Engineers Australia

2021 Tasmania International Symposium

Offshore Geotechnical Engineering: Challenges in Wind, Wave and Tidal Renewable Energy

Keynote Speakers: Barry Lehane, Yinghui Tian, Conleth O’Loughlin, Leung Chun Fai, Ana Page, David White, Amin Barari and Britta Bienen

Symposium Overview

The offshore wind, wave and tidal energy sector is booming globally. Tasmania is now one of only a few places worldwide entirely powered by 100% renewable energy, with the state expecting to reach 200% by 2040. Tasmania’s ocean, tidal, and offshore energy resources are key in moving towards a fully self-sufficient, fully-green energy supply.

From a structural engineering point of view, offshore engineering developments have led to durable and cost-effective construction materials for tidal wave, and reliable anchoring and mooring systems. Geotechnical engineering considerations remain of prime importance for all offshore foundation structures and continue to present a wide variety of challenges for practitioners and researchers.

This symposium presents an overview of current state-of-the-art practices and innovations. This includes new research, case studies and advanced technologies, as well as reliability, safety, and observational design, highlighting the current and future development of international projects. The symposium brings together professional engineers, researchers and industrial specialists to discuss their experiences in offshore geotechnical engineering for the renewable energy sector.

Schedule

StartFinish
AGS Chapter Chair, Symposium Introduction
Ali Tolooiyan
University of Tasmania
15:4015:50
AGS Chapter Secretary, Symposium Introduction
Ashley Dyson
University of Tasmania
15:5016:00
Barry Lehane
Univeristy of Western Australia
16:0017:00
Yinghui Tian
University of Melbourne
17:0018:00
Conleth O’Loughlin
University of Western Australia
18:0019:00
Leung Chun Fai
National University of Singapore
19:0020:00
Ana Page
Norwegian Geotechnical Institute
20:0021:00
David White
University of Southampton
21:0022:00
Amin Barari
Alborg University
22:0023:00
Britta Bienen
University of Western Australia
23:0000:00

Presentation Breakdown

Presentation: 40 minutes
Question and answers: 15 minutes
Break before next presentation: 5 minutes

Keynote Speakers

Barry Lehane Professor, School of Civil, Environmental and Mining Engineering, University of Western Australia

“A Simple Rotational Spring Model for Laterally Loaded Rigid Piles in Sand”

Abstract

Monopiles are the most popular foundation for offshore wind turbines. These foundations typically have a low length to diameter ratio and undergo a rigid body rotation when subjected to lateral load. This presentation presents results from an extensive numerical investigation involving 3D finite element analyses to demonstrate that a monopile response in sand can be represented using a single non-linear rotational spring located at a depth of about 0.75 times the pile embedment. Expressions for the elastic response of a monopile under very low rotations are developed and these combined with observations from measured non-linear variations of rotational stiffness, that are supported by the numerical analyses, are used to develop a simple approximate expression that can be used to determine the response of a monopile to a monotonic lateral load in sand.

Biography

Professor Barry Lehane has worked as a practitioner and academic in geotechnical engineering since 1984. Barry obtained his Civil Engineering degree from University College Cork in Ireland and then worked with Arup Geotechnics in London until he began his PhD at Imperial College, London in 1989. Following completion of his PhD in 1992, he again worked with Arup in London and Hong Kong before taking up a lecturing position at Trinity College in 1994. He moved to Perth in 2002 and has remained as a Professor at the University of Western Australia since then. Barry has published more than 250 technical papers in international journals and conferences, and he continues to consult widely on a wide variety of national and international projects.

Yinghui Tian Associate Professor, Department of Infrastructure Engineering, University of Melbourne

“Geotechnical behaviour of offshore plate anchors and moorings”

Abstract

With offshore renewable industry going into deep water, floating turbines are being used. This requires secure and efficient mooring and anchoring of the floating facilities. The knowledge of anchoring systems obtained from the traditional oil and gas development is reviewed in this presentation. Detailed finite element study of chain link is presented and a long chain analysis progress is developed. Large deformation of anchor installation is also discussed to provide insight for anchoring solution for offshore renewables.

