Design of Foundations and Anchors in Rock for Offshore Wind Energy Systems

Offshore wind farms typically comprise arrays of fixed-base structures supported by piled foundations embedded in sand or clay soils. Future planned developments in European coastal waters include sites where the bedrock is close to the seabed surface. At such sites, piled foundations are installed by drilling and grouting. For deep water sites, future developments involving floating offshore wind systems are envisaged; floating wind systems typically require anchors to moor the system to the seabed.
Much of the recent offshore wind farm development in European waters has exploited sites where the soils (sand and/or clay) are suitable for piled foundations to be installed by percussion methods. Over the last decade or so, considerable experience has been accumulated on the design and installation of foundations for sites of this type. There is much less accumulated knowledge on the design of foundations/anchors for sites where the bedrock is close to the seabed surface; such sites are therefore often considered to be relatively unattractive. New design procedures are therefore needed to facilitate the further expansion of offshore wind generation to sites where installation of foundations/anchors into rock is required. The current project will contribute directly to this need.
The design of foundations and anchors for offshore wind turbine structures requires a range of design cases to be addressed. Procedures are needed to ensure that the stiffness of the foundation/anchor system lies within appropriate bounds to ensure that the dynamic performance of the overall structure is adequate. It is also necessary to ensure that the strength of the foundation/anchor is sufficient to withstand foreseeable storm loading conditions. Considerations are needed on the risk of fatigue failures within the steel supporting structure and on ensuring that accumulated foundation deformations (due to prevailing wind and wave conditions) are kept within defined bounds. The current project will deliver design procedures that will support the specification of structures and foundations that satisfy these design constraints.
In the initial stages of the research the project will involve the development of 3D finite element models of the performance of anchors and piles embedded in rock. Studies will be conducted on appropriate constitutive models to represent the behaviour of the rock and grout. For practical design activities, 3D finite element analysis has the disadvantage that the calculations often require lengthy run times. New alternative design models will therefore be developed that facilitate rapid design calculations. These models will be based on a one dimensional (1D) finite element framework in which the pile or anchor is modelled as an embedded beam. The 1D model will be calibrated using a limited number of more detailed finite element analyses. Initial work will focus on monotonic loading, but the project may also consider cyclic loading effects.
This project falls within the EPSRC 'ground engineering' and 'structural engineering' research areas. The research is also related to the 'wind power' research area.
The project is being conducted in collaboration with Geowynd (a specialist engineering consultancy).

This outward-facing doctoral training centre will create impact through knowledge enhancement and leadership development which will have significant benefit for society, people and the economy.

Societal Impacts:
A very large increase in renewable energy generation, mainly wind, wave and tidal, is expected in the coming years and decades to meet the UK Government and international obligations to reducing greenhouse gas emissions by at least 80 per cent by 2050 when compared to 1990 levels. In particular, the Offshore Wind Industry Council is proposing, under a Sector Deal, to deliver 30GW of offshore wind by 2030 and 50GW by 2050, whilst reducing the average price of electricity by 18%. The longer term societal and economic impacts arise from the difference that the CDT programme and its graduates make to the UK realising this medium-term and longer-term target. The societal impact of meeting these targets, over failing to meet them, can be calculated in avoided CO2, increased sustainability, security and resilience of the energy system in a safe, affordable and environmentally sensitive manner.

People Pipeline and Skills:
There is a widely recognised skills gap in renewable energy both in UK and Europe. Hence, the proposed CDT is timely contributing significantly to meeting the sector's skills demand by the provision of highly trained engineering leaders, expert in a broad range of wind and marine energy technologies and engineering. Most of the CDT graduates will be expected to take up posts in the growing commercial wind and marine energy sectors, and quickly rise to positions of leadership and influence. Some graduates will remain in the higher-education sector and develop academic careers providing much needed increased capacity and capability resulting in a positive impact through an expanded research-base and capability to deal with the inevitable research challenges of the sector as it develops further commercially.

Students will be mentored and encouraged to take a proactive role in creating impact with their research whilst observing Responsible Research and Innovation (RRI). All the Universities participating in this CDT proposal have explicit policies and resources in place to support knowledge exchange and impact and also public engagement. These support the students throughout their studies to engage in broader dialogue and deliberation and to be aware of the potential impacts and implications of their research.

Our CDT students will also engage in outreach activities and impact the wider community through the well-established Professional Engineering Training Scheme (PETS): this scheme is managed and directed by the students and provides opportunities to engage in outreach activities and to work with peers. e.g. PETS runs a schools and colleges programme wherein the students organise visits to schools and colleges to provide information about renewable energy and a basic introduction to the technology involved.

Economic Impact:
The low-carbon and renewable energy sector is estimated to increase five-fold by 2030, potentially bringing two million jobs to the UK. In particular, an ambitious Sector Deal for industry proposed by Government as part of its Clean Growth Strategy could see a total installed capacity of 30 GW of offshore wind by 2030 with the potential to create at least 50,000 jobs across the UK. If achieved, this would be a six fold increase from the current installed capacity and would make offshore wind the largest source of domestic electricity. To ensure resilience, it is also important to retain and develop the leading UK Wave and Tidal position. With the direct and indirect value added to the UK supply and installation chain in terms of job creation, intellectual property exploitation, and sales of wind, wave and tidal technology and services, the proposed CDT will make an important contribution through knowledge enhancement and leadership development.