits cannot recognize whether cells are dead or alive. This is a major shortcoming, because all microbiological standards for water quality and effi ciency of water disinfection are related to the number of viable bacterial cells. Separation of live from dead bacterial cells in a microfl uidic device prior to immunochemical detection of cells can overcome this limitation. Non-uniform electric fi elds can be used to induce the motion of polarizable cells by generating dielectrophoresis (DEP). In nonuniform electric fi elds, the particles suspended in a fl uidic medium are electrically polarized and experience a net electric force. (Gascoyne et al. 2002). The magnitude and direction of this force is strongly dependent on cell size, frequency of electric fi elds, the dielectric properties such as conductivity and permittivity of the particle and suspending medium. Hence, this property can be employed for selective separation of live and dead bacterial cells under a specifi c frequency of applied electric fi elds.

DEP is due to the polarization effects in cells under specifi c frequency of applied non-uniform electric fi eld. Dielectrophoretic force (FDEP) acting on a spherical cell in an electric fi eld gradient is given by the expression (Markx et al. l997):

(1)

where r is the radius of cells, εm is the permittivity of the suspending medium, ∇ is the gradient operator, Erms is

MICROFLUIDIC SEPARATION OF LIVE AND DEAD BACTERIAL CELLS FOR

ENVIRONMENTAL MONITORINGVolodymyr Ivanov ([email protected])

Charles Yang Chun ([email protected]) Kumaravel Kandaswamy ([email protected])

Lewpiriyawong Nuttawut ([email protected])

ABSTRACT: Fast detection of live bacterial cells is an essential procedure in monitoring of water quality and environmental safety. Dielectrophoresis (DEP) is a rapid and cost-effi cient method for cell sorting. DEP is the movement of polarized cells due to non-uniform AC electric fi elds. The frequency of DEP and the pattern of non-uniform electric fi eld are the most important factors of DEP cell separation. Hence we optimized the frequency of applied AC electric fi elds through velocity measurements in order to generate the dielectrophoretic force (FDEP) required for a continuous separation of live from dead bacterial cells.

230 )(Re2 rmsmDEP EKrF

the root mean square of an electric fi eld, and Re [K (ω)] is the real part of the Clausius-Mossotti (CM) factor that depends on the complex permittivity of both the particle and medium. Hence, this CM factor determines the effective polarizablity of the particle. In the case of a spherical particle, the CM factor is given by

(2)

where subscript p and m refer to the particle and the medium respectively, ε and σ are the permittivity and conductivity of the dielectric, ω is the angular frequency of the applied electric fi eld (ω = 2πf) and j= (-1)1/2.

The frequency and the pattern of the applied non-uniform electric fi eld are the most important factors of DEP cell separation (Wang et al., 2007).

So, the aim of this research was to optimize the frequency of applied AC electric fi elds through velocity measurements in order to generate the dielectrophoretic force (FDEP) required for a continuous real-time separation of live from dead bacterial cells.

MATERIALS AND METHODS

E.coli DSMZ 1329 cells were grown in a Luria-Bertani (LB) medium overnight in a shaker at 370C with 120 rpm. Two aliquots of 1 ml cell suspension were centrifuged at 5000 rpm for 5 min. The cells biomass precipitates were washed three times with 1 ml of distilled (DI) water. Dead cells were prepared by adding 20% of allyl alcohol to the cell pellet and then the suspension was vortexed briefl y and incubated in the dark for 10 min. The dead cells pellets were then washed three times by centrifugation. Membrane permeable fl uorescent dye Syto9 from the LIVE/DEAD viability kit was added only to the samples of dead cells

,2

)(**

**

mp

spKi

impi j*),(



and incubated in the dark for 15 minutes. Then, the cell suspension was washed three times with DI water. The mixture of live and dead cell samples was obtained by adding 500 μl of live cells suspension (without fl uorescent labeling) and 500 μl of dead cells suspension (labeled with Syto 9) in a micro-centrifuge tube. The mixture was vortexed thoroughly and stored at 40°C in the dark for further analysis.

All the experiments were performed under an inverted microscope (a Nikon TE2000U). The cell images in the microfl uidic device were captured using NIS-elements 3.0 animation software from Nikon Instruments Inc (Figure 1). The horizontal velocity of the bacterial cells inside the channel during the separation was 5 μm/s. The vertical velocities of live and dead cells towards the electrode were measured experimentally (Figure 2). The mean velocity is given by the ratio of distance to time. The relation between the dielectrophoretic force and the velocity of cell is given by the following equation (Chin et al. 2007)

(3)

where vp is the velocity of the cell due to DEP is given by

(4)

D is the distance traveled by the cells from the electrode edge due to DEP (D = 50μm and 20 μm), and t is the time taken to reach the distance and η is the viscosity of the medium (water = 0.00089 Kgm-1s-1).

RESULTS

The dielectric parameters of live and dead cells such as permittivity, conductivity and depolarization factors were obtained from literature (Castellarnau et al. 2006; Suehiro et al. 2003) and used for the calculation of the optimal electrical frequencies for DEP separation of live and dead bacterial cells in water with a conductivity of 0.05 Sm-1.

The experimental separation of live and dead bacterial cells (Figures 2 and 3) was observed best at the frequency from 5 to 30 MHz when the input voltage is 10 Vpp. Hence, frequency plays a major role in the DEP separation of live from dead bacterial cells.

a

Fv DEP

p 6

tD

vp

Figure 1. Experimental measurement of velocity, D = 50μm or 20 μm from the electrode edge, “E” electrodes connected to the AC power source; the distance

between the electrodes was 200μm.

CONCLUSIONS

The frequency of applied AC electric fi eld and the pattern of non-uniform electric field generated are the most important factors for DEP separation of live from dead bacterial cell. Experimentally the optimum DEP frequency for separation of live and dead cells in the microchannels was determined and it is in the range of 5 to 30 MHz, however this optimum frequency depends on the dielectric properties of the suspending medium.

Figure 2. Vertical velocities of live and dead bacterial cells in water at different frequencies measured at the distance of

50 μm from the electrodes.



Figure 3. Vertical velocities of live and dead bacterial cells in water at different frequencies measured at the distance of

20 μm from the electrodes.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge research grant (Grant No. AcRF RG9/07) from the Ministry of Education, Singapore.

REFERENCES

[1] Castellarnau, M., Errachid, A., Madrid, C., JuaÌrez, A. & Samitier, J. 2006. Dielectrophoresis as a tool to characterize and differentiate isogenic mutants of Escherichia coli. Biophysical Journal 91, 3937-3945.

[2] Chin, H. K., Yee, C. L., Rodriguez, I., Yang, C. and Youcef-Toumi, K. 2007. Dynamic cell fractionation and transportation using moving dielectrophoresis. Analytical Chemistry 79, 6975-6987.

[3] Gascoyne, P. R. C. and Vykoukal, J. 2002. Particle separation by dielectrophoresis. Electrophoresis 23, 1973-1983.

[4] Hughes, M. P. and Hoettges, K. F. 2008. Bacterial Concentration, Separation and Analysis by Dielectrophoresis. In Principles of Bacterial Detection: Biosensors, Recognition Receptors and Microsystems, pp. 895-907.

[5] Markx, G. H., Rousselet, J. and Pethig, R. 1997. DEP-FFF Field-fl ow fractionation using non-uniform electric fi elds. Journal of Liquid Chromatography and Related Technologies 20, 2857-2872.

[6] Suehiro, J., Hamada, R., Noutomi, D., Shutou, M. and Hara, M. 2003. Selective detection of viable bacteria using dielectrophoretic impedance measurement method. Journal of Electrostatics 57, 157-168.

[7] Wang, L., Flanagan, L. and Lee, A. P. 2007. Side-wall vertical electrodes for lateral fi eld microfl uidic applications. Journal of Micro-electromechanical Systems 16, 454-461.



INTRODUCTION

To study the transport of coarse spherical particles, laboratory experiments were conducted in a two-dimensional inclined channel under rapid fl ow conditions. With laser-based image processing techniques, simultaneous measurements of the fl uid phase and solid phase were carried out, including their velocities, discharges, and solid concentration. The fi rst stage of this study focused on saltating motion of particles and the inter-phase interactions.

EXPERIMENTAL SETUP

Experiments were carried out in a narrow glass channel, 10 mm in width, 2 m in length and 20 cm in height, with an adjustable bed slope (see Figure 1). Two types of plastic beads, namely, Nylon and Polystyrene spherical beads were used, of which the specifi c densities were 1150 g/cm3 and 1050 g/cm3 respectively. The particle diameter was selected to be 6.5 mm, which was slightly smaller than the channel width in order to keep both the particles and the fl uid passing across the focal plane of the camera.

PARTICLE SALTATION IN A TWO DIMENSIONAL CHANNEL

Nguyen Ba Tuyen ([email protected])Cheng Nian Sheng ([email protected])

During each experiment, the fl uid discharge was kept constant, and the particles were then added into the fl ow at a constant rate; together they made the fl ow inside the channel well uniform over the major reach. The camera was focused on the mid-plane of the channel, and measurements

Figure 1. Experimental setup.

started when the fl ow had reached an almost steady state. For each run, recordings were taken over a long time period (at the frequency of 15 Hz, yielding at least 10,000 double-frame, 8-bit gray-scale images) in order to get a reasonable good average of the fl ow characteristics. The two frames of each image were separated by a time span of 500 μs for the purpose of correlation analysis.

DATA ANALYSIS

Raw data analysis was fi rst carried out to extract the fl ow and particle information from captured images. This step was successfully done thanks to the PIV (Particle Imaging Velocimetry) and PTV (Particle Tracking Velocimetry) techniques. The PTV method (see Figure 2) determines the velocity fi eld by tracking individual tracer (particle), while the PIV method assumes the suitable tiny tracers to represent the whole fl ow fi eld.

Figure 2. Particle Tracking Velocimetry principle.

To facilitate the PTV analysis, particles were fi rst identifi ed from raw images. Although all particles had an almost constant size when they appeared on images, the differences in locations and relative positions, however, caused them to have different shapes (imperfect) and degrees of brightness. Therefore, those particles must fi rst be distinguished from the background to get the information on their centers and radii. Major steps to implement this task are sketched in Figure 3.



RESULTS AND DISCUSSIONS

The instantaneous fl ow velocity fi elds (2D) with and without particles were obtained with PIV analysis - Dantec Dynamics software (v2.10). Typical ensemble-average fl ow velocity fi elds (for longitudinal velocity Uf and vertical velocity Vf respectively) are presented in Figure 4. They show the uniformity of the fl ow characteristics in the longitudinal direction. Nevertheless, the result shows only a small change when the selected solid particles were added.

Figure 3. Particle characterization technique.

Figure 4. Flow velocity fi elds obtained with PIV technique (upper panel: Uf; lower panel: Vf).

The above mentioned PTV techniques were successfully realized. Figure 5 shows the particle distribution probability over the fl ow depth (i.e. an indicator for the vertical particle concentration profi le, CP vs. z), and the particle longitudinal velocity (UP) profi le. Hereafter the double averaging technique was applied to average the particle information both over time (ensemble average) and over space (along the fl ow direction).

In the presence of the injected beads, the fl ow always showed a lag in its longitudinal velocity when compared to the case without particles. This can be seen in Figure 6 (both cases were carried out with the same fl uid and solid discharges). For heavier beads, the lag is quite clear.

Figure 5. Particle fl ow characteristics.

Figure 6. Velocity distributions of two phase fl ows for different particle densities (a) Nylon particles; (b) Polystyrene particles



REFERENCES

[1] Ancey, C., Bohm, T., Jodeau, M., & Frey, P. (2006). Statistical description of sediment transport experiments. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 74(1).

[2] Armanini, A., Fraccarollo, L., & Larcher, M. (2008). Liquid-granular channel fl ow dynamics. Powder Technology, 182(2), 218-227.

[3] Bohm, T., Ancey, C., Frey, P., Reboud, J. L., & Ducottet, C. (2004). Fluctuations of the solid discharge of gravity-driven particle fl ows in a turbulent stream. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 69(6 1).

CONCLUDING REMARKS

Both PIV and PTV techniques were successfully applied to the study of the characteristics of the two phases in the rapid fl ow down a steep slope. The preliminary result shows that solid particles have signifi cant infl uence on the fl uid fl ow. Further investigation will be conducted to quantify inter-phase relationships, based on the same data processing method developed.



INTRODUCTION

Physiological heterogeneity in microbial aggregates is usually attributed to the genotypic diversity and gradients of nutrients and metabolites inside cell aggregate. However, even within a cellular aggregate of pure culture the physiological heterogeneity of bacterial aggregates can also be detected. Biofi lms and biogranules are the microbial aggregates that include physiologically different cells. The packing of cells within the microbial aggregate causes the concentration gradient of nutrients from the periphery to the core and the gradient of metabolic products conversely. Therefore, the nutrients are depleted in the centre of the aggregate due to the limitation of access of the substrate by diffusion (Stewart and Franklin, 2008). Cells from a different cell cycle or life cycle (Ivanov et al., 2008a) also cause physiological heterogeneity in microbial aggregates.

Characterization of the physiological states of individual bacterial cells in a cell aggregate is useful in understanding of the aggregate structure and function as well as in the process modeling and bioreactor design. One of the most effective techniques for analysis of respiration and growth activities of individual cells in a cell aggregate is an application of fl uorescent dye 5-cyano-2,3-ditolyl tetrazolium chloride(CTC), monotetrazolium redox dye producing a fl uorescent formazan (CTF) during respiration, and other dyes in combination with the confocal laser scanning microscope (CLSM) (Stewart and Franklin, 2008).

Aerobically growing aggregates of Pseudomonas veronii cells can be used effectively for wastewater treatment (Ivanov et al., 2008b). In the present study, the physiological heterogeneity of cellular aggregates of Pseudomonas veronii in terms of respiratory activity were visualized by CTC staining coupled with the CLSM technique.

PHYSIOLOGICAL HETEROGENEITY OF AEROBIC BACTERIAL AGGREGATES

Saeid Rezaeinejad ([email protected])Volodymyr Ivanov ([email protected])

ABSTRACT: Microbial aggregates such as biofi lm consist of bacterial cells with different physiological states. Evaluation of physiological heterogeneity within microbial aggregates might be useful for process modeling and bioreactor design. Tetrazolium dye of CTC is suitable probe for determination of respiratory activity as physiological parameter of cell.


One colony of self-aggregated cells of Pseudomonas veronii strain B (Ivanov and Wang, 2008b) was used for the inoculation of 500 ml sterile medium containing (g l-1): peptone, 20; NaCl, 5; and glucose, 5. Cell aggregates were grown in the shaker at 200 rpm and 30ºC with a daily replacement of thesuspension after 5 min settling with a sterile fresh medium.

CTC (Polyscience, Inc., Warrington, PA, USA) was used as 100 μl of the stock solution (50mM) added to a test tube containing cellular aggregates suspended in 900 μl phosphate buffered saline (PBS) and incubated for 2 hours at 30ºC. Stained cell granules were viewed using an Olympus Fluview FV300 confocal laser scanning microscope (CLSM) (Olympus Optical, Tokyo, Japan). The optical cross-sections of cell aggregate with 5 μm intervals between the slices were acquired, summarized, and integrated red fl uorescence intensity of CTF along one axis of aggregate calculated.


The respiratory activity profi le within the cellular aggregate of Pseudomonas veronii demonstrates the presence of three layers (Figures 1 and 2):

(1) the outer layer of cells with low respiratory and, probably, growth activities on the depth of 10 μm from the edge of the aggregate;

(2) the intermediate layer of cells with the highest respiratory, and probably, growth activities between 10 to 20 μm from the edge of the cellular aggregate; and

(3) cells with the lowest respiratory, and probably, growth activities in the center of cellular aggregate.



Figure 1. CLSM image of cellular aggregate of Pseudomonas veronii stained with CTC

(red fl uorescence of CTF is shown). One section of scale bar shows 10 μm.

The profi le in Figure 2 shows that respiration and growth activities are not homogenously distributed inside the cellular aggregate. Only one intermediate layer is ensuring these activities while the outer and inner parts of the cellular aggregate are slow respiring and growing cells. It is known that slow respiring and growing cells are most resistant to toxic substances and unfavorable conditions. Therefore, the low respiration activity of the outer layer of cells explains the lower sensitivity of the microbial aggregates to toxic substances in comparison with the sensitivity of the suspended cells.

Figure 2. Respiratory activity profi le (i.e. red fl uorescence of CTF shown by solid black curve) in cell aggregate.

Transparency of Pseudomonas veronii aggregate for the visible light is shown by brown curve.

ACKNOWLEDGEMENTS

This research was supported by Nanyang Technological University, Singapore.

REFERENCES

[1] Stewart, P.S. and Franklin, M.J., (2008). Physiological heterogeneity in biofi lms. Nature Reviews, 6: 199-210.

[2] Ivanov, V., Rezaeinejad, S., Yi, S. and Wang, X.H. (2008a). Physiological heterogeneity of suspended microbial aggregates. Water Science and Technology, 58(12): 2435-2441.

[3] Ivanov, V., Wang, X.H., (2008b). Starter culture of Pseudomonas veronii strain B for aerobic granulation. World J. Microbiol. Biotechnol., 24: 533-539.



INTRODUCTION Silt screen, as one of the adopted management practices for sediment control in an aquatic environment, is a textile-like structure that is deployed to control and contain suspended sediment movement in the water body. Despite its popularity, the effectiveness of the silt screen has been viewed with skepticism. Among the various reasons is the fact that the silt screen’s working mechanism is not well understood. In particular, the interactions among the silt screen, fl ow and the containment, i.e. sediment, still remain largely unknown.

This article discusses preliminary results of the experiments on the interactions between the silt screen and fl ow. The latter is expected to be the primary driver and process that determines the performance of the silt screen as a sediment containment device.

METHODOLOGY

The experiments were conducted in a fl ume channel of dimension 500 cm length x 30 cm width x 45 cm height. A sample of silt screen SC150, supplied by Kiaratex1, was used in the experiments. In this experiment, the silt screen spanned the width of the channel and was placed perpendicular to the fl ow. The properties of the silt screen as given by the manufacturer are listed in Table 1.

Table 1. Properties of Kiaratex SC150

Material Polyester

Weight > 600 g/m2

Thickness > 1.2 mm

Seawater Permeability < 7.5 x 10-3 cm/s

Apparent Opening Size < 45 μm

PRELIMINARY INVESTIGATION OF BEHAVIOR OF SILT SCREENS AS SEDIMENT CONTROL EQUIPMENT

Vu Thu Trang ([email protected])Tan Soon Keat ([email protected])

ABSTRACT: Silt screen is a popular mitigation measure for sediment containment in aquatic environment. Experimental studies showed that the deployment of silt screen drastically changed the fl ow’s velocity profi le and led to the formation of recirculation areas in the vicinity of the screen. The upstream fl ow conditions and the length of the silt screen were crucial parameters in determining the characteristics of the resultant fl ow, which in turn defi ned the sedimentation process.

In the experiments, the silt screen was suspended from a fi rm support from above (instead of fl oater or buoy) and the lower end was weighed down using a metal rod (1 kg) as the ballast/sinker. The fl ow characteristics of the region around the silt screen were investigated using the technique of Particle Image Velocimetry (PIV). Measurements were conducted at the mid-plane of the channel as shown in Figure 1. The images of the fl ow fi eld were captured using a 12-bit charge-couple device (CCD) camera with a resolution of 1600 x 1200 pixels, viewing area of 300 mm x 225 mm and a frame rate of 15 Hz.

Measurements were conducted at the mid-plane both upstream and downstream of the silt screen. Three fl ow velocities (namely, 0.05 m/s, 0.1 m/s and 0.2 m/s) and various screen penetration ratios were considered. The screen penetration ratio was defi ned as the ratio between the screen’s length and the water depth.

1Kiaratex – www.kiaratex.com

Figure 1. Particle Image Velocimetry experimental setup.



PRELIMINARY RESULTS

The streamlines and velocity vector fi eld in the vicinity of the silt screen were obtained from the PIV images. Figure 2 shows the streamlines and velocity vector fi eld of the screen with penetration ratio of 1.

In the raw data collected from the measurement, the silt screen profi le and the light-refl ected area were masked prior to image-processing. During the experiments, and when the screen was not anchored adequately, fl aring of the screen was observed. The degree of fl aring depends on the magnitude of the fl ow, and is also affected by the silt screen properties (permeability and fl exibility). We attempt to correlate the degree of fl aring with the normalized effective screen length lne, which can be estimated based on equation (1):

lne = le/l0 (1) In formula (1), le denotes the projected length of the screen in the vertical plane, and l0 is the length of the screen. Visual observations made during the experiments showed an inverse relationship between normalized effective screen length and incoming fl ow velocity.

From the streamlines and velocity obtained from the measurements, it can be concluded that the presence of a silt screen in water signifi cantly changes the fl ow patterns. Firstly, a region of retardation of fl ow in the vicinity of the screen was clearly discernible. This phenomenon has been reported in previous studies on silt screen (Elastec/American Marine Inc., 2009; JBF Scientifi c Corporation, 1978; Yasui, Deguchi & Ono, 1999). The low velocity was observed in the fl ow recirculation areas at the upper layer of both upstream and downstream of the silt screen.

Figure 2 suggests that the size of the recirculation regions varies with the predominant fl ow velocity. In this experimental setup, the largest recirculation areas at both upstream and downstream regions are detected at the smallest predominant fl ow velocity of 0.05 m/s. An increase in velocity reduces the normalized effective screen length, and thus enlarges the infl uence zone of the fl ow to/from the gap. Consequently, recirculation is weakened as the fl ow velocity increases, as can be deduced from Figure 2.

Besides, the fl ow patterns show the formation of a strong fl ow in the gap between the screen’s lower end and the fl ume bottom, resulting in a so called jet-like fl ow. Such diversion of fl ow can be explained as a result of the screen’s low permeability, as noted in Table 1. The velocity observed in the jet-like fl ow can be as high as 0.3 m/s – 0.6 m/s when the environmental fl ow changes from 0.05 m/s to 0.2 m/s. This velocity change can be quantifi ed by the normalized gap velocity, which is defi ned as the ratio of the velocity in the gap to the “upstream” velocity. The variation of the maximum value of the normalized gap velocity is shown in Figure 3.

Figure 2. Mean velocity vector fi eld in the vicinity of silt screen (with upstream velocity of (a) 0.05 m/s;

(b) 0.1 m/s; and (c) 0.2 m/s).

(a)

(b)

(c)



Figure 3 shows a decreasing trend in the maximum normalized gap velocity with increasing environmental fl ow velocity. This inverse relationship is caused by the effect of “upstream” velocity on normalized effective screen length. As this velocity decreases, the normalized effective screen length increases, creating further contraction of the fl ow passing the screen. As a result, the ratio between velocity in the gap and upstream velocity increases.

The presence of the above-mentioned two fl ow patterns, namely, recirculation at both sides of the silt screen and a “jet-like” fl ow at the bottom, brings into question the ability and effectiveness of the current practice of using a silt screen to control and contain suspended sediment movement. It is expected that sediment suspended in the circulation regions is kept within the silt screen containment area. However, this so-called “effective” region has not been quantifi ed and its characteristics depend on incoming fl ow conditions, as discussed above. On the other hand, due to its high velocity, the “jet-like” fl ow patterns at the bottom has great potential for transporting sediment further downstream, which may not be desirable for sediment containment purpose.

Figure 3. Maximum normalized gap velocity vs. upstream velocity (in the case of screen penetration ratio = 1).

SUMMARY

The preliminary results of the laboratory measurement of the fl ow characteristics in the presence of a silt screen reveal a number of important aspects on the working mechanism of the current silt screen, which could well have contributed to the uncertain performance of silt screen deployment. Further study of the fl ow characteristics, and the interactions between the fl ow and the sediment, is necessary to resolve the problem currently encountered in applications involving silt screen deployment.

REFERENCES

[1] Elastec/American Marine Inc. 2009. Turbidity curtains. from www.turbiditycurtains.com

[2] JBF Scientifi c Corporation. 1978. An analysis of the functional capabilities and performance of silt curtains (No. D-78-39)

[3] Yasui, A., Deguchi, I. and Ono, M., 1999. Performance of silt protector in three dimensional fl ow. Proceedings of the 1999 Ninth International Offshore and Polar Engineering Conference (Vol. 3), Brest, France, 30 May - 4 June 1999, 781-786.



INTRODUCTION

Dyes contamination in the aquatic ecosystem has been increasing over the past decades, posing a threat to human health and the environment. The presence of dyes in natural water bodies may have a deleterious impact on the food chain as colour can absorb and refl ect sunlight entering the water, and consequently bacteria may not grow suffi ciently and self-purifi cation of water bodies slows down (Özcan et al., 2007). Moreover, dyes contamination implies their incomplete removal during biological wastewater treatments.

Among different potential technologies, adsorption by activated carbon has gained wide acceptance due to its high capacity in the removal of dyes, other organic compounds, and a broad spectrum of inorganic compounds generally discharged from industries (Kennedy et al., 2007; Liu and Shen, 2008a) as well as to its low cost, high effi ciency, easy operation, and fast kinetics (Özcan et al., 2007). This study aimed to investigate the feasibility of adsorption of the selected organic dyes, Rhodamine B (RB) and Methyl Orange (MO) by commercial granular activated carbon (GAC) with a special focus on adsorption isotherms, kinetics, and thermodynamics.


Commercial GAC, having a specifi c surface area of 1,000 m2/g and a total pore volume of 0.6 cm3/g (by BET method), was obtained from the Calgon Carbon Corporation (USA). The two types of organic dyes, RB and MO, were purchased from Fisher Scientifi c (USA). Batch adsorption experiments were carried out in a 1-L agitated batch reactor. In the study of adsorption isotherms, experiments were

REMOVAL OF ORGANIC DYES BY ACTIVATED CARBON ADSORPTION

Lily Ganda ([email protected])Liu Yu ([email protected])

performed at solution pH with the temperature being fi xed at 298 K while GAC dose and initial dye concentrations were varied. For the kinetic study, a fi xed GAC dose of 10 g/L and initial solution concentrations of 10-5 M and 10-4 M for RB and MO, respectively, were applied. For the thermodynamic study, the temperature was varied from 303 to 333 K. The concentration of dye in solutions was determined spectrophotometrically.


Adsorption Isotherms

Langmuir and Freundlich isotherm equations (equations 1 and 2) were employed to analyze the experimental data obtained. The isotherm data derived at 298 K were fi tted to Langmuir and Freundlich models (Figure 1), with a higher correlation coeffi cient belonging to the Langmuir plot.

Langmuir isotherm:

(1)

Freundlich isotherm:

(2)

The maximum adsorption capacities of RB and MO onto GAC at solution pH, determined from the Langmuir isotherm equation, were equal to 9.98 x 10-6 and 4.50 x 10-3 mol/g, respectively. The summary of the parameters of two isotherms obtained from experimental data are presented in Table 1, while the Langmuir separation factors, RL, for RB and MO adsorption are presented in Table 2. Since all values of RL lie between 0 and 1, it is evident that the adsorption of RB and MO onto commercial GAC is of a favorable shape.

eL

eLe CK

CKqq

1max

neFe CKq /1

Table 1. Parameters estimated from Langmuir and Freundlich isotherms for RB and MO Dye Langmuir Freundlich

qmax KL R2 KF 1/n R2

(mol/g) (L/mol) (mol/g(L/mol)1/n)

R B 9.98 x 10-6 1.594 x 105 0.9982 9.17 x 10-5 0.2312 0.9966

MO 4.50 x 10-3 9.197 x 101 0.9958 3.64 x 10-1 0.9880 0.9717



equation in order to understand the reaction pathways and to determine the mechanism of adsorption. The plots of the three kinetic models are shown in Figure 2.

Table 2. Determination of RL for RB and MO adsorption onto GAC

Dye Ce (mol/L) KL (L/mol) RL

Rhodamine B 1.34 x 10-5 1.594 x 105 0.3189 2.20 x 10-5 1.594 x 105 0.2219 3.18 x 10-5 1.594 x 105 0.1648 Methyl Orange 2.79 x 10-5 91.97 0.9974 3.56 x 10-5 91.97 0.9967 4.88 x 10-5 91.97 0.9955

Adsorption Kinetics

Various kinetic models have been applied to the experimental data, such as pseudo-fi rst order equation, pseudo-second order equation, and the recently developed general rate law

(a)

(b)

Figure 1. Adsorption isotherms of (a) RB and (b) MO derived at 298 K.

xtx

t kdt

d

e

tt q

q1

(a)

(b)

Figure 2. Adsorption kinetics of (a) RB and (b) MO by GAC.

The general rate law equation (Liu and Shen, 2008b) can be expressed as follows:

(3)

(4)

where kx is the rate constant and x is the adsorption reaction order. The calculated correlation coeffi cients are closer to unity for the general rate law equation, which are equal to 0.9938 and 0.9998 for RB and MO adsorptions, respectively. Thus, it can be concluded that the adsorption reaction on the surface of the adsorbent was the most dominant rate-controlling step. Hence, change in the effective number of adsorption sites at the surface of adsorbent during adsorption



was the main factor, as explained by the general rate law (Liu and Shen, 2008b).

Thermodynamics of Adsorption

The rate constants calculated from the general rate law equation were then implemented to derive the activation energy (Ea) of the adsorption processes.

(5)

where k is the rate constant, Ea is Arrhenius activation energy of adsorption, A is Arrhenius factor, R is gas constant, which is equal to 8.314 J/K.mol and T is absolute solution temperature (Doganˆ et al., 2007).

The thermodynamic parameters, such as the change in free energy (∆G°), enthalpy (∆H°), and entropy (∆S°) associated to the adsorption process, were determined by using the following equations:

(6)

(7)

(8)

Table 3 listed the values of ∆G°, ∆H°, ∆S°, and Ea at various temperatures (303 to 333 K) for both RB and MO. The relatively low values of Ea for adsorption of both dyes seem to indicate that the adsorption had a low potential barrier, thus it would be subjected to a physisorption mechanism. This view is also evidenced by the ∆G° values in the range of -20 to 0 kJ/mol. Positive values of enthalpy imply that the adsorptions of both Rhodamine B and Methyl Orange were endothermic in nature. Positive entropy values suggest increased randomness at the solid-liquid interface during adsorption, whereas the negative ∆G° values show a spontaneous adsorption process.

RT

EAk alnln

e

eC C

CCK

)( 0

CKRTG ln

RTH

RS

KCln

Table 3. Thermodynamic parameters of RB and MO adsorption

Dye T KC ∆G° ∆H° ∆S° Ea

(K) (kJ/mol) (kJ/mol) (J/K.mol) (kJ/mol)

RB 303 15.95 -6.977 5.075 39.76 42.3 313 17.18 -7.401 5.075 39.76 42.3 323 17.52 -7.689 5.075 39.76 42.3 333 19.40 -8.210 5.075 39.76 42.3 MO 303 6.94 -4.879 73.21 258.4 34.3 313 19.83 -7.774 73.21 258.4 34.3 323 54.56 -10.740 73.21 258.4 34.3 333 89.91 -12.455 73.21 258.4 34.3

CONCLUSIONS

Granular activated carbon adsorption showed high feasibility in the removal of organic dyes, Rhodamine B and Methyl Orange, from aqueous solutions. The adsorption equilibrium and kinetic data of the two model dyes were better described by the Langmuir isotherm and the general rate law kinetic model, respectively. The thermodynamic data showed that adsorptions of the two model dyes were spontaneous, endothermic and physisorption processes.

REFERENCES

[1] Doganˆ , M., Ozdemirʺ , Y. and Alkan, M., 2007. Adsorption kinetics and mechanism of cationic methyl violet and methylene blue dyes onto sepiolite. Dyes and Pigments 75, 701-713.

[2] Kennedy, L.J., Vijaya, J.J., Sekaran, G. and Kayalvizhi, K., 2007. Equilibrium, kinetic and thermo-dynamic studies on the adsorption of m-cresol onto micro- and mesoporous carbon. Journal of Hazardous Materials 149, 134-143.

[3] Liu, Y. and Shen L., 2008a. From Langmuir kinetics to fi rst- and second-order rate equations for adsorption. Langmuir 24, 11625-11630.

[4] Liu, Y. and Shen, L., 2008b. A general rate law equation for biosorption. Biochemical Engineering Journal 38, 390-394.

[5] Özcan, A., Özcan, A.S. and Gök, Ö. (Eds.), 2007. Adsorption Kinetics and Isotherms of Anionic Dyes of Reactive Blue 19 from Aqueous Solutions onto DTMA-sepiolite. Nova Science Publisher Inc., New York.



INTRODUCTION

Effi ciently making use of biological processes to recover useful energy from organic wastes is always a goal for the wastewater treatment. Microbial fuel cell (MFC) is a very popular and promising bio-electrochemical power source for directly recovering electrical energy from carbohydrates as well as organics in wastewater. Electricity production in an MFC principally comprises four steps: (i) anodic bio-catalyzed oxidation of organic matter; (ii) physical electron transfer to the electrode via microbial self-produced chemical shuttles (Rabaey et al. 2004), biologically produced nanowires (Reguera et al. 2005), or chemically active redox enzymes (Kaufmann et al. 2001) with simultaneous proton transport in solution from the anode into the cathode; (iii) electron conduction across the external circuit; and (iv) cathodic reduction of oxidants.

In MFCs, catholytes such as potassium ferricyanide (Min et al. 2004; Schroder et al. 2003; Rabaey et al. 2003) or potassium permanganate (You et al. 2006) can be used for optimizing cathodic reactions. These liquid-state electron acceptors, however, may be impractical and unsustainable for practical uses due to a requirement of regeneration. Alternatively, an air-cathode MFC allows use of oxygen freely available in the air as the electron, improving the sustainability and decreasing the operational costs of the cell (Liu et al. 2004). Previously reported air-cathode MFCs have used a single tube as the main body with the anode and cathode placed on opposite sides (Liu et al. 2005a; Liu et al. 2005b; Cheng et al. 2006). Such a design pattern may be problematic for scale up because close electrode spacing can lower the overall capacity of the system. On the other hand, power generated with air-cathode MFCs is usually lower than that produced by liquid-chemical

TUBULAR MICROBIAL FUEL CELL FOR EFFICIENT WASTEWATER TREATMENT AND BIOLOGICAL

POWER GENERATIONShi-Jie You ([email protected])

Luo Peng ([email protected])Jing-Yuan Wang ([email protected])

ABSTRACT: Reported in this study is a novel tubular microbial fuel cell (MFC) for effi cient electricity generation along with wastewater treatment. By continuously feeding artifi cial wastewater into the system, a maximum power density of 50.2 W m-3 could be obtained at current density of 216 A m-3 (external resistance of 22 ohm). As indicated by electrochemical impedance spectroscopy (EIS) analysis, charge transfer resistance (Rc), ohmic resistance (Rohm) and diffusion resistance (Rd) accounted for 22.6%, 50.2% and 26.3% of total internal resistance Large fraction of ohmic resistance mainly originated from the inherent limitation of the system in relation to the reactor design structure and electrolyte characteristics. Such design confi guration is more advantageous by its virtue of low internal resistance and high power density, which provides a proof-in-concept and new approach to optimize the air-cathode MFC design and operation.

catholyte MFCs. Thus, there is a need to further improve the electrochemical performance of air-cathode MFCs.

The goals of the present study were to: (i) examine continuous power generation in graphite-granule, membrane-less tubular air-cathode MFC (GTMFC), and (ii) evaluate internal resistance using electrochemistry impedance spectroscopy (EIS).

MATERIALS & METHOD

The GTMFC was constructed using a 3 cm-diameter and 13.5 cm-high cylindrical Plexiglas tube with the total volume of 95 mL. A cover was placed on the top to collect the effl uent stream, and an infl uent port was placed at the bottom of the reactor. Holes (2.0 mm in diameter) were homogenously drilled through the wall, resulting in a geometrical surface area of 60 cm2 available for proton transport. Anodic carbon granules (Jiangsu province, China) were screened to produce diameters of 3-5 mm (55 m2m–3). The wet volume of the anodic zone was 55 mL. The granules were connected to the circuit using a graphite rod inserted into the packed bed. The cathode was made of a piece of fl exible carbon cloth (30% wet proofi ng; 90 cm2) tightly bonded around the outside wall. Fine C/Pt powders (Pt content 20%; E-TEK) were coated onto the inside surface of the cathode at a loading rate of 0.8 mg-Pt cm-2 perfl uorosulfonic acid (Nafi on) solution as a binder. The GTMFC was inoculated with anaerobic sludge and seed sludge with nutrient solution was continuously fed into the MFC. The anodic medium contained (per liter of deionized water): glucose (1.0g; 1000g mgCOD/L),



NaHCO3 (1 g), KCl (0.13 g), NaH2PO4 (4.22 g), Na2HPO4 (2.75 g), (NH4)2SO4 (0.56 g), MgSO4·7H2O (0.2 g), CaCl2 (15 mg), FeCl3·6H2O (1 mg) and MnSO4·H2O (20 mg). Trace elements were also added in the solution as previously described (Lovley et al. 1988). Anolyte was continuously added into the reactor at a fi xed fl ow rate of 0.4 mL min-1, and recirculated from the upper port back to the bottom using two separate peristaltic pumps.

Voltage generated during experiments for long-term operation were recorded directly every 1 min using a dual-channel voltage collection instrument. Voltage was converted to power density based on the anodic liquid volume (W m-3). The external resistor (REX) was varied over the range of 1-1000 Ω to obtain a polarization curve. The observations of bacterial morphologies on the granule carbon (anode) were performed using scanning electron microscope (SEM) (Hitachi, S570; Japan). Internal resistance was characterized using electro-chemistry impedance spectrometer (EIS) methods.

RESULTS & DISCUSSION

During the start-up phase, the anodes in the GTMFC were colonized using seed sludge and a glucose solution (1000 mgCOD L-1) in a continuous feed operational mode. As is shown in Figure 1, there was a gradual increase in voltage across the resistor (REX=50 Ω) over an initial time interval of 0-326 h (accumulation period), with the voltage stabilizing at 0.376 V during the next 50 h period (326-375 h).

Removing the seed sludge from the inlet fl ow increased power output slightly, with subsequent electricity production from the glucose-only medium sustained at a stable voltage of 0.384 V for an operational time of about 110 h (375-485 h). This implies that electron-transferring (exoelectrogenic) bacteria colonized the granules and were able to catalyze glucose oxidation and produce current. The morphologies of the bacteria on the anodic carbon granules are seen in SEM images in Figure 1.

To examine the dependence of the voltage drop and power on current, a polarization curve was obtained as shown in Figure 2. The open circuit voltage (OCV) of the cell was 0.71 V and the maximum volumetric power of 50.2 W m-3 was produced at a current density of 216 A m-3 (0.246 V; REX=22 Ω).

The steep voltage decline at low current density (<50 A m-3) seems likely to have resulted from the resistance associated with activation losses. The maximum power point occurs over a linear portion of the V-I curve, demonstrating an ohmic limitation occurring over a wide region. Although the maximum power of 50.2 W m-3 here was at the same level of 51 W m-3 obtained by Cheng et al. (2006) in an air-cathode MFC, GTMFC appears to be more advantageous because of its ability of holding larger liquid volumes, which is more suitable for large-scale wastewater treatment.

Figure 1. (Up): Continuous voltage generation time profi les for the GTMFC at a fi xed resistor of 50 Ω. A, a lag phase

(0-326 h); B, stable voltage output (326-375 h); and C, stable voltage generation in the absence of seed sludge (375-485 h).

(Down): Morphologies of microorganisms forming on the surface of the anodic granule carbon.

By fi tting the experimental data into an equivalent electrical circuit (He et al. 2006) using nonlinear least-squares (NLSQ) procedure, we obtained a Nyquist plot (Figure 3). Overall Rint of 27 Ω consisted of an ohmic resistance (Rohm) of 13.8 Ω (51.1%), a charge-transfer resistance (Rc) of 6.1 Ω (22.6%) and a diffusion resistance (Rd) of 7.2 Ω (26.3%). The Rd of 26.3 % observed here seems to be much higher than that of 8.5% reported for an internal-cathode MFC (He et al. 2006). This seems likely to be a consequence of a limitation to proton or oxygen transfer

Figure 2. Power generation and voltage as function of operating current density in the MFC with glucose

(1000 mgCOD L-1) as the substrate.



onto the catalyst layer. Rohm=13.8 Ω observed here is actually lower than the majority of previously reported values for two-chambered oxygen-cathode MFCs (Min et al. 2005) and a single chambered air-cathode MFC (Liu et al. 2004; Liu et al. 2005a).

CONCLUSIONS

We developed a graphite-granule anode, tubular air-cathode MFC (GTMFC) capable of continuous electricity generation from glucose-based substrates. This GTMFC produced a maximum volumetric power of 50.2 W m-3 at current density of 216 A m-3 (REX=22 Ω). This study suggests a feasible and simple method to reduce internal resistance and improve power generation of sustainable air-cathode MFCs.

REFERENCES

[1] Rabaey, K., Boon, N., Siciliano, S.D., Verhaege, M., and Verstraete, W., 2004. Biofuel cells select for microbial consortia that self-mediate electron transfer. Appl. Environ. Microbiol., Vol. 70, pp. 5373-5382.

[2] Reguera, G., McCarthy, K.D., Mehta, T., Nicoll, J.S, Tuominen, M.T., and Lovley, D.R., 2005. Extracellular electron transfer via microbial nanowires. Nature, Vol. 435, pp. 1098-1101.

Figure 3. Nyquist plots of impedance spectra of the GTMFC. Experimental data were obtained and then simulated

using the equivalent electrical circuit.

[3] Kaufmann, F., and Lovley, D.R., 2001. Isolation and characterization of a soluble NADPH-dependent Fe(III) reductase from Geobacter sulfurreducens. J. Bacteriol., Vol. 183, pp. 4468-4476.

[4] Oh, S.E., Min, B., and Logan, B.E., 2004. Cathode performance as a factor in electricity generation in microbial fuel cells. Environ. Sci. Technol., Vol. 38, pp. 4900–4904.

[5] Schroder, U., Nieben, J., and Scholz, F., 2003. A generation of microbial fuel cells with current outputs boosted by more than one order of magnitude. Angew. Chem. Int. Ed. Engl., Vol. 42, pp. 2880-2883.

