Research Group for Sustainable and Resilient Infrastructures

EPSRC EP/V040235/1PI: Prof Qingwei Ma; Co-I: Dr Shiqiang Yan

Although there is a long history of research of wave energy convertors (WECs), there are still many challenges that make it difficult to develop effective, reliable and economically viable WECs. One of the challenges is the lack of robust modelling tools to assess survivability of WECs under extreme marine environments that cause extreme loads and large responses. Survivability of WECs needs to be concerned not only in the design stage but also when operational to maximise the amount of harnessed energy and minimise the risk of damage. To assess and analyse the survivability of WECs, one must identify survival conditions, quantify loadings and responses of WECs and characterise the pressure and velocity field of WECs under survival conditions. Identification of survival conditions for WECs requires not only the consideration of severe storms but also of loads and responses of WECs in shorter steep seas, which is different from that for other offshore structures that may just need to consider severe storms giving the largest wave heights. High precision quantification of loadings and responses of WECs must consider wave breaking and viscosity, which will provide dominate factors for conceptual design and to determine if the device needs to be shut down. Characterisation of the pressure and velocity fields of WECs needs to resolve two-phase flow with vortex structures to sufficient detail, which will provide information for structural and components design. In addition, as the waves in the survival conditions are highly nonlinear, they must be simulated for a long propagating duration in a large domain to allow them to sufficiently evolve. Therefore, the numerical modelling tools for analysing WEC survivability should have the capability of dealing with breaking waves and two-phase flow and accurately estimating the effect of viscosity in turbulent states. In the meantime, the tools must be fast enough so that engineers can simulate the cases within practical time-scales for design.

Many numerical models with various levels of accuracy and efficiency exist, but none of them can adequately deal with the extreme conditions found in practice. Some models are phase-averaged, being computationally efficient but not sufficiently accurate. Some models are phased-resolved, based either on the potential theory or the viscous theory. The most advanced potential models are fully nonlinear and much faster than viscous models, but could not deal with wave breaking and turbulence which always occurs for WECs. The viscous models can theoretically deal with the physical phenomena but are generally very computationally expensive, perhaps also suffering from unwanted numerical dissipation. This project will develop a novel numerical modelling suite by combining different models and by proposing new numerical approaches and machine learning techniques, which will be more accurate and require less computational effort. The modelling suite will be able to automatically go up to fully nonlinear simulations and down to linear simulations depending on the level of nonlinearity of waves and their interaction with the WECs. The new modelling suite will be validated by data measured from WEC models in the laboratory and real devices at sea, and will be applied to assess the parameters relevant to the survivability and reliability of WECs.

During the project, an advisory board will be set up to give the suggestions on specific research topics, and regular project meetings/workshops will be held to attract the interests of WECs stakeholders and disseminate the research outcomes. Our project partners will be invited to be a member of the advisory board and to attend or contribute to the meetings/workshops. Databases for different types of WECs will be created during this project, which will be accessible by general public.