Biography

Yinghui Tian is an Associate Professor at the Department of Infrastructure Engineering of the University of Melbourne. Prior to his appointment at Melbourne, he had a ~12 year research experience at the Centre for Offshore Foundation Systems (COFS) of the University of Western Australia. He was recently awarded the prestigious Australian Research Council (ARC) Future Fellowship to support his cutting edge research in offshore anchoring systems and renewable energies. He has been working in he area of offshore geotechnics to convert the innovative research outcomes to engineering practice and design. This includes the two suites of computer software (UWAINT and CASPA, developed together with Prof Mark Randolph and Mark Cassidy). The UWAINT package is licensed to JP Kenny and Technip for dynamic stability analysis of offshore pipelines of Australian North West Shelf projects. The CASPA (Chain And SEPLA Plasticity Analysis) program is licensed to industry leader ExxonMobil to analyse the anchoring solutions for floating platforms in ultradeep (>1000 m) water. He is the recipient of the Institution of Civil Engineers (ICE) David Hislop Award for the best paper on offshore engineering in 2017. He is currently the associate editor of ASCE Journal of Pipeline Systems Engineering and Practice.

Conleth O’Loughlin Associate Professor, Centre for Offshore Foundation Systems, University of Western Australia

“Allowing for seabed strength changes in the design of foundations for offshore  renewable energy devices”

Abstract

As for oil and gas floating facilities, floating offshore renewable energy devices require moorings and anchors to keep them on station. However, floating offshore renewable energy devices are much more dynamic structures than floating oil and gas facilities, such that the anchors experience many more loading cycles over their lifetime. Although cyclic loading induces excess pore pressures that reduce soil strength, over time consolidation causes soil strength to increase, potentially to values that are higher than the initial strength. There is an appetite for realising these strength changes in the design of an offshore floating renewable energy device as the cost of the anchors and mooring system is a relatively high proportion of the installed cost, and the consequences associated with a geotechnical failure event are much less severe than for an oil and gas facility. This presentation discusses penetrometer testing protocols that can be used to detect these strength changes, provides examples of where these strength changes have been observed via changes in system capacity and describes a digital twin approach that can be used to calculate these capacity changes for a given time history of loading.   

Biography

Conleth O’Loughlin is an Associate Professor at the Centre for Offshore Foundation Systems at the University of Western Australia and is the Director of the National Geotechnical Centrifuge Facility. He received his Civil Engineering Degree from The Queen’s University of Belfast in 1997 and his PhD from Trinity College Dublin in 2002. His research interests include anchoring systems, penetrometer testing and foundation response of offshore wind turbines. He has published over 150 technical papers, which have received 4 paper awards, the most recent of which is the 2021 Telford Gold Medal awarded by the ICE in the UK. He is an Associate Editor for Géotechnique Letters and is the Chair of the Editorial Board of the International Journal of Physical Modelling in Geotechnics.

Leung Chun Fai Professor, Department of Civil and Environmental Engineering, National University of Singapore

“Offshore anchor research at National University of Singapore”

Abstract

Over the past decade, extensive research studies have been conducted at the National University of Singapore using numerical and centrifuge modelling technique. The first part of the presentation will highlight the research achievement on offshore plate anchors in uniform and normally consolidated clay. An important aspect of the centrifuge model study is the fabrication of a novel anchor installation system enabling the base of the anchor following the settling clay during the consolidation stage of the centrifuge model tests. As the anchors may not be installed in its desired orientation, the results of inclined anchors are evaluated by comparing the failure mechanism obtained from numerical predictions and centrifuge model observations. The second part of the presentation will cover the numerical modelling of drag anchors and the practical implications of the findings. The findings on the effects of anchor installation trajectory and anchor fluke angle will also be reported.

Biography

Prof CF Leung is Emeritus Professor in the Department of Civil and Environmental Engineering, National University of Singapore. His research interests include offshore and marine geotechnics. For offshore geotechnics, he had conducted extensive funded studies on jack-up spudcan foundations, offshore anchors and pipelines granted by government agencies and the industry. Prof Leung has served as an offshore geotechnical consultant for offshore engineering projects in several parts of the world, notably two spudcan-pile interaction studies, pipeline-seabed interaction, and uplift of offshore foundation. He is a member of the ISO Jack-up Panel P4 on jack-up foundation and ISSMGE TC209 Offshore Geotechnics; as well as serving as an editorial board member for offshore engineering journals.