[6] Rabaey, K., Lissens, G., Siciliano, S.D., and Verstraete, W., 2003. A microbial fuel cell capable of converting glucose to electricity at high rate and effi ciency. Biotechnol. Lett., Vol. 25, pp. 1531–1535.

[7] You, S.J., Zhao, Q.L., Zhang, J.N., Jiang, J.Q., and Zhao, S.Q., 2006. A microbial fuel cell using permanganate as the cathodic electron acceptor. J. Power Sources., Vol. 162, pp. 1409-1415.

[8] Liu, H., and Logan, B.E., 2004. Electricity generation using an air-cathode single chamber microbial fuel cell in the presence and absence of a proton exchange membrane. Environ. Sci. Technol., Vol. 38, pp. 4040-4046.

[9] Liu, H., Cheng, S., and Logan, B.E., 2005a. Production of electricity from acetate or butyrate using a single chamber microbial fuel cell. Environ. Sci. Technol., Vol. 39, pp. 658-662.

[10] Liu, H., Cheng, S., and Logan, B.E., 2005b. Power generation in fed-batch microbial fuel cells as functions of ionic strength, temperature and reactor confi guration. Environ. Sci. Technol., Vol. 39, pp. 5488-5493.

[11] Cheng, S., Liu, H., and Logan, B.E., 2006. Increased power generation in a continuous fl ow MFC with advective fl ow through the porous anode and reduced electrode spacing. Environ. Sci. Technol., Vol. 40, pp. 2426-2432.

[12] Lovley, D.R., and Phillips, E.J.P., 1988. Novel mode of microbial energy metabolism: organic carbon oxidation coupled to dissimilatory reduction of iron or manganese. Appl. Environ Microbiol., Vol. 54, pp. 1472-1480.

[13] He, Z., Wagner, N., Minteer, S.D., and Angenent, L.T., 2006. An upflow microbial fuel cell with an interior cathode: assessment of the internal resistance by impedance spectrscopy. Environ. Sci. Technol., Vol. 40, pp. 5212-5217.

[14] Min, B., Cheng, S., and Logan, B.E., 2005. Electricity generation using membrane and salt bridge microbial fuel cells. Wat. Res., Vol. 39, pp. 942-952.



INTRODUCTION

Vegetation in rivers has signifi cant effects on hydrodynamic characteristics such as velocity distribution and turbulence structures. For the emergent case, the velocity profi le is mostly uniform over the depth [7]. For the submerged case, the velocity profi le is normally S-shaped [2, 5]. Kouwen et al. (1969) [5] showed that the fl ow velocity outside the fl exible vegetation varies in proportion to the logarithm of the distance from the channel bed and may be represented by the following equation:

(1)

where u is the velocity at a distance, z, from the bed, u* is the shear velocity, hv is the height of vegetation, uhv is a slip velocity at a distance z=hv, and κ is the Karman constant. Other similar studies have also been reported by [1, 4].

Recently, Nezu and Sanjou (2008) [6] used the penetration depth (hp) to divide the canopy fl ow region into the three sub-zones as shown in Figure 1. They presented that if h/hv decreases, the thickness of the log-law zone, i.e., h – hlog, becomes smaller, and this zone disappears at the critical depth h/hv = hc/hv ≈ 1.5 - 2.0. Obviously, hc is infl uenced by vegetation density and fl exibility.

In previous studies, there were different methods to apply the logarithmic velocity profile to the vegetated flow conditions, but few of them could be used to analyze the velocity profi le under the condition of h/hv ≈ 1 - 2.0. In this study, the velocity profi les were observed through a laboratory experiment, designed with a series of rigid vegetation models, under shallow fl ow conditions (h/hv ≤ 2). By analyzing the data collected, a simplifi ed model for evaluating the emergent and submerged velocity profi le is presented.

VELOCITY DISTRIBUTION OF VEGETATED OPEN CHANNEL FLOWS

Nguyen Hoai Thanh ([email protected])Cheng Nian Sheng ([email protected])

ABSTRACT: Experimental studies were performed to investigate velocity profi les and turbulence properties of vegetated open channel fl ows. The experimental results show that the velocity distributions signifi cantly deviate from the traditional logarithmic or power law, in particular, for shallow fl ow conditions. By analyzing the data collected and considering that the mixing length is subject to both vegetation confi guration and fl ow depth, a linear function is proposed for describing the velocity variation in the presence of vegetation.

Figure 1. Schematized fl ow model for canopy fl ow (Nezu and Sanjou, 2008).

LABORATORY EXPERIMENTS

Experiments were carried out in a rectangular fl ume which was 12 m long, 0.3 m wide, and 0.45 m deep, with glass walls and a steel bottom (Figure 2). The vegetation was modeled as an array of circular cylinders and was set at the perspex frame placed on a fl ume bottom. In these experiments, the rods had a uniform length of 100mm and the vegetation confi gurations were shown in Table 1. A set of fi ve fl ow depths h (10, 13, 15, 17, 20 cm) was adopted. The fl ume slope was set at 0.004 for all cases. The fl ow depth along the test section was measured to make sure all fl ows tested were uniform. The fl ow discharge was recorded from the electronic fl ow meter.

Mean velocity components (u, w) in the stream-wise (x) and vertical (z) directions, respectively were measured using a 2-D Laser Doppler Anemometer (LDA). The measuring location is shown in Figure 3. Flow velocities were recorded from the fl ume bottom to the free surface.

v

h

h

z

u

u

u

u v ln1

**



ANALYSIS OF EXPERIMENTAL RESULTS

The measured velocity profi les clearly showed a sudden change in the upper edge of vegetation (Figure 4). That turning point divided the velocity profi le into two layers. In the vegetation layer, i.e. z < hv, the velocity is relatively small and almost uniform. The thickness of vegetation layer is defi ned here as z1. In the surface layer, i.e. z > z1, the fl ow velocity rapidly increases. The thickness of surface layer is z2 = h - z1.

Figure 2. The fl ume system

Table 1. Summary of experimental conditions and vegetation confi gurations

Case dv N Cv=Nπdv2/4

mm Rods/m2

A60 3.15 556 0.004 B60 6.641 556 0.019 C60 8.258 556 0.030

B30 6.641 2222 0.077 C30 8.258 2222 0.119

Figure 3. Velocity measuring location.

Figure 4. Flow velocity profi le for case A30, h = 17 cm.

By analyzing the data collected, a correlation was observed between z1/h and hv/h (Figure 5), namely,

(2)08.0)ln(036.007.11v

v Ch

h

h

z

Figure 5. Relationship between z1/h ~ hv/h.

Mean fl ow velocity of the vegetation layer

In the analysis, we assume that the fl ow inside the vegetation layer is similar to that through porous media. The following quadratic form is used to extend Darcy’s law to the fl ow through porous media with signifi cant inertial effects:



(3)

where uv is the superfi cial vegetated fl ow velocity, i is the hydraulic gradient, a and b are coeffi cients. With dimensional analysis, Eq. 3 can be expressed as

(4)

where

(5)

(6)

(7)

μ is the dynamic viscosity, and ε = 1- Cv

From (6), the superfi cial vegetated fl ow velocity (uv) can be calculated by

(8)

In the subsequent analysis, the experiment data are used to explore variations in the two parameters A and B in Eq. (4). First, i

is plotted against Rev as shown in Figure 6. For the emergent fl ow conditions, the best fi t of experiment data to the Eq. (4) gives A = 0.548 and B = -2195. For the submerged fl ow condition, both parameters A and B are not constant, but generally varying with the fl ow depth, and thus hv/h. The best-fi t equations are as follows

and

(9)

vv BAiLv

ReRe23*

vv dg

L1

3/1

2

2

*

vvvv

duRu

11

Re

vd1vR

v

vvv d

vCu

Re

3*vL

1.026 hh

-0.659 vA 4226 - h

h2889 vB

Figure 6. Relation between i 3*vL and Rev

Flow velocity profi le of the surface layer and mixing length estimation

In Figure 7, the velocity u for the surface layer is plotted against (z-z1)/(h-z1), and varied in an almost linear fashion. The mixing length approximation is applied in the region

of fl ow above the vegetation elements. It is defi ned as

(10)

Next, the shear velocity is estimated as and du/dz is calculated by fi tting the observed fl ow velocity profi le in the surface layer. To examine the effects of the vegetation concentration on the mixing length, the hydraulic radius Rv given by Eq. (7) is plotted against the estimated values of Lmx with the data grouped according to their values of the depth above vegetation hs, (Figure 8). The result shows that the relationship of Lmx ~ Rv is almost linear and can be expressed in the following form:

(11)

where α and β are coeffi cients. Furthermore, it can be seen that α -value is almost constant, while β varies linearly with hs. As a result, the value of α and β can be written as

α = 0.010 and (12)

vmx RL

257.0279.0 sh

Figure 8. Relationship of Lmx with Rv

Figure 7. (z-z1)/(h-z1) plotted against u with (z1 ≤ z ≤ h).

2

vbuaui v

dzduu

Lmx /*



Using Eqs. (11) and (12), the mixing length can be expressed as

(13)

Applying Eqs. (10) and (13), the fi nal expression for the fl ow velocity in surface layer then becomes:

(z1 ≤ z ≤ h) (14)

where uz1 is the fl ow velocity at the interface of vegetation layer and surface layer. From the experimental data, a correlation was also observed between uz1/u* and uv/u*, namely

(15)

CONCLUSIONS

The theory of fl ow through porous media can be applied to describe the fl ow within a canopy for both emergent and submerged conditions. For shallow fl ow conditions, the experimental results show that the velocity distributions signifi cantly deviate from the traditional logarithmic or power law. The fl ow velocity profi le is considered using the assumption of a single mixing length in the surface zone. A simplifi ed model is proposed to predict the velocity profi le for submerged shallow fl ow conditions. This was validated by fl ume experiments with the range of vegetation concentration Cv = 0.004 - 0.120. Finally it is important to note that the analysis described in this study applies only to shallow fl ow conditions with h/hv ≤ 2, and the experiments were conducted with rigid cylinders to simulate aquatic vegetation. In reality, such vegetation is often fl exible and has other effects on the velocity profi le, especially near the vegetation edge.

257.0279.0010.0 svmx hRL

REFERENCES

[1] Baptist, M. J., Babovic, V., Uthurburu, J. R., Keijzer, M., Uittenbogaard, R. E., Mynett, A., and Verwey, A. 2007. “On inducing equations for vegetation resistance.” Journal of Hydraulic Research, 45(4), pp. 435-450.

[2] Carollo, F. G., Ferro, V., and Termini, D. 2002. “Flow velocity measurements in vegetated channels.” Journal of Hydraulic Engineering-ASCE, 128(7), pp. 664-673.

[3] Ergun, S. 1952. “Fluid fl ow through packed columns.” Chem. Eng. Prog., 48 (2), pp. 89-94.

[4] Klopstra, D., Barneveld, H. J., Van Noortwijk, J. M., and Van Velzen, E. H. 1997. “Analytical model for hydraulic roughness of submerged vegetation.” Proceedings, Congress of the International Association of Hydraulic Research, IAHR, San Francisco, CA, USA, pp. 775-780.

[5] Kouwen, N., Unny, T. E., and Hill, H. M. 1969. “Flow retardance in vegetated channels.” J. Irrig. Drain. Div., Am. Soc. Civ. Eng, 95(IR2), pp. 329-342.

[6] Nezu, I., and Sanjou, M. 2008. “Turburence structure and coherent motion in vegetated canopy open-channel fl ows.” Journal of Hydro-Environment Research, 2(2), pp. 62-90.

[7] Tsujimoto, T., and Kitamura, T. 1990. “Velocity profi le of fl ow in vegetated-bed channels.” KHL Communication 1990, 1, pp. 43-55.

mx

z

Lzz

uuzu )()( 1

*

1

204.0972.0**

1

u

u

u

u vz


INFRASTRUCTURE SYSTEMS AND MARITIME STUDIES

A SAFETY STOCK PLANNING MODEL FOR GLOBAL SUPPLY CHAINS

Seyed Mehdi Zahraei ([email protected])

Teo Chee Chong ([email protected])

ABSTRACT: The purpose of this research is to develop a safety stock planning model for global supply chains. A single-stage model is fi rst developed and it is then extended to model multistage supply chain networks. The proposed model is capable of modeling general supply chain networks with different review period at each stage. In addition, the proposed production function enables the characterization of production requirements at production facilities, which make possible the consideration of tradeoffs between capacity, inventory and lead-time in the model.

INTRODUCTION

As a result of extensive globalization and offshore sourcing prevalence, supply chain design and planning has become more important than ever. A major concern of global supply chain management is how to determine the optimal level of safety inventory throughout the supply chain in order to provide a high level of service to customers without carrying excessive inventory. The safety inventory is held to protect against uncertainties in demand and/or supply. Safety stock planning for a supply chain involves the setting of the safety stock level at each supply chain stage for all intermediate and fi nished products at their respective locations to meet the target service level.

The existing safety stock planning models have some important limitations (see Graves & Willems 2003 for a review). First, most models consider network confi gurations with restrictive demand fl ow (e.g., serial fl ow network or spanning tree network). Second, most models assume periodic review policies with a common review period for all supply chain stages. Third, very few models consider production capacities and production related costs at the production stages. In the view of these limitations, the objective of this research is to develop a safety stock planning model that simultaneously addresses these issues. In particular, the model considers a general multistage supply chain network confi guration where stages throughout the supply chain are allowed to have different review periods and the capacities at the production stages are explicitly considered.

MODEL ASSUMPTIONS

• Every supply chain stage adopts a make-to-stock strategy.

• The supply chain is modeled as a network of nodes and arcs; each node represents a facility in the supply chain while each arc that connects two facilities denotes that the upstream facility supplies the downstream facility.

• The supply chain facilities are classifi ed as production facilities (e.g., production and assembly plants) and service facilities (e.g., distribution centers and retailers). A production facility processes raw material supplied by its upstream facilities to produce a processed product. Inventories at the production facility consist of raw material inventory, work-in-process inventory and processed material inventory.

• The inventories are further classified into storage stages and production stages. Raw material inventories at production facilities and the inventories at service facilities are classifi ed as storage stages. Work-in-process and processed material inventories in production facilities are classifi ed as production stages.

• All inventories are managed according to the periodic-review base-stock replenishment policy. Furthermore, each stage is allowed to have a different review period from other stages. It is assumed that all stages have a common planning time bucket (e.g., a month or a quarter) but each stage has a review period that is shorter than or equal to the time bucket. In order to achieve dissimilar review periods among the stages, there are sub-periods within the time bucket that represents the review periods of the downstream ordering stages to permit multiple demand arrivals within the underlying planning time bucket. Without loss of generality, it is assumed that each discrete time period t has a length of one time unit. Furthermore, each time period t of stage i is sub-divided into pi equal subintervals of sub-period si, where si = 1, 2,… pi. In addition, pi is defi ned as pi = 1/∆, where ∆ is the length of each sub-period at stage i.

• The stages that serve the end-item demands are defi ned as demand stages. For each demand stage i, the end-item demand process is assumed to be independent and identically distributed over time with an average demand per period of μi.

• The planned production lead-time at each production stage i is fi xed and denoted by Ti. When the replenishment requirement exceeds the production capacity, it is assumed that the production stage takes expediting actions (e.g., overtime or subcontracting) to meet the



planned production lead-time while incurring additional costs.

• Each stage i has a target inventory level to meet a specifi ed service level. When the orders arrive and get fulfi lled from the inventory, the inventory level decreases from the inventory target level. The difference between the actual and the target inventory levels is known as the inventory shortfall, which is denoted by Xit.

SINGLE-STAGE MODEL

A single-stage model is fi rst developed to represent the inventory replenishment at each production and storage stage. The replenishment requirement at a production stage is the production output required to fi ll the inventory shortfall at the processed material inventory within the planned production lead-time.

It is assumed that the demand arrival to stage i (either an end-item demand or demand from an upstream stage) in time bucket t is denoted by Dit and it is assumed that it arrives uniformly within each period t. The replenishment requirements are derived as a function of inventory shortfall and demand arrivals given by:

Rit = βiSit + γiDit (1)

Where

βi = 1 – (1–(∆i/Ti))Pi

and

The variable Rit signifi es the replenishment requirements in period t at stage i and Sit denotes the inventory shortfall at the start of period t at stage i prior to any demand arrival.

Based upon the periodic review base stock policy, the storage stage replenishes a quantity that equals to the demand arrivals plus the inventory shortfall in each period t. Thus, the replenishment requirement in (1) for storage stages is stated as:

Rit = Sit + Dit (2)

SERIAL NETWORK MODEL

The development of the serial network model is fi rst discussed before it is extended to model the general supply chain network in the next section. To model a serial multistage network, the production function in (1) is expressed in matrix notation by:

Rt = FSt + GDt (3)

where Rt = {R1t, …, Rmt}ʹ, St = {S1t, …, Smt}ʹ, Dt = {D1t, …, Dmt}ʹ are column vectors and m is the number of stages. In addition, F is a diagonal matrix with βi (i = 1, 2, …, m) as its diagonal elements. G is a diagonal matrix with γi (i = 1, 2, …, m) as its diagonal elements. The coeffi cients for storage stages are βi = 1 and γi = 1 as defi ned. Demand arrivals can be expressed in matrix form as:

Dt = ΦRt (4)

where Φ is a square matrix with elements Φij; Φij is a positive scalar associated to each arc and it indicates the number of units of material supplied by upstream stage i for each unit of replenishment ordered or required by downstream stage j. By substituting (4) into (3), one can fi nd St as:

St = F-1(I – GΦ)Rt (5)

where I is an identity matrix. The inventory shortfall balance equation is given by:

St = St-1 – Rt-1 + Dt-1 + (6)

where is a column random vector that represents the demand arrivals at the demand stages as well as the noise arrivals at the other stages. The vector has the end-item demand Di,t-1 for the demand stages and for the other stages. The term , is a zero-mean noise term that represents any demand arrival variability at the stage i in period t. By substituting (4) and (5) into (6), and by repeatedly iterating Rt and assuming an infi nite history of the system, it is observed that

(7)

where H = (I – GΦ)-1 and M = I – H (I – Φ). The expected value of vector is given by vector μ, which is a column vector with expected demand μi, in the demand stages as the only non-zero elements, since is a zero-mean term by defi nition. The expectation and the variance of the replenishment vector are given by:

E[St] = (I – Φ)-1μ (8)

(9)



where Var( ) is a covariance matrix that consists of the variance of Dit and the covariances of the noise terms .

The processed material inventory at production facilities should be set high enough to cover the inventory shortfall Xit during the planned production lead-time. In contrast to Sit, Xit signifi es the inventory shortfall at the start of period t after the fi rst demand arrival; thus it represents the biggest inventory shortfall within period t and refl ects the highest likelihood to stockout. To obtain the safety stock level for a specifi c service level, it is essential to characterize the fi rst two moments of Xit given by:

(10)

(11)

where W = (F-1 (I – GΦ) + ∆Φ). If the end-item demand and the inherent variability of the demand fl ow between stages are assumed to be normally distributed, Xit would also be normally distributed. The base-stock level at the production stages can then be set by:

(12)

where zi is the safety factor at stage i and its value refl ects the desired service level in fulfi lling the customer demand. Specifi cally, CDF(zi) is the probability that the safety-stock is able to cover the demand variability, where the CDF is the cumulative distribution function of a standard normal variable. In (12), E[Xit] and Var(Xit) are calculated by (10) and (11) respectively. In addition, the base-stock level at the storage stages is given by:

(13)

where Li is the replenishment lead-time, Δii is the review period at stage i that replenishes from its upstream stage j (i.e., the sub-period length at stage j), and E[Rit] and Var(Rit) are calculated by (8) and (9) respectively.

EXTENSION TO GENERAL NETWORK CONFIGURATION

The serial fl ow model is extended to model the general supply chain networks in which each stage can be connected to multiple upstream and/or downstream stages. If a production stage requires more than one kind of raw material for production, it keeps an inventory for each kind of raw material and each raw material inventory is modeled as an individual storage stage.

If a stage is connected to multiple downstream stages, as discussed earlier, the sub-period length at each stage is its downstream stage’s review period. However, the modeling challenge arises if there are multiple downstream stages with different review periods. In this case, it is assumed that each downstream stage is served by a separate inventory; thus the multiple downstream stages are served by a group of

stages with a single aggregate base-stock level. By doing so, the risk-pooling and the correlation at downstream stages demands are considered. The aggregate values equivalent to (8) to (11) for each group of stages are given by:

(14)

(15)

(16)

(17)

where A represents the set of stages in the group and E[Ri], Var[Ri], E[Xi] and Var[Xi] are calculated by (8), (9), (10) and (11), respectively. The covariance terms in (15) and (17) are the off-diagonal elements in the matrices of Var(Rt) and Var(Xt) in (9) and (11), respectively. The base-stock levels are set in the same way as those for the serial network model in (12) and (13).

R E S E A R C H C O N T R I B U T I O N S A N D DIRECTIONS FOR FUTURE RESEARCH

The proposed model considers general supply chain networks with different review periods at its stages. In addition, the production function in (1) enables the characterization of production requirements at production facilities, which makes possible the consideration of production capacities.

However, several research opportunities exist to address the model’s limitations. For example, it would be a useful enhancement to the model if it can be embedded into optimization procedures to determine the optimal safety stock levels and the planned production lead-times with the objective to minimize the total supply chain cost. In the model, the noise term is employed to model the non-uniform demand arrival; it would be worthwhile to study the accuracy of such a model and to determine if it would be possible to improve its accuracy. Further, there is an opportunity to incorporate the global supply chain complexities into the model to address the growing importance of global supply chain management (see Bhatnagar & Teo 2009 for a review of these global supply chain issues).

REFERENCES

[1] Bhatnagar, R. and Teo, C. C. 2009. Role of Logistics in Enhancing Competitive Advantage: A Value Chain Framework for Global Supply Chains. International Journal of Physical Distribution & Logistics Management, 39(3): 202-226.

[2] Graves, S.C. and Willems, S. 2003. Supply chain design: safety stock placement and supply chain confi guration. In Kok, A. G. d. & Graves, S.C., editors, Handbooks in OR & MS, Elsevier, Vol. 11, pp. 95-132.



ACCURACY OF GPS HEIGHTING IN THE SINGAPORE CONTEXT

Tor Yam Khoon ([email protected])

ABSTRACT: A geometric geoid for Singapore mainland had been modelled using ellipsoidal heights derived from Global Positioning System (GPS) and reduced levels obtained from precise levelling of 464 benchmarks. The geoid model is useful in converting an observed ellipsoidal height, which is a height above a mathematical model of the earth, to a height above mean sea level – a height reference for engineering construction works. Accuracy of 3 to 5 cm had been verifi ed.

INTRODUCTION

A Geometric Geoid model for Singapore was modelled using the geoidal heights derived from the ellipsoidal heights acquired using Global Positioning System (GPS) and the reduced levels of 404 Precise Level Bench Marks (PLBMs). These PLBMs cover the whole of the Singapore mainland. 60 test benchmarks were used to verify the accuracy of the geoid model. This paper reports on the achieved accuracy of the reduced levels derived from the model.

RE-ESTABLISHING OF SINGAPORE PRECISE LEVELLING NETWORK

A complete re-levelling of the Singapore Precise Leveling Network was the fi rst step in creating a Geoid Model of Singapore.

Figure 1 shows the overall layout of the levelling routes carried out in this project.

Figure 1. Overall layout of leveling routes.

The leveling routes were organised into 4 batches. There are common benchmarks between the 4 batches so as to form a homogeneous levelling network covering the whole of the Singapore mainland.

Two-way levelling was performed between two PLBMs within the specifi cation of ± 2.5√K mm with K in km. A GPS Real Time Kinematic (RTK) heighting, comprising 20 readings with single initialisation per PLBM, was also obtained.

Reduced levels of seven Fundamental Benchmarks, i.e. FBM104, FBM106, FBM107, FBM108, FBM109, FBM110 and FBM111, were also determined in this project (Figure 2). STDBM6 was adopted as the reference benchmark and its stability was confi rmed with 116 other existing benchmarks with differences of less than 3 mm.

RESULTS OF LEAST SQUARES

Figure 2. Locations of Fundamental Bench Marks and STDBM6.

ADJUSTMENT

STDBM6 and the other 116 existing PLBMs were held fi xed in an absolute (or fully) constraint least squares adjustment after a minimum constraint least squares adjustment which detected outlying observations. These outlying observations were re-observed before the fully constraint solution. The parameters for the least squares adjustment carried out using Move3D are shown in Table 1.



Table 1: Parameters for Least Squares Adjustment

STATIONS

Number of known stations 117

Number of unknown stations 3081

Total 3198

OBSERVATIONS

Height differences 5608

Known coordinates 117

Total 5725

UNKNOWNS

Coordinates 3198

Total 3198

Degrees of freedom 2527

Figure 3 shows the distribution of the corrections to the approximate reduced levels of the benchmarks. About 90% of the corrections are within 6 mm. The corrections are quite well distributed, approximating a normal curve distribution. No discernable bias was found in the adjustment.

Figure 3. Distribution of the Corrections to Approximate Reduced Levels.

GEOMETRIC GEOID MODELLING

Stepwise Multiple Regression using the method of forward selection was used to compute the polynomial equation for the geometric geoid for the mainland of Singapore.

43 independent variables derived from the easting and northing coordinates of 464 PLBMs were made available to compute the multiple regression surface to best fi t the 464 PLBMs with geoid separations (GS), which are the dependent variables in the formulation. In the stepwise method, each independent variable is added one by one to the equation. Only the signifi cant independent variables are retained in the progressive process. 60 benchmarks were found to be unable to fi t in with the models. Figure 4 shows

the distribution of the differences between the adjusted reduced levels (from precise leveling) and reduced levels derived from the geometric geoid of the 60 PLBMs which were rejected in the geoid modelling. 55% of the differences are about 0.05 m and about 22% have differences ranging from about 0.2 m to greater than 1 m.

Figure 4. Distribution of the differences between adjusted and geoid-derived reduced levels of the 60 PLBMs

rejected in the geoid modelling.

Only fi ve independent variables and a constant term were ultimately adopted as shown in Eq. (1):

GS = 8.94184 + 2.08529*E – 0.16502*N – 0.661429*E2 – 0.139884*N2 + 0.232462*E6*N (1)

where,

E and N are normalized values of the easting and northing coordinates, i.e. ranging from 0 to 1.

VERIFICATION OF GEOMETRIC MODEL

The geometric geoid was verifi ed using two test data sets. The fi rst set comprises 26 post-processed static GPS observations and 6 RTK observations. The differences between the adjusted reduced level as computed in this project and the reduced levels deduced from the geometric geoid range from -0.034 m to 0.059 m.

The 60 PLBMs which were previously rejected in the geoid modeling had their ellipsoidal heights re-observed using RTK techniques and used as the second test data set. The well distributed fi rst (blue) and second (red) Test PLBMs are illustrated in Figures 5.



Figure 5. Distribution of First (Blue) and Second (Red) Test PLBMs.

Errors were found in the previous RTK ellipsoidal heights of these 60 PLBMs. Figure 6 shows the distribution of the differences in the resurveyed RTK ellipsoidal heights. Differences of up to about - 0.4 m were found in the RTK heights. Other large errors (about 1 m and greater) as shown in Figure 4 were attributed to clerical errors.

Figure 7 illustrates the distribution of the differences between the adjusted and the geoid-derived reduced levels of all 464 PLBMs. About 82%, 95% and 99% of the PLBMs have their differences between the adjusted and geoid-derived reduced levels confi ned to within ±0.030 m, ±0.040 m and ±0.050 m, respectively.

Figure 6. Distribution of the differences in resurveyed RTK ellipsoidal heights.

RECOMMENDED PROCEDURE FOR RTK HEIGHTING

Two sets of tests were carried out to ascertain the optimum way of performing RTK heighting as it is a critical component in deriving reduced levels from the Geoid Model:

(1) 5 RTK heights obtained with individual initialization; and

(2) 5 RTK initializations with 3 RTK heights each.

In Set (1), the median of the 5 RTK heights in Set (1) was adopted as the ellipsoidal height. And for Set (2), the median of the medians of the 3 RTK heights was adopted. The purpose of re-initialization is to detect incorrect ambiguity resolution giving rise to wrong ellipsoidal height.

A consideration on the choice of the optimum RTK observation, besides the results, would then depend on the time duration of the two tests. Both tests took between 20 minutes to slightly more than 30 minutes. So, the repeated observations in each initialization does not take more time than the initialization process which gives confi dence to the correct ambiguity resolution in each RTK reading.

Both tests seem to give comparable results. The differences are within 30 mm. Thus, it is recommended to adopt 5 RTK initializations with 3 RTK heights each as the desirable method for the RTK heighting.

CONCLUSIONS

The geometric geoid, as determined using multiple regression forward stepwise method, RTK heighting and the precise leveling, is able to achieve accuracy to within ±0.030 m, ±0.040 m and ±0.050 m for 82%, 95% and 99%, respectively.

Figure 7. Distribution of the differences between adjusted and geoid-derived reduced levels of 464 PLBMs.



It is recommended to perform 5 separate initializations and to acquire 3 readings in each, i.e. a minimum of 15 readings in all for each benchmark. The middle value of the 5 middle values of the 5 sets of readings is to be used to derive the reduced level from the ellipsoidal height and the geoid model.

The geometric geoid is suited for engineering applications which can accommodate a ±5 cm uncertainty in the height.

ACKNOWLEDGEMENT

The author would like to acknowledge and extend his heartfelt gratitude to the staffs of Land Survey Services of Singapore Land Authority, especially Dr Victor Khoo and Mr Rashid Md Noor, who had made the gathering of the valuable information possible.



CHARACTERISTICS OF NON-RECURRENT CONGESTION ON

EXPRESSWAY NETWORKGopinath Menon ([email protected])

ABSTRACT: Singapore has 161 km urban expressway network with grade separated junctions. An expressway monitoring and advisory system (EMAS) handles non-recurrent congestion caused by incidents (breakdowns and accidents). EMAS control centre operators detect incidents, send out vehicle recovery crews (VRC) to help vehicles in distress and forewarn approaching motorists of the incidents via variable message signs along the expressways. July 2008 data shows an average of 42 incidents per day, spread evenly across the network. 28% of the incidents are traffi c accidents, with 1 in 4 being chain collisions. 85% of vehicle breakdowns are caused by mechanical faults and punctured tyres. Average VRC response time is 8.3 min.

EXPRESSWAY NETWORK

Singapore has nine expressways with a total length of 161 km out of a total of 3325 km of roads (as of 2008) The network includes two tunnel sections of the Central Expressway. The latest expressway, a new underground expressway, the Kallang Paya Lebar Expressway was opened in September 2008.

Expressways are high speed roads (speed limit 70 km/hr to 90 km/hr) with grade separated junctions. The number of lanes varies from 3 to 5 per direction with shoulders on both sides for vehicles in distress to stop. Pedestrians/ cyclists are prohibited on the expressway. Vehicles with a posted speed limit of 40 km/hr (engineering vehicles etc) are also banned from using them.

Because of the urbanised nature of the island, pedestrian overhead bridges and underpasses are provided for pedestrians to cross expressways where needed. There are no bus stops except for one or two sections (where bus bays are provided) and only express buses use the expressways.

The expressway network connects major areas of activity such as the city, new towns, industrial estates, the port and the airport. 55% of all travel is on expressways.

Expressways suffer from non-recurring congestion caused as a result of incidents such as vehicle breakdowns and accidents. Incidents do not only throttle traffi c fl ow, they can also cause secondary accidents by motorists gawking at the cause of the incident. The Federal Highway Administration of USA estimates that 25% of all congestion is caused by incidents [1]. It is thus very cost-effective to have systems in place to manage non-recurring congestion.

EXPRESSWAY MONITORING AND ADVISORY SYSTEM (EMAS) [2]

EMAS is an incident management system, used to manage traffi c on the expressway network, implemented in 1998. The Intelligent Transport Systems Centre (ITSC) is the heart of all of the Land Transport Authority’s intelligent transport systems. EMAS is controlled from ITSC by operators at the central control room.

EMAS detects incidents as they occur, sends out vehicle recovery crews (VRC) to remove vehicles involved in incidents on the expressways ( and call out the Traffi c Police in case of injury accidents) and forewarns approaching motorists of the traffi c conditions that they are likely to face, so they can make informed choices of what they want to do. In this way, EMAS minimises downtime of the expressway network by removing obstructions and prevents approaching vehicles from joining and contributing to the congestion.

EMAS has three sub-systems

a) Overhead detection cameras located strategically on lamp posts, overhead bridges, fl yovers to collect real time traffi c data and detect incidents and congestion as they occur to alert the control room operators

b) Overhead surveillance cameras (CCTV cameras) located at well-chosen locations (to give a full coverage of the network) to provide visual verifi cation of incidents, that the operators use when alerted of incidents by detection cameras.

The operators will activate the Vehicle Recovery Crew (See Figure 1), stationed at strategic locations or patrolling the expressway, to the incident site to remove the obstruction.



Working closely with the recovery crew, a team of Traffi c Marshals (who are Auxiliary Police Offi cers) carry out on-scene management duties like traffi c control and evidence preservation for accidents involving minor injuries. This is to improve on accident clearance time, especially for minor accidents. The Traffi c Police (TP) will be called out to handle all accidents involving major injuries and fatalities.

c) An information and dissemination system that forewarn motorists of the traffi c situation through well-positioned variable message signs such as traffi c information displays (TID), travel time displays (TTD) and traffi c sign displays (TSD).

Figure 1. Vehicle Recovery Crew*

TID shows message on incidents, planned maintenance works and events. (See Figure 2). TTD, located at entrance ramps shows estimated travel times (based on prevailing traffi c conditions) to major destinations. TSD, located on central medians is a smaller version of TID and is used when TIDs cannot be installed because of site constraints.

EMAS minimises non-recurring congestion and safety problems by quick deployment of vehicle recovery crew, and forewarning of other motorists. It provides motorists in distressed vehicles with timely assistance and allows other motorists to make informed decisions on their route choice.

Figure 2. Traffi c Information Display (TID)**courtesy LTA

DATA COLLECTION

EMAS obtains information from the network on traffi c volumes, traffi c speeds, traffi c incidents, traffi c congestion and incident recovery times.

This paper is based on information obtained from LTA by NTU; on the total number of incidents detected by the EMAS on the 8 expressways in July 2008 (The 9th expressway Kallang Paya Lebar Expressway was not opened yet during this period.) The data is used to investigate the characteristics of incidents, which often lead to non-recurring congestion

Monthly Trends

Table 1 shows the number of incidents on the expressway network that were spotted by the EMAS control centre and attended to by the Vehicle Recovery Crew (VRC) from July 2007 to July 2008.

The term incidents includes both non-accident incidents and accidents

The number of monthly incidents attended to, varies between 1173 and 1449 for the period of July 2007 to July 2008. Although there are some fl uctuations, a three month moving average smoothens out the variations. The monthly number of incidents is fairly constant.

The rest of the paper analyses the data for the month of July 08, considered a typical month. There were 1313 incidents attended to, in July 08.

Table 1. Monthly trends of incidents (July 07 –July 08)

Month Number of 3 month moving incidents average

July 07 1188

August 07 1205 1247

September 07 1347 1271

October 07 1261 1294

November 07 1275 1322

December 07 1430 1294

January 08 1177 1328

February 08 1378 1293

March 08 1323 1383

April 08 1449 1353

May 08 1287 1303

June 08 1173 1258

July 08 1313



Method of Detection of Incidents

Figure 3. Method of detection of incidents (July 08)

From Figure 3, the automatic camera system is only detecting 55% of the incidents. But together with the vehicle recovery crew who constantly patrol the network and the traffi c marshals, 87% of detections are by EMAS. The Traffi c Police also reports incidents on their normal patrols. The majority of the other incidents would have been detected, but what usually happens is that motorists (public) who carry mobile phones beat the system by calling the ITSC or the radio stations immediately. It is heartening to note that the motorists participate actively in contributing to about 12% of the calls. Obviously, they are aware of the existence of EMAS and its usefulness in minimising non-recurring congestion.

(LTA carries out surveys to gauge the driver reaction on the usefulness of the EMAS on score of 1 to 6; 1 being very poor and 6 being excellent. The average score for 2007 (January to December) was 5.61 [3])

Summary of Incidents

Table 2 shows the number of incidents and the time taken by the vehicle recovery crew (VRC) to reach the location (response time), the fi gures in brackets refer to the respective ranks in that column.

Table 2. Number of incidents and response times in July 08 [4]

Expressway Length Number of Mean Std

Name* in km and incidents response Dev

Rank in and Rank time (mins) (min) brackets in brackets by VRC

Kranji KJE 9 (8) 54(8) 7.8 6.3

Pan Island PIE 43(1) 446(1) 9.3 6.9

Seletar SLE 13(6) 95(5) 8.1 6.2

Tampines TPE 15(5) 62(7) 8.1 6.2

East Coast ECP 19(3) 146(4) 8.3 6.3

Central CTE 16(4) 206(3) 7.8 6.7

Ayer Rajah AYE 27(2) 210(2) 8.3 6.3

Bukit Timah BKE 11(7) 94(6) 9.0 6.4

Total Network 1313 8.3 6.5

*Kallang Paya Lebar Expressway excluded because it was opened only in September 08)

Non-parametric rank correlation was carried out on the length of expressways vs. the number of incidents (Columns 2 and 3). Spearman’s rank correlation co-effi cient is 0.90. The value of 0.90 is compared with published tables for various levels of signifi cance. From the tables with 6 degrees of freedom (i.e. 8 – 2), the likelihood of the rank correlation of 0.9 occurring by chance is 1%. So we accept a high correlation of 0.9 between the two. Hence the longer the expressway, the greater the probability of an incident or in other words the incidents are well spread out over the network.

Daily Incidents

There were a total of 1313 incidents for the month of July 08, which works out to an average of 42 incidents per day. Figure 4 shows the number of incidents for a week in July 08, highlighting the differences between weekdays and weekends.

Figure 4. Number of incidents in a typical week (July 08)

In a further breakdown into days of the week, Saturdays and Sundays show average values of 44 per weekday, 42 per Saturday and 32 per Sunday, refl ecting the reduced traffi c volumes on Sundays, which seems to result in fewer incidents.

In the whole of the month of July 08, there were 744 hours (31 days x 24 hrs). There were no incidents for 180 hours amounting to 24% of the time, mostly in the early mornings after midnight.

ACCIDENT AND NON-ACCIDENT INCIDENTS

As mentioned before, incidents can be classifi ed into two types – non-accidents and accidents. Figure 5 shows the breakdown into details of incidents.

There were 363 accidents out of the total of 1313 incidents. Accidents constitute 28% of all incidents. In other words,



roughly 1 in 3 incidents is an accident. The number of vehicles involved in accidents is 741, which works out to about 2.04 vehicles per accident. 86 out of the 363 accidents were chain collisions. Approximately 1 in 4 of the accidents results in chain collisions, involving anything from 3 to 6 vehicles. This attests to the fact that some vehicles do not keep safe stopping distances between themselves when travelling.

Figure 5. Classifi cation into accidents and non-accident incidents (July 08) (Total 1313)

Of the 363 accidents, 35% were injury accidents which also resulted in 3 fatalities. 104 of the accidents involved single vehicles losing control, amounting to 28%. Single vehicle accidents are caused by motorists not having/or exercising proper control of their vehicles.

Accidents have repercussions since it takes, on average, a longer time to remove a vehicle involved in an accident because of the need for towing services (or Police presence and investigation). Hence accidents will, on average, cause longer periods of non-recurring congestion.

CAUSES OF NON-ACCIDENT INCIDENTS

Figure 6 shows the cause of non-accident incidents, mainly vehicle breakdown.

The main cause of vehicle breakdowns of mechanical faults and punctured tyres (total of 85%) may point to a lack of proper maintenance. In all such cases, the recovery crew tows the vehicle away from the expressway to the nearest designated car park, free of charge. It is unfortunate that about 5% of the broken down vehicles did not have suffi cient petrol when they entered the expressway. The unattended vehicles refer to those whose drivers have left the location by the time the VRC arrives.

Figure 6. Causes of vehicle breakdowns (July 08) (Total 881*)

*There were 69 other incidents involving litter on the road and pedestrians which are not included.

TYPES OF VEHICLES IN INCIDENTS

Figure 7 shows the percentage of vehicles involved in incidents

Figure 7. Types of vehicles involved in incidents (July 08)

Cars and taxis account for most of the incidents. The ranking of vehicles in this Figure 7 was compared with the ranking of the vehicle population in July 08. There is a one to one correspondence indicating that no one type of vehicle contributes more to incidents than another in relation to its population.

RESPONSE TIME OF VEHICLE RECOVERY CREW

Whenever an incident is detected at the control centre, the VRC is dispatched immediately. Non-recurring congestion starts when the incident happens. Response time is the time between detection of the incident and the arrival of the VRC at the scene of the incident. If the VRC spots the incident on its normal patrols, then the response time is zero. Recovery time is the time between the detection and the time that the obstruction is removed, so that traffi c fl ow can return to normal. Recovery time for non-accident incidents is in the order of less than half an hour. Recovery time for accidents can last much longer depending on the severity and whether there are injuries.



Table 2 shows that the mean (average) response time of the recovery crew for each expressway is less than 10 mins, the average being 8.3 min.

The mean response time during peak periods (7.30am -10.00 am and 5.00 pm - 7.30 pm) on the network is 9.5 mins as compared with 7.7 mins for off-peak periods. The mean response time for the network during the weekdays is 8.4 mins against 8.2 mins for a weekend

A test of signifi cance for the comparison of population means was carried out on the data (400 readings for peak periods and 913 for off-peak periods). The null hypothesis was that the mean response times were the same for peak and off-peak periods. This was rejected at the signifi cance level of 5%. This means that the increased traffi c volumes during the peak periods slow down response time by the recovery crew. However statistical tests do not show a difference in mean response times during the weekdays and weekends.

CONCLUSIONS

Incidents on the expressway network cause non-recurring congestion and may lead to secondary accidents. These are mitigated by constant monitoring of the expressways from

a control centre and sending out vehicle recovery crew to help vehicles in distress.

An audit of Singapore’s system for the month of July 08 shows that the control centre is effi cient in detecting and responding with the vehicle recovery crew within reasonable times. It takes the VRC slightly longer to get to the incident location during the peak periods because of heavier traffi c fl ow during peak periods. There is an average of 44 incidents attended to per day. The incidents are well spread out across the network. Accidents account for about 28% of the incidents. 85% of the non-accident incidents are vehicle breakdowns, possibly caused by a lack of proper maintenance of vehicles.