EPSRC EP/V039946/1 Investigators: Prof Qingwei Ma, Dr Shiqiang Yan

Wave energy globally has potential average power slightly less than wind but this has been unexploited to date. We are concerned here with wave energy converters (WECs) offshore, before the energy resource is reduced by shallow-water effects, which would be suitable for grid scale electricity generation. Individual WEC capacity has been considered to be much smaller than for wind turbines and cost of energy (COE) considerably larger. However, with multi-mode, multi-float systems, capacity may be similar to or greater than wind in some locations and COE has been estimated to be similar to offshore wind. Survivability in extreme waves needs to be established, along with reliability of components. The mooring is the most vulnerable structural component of an offshore wave energy converter. Snap loads are a particular problem in extreme waves, and also in intermediate waves affecting fatigue. There is a widespread consensus in the wave energy community that mooring system design and modelling is a major challenge that needs to be overcome. Although literature and design guidelines for conventional ocean engineering applications are abundant, in general they do not account for the requirements of wave energy conversion, where the mooring should not inhibit platform motion causing the energy generation. Design, optimization, and assessment of mooring systems require efficient hydrodynamic and dynamic mooring models, which should be fully coupled to represent all interactions. There are various mooring options: catenary slack moored, elastic taut moored, combinations with single point (buoy) moorings, and nylon/polyester ropes offer an economic option while reducing snap loads. While some progress has been made with nonlinear hydrodynamic WEC loading models for point absorbers, an efficient general nonlinear hydrodynamic loading model for multi-bodies, accounting for wave breaking, is presently not available. Computational fluid dynamics (CFD) simulations require days, even weeks, to run on multiple processors and is unreliable for complex dynamic problems. The intention here is generalise efficient linear hydrodynamic load models by including the fully nonlinear force component due to the pressure field in the waves, known as the Froude-Krylov force. This has improved predictions of response and mooring load, markedly in some cases. This will be advanced through comparison with experimental wave basin tests and formally generalised through system identification, for single and multi-bodies with a range of mooring configurations in representative, generally multi-directional wave fields and currents. The convenient simplification of linear wave input will also be assessed with a revised force formulation determined by system identification. These force formulations will be coupled with the general industry-standard mooring model Orcaflex accounting for dynamic and material properties enabling design optimization using multi-objective genetic algorithms. This will enable survivability, fatigue and reliability analyses.

EPSRC EP/T00424X/1 PI: Dr Shiqiang Yan; Co-I: Prof Qingwei Ma

The offshore wind industry has experienced significant growth in recent years, and continues to expand both in the UK and worldwide. Most of the offshore wind turbines installed to date are located in relatively shallow water and are mounted on fixed bottom support structures. Given the limitation of suitable shallow water sites available with high wind resources and also to reduce the environmental and visual impact of turbines, it is necessary to extend wind turbines to deeper water through the development of floating offshore wind turbine (FOWT) systems, which mount wind turbines on floating support platforms.

The project aims to fill an important gap in the design, manufacturing and testing of emerging FOWT techniques by specifically characterising extreme loading on FOWTs under complex and harsh marine environments. These are typically represented by storm conditions consisting of strong wind, extreme waves, significant current, rising sea level and complex interplay between these elements, through a coordinated campaign of both advanced CFD modelling and physical wave tank tests. This has direct relevance to the current and planned activities in the UK to develop this new technology in offshore wind.

In addition, the project aims to develop a suite of hierarchical numerical models that can be applied routinely for both fast and detailed analysis of the specific flow problem of environmental (wind, wave, current) loading and dynamic responses of FOWTs under realistic storm conditions.  As an integral part of the project, a new experimental programme will be devised and conducted in the COAST laboratory at the University of Plymouth, providing improved understanding of the underlying physics and for validating the numerical models. Towards the end of the project, fully documented CFD software and experimental data sets will be released to relevant industrial users and into the Public Domain, so that they may be used to aid the design of future support structures of FOWTs and to secure their survivability with an extended envelope of safe operation for maximum power output.

EPSRC EP/T026782/1 Investigators: Prof Qingwei Ma, Dr Shiqiang Yan

The proposed new CCP-WSI+ builds on the impact generated by the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI) and extends it to connect together previously separate communities in computational fluid dynamics (CFD) and computational structural mechanics (CSM). The new CCP-WSI+ collaboration builds on the NWT, will accelerate the development of Fully Coupled Wave Structure Interaction (FCWSI) modelling suitable for dealing with the latest challenges in offshore and coastal engineering.

Since being established in 2015, CCP-WSI has provided strategic leadership for the WSI community, and has been successful in generating impact in: Strategy setting, Contributions to knowledge, and Strategic software development and support. The existing CCP-WSI network has identified priorities for WSI code development through industry focus group workshops; it has advanced understanding of the applicability and reliability of WSI through an internationally recognised Blind Test series; and supported collaborative code development.

Acceleration of the offshore renewable energy sector and protection of coastal communities are strategic priorities for the UK and involve complex WSI challenges. Designers need computational tools that can deal with complex environmental load conditions and complex structures with confidence in their reliability and appropriate use. Computational tools are essential for design and assessment within these priority areas and there is a need for continued support of their development, appropriate utilisation and implementation to take advantage of recent advances in HPC architecture.

