Offshore structures, including offshore wind turbine foundations, marine renewable energy device support structures, bridge piers, and floating vessels, are routinely exposed to harsh environmental loads. These frequently drive the design. The physics and statistics of wave-structure interaction are complex and still not fully understood for strongly non-linear loads as experienced in the most severe conditions. The particular focus of this project is fixed offshore wind turbines. These are one of the most promising sources of clean energy; and central to the UK's ambitions to become carbon neutral. The price of offshore wind has fallen significantly over the past ten years. Part of this reduction has been due to improvements in technical understanding leading to less conservative designs. Recently, there has been a trend to move to more exposed and deeper water locations with 'better' wind resources. However, such locations are susceptible to more extreme wave heights and subsequently more severe loading. These changes have increased the importance of wave loading models able to give accurate predictions of base shear and moment time-series. It is important that such models predict not only the magnitude of the load but also the correct frequency content of the loading. For instance, a large slamming load may be of sufficiently short duration that the load is not simply transmitted to the foundation. Further, structures are typically designed so as to avoid the natural frequency of the storm waves. However, if loading was to occur at higher harmonics of the fundamental wave frequencies these may coincide with the structure's natural frequencies, thus greatly increasing their importance for design. For structural fatigue assessment very long time series are required. Therefore, experimental and high-fidelity numerical models are too resource-intensive to be directly useful for practical engineering calculations. A highly efficient yet still sufficiently accurate alternative is required. The physics of wave loading is typically split into non-breaking and breaking loads. These have different magnitudes and timescales as they are dominated by different physical phenomena. For non-breaking waves, traditionally the Morison equation has been widely accepted as the starting point for calculating wave loading on offshore structures by most modern design standards. For slender cylinders in the inertia regime such as the monopiles used for offshore wind, extensions have been made to the Morison model, taking wave kinematics as inputs. Predicting wave kinematics is itself a difficult task, particularly for severe yet random sea-states where both standard regular wave stream function theory and 2nd order random wave theory are imperfect models. Breaking waves are notoriously difficult to model numerically and to measure experimentally due to the violence of the hydrodynamics and scaling issues. Various models have been proposed to simulate the time history of the loading. However, when calculating extreme responses and foundation reactions for dynamically sensitive structures, it is generally sufficient to know the total applied impulse (and where it acts) for impact loads rather than the exact time-history. Estimating the impulse is far more robust, quicker and the physics can more easily be modelled. We aim to revolutionize load calculations on offshore structures using novel fluid mechanics to develop fast reduced-order engineering models. While the focus of this work will be examining the impact of extreme wave loading on offshore wind turbine foundations, the ideas and tools generated will be more broadly applicable. We will develop a computationally fast method and an open source tool to be used by practicing engineers in industry to model long-term cyclic loading, leading to more efficient designs of offshore structures, reducing construction cost whilst preserving function and reliability.

This project will enhance the design and development of floating offshore renewables, in particular offshore floating wind as commercially viable electricity infrastructure through a risk based approach allowing to build resilience against extreme events. The socio-economic challenge is the increasing energy need in emerging economies, such as China, which causes grave air pollution and CO2 emissions. The project work focusses on China, where heavy air pollution alone is estimated to have caused 2.2million premature deaths. Sustainable energy generation, thus replacing coal-fired power plants is one of the solutions to address this problem. In China specifically, the energy demand is at its highest along the industrialised and densely populated coastal regions. The challenge for a renewable energy supply is that the solar, wind and hydro resource are primarily located in the NW and SW of China and electricity transmission via the grid is already constrained. The Chinese government therefore has identified offshore wind energy as one of the primary energy resources with a potential of over 500GW of installed capacity, capable to produce up to 1,500 TWh of electricity per year, which would offset as many as 340 coal-fired power stations. Whilst initial installations in shallow waters near the coast have been made, over 1/3rd of the resource is located in deeper water (>40m) and will require floating installations. Offshore wind energy generation is currently more expensive than fossil fuels in China, and the risk of typhoon damage is high. The project has a fourfold approach: 1.Enhanced environmental modelling to accurately determine extreme loadings; 2. Assessment of novel, porous floating offshore wind structures and active damping mechanisms; 3. Enhanced numerical modelling techniques to efficiently calculate the complex coupled behaviour of floating wind turbines; 4. Risk based optimisation of devised designs and engineering implications. This combined approach is carried through distinguished scientific research expertise and leading industry partners in the field of offshore wind. To maximise the impact and benefits of this research the project places large emphasis on knowledge exchange activities, industry liaison and the establishment of cross-country research capacity to foster the global commercial realisation of offshore floating wind energy. The project is an interdisciplinary, cross-country collaboration with leading research Universities and industry partners. The academic expertise from the University of Exeter, the University of Edinburgh and University of Bath in the areas of Environmental assessment and modelling, Hydrodynamic design, Advanced computational modelling and risk based reliability engineering is matched with Dalian University of Technology and Zhejiang University as two of the leading Chinese research institutions in Ocean Engineering and Offshore Renewable Energy. Whilst the project carries out fundamental engineering research, strong industrial partnerships in both countries will facilitate industry advice and subsequent research uptake. The strong industrial UK support for this project through the ORE Catapult, DNV-GL, ITPE is matched with wider international support through EDF (France) and DSA (Canada), as well as the Chinese project partners MingYang Wind Power Ltd (3rd largest wind manufacturer in China), the National Ocean Technology Centre, NOTC, (institutional responsibility for marine spatial planning) and the 'Shanghai Investigation, Design & Research Institute', SIDRI (State-owned offshore wind project developer in China), demonstrates the timeliness and industrial relevance of the proposed research. All partners are committed to support the establishment of a long-lasting research base to develop resilient and cost effective offshore floating wind energy systems through collaborative research and innovation efforts, as well as capacity building and knowledge exchange.