REFERENCES

[1] http://www.fhwa.dot.gov/congestion

[2] Land Transport Authority, 2006. “Intelligent Transport System Centre.” Pamphlet.

[3] Menon, G. & Quek, S.K., 2008. “Intelligent Transport System – a step by step process.” Intelligent Transport System (ITS) Asia Pacifi c Conference.

[4] Ng, L.O., 2009. “Profile of incidents on Singapore’s expressways.” Final Year Project, Nanyang Technological University.



DYNAMIC ENCRYPTION TECHNIQUE FOR THE SECURITY AND EFFICIENCY

OF ATMS DATA TRANSMISSIONLum Kit Meng ([email protected])

Chang Tang-Hsien ([email protected]) Chang Yuan-Jui ([email protected])

ABSTRACT: This paper describes a dynamic encryption technique which concentrates on the information security of the data transmission of the Advanced Transportation Management System (ATMS) through modern cryptography, and is developed with the Java programming language in which the cryptography techniques would be adopted to protect the contents of data packets from masquerading, replying and tampering; and the encryption algorithms are used to transform the plaintext into the ciphertext via secret information (i.e., the secret key of symmetric cryptography and the public key pair of asymmetric cryptography). However, data switching of traffi c control systems nowadays is exposed and not protected, and the secret information algorithms during the encryption/decryption procedures are consistent and regular for the common cryptographic techniques. Furthermore, one could paralyze the traffi c control system and crack the cryptographic mechanism easily via the existing software or certain attacks. Hence, it is indispensable and necessary to establish and implement an encryption technique in which the secret information could be changeable for each message and suitable for the ATMS data transmission; we called it the dynamic encryption technique. Unfortunately, the process of improving the data security also has some negative effects on the core system. Therefore, the system operation effi ciency is also a major consideration. In addition, the security mechanism could be suitable for the existing communications media which the transportation fi eld commonly uses nowadays, namely: wired network communications and 3.5G mobile communications.

INTRODUCTION

ATMS is the major sub-system of ITS, and it makes use of monitor apparatuses, communications and other control technologies to obtain traffi c information and, subsequently to transmit or exchange the data from the Transportation Management Information Centre (TMIC) to the Transportation Communication and Information Station (TCIS) or beacons via network communications. Because of the need to transmit information, the communications technology becomes one of the important factors for ATMS.

The protocol of ATMS is dependent on the National Transportation Communication for ITS Protocol (NTCIP). In order to combine and not to collide with the common communications protocol, the stack of NTCIP refers to the model framework of International Standards Organization-Open System Interconnect (ISO-OSI). The ISO-OSI model makes NTCIP suitable with the common communications protocol; it means that NTCIP might meet the security issues in the open network environment as well.

As mentioned above, data packet switching nowadays is exposed and not protected. Someone can use existing software (e.g. Sniffer Pro, Iris, etc) to intercept the data packets from transmission processes easily. In addition, the internal framework of NTCIP which is similar to ISO-OSI, allows one to read, masquerade, eavesdrop, modify, tamper or reply to the original messages easily during the data transmission of traffi c control systems. These actions will cause ATMS to become paralyzed and disorder the signal

timing or infl uence the traffi c safety seriously further. A currently possible solution is to build an Intranet Network System up for ATMS (i.e., Virtual Private Network, VPN). While the communications environment of Intranet is closed, and the fi re-wall is well-controlled, the invading opportunity will be reduced, but the cost will be greater.

From these reasons, this research focuses on the information security of data transmission through modern cryptography and sets up a suitable encryption technique which aims at message packet interchanging and transmitting. Even though hackers intercept these message packets during the transmission process they can only get the ciphertexts and not the plaintexts (original messages). That is because the texts (or message packets) have been encrypted into ciphertexts, and each ciphertext needs the opposite key (secret key) to decrypt. Hence, hackers would not be able to know the actual content of each message packet, let alone masquerade or modify the message packets. Besides, in each encryption procedure, the dynamic security mechanism (DSM) of this research can provide a respective secret key for different message packets, and the secret key can be changed each time. Even if hackers use brute-force attacks, they would not get the correct content of message packets smoothly, due to the multiple protections of the DSM.

In order to improve the security level, the security mechanism might consume a lot of resources of the core system. How to increase security and at the same time not affect the original core system are the trade-off issues that will be studied in detail. On the other hand, this security mechanism could be operated not only on the Windows



operating system but also on other operating systems (e.g. Linux, Unix) while the DSM was practiced in the real condition. This research chooses Java programming language to be the development tool because the Java programming language comprises two important properties, namely: Java byte code can be executed on any computer OS with a Java Virtual Machine (JVM) and Java programming language is also an object-oriented programming language.

PROBLEM IDENTIFICATION

NTCIP is a family of communications protocols and data defi nition standards that have been designed to accommodate the diverse needs of various sub-systems and user services of ITS. The applications for NTCIP are generally divided into two categories: Centre-to-Centre (C2C) and Centre-to-Field (C2F) communications. For each category applications, NTCIP supports devices and each of the system usage in traffi c, transit, emergency management, traveler information and planning/data archiving systems.

At the beginning, the fi rst NTCIP standards developed were intended for C2F applications. This part involved a new application level standard termed Simple Transportation Management Protocol (STMP), a new sub-network level standard called the Point-to-Multi Point Protocol and several sets of new standards of data elements called dynamic object defi nitions at information level. Each standard specifi es one or more protocols to be used at the given level, and it is allowed and required to transmit a message between each of these standards. The course uses a series of standards to transmit messages called “Stacks of Standards” or “Protocol Stack”. During the messages transmissions process between each device, it is possible that, perhaps, a portion of the messages use a set of standard to transmit while the others use another standard to transmit.

NTCIP is the communications protocol framework which is specially designed for ITS. Therefore, NTCIP considers the particular requirements of ITS development to extend a new communications protocol framework which is different from former communications protocols. STMP is a tailor-made communications protocol for transportation system in NTCIP, and it is also a variation of Simple Network Management Protocol (SNMP) developed by NEMA to address low-bandwidth communications links and real-time device monitoring.

In addition, the data packet structure of NTCIP object is similar to ISO-OSI modulus, and the STMP message form is much simpler than the SNMP message form; therefore, attackers can read, modify or attack the message easily while they intercept these message packets. Thus, if the traffi c control management system is invaded, it will lead to severe consequences. Hence, the NTCIP Standards publisher, NEMA, also points out that it is necessary to establish a set of security mechanisms to resist attacks and

this security mechanism should be provided with fl exibility for different environments and conditions.

Therefore, the discussion below discusses some possible attacks that ATMS might encounter during the NTCIP object transmission even if we have already added cryptography techniques to it; namely: masquerade (see Figure 1), eavesdrop, man-in-the-middle-attack, modification of message and message reply, various attack, host invading, etc.

Figure 1. Masquerading Attack in ATMSData Transmission

RESULTS AND CONCLUSIONS

As mentioned, the purpose is to establish a suitable and dynamic security mechanism for ATMS data transmission by using the modern cryptography technologies. However, the security mechanism addition would also have negative effects on the core system due to the complex operations of the security mechanism. Besides, the operation effi ciencies are also an important consideration for this security mechanism. Consequently, 3 experiments were designed to test the DSM operations under the different conditions that we commonly encountered. The conclusions are summarized below.

• The DSM is based upon the hybrid cryptosystem which is composed of symmetry cryptosystems (RSA) and asymmetry cryptosystems (AES). There are no useful techniques in cracking the RSA and AES algorithms in a short time nowadays even using the brute-force attacks. Moreover, attackers might need to spend over 10 hours to crack the 56-bit secret key of AES algorithms using high computation-capability computers via the brute-force attack. On the other hand, the data transmission in ATMS or traffi c control is real-time. Therefore, the 128-bit AES secret key is enough for ATMS data transmission.

• The DSM utilizes the message digest algorithms in between the transmission processes to ensure the data integrity, and these message digests are composed of not only the ciphertexts but also the pre-stored passwords at each host as well; therefore, one could not masquerade the transmitters or receivers easily that way. Besides, the test results of these experiments demonstrate that the message digest operations generate fewer negative effects for the core systems.



• The security information (AES secret key and RSA public key pair) of DSM is obtained from the security random number generator and it utilizes the message digest which is calculated from each original data to be the seed-number. It modifi es the seed-number issues of random number generations of computers.

• As represented above, DSKG and DPKG use the message digest to be the seed-number and do not directly use the original message because the message digest algorithm is a one-way function; therefore, one cannot fi gure out the original data from the message digest even if one cracks the secure random number generator, which provides more protection for the data transmission.

• From the results of the series of experiments (see selected results given in Figures 2 and 3), we know that the time-consumption of DSM operations are dependent on the factors in the device operations and data transmission procedures; especially in the device operations. Therefore, both of the network bandwidth and device operation effi ciencies should be considered for DSM operations upon a suffi cient level of security is maintained.

• Although the test results indicated that the AES operations are not a noticeable factor for the DSM operations the NTCIP decryption procedures occupy almost one fi fth of the DSM operations and are operated by TCIS devices. Therefore, we should consider the AES operations for lower computation-capability TCIS devices.

Figure 3. DSM operation in different NTCIP object dispatch interval

Figure 2. DSM operation in different RSA public key pair length



IMPACT OF INCREASING CONTAINERSHIP SIZE ON PORTS

Thai Van Vinh ([email protected])

ABSTRACT: In the quest to achieve more economies of scale, it has become increasingly clear that there are no insurmountable technical barriers to further increases in the size of container vessels, as observed in designs developed for vessels up to 18,000 TEU and the current deployment of 11,000 TEU vessels such as the Emma Maersk (In fact, the calculated capacity of this vessel is 15,212 TEUs[1]). This however results in several major impact on ports on a number of aspects such as investment in physical infrastructures, changes in shipping patterns and ports of call, changes in port operations, concerns on safety, security, and environment protection, and requirements on port logistics development. In this paper, we aim to examine this topical issue.

TRADE, PORT THROUGHPUT AND TRENDS IN CONTAINERSHIP SIZE

It is forecasted that container trade will double by 2016 to reach 287 million TEUs (Twenty-foot Equivalent Unit), and more than double by 2020 to exceed 371 million TEUs. In 2009, world trade is expected to decline for the fi rst time since 2001 as a direct result of the US economic slowdown, subprime credit crisis, surging commodity prices, in particular oil, weakness of the USD and the lasting boom in many countries and sectors which has led to excess capacities. Nevertheless, global container trade, as part of world seaborne trade, will continue to grow at a rate of 7-8% per annum till 2015, as per the estimate of UNESCAP[2].

As the container trade grows, the ships serving it will become larger to take advantage of economies of scale. Indeed, containerisation has witnessed a progressive increase in maximum ship size over the years. Containerships have evolved to the sixth generation today with a carrying capacity of 14,500 TEUS and have been named as the ‘New Panamax’ generation. Meanwhile, there are also no insurmountable technical barriers as concept designs for Suezmax (capacity of about 15,000 TEUs) and Malaccamax (capacity of about 18,000 TEUs) containerships already exist.

The launch of operations of two 8,000-TEU vessels, Excel Maersk of Maersk-Sealand and Shenzen of OOCL in 2003 marked the beginning of the very-large-containership’s era. The largest classes of ships on order and beginning to enter service are in the 13,000- to 14,000-TEU range, with the Emma Maersk being the fi rst of this generation. According to Journal of Commerce[3], by the end of 2008 vessels of 6,000-TEU or more constituted about 25% of the global container fl eet capacity. By 2010, there will be many Suezmax containerships with 15,000-TEU capacity, while by 2015 the size could rise to 18,154-TEUs (Malaccamax ships).

There are explanations for the quest to deploy increasingly larger containerships, including the attempt to achieve more economies of scale and to become market leaders in container shipping by consolidating and strengthening the relative strategic positions of the world’s top container lines. Larger ships offer considerable economies of scale (increased capacity with higher speeds at lower costs per TEU). Samsung Heavy Industry recently reviewed the cost of ship building between two 6,200-TEU vessels and one 12,000-TEU vessel and found that there was approximately 16% reduction in costs by building one of the latter rather than two of the former. A vessel of 12,000-TEU on a long distance route would generate about 11% cost saving per container slot compared to a 8,000-TEU vessel, and even 23% compared to a 4,000-TEU vessel[4]. Drewry Shipping Consultants[5] also made a similar calculation to indicate potential cost differences of around 50% between a Panamax ship of 4,000-TEU and a mega post-Panamax vessel of 10,000-TEU. The in-house ship cost model of Meyrisk and Associates[6] indicated that the cost per TEU per day for a 2000-TEU ship is only a little over half that for a 500-TEU ship.

Figure 1. Six Generations of ContainershipsSource: Hofstra University.



IMPACT OF INCREASING CONTAINERSHIP SIZE ON PORTS

As the size of containerships continues to increase, serving these ships present several issues for ports from various aspects below:

Physical Infrastructure Investments

Since containerships increase their size in all dimensions, e.g. length, width and draft, ports need to make hefty investments in terms of infrastructure to accommodate these mega-vessels. The fi rst investment is to deepen the water-depth at berths. Many ports have begun to dredge their access channel to reach the required water-depth for bigger containerships. For example, the A$590 million Port Phillip Bay Channel Deepening Project, once completed, will provide Post Panamax Plus vessels calling at the Port of Melbourne in Australia with 14m draught access at all tides[7]. Ports may also need to have wider channels for ships, as well as suffi cient area to accommodate the larger number of containers that will accumulate before the ship arrives and as she is being discharged and loaded. In addition, ports also need to invest in high-speed cargo handling equipment such as Panamax and post-Panamax gantry cranes that can handle 22-23 container rows and other sophisticated yard equipment to increase terminal handling productivity and shorten ship turnaround time in ports. It is worth noticing that the above investments have not yet included those to secure access to the terminals by road, rail, and inland waterways, which will be essential for the effective distribution of goods to extended port hinterlands such as Inland Clearance Depots.

Changes in Shipping Patterns and Ports of Call

Larger ships require container consolidation at designated hub ports and therefore international shipping networks have changed to favour the hub-and-spoke than the point-to-point network. As vessels become larger (above 5,000-TEU) round-the-world services through Panama Canal decrease while pendulum services of North America/Asia/ Europe increase extensively. As a result, vessels of 12,000-15,000-TEU may be introduced into pendulum services

Figure 2. Economies of Scale in Containership Operation (US$/TEU/day at sea)

Source: AADCP (2005)

in the future. There has been a prediction that shipping trade performed by 15,000-TEU vessels is completed in 4 mega-hub transshipment off-shore fl oating ports around the world[8]. A recent study[9] also proposed a more radical approach involving a fl eet of 15,000-TEU vessels providing a two-way equatorial round-the-world service through an enlarged Panama Canal (which is due to be completed by 2014). This fl eet would service 7 strategically located transhipment hub ports, located in the Mediterranean (serving Europe), Southeast Asia (serving Asia), and the Caribbean (serving North America).

What this means for ports is that some ports are striving more intensely to capture the opportunity created by the deployment of increasingly larger containerships while others may be left out of the operation patterns of these vessels. This would create a new port hierarchy with some port classifi cation categories such as global (world-class) hub ports, regional hub ports, important secondary ports, and feeder or regional ports. The other effect is that port competition will be more intense as ports compete to become direct ports of call or even hub ports.

Changes in Port Operations

The deployment of mega-containerships implies major challenges in terms of terminal productivity to shorten ship turnaround time in ports. If 12,000-TEU or 15,000-TEU containerships begin their operations, the existing handling method at container terminals serving 5,000-TEU ships can become uneconomical due to longer ship turnaround time, while shipping lines expect a similar service time, normally within 24 hours, for these vessels. For example, suppose an existing 5,000-TEU containership is deployed in a shipping route consisting of 3 ports. At every port the occupancy ratio of the ship is 90% for both loading and discharging, and the ratio between TEU/moves is 1.5, which means the 5,000 TEUs onboard the ship can be converted to a number of container moves handled by ship-to-shore gantry cranes by divided by this ratio. At each port the loading and discharging are handled by an average of 5 gantry cranes, with the average productivity of 23 moves per crane per hour. Given this assumption, the total handling time at each port will be 17.4 hours (5000TEUs x 2 x 90%/1.5/3/5/23). If the ports are now serving 12,000-TEU vessels and all the assumptions remain unchanged, e.g. there is no change of handling productivity, the total handling time at each port will be 41.7 hours (12000TEUs x 2 x 90%/1.5/3/5/23), which is not acceptable by shipping lines. In order to complete the loading/discharging work within 24-hour period (in this case 21 hours), at least 46 moves per hour per crane must be handled while the number of crane per ship remains the same. That is a 200% increase in handling productivity. Otherwise, the port must deploy 10 cranes to handle containers from both sides of the vessel on the indented berth system. This concept was already introduced into reality at the Ceres Paragon Terminal in the Port of Amsterdam, the Netherlands.

Clearly, in order for ports to capture the opportunity to accommodate increasingly bigger containerships, operations process re-engineering, new port design and changes in



port operations system and handling technology must be taken into consideration. New concepts for terminals, such as using an indented berth system, are not necessarily theoretical. Container cranes can be either renovated or developed differently from the existing methods in order to facilitate improved productivity at berths. It is also critical to improve the productivity of quay transfer operations (between berths and yards), as well as of the yards themselves to match with those of handling operations at berths. Perhaps the most radical proposed change in this respect is the design and deployment of the semi- or fully automated container terminals where unmanned operations systems are conducted by high-tech equipment such as AGVs (Automated Guided Vehicles) guided by radio frequency, and supported by intelligent operations systems. This is already in operation at the ECT (European Combined Terminals) in the Netherlands, CTA in Germany, and Brisbane Container Terminal in Australia.

Safety and Environmental Concerns

The use of mega-containerships certainly provokes concerns in ports in terms of safety, security, and environmental protection. Bigger containerships are harder to control and mistakes can be a costly and fatal affair. For instance, a collision or grounding of a big containership in the main channel can bring port operations and resulting regional economic activities to a halt. It is therefore important for ports to have in place the vessel traffi c management systems (VTMS) operated by qualifi ed port offi cers. Besides, expertise in terms of harbour pilotage must be made available in order to ensure the safe arrival and departure of ships. It is clear that if a port expands to accommodate bigger ships they must ensure that the level of expertise of its personnel involved in critical operations is increased. Bigger ships also generate more garbage, oily slop, emit more exhaust from the engines that cause problems to the environment and discharge more ballast water which introduces harmful aquatic organism to the local marine ecology. The dredging operations and improper disposal of dredging wastes can destroy the habitats of marine species. It is therefore important that any port development such as dredging and expansion needs to conduct the Environment Impact Assessment (EIA) which identifi es the environmental infl uences of any proposed change of operations. Besides, ports need to have effective oil and chemical response capabilities and conduct regular drills to ensure their preparedness and readiness to safeguard the marine environment.

Port Logistics Development

In the context of accommodating bigger ships, ports would have to add value to the services they are providing and not just stick to the traditional role of loading, discharging and storage of cargo. A hub port where large containership would call must not only be a simple hub port, but also become a logistical platform. The port today is no longer an isolated entity but part of the integrated supply chains. Shippers will choose between chains based on competitive advantage and value gained in which port is an embedded element, rather than the port itself. In this context, by

adding services such as distriparks and freeports where value-added activities such as labelling, packing, etc. are conducted, ports would be able to retain and attract shipping companies whose logistics system depends on these value-added services.

One of fundamental concepts in supply chain management is the integration of business processes of supply chain partners. In the context of ports, this indicates that ports must function as a logistical platform with horizontal and vertical process integration with their supply chain partners such as inland clearance depots, rail operations, trucking, inland waterway operations, feeder system, forwarding, and other value-added activities. As mega-containerships call at the port, a huge volume of containers will be marshalled from and to the port area, and therefore connection to the port’s hinterland is critically important. In the future, the port competitiveness will depend on an integrated and effi cient transport network to and from the port and thus the close cooperation and coordination with other supply chain partners will be critical to provide value-added services to the port’s clients.

WHAT’S NEXT?

Although the shipping industry is currently affected by the economic downturn with reduced demand and a number of ships being laid off, it does not necessarily mean that the trend of increase in ship size is completely phased out. Indeed, due to the cyclical nature of shipping, this is the good time for ports to start preparing resourcefully for the next wave where impact of big containerships on ports cannot be understated.

REFERENCES

[1] AXS Alphaliner 2006, ‘Emma Maersk – TEU Capacity Analysis’.

[2] UNESCAP 2007, ‘Regional Shipping and Port Development – Container Traffi c Forecast 2007 Update’.

[3] Journal of Commerce 2008, ‘Ship Size Hit a Ceiling’.

[4] Cullinane, K. and Khanna, M. 2000, ‘Economies of Scale in Large Containerships – Optimal Size and Geographical Implications’, Journal of Transport Geography, Vol. 8, No. 3, pp. 181-195.

[5] Drewry Shipping Consultants 2001, ‘Post-Panamax Containership: The Next Generation’.

[6] Australia-ASEAN Development Cooperation Program (AADCP) 2005, ‘Promoting Effi cient and Competitive Intra-ASEAN Shipping Services’.

[7] Port of Melbourne Corporation 2008, ‘Channel Deepening Project’.

[8] Payer, H G. 1999, ‘Feasibility and Practical Implications of Containerships of 8000, 10000 or even 15000-TEU’. Terminal Operations Conference & Exhibition.

[9] Ashar, A. 2000, ‘The Forth Revolution and Transshipment Potentials for Panama Ports’. Terminal Operations Conference & Exhibition.



RELIABILITY ASSESSMENT OF BASAL HEAVE STABILITY

Goh Teck Chee Anthony ([email protected])Wong Kai Sin ([email protected])

INTRODUCTION

One potential failure mechanism that needs to be considered for the design of braced excavations in soft clays is basal heave instability. There are many uncertainties associated with the calculation of the basal heave factor of safety, including the variabilities of the loadings and geotechnical soil properties. To account for these uncertainties in a deterministic analysis, a safety factor of about 1.5 is typically recommended (e.g., Terzaghi et al. 1996). This paper demonstrates the potential of the reliability index based approach to evaluate the basal heave stability of wide excavations in clay. By using basic structural reliability concepts that refl ect the degree of uncertainty of the underlying random variables in the analyses, engineers will have an increased awareness of the uncertainties and their effects on the probability of failure.

RELIABILITY INDEX

In many civil engineering applications, the assessment of safety is made by fi rst establishing a relationship between the load S of the system and the resistance R. For a load S and resistance R, with mean values denoted by mS and mR, respectively, the boundary separating the safe and “failure” domains is the limit state surface (boundary) defi ned by

G(x) = R – S = 0 (1)

in which x denotes the vector of the random variables. Mathematically, R > S or G(x) > 0 would denote a “safe” domain. An unsatisfactory or “failure” domain occurs when R < S or G(x) < 0. The calculation of the probability of failure Pf involves the determination of the joint probability distribution of R and S and the integration of the probability density function (pdf) over the failure domain.

A well-developed approximate alternative is to use the fi rst-order reliability method (Hasofer and Lind 1974) in which the limit state surface is transformed into a space of standard normal uncorrelated variates, wherein the shortest distance from the transformed limit state surface to the origin of the reduced variates is the reliability index β (Cornell 1969).

For the unique case of a linear limit state surface and normally distributed random variables, the linear (planar) limit state surface is given by

G(x) = a0 + a1X1 + a2X2 + … anXn (2)

in which the ai terms (i = 0, 1, 2, … n) are constants and the Xi terms are uncorrelated random variables with mean mXi and standard deviation σXi. The reliability index can expressed as (e.g., Li et al. 1993; Nowak 2000)

(3)

BASAL HEAVE FACTOR OF SAFETY

For wide excavations in which the excavation width B is larger than the excavation depth H, Terzaghi (1943) proposed the simple failure mechanism shown in Figure 1. Replacing the term (B/√2) with B1, the factor of safety FS (accounting for a surcharge q adjacent to the excavation, and different undrained shear strengths adjacent and beneath the excavation) is given by:

FS = (4)

Only isotropic clays are considered. The depth to the hard stratum is assumed to be large so that T/B > 1/√2. In addition, it is assumed that the wall has enough capacity not to fail under the action of deep-seated soil movements.

5.7cubB1

(γH+q)B1 – cuhH

Figure 1. Basal heave failure for wide excavations.



For a wide excavation with four random variables (cub, cuh, q, and γ) and the factor of safety expression in Eq. (4), the limit state surface can be expressed as

G(cub, cuh, q, γ) = 5.7cubB1 – γHB1 – qB1 + cuhH (5)

Since this is a linear equation with four variables (cub, cuh, q, γ), Eq. (3) can be used directly to determine the reliability index β:

β = (6)

For Gaussian-distributed random variables, the probability of failure (FS ≤ 1) is Pf = 1 – Φ(β), in which Φ is the cumulative normal density function.

RESULTS

Analyses were carried out for a wide excavation (B > H) with four random variables (cuh, cub, q, and γ) and FSmean values ranging from 1.1 to 2.0. FSmean is the factor of safety computed using the mean values of the parameters and is calculated based on Eq. (4). Since the limit state surface is linear, Eq. (6) was used to determine β and the corresponding Pf. The analyses were carried out for normally distributed and uncorrelated random variables. In all the analyses, the mean and COV of the surcharge adjacent to the excavation q and the unit weight of the clay γ are assumed to be unchanged (mq = 10 kPa/m, COVq = 0.2, σq = 2 kPa/m; mγ = 16 kN/m3, COVγ = 0.15, σγ = 2.4 kN/m3). For the analyses presented, the COVs of cuh and cub (for simplicity, the term COVcu is used) were assumed to be of the same magnitude. Studies have shown that a reduction in the COV of cuh did not signifi cantly change the Pf (Goh et. al. 2008). The depth to the hard stratum T is assumed to be large such that T/B > 1/√2.

The results in Figure 2 highlight the signifi cant infl uence of the COVcu of the clay on Pf as the COVs of both cuh and cub are increased from 0.1 to 0.6. As expected, for a given FSmean, Pf increases as the COVcu increases. For example, for FSmean = 1.4, Pf increases almost nine times as the COVcu increases from 0.1 to 0.4. For FSmean = 2.0 and COVcu = 0.6, the probability of basal heave failure is still fairly high (approximately 20%). The results highlight the inconsistency in the relationship between the factor of safety and the underlying level of risk. A larger factor of safety does not necessarily imply a smaller level of risk because its effect can be negated by the presence of larger uncertainties in the design parameters.

(5.7B1σcub)2 + (HB1σγ)2 + (B1σq)2 + (Hσcuh)2 √

5.7mcubB1 – mγHB1 – mqB1 + mcuhH

CONCLUSIONS

A series of analyses for wide excavations have been carried out to evaluate the reliability index for basal heave factor of safety. The results show that the same factor of safety can have vastly different levels of risk depending on the degree of uncertainty of the design parameters. The determination of the reliability index provides a systematic method for evaluating the infl uences of the uncertainties in the various parameters affecting FSmean and can be used to assist design engineers assess the acceptable level of risk.

REFERENCES

[1] Cornell, C.A. 1969. “A probability-based structural code.” J. Amer. Concrete Inst., Vol. 66, No. 12, pp. 974-985.

[2] Goh, A.T.C., Kulhawy, F.H. and Wong, K.S. 2008. “Reliability assessment of basal-heave stability for braced excavations in clay.” J. Geotechnical & Geoenvironmental Eng., Vol. 134, No. 2, pp. 145-153.

[3] Hasofer, A.M., and Lind, N.C. 1974. “An exact and invariant fi rst-order reliability format.” J. Eng. Mech., Vol. 100, No. 1, pp. 111-121.

[4] Li, K.S., Lee, I.K., and Lo, S.C.R. 1993. “Limit state design in geotechnics.” Proc. Probabilistic Methods in Geotech. Eng., Canberra, Australia, pp. 29-44.

[5] Nowak, A. S. 2000. Reliability of structures. McGraw-Hill, New York.

[6] Terzaghi, K. 1943. Theoretical soil mechanics. John Wiley & Sons, New York.

[7] Terzaghi, K., Peck, R.B. and Mesri, G. 1996. Soil mechanics in engineering practice, 3rd edition, John Wiley & Sons, New York.

Figure 2. Plot of Pf for wide excavations (H = 10 m, B = 20 m and cuh = 25 kPa).



RESPONSE CHARACTERISTICS OF A RESIDUAL SOIL SLOPE TO RAINFALL

Harianto Rahardjo ([email protected])Lee Tsen-Tieng, Daryl

Leong Eng Choon ([email protected])Rezaur Rahman Bhuiyan ([email protected])

INTRODUCTION

It is well recognized that rainfall induced slope failures are mainly caused by infi ltration of rainwater. Therefore, quantifi cation of the fl ux boundary condition across the slope surface with respect to infi ltration and its effect on the pore-water pressure conditions are essential for characterising slope responses to rainfall. Usually, long term synchronized measurements on changes in pore-water pressures, water content, runoff generation and infi ltration into a slope in response to rainfall events are ideal for characterising slope responses. Such detailed measurements, although desirable, are however scanty due to the availability of resources, budget and time constraints.

The objective of this article is to show how slope responses to rainfall are characterized and share knowledge gained from such studies performed on a residual soil slope in Singapore (Rahardjo et al. 2005).

METHODOLOGY

A residual soil slope in Singapore was instrumented with pore-water pressure, water content, runoff and rainfall measuring devices and studies on characterising slope responses were carried out under natural and simulated rainfalls.

Site Description and Characterization

The study was conducted in an experimental plot located on a cut slope in NTU (Nanyang Technological University) campus, hereinafter called the NTU CSE slope (Figure 1). The slope surface was about 14 m wide and 24 m long rising to a height of 12 m (gradient 2:1). A berm was cut into the slope during landscaping and a horizontal drain runs across the berm. The slope is well covered with Buffalo grass.

Average annual climatic conditions in the study area are precipitation 2300 mm, potential evaporation 1800 mm, and mean temperature 26°C.

Figure 1. Generalized soil profi le of the NTU-CSE slope (Adapted from Rahardjo et al. 2005)

The slope is mainly underlain by the residual soils derived from the weathering of the sedimentary Jurong Formation. During site investigations in late 1997 six boreholes were drilled into the slope in order to characterize the slope. Undisturbed soil samples for laboratory tests were collected using a Mazier sampler. Based on the borehole profi les, the slope was characterized with two soil types: Orange Silty Clay and Purple Clayey Silt. The idealized soil profi le is shown in Figure 1. The Orange Silty Clay (Type 1) extends to a depth of about 1.5 m. The Purple Clayey Silt (Type 2) layer was found at a depth of 1.5 to 2.0 m below the surface and is about 4 to 5 m thick. The index properties and hydraulic properties of the two main groups of soils as determined from laboratory tests are shown in Table 1.



Table 1. Soil properties of the NTU-CSE slope

Property Purple Clayey Silt Orange Silty Clay Type 2 Type 1

PI (%) 13.5 21.0

LL (%) 34.0 47.0

G 2.72 2.67

ρs (Mg/m3) 2.27 1.86

θw (%) 13.0 35.0

θs (%) 26.1 48.3

USCS CL CL

ks (m/s) 1.67 × 10–7 5.18 × 10–6

PI: Plasticity Index; LL: Liquid Limit: Gs: Specifi c Gravity: ρs: Saturated Density: θw: Saturated Volumetric Water Content: θs: Saturated Volumetric Water Content; USCS: Unifi ed soil classifi cation system; ks: Saturated permeability

The soil water characteristic curves of the soils obtained from pressure plate tests in the laboratory are shown in Figure 2. The fi tted lines in Figure 2 were derived using the equation of Fredlund and Xing (1994). The Orange Silty Clay was found to have higher water content than the Purple Clayey Silt. The gravimetric water content of the Orange Silty Clay ranged between 25 to 35% and the soil appears to retain the water content throughout the suction range after the fi rst initial drop (Figure 2).

The Purple Clayey Silt was found to retain its gravimetric water content across a narrow range between 9 and 13% (Figure 2). This implied that the Orange Silty Clay has a higher porosity and is able to retain more water per unit volume than the Purple Clayey Silt. The saturated coeffi cient of permeability as obtained from a falling head permeability test of the Orange Silty Clay was found to be about one order of magnitude greater than that of the Purple Clayey Silt (Table 1).

Figure 3. Setup for rainfall simulation and synchronized measurement of rainfall, runoff, infi ltration, pore-water pressure

and soil water content measurement (Rahardjo et al. 2005)

Figure 2. Soil-water characteristics curves (drying phase) for the Orange Silty Clay and the Purple Silty Clay

(Adapted from Rahardjo et al. 2005)

Field Instrumentation and Data Collection

The investigation on characterization of slope responses to rainfall involved four type of measurements: (i) rainfall input to the slope under both natural and simulated conditions, (ii) runoff on the slope in response to rainfall, (iii) pore-water pressure changes in the slope in response to infi ltration and redistribution, and (iv) soil water content variations in the slope in response to rainfall.

(i) Artifi cial rainfall was simulated using microspray nozzles (Figure 3) installed at 1.8 m height above the ground on a retractable metal frame assembly and each spray could cover a circular area of about 2.5 m in diameter with reasonably uniform distribution of rainfall. By calibrating the water supply to the nozzles through valves, rainfall of different intensities was produced. A group of eight nozzles was found to be suffi cient to cover the plot and produce the desired rainfall intensity. Natural rainfall on the slope was recorded by a tipping bucket rain gauge (Figure 3) of 0.25 mm per tip resolution.

(ii) Surface runoff in the slope was measured by using a capacitance water depth probe housed vertically inside a perspex fl ume at the lower end of the plot (Figure 3). Runoff measurements were made alternately at four locations (area A, B, C and D, see Figure 4) on the slope. Corrugated zinc sheets, 300 mm high, driven about 100 mm into the ground were used to border the plots (Figure 3). Each runoff plot measured about 22.5 m2 (9 m × 2.5 m) in size. The boundaries guided the surface runoff into the perspex fl ume. Data on surface runoff was collected only during a rainfall event and at a 10 s interval resolution.

(iii) Pore-water pressure changes in the slope in response to infiltration were measured by standard Jet fill tensiometers. Each tensiometer was fitted with a pressure transducer for automated measurement.



Seven rows of tensiometers (designated row A to G downslope) were installed in the slope (Figure 4). Each row was designed to measure pore-water pressures at depths of about 0.5, 1.1, 1.4, 2.3, and 3.2 m (designated as column 1 to 5) below the ground surface, spaced 0.5 m apart. The spacing between consecutive rows was 2.5 to 3 m. Figure 4 shows the details of the fi eld instrument layout. Prior to installation, all tensiometers were tested to ensure that the ceramic tips were free from cracks and pressure transducers were calibrated individually using a digital pressure calibrator.

Figure 4. Plan view of the NTU-CSE slope showing layout of instruments (Adapted from Rahardjo et al. 2005)

Casagrande type piezometers, consisting of a 25 mm diameter PVC (Polyvinyl Chloride) standpipe attached to a porous stone tip, were installed in fi ve boreholes (Figure 4) in the slope. The piezometer tips were positioned about 10 m below the ground surface. Each piezometer porous tip housed a submersible water depth transmitter for long term and automatic readings of groundwater table fl uctuations in response to rainfall. Prior to fi eld installation each transmitter was calibrated in a pressure chamber to measure gauge pressure from 0 to 20 m of water. Tensiometer and piezometer readings were scanned at 20 minute intervals by data loggers and were stored in a personal computer.

(iv) The average water content of the surface soils (0.15 m depth) in the slope before and after a rainfall event was measured by TDR (Time Domain Refl ectometry) techniques. TDR measurements were made near each tensiometer location (Figure 4). More details of the fi eld instrumentation can be found in Rahardjo et al. (2005).

OBSERVATIONS AND ANALYSIS

Simulated Rainfall & Infi ltration

During February 1998 fi ve simulated rainfall experiments were conducted in area A of the slope. A second set of fi ve experiments with simulated rainfall was conducted between 17 November 1998 and 5 January 1999 in areas A to D. The simulated rainfall experiments were intended to help understand infi ltration effects on the residual soil slope under controlled rainfall conditions.

To make a comparison between the hydrographs from simulated rainfall events, each simulated rainfall and associated runoff and infi ltration record from the fi rst set of rainfall simulation experiments were plotted in Figure 5.

The infi ltration rates shown in Figure 5 were derived by subtracting runoff rates from rainfall rates. This probably produces a slight over-estimation of the infi ltration rate because other losses (interception and evaporation) which may reduce infi ltration rates are not accounted for. However, the derived infi ltration rates (a loss in input) nevertheless provide an estimation of the percentage of rainfall not contributing to surface runoff generation.

A few features of infi ltration characteristics on the residual soil slope, apparent from Figure 5, are that the minimum infi ltration rate decreases with an increase in the duration of rainfall application. The time to runoff decreased with an increase in the rainfall intensity. This indicated that the higher the rainfall intensity, the earlier the initial abstraction is satisfi ed. Total runoff as a percentage of total rainfall increases and total infi ltration as a percentage of the total rainfall decreases with subsequent rainfall events. It is noted that during the rainfall event of 9 February 1998, the runoff rate did not exceed the infi ltration rate and the rise in runoff rate is slow. This is due to the relatively dry soil conditions that of subsequent runoff events however show an early prevailed before the rainfall event. The hydrographs time to runoff, a rapid rising limb, a runoff rate exceeding the infi ltration rate during steady state runoff and a runoff rate increasing from rainfall to rainfall. Further analyses of the data suggested that about 40 to 74% of the total rainfall amount contributes to infi ltration depending on the rainfall intensity, duration and antecedent water content conditions in the slope.



Water Content Variation Due to Rainfall

Analyses of the average volumetric water contents within 15 cm depths obtained from TDR measurements before and after each rainfall events near each tensiometer location between row A to row D (see Figure 4) suggested the existence of a general trend in the water content data.

The volumetric water content near the toe (row D) of the slope appeared to be always (before or after rainfall) higher than those at the crest (row A). The existence of relatively higher water content near the slope toe than at the crest before and after rainfall events suggested the existence of subsurface fl ow within the soil layers in a downslope direction towards the toe of the slope. Water in the upper slope areas drains vertically downwards, and to the lower slope areas as subsurface fl ow. As a result, there is more drainage on the upper slope areas and more water retention on the lower slope areas. The lower slope areas remain wetter than the upper slope areas and therefore show higher water content than the crest. The change in volumetric water content in the slope due to a rainfall appeared to be infl uenced by the amount of the rainfall and the number of dry days between rainfall events.

Natural Rainfall & Infi ltration

During December 1998 and January 1999, data on natural rainfall runoff events were collected for 27 rainfall events on the slope. Data from these 27 rainfall events were analysed to determine total runoff resulting from each rainfall event, total runoff and infi ltration expressed as a percentage of total rainfall and the peak intensity of each rainfall event. The runoff coeffi cients (ratio between runoff and rainfall amount in percentage) in the slope for all runoff-generating rainfalls varied from 11% to 45% with an average value of 25%. The data suggested that usually rainstorms in excess of 10 mm generate runoff, even under dry antecedent conditions.

In Figure 6, infi ltration amounts (as a percentage of total rainfall) are plotted against rainfall amount records from 27 natural and 10 simulated rainfalls monitored in the slope. It appears from Figure 6 that rainfall events which produce small total amounts of rainfall may contribute fully to infi ltration. This suggests the existence of a threshold rainfall amount. Any rainfall below this amount will not produce any runoff and the whole rainfall may end up as infi ltration. With reference to Figure 6 (dotted line) this threshold appears to be about 10 mm of total rainfall. Beyond the threshold rainfall, the percentage of rainfall contributing to infi ltration decreases with increasing total rainfalls.

Analyses of the infi ltration data suggested that in residual soil slopes total infi ltration could range between 40% to about 100% of the total rainfall depending on the rainfall amount. The relationship (Figure 6) derived from the rainfall records in the residual soil slope has practical signifi cance. If the rainfall amount is known, Figure 6 could indicate the fraction of the rainfall that could become infi ltration. This may be useful for seepage analysis that requires this information as fl ux boundary conditions.

Figure 5. Comparison of hydrographs of simulated rainfall events in area A of the NTU-CSE slope

(Adapted from Rahardjo et al. 2005). R, Q, and I denotes rainfall, runoff and infi ltration, respectively. Subscripts V and I denotes volume and maximum fl ow rate respectively. T and Tc

denotes rainfall duration and time to runoff respectively. % refers to percentage of rainfall volume.



Pore-water Pressure Variation Due to Rainfall

Figure 7 shows an enlarged view of the pore water pressure variation in the slope in response to the rainfall event (simulated) of 20 February 1998 at selected locations. The tensiometers at 0.5 depths were inoperative during February 1998 due to instrument malfunction. Therefore, data from tensiometers at 0.5 m is not presented. All tensiometers at shallow depths (1 to 2 m) showed a response to the rainfall event. The tensiometers near the slope crest (row B) and at shallow depths showed the earliest and most noticeable response to the wetting front due to infi ltration. The tensiometers near the toe (e.g. row C, 1.4 m depth) showed a delayed response. The tensiometer at greater depth (3.2 m) however did not show any response to this rainfall. It is interesting to note that in less than about 10 minutes from the onset of rainfall, the tensiometers at shallow depths showed responses to the infi ltrating rainwater by changing pore-water pressures.

Figure 6. Percent infi ltration as a function of rainfall


Figure 7. Pore-water pressure changes due to simulated rainfall on 20 February 1998 in area A of the NTU-CSE slope


Figures 8 and 9 show the typical daily variation of pore water pressures at different depths and locations in the slope in response to dry and wet climatic conditions. The wet

conditions are a consequence of both natural and simulated rainfall events between 8 and 22 February 1998. Rainfall events with a small total rainfall amount (e.g. 15 February 1998) only affect the pore water pressures at shallow depths (Figure 9). The small natural rainfall event (about 2 mm) during 17 February 1998 did not show any effect on the pore-water pressures in any locations in the slope (Figure 9). Tensiometer data (Figures 8 and 9) suggest that the zone of infl uence of infi ltration extends to about the 3 m depth. However, tensiometers at shallow depths showed a quick response to rainfall and redistribution. The tensiometers at a greater depth showed a delayed response. The nearly instant change in pore water pressures at different depths during a rainfall event (Figures 8 and 9) indicates a fast infi ltration rate into the slope. This however, does not lead to a constant wet soil condition as can be seen in the gradual suction recovery between rainfall events. Figures 8 and 9 show that during dry periods matric suctions (negative pore water pressures) prevail at shallow depths but gradually decrease with increasing depths. Positive pore water pressures observed at different depths (Figures 7, 8 and 9) are a consequence of development of a perched water table.