Both the CFD and CSM communities have similar challenges in needing computationally efficient code development suitable for simulations of design cases of greater and greater complexity and scale. Many different codes are available commercially and are developed in academia, but there remains considerable uncertainty in the reliability of their use in different applications and of independent qualitative measures of the quality of a simulation.

One of the novelties of this CCP is that in addition to considering the interface between fluids and structures from a computational perspective, we propose to bring together the two UK expert communities who are leading developments in those respective fields. The motivation is to develop FCWSI software, which couples the best in class CFD tools with the most recent innovations in computational solid mechanics. Due to the complexity of both fields, this would not be achievable without interdisciplinary collaboration and co-design of FCWSI software.

The CCP-WSI+ will bring the CFD and CSM communities together through a series of networking events and industry workshops designed to share good practice and exchange advances across disciplines and to develop the roadmap for the next generation of FCWSI tools. Training and workshops will support the co-creation of code coupling methodologies and libraries to support the range of CFD codes used in an open source environment for community use and to aid parallel implementation. The CCP-WSI+ will carry out a software audit on WSI codes and the data repository and website will be extended and enhanced with database visualisation and archiving to allow for contributions from the expanded community. Code developments will be supported through provision and management of the code repository, user support and training in software engineering and best practice for coupling and parallelisation.

By bringing together two communities of researchers who are independently investigating new computational methods for fluids and structures, we believe we will be able to co-design the next generation of FCWSI tools with realism both in the flow physics and the structural response, and in this way, will unlock new complex applications in ocean and coastal engineering

EPSRC EP/M022382/1 Investigators: Prof Qingwei Ma, Dr Shiqiang Yan

The proposal is to establish a new Collaborative Computational Project (CCP) serving the UK re-search community in the area of wave structure interactions (WSI). The new CCP-WSI will bring together computational scientists, Computational Fluid Dynamics (CFD) specialists and experimentalists to develop a UK national numerical wave tank (NWT) facility fully complementary to existing and future UK experimental laboratory facilities for marine, coastal offshore engineering and thus support leading-edge research in an area of high national importance. Substantial progress has been made on a number of past and current EPSRC project grants held by the lead partners in this CCP bid to develop and test the primary elements of a numerical wave tank and to carry out cutting edge wave impact experiments alongside new opensource CFD code development. We believe it is timely to focus the activities of the community on the development of opensource NWT code held within a central code repository (CCPForge). The code will be professionally software engineered and maintainable, tested and validated against measurement data provided by the partner experimentalists, whilst remaining sufficient flexibility to meet the requirements of all members of the WSI community. This model for sharing developments collaboratively within a consortium of partners within a central code repository that is sustainably managed for the future has been developed by the lead partners in related EPSRC funded research projects. The proposed CCP-WSI would extend the framework and methodology for sharing and future proofing EPSRC funded code developments in wave structure interaction to the wider community. This is proposed through a programme of community events and activities which are designed to foster the links between experimentalists and those performing computations, between industry users, academics and the interested public.

EPSRC funded project

EPSRC-funded project

Comprehensive framework that utilises multi-scale modelling, high-performance materials and innovative sensing systems for sustainable design and multi-hazard risk mitigation.

Research supported through the Royal Academy of Engineering / Pell Frischmann Chair to City, University of London

Project funded by the Department for Transport through T-TRIG. PI: Dr Alfredo Camara, Co-I: Dr Chetan Jagadeesh. Project partners: Highways England and Connect Plus Services.

The project aims at developing a cost-effective wind shielding that adapts to the existing weather conditions in order to maximise the protection to the vehicles while reducing the forces transmitted to the structure, making this solution ideal to extend the traffic operability in new and existing bridges.
Download the public report here.

Many structures, such as bridges, buildings, towers and masts are critical for the society so it is important to take advantage of new technologies to ensure that they are safe. This project will develop modern application to include disparate sources of information about existing structures such as sensors, non-destructive testing, measurements, etc. to quantify structural performance.