Ana Page Section Head, Advanced Modelling, Norwegian Geotechnical Institute

“Streamlined analysis of foundations for offshore wind farms”

Abstract

The last decade has seen offshore wind become a competitive and viable energy source on an international scale. From a foundation engineering perspective, this has been driven by improving methods and tools used in the design of offshore wind turbines (OWT). Furthermore, different disciplines have become more integrated within OWT time-domain analyses used to estimate different loading scenarios. The projects REDWIN and REDWIN 2 have provided important developments for these two aspects. The REDWIN project (2015-2018) improved modelling of the foundation response within integrated dynamic time-domain analyses of OWT by developing macro-element models for typical foundation concepts. These models exhibit characteristic foundation behaviour such as nonlinearity, coupled response from different load components and hysteretic load-dependent damping. The simplicity of these models make them easily applicable in engineering practice, and they have been so far implemented in more than seven integrated OWT analysis tools. The REDWIN 2 project (2019-2022) has focused on advancing and consolidating foundation engineering tools and methods, enabling foundation designers to apply recent research and development results in design practice. REDWIN 2 has developed a streamlined design process, utilising state-of-the-art tools, including intelligent ground models, clustering strategies based on the geotechnical, environmental and structural considerations, a simplified load assessment module, which can be used at an early design stage, and a foundation optimization routine incorporating all geotechnical and structural design limit states. This presentation will cover the main outcomes of these two projects, showing both highlights and plans for future activities.

Biography

Dr. Ana Page is a senior researcher and engineer at the Norwegian Geotechnical Institute, and has had the role of Section Head for Advanced Modelling since 2020. She completed her PhD in 2018 at the Norwegian University for Science and Technology in Trondheim, as part of the REDWIN project. Ana has worked across a broad range of technical applications at NGI, with a focus on numerical simulations. Ana works closely with industry stakeholders, ensuring that research results are brought into play within projects, and also enabling models to be tested and evaluated in real-world environments. This includes the implementation of the REDWIN models in the OC6 calibration project coordinated by NREL. Currently, Ana is responsible for NGI’s team within numerical modelling with activities across analysis scales from DEM/micromechanics to full-scale integrated systems such as coupling analysis and instrumentation within a digital twinning framework.

David White Professor, Dept Civil, Maritime & Environmental Engineering, University of Southampton

“Geotechnical engineering challenges at the frontiers of offshore wind”

Abstract

The expansion of offshore wind energy brings new geotechnical challenges. The UK has been at the forefront of offshore wind development, with 10 GW of capacity currently installed, representing approximately 50% of the global capacity. However, current UK government forecasts require at least 100 GW to be installed by 2050, and perhaps double this depending on the growth of a hydrogen economy. This accelerated growth, which requires venturing into new regions of ocean, raises the importance of many geotechnical challenges.  This presentation will begin by introducing the state of the UK’s offshore wind developments, alongside the required growth to meet Net Zero commitments. This will be followed by outcomes of recent research addressing four geotechnical challenges: (i) Foundation and anchoring systems for floating facilities: including research to harness whole life variations in their stiffness and capacity.  (ii) Cable integrity: including thermal interactions between buried cables and the surrounding seabed, which control the maximum power transmission. (iii) Rocky seafloors: new approaches to stabilise infrastructure on the hard seafloors found in frontier regions of offshore renewable energy. (iv) Site characterisation: rethinking offshore surveys, as we move from the single-point focus of oil and gas platforms to the distributed infrastructure of offshore wind. These examples highlight the opportunities to rethink offshore geotechnical design to suit offshore renewables, recognising the new seabed conditions, different design constraints, and the mass production aspects. The potential for innovation and new technologies also highlights the opportunity for the best future engineers to find a green career in offshore geotechnics.

Biography

David White is Professor of Infrastructure Geotechnics at the University of Southampton, UK, based at the UKCRIC National Infrastructure Laboratory.  He completed MEng and PhD degrees at the University of Cambridge, UK, then remained in Cambridge as a Research Fellow and then University Lecturer. In 2007 he was appointed Professor at the University of Western Australia in Perth, holding an ARC Future Fellowship (2009-2012) and then the Shell Chair of Offshore Engineering (2013-2017).  His research is primarily concerned with offshore energy facilities, ranging across cable, pipeline, foundation and anchoring systems as well as soil characterisation. His research has led to >350 publications, which have received 14 best paper awards and have influenced international design practice. He has authored contributions to design standards and guidelines published by DNV, ISO and the API. He is active in engineering practice, as a consultant to the offshore industry to support the transfer of research into practice. He is a Co-Director of the EPSRC Offshore Renewable Energy (ORE) Supergen Hub (supergen-ore.net), which connects the UK’s ORE research community. He has been elected a Fellow of the Royal Academy of Engineering, the Institution of Civil Engineers and the Royal Institution of Naval Architects.