Figure 9. Time series of rainfall and pore-water pressures between 15 and 22 February 1998 in area A of the NTU-CSE

slope (Adapted from Rahardjo et al. 2005)

Figure 8. Time series of rainfall and pore-water pressures between 8 and 15 February 1998 in area A of the NTU-CSE

slope (Adapted from Rahardjo et al. 2005)



Piezometers installed in the slope (Figure 4) did not show any response during the monitoring period indicating that the groundwater table was located below the depth of the piezometer tips. In the residual soil slope under investigation, the formation of a perched water table and the resulting positive pore water pressures development could be initiated by two processes. First, variations of unsaturated permeability of the soil with matric suctions (i.e. permeability function) and second, the decreasing saturated permeability with increasing depths (due to the decrease in the degree of weathering at greater depths).

The advancement of the infi ltrating rainwater into deeper depths is affected by the unsaturated permeability of the soil in front of the wetting front that is still at its initial matric suction. The low unsaturated permeability in front of the wetting front impedes the downward vertical movement of water. As the advancing wetting front reaches the boundary between the permeable (Orange Silty Clay) and the relatively less permeable (Purple Clayey Silt) soil layer, the movement is further impeded due to a reduction in the saturated permeability (Table 1). As a result, the infi ltrating rainwater collects at the less permeable soil layer (Figure 1) and a build up of positive pore water pressures is observed in Figures 7, 8 and 9. The positive pore-water pressures are sustained for a period with a gradual decrease in magnitude. The recovery of matric suction is dependent on how effi ciently the slope vegetation and climatic conditions accelerate the decrease in pore water pressures.

By using all the tensimeter data a relationship (Figure 10) between the increase in pore water pressure and rainfall amount monitored in the slope was attempted. Although there is considerable scatter (r2 = 0.517), the trend in the data set can be seen. The equation shown in Figure 10 has a negative intercept indicating that a rainfall greater than 1.38 mm is needed to initiate a rise in pore-water pressure. This is consistent with the concept that rainfalls of a small magnitude may not be available to the soil to contribute to an increase in pore-water pressure as they will be intercepted by the slope vegetation. The relationship shown in Figure 10 appears to have some practical signifi cance in assessing possible risk of slope failures (Rahardjo et al., 2005).

CONCLUSIONS

The results of natural and simulated rainfall runoff experiments suggest that a large proportion of the rainfall contributes to infi ltration in the residual soil slope. A rainfall may contribute from 40% of its total rainfall to about 100% as infi ltration depending on the rainfall amount. A threshold rainfall of about 10 mm was identifi ed. Storm events resulting in a total rainfall above this threshold are capable of producing surface runoff. Infi ltration and runoff amount, as well as the relative increase in pore water pressure due to a rainfall, are found to be infl uenced by the antecedent rainfall in the slope. The characteristics of infi ltration processes, runoff generation and pore water pressure changes identifi ed in this study may have relevance for the assessment of rainfall induced slope instability in residual soil slopes under similar climatic conditions in different geographic regimes.

ACKNOWLEDGMENT

The work was funded by a research grant from National Science and Technology Board, Singapore (Grant NSTB 17/6/16: Rainfall-induced slope failures).

REFERENCES

[1] Rahardjo H., Lee, T.T., Leong, E.C. and Rezaur, R.B. (2005). Response of a residual soil slope to rainfall. Canadian Geotechnical Journal, 42: 340–351.

[2] Fredlund, D.G. and Xing, A. (1994). Equations for the soil-water characteristic curve. Canadian Geotechnical Journal, 31(3): 521–532.

Figure 10. Relationship between rainfall and the increase in pore-water pressures (Adapted from Rahardjo et al. 2005)


STRUCTURES AND MECHANICS

A SIMPLE MATHEMATICAL FORMULATION FOR BEND

STIFFENER ANALYSISTong Dongjin ([email protected])Low Ying Min ([email protected])

ABSTRACT: Bend stiffeners designed to protect fl exible risers against over-bending at the connection with the fl oating structures are usually modelled as elastic cantilever beam whose bend stiffness varies along its length. This paper fi rstly presents a simple and effi cient Numerical Beam Model for analyzing a bend stiffener based on the fi rst principle of curvature-moment relationship. The two principal sources of non-linearly, namely the geometric non-linearly and the material non-linearly, are considered. A straightforward numerical solution method is applied instead of using complex non-linear ordinary differential equations to solve the non-linear problem. A fi nite element analysis with ABAQUS/Standard is performed to validate the numerical method. The results demonstrate that the numerical method agrees well with the fi nite element analysis.

INTRODUCTION

Bend stiffeners are typically polymeric structures with a conical shape, designed to protect fl exible risers against over-bending at the connection with the fl oating structures as shown in Figure 1. Thus, they are of vital importance to deep water oil and gas production systems. Existing bend stiffeners are made of polyurethane material usually with an initial cylindrical part followed by a conical shape.

Figure 1. Typical Bend Stiffener Confi guration.

A large defl ection cantilever model is widely used to determine the stress and defl ection of a bend stiffener under static load. The general method used to obtain the beam defl ection curve for a large defl ection beam is based on elliptic integral formulation (Wang et al. 1997). This approach requires solving complex mathematical equations. Caire and Vaz (2007) proposed a set of four non-linear ordinary differential equations from geometrical compatibility, equilibrium of forces and moments and constitutive equations to the effect of fl exible pipe non-linear bending stiffness behavior on bend stiffener analysis. In their study, the non-linear ordinary differential equations are solved with a numerical solution with the shooting method. In this paper we develop a simple and effi cient mathematic formulation for analyzing a bend stiffener based on the fi rst principle of curvature-moment relationship. The

two principal sources of non-linearity namely the geometric non-linearity and the material non-linearity, are considered. A straightforward numerical methodology is applied instead of using complex non-linear ordinary differential equations to solve the non-linear problem.

A fi nite element analysis with ABAQUS/Standard using solid/beam element is performed to validate the numerical method. A truss element with zero bending stiffness is introduced to simulate bend stiffener/riser inextensible behavior in the fi nite element analysis.

NUMERICAL BEAM MODEL

Due to the presence of nonlinearities, closed form solutions do not exist and thus a numerical procedure is developed. In addition, the calculation process is iterative. The following assumptions are made during the calculation process:

1) Cross-sections remains plane

2) Large displacements are permitted but strains are small

3) Polyurethane is assumed to be symmetrical in tension and compression

4) Pipe and stiffener are inextensible.

The iterative process is separated into two stages. The fi rst stage is to provide an initial perturbation to the profi le of the bend stiffener. The bending moment along the bend stiffener under the static load T with tension angle of α can be written as

M(x) = T sin (α). (xt – x) - T. cos (α). (yt - y) (1)

where xt and yt are the Cartesian coordinates.



Once the moment is obtained, the curvature k at any point along the bend stiffener can be determined based on the moment–curvature relationship. The pipe structure exhibits an approximately bi-linear hysteric bending moment against curvature relationship arising from the progressive activation of friction and consequential slipping between adjacent layers. The fl exible pipe bending stiffness substantially reduces after a given critical curvature (kcr) as shown in Figure 2, in which, (EI)1 and (EI)2 represent the no-slip pipe bending stiffness (also known as stage 1 pipe stiffness) and full-slip pipe bending stiffness (also known as stage 2 pipe stiffness) respectively.

Figure 2. Bending Moment and Curvature relation of Flexible Pipe

The following bending moment – curvature relation is applied to the system before and after the slip between adjacent layers.

M = MBs + Mpipe = g(k) + k × (EI)1 (2a)

when k ≤ kcr

M = MBs + Mpipe = g(k) + k × (EI)1 + (k - kcr)(EI)2 (2b)

when k > kcr

where g(k) represents the moment contributed by the bend stiffener and it is a function of k for the given material. Due to the nonlinearity of the bend stiffener material, g(k) must be obtained numerically.

Since the above equation gives the moment for the section with a given curvature, whereas what is needed is the curvature as an explicit function of the moment, this function g is obtained by fi tting to a third-order polynomial so that one may express k = g(M). Based on the defi nition of curvature as

k = (3)

kM = [ ]/[1 + (y')2]1.5

y"[1 + (y')2]1.5

(y')N(i–1) – (y')M

xN(i–1) – xxi

once the curvature is obtained, the slope dy/dx and subsequently the x and y coordinates can be determined numerically based on boundary conditions dy/dx(0) = 0, y(0) = 0 and x(0) = 0. The above calculation is carried by using a standard spreadsheet such as EXCEL. When the error of the vertical defl ection at the tip falls to less than 2%, the analysis is considered to have converged.

FINTE ELEMENT METHOD

In order to study the local stress distribution and to verify the result obtained from the numerical method, a fi nite element model was constructed to simulate the bend stiffener and pipe under given static loads. Solid elements are used in the model. As the bend stiffener base is built into the rigid platform, all the degrees-of-freedoms (a total of three for solid elements) of the nodes at the root of the bend stiffener are fi xed.

Initially, we tried to model the structure using two layers. The outer layer is the bend stiffener main body which is made of non-linear material. The inner layer is a hollow pipe that represents the riser, whose material is linear elastic. The thickness of the pipe is chosen to satisfy a given EI value, which is typically small for a fl exible riser. However, it was found that the structure elongated considerably under the application of horizontal + vertical loads. In reality, this does not happen as the axial stiffness (EA) of a fl exible riser is generally quite high. However, using solid models, which are homogenous, unlike actual fl exible risers, it is impossible to model a hollow section with a large EA and yet a very small EI, since the two are related. This problem did not emerge in the numerical method, because therein it was assumed that the bend stiffener and pipe structure was inextensible.

To overcome this problem, we propose to further include a truss element with zero bending stiffness and infi nite axial stiffness at the centre of the bend stiffener. This new section is shown in Figure 3. The rationale is to allow the truss element to take most of the tension loads, while the bend stiffener resists most of the bending moments. This is a better representation of the composite behaviour of the bend stiffener and fl exible riser.

Figure 3. Bend Stiffener Section.



An exemplary finite element model with the stress distribution and defl ection shape under the applied loading (Tension = 1900 kN, Angle = 10 deg, Temperature = 0 deg) is shown in Figure 4.

Figure 4. Bend Stiffener Defl ection Shape.

COMPARATIVE STUDY

In the preceding section, results from the numerical method and FEM are compared. Table 1 gives the geometrical properties of the bend stiffener used in this study.

Table 1 – Geometrical properties of the Bend Stiffener Length (m) Tip OD (m) Root OD (m) ID (m)

5.135 0.585 1.196 0.517

Bend stiffeners made from two types of material (material A and material B) with different stress-strain curves have been studied. For each material, three load cases have been considered as shown in Table 2. The cable stiffness values are 393.10 kNm2 for material A and 177.30 kNm2 for material B.

Table 2 – Summary of Analysis Cases

Cases Material Cable Tension Angle Stiffness Force (Deg) (kN.m2) (kN)

A1 A 393.1 1900 10

A2 A 393.1 1700 12.5

A3 A 393.1 1400 17.5

B1 B 177.4 1900 10

B2 B 177.4 1700 12.5

B3 B 177.4 1400 17.5

The results in terms of defl ections and maximum stresses are shown on Table 3(a)-(b), which indicates that the results agree well with the numerical method and FEM analysis.

Table 3 (a) - Result Comparison on Defl ections

Cases

Vertical Horizontal Defl ection Defl ection

NUMERICAL ABAQUS NUMERICAL ABAQUS (mm) (mm) (mm) (mm)

A1 446 455 24.6 22.5

A2 536 543 35.7 34.1

A3 695 700 61.2 59.7

B1 550 561 35.7 33.4

B2 669 684 53.5 52.0

B3 892 912 96.3 97.1

Table 3 (b) - Result Comparison on Stresses

Cases

Max Stress

NUMERICAL ABAQUS (MPa) (MPa)

A1 5.1 5.4

A2 5.8 6.1

A3 6.9 7.4

B1 3.7 3.9

B2 4.3 4.4

B3 5.2 5.3

CONCLUSIONS

Bend stiffeners designed to protect fl exible risers against over-bending at the connection with the fl oating structures are usually modelled as elastic cantilever beams whose bend stiffness varies along its length. This paper fi rstly presents a simple and effi cient mathematical formulation for analyzing a bend stiffener based on the fi rst principle of curvature-moment relationship. The two principal sources of non-linearity, namely the geometric non-linearly and the material non-linearly, are considered. A straightforward numerical method is applied instead of using complex non-linear ordinary differential equations to solve the non-linear problem. A fi nite element analysis with ABAQUS/Standard is performed to validate the numerical method. The results demonstrate that the numerical method agrees well with the fi nite element analysis.

REFERENCES

[1] Vaz, M.A., Lemos, C.A.D. and Caire, M. 2007, A Nonlinear Analysis Formulation for Bend Stiffeners. J. Ship Research, 51(3), 250-258.

[2] Wang, C.M, Lam, K.Y., He, X.O. and Chucheepsakul, S. 1997, Large Defl ections of an End Supported Beam Subjected to A Point Load. Int. J. Non-Linear Mec., 32(1), 63-72.



DEVELOPMENT OF NODAL-BASED DDA IN ROCK MASS MODELLING

Bao Huirong ([email protected]) Zhao Zhiye ([email protected])

INTRODUCTION

The discontinuous deformation analysis (DDA) (Shi, 1988) is a discontinuum-based method. It chooses the displacements and strains of the blocks as variables and solves the equilibrium equations in the same way as the fi nite element method (FEM) does. Hence, one attractive advantage of the DDA is that an existing FEM code can be readily transformed into a DDA code while retaining all the advantageous features of the FEM. The DDA has emerged as a more attractive model than the continuum-based methods for geomechanical problems due to its intrinsic feature of block discontinuity at the contact boundaries. Being coupled with the fi nite element mesh, the nodal-based DDA method has the ability of treating crack initiation and propagation inside a block more accurately and effi ciently.

THEORY OF THE NODAL-BASED DDA

In the nodal-based DDA (NDDA), the triangular element is the basic analysis object and the nodal displacements become the unknowns of the simultaneous state equation. A group of triangular elements build up a block. The grid lines can be referred to as virtual joints, which will fracture when certain failure criterion is triggered. The topology of the NDDA model is illustrated in Figure 1.

For a triangular element, the three nodes provide six unknowns, {ui, vi, uj, vj, um, vm}T. In a special case where the block is triangular and includes only one triangular element, the six unknowns of the NDDA are equivalent to the unknowns of the original DDA. Using {ui, vi, uj, vj, um, vm}T as element unknowns makes it possible to unify continuous and discontinuous region in the analysis.

For a triangular element, the three nodes provide six unknowns, {ui, vi, uj, vj, um, vm}T. In a special case where the block is triangular and includes only one triangular element, the six unknowns of the NDDA are equivalent to the unknowns of the original DDA. Using {ui, vi, uj, vj, um, vm}T as element unknowns makes it possible to unify continuous and discontinuous region in the analysis.

The Mohr-Coulomb criterion is employed as the failure criterion. A crack is introduced when the normal stresses or the shear stresses reach the ultimate strength, and the topology of the system needs to be updated so that this crack can be considered in the next time step. In a continuum media, cracks are not independent to each other. The occurrence of one crack will affect the behaviour of the other cracks. In the NDDA, a fracture sequence is employed inside each time step. The crack updating procedure includes four steps:

Step 1. Compute the weighted-average normal stress and shear stress on the grid lines among all elements.

Step 2. Look for the grid line which will crack fi rst according to their failure time and mark this grid line as a crack, then insert new nodes if needed.

Step 3. Update the mesh and all related information of the nodes and elements.

Step 4. Compute the updated system again and go back to step 1, unless the last time step has been reached.

In Step 2, the most important task is to check the failure time sequence, which is based on the failure time of each mesh grid. Two cases should be considered for the failure time of each grid line: tensile failure time and shear failure time. The smaller one is the failure time of that grid line.

Figure 1. Illustration of a nodal-based DDA model.



APPLICATIONS

Example 1

This example is designed to validate the ability of the NDDA in the analysis of the P-wave propagation in an elastic rock bar with free ends. The elastic rock bar is 1 meter long and 0.03 meter in height, as shown in Figure 2. The material properties and analysis parameters are shown in Table 1.

Figure 2. Confi guration of the bar (1m×0.03m).

Table 1. Analysis parameters

Unit mass: 2600 kg/m3

Young’s modulus: 50 GPa

Poisson’s ratio: 0.25

Friction angle of rock: 30˚

Cohesion strength: 24 MPa

Tensile strength: 18 MPa

Friction angle of crack: 25˚

Time step size: 1×10-6 s

Max displacement ratio: 0.1

SOR factor: 1.0

Total analysis time: 0.002s

In this example, the P-wave pulse is generated by pressure applied on the left boundary of the bar. It is a triangular P-wave pulse with the peak value of 25MPa and the rising time and dropping time are both 2×10-5s. The results obtained by the NDDA are shown in Figure 3. The compressive wave is refl ected as a tensile wave at the free end and the refl ected wave is superposed with the tail of the incident wave. Finally, the tensile stress wave generates fractures at the place with some distance from the free end. The fi rst crack appears at step 256 (time instant 0.0002560s), and runs through the whole section at step 261 (time instant 0.0002562s).

Figure 3. Analysis results from NDDA.

(a) step 200 (0.0002s)

(b) step 256 (0.000256s)

(c) step 261 (0.0002562s)

(d) step 1016 (0.001s)

The horizontal particle velocity time histories at three different measure points, start point, midpoint, end point (i.e. nodes 343, 679, 171), are presented in Figure 4. The peak value of the particle velocities shown in the Figure 4a and 4b will fi nally be reduced to the average velocity of the bar. In Figure 4c, the curve shape should be similar to the one shown in the Figure 4a if there is no crack occurring. However, during the fi rst circle when velocity curve drops from the peak value, the particle velocity at the right free end starts to fl uctuate around a value until stable because some stress waves are refl ected at the crack surface. The calculated P-wave velocity propagating through the bar is 4386m/s and the theoretical one calculated using the elastic constants is 4385m/s. The velocity obtained by the NDDA program for the P-wave propagation agrees well with the theoretical value.

Example 2

A numerical test on a Brazilian disc of rock materials was studied to validate the feasibility of the NDDA on dealing with crack initiation and propagation. Assume the test material is a continuous, isotropic and homogeneous elastic body. The diameter of the rock disc is 50 mm. The dimension for the rectangular loading plate is 50×10 mm2. The thickness of disc and rigid plate are 25 mm, namely the thickness-to-diameter (T/D) ratio is 0.5.The material properties are shown in Table 2. The load is applied by the displacement of two rigid plates with a speed of 0.2 m/s.

The results from the NDDA are shown in Figure 5. The fi rst crack occurs at around 0.00214 s and propagates toward the contact point with rigid plate very quickly. The numerical experiment results agree well with the laboratory observations.

Table 2. Analysis parameters

Rock sampleUnit mass 2600 kg/m3

Young’s modulus 10 GPaPoisson’s ratio 0.25Friction angle 25˚Cohesion strength 25 MPaTensile strength 12 MPa Rigid plateUnit mass 7800 kg/m3

Young’s modulus 2000 GPaPoisson’s ratio 0.25Friction angle 25˚Cohesion strength 2500 MPaTensile strength 2500 MPaFriction angle of crack 20˚ Control parameterPenalty stiffness 4000 GN/mTime step size 1×10-5sMax displacement ratio 0.01SOR factor 1.0Total analysis time 0.003s



Figure 4. Horizontal particle velocity at different measuring points.

CONCLUSIONS

With the addition of fi ne element discretization in each block, the nodal-based DDA can provide more realistic deformation ability for each block and consequently more precise stress distribution fi led for crack initiation in it. In the fi rst example, it is found that the NDDA is able to model the wave propagation accurately because it is a continuum-based method when no crack occurs. In the second example, while cracks occur among elements, it becomes a discontinuum-based method and the kinematics of blocks comes into action. The numerical results agree well with the laboratory observation.

REFERENCES

[1] Shi, G., “Discontinuous deformation analysis - a new numerical model for the statics and dynamics of block systems”, PhD thesis, 1988, University of California: Berkeley.

Figure 5. Results from NDDA.

(a) start point

(b) midpoint

(c) end point

(a) fi rst crack occurrence

(b) cracks propagation

(c) fi nal failure



DEVELOPMENT OF NUMERICAL MANIFOLD METHOD AND ITS

APPLICATION IN ROCK ENGINEERINGMa Guowei ([email protected])

He Lei ([email protected])An Xinmei ([email protected])

ABSTRACT: The numerical manifold method is a combination of the fi nite element method (FEM) and discontinuous deformation analysis (DDA) method. It provides a robust numerical solution to a solid medium with dense discontinuities. Basic theories of the NMM are introduced. Applications of the 2D-NMM, including the modeling of multiple discrete blocks, the modeling of strong discontinuities, and the 3D-NMM, including 3D block cutting, the displacement and deformation modeling, are presented, respectively.

INTRODUCTION

Discontinuum-based numerical methods, the distinct element method (DEM) originated by Cundall [1] and the discontinuous deformation analysis (DDA) method pioneered by Shi [2], are suitable for the simulation of large-scale displacements of individual blocks, block rotations, and complete detachment. The problem domain is treated as an assemblage of rigid or deformable blocks with contacts between them identifi ed and continuously updated during the entire motion and deformation process. Individual discrete blocks can be fractured or fragmented, which is in essence a process of transition from continua to discontinua, and is well represented by the combined continuum and discontinuum based numerical methods, such as combined fi nite-discrete element method [3] and numerical manifold method (NMM) [4]. The NMM, initially proposed by Shi in 1991, gains its name from the mathematical notion of manifold.

BASIC THEORY OF NMM

In Figure 1, three basic components in NMM, namely the mathematical cover (MC), the physical cover (PC), and the cover-based manifold element (CE), are presented. The portrait of the physical problem including the problem domain in which the physical problem is defi ned, and all the physical features such as the internal discontinuities (e.g. cracks, joints, material interfaces, holes, etc.) and the external geometries on which boundary conditions are prescribed is referred to as a physical domain (Figure 1a), whereas mathematical domain is independent but completely covers the physical domain (Figure 1b). The mathematical domain is constructed as a union of a fi nite number of small patches, called mathematical covers (MCI), which are of arbitrary shape, overlap each other partially or completely, and are completely independent of the physical domain. However, their union must be large enough to cover the

entire physical domain. There are two mathematical covers in total (MC 1 and MC 2 (Figure 1c)).

Figure 1. NMM components in 2D-NMM: (a) physical domain; (b) mathematical domain; (c) mathematical covers;

(d) physical covers; (e) cover-based manifold elements.

The physical covers are the intersection of mathematical covers and the physical domain. If completely cut by the physical features, a mathematical cover MC I will be partitioned into several physical covers, denoted as PCj

I

(j =1~mI), as two physical covers in Figure 1d (PC11 and

PC12).

The cover-based manifold element is defi ned as the common region shared by several physical covers. The four physical covers in Figure 1d fi nally form fi ve cover-based manifold elements, shown in Figure 1e. Figure 2 shows the three basic components of the 3D-NMM. There are two mathematical covers in total, i.e. a sphere mathematical cover MC 1 and a hexahedron mathematical cover MC 2. The pyramid defi nes the physical domain. Intersected with the physical domain, PC1

1 and PC12 are generated, which fi nally form

three cover-based manifold elements in Figure 2c.



APPLICATIONS OF NMM

Modeling of Multiple Discrete Blocks

Figure 3, the numerically obtained result of a typical domino run problem is consistent with the experimentally observed phenomenon, which consists totally 41 rectangular blocks with the size of 20mm×150mm and the spacing of 30mm on a horizontal surface. The material parameters are: Young’s modulus E = 200GPa, and Poisson’s ration ν = 0.3. The fi ction coeffi cient μ between the blocks and the horizontal surface is 0.3.

Figure 2. NMM components in 3D-NMM: (a) physical domain and mathematical covers; (b) physical covers;

(c) cover-based manifold elements.

(a) (b)

(c)

Figure 3. Toppling process of a series of blocks modeled by the NMM.

Modeling Strong Discontinuities

Numerical examples of the same parameters in Refs. [5] and [6] have demonstrated effi ciency and robustness of the NMM in modeling complex cracks and their growth. Figure 4 with a tree-shaped crack under bi-axial tension in a fi nite plate is examined. The regular mathematical covers for the central part of the problem are depicted. The convergence of the stress intensity factors (SIFs) at crack tip D is observed when the mathematical covers are gradually refi ned.

Block Cutting

Concave blocks and multiply connected blocks are modeled, which cannot be fulfi lled by other cutting algorithm [7]. Figure 5 depicts the cutting of a complex tunnel system in a jointed rock mass, and the cutting of a slope in a jointed rock mass.

Figure 4. Modeling a tree-shaped crack with the NMM: (a) a problem with a tree-shaped crack;

(b) part of the mathematical covers; (c) SIFs at crack tip D.

(a)

(b) (c)

(a) (b)

Figure 5. Cutting examples.

Effect of Cover Size and Orientations

In Figure 6, A 2m×2m×0.1m plate is subjected to the gravity load with g=10 and fi xed at four corners, with material properties of E=10GPa, v=0.3, ρ=1200kg/m3. Six mathematical covers with sizes s= 0.52, 0.32 0.22, 0.12, 0.08, 0.05 are used to examine the cover size effect. 190, 684, 1104, 3706, 8100, 19200 cover-based manifold elements are generated respectively with zero dynamical ratio. Results are convergent and stable with the increase of the mesh density. In Figure 7, the same plate is subjected to a constant point load L=5 at the center with fi xed four corners. The dynamical ratio is set as 0.999 to investigate dynamical response fully. Z direction displacement histories of the center point (Figure 8) shows that the orientation of mathematical covers has a negligible effect on the plate maximum displacement at the center.



REFERENCES

[1] Cundall, P.A., 1971. A computer model for simulating progressive, large scale movements in blocky rock systems. Proceedings of the International Symposium on Rock Fracture, Nancy, France, II-8.

[2] Shi, G.H., 1988. Discontinuous Deformation Analysis – A new numerical model for the static and dynamics of block systems. PhD Dissertation, Department of Civil Engineering, UC Berkeley.

[3] Munjiza, A., 2004. The combined fi nite discrete element method. Wiley, Chichester.

[4] Shi, G.H., 1991. Manifold method of material analysis. Trans. 9th Army Conf. on Applied Mathematics and Computing, Minneapolis, Minnesota, pp. 57-76.

[5] Ma, G.W., An, X.M., Zhang, H.H. and Li, L.X., 2009. Modeling complex crack problems with numerical manifold method. International Journal of Fracture, 156 (1), pp. 21-35.

[6] Zhang, H.H., Li, L.X., An, X.M. and Ma, G.W., 2009. Numerical analysis of 2-D crack propagation problems using the numerical manifold method. Submitted to Engineering Analysis with Boundary Elements.

[7] Ma, G.W. and He, L., 2009. Development of 3-D numerical manifold method. Submitted to International Journal of Computational Methods.

(a) Model (b) Convergence of deformation

Figure 6. Deformation convergences with decrease of cover size.

Figure 7. Geometry of mesh designs for mesh orientation effect study.

Figure 8. Z-displacement histories of center point.



EXPERIMENTAL FATIGUE STUDY OF PARTIALLY OVERLAPPED CIRCULAR

HOLLOW SECTION K-JOINTSChiew Sing Ping ([email protected])

Lee Chi King ([email protected])Lie Seng Tjhen ([email protected])

Nguyen Thi Bich Ngoc ([email protected])

INTRODUCTION

In this study, the reliability of the geometrical models and the mesh generation procedure specifi cally developed for the modelling of partially overlapped circular hollow section K-joints [1] are validated by comparing the modelling results with full scale tests results. Static tests were applied to study the stress concentration factors while fatigue tests were applied to study the stress intensity factor and the fatigue life of the joints. The results obtained [2] indicated that the uncracked joint model could lead to reliable stress concentration factor estimations while the cracked joint models could lead to conservative stress intensity factor and residual fatigue life predictions close to experimental results.

TEST SET UP AND SPECIMENS

The dimensions of two full-scale partially overlapped circular hollow section (CHS) K-joints named as Specimen S1 and Specimen S2 are shown in Figure 1. The sizes of the CHS sections are deliberately selected to be almost identical in order to study the effects of the loading on the distribution of the stress concentration factor (SCF) of the joints. The CHS employed to construct the joints fully complied with the design code [3]. All welding was performed to fully comply with the American Welding Society specifi cation [4]. During testing the specimens were fi xed at the two ends of the chord and the overlap brace while loadings were applied at the end of the through brace by three mutually perpendicular actuators.

Tests Conducted

Both static and fatigue tests were conducted for the two specimens. For the static test, the three basic loading cases, namely axial loading (AX) and in-plane bending (IPB) and out-of-plane bending were applied in turn for the study of the SCF and the hot spot stress distributions along the weld toes of the intersection curves. For the fatigue test, combined AX (200kN) and IPB (±45kN) sinusoidal constant

amplitude cyclic loadings of 0.2Hz were applied. The loading direction of the IPB loading applied to Specimen S1 was exactly opposite to that applied to Specimen S2. Such loadings were specially arranged so that for Specimen S1, a crack was eventually induced along the intersection curve between the chord and the through brace (Curve 1 in Figure 1). While for Specimen S2, the joint eventually failed by a crack induced along the intersection curve between the through and the overlap brace (Curve 3 in Figure 1). In the fatigue test, cyclic loading was applied until the joints were fi nally broken with the formation of through thickness cracks detected. The junction parts were cut out and opened up for crack shape measurements.

Figure 1. Dimension of specimens.

WELD PROFILE MODEL FOR UNCRACKED JOINTS

As it was expected that the peak hot spot of stress would be located along the crown of Weld 1 on the through brace side for Specimen S1 and along the crown of the through brace side of Weld 3 for Specimen S2, Figure 2 and Figure



3 plot the modelled and the actual weld thickness (Tw) along the through brace side of Weld 1 for Specimen S1 and the through brace side of Weld 3 for specimen S2, respectively. It can be observed that the modelled weld thickness resembled the actual weld shapes and both of them satisfi ed the American Welding Society specifi cation [4] with the actual weld thickness larger than the modelled thickness (especially at crown heels).

Figure 3. Weld thickness for Specimen S2.

Figure 2. Weld thickness for Specimen S1.

SCF PREDICTIONS

Figure 4 shows the hot spot stress distribution when the Specimen S1 is subjected to IPB loading. For Specimen S2, the corresponding hot spot stress distribution is shown in Figure 5. A detailed investigation was carried out to compare the experimental results against the FE stress distributions based on the following models:

(i) Models based on the measured weld thickness

(ii) Models based on the proposed weld thickness [1]

(iii) Models without weld details

It was found that the SCF results obtained from the measured thickness are most accurate while the proposed weld model produced reasonable SCF predictions for the specimens tested. However, results from models without weld details always overestimated the SCF by a considerable margin.

Figure 5. Hot stop stress distribution under IPB around Weld 3 for Specimen S2.

Figure 4. Hot stop stress distribution under IPB around Weld 1 for Specimen S1.

STRESS INTENSITY FACTOR (SIF) PREDICTION In order to obtain a complete picture of the SIF as the crack developed, a number of models corresponding to different crack depths and crack lengths subjected to cyclic loading were created [2]. The results obtained from these models were then compared with the experimental measurements.

As the mesh generation procedure employed could allow the user to generate solid fi nite element meshes with crack surface details corresponding to any crack surface angle ω within the range [-20o,20o], several sets of meshes corresponding to different values of ω were generated and analysed. Figure 6 and Figure 7 compare the SIF at the deepest point obtained from the experiments with the proposed models with different values of ω. for the Specimens S1 and S2, respectively. For Specimen S1, it can be seen that the models with smaller absolute values of ω (ω =0o,-5o) gave SIF values closer to the experimental results during the initiation phase of the crack propagation. Note that in Figures 5 and 6, a’ and t are, respectively, the depth of the surface crack and the thickness of the section. On the other hand, the fi nite element models with larger



absolute values of ω (ω =-10o,-15o) gave SIF values closer to the experimental values at the end of the crack propagation. In general, for both specimens, good correlations with test results were obtained for all models, including the model with ω = 0o, which was able to achieve the closest approximation to the experimental result. Hence, it can be concluded that if the exact geometry of the crack surface angle is unknown, a value of ω = 0o is recommended.

Figure 6. SIF predictions at the deepest point of surface crack for Specimen S1.

RESIDUAL FATIGUE LIFE PREDICTION

With the value of SIF at the deepest point of a surface crack known, it is possible to estimate the residual life of a cracked joint from fracture mechanics using the Paris Law [2]. The residual fatigue lives for Specimens S1 and S2 were estimated by integrating the data shown in Figures 6 and 7 with appropriate values of material parameters, which are corresponding to the API-5L pipes tested in ambient temperature conditions [5]. Figure 8 compares the residual fatigue life predictions obtained by using the proposed numerical models with crack details with different crack surface angles (measured values, ω∈[0o,-15o] for Specimen S1 and ω∈[0o, 15o] for Specimen S2) against the actual life recorded. For both specimens, as expected, the numerical models based on the measured geometry gave the most accurate predictions. For Specimen S1, all the models gave conservative residual fatigue life predictions. In addition, the fi nite element model with crack surface angle ω = 0o gave a prediction slightly more conservative than the model based on the measured crack shape. For Specimen S2, as the SIF predictions from all models (including the one based on measured geometry) are not conservative in the initiation phase of the crack propagation, the predictions of the residual life in the range a’/t≤0.6 are not conservative. However, the model with crack surface angle ω = 0o could be used in practice as it produces a conservative prediction when a’>6mm.

Figure 8. Residual fatigue life prediction by using different models.

Figure 7. SIF predictions at the deepest point of surface crack for Specimen S1.



REFERENCES

[1] Lee CK, Chiew SP, Lie ST, Nguyen TBN, 2009, Fatigue study of partially overlapped CHS K-joints. Part 1: geometrical models and mesh generation. Engineering Fracture Mechanics Vol. 76, No. 16, pp: 2445-2463.

[2] Chiew SP, Lee CK, Lie ST, Nguyen TBN, 2009, Fatigue study of partially overlapped CHS K-joints. Part 2: Experimental study and validation of the numerical model. Engineering Fracture Mechanics Vol. 76, No. 15, pp: 2408-2428.

[3] Zhao, X.L., Herion, S., Packer, J.A., Puthli, R., Sedlacek, G., Wardenier, J., Weynand, K., van Wingerde, A. and Yeomans, N., 2000. Design Guide for Circular and Rectangular hollow Section Joints under Fatigue Loading. CIDECT, TUV Germany.

[4] American Welding Society, 2008. ANSI/AWS D1.1/D1.1M-2008 Structural Welding Code-Steel, Miami, USA.

[5] Barsom, J.M., and Novak, S.R., 1977. Subcritical crack growth in steel bridge members, NCHRP Report 181, Transportation Research Board, National Research Council.

CONCLUSIONS

In this study, by comparing the experimental results obtained from full scale tests with the numerical modelling results, it is shown that the geometrical models and the mesh generation procedures adopted [1] could lead to consistent and reliable modelling results for partially overlapped CHS K-joints with and without cracks. It is shown that the proposed fi nite element models could reproduce the SCF distributions along all intersection curves of the uncracked joint and the SIF values at the deepest point of the surface crack. Hence, the models are also able to estimate the residual fatigue life for a cracked joint with reasonable accuracy.



FLUID VISCOUS DAMPERS FOR BUILDINGSHuang Yin-Nan ([email protected])

Hwang Jenn-Shin ([email protected])

ABSTRACT: The existing design formulas for supplemental viscous dampers for buildings, such as those provided in FEMA 356, were derived based on the shear-building assumption. However, for medium- to high-rise buildings, where fl exural deformation can be signifi cant when the buildings are subjected to seismic loading, the existing formulas overestimate the damping ratio contributed by viscous dampers. In this article, modifi ed design formulas developed to include both shear and fl exural deformations of buildings are presented. The modifi ed formulas are derived for four installation schemes of viscous dampers, including diagonal-, Chevron-, upper toggle- and lower toggle-brace-damper systems. Sample results of shaking table tests are also presented to demonstrate the effectiveness of viscous dampers and impact of installation schemes of dampers.

INTRODUCTION

Existing design formulas for viscous dampers such as those presented in FEMA 356 (2000) have provided convenient tools for practical engineers to determine the damping coeffi cients of supplemental viscous dampers for buildings. The existing formulas are based on the “shear-building” assumption and ignore the impact of fl exural deformation of a building on the effectiveness of dampers in reducing seismic responses. The formulas are not appropriate for medium- to high-rise buildings where the fl exural deformation can be as signifi cant as the shear deformation when the buildings are subjected to ground shaking, and the vertical relative deformation may be comparable to the horizontal relative displacement between the ends of the damper.

This article presents new formulas for the design of viscous dampers with several widely used installation schemes, including diagonal-, Chevron-, and toggle-brace systems, as shown in Figure 1. The new formulas take into account both relative vertical and horizontal deformations between the two ends of a viscous damper so that the axial deformation of the damper and the energy dissipated by the damper can be better captured. Sample results of a series of shaking table tests are also presented to demonstrate the effectiveness of viscous dampers in reducing seismic responses of buildings.

NEW FORMULAS FOR THE DESIGN OF LINEAR VISCOUS DAMPERS FOR BUILDINGS

In FEMA 356, the formula for estimating the damping ratio contributed from the energy dissipation devices is

(1)

Figure 1. Installation scheme of viscous dampers.

a. Diagonal brace b. Chevron brace

c. Upper-toggle d. Lower-toggle

where Ej is the total energy dissipated by energy dissipation j device in a cycle of motion; and Ut is the maximum potential (strain) energy of the structure and can be represented using Eq. (2)

(2)

where mj is the mass of the j-th story of the structure; φj is the horizontal modal displacement of the j-th story; T is the natural period of the structural vibration.

Figure 2 presents the deformation of a frame panel with a diagonally installed linear viscous damper subjected to an earthquake with respect to its original shape. The displacement of the damper is

(3)

where u and v are the horizontal and vertical displacements of the beam column joint b relative to the beam column joint d, respectively.



Assume that u and v can be represented using u(t) = u0 sinωt and and v(t) = v0sinωt the velocity of the damper is

(4)

The work done by the damper in a cycle of sinusoidal motion is

(5)

where C is the damping coeffi cient of the damper. Expressed in terms of the modal coordinate, the energy dissipated by the dampers installed in a multi-story structure is equal to

(6)

where (φh)rj and (φv)rj are the horizontal and vertical relative displacements between the ends of the j-th damper in the fi rst vibration mode.

Substitute Eqs. (2) and (6) into Eq. (1) and the damping ratio contributed by the linear viscous dampers in the structure can then be derived as

(7)

where mi is the mass of the i-th fl oor and (φh)i is the fi rst mode displacement in the horizontal direction at the level of the ith fl oor. The value of (φh)rj is positive when b moves to the right to b" and that of is positive while b is deformed downward to b".

The damping ratios for a structure equipped with linear viscous dampers using the confi gurations of panels b, c and d of Figure 1 can be derived using a procedure similar

Figure 2. Deformation of a frame panel with a damper installed using a diagonal brace.

∫

to that presented above and the results are summarized in Table 1 and Eq. (8):

(8)

More information for the derivation of Eq. (8) and coeffi cients of Table 1 can be found in Hwang et al. (2008), which also presents the formulas for the equivalent damping ratio of a structure equipped with nonlinear viscous dampers.

Table 1. Magnifi cation factors for various installation confi gurations of dampers

Magnifi cation Factor

Confi guration Horizontal Vertical fh fv

Diagonal Brace cos θ cos θ

Chevron Brace 1 H/D

Upper Toggle

Lower Toggle

SHAKING TABLE TESTS

Based on the factors of Table 1, the confi gurations of Figures 1c and 1d, i.e., upper and lower toggle-brace confi gurations, can produce a much higher value of magnifi cation factor fh than the diagonal-brace confi guration and therefore result in a much higher damping ratio given a set of viscous dampers.

To study the impact of installation confi guration of dampers on seismic responses of structures, a series of shaking table tests were conducted using a scaled three-story steel moment-resisting frame with and without linear viscous dampers (Hwang et al. 2005). Two confi gurations for the installation of dampers were studied, including diagonal-brace (see Figure 3a) and upper-toggle-brace (see Figure 3b) confi gurations.

The structure of Figure 3 was composed of three parallel moment resisting frames in the longitudinal (X) direction and two exterior dual systems together with a central moment resisting frame in the transverse (Y) direction. To simulate the seismic reactive mass, lead blocks were attached to the fl oors of the test structure. The story weights for the 2nd, 3rd and 4th fl oors were 92 kN, 92 kN, and 80 kN, respectively. The fi rst-mode frequency of the test structure in the X direction is 3 Hz.

Figure 4 presents the roof displacements of the test structure subjected to a ground motion recorded during the 1940 El Centro earthquake. Panels 1, 2 and 3 of Figure 4 present



the results for the bare (no dampers), diagonal-brace and toggle-brace structures, respectively.

The peak roof displacements of panels 1, 2 and 3 of Figure 4 are 24.5, 12.7 and 8.5 mm, respectively. The displacement response is greatly reduced due to the installation of viscous dampers. The toggle-brace-damper system performs better than the diagonal-brace-damper one and the two systems have comparable demand on damper forces.

CONCLUSIONS

In this article, new formulas for the design of viscous dampers for structures are presented. The new formulas account for the effects of both shear and flexural deformations of a structure, enable a more accurate estimate on the damping ratio of a structure equipped with viscous dampers and are applicable for the design of both linear and nonlinear viscous dampers.

Sample results of shake table tests for a steel moment resisting frame with and without viscous dampers are also presented. The seismic responses of the test frame were greatly reduced due to the installation of viscous dampers and the toggle-brace-damper system was more effi cient in controlling the seismic responses of the test frame than the diagonal-brace-damper system.