Structural optimisation techniques are widely used in routine design of aeronautical, mechanical and naval structural systems. In routine civil engineering practice, however, optimum structural design is pursued either with the aid of the designer’s experience or a manual trial-and-error process. For complex problems, these approaches are often inadequate and drive to uneconomical designs. This research will develop a novel, automated framework for the optimum design of reinforced concrete buildings in earthquake prone regions that maximises resilience and sustainability of these structural systems.

Safe structural design requires that demands in terms of forces and deformations remain below respective structural capacities. Often, structural capacities cannot be determined by numerical methods and experimental testing is required. For structures subjected to cyclic loads, such as the ones imposed by earthquakes, quasi-static cyclic tests are typically employed, where test specimens are subjected to predefined force and/or deformation histories of demands, named loading protocols.

In many cases, existing loading protocols are not representative of anticipated seismic demands and thereby may either underestimate structural capacities leading to uneconomical designs or overestimate capacities driving to catastrophic failures. This research aims at developing loading protocols that reflect accurately seismic demands of various structural systems (e.g. reinforced concrete, masonry and timber buildings) in order to produce realistic estimates of their structural capacities.

Researcher: Dr Binh Le (previously Dr Sam Divall)

Supervisor: Dr Richard Goodey

Description: The primary objective of the research is to establish clear, relatively simple guidelines for the construction of shafts in close proximity to existing structures. The research will centre on addressing current issues of concern and the main aims are:

• To evaluate the source, distribution and extent of ground movements caused by shaft construction in clay.
• To evaluate the effect of these movements on nearby existing infrastructure.
• To investigate the influence of the shaft's cross-sectional shape, particularly the orientation of the major and minor axes of an elliptical shaft relative to existing infrastructure.

This research project is supported by The Leverhulme Trust.

Outputs: Le et al. (2019) and Divall & Goodey (2016)

Researcher: Dr Jignasha Panchal

Principal Investigator: Dr Andrew McNamara

Description: Centrifuge modelling techniques will investigate methods of reducing ground movements in soft clays arising from deep excavations. This project will focus on feasible construction methods that can be implemented on site to reduce the effects of heave and subsequently mitigate movements behind the wall.

Outputs: Panchal (2018), Panchal et al. (2018), Panchal et al. (2017), and

Panchal et al. (2017) Effects of wall embedment on base heave failure arising from deep excavations in soft soils, Proceedings in the 9th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground, Sao Paulo, Brazil.

Panchal & McNamara (2016) Excavation techniques to reduce ground movements in soft soils, Proceedings in the 14th BGA Young Geotechnical Engineering Symposium, Glasgow, Scotland.

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Researcher: Dr Hitesh Halai

Supervisor: Dr Andrew McNamara

Description: The London Geotechnical Centrifuge is used to model compensation grouting behind a retained 12m deep excavation. The research study examines the effectiveness of the technique in controlling surface ground movements and the impact on the retaining wall during and after an excavation. The results could provide a better understanding of the limitations present when considering its use behind excavations.

Outputs: Halai (2018), Halai & McNamara (2014) and Halai et al. (2012)

Researchers: Dr Jignasha Panchal, Dr Andrew McNamara & Dr Rohit Gorasia

Description: The Federation of Piling Specialists published guidelines for calculating the pullout forces of temporary steel casings used in rotary bored pile construction.  The research was undertaken in collaboration with Balfour Beatty Ground Engineering and Cementation Skanska Ltd which involved field testing and a series of centrifuge tests.  The centrifuge tests were carried out using the geotechnical centrifuge facility at City, University of London.  An assessment has been made of the influence of casing diameter, embedment and overburden stress on pullout forces.

Outputs: Gorasia et al. (2014) and Panchal & McNamara (2017).

Researcher: Dr Sadegh Nadimi

Supervisor: Dr Joana Fonseca

Outputs: Nadimi (2017), Nadimi & Fonseca (2017a) and Nadimi & Fonseca (2017b)

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Researcher: Dr Deqiong Kong

Principal Investigator: Dr Joana Fonseca

This  is an EPSRC First Grant funded project.