Amin Barari Associate Professor, Department of the Built Environment, Aalborg University

“A Transition from conventional design of suction caissons to their performance in emerging offshore markets”

Abstract

Despite the 2011 Fukushima Daiichi nuclear power plant disaster, the number of large-scale offshore wind farms under construction is growing, in accordance with the 21st meeting of the Conference of Parties (COP 21). Skirted foundations are increasingly being incorporated into the design of offshore wind turbine structures and facilities to help them withstand combined vertical (V), horizontal (H), and moment (M) loading conditions. One of the major concerns of designing offshore wind turbine foundations is also to address the effects of cyclic loading coming from, especially, wave loading. These cyclic loads have been shown to act on surrounding soil and affect its properties. For example, these changes can potentially alter the stiffness and natural frequency of a foundation system. As a result, a shift from a design or target frequency to a value closer to forcing excitation frequencies can occur. On the other hand, as the deployment of offshore wind energy rises globally, there is the need for the appropriate sites for the installation of wind farms where energy could be generated efficiently. Many of these sites lie in regions where seismic activity presents a significant threat to stability and normal functioning of the turbines. This presentation therefore presents some critical findings regarding the Macro-Element model of an entire soil- caisson system, cyclic-loaded caisson foundations in saturated sand and the performance of caisson skirts as a liquefaction countermeasure in liquefiable soils.

Biography

Amin Barari is Associate Professor in geotechnical engineering at Aalborg University, working in the areas of offshore geotechnics and seismic response of earth systems, with focus on soil-structure interaction and consequences of soil liquefaction. Amin completed his PhD in the area of geotechnical engineering at the Aalborg University, Denmark in 2012 where he was subsequently employed as postdoc fellow until 2015. He subsequently took up postdoc position at Virginia Tech, USA after visiting research associate position at the Technical University of Denmark, in 2015. His publications have received more than 2695 citations according to Google Scholar (h-index: 32). He has also been privileged with publishing over 60 selected journal papers. He is co-founder of the Mechanical Sciences Journal sponsored by the Delft University of Technology and serves in the International Technical Committee TC209 (Offshore Geotechnics) of the ISSMGE and had also been part of organizing committee in 36th International Conference on Ocean, Offshore & Arctic Engineering (OMAE 2017, Norway), 35th International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2016, South Korea), International Conference on Ships and Offshore Structures (ICSOS), Hamburg, 2016 and Seventh International Conference on Case Histories in Geotechnical Engineering, Chicago, 2013.

Britta Bienen Associate Professor, Centre for Offshore Foundation Systems, University of Western Australia

“On the installation of offshore wind farms”

Abstract

Before offshore wind turbines can deliver green energy, these immense structures need to be placed on strong foundations. The installation of offshore wind turbine (OWT) foundations is not only challenging in terms of the remote and complex operations offshore, but also in terms of accuracy of prediction in the design phase. Site investigation data is typically obtained at turbine locations, but not within the footprint of the jack-up installer vessel that needs to provide a safe and stable working platform to install the foundations, with heavy crane lift operations concentrating forces. To address gaps in current industry guidelines specifically for jack-up wind installer vessels, a group of over 30 organisations has come together in a Joint Industry Project to produce Jack-up Renewable Energy Guidelines (J-REG). The initial contact of jack-up spudcans on the often dense sand seabed may lead to large forces transmitted to the leg-hull connection. In geotechnical terms, this requires prediction of soil-structure-interaction involving rapid shearing of saturated sand with the potential for cavitation in shallow waters. This provided the impetus to develop numerical tools on the basis of the Material Point Method, enabling soil-structure-interaction analysis featuring very large deformations, coupled pore fluid-stress response and requiring advanced soil constitutive models. Monopile installation is another example application with similar requirements, with a growing body of research highlighting the effect of the installation process on the in-service performance. Recent developments enable relevant physical evidence to be obtained from centrifuge modelling, de-risking OWT foundation installation.

Biography

Professor Britta Bienen is based at the Centre for Offshore Foundations Systems within the Oceans Graduate School at the University of Western Australia, leading research activities related to foundations for offshore wind turbines. Britta received her Dipl.-Ing. from RWTH Aachen, Germany, in 2002 and her PhD from UWA in 2008. Britta was appointed Lloyd’s Register Foundation (LRF) Chair in Offshore Foundations, leading this Centre of Excellence 2018-2020. Britta is the 2020 John Booker medal recipient, awarded by the Australian Academy of Science, for her contributions to the development of practical predictive methods for soil-structure interaction problems. She currently serves on the Australian Research Council (ARC) College of Experts (2021-2023). Britta enjoys collaboration across academia and industry and is actively involved in the development of industry guidelines, through her membership of relevant ISO committees and collaboration in Joint Industry Projects (InSafe, J-REG).

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