REFERENCES

[1] Federal Emergency Management Agency (FEMA). (2002). “Prestandard and commentary for the seismic rehabilitation of buildings.” Rep. No. 356, Washington, D.C.

[2] Hwang, J.-S., Huang, Y.-N., and Hung, Y.-H. (2005). “Analytical and experimental study of toggle-brace-damper systems.” Journal of Structural Engineering, ASCE, 131(7), 1035-1043.

[3] Hwang, J.-S., Huang, Y.-N., Yi, S.-L., and Ho, S.-Y. (2008). “Design formulations for supplemental viscous dampers to structures.” Journal of Structural Engineering, ASCE, 134(1), 22-31.

Figure 3. The test structure with linear viscous dampers installed using a) diagonal-brace confi guration and

b) upper-toggle-brace confi guration

Figure 4. Roof displacements of the test structure subjected to 80% El Centro earthquake.

25



J-INTEGRAL DECOMPOSITION FOR THE COMPUTATION OF 3D STRESS INTENSITY

FACTORS IN CRACKED STRUCTURESLie Seng Tjhen ([email protected])

INTRODUCTION To assess the structural integrity of a cracked structure, it is essential to estimate the stress intensity factor (SIF) K at the crack tip as accurately as possible [1]. The Finite Element Method (FEM), coupled with the J-integral [2], has been employed successfully for many years, and more recently, the Boundary Element Method (BEM) [3] has also received attention from the engineering community because it is more suited to the evaluation of the J-integral since the required stresses, strain and derivatives of strain can be accurately obtained at internal points in the body given the surface displacements and tractions. These internal point solutions utilize boundary integral equations and, hence, no discretization of the domain is required. The J-integral is then calculated by integrating stress, strain and derivative of the strain products found from the internal points along a contour in a plane perpendicular to the crack front and also over the area enclosed by the contour. Hence, the J-integral is accurately calculated without changing the surface mesh.

In order to obtain the Mode-I, II, III J-integrals, the stress and strain products and stress and derivative of strain products are combined from points symmetric to the crack plane. These integrands are then integrated over the symmetric contour and area enclosed by that contour to yield two parts of the J-integral: one comprising of symmetric elastic fi elds called JS and the other comprising of anti-symmetric elastic fi elds called JAS. The integral JS is equal to the Mode-I J-integral, whereas the integral JAS contains both the Mode-II, III J-integrals. The decomposition method proposed in Ref. [4] shows the details of decoupling of the Mode-II, III stresses, strains and derivatives of strain. The stress intensity factors are then obtained directly from the Mode-I, II, III J-integrals. In this study, the relevant equations are implemented into the standard 3D BEM codes, and a penny-shape crack located at the centre of an infi nite cylinder subjected to remote stress is analyzed to test the accuracy of this method.

FORMULATION OF MIXED MODE J-INTEGRALS

For each of the three modes of fracture, there is a corresponding J-integral, namely, JI, JII and JIII and these are related to Jk as follows:

J1 = J I + J II + J III (1)

(2)

The J-integrals JM for each mode M = I, II and III are defi ned as

(3) where M = I, II, III and Γε is a contour normal to the plane x3 = 0 of vanishing radius ε which proceeds in the anti-clockwise direction. In Eq. (3), σij and ui are the mode M stresses and displacements respectively, and

. It can be shown that JM is path independent.

By taking the limit of ε → 0, the area integral over Ωε enclosing the crack tip will tend to zero and further expanding and utilizing the defi nition of JM in the Eq. (3), will yield

(4)

M = I, II, III

Alternatively, one can also defi ne Eq. (3) using the GIII integral as

(5)

where Γε is a contour of vanishing radius ε in the x3 = 0 plane, perpendicular to the crack front and

(6)

M M

JM = ∫ο Γε WMn1 – σij nj dΓM ∂ui∂x1

M

WM = ∫0

ε σij d εij

M M

JM = ∫ Γε WMn1 – σij nj dΓM ∂ui∂x1

M

= ∫ C WMn1 – σij nj dΓM ∂ui∂x1

M

+ ∫ Ω(C) + dΩ∂σi1∂x1

M ∂σi2∂x2

M ∂σui1∂x1

M

J2 = –2√J IJ II

+ ∫ Ω(C) σi3 dΩ∂2ui

∂x1 ∂x3

M

M

GIII = ∫ο Γε W3n1 – σ3j nj dΓ∂u3∂x1

W3 = ∫ 0 σ3j dε3j

ε3j



For linear elasticity, the relationship between J1 and the Mode–I, II and III stress intensity factors can be obtained by substituting the three dimensional stress fi elds. This produces

(7)

where E* is the Young’s modulus E for plane stress, E* = E/(1- v 2) for plane strain and μ is the shear modulus. Eqs. (1) – (7) can be used to obtain the Mode-I, II and III stress intensity factors from J1, J2 and GIII as follows:

(8)

(9)

(10)

However, the use of J2 leads to numerical diffi culties as it will involve integration of singular elastic fi elds over the crack surface. The novel approach described in Ref. [4] is to avoid the use of J2. The fi rst step is to split the J1

integral into two parts, namely,

J1 = JS + JAS (11)

where JS is found from the symmetric elastic fi elds about the crack plane, whereas JAS utilizes the anti-symmetric elastic fi elds. The integral JS is equal to J1 as the Mode-I elastic fi elds are symmetric about the crack plane. This leaves JAS = JII + JIII, from which JII and JIII are decoupled by the decomposition method. Eq. (7) is then used to calculate the Mode-I, II and III stress intensity factors along the crack front.

EMBEDDED PENNY-SHAPE CRACK IN AN INFINITE DOMAIN

A circular crack located at the centre of a large cylinder of radius d and height 2h shown in Figure 1 is modeled and analyzed using the 3D BEM codes. The stress intensity factors for this confi guration should be very close to a penny-shaped crack under remote tensile loading in an infi nite elastic body. The crack radius is a and the tensile stress σ is applied at both ends of the cylinder. The ratio of a/d = 0.1, h/d = 1.5, E = 210.0E+03, and σ = 10.0 and v = 0.3 are used in this particular example. The exact value of KI = 2σ/π√πa, and KII and KIII are both equal to zero.

The crack body is modelled using two BEM sub-domains, and each sub-domain contains 374 nodes and 132 elements. Figure 2 shows the mesh density of the two BEM sub-domains. The J-integral contour to crack radius of r/a = 0.397, and the computed stress intensity factors KI along the crack front are tabulated in Table 1 and also plotted in Figure 3 respectively.

Figure 2. Boundary element mesh density of the two domains.

Figure 1. Penny-shaped crack embedded in a cylinder.

Figure 3. Stress intensity factors KI, KII, KIII along the crack front.

J1 = J I + J II + J III = (KI + KII) + KIII21

E➨

2 212μ

KII = √E➨ (√J1 – J2 – GIII + √J1 + J2 – GIII )12

KI = √E➨ (√J1 – J2 – GIII + √J1 + J2 – GIII )12

KIII = √2μGIII



Table 1. Results of stress intensity factors KI along the crack front

No. Angle Radius KI (Exact) KI (BEM) KI % Error

1 0 0.39700000 11.28379167 11.22765000 -0.498

2 30° 0.39700000 11.28379167 11.23550000 -0.428

3 60° 0.39700000 11.28379167 11.20570000 -0.692

4 90° 0.39700000 11.28379167 11.18323000 -0.891

5 120° 0.39700000 11.28379167 11.19326000 -0.802

6 150° 0.39700000 11.28379167 11.21187000 -0.637

7 180° 0.39700000 11.28379167 11.22170000 -0.550

8 210° 0.39700000 11.28379167 11.23817000 -0.404

9 240° 0.39700000 11.28379167 11.20725000 -0.678

10 270° 0.39700000 11.28379167 11.19026000 -0.829

11 300° 0.39700000 11.28379167 11.20167000 -0.728

12 330° 0.39700000 11.28379167 11.21321000 -0.626

CONCLUSIONS

In summary, the decomposition method produces very accurate Mode-I, II, II stress intensity factors for a penny-shape crack embedded in an infi nite domain. Table 1 shows that the J-integrals are in close agreement with the theoretical stress intensity factors for the entire range of θ = 0° – 360°. The optimum radius r is found to be equal to 0.397a, where a is the radius of the crack.

REFERENCES [1] Anderson, T.L., 2005. Fracture Mechanics: Fundamentals and

Applications. 3rd Edition, CRC Press, Boca Raton, USA.

[2] Rice, J.R., 1968. “A Path Independent Integral and the Approximate Analysis of Strain Concentration by Notches and Cracks”. Journal of Applied Mechanics, ASME, Vol. 35, pp. 379-386.

[3] Ang, W.T. 2007. A Beginner’s Course in Boundary Element Methods, Universal Publishers, Boca Raton, USA.

[4] Rigby, R.H. and Aliabadi, M.H., 1998. “Decomposition of the Mixed-mode J-Integral – Revisited”. International Journal of Solids and Structures, Vol. 35, No. 17, pp. 2073-2099.

[5] Tada, H., Paris, P.C. and Irwin, G.R., 2000. The Stress Analysis of Cracks Handbook. 3rd Edition, American Society of Mechanical Engineers, New York, USA.



NUMERICAL MODELLING OF PARTIALLY OVERLAPPED CIRCULAR HOLLOW SECTION

K-JOINTS FOR FATIGUE ANALYSISLee Chi King ([email protected])

Chiew Sing Ping ([email protected])Lie Seng Tjhen ([email protected])

Nguyen Thi Bich Ngoc ([email protected])

INTRODUCTION

In this study, a set of consistent geometrical models is developed for the fi nite element modelling and fatigue analysis of partially overlapped circular hollow section K-joints. To accomplish the geometrical models, an accompanying set of automatic finite element mesh generation procedures is developed. These automatic mesh generation procedures are able to discretize the joint into different types of meshes for the analysis of uncracked and cracked joints. In this article, concise descriptions of the geometrical models and the mesh generation procedures are given. Details of the geometrical modelling and the mesh generation procedures can be found in reference [1].

GEOMETRICAL MODELLING

The main method adopted in this study to obtain realistic geometrical models of partial overlapped CHS K-joint is based on a hierarchical modelling approach which follows the fabrication sequence of real joints. The geometrical models are constructed in the following steps:

(1) Modelling of the intersection curves and intersection points (Figure 1),

(2) Modelling of weld profi le (Figure 2), and

(3) Modelling of the surface crack shape and crack front details (Figure 3).

AUTOMATIC MESH GENERATION

Similar to the derivation of the geometrical models, the mesh generation steps were carried out in a hierarchical manner. The starting point is the generation of a surface mesh, which is then converted into a solid mesh using an extrusion algorithm [2]. Eventually, additional details such as weld profi le and surface cracks are added to the mesh. This method of mesh generation is fl exible in such a way that at different stages, meshes with different levels of detail can be generated and employed for different applications. In particular, surface mesh (Figure 4) could be employed

for the quick assessment of the ultimate strength of the joint. While in the case that a quick assessment of stress concentration factor is needed, the hybrid model (Figure 5) which contains mainly surface elements and a small number of solid elements could be used. For a more detailed study on the distribution of hot spot stress, full solid meshes without (Figure 6) or with (Figure 7) welding details will be created by using the extrusion algorithm [2] and a weld profi le meshing procedure. Eventually, when a full numerical study for a crack joint is needed, a solid mesh with weld and crack details (Figure 8) can be generated by employing a specially designed procedure that inserts the crack details at appropriate locations along the weld toe.

Figure 1. Intersection curves model.

Figure 2. Weld profi le model.



Figure 3. Surface crack model.

Figure 6. Solid mesh without welding details for the joint.

Figure 4. Surface mesh for the joint.

Figure 5. Hybrid mesh for the joint.

Figure 7. Solid mesh with welding details for the joint.

Figure 8. Solid mesh with surface crack details for the joint.

APPLICATION RANGE AND EXAMPLES

The proposed mesh generation scheme is applicable to the special case of identical chord and braces diameter even when the joint has a high overlap ratio of 80%. Note that such special cases were not covered by the mesh generators created in the well cited works by Cao et al. [3] and Lie et al. [4]. An example of the mesh with same chord and braces dimensions and with an overlap ratio of 80% is given in Figure 9. Furthermore, as the current mesh generation scheme is also designed for different values of intersection angles between the braces and the chord, it could be used to generate meshes for partially overlapped N-joints as shown in Figure 10.



CONCLUSIONS

In this study, a set of consistent and reliable geometrical models and a corresponding set of hierarchical mesh generation procedures were developed. The mesh of a partially overlapped CHS K-joint is fi rst created in the form of a surface mesh, which is then converted into a solid mesh. Weld and crack details are then added subsequently using a series of mapping procedures. The mesh generator is able to handle a wide range of parameters including the case of identical chord and braces dimensions with a large overlap ratio.

REFERENCES

[1] Lee, C.K., Chiew, S.P., Lie, S.T. and Nguyen, T.B.N., 2009. “Fatigue study of partially overlapped CHS K-joints. Part 1: geometrical models and mesh generation”. Engineering Fracture Mechanics, Vol. 76, No. 16, pp: 2445-2463.

[2] Lee, C.K. and Xu, X.Q., 2005. “A new automatic adaptive 3D solid mesh generation scheme for thin-walled structures”. International Journal for Numerical Methods in Engineering, Vol. 62, No. 11, pp. 1519-1558.

[3] Cao, J.J., Yang, G.J. and Packer, J.A., 1997. “FE Mesh Generation for Circular Tubular Joints with and without Cracks. Proceedings of the 7th International Offshore and Polar Engineering Conference, Honolulu, USA, Vol. IV, pp. 98-105.

[4] Lie, S. T., Lee, C. K., and Wong, S. M., 2003. Model and Mesh Generation of Cracked Tubular Y joints. Engineering Fracture Mechanics, Vol. 70, pp. 161-184.

Figure 9. A mesh with identical braces and chord size and 80% overlap ratio.

Figure 10. A mesh for an N-joint.



PLASTIC COLLAPSE LOADS AND CTODS OF A CRACKED SQUARE HOLLOW SECTION (SHS) K-JOINT

Lie Seng Tjhen ([email protected])Zhang Baofeng ([email protected])

Yang Zhengmao([email protected])

INTRODUCTION

In order to get the actual plastic collapse load of a cracked K-joint, a full-scale specimen was tested under incremental loads up to failure [1]. The K-joint was fi rst fatigue tested using the “Orange Rig” servo-hydraulic testing frame available in the Construction Technology Laboratory. Figure 1 shows the actual surface crack located at the hot spot stress location of the joint. The crack shape was then measured using the Alternating Current Potential Drop (ACPD) technique [2]. This particular specimen was fabricated using BS4360 structural steel of Grade 50D [3]. The weld profi le and the specimen preparation were carried out in accordance with the American Welding Society (AWS) Structure Welding Code–Steel D1.1/D.1.1M:2006 [4] specifi cations. The specimen material yield stress is 380.3 MPa.

TEST RIG AND LOADING SYSTEM

A specially designed “Yellow Rig” testing frame shown in Figure 2 was used to test the cracked SHS K-joint. The ends of the chord were fi xed with respect to the test rig. The load was applied on the end of the brace through the spreader beam which was supported by two hydraulic jackets as shown in Figure 3. Each hydraulic jacket is capable of producing static load of up to 1000 kN.

Figure 1. Surface crack located at hot spot stress region.

Figure 2. “Yellow Rig” testing frame set-up for K-joint specimen.

Figure 3. Load system used to test the K-joint specimen.



CRACK MOUTH OPENING DIPLACEMENT (CMOD)

A set of 3 LVDTs with a stroke capacity of 10 mm was used to measure the crack mouth opening displacement (CMOD) along the crack front as shown in Figure 4. One block and one bracket were attached to the chord face and brace face, and in turn three LVDTs were fi xed to the bracket. The three LVDTs were in contact with the block so that the vertical displacement of points 1 and 2 and the horizontal displacement of point 3 relative to the brace could be measured simultaneously.

In order to transfer the measurements obtained to the crack mouth opening displacement, an extrapolation approach was adopted in the test as shown in Figure 5. If the region between the crack and the measured point is treated as a rigid body, the displacements at the measured points are caused by the displacements and rotations of the crack faces. If the displacement measured by LVDTs 1, 2 and 3 are expressed as d1, d2 and l, the following relationships can be found as follows:

, rotation of crack (1)

dc = d1 – γ • L1, vertical displacement of crack mouth (2)

lc = l – l' = / – γ • h, horizontal displacement of crack mouth (3)

, and crack mouth opening

displacement (CMOD) (4)

where L1, L2 and L3 are the respective distances from the LVDTs 1, 2 and 3 to the weld toe, γ is the rotation angle of crack face which is equal to the rotation angle of the chord face, l’ is the horizontal displacement caused by the block rotation, h is the vertical distance of the LVDT 3 away from the chord face, and it can be calculated from

h = h0 + d1 + γ • (L3 – L1), vertical distance (5)

BRACE END AXIAL LOAD AND DISPLACEMENT

The brace end displacement was obtained from an LVDT with a stroke capacity of 50 mm that was calibrated and attached to the bottom of spreader beam aligned with the centreline of the brace and the two ends of the spreader beam. The load was obtained via load cell, and the load was also measured using the strain gauges attached at the middle of the brace to confi rm the load readings.

COMPARISON BETWEEN NUMERICAL AND EXPERIMENTAL RESULTS

ABAQUS [5] general purpose fi nite element program was used to analyze all the cracked and uncracked models to produce the load-displacement curves and crack mouth opening displacements. Figure 6 shows the load-displacement curve for the K-joint subjected to brace end axial loads. The elastic load was up to 600 kN, then this curve turned into the plastic region. From the ACPD readings, it can be found that the crack showed an obvious ductile tearing until the load reached 1115 kN, then cracked through the chord wall. After this point, the load could still increase slightly to the maximum load of 1143 kN before it dropped down.

Figure 4. Dimensions of the LVDTs before the test.

Figure 5. Dimensions of the LVDTs during the test.

Figure 6. Load versus displacement curve of theK-joint specimen.



Figure 7 shows the comparison of crack mouth opening displacement (CMOD) versus brace end axial loads. From the above results, it can be seen clearly that a close agreement is obtained between the numerical and the experimental results before the joint failed by brittle fracture.

Figure 7. Load versus CMOD curves of the K-joint specimen

CONCLUSIONS

It can be seen that the K-joint specimen has a notable plastic deformation. Compared with the numerical curves which do not model the crack ductile tearing, the experimental loads are slightly lower than the numerical ones. Before the crack propagated signifi cantly, the numerical curve is close to the experimental one. Hence, the proposed numerical model is reliable, and it is suitable to be used for analyzing plastic collapse loads [6] and the crack driving force of cracked SHS K-joints.

REFERENCES

[1] Lie, S.T., Lee, C.K., Chiew, S.P. and Yang, Z.M., 2006. A Consistent Crack Modelling and Analysis of Rectangular Hollow Section Joints. Finite Elements in Analysis and Design – An International Journal for Innovations in Computational Methodology and Application, Vol. 42, No. 8-9, pp. 639-649.

[2] Dover, W.D., Dharmavasan, S., Brennan, F.P. and Marsh, K.J., 1995. Fatigue Crack Growth in Offshore Structures. Engineering Materials Advisory Services Ltd., Chameleon Press, London, UK.

[3] Yang, Z.M., Lie, S.T. and Gho, W.M., 2007. Failure Assessment of Cracked Square Hollow Section T-Joints. International Journal of Pressure Vessels and Piping, Vol. 84, No. 4, pp. 244-255.

[4] American Welding Society (AWS), 2006. ANSI/AWS D1.1/D1.1M:2006, Structural Welding Code – Steel. Miami, USA.

[5] ABAQUS, 2006. Theory Manual. Version 6.4, Hobbit, Karlsson & Sorensen Inc., USA.

[6] 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.



ROCK BLAST SIMULATION BY DISCONTINUOUS

DEFORMATION ANALYSISZhao Zhiye ([email protected])

Zhang Yun ([email protected])

INTRODUCTION

Rock blasting is a rock excavation technique most widely used in the mining and construction industry due to its reliability, economy and safety. The boreholes are loaded with explosives and blasted in a prearranged sequence to fracture, fragment and displace a well defi ned portion of the rock from its natural position. The goal of a blast design is to attain the expected technical target (advance and good contour) at an economical cost. Cost saving and less vibration and damage in the surrounding rock may be achieved by optimising parameters in the blast design. As blast experiments are very expensive and site results are diffi cult to obtain, the numerical methods on simulating such problems become desirable and important.

The discontinuous deformation analysis (DDA) proposed by Shi (1988) is a discrete element method to investigate the two-dimensional behaviour of a fractured rock mass, and has been used recently to model the motions of blocky systems in rock engineering. Due to its inherent discontinuous features in its fundamental formulations, the DDA can be employed effi ciently to model both the static and the dynamic problems of rock masses containing parallel or intersecting fractures, especially in stability analysis of rock slopes and underground structures. For continuous analyses where the rock mass consists of an intact block without fractures, the DDA can be used as an FEM program by gluing all the subblocks together with very strong joint properties (Lin et al. 1996). For discontinuous analysis where the rock mass contains multiple blocks separated by fractures, all the blocks can be assembled to interact with each other with the real joint properties. The ability to solve both the continuous and the discontinuous problems makes the DDA an effi cient method to model a fractured rock mass under dynamic loads.

NUMERICAL BLAST SIMULATION BASED ON DDA

Drill and blast in rock mass

The drill and blast technique is a kind of method to detach the rock in excavation. Since it is suitable for hard rock (e.g. granite, gneiss, basalt, quartz) as well as for soft rock (e.g. marl, loam, clay, chalk), drill and blast is applicable

for rocks with varying properties. Moreover, drill and blast is advantageous for: (a) relatively short tunnels, where a tunnel boring machines (TBM) is not suitable; (b) very hard rock; (c) non-circular cross section.

The tunnel blasting is a much more complicated operation than the bench blasting because the only free surface that initial breakage can take place towards to is the tunnel face (Zare & Bruland 2006). The blast design has a direct infl uence on the time consumption and construction cost in the constructions of tunnels. The most important operation in the tunnel blasting procedure is to create an opening in the face in order to develop another free surface in the rock. This is the function of the hole-cut design. The parallel hole-cut is the most popular one in operations with mechanized drilling. The parallel cut consists of one or more larger diameter unloaded boreholes. All holes are drilled at a right angle to the face and parallel to the tunnel direction. It is easy to drill and does not require a change in the feed angle.

DDA Model Description In this section, the DDA method is selected as the discontinuous method for simulating the fracture generation of rock mass induced by the explosives. The objective is to study whether the DDA method can be applied as a reliable numerical method for such practical problems. Considerations are mainly concentrated on the fracture generation processes on different loading history.

During the blasting process, the rock mass will change from continuous rock mass to a discontinuous state with fractured rock mass. A DDA program is developed specifi cally for the crack formation analysis. In every time step, the program will automatically check all joint boundaries with the Mohr’s and cut-off (tensile) criteria. With the gray as the background colour of the specimen, all the joint boundary lines are drawn gray at fi rst. If the strength boundaries reach the criteria of failure, cracks will initiate indicated by red lines in the next time step. The fractured block will thus detach from the major part and move independently.

A DDA model is constructed based on the charge design in the experiment as shown in Figure 1(a). 5516 blocks



have been used and each charge hole is modeled by six loading points around the charge hole. The outside four boundaries are free surfaces and the rock mass could be moved in the outward directions. A dynamic analysis mode is applied and no damping effect is considered. The explosive is simulated by the load history curve at each loading point. The simplifi ed curve used in this model is shown in Figure 1(b). The t in the fi gure is a unit which could be changed to any value for the consideration of different blast duration. For the rock mass, the data from the laboratory tests on the Bukit Timah granite at the fi eld site are adopted in this study. The average density of the rock is 2650kg/m3, Poisson’s ratio is 0.16 (Hao et al. 2002), Young’s modulus of the intact granite is 73.9GPa, uniaxial compressive strength is 186MPa, and tensile strength is 16.1MPa (Hao et al. 2001).

Figure 1. (a) Block confi guration of the DDA model; (b) Loading history of the explosive Figure 2. (a) Crack initiation; (b) Detached body of the rock

mass; (c) Connected and non-connected cracks.

(a)

(b)

initiated around the charge holes after explosion. The cracks are starting to generate and beginning to propagate in the radial direction. During the development of those radial cracks, some radial cracks could meet and form a closed loop. The other cracks are continuing to propagate outward. Figure 2(b) shows the formation of the detached body as highlighted in yellow lines. More and more cracks from the adjacent charge holes meet and form the closed district. With suffi cient cracks, the closed loop will form a separate body detached from the other part. The cracks will also stop to propagate for the energy assumption during the formation of the detached body. Figure 2(c) displays two crack modes in detail: connected cracks and non-connected cracks.

(a)

(b)

(c)

Result Discussions

After the numerical simulations, the crack confi guration analysis is carried out. Figure 2(a) shows the cracks

In this blast design, the control of the detached body is an important technique. The purpose of the design is to produce the detached bodies suffi cient with suitable size and less impact on the surrounding rock mass. Therefore,



Figure 3. Blast sequence of the rock mass model.

many factors e.g. the charge magnitude, coupled type, delay time need to be considered. The numerical simulation is also conducted using the DDA method to study the effect of delay time on the rock fragmentation.

In Case 1, 12 charge holes are considered to blast at the same time. The t in Figure 1(b) is taken as 0.1, indicating that the rising time to the peak pressure 150 MPa is 0.1ms. The time interval of each time step is taken as 2.5 μs. The maximum displacement ratio in the DDA program is set as 0.001. The charge holes for Cases 2 and 3 will be blasted in sequence. The inside four holes will be detonated fi rst, and after an interval, the outside four holes will follow and fi nally the middle four holes will start at the third stage, see the sequence shown in Figure 3. The time interval here is 1ms for Case 2 and 2 ms for Case 3, respectively. All the other parameters are the same as in the Case 1.

Case 1

Case 2

Case 3

The cracks surrounding the charge holes will start to occur soon after the detonation of the explosives. The fi nal crack generation will be stable after all the charge holes are blasted. The process for Case 2 and Case 3 is similar to Case 1, and the results for all cases are put together as shown in Figure 4. The yellow lines are sketched for the detached body of rock mass. It could be clearly seen that Case 1 has the least amount of detached parts and Case 2 generates the most detached parts. Therefore, the sequence blast with time interval delay is better than the simultaneous explosion. For loading time interval, the case of 1 ms delay will give the best blast effect.

CONCLUSIONS

Rock blasting design is important in the rock excavation, and has a direct impact on the control of the fragmentation size. The purpose of the hole-cut design is to produce enough fragmentations with suitable size and less impact on the surrounding rock mass. The numerical simulation could be carried out by the discontinuous method based on the concept of failure of the rock mass strength. The DDA method considered several different infl uence effects. The results show that the numerical method could be a good

support for the future blasting design for its effi ciency, economy and feasibility.

REFERENCES

[1] Hao, H., Wu, C. and Zhou, Y. 2002. Numerical analysis of blast-induced stress waves in a rock mass with anisotropic continuum damage models. Part 1: equivalent material property approach. Rock Mechanics and Rock Engineering, 35(2): 79-94.

[2] Hao, H., Wu, Y.K., Ma, G.W. and Zhou, Y.X. 2001. Characteristics of surface ground motions induced by blasts in jointed rock mass. Soil Dynamics and Earthquake Engineering, 21(2): 85-98.

[3] Lin, C.T., Amadei, B., Joseph, J. and Jerry, D. 1996. Extensions of discontinuous deformation analysis for jointed rock masses. International Journal of Rock Mechanics and Mining Sciences & Geomechanics, 33(7): 671-694.

[4] Shi, G. 1988. Discontinuous deformation analysis - a new numerical model for the statics and dynamics of block systems. Ph.D. Thesis, in Civil Engineering. University of California: Berkeley.

[5] Zare, S. and Bruland, A. 2006. Comparison of tunnel blast design models. Tunneling and Underground Space Technology, 21: 533-541.

Figure 4. Final Crack confi gurations of Cases 1, 2 and 3.



SEISMIC PERFORMANCE ANALYSIS AND TREMOR MONITORING FOR

BUILDINGS IN SINGAPORELiping Huang ([email protected])Qiwei Zhang ([email protected])

Kusnowidjaja Megawati ([email protected])Tso-Chien Pan ([email protected])

ABSTRACT: Disastrous earthquakes occurred frequently along the Sumatran subduction zones and Sumatran fault, which are located several hundred kilometers from Singapore. Although there is no local seismic activity, evaluating the seismic capacity of existing buildings in Singapore is necessary due to defi ciency of seismic design consideration. In present study, FE model and fi eld tremor monitoring were combined to evaluate the seismic behaviors of typical buildings in Singapore when subjected to strong ground motion occurred in long-distance area.

INTRODUCTION

Singapore, an island state located at latitude 1.3° N and longitude 103.8° E with an area of about 700 km2, and is relatively far from earthquake zones in Sumatra. It is, however, frequently shakened by large-magnitude earthquakes along the Sumatran subduction zone and the Sumatran fault. As shown in Figure1, many earthquakes of a magnitude larger than 7 have occurred in Sumatra since 1900, and the latest one on 30 September 2009 was the Mw 7.6 earthquake, off the city of Padang, about 492 km Southwest of Singapore.

Figure 1. Earthquakes with magnitude equal to or larger than 7 since 1900 on Sumatra area (from USGS).

Singapore has low local seismic activity, and seismic-resistant design has not been implemented in Singapore. Although it is far from seismic zones, it is necessary to conduct some research work on evaluating the seismic capacity of existing buildings in Singapore.

Thirty-six private residential and commercial buildings have been selected for the seismic instrumentation programme under the Building and Construction Authority (BCA). One triaxial seismic sensor is installed at the base of each building and another one at the roof. However, six buildings with vertical and horizontal confi guration irregularities have been selected for detailed instrumentation, involving six triaxial sensors in each building.

The present study is to focus on evaluating the behaviours of typical buildings in Singapore when subjected to ground motions from long-distance earthquakes. Our research combines fi eld tremor monitoring with seismic performance analysis of the building using ETABS.

BUILDING PERFORMANCE ANALYSIS

3D fi nite element models of the instrumented buildings have been constructed based on as-built drawings. The slabs were assumed to be rigid in plane and fl exible out of plane. Because seismic-resistance has not been considered, most of the buildings have very complicated fundamental mode shapes, where lateral and torsional modes are coupled. The typical fi rst mode shape of these buildings is shown in Figure 2.



Nonlinear pushover analysis is performed to determine the seismic capacity. Pushover analysis can trace the sequence of yielding and failure of structural members, as well as the progress of the overall capacity curve of the structure.

Pushover analysis uses an incremental iterative solution of the static equilibrium equation to obtain the response of structure to the increasing lateral loads. The procedure continues until the structure becomes unstable or reaches a predetermined collapse limit. Pushover analysis represents the inertial forces which would be experienced by the structure when subjected to ground shaking.

The fi nite element formulation can be written as follows:

KU=P

where K is the nonlinear stiffness matrix, U is the displacement vector, and P is the predefi ned load vector applied laterally over the height of the structure with relatively small load increments.

For each iteration, the reaction vector is

P6 – ∑∫V BT.σNL.dV where B is the strain-displacement matrix of each element and σNL is the element nonlinear stress vector. The reaction vector is re-applied until convergence to a specifi ed tolerance is reached

ΔU = [KT]–1.(λP0 – P6)

where ΔU is the calculated displacement increment, KT is the nonlinear stiffness matrix, λ is the load factor, and P0 is the equilibrated load of the previous iteration.

The basic analysis steps consist of a pushover analysis of a multi-degree-of-freedom (MDOF) system, transformation of the MDOF system to an equivalent single-degree-of-freedom (SDOF) system, determination of the target displacement, and the determination of all relevant demand quantities.

Figure 2. Typical 1st Mode Shape (Torsion).

The analysis was performed using the program ETABS. The direction for applying lateral load is determined by the fi rst translation direction. The fl exural behaviour of the beams and columns was modelled by one-component lumped plasticity elements, composed of an elastic beam and two inelastic rotational hinges. The element formulation was based on the assumption of an infl ection point at the midpoint of the element. The defi nition of hinge property is according to ATC-40 and FEMA273.

The typical pushover analysis results are shown in Figures 3 – 5.

Figure 3. Pushover Curve (Base Shear (V) vs. Monitored Displacement (∆roof)).

Figure 4. Pushover Curve (Conversion to ADRS Spectra).



Figure 5. Hinge Status of Building.

FIELD TREMOR MONITORING

The seismic responses of the buildings depend on the amplitude and distribution of dynamic deformation and duration.

It is known that soft soil deposits may amplify bedrock motions and may also prolong the predominant period of the ground motion on the surface. When the soil deposit and the building have the same fundamental period, resonance happens and will cause an amplifi ed structural response. Therefore, many buildings located at soft soil deposits on the Kallang formation and reclaimed land have experienced ground tremors from Sumatran earthquakes. The distribution of soil condition of Singapore is shown in Figure 6.

Figure 6. Geological map of Singapore.

Figure 7 shows the ground motion and roof response of a 12-storey building recorded during the magnitude 7.6 earthquake on 30 September 2009. In Figure 8, the maximum ground acceleration, velocity, and displacement show correlation with short-period, medium-period and higher-period range. Combined with the structural analysis result, the roof maximum displacement in this event is still far from the yielding point as shown in Figure 9.

Figure 7. Acceleration time series on one building under 30 Sep 2009, 10:16:09 UTC, Mw 7.6, R = 491 km.

Figure 8. Combined D-V-A response spectrum for the ground motion corresponding to Figure 7.



Figure 9. Roof displacement vs. roof acceleration curve.

REFERENCES

[1] ATC, 1996. Seismic Evaluation and Retrofi t of Concrete Buildings, Vol. 1, ATC-40 Report, Applied Technology Council, Redwood City, California.

[2] FEMA, 1997. NEHRP Guidelines for the Seismic Rehabilitation of Buildings, Developed by the Building Seismic Safety Council for the Federal Emergency Management Agency Report No. FEMA 273, Washington, D.C.



SUPER ELEMENT METHOD IN THE MODELING OF LARGE-SCALE

STRUCTURE WITH LOCAL NONLINEARITYYuan Weifeng ([email protected])Tan Kang Hai ([email protected])

ABSTRACT: Numerical simulation of large-scale structures may incur tremendous computational costs due to the huge number of degrees of freedom. To improve the effi ciency of fi nite element analysis without the accompanying loss of accuracy, a super element method is proposed in this paper. Based on this method, the entire structure can be divided into linear and nonlinear zones. Using the proposed approach, all the linear zones can be merged into just one super element, regardless whether they are inter-connected or not. Thus, the total number of degrees of freedom of the original fi nite element model can be reduced signifi cantly.

INTRODUCTION

The fi nite element method (FEM) is an important tool used in numerical analysis. It is well known that the computational cost in FEM analysis is dependant on the number of degrees of freedom (DOFs) for the model under investigation. To improve computational effi ciency, one obvious way is to reduce the number of elements. However, some important details of structural response may be glossed over since using fewer elements usually results in poor accuracy. To achieve a practical balance between effi ciency and accuracy, the super element method is widely used in FEM analyses for various problems (Korczak and Patera, 1986; Birgersson and Finnveden et al, 2005; Lukasiewics, 1987). Briefl y, the basic concept of the super element method is to treat structural members as a continuous body and then discretize this body into super elements defi ned as any cluster of contiguous elements (Jiang and Olson, 1994; Cao, 1992). In this way, each super element may consist of different types of members which possess various shapes, materials properties, and boundary conditions. Using the super element method, the task of modeling can be simplifi ed by including intricate details inside the super element itself. At present, the methods for constructing super elements are usually based on substructure and static condensation techniques (Axelsson and Barker, 2001). As a result, the sizes of the system matrices in an analysis are reduced since only the DOFs retained for the super elements are used. Hence, computational benefi t can be reaped in subsequent analyses where super elements are re-utilized.

In this paper, a simple approach for constructing a super element is introduced. The novelty of the proposed approach is that all the disparate zones of the linear members can be integrated into one super element, even if they are not inter-connected.

METHODOLOGY

As shown in Figure 1, it is assumed that a structure under various loads and boundary conditions is discretized into fi nite elements. The fi nite element model consists of two zones depicted by black and gray lines, respectively. Without loss of generality, the black line zone is assumed to be the nonlinear zone consisting of key members, which respond nonlinearly to the external loads. On the other hand, the gray line zone is defi ned as the linear zone in which all members experience linear deformations. For simplicity, it is also assumed in Figure 1 that the boundary joints shared between the nonlinear and linear zones are numbered by 1, 2, 3, 4 and 5.

Figure 1. Illustration of a typical fi nite element model of a structure.

Based on the FE model given in Figure 1, one obtains the following system equation:

KU = P (1)



where K is the stiffness matrix, U and P are the unknown nodal displacement and known nodal force vectors, respectively. For a nonlinear problem, K is dependent on U.

It should be noted that all the boundary conditions are incorporated in Eq. (1). By solving this equation, nodal displacements can be obtained. Generally, a full nonlinear analysis for the structure given in Figure 1 is very time consuming if the size of K is large. However, all the members in the linear zone can be grouped into one super element to simplify the nonlinear analysis. The procedure includes four steps described below:

Step 1) Create a fi ctitious structure by replacing the nonlinear members with “weak” members in the nonlinear zone.

It is defi ned that the weak members (indicated by black dash lines in Figure 2) and the original nonlinear members share the same geometrical properties, but the Young’s modulus of weak members is much lower than that of original members. Meanwhile, the external loads applied at the linear zone have to be ignored in the fi ctitious structure while the original boundary conditions remain the same.

Figure 2. The original members are replaced by fi ctitious weak members.

Step 2) Build up the system equation based on fi ctitious structure.

Eq. (2) is the system equation corresponding to the fi ctitious structure shown in Figure 2. It is similar to Eq. (1). In this equation, the subscript “f” denotes “fi ctitious”. In the nodal force vector, only P1 ~ PN are taken into account.

KfUf = Pf (2)

Step 3) Generate the specifi c load cases to evaluate the stiffness matrix of the super element.

Firstly, solve Eq. (2) to obtain the nodal displacement vector Uf. It is assumed that a typical node A has nonzero deformation along the ith DOF when the fi ctitious structure

is subjected to loads P1 ~ PN. This node is selected to be a node of the super element. Its deformation along the ith DOF is denoted by uj as well. For convenience, the displacement vectors at the joints are denoted by Uf , Uf , Uf , Uf , and Uf . These are all ND x 1 vectors if the DOFs at each joint is ND. In the superscripts, the letters in front of the commas indicate the identities of the nodes, while the numbers behind the commas are for load cases. In this paper, the load case number for Pf (the combination of loads P1 ~ PN) is set to ‘0’.

Secondly, apply a generalized unit load along each degree of freedom at each joint to create fi ctitious load cases, and calculate the corresponding displacement vectors of node A and the joints. In Figure 2, the total number of fi ctitious load cases will be 5ND since there are fi ve joints between the nonlinear and linear zones.

Thirdly, group the entire fi ctitious structure into one super element which consists of node A and node 1, 2, 3, 4 and 5. Denoted by

KS, the stiffness matrix of the super element

satisfi es Eq. (3).

(3)

It should be noted that the ‘1’ on the right hand side of Eq. (3) represents

Pf. The reason that the vector Pf can be

described by a fi ctitious unity is that the nodal loads in Pf are applied to the fi ctitious structure proportionally. For consistency, it is assumed that this fi ctitious load is applied along the direction of uf . Based on Eq. (3), one obtains:

KS = UI-1 (4)

where KS is a (5ND + 1) × (5ND + 1) matrix. Step 4) Assemble the super element and the key

members in the nonlinear zone to create a simplifi ed structure.

As shown in Figure 3, the simplifi ed structure consists of the super element and the key members in the nonlinear zone. The super element contains six nodes, viz. node A and nodes 1~5. In this structure, the real external loads P1 ~ PN are replaced by a fi ctitious unit load acting at node A, while the boundary conditions in the linear zone are ignored since their infl uences have been incorporated into the stiffness matrix of the super element. In the nonlinear zone, both the original boundary conditions and the external loads remain unchanged. The global stiffness matrix of the simplifi ed structure can be assembled easily using the traditional FEM approach.

A,0

1,0

2,0 3,0 4,0 5,0

A,0



NUMERICAL EXAMPLE

Consider a simple two-dimensional frame given in Figure 4. The dimensions of the cross-section of each beam are set to be 0.05×0.05. Without super elements, the entire structure is divided into 32 two-node beam elements to conduct traditional FEM analyses. Besides, to demonstrate the proposed approach, all the elements at the second story are grouped into one super element. The material properties of both super and normal elements are identical. Young’s modulus is set to 1 × 106 and Poisson’s ratio is set to 0.3. The loads applied to the original frame are P1 = P2 = 1.0.

In Figure 4, since the two stories share only two joints at the boundary, i.e. node 6 and 12, the super element consists of three nodes. Without loss of generality, node 25 is selected to be another node of the super element. In total, the super element (the gray triangle) has seven DOFs including four displacements and two rotations at nodes 6 and 12 and one fi ctitious displacement along y – axis at node 25. In the calculation the Young’s modulus of weak elements is set to 1 × 102.

Figure 3. The simplifi ed structure consists of super elements and key members.

obtained by the proposed super element method have very good accuracy if the members within the linear zones are not highly nonlinear. Figure 6 illustrates the shapes of the deformed frame when the load factor is 30. It can be seen that the two kinds of results have very good agreement.

Figure 4. A two-dimensional frame is simplifi ed by using super element.

Figure 5. Comparison between the displacements at node 9.

CONCLUSIONS

This paper proposes a super element method to simplify nonlinear FEM analysis. Using the present method, the DOFs of a large scale structure can be reduced signifi cantly. Through a weak element approach for members in the nonlinear zone, the linear members in linear zones can be grouped into just one single super element regardless whether the linear zones are inter-connected or not. The numerical example shows that this method can be easily implemented and has great potential in the simulation of large complex structures. On the other hand, it must be mentioned that the global stiffness matrix of a structure is generally symmetric in traditional FEM but it is non-symmetric when the super element method is used. However, although non-symmetric system matrix may cause additional requirements for CPU time, the overall calculation is still effi cient since the total DOFs are much fewer than that in traditional FEM. Additionally, some techniques, such as iteration algorithm can be used to minimize the loss induced by non-symmetric matrix.