Outputs: Kong & Fonseca (2019), Fonseca et al. (2018), Kong & Fonseca (2018), Nadimi & Fonseca (2017) and Kong & Fonseca (2017)

Principal Investigator: Dr Joana Fonseca

Description: This study investigates the networks of stress transmitting particles based on the geometrical data obtained from micro-CT images. This study contributes with unique insights into the influence of contact and grain morphologies on the process of the stress transmission from grain-to-grain and consequently, on the deformation and macro-scale response of the material.

Outputs: Fonseca et al. (2015)

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Researcher: Dr Binh Le

Supervisor: Professor Neil Taylor

Description: In weak or unstable ground conditions, tunnelling induced movements could be controlled by providing Forepoling Umbrella System ahead of the tunnel face. This research, through centrifuge modelling techniques, aims to obtain the key features affecting the efficiency.

Outputs: Le & Taylor (2018), Le & Taylor (2017), Le & Taylor (2016), Le et al. (2015) and Le & Taylor (2014)

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Researcher: Dr Sam Divall

Co-researchers: Professor Neil Taylor & Dr Ming Xu

Description: Construction techniques are conducted to form a pre-lining in unfavourable ground conditions when tunnelling.  Often this technique can take the form of injected grout steel pipes as forepoling by or the installation of bars around the periphery of the face, typically over the upper quarter or third of the excavated profile.  A series of eight plane strain centrifuge model tests investigating the effect of inserting inclusions around the annulus of a single tunnel in overconsolidated clay has been conducted using the geotechnical centrifuge at City, University of London.

Outputs: Divall et al. (2016)

Researcher: Dr Neil Phillips

Supervisor: Professor Sarah Stallebrass

Description: The research project has designed a laboratory mixing test using a planetary mixer to aid in the prediction of the grading of excavated soil after transportation through the slurry pipeline. To aid in the disaggregation breakdown, soil classification tests were also carried out. Understanding the amount a soil disaggregates during transportation is key when specifying the separation plant.

Outputs: Stallebrass et al. (2015) and Phillips et al. (2014)

Principal Investigator: Dr Joana Fonseca

Description: This project looks at the change in soil microstructure around the probe during cone penetration to investigate the failure mechanism and the processes controlling drainage in silt. It uses image analysis of backscattered electron (EPMA) images of polished thin sections prepared from frozen samples. Understanding the mechanisms of grain reorientation following cone penetration can help explaining the drainage patterns controlling the cone resistance and the development of pore pressures.

Outputs: Paniagua et al. (2015)

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Researcher: Dr Sam Divall

Supervisor: Dr Richard Goodey

Description: Therefore, a series of plane strain centrifuge tests was carried out investigating twin tunnelling-induced settlements in overconsolidated clay. Apparatus necessary to perform these tasks required a significant amount of time to develop and was relatively complex. The main variables were the spacing between the tunnels, both horizontally and vertically, and the magnitude of volume loss. The tests were conducted at 100g where the cavities represented two 4m diameter tunnels at (usually) a depth of 10m at prototype scale. The tests utilised novel apparatus designed during the research to enable the simulation of the construction processes related to volume loss in separate sequential tunnels.

Outputs: Divall & Goodey (2012), Divall et al. (2014), Divall & Goodey (2015), Divall et al. (2017a) & Divall et al. (2017b)

Researcher: Dr Rohit Gorasia

Supervisor: Dr Andrew McNamara

Description: This research concerns the influence of ribs on the ultimate capacity of a bored pile in overconsolidated clay. Ribbed bored piles are known to give increased shaft capacity in comparison to conventional straight shafted bored piles.  Experimental data were obtained from a series of 23 centrifuge model tests undertaken at 50g. The geometry of the model was such that it was possible to test two piles with each test. Of the two piles tested one was always a plain pile, this allowed for direct comparison to the ribbed pile in the same test and hence any inconsistency in the soil sample to be accounted for. The performance of several rib designs and spacings were investigated, whilst the pile inner diameter and length remained constant. A series of datum tests were conducted to verify the accuracy and repeatability of the testing equipment. Four rib types were tested; concentric ribs, helical ribs, tapered ribs and under reamed ribs. The use of ribs was found to always increase the ultimate capacity of a pile. Of all the rib profiles tested the helical profile was shown to be the most effective.

Outputs: McNamara & Gorasia (2016)