REFERENCES

[1] Axelsson O and Barker VA, (2001), Finite Element Solution of Boundary Value Problems: Theory and Computation, SIAM 2001.

[2] Birgersson F, Finnveden S and Nilsson SM, (2005), A spectral super element for modelling of plate vibration, Part 1: General Theory, 287 (1-2), 297-314.

[3] Cao ZY, (1992), Super Element Method for Complex Structure Analysis. Mechanics and Practice, 14 (4), 10-14.

[4] Finnveden S, (1994), Exact Spectral Finite Element Analysis of Stationary Vibrations in Rail Way Car Structure. Acta Acustica, 2, 461-482.

[5] Korczak KZ and Patera AT, (1986), An Isoparametric Spectral Element Method for Solution of the Navier-Stokes Equations in Complex Geometry. Journal of Computational Physics, 62, 361-382.

[6] Lukasiewics SA, (1987), Geometrical Super-Elements for Elasto-Plastic Shells with Large Deformation. Finite Elements in Analysis and Design, 3, 199-211.

The comparison between traditional FEM and the super element method is depicted in Figure 5 and 6. In Figure 5, the results show that the vertical displacement at node 9 increases as P1 and P2 become larger. The two curves are very close when the load factor is smaller than 25 but they separate thereafter. This means that the results



WATER SATURATION EFFECTS ON SEDIMENTARY ROCKS

Ma Guowei ([email protected])Wu Wei ([email protected])

ABSTRACT: The study investigated the uniaxial compressive strength of sedimentary rocks, including sandstone and siltstone, in dry and saturated conditions and found that the uniaxial compressive strength of siltstone is more sensitive to water than that of sandstone, but the sedimentary rocks under both conditions can be assigned the same rating based on the use in Rock Mass Rating (RMR).

INTRODUCTION

The hydro-mechanical properties of rock mass are a signifi cant consideration for rock engineering design and construction. Rock mass consists of intact rock blocks and various discontinuities, such as joints, cracks, bedding planes. For low permeability rocks, the discontinuities always provide the major pathways for water while the permeability of the intact rock blocks is generally very low [1]. The strength and deformation of the rocks affected by water are mainly due to the hydro-mechanical properties of discontinuities and these behaviors are more pronounced in fi ne-grained sedimentary rocks. Euguler and Ulusay [2], Gutierrez et al. [3], and Backstrom et al. [4] recognized that the water had a remarkable infl uence on the mechanical properties of rocks. Generally the presence of water reduced the compressive strength and elastic modulus and affected the stress-strain behavior. However, rocks from different origins may display diverse water sensitivity due to their physical properties and chemical compositions.

In the present study, the uniaxial compressive strength and Young’s modulus of the Singapore sedimentary rocks were studied to estimate the water saturation effects on rock strength, deformation, and failure mode. The sound velocity before and after testing were also investigated.

LABORATORY TESTING OF THE SEDIMENTARY ROCKS

Rock Specimen Selection and Sampling

Fifteen saturated rock blocks were collected from a sedimentary rock formation, transported in containers with sea water, and cured at the geotechnical workshop to maintain the saturated state. Twenty saturated cylindrical rock specimens of 50 mm diameter and 100 mm height without obvious micro-fractures on the surface were cored from these rock blocks, which is generally normal to the sedimentary beddings. They were then separated into

four groups – sandstone in dry condition, sandstone in saturated condition, siltstone in dry condition, and siltstone in saturated condition. The four groups were tested and analyzed separately. The average bulk density, dry density, water content, and porosity of the two rock types were measured, as listed in Table 1.

Table 1. Physical parameters of the sedimentary rocks.

Physical parameter Siltstone Sandstone

Bulk density (kg/m3) 2761 2716

Dry density (kg/m3) 2736 2730

Water content (%) 0.39 0.33

Porosity (%) 1.06 0.91

Sound Velocity Test

The sound velocity was measured by using a PUNDIT plus test system. The results indicated that water had a remarkable effect on the sound velocity that transmitted through the height of rock specimens, sandstone, and siltstone, as shown in Figure 1. The sound velocity in saturated specimens was generally higher than that in dry specimens. Since sound velocity has a higher propagating velocity in water than in air, the test results revealed that water had been successfully kept in the specimens during delivery, manufacturing, and testing.

Uniaxial Compression Test

The uniaxial compression test, based on the ISRM suggested method [5], was conducted on the specimens by using a computer-controlled, servo-hydraulic testing machine having a maximum loading capacity of 2.67 MN. The specimen was applied a measured load in axial direction continuously at a constant stress rate of 0.53 MPa/s such that the failure occurred within 5-10 mins of loading. A LVDT was installed near the specimen vertically to record the axial deformation of the specimen.



The test results of uniaxial compressive strength showed that there was a general reduction on the strength of the sedimentary rocks with the water saturation effect, as shown in Figure 2. It can be concluded that the uniaxial compressive strength of siltstone is more sensitive to the water effect than that of the sandstone. From Table 2, the strength of siltstone is reduced by 32% due to the saturation effect, while that of sandstone is reduced only by 6%. Based on the strains at peak stress, saturated siltstone (0.32%) shows a larger deformability than the dry siltstone (0.26%). However, such a water saturation effect on dry sandstone (0.37%) and saturated sandstone (0.38%) is not signifi cant. Sandstone has a larger Young’s modulus than that of siltstone. From the test results, the water effect on the Young’s modulus of both rocks is limited.

I: Dry siltstone; SI: Saturated siltstone; A: Dry sandstone; SA: Saturated sandstone.

The error bars indicate the range (minimum to maximum) of the measured sound velocity.

Figure 1. Test results of sound velocity.

Table 2. Test results of uniaxial compressive strength.

Siltstone

No Stress Strain Young’s (MPa) (%) Modulus (GPa)

I*1 171.09 0.28 65.41

I2 164.83 0.30 57.51

I3 204.67 0.34 64.75

I4 180.23 0.31 60.64

I5 219.25 0.38 58.41

Ave 188.01 0.32 61.34

SI**1 123.02 0.23 59.54

SI2 138.45 0.28 61.13

SI3 128.67 0.28 61.81

SI4 127.01 0.24 56.04

SI5 125.89 0.26 62.29

Ave 128.61 0.26 60.16

Sandstone

No. Stress Strain Young’s (MPa) (%) Modulus (GPa)

A*1 293.17 0.38 79.97

A2 341.90 0.44 80.73

A3 298.90 0.41 73.56

A4 223.34 0.38 71.60

A5 192.31 0.26 75.04

Ave 269.92 0.37 76.18

SA**1 232.02 0.32 76.01

SA2 241.19 0.37 75.31

SA3 298.43 0.43 76.79

SA4 231.67 0.35 75.77

SA5 271.47 0.41 74.83

Ave 254.96 0.38 75.74

*: Dry condition, **: Saturated condition.

DISCUSSION

Figure 3(a) shows that siltstone displays shear failure along fractures under static loading. The properties of fractures, which are sensitive to water, signifi cantly affect the strength of siltstone, resulting in its higher water sensitivity. However, sandstone has a higher deformability under the increasing loading than siltstone (Figure 3 (b)). At failure, the specimen always explodes into pieces and is insensitive to fractures. Therefore, sandstone appears to be more independent of the presence of water. It is worth noting that the core of saturated siltstone is generally dry after failure. The water mainly appears around the factures and the edges of the specimen due to coring and manufacture. It is thus apparent that the reduction of the specimen strength is attributed mainly to the water effect on the fractures in the rock specimens.

I : Dry siltstone; SI: Saturated siltstone; A: Dry sandstone; SA: Saturated sandstone.

The error bars indicate the range (minimum to maximum) of the measured uniaxial compressive strength.

Figure 2. Test results of uniaxial compressive strength.



According to the popular design codes for underground projects, Q-system and Rock Mass Rating (RMR), the test results of water saturation effect on the sedimentary rocks can be incorporated to the RMR system, which considers the uniaxial compressive strength of intact rock material. The Q-system also uses the uniaxial compressive strength but indirectly with the principal stress and tensile stress. Due to the lack of these parameters, the method will not be discussed here. The test results show that the average uniaxial compressive strength of sandstone determined in the present study in dry and saturated condition are 269.92 MPa and 254.96 MPa, respectively, both of which are larger than 250 MPa. The tested sandstone in the both conditions can therefore be assigned the same rating of “exceptionally strong”. Similarly, the average uniaxial compressive strength of siltstone in dry and saturated condition are 188.01 MPa and 128.61 MPa, respectively, both of which are in the range of 100-250 MPa. Siltstone in both dry and saturated conditions can be assigned the same rating of “very strong”, according to the RMR system. Therefore, from the test results, the sedimentary rocks under dry and saturated conditions can be assigned the same rating.

CONCLUSIONS

The uniaxial compression test on the sedimentary rocks has been conducted by using the computer-controlled, servo-hydraulic testing machine. From the test data and analysis, the following points can be concluded.

1) The higher sound velocity in saturated specimens than in dry conditions indicated that water was successfully kept in the specimens during delivery, manufacture and testing.

(a) siltstone; (b) sandstone.

Figure 3. Rock specimens after testing.

2) The uniaxial compressive strength of siltstone is more sensitive to water than that of sandstone. The strength of siltstone was reduced by 32% with the effect of saturation, while that of sandstone was reduced by 6%. Siltstone mainly displays shear failure along fractures which are sensitive to the presence of water, while sandstone appears to become denser with the increasing loading and shows a higher deformability than siltstone.

3) With reference to the uniaxial compressive strength of intact rock material for the use in Rock Mass Rating (RMR), the sedimentary rocks under dry and saturated conditions, including sandstone and siltstone, can be assigned the same rating based on the present experimental results.

4) The results of the present study were based on the current testing situation and geological condition. In addition, other parameters, such as triaxial compressive strength and shear strength, shall also be studied to fi nd a more reasonable conclusion on the water saturation effect.

REFERENCES

[1] Min, K.B., Jing, L.R. and Stephansson, O., 2004. “Determining the Equivalent Permeability Tensor for Fractured Rock Masses Using a Stochastic REV Approach: Method and Application to the Field Data from Sellafi eld, UK”. Hydrogeology Journal, 12, pp. 497-510.

[2] Euguler, Z.A. and Ulusay, R., 2009. “Water-induced Variations in Mechanical Properties of Clay-bearing Rocks”. International Journal of Rock Mechanics and Mining Sciences, 46, 2, pp. 355-370.

[3] Gutierrez, M., Oino, L.E. and Hoeg, K., 2000. “The Effect of Fluid Content on the Mechanical Behaviour of Fractures in Chalk”. Rock Mechanics and Rock Engineering, 33, 2, pp. 93-117.

[4] Backstrom, A., Antikainen, J., Backers, T., Feng, X.T., Jing, L.R., Kobayashi, A., Koyama, T., Pan, P.Z., Rinne, M., Shen, B.T. and Hudson, J.A., 2008. “Numerical Modelling of Uniaxial Compressive Failure of Granite with and without Saline Porewater”. International Journal of Rock Mechanics and Mining Sciences, 45, 7, pp. 1126-1142.

[5] R. Ulusay and J. A. Hudson, 2007. “The Complete ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 1974 – 2006.” pp. 151-156.


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.

PROJECT TITLE PRINCIPAL INVESTIGATOR

External Projects

Membrane distillation: module design optimisation through modelling and Anthony Gordon Fane evaluation [email protected]

Integrated multiple-hazards research programme for resilient structures Tan Kang Hai [email protected]

Effects of catenary and membrane actions on the collapse mechanisms of RC Tan Kang Haibuildings – behaviors of structural elements [email protected]

Rapid repair of airfi eld pavement sub-base using lightweight geofoam Goh Teck Chee, Anthony [email protected]

Aquaporin Based Biomimetric Membranes For Water Reuse and Desalination Anthony Gordon Fane [email protected]

Sichuan earthquake - New School New Hope Li Bing [email protected]

Sichuan earthquake - A drop of Hope Li Bing [email protected]

The infl uence of fl oor slabs and transverse beams on the behavior of RC Li Bing beam-column joints under loss of column scenarios [email protected]

Biofouling in reverse osmosis in water reclamation & desalination Anthony Gordon Fane [email protected]

Sediment plume in waves Phase 2 (SMART subward agreement No. 20) Law Wing-Keung, Adrian [email protected]

Energy effi ciency and indoor air-conditioned buildings Chang Wei-Chung [email protected]

Study on the effect of UV on microbial critical fl ux and biofi lm formation Anthony Gordon Faneon reverse osmosis membranes [email protected]

Design, construction and testing of bioirontech reactor for recalcitrant organics Volodymyr Ivanov removal Phase 1A - process development of bioirontech for degradation of [email protected] organics

Water and energy in the urban water cycle - improving energy effi ciency in Ng Wun Jern municipal wastewater treatment [email protected]

Biocement - a new sustainable and energy saving material for construction Chu Jian and waste treatment [email protected]

Explore concept of membrane action in slabs to reduce fi re protection for beams Tan Kang Hai [email protected]


RESEARCH PROJECTS

Characterization and modeling of storm runoff from a tropical catchment with Chua Hock Chye Lloyddiverse landuse [email protected]

Development and assembling of high effi ciency dye sensitized solar cells and Sun Delai, Darrenwater cleavage - hydrogen production reactor using novel nano Structured TiO2 [email protected] fi ber/tube/membrane

Remote Stress Monitoring System (RSMS) for Safe Storage of CNG Tank Lie Seng Tjhen Cylinders under High Pressure [email protected]

Internal Projects

Plane wave absorbers for wave power generation Law Wing-Keung, Adrian [email protected]

Integrated simulation and optimization approaches for supporting environmental Qin Xiaosheng and water resources management [email protected]

Contemporary research issues in Maritime Business and Management Thai Van Vinh [email protected]

Development of novel hollow fi ber membranes for water treatment Wang Rong [email protected]

Differentiating natural rock discontinuities from drilling breaks for Wong Ngai Yuen underground engineering design purpose [email protected]

PROJECT TITLE PRINCIPAL INVESTIGATOR


RESEARCH PROJECTS

COMPLETED PROJECTS

Molecular Basis of Formation of Active but Non-Culturable Environmental Bacterial PathogensPrincipal Investigator: Gin Yew-Hoong, KarinaReport No.: CEE/2009/188

A comprehensive and rapid assessment of the microbial quality of water is critical owing to the escalating threat posed by current and emerging pathogens and bio-terrorism. Most of the bacterial human pathogens and their indicators have been demonstrated to exist as active/viable but non-culturable forms (ABNC/VBNC) in food and water. This poses a challenge in the environmental monitoring of these pathogens using traditional culturing and/or molecular techniques. While there has been enormous interest in the formation of ABNC/VBNC in a wide variety of human bacterial pathogens, the transient gene expression of key functional genes, which effectively differentiates ABNC towards dormancy from the normal cells in response to the environmental stress, continues to remain unexplored, partly due to our inability to make pure ABNC preparations. As a continuation of our earlier work on the differential measurement of ABNC, cell separation of ABNC will be undertaken using fl uorescence activated cell sorting (FACS), followed by the microarray-based assessment of key functional genes, with the view to gain insight into the molecular basis of formation of ABNC. Some of the prominently expressed genes will be used as marker(s) for differential species specific monitoring using in situ molecular methods of ABNC forms (E. coli and/or Klebsiella sp.). Data can be extrapolated for the detection of other gram negative bacterial pathogens in ABNC forms.

Arsenic Treatment Project (Dan Phuong District, Ha Tay Province, Vietnam)Principal Investigator: Li BingReport No.: CEE/2009/189

The objective of this development project is to establish a model for household level arsenic treatment which will be easily replicated in areas where arsenic level is very high.

The site (Phuong Tien Village) chosen for implementation had arsenic level in tube-well water that is much higher than the Vietnam Ministry of Health Standard of 0.01 mg/l for drinking water.

An Innovative 2D Imaging Flow Cytometer for Waterborne Microbial DetectionPrincipal Investigator: Gin Yew-Hoong KarinaReport No.: CEE/2009/190

One of the challenges faced today in microbial risk assessment is the speed and accuracy of detection for pathogens or their indicators. In this proposal, we present a novel optical technique for the detection and enumeration of Cryptosporidia. The principle is similar to fl ow cytometry, but instead of interrogating particles one at a time, single fi le, through a laser beam, the new technique uses a plane of particles in two dimensions traversing a laser sheet and subsequently analyzing (what?) by a CCD camera. By expanding the analysis to a fi eld of particles instead of one particle at a time, the speed and effi ciency of analysis can be shortened considerably. In addition, capturing a 2D image of a plane of particles enhances the confi dence level of analysis and results in better resolution/identifi cation of target cells. Sample preparation or preconcentration of cells prior to analysis will be facilitated by continuous centrifugation. In this process, an in-house design, which makes use of centrifugal elutriation to improve the separation process (and hence, analysis time) of commercial centrifuges, will be optimised.

Identifi cation of target cells can be carried out by antibodies specifi c for Cryptosporidium. However, antibody-based probes are currently not able to distinguish between live and dead cells and hence, fl uorogenic staining techniques will also be used to determine oocyst viability via cell wall integrity. These are relatively established techniques, albeit time consuming. Literature has also shown that Cryptosporidia are auto-fl uorescent with UV excitation. We also plan to explore this further by conducting fundamental studies to determine if specifi c fl uorescence signatures (including lifetime) can be used to uniquely identify Cryptosporidium and perhaps, also their viability. If this can be done, the process of antibody and viability staining can be removed, thus saving even more time in the analysis. Ultimately, shortening the analysis time to about an hour or less will lead to a quicker response by authorities, thereby protecting public health.


RESEARCH PROJECTS

Fouling of Reverse Osmosis and Nanofi ltration Membranes by Biological Macromolecules - Probing the Foulant-Membrane and Foulant-foulant InteractionsPrincipal Investigator: Tang ChuyangReport No.: CEE/2009/191

Membrane processes are of increasing importance in water and wastewater treatment applications, especially where the product water is intended for potable use.

However, unresolved fouling problems limit the cost effectiveness in both reverse osmosis (RO) and nanofi ltration (NF) membrane applications. Fouling is a complex phenomenon, which can be caused by a great variety of compounds (microorganisms, organic macromolecules, colloids, etc.) as well as specifi c water quality conditions (e.g. high hardness). Progress in the development of new and improved reverse osmosis (RO) and nanofi ltration (NF) membranes depends on our detailed understanding of the complex physical, chemical and biological processes that occur at the surface of and within the membrane. The proposed project aims to elucidate membrane fouling through closely coordinated laboratory tests and model development. Proteins and alginate will be used as model foulants due to their important roles in membrane fouling.


RESEARCH PROJECTS

PhD THESES

Overall Benefi t-Duration Optimization and its Genetic Algorithm Application in Construction Project SchedulingCandidate: Pan HengReport No: CEE/PhD/2009/195

In this research, an Overall Benefi t-Duration Optimization (OBDO) concept that represents an innovative scheduling optimization scheme and maximizes overall benefi t is proposed. An integrated model for OBDO is developed applying genetic algorithm (GA) and named as GAOBDO. GAOBDO model maximizes overall benefi t and prone to profi tability of owner. In order to facilitate practitioners’ practical usage, GAOBDO model is recorded as a VBA (Visual Basic for Application) macro program in Microsoft Project 2003 for computer implementation to maximize its benefi ts. After experimenting on various cases, it demonstrates feasibility of OBDO concept and practicability of GAOBDO model. Sensitivity analysis and cross sensitivity analysis are also conducted to explore contributive effects of GA application to global optimum solutions to OBDO. Integration of GAOBDO model with Microsoft Project 2003 brings direct benefi ts to optimization process and to applications of end users in project scheduling domain. Conclusion of this research study and suggestions for future research development are also outlined.

Use of Seismic Waves for the Characterization of Soil PropertiesCandidate: Mohammad Harunur Rashid MeerReport No: CEE/PhD/2009/196

Seismic waves can be employed in the fi eld and in the laboratory for characterizing soil. Seismic waves propagating through soils induce very low level of strains. Using the framework of linear elasticity, the wave propagation velocity can be linked to the elastic parameters of the soil.

This study investigates soil properties using elastic waves in the fi eld as well as in the laboratory. Continuous Surface Wave (CSW) and microtremor surveys were conducted at seven sites in Singapore. Borehole logs were available for all the sites. Pulse transmission tests using ultrasonic velocity test system were conducted in the laboratory. The Spatial Auto-Correlation (SPAC) method was used to analyze the data from microtremor survey to compute the dispersion curve. The dispersion curves obtained from the CSW and microtremor surveys for the same site were not coincidental but the discrepancy did not have any signifi cant effect on the shear wave velocity profi le. To obtain the shear wave velocity profi le from the dispersion curve, wavelength-

depth factor and linear inversion methods were used. The depth of investigation obtained from microtremor surveys was limited by array size. Because of site constraint, the array size of the microtremor is limited to 10 m with the maximum depth of investigation limited to 16 m. A modifi ed wavelength-depth method was developed in this research and the method was verifi ed using data from published literature. The modifi ed wavelength-depth method was found to provide a better estimate of the shear wave velocity profi le which can be used as the initial model for more accurate inversion schemes.

Ultrasonic velocity tests were conducted on compacted unsaturated soil samples to investigate the effect of degree of saturation and confi ning pressure on compression wave and shear wave velocities. It was found that degree of saturation did not have signifi cant effect on shear wave velocity but compression wave velocity was found to be dependent on degree of saturation. A relationship between compression wave velocity with shear wave velocity and degree of saturation was developed. The relationship could be used to estimate compression wave velocity of an unsaturated soil/rock/concrete within ±20% error.

Ultrasonic velocity tests and triaxial compression tests were conducted on undisturbed soil samples to measure the small-strain stiffness and stiffness with strain relationship of soil. The compression wave velocity and shear wave velocity were measured by ultrasonic velocity test. The measured shear wave velocity by ultrasonic velocity test was compared with the shear wave velocity obtained from CSW and microtremor survey methods. The comparison showed good agreement with a discrepancy of ±30%. The small-strain stiffness of soil was measured by triaxial compression test using local strain measurement transducers. The effects of void ratio, confi ning pressure and plasticity index on the stiffness-strain relationship of soil were investigated. It was found that increase in void ratio reduces the stiffness of soil, however, increase in confi ning pressure and plasticity index increase the shear stiffness of soil. It was also found that the effects of void ratio and confi ning pressure are more signifi cant than the effect of plasticity index on stiffness-strain relationship of soil. Some empirical relationships were used in this study to compare with the shear wave velocities obtained by CSW survey method. It was found that the discrepancy between shear wave velocities from empirical relationships and CSW survey method is from ±17% to ±40%.


RESEARCH PROJECTS

Studies of Drivers’ Responses to ATIS Information in Incidents: System and ApplicationsCandidate: Jin MingReport No: CEE/PhD/2009/197

ATIS is the one of the important sub-systems of ITS designed to provide real time traffi c information to drivers. The benefi t of ATIS is extraordinary, especially in contexts of incidents. With ATIS information, drivers could avoid or be diverted from the congested road or lane so a high level of effi ciency and safety could be maintained. However, the effectiveness of ATIS information is critically dependent on how drivers would understand and response.

The Kallang/Paya Lebar Expressway (KPE) in Singapore is a predominantly underground expressway in construction at the time this study was carried out. Since a great portion of sections of the KPE are underground tunnels, it creates unique challenges for the prevention of congestion, accident and fi re. As measures to achieve above challenges, comprehensive message broadcasting schemes were to be introduced to broadcast traffi c information via ATIS to provide advisory and warning information in cases of congestion, accidents, and emergency evacuation. It is expected that with the implementation of this equipment and the schemes, a high level of effi ciency and safety of KPE can be maintained. However, the knowledge on how drivers would response to those schemes still remained insuffi cient. Such knowledge is essential, not only to fi ne-tune the schemes in KPE, but also for design and operation of similar ATIS system in general.

The challenge remains on the methodology to collect suffi ciently detailed data to understand drivers’ responses to those schemes, which motivate the development of a traffi c-driving simulator, integrating a driving simulator with a traffic simulator, which allows simulation of complicated scenarios in which the traffi c information was broadcasted on different information devices according to the traffi c schemes. As applications of the simulator, driving behaviour surveys were carried out to study a number of issues relating to the tunnel expressway and the new information systems and schemes to be used. The subjects’ driving behaviour with the presence of traffi c information was captured in great detail in a non-obtrusive manner through careful designs of the experiments. A number of scenarios were simulated to study the traffi c schemes in contexts of accident, congestion and fi re emergency evacuation. Statistical tests and discrete choice models are used to analyse the empirical study results. A paper-based perception survey was also carried out to study drivers’ understanding and to existing VMS messages.

The applications of the traffi c-driving simulator in this study have proven that the simulator can provide a critical observation basis for studies of driving behaviour with presence of ATIS in incidents contexts. Firstly, the traffi c-driving simulator can be used to study drivers’ behaviour

in extreme conditions which may never be investigated at fi eld. Secondly, the simulator can allow collection of data at various levels of attributes in high degree of realism with driving experience similar to real situation. Thirdly, the simulator can allow optimal experiment control and data collection at different levels. With all the effects, the data collected contains rich information to support statistical analyses and development of behavioural models. The empirical results have shown that there are reasonable correlations between drivers driving behaviour and the attributes of scenarios, such as ATIS information provided and traffi c conditions.

In the study of driving behaviour with presence of ATIS information in a road accident resulting in lane closure, the results reveal that the ATIS scheme is effective not only in inducing an early merging of traffi c, but also in reducing the hazardous lane changing. However, despite the fact that ATIS is effective to prevent lane changing near the bottleneck and as a result drivers would be able to perform a smoother and safer lane changing manoeuvre, it should be noted that there were still considerable proportion of drivers didn’t comply with the instruction given through the ATIS. The analysis on vehicular speed suggests that ATIS may result in slightly slower average traffi c speed in the alert zone, where LCS were displaying fl ashing amber cross symbols or red cross symbols.

In the studies of fi re emergency evacuation, the results indicate that visual messages by themselves may not be suffi cient to provide compelling information to let drivers to realise the imminent threat of the fi re incident and comply with the suggested evacuation instructions. When audio messages were also broadcasted together with the visual information provided by signage, high compliances to the combined information were observed. However, there are also some evidences to indicate that when the audio information was not consistent with the site-specifi c visual cue, drivers may not follow the audio instructions until some relevant visual information were seen to confi rm the instructions. These results suggest that even with radio announcement, drivers may still need the site-specifi c information on the signage as guidance.

Drivers’ route switching behaviour with the presence of ATIS information in road congestion was also studied, the results reveal that factors such as VMS messages describing extent of congestion and the cause of the congestion, speeds at decision points, attributes on alternative routes, e.g. familiarity, travel time and distance, and the location of drivers at starting points and when they saw the VMS messages, are contributing to their route decisions. The above results are consistent with past study results, which further prove that the traffi c-driving simulator is able to capture drivers’ route switching behaviour.

Although the signifi cant results were obtain in applications of the traffi c-driving simulator in study, limitations of the traffic-driving simulator in these applications are


RESEARCH PROJECTS

also identifi ed. Firstly, the simulation sickness is the side effects that can’t be totalled removed. Therefore, further research efforts are required to minimize the simulation sickness. Secondly, validity of the traffi c-driving simulator is another limitation which requires fi eld validations in future works.

An Intelligent Simulation System for Studying Impacts of Multimodal Traveller Information in an Urban Transportation NetworkCandidate: Abdul Ahad MemonReport No: CEE/PhD/2009/198

Travel mode choice behaviour is inherently infl uenced by travellers’ knowledge about travel conditions. Timely provisions of traveller information via Intelligent Transportation Systems (ITS) can contribute in improving transport network efficiency. The advents of ITS are bringing improvements to public transport. However, despite rapid advancements much remains to be known about ITS applications, which motivates the present research to develop an Intelligent Network Simulation Model (INSIM), and to apply the system to study the impacts of providing Integrated Multimodal Traveller Information (IMTI). The functionality of INSIM was demonstrated through a set of simulated experiments under congested travel conditions. Several IMTI schemes were applied via INSIM to study how regular car users may be infl uenced to switch to public transport. The research findings contribute to advancements on several substantive issues that have not been systematically investigated to date. The limitations in modelling and simulation techniques are also highlighted which provide scope for future extension.

Precast Shear Wall with Horizontal ConnectionCandidate: Han HongshengReport No: CEE/PhD/2009/199

In order to investigate performance of precast walls with horizontal connection, six shear walls, two monolithic walls acting as prototypes and four precast shear walls serving as counterparts, have been designed, manufactured and tested. Two kinds of steel sections, channels and I-Beams have been used in these walls serving as fl exural reinforcement. The infl uence of number of shear connectors in the horizontal connection on the behavior has also been studied.

All specimens have been tested under reversed cyclic load to failure. Similar ultimate strength, drift ratio were observed between these monolithic walls and their precast counterparts in the experiment.

Based on cracking patterns and records of strain gauges placed horizontal and vertical reinforcement, strut-and-tie models of each specimen during different loading stages have been developed.

A nonlinear fi nite element program, DIANA 8.0, has been used to study the behavior of specimens under cyclic loads. Two dimensional and three dimensional models have been built to simulate behavior of these specimens. However, the ultimate strength of wall with I-beams is underestimated 15% by two dimensional model. The yield strength, ultimate and ductility were predicted with a high agreement by three dimensional models for all walls.

Advection and Dispersion of Pollutants under Regular and Random WavesCandidate: Huang GuoxingReport No: CEE/PhD/2009/200

The objective of this project is to investigate, analytically and experimentally, the advection and dispersion processes of pollutants in the ocean due to surface waves. The wave-induced drift of small fl oating objects is studied as well.

In the fi rst part of this study, the drift velocity under random waves is investigated analytically. Some observations and measurements of the drift velocity of an oil patch (modelled as a fl oating polyethylene sheet) are presented under both deep and shallow water wave conditions.

In the second part, whether surface fl oating substances would disperse in a random wave fi eld due to Stokes drift is investigated. The present investigation shows that the drift velocity in random waves is actually a time-independent and would not lead to a surface dispersion on fl oating substances. Experimental results are presented to support the theoretical analysis. In addition, following a similar approach as Law (2000), the Taylor dispersion of pollutants under random wave condition is studied.

In the last part, we investigate the drift velocity of a small rigid fl oating object driven by regular waves in deep water. Experimental observations were fi rst presented on the drift behavior of square, circular and elliptical objects by means of an infrared motion monitory system. These objects possessed different drag and added mass coeffi cients, and the measurements on the drift velocity of these objects clarifi ed some outstanding issues. The theoretical drift of a small thin fl at plate was then derived.

Reliability Assessment of Damaged Ductile RC Frame Structures against Progressive Collapse in Close-in Detonation ConditionsCandidate: Huang ZhiweiReport No: CEE/PhD/2009/201

The most devastating effect of a close-in blast event on structures is the progressive collapse of the building after the failure of a primary structural member. In order to prevent the structural failure in this manner, the alternative load path method is generally considered as the most practical and effi cient approach for structural design and assessment


RESEARCH PROJECTS

and has been widely adopted by current building codes and research activities. However, the implementations of this method are generally in a deterministic manner where all related parameters are assumed to be well-defi ned and deterministic. In reality, the random variations of the quantities including the applied loads, strength and stiffness of all construction materials and structural geometries are inevitable and have a signifi cant infl uence on structural safety. Considering this fact, structural reliability assessment based on the probability theory should be the most sensible way for evaluating structural safety. Current available assessment methods need huge amount of computational work and thus are limited in the structural design and assessment practices.

This thesis developed a practical approach for the reliability assessment of damaged ductile reinforced concreter (RC) frame structural systems against progressive collapse in close-in detonations. Based on the developed approach, parametric studies were carried out to investigate the effects of different parameters on the reliability of damaged structures and to study the most effi cient method to improve the structural safety in close- in detonation conditions.

Kinetic and Metabolic Behaviors of Aerobic Granules Developed in Sequencing Batching ReactorCandidate: Li YongReport No: CEE/PhD/2009/202

This research is focused on the kinetic and metabolic behaviors of aerobic granules by both modeling and experimental approaches. A one-dimensional model was developed and successfully applied to aerobic granular sludge SBR. The diffusion profi les of organic substrate and dissolved oxygen in aerobic granules were simulated using the proposed model system under varies conditions. The model system developed was further extended to study of the calcium accumulation mechanism in acetate-fed aerobic granules. It was demonstrated from both experimental and stoichiometric approaches that the accumulation of calcium ions was closely related to the size-dependent diffusion limitation of oxygen inside aerobic granules. To further look into metabolic and kinetic behaviors of aerobic granules, a series of respirometric experiments were conducted using aerobic granules with different sizes. Stoichiometric analyses further revealed that aerobic granules with different sizes exhibited the similar response pattern in each metabolic phase, i.e. the metabolism of aerobic granules would be unlikely dependent on their sizes. For instance, the conversion yields of external DOC to storage material by different-size aerobic granules were found to be comparable. Finally, it is verifi ed that SRT would not be essential for successful aerobic granulation.

Molecular and Monte-Carlo Simulation of Thermal Transport in AFM-Based Data StorageCandidate: Liu XiangjunReport No: CEE/PhD/2009/203

This research work focuses on analyses of heat transfer in the thermal-assisted AFM-based data storage system by using non-equilibrium molecular dynamics (NEMD) and direct simulation Monte Carlo (DSMC) methods. A new design and simulation platform has been developed to build up an effective model so as to evaluate various possible spatial, temporal and temperature confi gurations at nanometer spaced thermal-assisted AFM-based data storage system. The thermal characteristics of Si nano-wires and AFM nano-tips were investigated using the NEMD method based on Tersoff potential and Fourier’s theorem. The results show that the length of nanostructures has remarkable effects on their thermal conductivities. Furthermore, the heat transfer through rarefi ed gases in micro-/nano-gaps was studied using the DSMC method based on the Variable -Hard-Sphere model and Larsen-Borgnakke model. The effects of Knudsen number and wall temperature on heat transfer were investigated. Finally, the radiation and heat conductions between a heated AFM nano-tip and storage media were analyzed. The results provide useful guidelines for rational design and optimization of the data storage system.

Effects of Microbial Community, Lipids and Pretreatment on the Performance of Two-Phase Anaerobic DigestionCandidate: Liu XueyanReport No: CEE/PhD/2009/204

Compared to conventional anaerobic digestion (AD), two-phase AD strategy, in which acidogenesis and methanogenesis reactions can be optimized separately, offers a robust and fl exible means to better control the process of decomposing organic solid waste to renewable energy at an upgraded level. In recent years, a modifi ed two-phase AD system, known as the hybrid anaerobic solid-liquid (HASL) system, was successfully developed by the Nanyang Technological University (NTU). The HASL system is characterized by recirculating alkaline methanogenesis phase broth to buffer the quick food waste acidity that is often encountered in the acidogenesis phase, so as to realize a self-relief of pH inhibition with no need for external chemical addition. Albeit the HASL system has demonstrated excellent capacity in overcoming the inherent pH issue in conventional food waste AD, information about its potential in mineralizing the recalcitrant food waste components is very limited. Technically, food waste is a mixture of organic substances with various biodegradabilities. The recalcitrant fraction tends to pass through the AD system without suffi cient degradation. Some hydrolyzed products from food waste


RESEARCH PROJECTS

may even be toxic to AD responsible microbial organism. Meanwhile, the effi ciency of the hydrolysis, the rate-limiting step in AD, also determines the ultimate methane yield in the overall process. Thus, enhancement of hydrolysis is critical to improve the overall performance. For these regards, this thesis is focused on the infl uence of the food waste recalcitrant fraction on the performance of the HASL and the enhancement of hydrolysis by thermal and freeze/thaw pretreatments, with molecular biotechnology as an insightful tool.

In the fi rst part of the study, the HASL was started up by enriching slow growing methanogens in the form of anaerobic granules in the methanogenic reactor. The successful startup in this step will ensure methanogenesis reaction will not be a rate limiting step in subsequent food waste AD studies. Fluorescence in situ hybridization (FISH) technique was employed in conjunction with a confocal laser scanning microscopes (CLSM) to visualize the methanogens community in anaerobic granules. The amount of methanogens was also quantifi ed by an innovative molecular tool termed as specifi c binding of Arc915 probe, i.e. specifi c binding of Arc915 probe was in linear function with the concentration of menthanogens population in anaerobic sludge when it was between 1.4 and 14.0 mg mL-1. The accuracy of this new method was within 5 to 12%, which was a typical accuracy for the parameter measurements of microbial growth and activity and thus provided a better means for subsequent microbial studies in the two-phase AD.

In the second part of the study, the effect of lipids, the major recalcitrant food waste component, on the HASL system performance was investigated by digesting food waste with different percentages of lipids. It was shown that the lipid content has a two-faced effect on the HASL system. According to present studies, the positive effect of lipids dominated AD, with a greater than 88% COD removal and an 18% increase of methanogens growth rate when its contents were controlled within the range of 20-30%. Lipids content higher than 40% would be unfavorable for two-phase AD due to the toxicity of the long chain fatty acids produced by hydrolysis of lipids, which is refl ected by lower COD removal and slower methanogens growth rate.

The potential role of food waste pretreatment in the HASL performance enhancement was studied by the thermal and freeze/thaw methods in the third and fourth parts respectively. The optimal temperature and duration in both pretreatments for a defi ned food waste was determined in a series of batch experiments and verifi ed in the subsequent HASL performance study. It was found that both thermal and freeze/thaw pretreatments enhanced the performance of the HASL system in terms of higher and faster SCOD, VFA and methane production, which reduced the time needed to produce the same quantity of methane, up to 25%-48% with thermal pretreatment and around 42% with freeze/thaw pretreatment.

The positive effect of thermal pretreatment on the HASL system can also be ascribed to the superior microbial community being successfully cultivated separately in the two-phase reactors. Polymerase chain reaction and the denaturing gradient gel electrophoresis (PCR- DGGE) technique showed that the number and types of dominant species in the acidifi cation phase changed dramatically with the extent of thermal pretreatment, answering the reason why better hydrolysis and acidifi cation results were obtained with pretreated food waste.

Finally, the stability, toxicity and fertility of the HASL residue were testifi ed through a series of tests. Results showed that the residue had positive effects on cucumber growth. It had shown fertility and non-toxicity from 1% to 3% extract concentration, and seed germination was improved signifi cantly at 0.5 - 1 g L-1 extract concentration. However, the residue from the HASL system was still unstable because of a relatively high C/N ratio and consequently could not be applied directly as fertilizer without any further treatment.

Keywords: anaerobic digestion (AD), F420, FISH, food waste, freeze/thaw, hybrid anaerobic solid-liquid (HASL) system, lipids, methanogens, PCR-DGGE, thermal pretreatment

Model and Mesh Generation of Partially Overlapped Circular Hollow Section K-joints for Fatigue StudiesCandidate: Nguyen Thi Bich NgocReport No: CEE/PhD/2009/205

In this study, a novel and consistent geometrical model and mesh generation technique is proposed for partially overlapped circular hollow section (CHS) K-joints with and without crack. Welding parameters are verifi ed and adjusted by the measurement of welding thickness on small and full scale specimens. For the mesh with crack, a general model for the inclined crack surface and an unsymmetrical crack front are proposed. Based on the developed geometrical model, a new mesh modelling method is proposed for partially overlapped CHS K-joints. The mesh generator is constructed such that at each step, a particular mesh can be exported depending on the complexity of the particular fatigue problem under consideration. The application range of the mesh generator is extended for special cases of identical chord and braces dimensions as well as large overlapped percentage. Most importantly, it is able to generate a solid mesh with welding details and surface crack of any length and locates at either sides of the joint intersection. In the experimental program, two full-scale partially overlapped CHS K-joints were tested under cyclic combined loads. The weld profi le, shape and surface of the crack of the two full-scale specimens were measured. It is noted that the fatigue test with a certain combination of loading was able to cause the crack to occur along the brace side of the weld.


RESEARCH PROJECTS

The mesh generator is used to generate fi nite element (FE) models with exact geometry of the two tested partially overlapped CHS K-joints. The numerical stress concentration factor (SCF) and stress intensity factor (SIF) values obtained from these models compare well with the respective results obtained from the two tested specimens. In addition, several FE models for the assessment of SCF and SIF values are presented for comparison and consideration. Furthermore, residual life prediction procedure and a safety factor for partially overlapped CHS K-joints are proposed.

Seismic Performance of Reinforced Concrete Structural Squat Walls with Limited Transverse ReinforcementCandidate: Xiang WeizhengReport No: CEE/PhD/2009/206

An experimental program has been carried out to explore the local and global responses of a total of eight squat RC structural walls with limited transverse reinforcement. The global and local behavior of these RC walls from the experiments carried out is described in detail. Reasonable strut-and-tie models for RC structural walls with and without axial loads are then developed to aid in better understanding the force transfer mechanism and contribution of reinforcement in RC walls based on the experiments carried out. Next, an analytical approach, combining the inelastic fl exure and shear components of deformation, is proposed to properly evaluate the initial stiffness of tested RC walls. A simple expression is proposed to determine the initial stiffness of squat RC walls. Finally, a nonlinear fi nite element analytical procedure for squat RC structural walls under cyclic loadings is used to report the infl uence of several paramount parameters such as axial loads, longitudinal reinforcements in the wall boundary elements, aspect ratio, area of boundary columns and the presence of construction joints at the wall base on the global behavior of squat RC walls.

Static and Cyclic Behavior of Steel Beams Retrofi tted with Fiber Reinforced Polymer LaminatesCandidate: Yu YiReport No: CEE/PhD/2009/207

The rapid deterioration of aging steel infrastructures requires some signifi cant attention in developing new techniques for effective and economical revival of these structures. External bonding of fi ber reinforced polymer (FRP) laminates is a promising method for strengthening such structures. This thesis presents a study on performance of FRP-steel joints and steel beams retrofi tted with FRP under static and cyclic loading.

Experiments on different types of FRP-steel adhesive joints were performed to have a fundamental understanding of the bond property and the adhesive failure behavior. Based on the experimental results, fi nite element (FE) analyses were conducted to explore in detail the stress and strain distribution along the bondline. Flexural behavior of steel beams strengthened or repaired with bonded FRP laminates under static loading was experimentally investigated. A simple analytical solution was developed for the fl exural capacity of FRP strengthened steel beams. A bond failure model was proposed to predict bond failure load under static loading. The bond failure model can be incorporated into numerical modelling to simulate the static behavior of FRP strengthened steel beams with bond failure process. Parametric study was performed subsequently and the relationships between bond strength and different strengthening parameters were found out. Bond performance under cyclic loading of FRP-steel joints and FRP strengthened steel beams as well as fatigue strengthening effect of FRP laminates on damaged steel beams were explored in three series of experiments respectively. Failure modes, stress distribution and relationship between the load level and number of cycles to failure were observed and analyzed.

Improving Learning Effectiveness for International Construction Joint VenturesCandidate: Zhang LitingReport No: CEE/PhD/2009/208

This research conducts learning in international construction joint ventures (ICJVs). It aims to develop a learning model to identify the determinants of learning and assess their impact on learning effectiveness, then to improve learning effectiveness in ICJVs.

A theoretical framework is developed to investigate the relationship among four constructs of the model, namely, learning conditions at the JV’s pre-inception stage, JV’s characteristics at the JV’s formation and organizing stage, learning actions at the JV’ implementation and adjustment stage and the learning effectiveness at the JV’s completion and evaluation stage. Through case study, quantitative study and statistical analysis, it is found that there are positive relationships among the four constructs. It also identifi ed a partner’s development feasibility, learning capability, learning intent, a JV’s operational characteristics, interactions and relationships, cognitive learning actions and behavioral learning actions as seven critical learning determinants. These fi ndings strengthen the use of the research model for construction companies to improve learning effectiveness and performance when they participate in ICJVs.


RESEARCH PROJECTS

Critical and Sustainable Fluxes of Mixed and Flocculated Feeds during Membrane FiltrationCandidate: Zhang YanpengReport No: CEE/PhD/2009/209

The disadvantage of microfi ltration is that the fi ltration fl ux declines with time due to a cake layer of deposit formed or the blockage in the membrane pores. This thesis presents the study of particle deposition on the membrane surface during separating mixed and fl occulated feeds using the Direct Observation Through the Membrane (DOTM) technique.

This study aims to find sub-critical strategies and to identify methods to increase sustainable fl ux for mixed and fl occulated feeds. Uniform and mixed latex particles are selected as the mono- and bi-disperse suspensions and fl occulated hematite particles are used as the poly-disperse suspensions. The investigation focused on measuring the critical fl uxes of these suspensions under various conditions.

The mechanisms of particle deposition of mixed and flocculated feeds are observed using the DOTM. Enhancement in critical fl ux is found in the presence of larger particles due to the increased back diffusions. The enhancement induced by electro-magnetic fi eld (EMF) is also mentioned in this thesis.

Catalytic Reductive Dechlorination of Chlorinated Benzenes with Nanoscale Pd/Fe Particles: Kinetics, Mechanism, and Infl uences of Aqueous MatrixCandidate: Zhu Bao-WeiReport No: CEE/PhD/2009/210

This research demonstrated that chlorinated benzenes could be effectively reductive dechlorinated by the nanoscale Pd/Fe particles. The Pd/Fe nanoparticles were synthesized by the method of wet chemical reduction with sodium borohydride followed by post-coating with palladium. Pd was the only reactive site towards chlorinated benzenes in the Pd/Fe system. A kinetic model is constructed based on the pseudo-fi rst-order kinetics to fi t the experimental results for the reactions, enabling identifi cation of the major and minor dechlorination pathways of 124TCB. Infl uence of geochemical conditions on the dechlorination reaction was investigated by conducting the experiment in the presence of anions such as nitrate, nitrite, phosphate, carbonate, silicate, sulfi te, sulfi de, and perchlorate in the aqueous solutions. The infl uences of amphiphiles on the dechlorination of 124TCB by the Pd/Fe nanoparticles were comprehensively examined in the presence of natural organic matters (NOM) and fi ve different surfactants, namely cationic CTAB (cetyltrimethylammonium bromide) and DPC (dodecylpyridinium chloride), anionic SDS (sodium deodecyl sulfate), and nonionic NPE (nonylphenol ethoxylate) and TX-100 (octylphenolpoly (ethyleneglycolether)x). Reactivity of the supported Pd/Fe nanoparticles towards 124TCB was investigated with chitosan and silica as supports.


PUBLICATIONS

PUBLICATIONS

Publications of academic staff in journals and conference proceedings during the period from 2008 to 2009. Authors who are not members of the School are indicated by*.

Anggadjaja, E.* and Teng, S., 2008. “Edge-column slab connections under gravity and lateral loading.” ACI Structural Journal, Vol. 105, No. 5, pp. 541-551.

Annamdas, V.G.M. and Soh, C.K., 2008. “Three-dimensional electromechanical impedance model for multiple piezoceffamic transducers - structure interaction.” Journal of Aerospace Engineering, Vol. 21, No. 1, pp. 35-44.

Annamdas, V.G.M., Yang, Y.W. and Liu, H., 2008. “Current development in fi ber Bragg grating sensors and their applications - Art No. 69320d.” Proceedings of the Conference on Sensors and Smart Structures Technologies for Civil, Mechanical and Aerospace Systems, San Diego, CA, pp. D9320-D9320.

Arulrajah, A.*, Bo, M.W.* and Chu, J., 2009. “Instrumentation at the Changi land reclamation project, Singapore.” Geotechnical Engineering, Proceedings of the ICE, London, Vol. 162, pp. 33-40.

Atchariyawut, S.*, Jiraratananon, R.* and Wang, R., 2008. “Mass transfer study and modelling of gas-liquid membrane contacting process by multistage cascade model for CO2 absorption”. Separation and Purifi cation Technology, Vol. 63, No. 1, pp. 15-22.

Aw, T.G., Gin, K.Y.H., Oon, L.L.E.*, Chen, E.X.* and Woo, C.H.*, 2009. “Prevalence and genotypes of human noroviruses in tropical urban surface waters and clinical samples in Singapore.” Applied and Environmental Microbiology, Vol. 75, No. 15, pp. 4984-4992.

Bahador, S.D., Yang, Y. and Zhang, L., 2008. “Strain transfer models for strain actuators.” Proceedings of the International Conference on Multifunctional Materials and Structures, Hong Kong, pp. 254-257.

Bhatnagar, R.* and Teo, C.C., 2009. “Role of logistics in enhancing competitive advantage: A value chain framework for global supply chains”. International Journal of Physical Distribution and Logistics Management, Vol. 39, No. 3, pp. 202-226.

Bai, H.W., Zhang, X.W., Pan, J.H., Sun, D.D. and Shao, J.H., 2009. “Combination of nano TiO2 Photocatalytic Oxidation with Microfi ltration (MF) for natural organic matter removal”. Water Science and Technology: Water Supply, Vol. 9, No. 1, pp. 31-37.

Blanquez, P.* and Guieysse, B., 2008. “Continuous biodegradation of 17 beta-estradiol and 17 alpha-ethynylestradiol by trametes versicolor.” Journal of Hazardous Materials, Vol. 150, No. 2, pp. 459-462.

Bo, M.W.*, Wong, K.S. and Choa, V., 2008. “Constant rate of displacement test on ultra-soft soil.” Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, Vol. 161, No. 3, pp. 129-135.

Brownjohn, J.M.W.* and Pan, T.C., 2008. “Identifying loading and response mechanisms from ten years of performance monitoring of a tall building.” Journal of Performance of Constructed Facilities, Vol. 22, No. 1, pp. 24-34.

Brownjohn, J.M.W.* and Pan, T.-C., 2009. “Structural health monitoring of a tall building.” Encyclopaedia of Structural Health Monitoring, John Wiley and Sons, UK, pp. 2233-2242.

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, Vol. 135, No. 3, pp. 431-443.

Chang, S., Fane, A.G., Waite, T.D.* and Yeo, A.P.S., 2008. “Unstable fi ltration behavior with submerged hollow fi ber membranes”. Journal of Membrane Science, Vol. 308, No. 1-2, pp. 107-114.

Chang, V.W.C., Hildemann, L.M.* and Chang, C.H.*, 2009. “Dilution rates for tailpipe emissions: Effects of vehicle shape, tailpipe position, and exhaust velocity.” Journal of the Air and Waste Management Association, Vol. 59, No. 6, pp. 715-724.

Chang, V.W.C., Hildemann, L.M.* and Chang, C.H.*, 2009. “Wind tunnel measurements of the dilution of tailpipe emissions downstream of a car, a light-duty truck, and a heavy-duty truck tractor head.” Journal of the Air and Waste Management Association, Vol. 59, No. 6, pp. 704-714.


PUBLICATIONS

Chao, H.P.*, Lee, J.F.*, Lee, C.K.*, Huang, F.C. and Annadurai, G.*, 2008. “Volatilization reduction of monoaromatic compounds in nonionic surfactant solutions.” Chemical Engineering Journal, Vol. 142, No. 2, pp. 161-167.

Chen, P.H., 2008. “Integration of cost and schedule using extensive matrix method and spreadsheets.” Automation in Construction, Vol. 18, No. 1, pp. 32-41.

Chen, P.H. and Shahandashti, S.M., 2008. “Stochastic scheduling with multiple resource constraints using a simulated annealing-based algorithm.” Proceedings of the 25th International Symposium on Automation and Robotics in Construction, Vilnius, Lithuania, pp. 447-451.

Chen, P.H. and Truc, N.T.L., 2008. “Automatic 3D modeling development and application for hydraulic construction.” Proceedings of the 25th International Symposium on Automation and Robotics in Construction, Vilnius, Lithuania, pp. 435-439.

Chen, P.H. and Truc, N.T.L., 2008. “Computer-aided visual communication for way-fi nding in emergency in indoor environment.” Proceedings of the 25th International Symposium on Automation and Robotics in Construction, Vilnius, Lithuania, pp. 440-446.

Chen, P.H. and Feng, F., 2009. “A fast fl ow control algorithm for real-time emergency evacuation in large indoor areas.” Fire Safety Journal, Vol. 44, No. 5, pp. 732-740.

Chen, P.H. and Shahandashti, S.M., 2009. “Hybrid of genetic algorithm and simulated annealing for multiple project scheduling with multiple resource constraints.” Automation in Construction, Vol. 18, No. 4, pp. 434-443.

Chen, P.H. and Weng, H.J., 2009. “A two-phase GA model for resource-constrained project scheduling.” Automation in Construction, Vol. 18, No. 4, pp. 485-498.

Chen, P.H., Yang, Y.C.* and Chang, L.M.*, 2009. “Automated bridge coating defect recognition using adaptive ellipse approach.” Automation in Construction, Vol. 18, No. 5, pp. 632-643.

Chen, Z.*, Ren, N.*, Wang, A.*, Zhang, Z.P. and Shi, Y.*, 2008. “A novel application of TPAD-MBR system to the pilot treatment of chemical synthesis-based pharmaceutical wastewater.” Water Research, Vol. 42, No. 13, pp. 3385-3392.

Cheng, N.S., 2008. “Comparison of settling-velocity-based formulas for threshold of sediment motion.” Journal of Hydraulic Engineering, ASCE, Vol. 134, No. 8, pp. 1136-1141.

Cheng, N.S., 2008. “Formula for the viscosity of a glycerol-water mixture.” Industrial and Engineering Chemistry Research, Vol. 47, No. 9, pp. 3285-3288.

Cheng, N.S., 2008. “Formulas for friction factor in transitional regimes.” Journal of Hydraulic Engineering, ASCE, Vol. 134, No. 9, pp. 1357-1362.

Cheng, N.S., 2009. “Comparison of formulas for drag coeffi cient and settling velocity of spherical particles.” Powder Technology, Vol. 189, No. 3, pp. 395-398.

Cheng, N.S., Hao, Z.Y. and Tan, S.K., 2008. “Comparison of quadratic and power law for nonlinear fl ow through porous media.” Experimental Thermal and Fluid Science, Vol. 32, No. 8, pp. 1538-1547.

Chiew, S.P., Lee, C.K., Lie, S.T. and Nguyen, T.B.N., 2008. “Fatigue modeling for partially overlapped CHS K-joints with surface crack.” Proceedings of the 12th International Symposium on Tubular Structures, Shanghai, China, pp. 119-126.

Chong, T.H., Wong, F.S.* and Fane, A.G., 2008. “Implications of critical fl ux and cake enhanced osmotic pressure (CEOP) on colloidal fouling in reverse osmosis: Experimental observations.” Journal of Membrane Science, Vol. 314, No. 1-2, pp. 101-111.

Chong, T.H., Wong, F.S.* and Fane, A.G., 2008. “The effect of imposed fl ux on biofouling in reverse osmosis: Role of concentration polarisation and biofi lm enhanced osmotic pressure phenomena.” Journal of Membrane Science, Vol. 325, No. 2, pp. 840-850.

Chu, J. and Wanatowski, D.*, 2008. “Instability conditions of loose sand in plane strain.” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 134, No. 1, pp. 136-142.

Chu, J. and Wanatowski, D.*, 2009. “Effect of loading mode on strain softening and instability behavior of sand in plane-strain tests.” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 135, No. 1, pp. 108-120.


PUBLICATIONS

Chu, J., Bo, M.W.* and Arulrajah, A.*, 2009. “Reclamation of a slurry pond in Singapore.” Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, Vol. 162, No. 1, pp. 13-20.

Chu, J., Bo, M.W.* and Arulrajah, A.*, 2009. “Soil improvement works for an offshore land reclamation.” Proceedings of the Institution of Civil Engineers - Geotechnical Engineering, Vol. 162, No. 1, pp. 21-32.

Chua, L.H.C. and Shuy, E.B., 2008. “Laboratory studies on the coupled oscillations between an internal density interface and a shear layer.” Journal of Engineering Mechanics, ASCE, Vol. 134, No. 4, pp. 348-352.

Chua, L.H.C., Wong, T.S.W. and Sriramula, L.K., 2008. “Comparison between kinematic wave and artifi cial neural network models in event-based runoff simulation for an overland plane.” Journal of Hydrology, Vol. 357, No. 3-4, pp. 337-348.

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 2009, Vol. 36, pp. 67-73.

Dey, S.*, Chiew, Y.M. and Kadam, M.S.*, 2008. “Local scour and riprap stability at an abutment in a degrading bed.” Journal of Hydraulic Engineering, ASCE, Vol. 134, No. 10, pp. 1496-1502.

Dharma, R.B. and Tan, K.H., 2008. “Experimental and numerical investigation on ductility of composite beams in the hogging moment regions under fi re conditions.” Journal of Structural Engineering, ASCE, Vol. 134, No. 12, pp. 1873-1886.

Ding, H.B. and Wang, J.Y., 2008. “Responses of the methanogenic reactor to different effl uent fractions of fermentative hydrogen production in a phase-separated anaerobic digestion system.” International Journal of Hydrogen Energy, Vol. 33, No. 23, pp. 6993-7005.

Ding, H.B., Liu, X.Y., Stabnikova, O. and Wang, J.Y., 2008. “Effect of protein on biohydrogen production from starch of food waste.” Water Science and Technology, Vol. 57, No. 7, pp. 1031-1036.

Du, H.L.*, Xu, L.M.*, Hu, H.P.*, Hu, Y.T.*, Chen, X.D.*, Fan, H. and Yang, J.S.*, 2008. “High-frequency vibrations of corrugated cylindrical piezoelectric shells.” Proceedings of the 165th Forum of Young Scientists on the Challenges on Wave Propagation in Elastic Solids in Information Era, Ningbo, China, pp. 564-572.

Ehrlich, M. and Kong, R.T.L., 2008. “Modelling country reliability in public private partnership infrastructure projects.” Proceedings of the 25th International Symposium on Automation and Robotics in Construction, Vilnius, Lithuania, pp. 751-758.

Fan, H.S.L., 2008. “Challenges in transport planning and congestion management.” Proceedings of the 13th International Conference of the Hong Kong Society for Transportation Studies, Hong Kong, pp. 419-428.

Fan, S.C. and Li, S.M.*, 2008. “Boundary fi nite-element method coupling fi nite-element method for steady-state analyses of dam-reservoir systems.” Journal of Engineering Mechanics, ASCE, Vol. 134, No. 2, pp. 133-142.

Fane, A.G., 2008. Submerged membranes, Chapter in “Advanced Membrane Technology and Applications.” Li, N., Fane, A.G., Ho, W.S. and Matsuura, T. (Eds), Wiley, ISBN: 978-0-471-73167-2.

Fane, A.G. and Chang, S., 2008. Techniques to enhance the performance of Membrane processes, Chapter in “Handbook of Membrane Separations; Chemical, Pharmaceutical and Biotechnological Applications”. Pabby, Rizvi and Sastre (Eds), CRC Press, ISBN: 9780849395499, ISBN 10: 0849395496.

Fane, A.G., Schwinge, J.*, Genkin, G.*, Hilal, N.* and Chong, T.H., 2008. Review of “Colloidal Fouling in Spiral Wound Modules”. Report for Middle East Desalination Research Centre, Muscat, Oman.

Fane, A.G., Chong, T.H. and Le-Clech, P.*, 2009. “Fouling in Membrane Processes”. Chapter 6 in Membrane Operations, Innovative Separations and Transformations, Drioli, E. and Giorno, L. (Eds), Wiley–VCH, ISBN: 978-3-527-32038-7.

Fane, A.G., Wang, R. and Yue, J.*, 2009. “Membrane Technology: Past, Present and Future” in Handbook of Environmental Engineering, Vol. 13, ‘Membrane and Desalination Technologies’, L.K.Wang et al. (Eds), Humana Press (publication in 2009).

Feng, J., Zhu, B.W. and Lim, T.T., 2008. “Reduction of chlorinated methanes with nano-scale Fe particles: Effects of amphiphiles on the dechlorination reaction and two-parameter regression for kinetic prediction.” Chemosphere, Vol. 73, No. 11, pp. 1817-1823.


PUBLICATIONS

Fernandez-Alvarez, P.*, Le Noir, M.* and Guieysse, B., 2009. “Removal and destruction of endocrine disrupting contaminants by adsorption with molecularly imprinted polymers followed by simultaneous extraction and phototreatment.” Journal of Hazardous Materials, Vol. 163, No. 2-3, pp. 1107-1112.

Fujikake, K.*, Li, B. and Soeun, S.*, 2009. “Impact response of reinforced concrete beam and its analytical evaluation.” Journal of Structural Engineering, ASCE, Vol. 135, No. 8, pp. 938-950.

Fung, T.C. and Chen, Z.L., 2008. “Precise time-step integration algorithms using response matrices with expanded dimension.” AIAA Journal, Vol. 46, No. 8, pp. 1900-1911.

Gao, F. and Gho, W.M.*, 2008. “Parametric equations to predict SCF of axially loaded completely overlapped tubular circular hollow section joints.” Journal of Structural Engineering, ASCE, Vol. 134, No. 3, pp. 412-420.

Gao, F. and Lu, Y.*, 2009. “An acceleration residual generation approach for structural damage identifi cation.” Journal of Sound and Vibration, Vol. 319, No. 1-2, pp. 163-181.

Gao, L.*, Yu, S.C.M.*, Ai, J.J.* and Law, A.W.K., 2008. “Circulation and energy of the leading vortex ring in a gravity-driven starting jet.” Physics of Fluids, September, Vol. 20, Issue No. 9, Article No. 093604.

Ghol, W.M.* and Yang, Y., 2008. “Parametric equation for static strength of tubular circular hollow section joints with complete overlap of braces.” Journal of Structural Engineering, ASCE, Vol. 134, No. 3, pp. 393-401.

Goh, A.T.C., Kulhawy, F.H.* and Wong, K.S., 2008. “Reliability assessment of basal-heave stability for braced excavations in clay.” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 134, No. 2, pp. 145-153.

Goh, A.T.C., Phoon, K.K.* and Kulhawy, F.H.*, 2009. “Reliability analysis of partial safety factor design method for cantilever retaining walls in granular soils.” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 135, No. 5, pp. 616-622.

Goh, K.H., Lim, T.T. and Chui, P.C., 2008. “Evaluation of the effect of dosage, pH and contact time on high-dose phosphate inhibition for copper corrosion control using Response Surface Methodology (RSM).” Corrosion Science, Vol. 50, No. 4, pp. 918-927.

Goh, K.H., Lim, T.T. and Dong, Z.*, 2008. “Application of layered double hydroxides for removal of oxyanions: A review.” Water Research, Vol. 42, No. 6-7, pp. 1343-1368.

Goh, K.H., Lim, T.T. and Dong, Z.L.*, 2009. “Enhanced arsenic removal by hydrothermally treated nanocrystalline Mg/Al layered double hydroxide with nitrate intercalation.” Environmental Science and Technology, Vol. 43, No. 7, pp. 2537-2543.

Gu, J. and Zhao, Z.Y., 2009. “Considerations of the discontinuous deformation analysis on wave propagation problems.” International Journal for Numerical and Analytical Methods in Geomechanics, Vol. 33, No. 12, pp. 1449-1465.

Guieysse, B., Hort, C.*, Platel, V.*, Munoz, R.*, Ondarts, M.* and Revah, S.*, 2008. “Biological treatment of indoor air for VOC removal: Potential and challenges.” Biotechnology Advances, Vol. 26, No. 5, pp. 398-410.

Guo, C.-H., Stabnikov, V. and Ivanov, V., 2009. “The removal of phosphate from wastewater using anoxic reduction of iron ore in the rotating reactor.” Biochemical Engineering Journal, Vol. 46, pp. 223-226.

Hao, Z., Zhou, T.*, Chua, L.P. and Yu, S.C.M., 2008. “Approximations to energy and temperature dissipation rates in the far fi eld of a cylinder wake.” Experimental Thermal and Fluid Science, Vol. 32, No. 3, pp. 791-799.

Hao, Z., Zhou, T.*, Zhou, Y.* and Mi, J.*, 2008. “Reynolds number dependence of the inertial range scaling of energy dissipation rate and enstrophy in a cylinder wake.” Experiments in Fluids, Vol. 44, No. 2, pp. 279-289.

Hay, Choon Teck, Khor Swee Loong, Darren Delai Sun and James O. Leckie*, 2009. “Infl uence of a prolonged solid retention time environment on nitrifi cation/denitrifi cation and sludge production in a submerged membrane bioreactor”. Desalination, Vol. 245, pp. 28-43.

Huang, Y.-N., Whittaker, A.S.* and Luco, N.*, 2008. “Maximum spectral demands in the near-fault region.” Earthquake Spectra, Vol. 24, No. 1, pp. 319-341.

Huang, Y.-N., Whittaker, A.S.* and Luco, N.*, 2008. “Performance assessment of conventional and base-isolated nuclear power plants for earthquake and blast loadings.” MCEER-08-0019, Multidisciplinary Center for Earthquake Engineering Research, State University of New York, Buffalo, NY.


PUBLICATIONS

Huang, Y.-N., Whittaker, A.S.* and Luco, N.*, 2008. “Seismic performance assessment of nuclear power plants.” Proceedings of the 14th World Conference on Earthquake Engineering, Beijing, China, Paper No. S20-0007.

Huang, Y.-N. and Whittaker, A.S.*, 2009. “Response of conventional and base-isolated nuclear power plants to blast loading.” Proceedings of the 20th International Conference on Structural Mechanics in Reactor Technology, Espoo (Helsinki), Finland.

Huang, Y.-N., Whittaker, A.S.* and Luco, N.*, 2009. “Orientation of maximum spectral demand in the near-fault region.” Earthquake Spectra, Vol. 25, No. 3, pp. 707-717.

Huang, Y.-N., Whittaker, A.S.* and Luco, N.*, 2009. “Seismic performance assessment for safety-related nuclear structures.” Proceedings of the 20th International Conference on Structural Mechanics in Reactor Technology, Espoo (Helsinki), Finland.

Huang, Y.-N., Whittaker, A.S.*, Kennedy, R.P.* and Mayes, R.L.*, 2009. “Assessment of base-isolated nuclear structures for design and beyond-design basis earthquake shaking.” MCEER-09-0008, Multidisciplinary Center for Earthquake Engineering Research, State University of New York, Buffalo, NY.

Hwang, J.-S.*, Huang, Y.-N., Yi, S.-L.* and Ho, S.-Y.*, 2008. “Design formulations for supplemental viscous dampers to structures.” Journal of Structural Engineering, ASCE, Vol. 134, No. 1, pp. 22-31.

Huang, Z.F., Tan, K.H., Toh, W.S.* and Phng, G.H., 2008. “Fire resistance of composite columns with embedded I-section steel - effects of section size and load level.” Journal of Constructional Steel Research, Vol. 64, No. 3, pp. 312-325.

Huang, Z.H., 2008. “Wave scattering by double slotted barriers in a steady current: Experiments.” China Ocean Engineering, Vol. 22, No. 2, pp. 205-214.

Huang, Z.H. and Ghidaoui, M.S., 2008. “Experiments on nonlinear wave scattering by a submerged rectangular step in the presence of a current.” Proceedings of the 18th International Offshore and Polar Engineering Conference (ISOPE 2008), Vancouver, Canada, pp. 599-606.

Huang, Z.H. and Liu, C.R., 2008. “A linear theory for wave scattering by double slotted barriers in weak steady currents.” China Ocean Engineering, Vol. 22, No. 2, pp. 215-226.

Huang, Z., Megawati, K., Qiu, Q., Sieh, K. and Pan, T.C., 2008. “Tsunami threat to Padang and Bengkulu, Sumatra, Indonesia: Part II. Tsunami Hazard Mitigation by Mangrove Forests”. 2nd Workshop on South China Sea Tsunami, Shanghai, China, 1-3 December 2008.

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 2009, Vol. 36, No. 1, pp. 93-97.

Hui Ying Yang, Siu Fung Yu, Shu Ping Lau, Xiwang Zhang, Darren Delai Sun and Guo Jun, 2009. “Direct growth of ZnO nanocrystals onto the surface of porous TiO2 nanotube arrays for highly effi cient and recyclable photocatalysts”. Small, in press and available online: http://www3.interscience.wiley.com/journal/122498529/abstract

Ivanov, V. and Chu, J., 2008. “Applications of microorganisms to geotechnical engineering for bioclogging and biocementation of soil in situ.” Reviews in Environmental Science and Biotechnology, Vol. 7, pp. 139-153.

Ivanov, V., Nejad, S.R., Yi, S. and Wang, X.H., 2008. “Physiological heterogeneity of suspended microbial aggregates.” Water Science and Technology, Vol. 58, No. 12, pp. 2435-2441.

Ivanov, V., Wang, X.H. and Stabnikova, O., 2008. “Starter culture of pseudomonas veronii strain B for aerobic granulation.” World Journal of Microbiology and Biotechnology, Vol. 24, No. 4, pp. 533-539.

Ivanov, V., Kuang, S.L., Stabnikov, V.* and Guo, C.H., 2009. “The removal of phosphorus from reject water in a municipal wastewater treatment plant using iron ore.” Journal of Chemical Technology and Biotechnology, Vol. 84, No. 1, pp. 78-82.

Jia, H. and Cai, Z.M., 2008. “Countermeasure research of the development of agricultural electronic commerce in Henan province.” Proceedings of the International Conference on Informationization, Automation and Electrifi cation in Agriculture, Zhenjiang, China, pp. 130-135.

Jia, H., Chen, Y.C., Lin, F., Zhang, J. and Coal Industry Publ, H., 2008. “Research on chamber tunnelling blasting vibration based on testing and fi nite element numerical simulation.” Proceedings of the 3rd International Symposium on Modern Mining and Safety Technology, Fuxin, China, pp. 786-790.


PUBLICATIONS

Jia, W.Z.*, Reitz, E.*, Sun, H., Li, B.*, Zhang, H.* and Lei, Y.*, 2009. “From Cu-2(OH)(3)Cl to nanostructured sisal-like Cu(OH)(2) and CuO: Synthesis and characterization.” Journal of Applied Physics, Vol. 105, No. 6.

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, No. 1-3, pp. 42-49.

Jiang, X., Yan, R.* and Tay, J.H., 2008. “Reusing H2S-exhausted carbon as packing material for odor biofi ltration.” Chemosphere, Vol. 73, No. 5, pp. 698-704.

Jiang, X., Yan, R.* and Tay, J., 2009. “Transient-state biodegradation behavior of a horizontal biotrickling fi lter in co-treating gaseous H2S and NH3.” Applied Microbiology and Biotechnology, Vol. 81, No. 5, pp. 969-975.

Jiang, X., Yan, R.* and Tay, J.H., 2009. “Developing sulfi de-oxidizing biofi lm on H2S-exhausted carbon for sustainable bio-regeneration and biofi ltration.” Journal of Hazardous Materials, Vol. 164, No. 2-3, pp. 726-732.

Jiang, X., Yan, R.* and Tay, J.H., 2009. “Simultaneous autotrophic biodegradation of H2S and NH3 in a biotrickling fi lter.” Chemosphere, Vol. 75, No. 10, pp. 1350-1355.

Jinadasa, K.*, Tanaka, N.*, Sasikala, S.*, Werellagama, D.*, Mowjood, M.I.M.* and Ng, W.J., 2008. “Impact of harvesting on constructed wetlands performance - A comparison between Scirpus grossus and Typha angustifolia.” Journal of Environmental Science and Health Part A - Toxic/Hazardous Substances and Environmental Engineering, Vol. 43, No. 6, pp. 664-671.

Jing, S. and Hu, J., 2009. “Temperature fi eld analysis of road structure of asphalt pavement based on FEM numerical calculation.” Proceedings of the 2nd International Conference on Modelling and Simulation, Manchester, England, pp. 207-210.

Jou, R.C.*, Lam, S.H., Kuo, C.W.* and Chen, C.C.*, 2008. “The asymmetric effects of service quality on passengers’ choice of carriers for international air travel.” Journal of Advanced Transportation, Vol. 42, No. 2, pp. 179-208.

Jou, R.C.*, Lam, S.H., Hensher, D.A.*, Chen, C.C.* and Kuo, C.W.*, 2008. “The effect of service quality and price on international airline competition”. Transportation Research Part E - Logistics And Transportation Review, July, Vol. 44, Issue 4, pp. 580-592.

Kao, C.M.*, Huang, K.D.*, Wang, J.Y., Chen, T.Y.* and Chien, H.Y.*, 2008. “Application of potassium permanganate as an oxidant for in situ oxidation of trichloroethylene-contaminated groundwater: A laboratory and kinetics study.” Journal of Hazardous Materials, Vol. 153, No. 3, pp. 919-927.

Kaur, S.*, Gopal, R.*, Ng, W.J., Ramakrishna, S.* and Matsuura, T.*, 2008. “Next-generation fi brous media for water treatment.” Mrs Bulletin, Vol. 33, No. 1, pp. 21-26.

Kong, D., Tiong, R.L.K., Cheah, C.Y.J., Permana, A. and Ehrlich, M., 2008. “Assessment of credit risk in project fi nance.” Journal of Construction Engineering and Management, ASCE, Vol. 134, No. 11, pp. 876-884.

Krisdani, H., Rahardjo, H. and Leong, E.C., 2008. “Effects of different drying rates on shrinkage characteristics of a residual soil and soil mixtures.” Engineering Geology, Vol. 102, No. 1-2, pp. 31-37.

Krisdani, H., Rahardjo, H. and Leong, E.C., 2008. “Measurement of geotextile-water characteristic curve using capillary rise principle.” Geosynthetics International, Vol. 15, No. 2, pp. 86-94.

Krisdani, H., Rahardjo, H. and Leong, E.C., 2009. “Use of instantaneous profi le and statistical methods to determine permeability functions of unsaturated soils.” Canadian Geotechnical Journal, Vol. 46, No. 7, pp. 869-874.

Kulkarni, S.A., Li, B. and Yip, W.K., 2008. “Finite element analysis of precast hybrid-steel concrete connections under cyclic loading.” Journal of Constructional Steel Research, Vol. 64, No. 2, pp. 190-201.

Kulkarni, S.A. and Li, B., 2009. “Investigations of seismic behavior of hybrid connections.” PCI Journal, Vol. 54, No. 1, pp. 67-87.

Kulkarni, S.A. and Li, B., 2009. “Seismic behavior of reinforced concrete interior wide-beam column joints.” Journal of Earthquake Engineering, Vol. 13, No. 1, pp. 80-99.

Kurniawan, A. and Ma, G., 2009. “Optimization of ballast plan in launch jacket load-out.” Structural and Multidisciplinary Optimization, Vol. 38, No. 3, pp. 267-288.


PUBLICATIONS

Kwon, Y.-N.*, Tang, C.Y. and Leckie, J.O.*, 2008. “Change of chemical composition and hydrogen bonding behavior due to chlorination of crosslinked polyamide membranes.” Journal of Applied Polymer Science, Vol. 108, pp. 2061-2066.

Lee, C.K. and Xu, Q.X., 2008. “Automatic adaptive FE analysis of thin-walled structures using 3D solid elements.” International Journal for Numerical Methods in Engineering, Vol. 76, No. 2, pp. 183-229.

Lee, M.L., Gofar, N.* and Rahardjo, H., 2009. “A simple model for preliminary evaluation of rainfall-induced slope instability”. Journal of Engineering Geology, Vol. 108, pp. 272-285.

Lee, P.F., Zhang, X.W., Sun, D.D., Du, J.H. and Leckie, J.O.*, 2008. “Synthesis of bimodal porous structured TiO2 microsphere with high photocatalytic activity for water treatment.” Colloids and Surfaces A - Physicochemical and Engineering Aspects, Vol. 324, No. 1-3, pp. 202-207.

Leong, E.C., Cahyadi, J. and Rahardjo, H., 2009. “Measuring shear and compression wave velocities of soil using bender-extender elements.” Canadian Geotechnical Journal, Vol. 46, No. 7, pp. 792-812.

Li, B. and Chua, H.Y.G., 2008. “Rapid repair of earthquake damaged RC interior beam-wide column joints and beam-wall joints using FRP composites.” Proceedings of the 2nd International Conference on Advances in Concrete and Structures, Changsha, China, pp. 491-499.

Li, B. and Pan, T.-C., 2008. “Lien Institute For the Environment [LIFE].’’ I2CTI Newsletter, International Institute for Construction Technology Information, 11 April 2008, No. 17.

Li, B. and Tran, C.T.N., 2008. “Reinforced concrete beam analysis supplementing concrete contribution in truss models.” Engineering Structures, Vol. 30, No. 11, pp. 3285-3294.

Li, B., Kulkarni, S.A. and Leong, C.L., 2009. “Seismic performance of precast hybrid-steel concrete connections.” Journal of Earthquake Engineering, Vol. 13, No. 5, pp. 667-689.

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, Elsevier, Vol. 239, pp. 455-469.

Li, B., Pan, T.C. and Tran, C.T.N., 2009. “Effects of axial compression load and eccentricity on seismic behavior of nonseismically detailed interior beam-wide column joints.” Journal of Structural Engineering, ASCE, 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 beam-wall connections.” ACI Structural Journal, Vol. 106, No. 5, pp. 591-599.

Li, B., Tran, C.T.N. and Pan, T.C., 2009. “Experimental and numerical investigations on the seismic behavior of lightly reinforced concrete beam-column joints.” Journal of Structural Engineering, ASCE, Vol. 135, No. 9, pp. 1007-1018.

Li, J.C. and Ma, G.W., 2009. “Experimental study of stress wave propagation across a fi lled rock joint.” International Journal of Rock Mechanics and Mining Sciences, Vol. 46, No. 3, pp. 471-478.

Li, K. and Tiong, L.K.R., 2008. “Financing and operating of Singapore’s urban rail transit infrastructure.” Proceedings of the 4th International Conference on Wireless Communications, Networking and Mobile Computing, Dalian, China, pp. 9026-9028.

Li, N.*, Fane, A.G., Ho, W.S.* and Matsuura, T.* (Eds), 2008. “Advanced membrane technology and applications.” Wiley, ISBN: 978-0-471-73167-2.

Li, Q.M.*, Ye, Z.Q., Ma, G.W., Jones, N.* and Zhou, H.Y., 2009. “The infl uence of elastic shear deformation on the transverse shear failure of a fully clamped beam subjected to idealized blast loading.” International Journal of Mechanical Sciences, Vol. 51, No. 6, pp. 413-423.

Li, X.B.*, Zhou, Z.L.*, Lok, T.S., Hong, L.* and Yin, T.B.*, 2008. “Innovative testing technique of rock subjected to coupled static and dynamic loads.” International Journal of Rock Mechanics and Mining Sciences, Vol. 45, No. 5, pp. 739-748.

Li, Y., Liu, Y., Shen, L. and Chen, F., 2008. “DO diffusion profi le in aerobic granule and its microbiological implications.” Enzyme and Microbial Technology, Vol. 43, No. 4-5, pp. 349-354.

Li, Y., Liu, Y. and Xu, H.L.*, 2008. “Is sludge retention time a decisive factor for aerobic granulation in SBR?” Bioresource Technology, Vol. 99, No. 16, pp. 7672-7677.


PUBLICATIONS

Li, Y., Liu, Y. and Wang, Z.W., 2009. “Stoichiometric analysis of dissolved organic carbon fl ux into storage and growth in aerobic granules culture.” Biotechnology Journal, Vol. 4, No. 2, pp. 238-246.

Lie, S.T. and Zhang, B.F., 2008. “Failure assessment of cracked circular hollow section (CHS) welded joints using BS7910:2005.” Proceedings of the 12th International Symposium on Tubular Structures, Shanghai, China, pp. 367-373.

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.” Advances in Structural Engineering, Vol. 12, No. 3, pp. 359-372.

Lie, S.T., Yang, Z.M.* and Gho, W.M.*, 2009. “Validation of BS7910:2005 failure assessment diagrams for cracked square hollow section T-, Y- and K-joints.” International Journal of Pressure Vessels and Piping, Vol. 86, No. 5, pp. 335-344.

Lim, C.L., Li, B. and Pan, T.-C., 2009. “Seismic performance of reinforced concrete frames with wall-like columns.’’ IES Journal Part A: Civil and Structural Engineering, Institution of Engineers, Singapore, Vol. 2, No. 2, pp. 126-142.

Lim, T.T. and Zhu, B.W., 2008. “Effects of anions on the kinetics and reactivity of nanoscale Pd/Fe in trichlorobenzene dechlorination.” Chemosphere, Vol. 73, No. 9, pp. 1471-1477.

Lim, T.T., Goh, K.H., Goei, R. and Dong, Z.L.*, 2009. “Mechanistic and thermodynamic studies of oxyanion sorption by various synthetic Mg/Al layered double hydroxides.” Water Science and Technology, Vol. 59, No. 5, pp. 1011-1017.

Listiarini, K., Sun, D.D. and Leckie, J.O.*, 2009. “Organic fouling of nanofi ltration membranes: Evaluating the effects of humic acid, calcium, alum coagulant and their combinations on the specifi c cake resistance.” Journal of Membrane Science, Vol. 332, No. 1-2, pp. 56-62.

Listiarini, Karina, Wei Chan, Darren Delai Sun and James O Leckie*, 2009. “Fouling mechanism and resistance analyses of systems containing sodium alginate, calcium, alum and their combinations in dead-end fouling of nanofi ltration membranes.” Journal of Membrane Science, in press.

Liu, C.R., Huang, Z.H. and Tan, S.K., 2008. “Study of nonlinear wave scattering by a submerged step in a fully nonlinear DBIEM numerical wave tank.” Proceedings of the 8th ISOPE Pacifi c/Asia Offshore Mechanics Symposium, Bangkok, Thailand, pp. 273-279.

Liu, H.L.* and Chu, J., 2009. “A new type of prefabricated vertical drain with improved properties.” Geotextiles and Geomembranes, Vol. 27, No. 2, pp. 152-155.

Liu, H.L.*, Chu, J. and Deng, A.*, 2009. “Use of large-diameter, cast-in situ concrete pipe piles for embankment over soft clay.” Canadian Geotechnical Journal, Vol. 46, No. 8, pp. 915-927.

Liu, J.X., Zhao, Z.Y., Deng, S.C.* and Liang, N.G.*, 2008. “Modifi ed generalized beam lattice model associated with fracture of reinforced fi ber/particle composites.” Theoretical and Applied Fracture Mechanics, Vol. 50, No. 2, pp. 132-141.

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., Deng, S.C.* 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 Technology, Vol. 30, No. 1, pp. 69-74.

Liu, X.J.*, Yang, J.P.* and Yang, Y.W., 2008. “Heat conduction analysis of nano-tip and storage medium in thermal-assisted data storage using molecular dynamics simulation.” Molecular Simulation, Vol. 34, No. 1, pp. 57-62.

Liu, X.J.*, Yang, Y.W. and Yang, J.P.*, 2009. “Direct simulation Monte Carlo on thermal distribution of rarefi ed gas under heated atomic force microscope nanoprobe.” Journal of Applied Physics, Vol. 105, No. 1, 013508.

Liu, X.Y., Ding, H.B., Sreeramachandran, S., Stabnikova, O. and Wang, J.Y., 2008. “Enhancement of food waste digestion in the hybrid anaerobic solid-liquid system.” Water Science and Technology, Vol. 57, No. 9, pp. 1369-1373.


PUBLICATIONS

Liu, Y., 2008. “New insights into pseudo-second-order kinetic equation for adsorption.” Colloids and Surfaces A – Physicochemical and Engineering Aspects, Vol. 320, No. 1-3, pp. 275-278.

Liu, Y. and Liu, Y.J., 2008. Reply to Comments on “Biosorption isotherms, kinetics and thermodynamics” Review. Separation and Purifi cation Technology, Vol. 63, No. 2, pp. 250-250.

Liu, Y. and Liu, Y., 2008. “Biosorption isotherms, kinetics and thermodynamics.” Separation and Purifi cation Technology, Vol. 61, No. 3, pp. 229-242.

Liu, Y. and Shen, L., 2008. “A general rate law equation for biosorption.” Biochemical Engineering Journal, Vol. 38, No. 3, pp. 390-394.

Liu, Y. and Shen, L., 2008. “From Langmuir kinetics to First- and Second-order rate equations for adsorption.” Langmuir, Vol. 24, No. 20, pp. 11625-11630.

Liu, Y. and Teng, S.S., 2008. “Nonlinear analysis of reinforced concrete slabs using nonlayered shell element.” Journal of Structural Engineering, ASCE, Vol. 134, No. 7, pp. 1092-1100.

Liu, Y., Teng, S. and Soh, C.K., 2008. “Three-dimensional damage model for concrete. I: Theory.” Journal of Engineering Mechanics, ASCE, Vol. 134, No. 1, pp. 72-81.

Liu, Y., Teng, S. and Soh, C.K., 2008. “Three-dimensional damage model for concrete. II: Verifi cation.” Journal of Engineering Mechanics, ASCE, Vol. 134, No. 1, pp. 82-89.

Liu, Y. and Wang, Z.W., 2008. “Uncertainty of preset-order kinetic equations in description of biosorption data.” Bioresource Technology, Vol. 99, No. 8, pp. 3309-3312.

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.Q. and Tay, J.H., 2008. “Infl uence of starvation time on formation and stability of aerobic granules in sequencing batch reactors.” Bioresource Technology, Vol. 99, No. 5, pp. 980-985.

Low, B.K., 2008. “Effi cient probabilistic algorithm illustrated for a rock slope.” Rock Mechanics and Rock Engineering, Vol. 41, No. 5, pp. 715-734.

Low, Y.M., 2008. “Prediction of extreme responses of fl oating structures using a hybrid time/frequency domain coupled analysis approach.” Ocean Engineering, Vol. 35, No. 14-15, pp. 1416-1428.

Low, Y.M. and Langley, R.S.*, 2008. “A hybrid time/frequency domain approach for effi cient coupled analysis of vessel/mooring/riser dynamics.” Ocean Engineering, Vol. 35, No. 5-6, pp. 433-446.

Low, Y.M. and Langley, R.S.*, 2008. “Understanding the dynamic coupling effects in deep water fl oating structures using a simplifi ed model.” Journal of Offshore Mechanics and Arctic Engineering, Transactions of the ASME, Vol. 130, No. 3, 031007-1-10.

Low, Y.M., 2009. “Effi cient vector outcrossing analysis of the excursion of a moored vessel.” Probabilistic Engineering Mechanics, Vol. 24, No. 4, pp. 565-576.

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. “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.

Lu, Y.* and Wei, J.W., 2008. “Damage-based inelastic response spectra for seismic design incorporating performance considerations.” Soil Dynamics and Earthquake Engineering, Vol. 28, No. 7, pp. 536-549.

Lu, Y.*, Chiew, Y.M. and Cheng, N.S., 2008. “Review of seepage effects on turbulent open-channel fl ow and sediment entrainment.” Journal of Hydraulic Research, Vol. 46, No. 4, pp. 476-488.

Lu, Y.*, Gu, X.M. and Wei, J.W., 2009. “Prediction of seismic drifts in multi-storey frames with a new storey capacity factor.” Engineering Structures, Vol. 31, No. 2, pp. 345-357.


PUBLICATIONS

Luo, T.*, Yao, Y.P.* and Chu, J., 2009. “Asymptotic state behaviour and its modeling for saturated sand.” Science in China Series E - Technological Sciences, Vol. 52, No. 8, pp. 2350-2358.

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.

Ma, G.W. and An, X.M., 2008. “Numerical simulation of blasting-induced rock fractures.” International Journal of Rock Mechanics and Mining Sciences, Vol. 45, No. 6, pp. 966-975.

Ma, G.W., An, X.M. and Wang, M.Y., 2009. “Analytical study of dynamic friction mechanism in blocky rock systems.” International Journal of Rock Mechanics and Mining Sciences, Vol. 46, No. 5, pp. 946-951.

Ma, G.W., An, X.M., Zhang, H.H.* and Li, L.X.*, 2009. “Modeling complex crack problems using the numerical manifold method.” International Journal of Fracture, Vol. 156, No. 1, pp. 21-35.

Ma, G.W., Huang, X. and Li, J.C., 2009. “Damage assessment for buried structures against internal blast load.” Structural Engineering and Mechanics, Vol. 32, No. 2, pp. 301-320.

Ma, G.W., Ye, Z.Q. and Shao, Z.S., 2009. “Modeling loading rate effect on crushing stress of metallic cellular materials.” International Journal of Impact Engineering, Vol. 36, No. 6, pp. 775-782.

Madhav, A.V.G. and Soh, C.K., 2008. “Uniplexing and multiplexing of PZT transducers for structural health monitoring.” Journal of Intelligent Material Systems and Structures, Vol. 19, No. 4, pp. 457-467.

Mao, R.*, Yu, S.C.M., Zhou, T.* and Chua, L.P., 2009. “On the vorticity characteristics of lobe-forced mixer at different confi gurations.” Experiments in Fluids, Vol. 46, No. 6, pp. 1049-1066.

Massih, D.*, Soubra, A.H.* and Low, B.K., 2008. “Reliability-based analysis and design of strip footings against bearing capacity failure.” Journal of Geotechnical and Geoenvironmental Engineering, Vol. 134, No. 7, pp. 917-928.

Maszenan, A.M. and Liu Yu, 2008. “From wastewater to safe water: The NTU Experience”. Asia Pacifi c Biotech News, Vol. 12, No. 13, pp. 35-39.

Megawati, K., Huang, Z., Qiu, Q., Sieh, K. and Pan, T.C., 2008. “Tsunami threat to Padang and Bengkulu, Sumatra, Indonesia: Part I. Source identifi cation and hydrodynamic modelling”. 2nd Workshop on South China Sea Tsunami, Shanghai, China, 1-3 December 2008.

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, Vol. 99, No. 2A, pp. 566-584.

Megawati, K., Sieh, K. and Pan, T.-C., 2009. “Sumatran Megathrust Earthquakes: What has happened, and what’s next?” Civil and Environmental Engineering Research Bulletin, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Issue 22, pp. 100-104.

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.

Meng, G.H., Chu, J. and Klotz, U.*, 2008. “Engineering properties of Bukit Timah residual soil at a tunnelling project site in Singapore.” Proceedings of the International Conference on Deep Excavation, 10-12 November 2008, Singapore.

Miao, A.W. and Yang, Y.W., 2008. “Monitoring vibrating structures using PZT impedance transducers.” Proceedings of International Conference on Multifunctional Materials and Structures, Hong Kong, pp. 85-88.

Moradas, G.*, Auresenia, J.*, Gallardo, S.* and Guieysse, B., 2008. “Biodegradability and toxicity assessment of trans-chlordane photochemical treatment.” Chemosphere, Vol. 73, No. 9, pp. 1512-1517.

Munoz, R.*, Kollner, C.* and Guieysse, B., 2009. “Biofi lm photobioreactors for the treatment of industrial wastewaters.” Journal of Hazardous Materials, Vol. 161, No. 1, pp. 29-34.

Narasimhan, S.*, Suresh, S., Nagarajaiah, S.* and Sundararajan, N., 2008. “On-line learning failure-tolerant neural-aided controller for earthquake excited structures.” Journal of Engineering Mechanics, ASCE, Vol. 134, No. 3, pp. 258-268.


PUBLICATIONS

Pan, J.H., Zhang, X.W., Du, A.J., Sun, D.D. and Leckie, J.O.*, 2008. “Self-etching reconstruction of hierarchically mesoporous F-TiO2 hollow microspherical photocatalyst for concurrent membrane water purifi cations.” Journal of the American Chemical Society, Vol. 130, No. 34, pp. 11256-11257.

Pan, T.-C., Li, B., Chu, J. and Megawati, K., 2008. “Recommendations for addressing seismic risk in Singapore.” ARUP-BCA Report, Protective Technology Research Centre, Nanyang Technological University.

Pan, T.-C., Megawati, K. and Li, B., 2008. “Seismic risk of the region surrounding Singapore.” Keynote Paper, Proceedings of the 11th East Asia-Pacifi c Conference on Structural Engineering and Construction (EASEC-11), 19-21 November 2008, Taipei, Taiwan.

Pan, T.-C, Megawati, K. and Lim, C.L., 2008. “Effect of Long-Distance Sumatra Earthquakes on High-Rise Buildings in Singapore.” Invited Paper, Proceedings of the 5th International Conference on Urban Earthquake Engineering, 4-5 March 2008, Tokyo, Japan, pp. 55-60.

Pan, T.-C., Shah, H.C.*, Wagh, S.S.* and Li, B., 2008. “Micro-Insurance for Natural Disasters Concepts, Present and Future Outlook.” Invited Paper, Proceedings of the 14th World Conference on Earthquake Engineering (14WCEE), 12-17 October 2008, Beijing, China, Paper S01-01-013.

Pan, T.C., You, X.T. and Lim, C.L., 2008. “Evaluation of fl oor vibration in a biotechnology laboratory caused by human walking.” Journal of Performance of Constructed Facilities, Vol. 22, No. 3, pp. 122-130.

Pan, T.-C., 2009. “Suggestions to Further Reform the Education System of China”. China and Globalization Research, Centre for China and Globalization, Issue 4, pp. 25-26 (in Chinese).

Phattaranawik, J.*, Fane, A.G., Pasquier, A.C.S.* and Wu, B., 2008. “A novel membrane bioreactor based on membrane distillation”. Desalination, Vol. 223, pp. 386-395.

Phattaranawik, J.*, Fane, A.G. and Wong, F.S.*, 2008. “Novel membrane-based sensor for online membrane integrity monitoring.” Journal of Membrane Science, Vol. 323, No. 1, pp. 113-124.

Phattaranawik, J.*, Fane, A.G., Pasquier, A.C.S.*, Bing, W. and Wong, F.S.*, 2009. “Experimental study and design of a submerged membrane distillation bioreactor.” Chemical Engineering and Technology, Vol. 32, No. 1, pp. 38-44.

Prochazka, P.P.*, Dolezel, V.* and Lok, T.S., 2009. “Optimal shape design for minimum Lagrangian.” Engineering Analysis with Boundary Elements, Vol. 33, No. 4, pp. 447-455.

Qian, G.R.*, Shi, J.*, Cao, Y.L.*, Xu, Y.F.* and Chui, P.C., 2008. “Properties of MSW fl y ash-calcium sulfoaluminate cement matrix and stabilization/solidifi cation on heavy metals.” Journal of Hazardous Materials, Vol. 152, No. 1, pp. 196-203.

Qian, Z.H., Tan, K.H. and Burgess, I.W.*, 2008. “Behavior of steel beam-to-column joints at elevated temperature: Experimental investigation.” Journal of Structural Engineering, ASCE, Vol. 134, No. 5, pp. 713-726.

Qian, Z.H. and Tan, K.H., 2009. “Defl ection behaviour of plate girders loaded in shear at elevated temperatures.” Journal of Constructional Steel Research, Vol. 65, No. 4, pp. 991-1000.

Qian, Z.H., Tan, K.H. and Burgess, I.W.*, 2009. “Numerical and analytical investigations of steel beam-to-column joints at elevated temperatures.” Journal of Constructional Steel Research, Vol. 65, No. 5, pp. 1043-1054.

Rahardjo, H., Indrawan, I.G.B., Leong, E.C. and Yong, W.K.*, 2008. “Effects of coarse-grained material on hydraulic properties and shear strength of top soil.” Engineering Geology, Vol. 101, No. 3-4, pp. 165-173.

Rahardjo, H., Leong, E.C. and Rezaur, R.B.*, 2008. “Effect of antecedent rainfall on pore-water pressure distribution characteristics in residual soil slopes under tropical rainfall.” Hydrological Processes, Vol. 22, No. 4, pp. 506-523.

Rahardjo, H., Rezaur, R.B., Leong, E.C., Alonso, E.E.*, Lloret, A.* and Gens, A.*, 2008. “Monitoring and modeling of slope response to climate changes.” Proceedings of the 10th International Symposium on Landslides and Engineered Slopes, Xian, China, pp. 67-84.

Rahardjo, H., Harnas, F.R., Leong, E.C., Tan, P.Y., Fong, Y.K. and Sim, E.K., 2009. “Tree stability in an improved soil to withstand wind loading”. Urban Forestry and Urban Greening, Vol. 8, No. 4.


PUBLICATIONS

Rahardjo, H., Leong, E.C., Satyanaga, A., Ng, Y.S., Henry, T.C.P. and Hua, C.J., 2009. “Slope stability against rainfall and preventive measures.” Invited Speaker, Proceedings of BCA Seminar 2009 – Structural Inspection and Maintenance of Building Safety, Singapore, 23 October 2009, pp. 1-31.

Rahardjo, H., Meilani, I., Rezaur, R.B. and Leong, E.C., 2009. “Shear strength characteristics of a compacted soil under infi ltration conditions”. Geomechanics and Engineering, Vol. 1, No. 1, pp. 35-52.

Rahardjo, H., Rezaur, R.B. and Leong, E.C., 2009. “Mechanism of rainfall-induced slope failures in tropical regions”. Keynote Lecture. Proceedings of the First Italian Workshop on Landslides (IWL): “Rainfall-induced Landslides: Mechanisms, Monitoring Techniques and Nowcasting Models for Early Warning Systems”, Departimento Di Ingegneria Civile, Seconda Universita di Napoli, Naples, Italy, 8 – 10 June 2009, Vol. 1, pp. 31-42.

Rahardjo, H., Santoso, V.A. and Leong, E.C., 2009. “Unsaturated soil mechanics for solving geotechnical problems.” Principal Speaker. Proceedings of the 1st International Conference on Sustainable Infrastructure and Built Environment in Developing Countries (SIBE 2009), Institut Teknologi Bandung (ITB), Bandung, Indonesia.

Ren, J.Z.*, Li, Z.S.* and Wang, R., 2008. “Effects of the thermodynamics and rheology of BTDA-TDI/MDI co-polyimide (P84) dope solutions on the performance and morphology of hollow fi ber UF membranes”. Journal of Membrane Science, Vol. 309, pp. 196-208.

Rong, H.C. and Li, B., 2008. “Deformation-controlled design of reinforced concrete fl exural members subjected to blast loadings.” Journal of Structural Engineering, ASCE, Vol. 134, No. 10, pp. 1598-1610.

Sachidanandham, R. and Gin, K.Y.H., 2009. “A dormancy state in nonspore-forming bacteria.” Applied Microbiology and Biotechnology, Vol. 81, No. 5, pp. 927-941.

Sachidanandham, R. and Gin, K.Y.H., 2009. “Flow cytometric analysis of prolonged stress-dependent heterogeneity in bacterial cells.” FEMS Microbiology Letters, Vol. 290, No. 2, pp. 143-148.

Sachs, T.* and Tiong, R.L.K., 2009. “Quantifying qualitative information on risks: Development of the QQIR method.” Journal of Construction Engineering and Management, ASCE, Vol. 135, No. 1, pp. 56-71.

Shao, D.D. and Law, A.W.K., 2008. “Salinity build-up due to brine discharges into shallow coastal waters.” Proceedings of the 2nd International Symposium on Physics of Fluids, Jiuzhaigou, China, pp. 541-544.

Shao, Z.S. and Ma, G.W.*, 2008. “Thermo-mechanical stresses in functionally graded circular hollow cylinder with linearly increasing boundary temperature.” Composite Structures, Vol. 83, No. 3, pp. 259-265.

Shaw, F., Liu, X., Megawati, K., Sieh, K., Tan, S. K., Huang, Z. and Pan, T.-C., 2008. “Tsunami hazard from the potential rupture of the Manila Trench.” Bulletin of Civil Engineering Research, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Issue 21, pp. 64-67.

Shi, L.*, Wang, R., Cao, Y.M.*, Liang, D.T.* and Tay, J.H., 2008. “Effect of additives on the fabrication of poly (vinylidene fl uoride-co-hexafl uropropylene) (PVDF-HFP) asymmetric microporous hollow fi ber membranes”. Journal of Membrane Science, Vol. 315, pp. 195-204.

Shi, L.*, Wang, R. and Cao, Y.M.*, 2009. “Effect of the rheology of poly (vinylidene fl uoride-co-hexafl uropropylene) (PVDF–HFP) dope solutions on the formation of microporous hollow fi bers used as membrane contactors”. Journal of Membrane Science, Vol. 344, pp. 112–122.

Sieh, K., Megawati, K. and Pan, T.-C., 2008. “The Elephant and the Tectonic Plate.” The Sunday Times, The Straits Times, Singapore, 9 March 2008, pg. 37.

Soares, A.*, Guieysse, B., Jefferson, B.*, Cartmell, E.* and Lester, J.N.*, 2008. “Nonylphenol in the environment: A critical review on occurrence, fate, toxicity and treatment in wastewaters.” Environment International, Vol. 34, No. 7, pp. 1033-1049.

Stabnikova, O., Ivanova, V., Larionova, I.*, Stabnikov, V.*, Bryszewska, M.A.* and Lewis, J.*, 2008. “Ukrainian dietary bakery product with selenium-enriched yeast.” LWT-Food Science and Technology, Vol. 41, No. 5, pp. 890-895.

Stabnikova, O., Liu, X.Y. and Wang, J.Y., 2008. “Anaerobic digestion of food waste in a hybrid anaerobic solid-liquid system with leachate recirculation in an acidogenic reactor.” Biochemical Engineering Journal, Vol. 41, No. 2, pp. 198-201.


PUBLICATIONS

Stabnikova, O., Liu, X.Y. and Wang, J.Y., 2008. “Digestion of frozen/thawed food waste in the hybrid anaerobic solid-liquid system.” Waste Management, Vol. 28, No. 9, pp. 1654-1659.

Suresh, R.*, Tjin, S.C. and Bhalla, S.*, 2009. “Multi-component force measurement using embedded fi ber Bragg grating.” Optics and Laser Technology, Vol. 41, No. 4, pp. 431-440.

Tan, K.H., Cheng, G.H. and Zhang, N., 2008. “Experiment to mitigate size effect on deep beams.” Magazine of Concrete Research, Vol. 60, No. 10, pp. 709-723.

Tan, K.H. and Qian, Z.H.*, 2008. “Experimental behaviour of a thermally restrained plate girder loaded in shear at elevated temperature.” Journal of Constructional Steel Research, Vol. 64, No. 5, pp. 596-606.

Tan, K.H. and Yuan, W.F., 2008. “Buckling of elastically restrained steel columns under longitudinal non-uniform temperature distribution.” Journal of Constructional Steel Research, Vol. 64, No. 1, pp. 51-61.

Tan, K.H. and Yuan, W.F., 2009. “Inelastic buckling of pin-ended steel columns under longitudinal non-uniform temperature distribution.” Journal of Constructional Steel Research, Vol. 65, No. 1, pp. 132-141.

Tan, S.B.K., Chua, L.H.C., Shuy, E.B., Lo, E.Y.M. and Lim, L.W., 2008. “Performances of rainfall-runoff models calibrated over single and continuous storm fl ow events.” Journal of Hydrologic Engineering, Vol. 13, No. 7, pp. 597-607.

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 fi lters.” Journal of Hydrologic Engineering, Vol. 14, No. 3, pp. 271-279.

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 fi lter algorithm.” Journal of Hydrologic Engineering, Vol. 14, No. 1, pp. 101-106.

Tang, C.Y., Kwon, Y.N.* and Leckie, J.O.*, 2009. “The role of foulant-foulant electrostatic interaction on limiting fl ux 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.Y., Kwon, Y.N.* and Leckie, J.O.*, 2009. “Effect of membrane chemistry and coating layer on physiochemical properties of thin fi lm composite polyamide RO and NF membranes I. FTIR and XPS characterization of polyamide and coating layer chemistry.” Desalination, Vol. 242, No. 1-3, pp. 149-167.

Tang, C.Y.Y., Kwon, Y.N.* and Leckie, J.O.*, 2009. “Effect of membrane chemistry and coating layer on physiochemical properties of thin fi lm composite polyamide RO and NF membranes II. Membrane physiochemical properties and their dependence on polyamide and coating layers.” Desalination, Vol. 242, No. 1-3, pp. 168-182.

Tay, J.-H., Tay, S.T.-L.*, Ivanov, V., Stabnikova, O. and Wang, J.-Y., 2008. “Compositions and methods for the treatment of wastewater and other waste.” US Patent: 7,393,452. Date of grant: 1 July 2008, Date of fi ling 1 April 11, 2003.

Teck, H.C., Loong, K.S., Sun, D.D. and Leckie, J.O.*, 2009. “Infl uence of a prolonged solid retention time environment on nitrifi cation/denitrifi cation and sludge production in a submerged membrane bioreactor.” Desalination, Vol. 245, No. 1-3, pp. 28-43.

To, P.C.*, Marinas, B.J.*, Snoeyink, V.L.* and Ng, W.J., 2008. “Effect of strongly competing background compounds on the kinetics of trace organic contaminant desorption from activated carbon.” Environmental Science and Technology, Vol. 42, No. 7, pp. 2606-2611.

Tu, Z.G. and Lu, Y., 2008. “A Robust Stochastic Genetic Algorithm (STGA) for global numerical optimization (Vol. 8, pg. 456, 2004).” IEEE Transactions on Evolutionary Computation, Vol. 12, No. 6, pp. 781-781.

Wanatowski, D.* and Chu, J., 2008. “Effect of specimen preparation method on the stress-strain behavior of sand in plane-strain compression tests.” Geotechnical Testing Journal, Vol. 31, No. 4, pp. 308-320.

Wanatowski, D.* and Chu, J., 2009. Discussion of “On equivalent granular void ratio and steady state behaviour of loose sand with fi nes”. Canadian Geotechnical Journal, Vol. 46, No. 4, pp. 482-482.

Wang, N.F., Yang, Y.W. and Tai, K., 2008. “Hybrid genetic algorithm for designing structures subjected to uncertainty.” Proceedings of the IEEE International Conference on System, Man and Cybernetic, Singapore, pp. 565-570.


PUBLICATIONS

Wang, N.F., Yang, Y.W. and Tai, K., 2008. “Optimization of structures under load uncertainties based on hybrid genetic algorithm.” Proceedings of the IEEE Congress on Evolutionary Computation, Hong Kong, pp. 4039-4044.

Wang, W.Y.* and Teng, S., 2008. “Finite-element analysis of reinforced concrete fl at plate structures by layered shell element.” Journal of Structural Engineering, ASCE, Vol. 134, No. 12, pp. 1862-1872.

Wang, X.H.* and Huang, X.Y., 2008. “A simple modeling and experiment on dynamic stability of a disk rotating in air.” International Journal of Structural Stability and Dynamics, Vol. 8, No. 1, pp. 41-60.

Wang, X.H.* and Ivanov, V., 2009. “Microbial structure of nitrifying granules and their estrogens degradation properties.” Water Science and Technology, Vol. 59, No. 9, pp. 1855-1862.

Wang, Z.H.* and Tan, K.H., 2008. “Green’s function approach for heat conduction: Application to steel members protected by intumescent paint.” Numerical Heat Transfer Part B, Fundamentals, Vol. 54, No. 6, pp. 435-453.

Wang, Z.H. and Tan, K.H., 2008. “Radiative heat transfer for structural members exposed to fi re: An analytical approach”. Journal of Fire Sciences, Vol. 26, No. 2, pp. 133-152. DOI: 10.1177/0734904107085746

Wang, Z.Q. and Cheng, N.S., 2008. “Infl uence of secondary fl ow on distribution of suspend sediment concentration.” Journal of Hydraulic Research, Vol. 46, No. 4, pp. 548-552.

Wang, Z.Q., Tan, S.K., Cheng, N.S. and Goh, K.W., 2008. “A simple relationship for crenulate-shaped bay in static equilibrium.” Coastal Engineering, Vol. 55, No. 1, pp. 73-78.

Wicaksana, F., Fane, A.G. and Law, A.W.K., 2009. “The use of constant temperature anemometry for permeate fl ow distribution measurement in a submerged hollow fi bre system.” Journal of Membrane Science, Vol. 339, No. 1-2, pp. 195-203.

Wong, P.C.Y., Kwon, Y.N.* and Criddle, C.S.*, 2009. “Use of atomic force microscopy and fractal geometry to characterize the roughness of nano-, micro-, and ultrafi ltration membranes.” Journal of Membrane Science, Vol. 340, No. 1-2, pp. 117-132.

Wong, S.F.* and Ting, S.K., 2009. “Use of recycled rubber tires in normal- and high-strength concretes.” ACI Materials Journal, Vol. 106, No. 4, pp. 325-332.

Wong, T.S.W., 2008. Discussion of “Ann and fuzzy logic models for simulating event-based rainfall-runoff” by Gokmen Tayfur and Vijay P. Singh, - Discussion. Journal of Hydraulic Engineering, ASCE, Vol. 134, No. 9, pp. 1400-1400.

Wong, T.S.W., 2008. Discussion of “Storm-water predictions by dimensionless unit hydrograph” by James C. Y. Guo. Journal of Irrigation and Drainage Engineering, ASCE, Vol. 134, No. 2, pp. 269-269.

Wong, T.S.W., 2008. “Effect of channel shape on time of travel and equilibrium detention storage in channel.” Journal of Hydrologic Engineering, Vol. 13, No. 3, pp. 189-196.

Wong, T.S.W., 2008. “How nature uses overland fl ow regime to maximize equilibrium detention storage and fl ood attenuation.” Hydrological Processes, Vol. 22, No. 26, pp. 5004-5012.

Wong, T.S.W., 2008. “How to review or not to review a paper.” Journal of Professional Issues in Engineering Education and Practice, Vol. 134, No. 4, pp. 327-328.

Wong, T.S.W., 2008. “How to write an award-winning paper.” Journal of Professional Issues in Engineering Education and Practice, Vol. 134, No. 1, pp. 11-11.

Wong, T.S.W., 2008. “Optimum rainfall interval and manning’s roughness coeffi cient for runoff simulation.” Journal of Hydrologic Engineering, Vol. 13, No. 11, pp. 1097-1102.

Wong, T.S.W., 2009. Closure to “Effect of channel shape on time of travel and equilibrium detention storage in channel” by Tommy S.W. Wong. Journal of Hydrologic Engineering, Vol. 14, No. 5, pp. 533-533.

Wong, T.S.W., 2009. “Evolution of kinematic wave time of concentration formulas for overland fl ow.” Journal of Hydrologic Engineering, Vol. 14, No. 7, pp. 739-744.

Wu, J., Le-Clech, P.*, Stuetz, R.M.*, Fane, A.G. and Chen, V., 2008. “Effects of relaxation and backwashing conditions on fouling in an aerobic membrane bioreactor”. Journal of Membrane Science, Vol. 324, pp. 26-32.


PUBLICATIONS

Wu, J., Le-Clech, P.*, Stuetz, R.M.*, Fane, A.G. and Chen, V., 2008. “Novel fi ltration mode for fouling limitation in membrane bioreactors”. Water Research, Vol. 42, No. 14, pp. 3677-3648.

Xu, H. and Liu, Y., 2008. “Mechanisms of Cd2+, Cu2+ and Ni2+ biosorption by aerobic granules.” Separation and Purifi cation Technology, Vol. 58, No. 3, pp. 400-411.

Xu, S.P. and Sun, D.D., 2009. “Signifi cant improvement of hydrogen generation rate using TiO2 photocatalyst enhanced with Cu”. International Journal of Hydrogen Energy, Vol. 34, Issue 15, pp. 6096-6104.

Xu, S.P., Zhang, X.W., Ng, J.W. and Sun, D.D., 2009. “Preparation and application of TiO2/Al2O3 microspherical photocatalyst for water treatment.” Water Science and Technology: Water Supply, Vol. 9, No. 1, pp. 39-34.

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.

Yan, S.W.*, Chu, J., Fan, Q.J.* and Yan, Y.*, 2009. “Building a breakwater with prefabricated caissons on soft clay.” Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, Vol. 162, No. 1, pp. 3-12.

Yang, S.Q.* and Tan, S.K., 2008. “Flow resistance over mobile bed in an open-channel mobile fl ow.” Journal of Hydraulic Engineering, ASCE, Vol. 134, No. 7, pp. 937-947.

Yang, Y. and Miao, A., 2008. “Effect of external vibration on PZT impedance signature.” Sensors, Vol. 8, No. 11, pp. 6846-6859.

Yang, Y.W., Annamdas, V.G.M., Wang, C. and Zhou, Y.X.*, 2008. “Application of multiplexed FBG and PZT impedance sensors for health monitoring of rocks.” Sensors, Vol. 8, No. 1, pp. 271-289.

Yang, Y.W. and Hu, Y.H., 2008. “Electromechanical impedance modeling of PZT transducers for health monitoring of cylindrical shell structures.” Smart Materials and Structures, Vol. 17, No. 1, 015005.

Yang, Y.W., Hu, Y.H. and Lu, Y.*, 2008. “Sensitivity of PZT impedance sensors for damage detection of concrete structures.” Sensors, Vol. 8, No. 1, pp. 327-346.

Yang, Y.W., Lim, Y.Y. and Soh, C.K., 2008. “Practical issues related to the application of the electromechanical impedance technique in the structural health monitoring of civil structures: I. Experiment.” Smart Materials and Structures, Vol. 17, No. 3, 035008.

Yang, Y.W., Lim, Y.Y. and Soh, C.K., 2008. “Practical issues related to the application of the electromechanical impedance technique in the structural health monitoring of civil structures: II. Numerical verifi cation.” Smart Materials and Structures, Vol. 17, No. 3, 035009.

Yang, Y.W., Liu, H. and Annamdas, V.G.M., 2008. “Monitoring damage propagation using PZT impedance transducers - art. No. 693410.” Proceedings of the Conference on Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure and Homeland Security 2008, San Diego, CA, pp. 93410-93410.

Yang, Y.W., Liu, H., Annamdas, V.G.M.* and Soh, C.K., 2009. “Monitoring damage propagation using PZT impedance transducers.” Smart Materials and Structures, Vol. 18, No. 4, 045003.

Yang, Y.W., Liu, X.J.* and Yang, J.P.*, 2008. “Nonequilibrium molecular dynamics simulation for size effects on thermal conductivity of Si nanostructures.” Molecular Simulation, Vol. 34, No. 1, pp. 51-55.

Yang, Y.W. and Zhang, L., 2008. “Modeling of an ionic polymer-metal composite ring.” Smart Materials and Structures, Vol. 17, No. 1, 015023.

Yao, Y.*, Tan, K.H. and Tang, C.Y., 2008. “The effect of a shear bond in the Rankine method for the fi re resistance of RC columns.” Engineering Structures, Vol. 30, No. 12, pp. 3595-3602.

Yao, Y.* and Tan, K.H., 2009. “Extended Rankine approach for bi-axially loaded steel columns under natural fi re.” Engineering Structures, Vol. 31, No. 5, pp. 1024-1031.

Yong-Bo, S.*, Zhi-Fu, D.* and Seng-Tjhen, L., 2009. “Prediction of hot spot stress distribution for tubular K-joints under basic loadings.” Journal of Constructional Steel Research, Vol. 65, No. 10-11, pp. 2011-2026.


PUBLICATIONS

You, S.J.*, Ren, N.Q.*, Zhao, Q.L.*, Kiely, P.D.*, Wang, J.Y., Yang, F.L.*, Fu, L.* and Peng, L., 2009. “Improving phosphate buffer-free cathode performance of microbial fuel cell based on biological nitrifi cation.” Biosensors and Bioelectronics, Vol. 24, No. 12, pp. 3698-3701.

Yu, S.C.M.*, Ai, J.J.*, Gao, L.* and Law, A.W.K., 2008. “Vortex formation process of a starting square jet.” AIAA Journal, Vol. 46, No. 1, pp. 223-231.

Yuan, W.F. and Tan, K.H., 2009. “Cellular automata model for simulation of effect of guiders and visibility range.” Current Applied Physics, Vol. 9, No. 5, pp. 1014-1023.

Zhang, H.Y., Wang, R., Liang, D.T.* and Tay, J.H., 2008. “Theoretical and experimental studies of membrane wetting in the membrane gas-liquid contacting process for CO2 absorption.” Journal of Membrane Science, Vol. 308, No. 1-2, pp. 162-170.

Zhang, L. and Yang, Y.W., 2008. “Three-dimensional charge redistribution of ionic polymer-metal composites with uncertainty in surface conductivity.” Proceedings of International Conference on Multifunctional Materials and Structures, Hong Kong, pp. 379-382.

Zhang, N., Tan, K.H. and Leong, C.L., 2009. “Single-span deep beams subjected to unsymmetrical loads.” Journal of Structural Engineering, ASCE, Vol. 135, No. 3, pp. 239-252.

Zhang, X.W., Du, A.J., Lee, P., Sun, D.D. and Leckie, J.O.*, 2008. “Grafted multifunctional titanium dioxide nanotube membrane: Separation and photodegradation of aquatic pollutant.” Applied Catalysis B-Environmental, Vol. 84, No. 1-2, pp. 262-267.

Zhang, X.W., Du, A.J., Lee, P.F., Sun, D.D. and Leckie, J.O.*, 2008. “TiO2 nanowire membrane for concurrent fi ltration and photocatalytic oxidation of humic acid in water.” Journal of Membrane Science, Vol. 313, No. 1-2, pp. 44-51.

Zhang, X.W., Pan, J.H., Du, A.J., Lee, P.F., Sun, D.D. and Lee, J.O., 2008. “Aggregating TiO2 (b) nanowires to porous basketry-like microspheres and their photocatalytic properties.” Chemistry Letters, Vol. 37, No. 4, pp. 424-425.

Zhang, X.W.*, Sun, D.D., Li, G.T.* and Wang, Y.Z.*, 2008. “Investigation of the roles of active oxygen species in photodegradation of azo dye AO7 in TiO2 photocatalysis illuminated by microwave electrodeless lamp.” Journal of Photochemistry and Photobiology A - Chemistry, Vol. 199, No. 2-3, pp. 311-315.

Zhang, X.W., Pan, J.H., Du, A.J., Xu, S.P. and Sun, D.D., 2009. “Room-temperature fabrication of anatase TiO2 submicrospheres with nanothornlike shell for photocatalytic degradation of methylene blue.” Journal of Photochemistry and Photobiology A - Chemistry, Vol. 204, No. 2-3, pp. 154-160.

Zhang, X.W., Pan, J.H., Du, A.J.H., Ng, J.W., Sun, D.D. and Leckie, J.O.*, 2009. “Fabrication and photocatalytic activity of porous TiO2 nanowire microspheres by surfactant-mediated spray drying process.” Materials Research Bulletin, Vol. 44, No. 5, pp. 1070-1076.

Zhang, X.W., Pan, J.H., Du, A.J., Fu, W.J., Sun, D.D. and Leckie, J.O.*, 2009. “Combination of one-dimensional TiO2 nanowire photocatalytic oxidation with microfi ltration for water treatment.” Water Research, Vol. 43, No. 5, pp. 1179-1186.

Zhang, X.W., Pan, J.H., Fu, W.J., Du, A.J. and Sun, D.D., 2009. “TiO2 nanotubes photocatalytic oxidation for water treatment.” Water Science and Technology: Water Supply, Vol. 9, No. 1, pp. 45-49.

Zhang, X.W., Zhang, T., Ng, J.W. and Sun, D.D., 2009. “High-performance multifunctional TiO2 nanowire ultrafi ltration membrane with hierarchical layer structure for water treatment”. Advanced Functional Materials, in press.

Zhang, Y.P, Chong, T.H., Fane, A.G., Law, A., Coster, H.G.L.* and Winters, H.*, 2008. “Implications of enhancing critical fl ux of particulates by AC fi elds in RO desalination and reclamation”. Desalination, Vol. 220, pp. 371-379.

Zhang, Y.Q.*, Lu, Y.* and Ma, G.W., 2008. “Effect of compressive axial load on forced transverse vibrations of a double-beam system.” International Journal of Mechanical Sciences, Vol. 50, No. 2, pp. 299-305.

Zhang, Z.P.*, Adav, S.S.*, Show, K.Y.*, Tay, J.H., Liang, D.T.*, Lee, D.J.* and Su, A.*, 2008. “Characteristics of rapidly formed hydrogen-producing granules and biofi lms.” Biotechnology and Bioengineering, Vol. 101, No. 5, pp. 926-936.

Zhao, X.B.*, Zhao, J.*, Cai, J.G.* and Hefny, A.M., 2008. “UDEC modelling on wave propagation across fractured rock masses.” Computers and Geotechnics, Vol. 35, No. 1, pp. 97-104.


PUBLICATIONS

Zhao, K.*, Fan, Y.Q.*, Wang, R. and Xu, N.P.*, 2008. “Preparation of closed macroporous Al2O3 membranes with a three-dimensionally ordered structure”. Chemistry Letters, Vol. 37, No. 4, pp. 420-421.

Zhao, Z.Y., Zhang, Y. and Liao, H.J.*, 2008. “Design of ensemble neural network using the Akaike information criterion.” Engineering Applications of Artifi cial Intelligence, Vol. 21, No. 8, pp. 1182-1188.

Zhao, Z.Y. and Gu, J., 2009. “Stress recovery procedure for discontinuous deformation analysis.” Advances in Engineering Software, Vol. 40, No. 1, pp. 52-57.

Zheng, W.Y. and Jia, H., 2009. “Study on characteristics of blasting stress distribution under water coupling charge by numerical simulation and model experiment.” Proceedings of the 2nd International Conference on Modelling and Simulation, Manchester, England, pp. 361-365.

Zhou, J.Z.*, Qian, G.R.*, Cao, Y.L.*, Chui, P.C., Xu, Y.F.* and Liu, Q.*, 2008. “Transition of Friedel phase to chromate-AFm phase.” Advances in Cement Research, Vol. 20, No. 4, pp. 167-173.

Zhou, Q. and Cheng, N.S., 2008. “Simultaneous measurements of particle settling velocity and oscillating-grid turbulence.” Proceedings of the 16th Asia and Pacifi c Division Congress of the International Association of Hydraulic Engineering and Research/3rd IAHR International Symposium on Hydraulic Structures, Nanjing, China, pp. 913-918.

Zhou, Q. and Cheng, N.S., 2009. “Experimental investigation of single particle settling in turbulence generated by oscillating grid.” Chemical Engineering Journal, Vol. 149, No. 1-3, pp. 289-300.

Zhou, T., Lim, T.T., Lu, X.H.*, Li, Y.Z.* and Wong, F.S.*, 2009. “Simultaneous degradation of 4CP and EDTA in a heterogeneous Ultrasound/Fenton like system at ambient circumstance.” Separation and Purifi cation Technology, Vol. 68, No. 3, pp. 367-374.

Zhou, Z.L.*, Li, D.Y.*, Ma, G.W. and Li, J.C., 2008. “Failure of rock under dynamic compressive loading.” Journal of Central South University of Technology, Vol. 15, No. 3, pp. 339-343.

Zhu, B.W., Lim, T.T. and Feng, J., 2008. “Infl uences of amphiphiles on dechlorination of a trichlorobenzene by nanoscale Pd/Fe: Adsorption, reaction kinetics, and interfacial interactions.” Environmental Science and Technology, Vol. 42, No. 12, pp. 4513-4519.

Zilouei, H.*, Guieysse, B. and Mattiasson, B.*, 2008. “Two-phase partitioning bioreactor for the biodegradation of high concentrations of pentachlorophenol using sphingobium chlorophenolicum DSM 8671.” Chemosphere, Vol. 72, No. 11, pp. 1788-1794.

EDITORIAL BOARDLeong Eng Choon – Chairman

Cheng Nian ShengJim Chen

Lie Seng TjhenTiong Lee Kong, Robert

Wong Kai Sin

EDITORIAL ASSISTANTJamillah Bte Sa’adon

ADDITIONAL COPIES AND ENQUIRIES

For general enquiries about this publication and request for additional copies, please write to:

ChairSchool of Civil and Environmental Engineering

Nanyang Technological University50 Nanyang AvenueSingapore 639798Tel: 65-67905264Fax: 65-67910676

Email: [email protected]

Published by School of Civil and Environmental Engineering, Nanyang Technological University, Singapore Printed by PHOTOPLATES PTE LTD

CONTENTS

MESSAGE FROM CHAIR 1

RENEWABLE RESOURCE TECHNOLOGY 1

CEE VISION AND MISSION 6

STATISTICS 7

• Faculty & Staff 7

• Publications, Patents and Research Grants 7

• Students Enrolment 7

BACHELOR DEGREE PROGRAMMES 8

GRADUATE STUDIES 10

ACHIEVEMENTS AND COMMENDATIONS 11

RESEARCH CENTRES 13

• Centre for Infrastructure Systems (CIS) 13

• DHI-NTU Centre 15

• Maritime Research Centre (MRC) 17

• Protective Technology Research Centre (PTRC) 20


• A review: Impact of suspended solids on corals and treatment technologies 25

• A study of bankline abutment scour 29

• Development of novel membranes for water and environmental applications 32

• Experimental study on biased fl ow behavior behind two side-by-side circular cylinders with unequal diameters 35

• Exploring dye-CNT nanocomposite as anode material for microbial fuel cells 38

• Hydraulic characteristics of jet-induced internal circulation in a water column 41

• Investigation of fl ow over a trapezoidal weir 44

• Microfl uidic separation of live and dead bacterial cells for environmental monitoring 47

• Particle saltation in a two-dimensional channel 50

• Physiological heterogeneity of aerobic bacterial aggregates 53

• Preliminary investigation of behavior of silt screens as sediment control equipment 55

• Removal of organic dyes by activated carbon adsorption 58

• Tubular microbial fuel cell for effi cient wastewater treatment and biological power generation 61

• Velocity distribution of vegetated open channel fl ows 64


• A safety stock planning model for global supply chains 68

• Accuracy of GPS heighting in the Singapore context 71

• Characteristics of non-recurrent congestion on expressway network 75

• Dynamic encryption technique for the security and effi ciency of ATMS data transmission 80

• Impacts of increasing containership size on ports 83

• Reliability assessment of basal heave stability 86

• Response characteristics of a residual soil slope to rainfall 88


• A simple mathematical formulation for bend stiffener analysis 94

• Development of nodal-based DDA in rock mass modelling 97

• Development of numerical manifold method and its application in rock engineering 100

• Experimental fatigue study of partially overlapped circular hollow section K-joints 103

• Fluid viscous dampers for buildings 107

• J-Integral decomposition for the computation of 3D stress intensity factors in cracked structures 110

• Numerical modelling of partially overlapped circular hollow section K-joints for fatigue analysis 113

• Plastic collapse loads and CTODs of a cracked square hollow section (SHS) K-joint 116

• Rock blast simulation by discontinuous deformation analysis 119

• Seismic performance analysis and tremor monitoring for buildings in Singapore 122

• Super element method in the modeling of large-scale structure with local nonlinearity 126

• Water saturation effect on sedimentary rocks 129

RESEARCH PROJECTS

• Ongoing projects 132

• Completed projects 134

• PhD Theses 136

PUBLICATIONS 143

civil engineering research no. 23 (2010)

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