Over the next decades, there will be a huge expansion of offshore renewable energy facilities to add electricity to the grid and reduce greenhouse gas emissions around the world. Globally, an estimated 17% annual growth from 22 GW to 154 GW in total installed offshore wind power capacity will be seen by 2030. The UK's Offshore Wind Sector Deal (2019) also sets out a goal for the offshore wind sector output being 30 GW by 2030. To meet the ambition of offshore wind energy exploration, it is of great importance to design cost-efficient foundations which, due to the complexity of subsea soil behaviour, remains a major challenge. Offshore foundation designs are well known to be conservative, which has led in part to the foundations accounting for 25-34% of the overall budget of offshore wind farms. The design of offshore foundations is particularly difficult for carbonate soils which cover roughly 35% of the ocean floor because (1) the complex mechanical behaviour of carbonate soils for which a reliable constitutive model is yet unavailable and (2) carbonate soils around foundations often experience large deformations, such as during foundation installation, leading to significant changes of their properties which are difficult to evaluate using traditional finite element techniques. The research proposed in this project aims to develop advanced computer models capable of predicting the mechanical response of carbonate sands at offshore foundations from the installation stage to the operational stage. This will be achieved by developing a novel numerical approach called the particle finite element method (PFEM), for analysing large-deformation soil-water-foundation interactions, and a self-learning simulation framework based on advanced deep-learning techniques for training data-driven constitutive models for carbonate sands. The developed PFEM with the trained data-driven constitutive model for modelling the responses of carbonate sands at offshore structure foundations will be validated under both standard laboratory conditions and high gravity centrifuge testing conditions. The success of the proposed research will not only improve our understanding of the behaviour of carbonate sands surrounding offshore foundations but also provide engineers with a robust open-source computer tool to analyse interactions between submerged carbonate sands and foundations with large deformations and help achieve cost-effective foundation solutions for offshore renewable energy developments.

The proposed research aims to develop an innovative mitigation device to protect the next-generation onshore and offshore wind farms from dynamic loading caused by extreme natural events. In 2020, 20% of the UK's electricity was obtained from wind using both onshore and offshore windfarms. In order to increase this percentage and help the UK address its climate change target, new wind farms, with taller and larger wind turbines, and situated in more extreme locations are planned. Projections of growth also indicate the expansion into emerging markets and construction of new wind farms in developing countries. Therefore, these next-generation wind turbines will have to cope with harsher climate conditions induced by stronger storms and taller sea waves, and extreme events such as earthquakes and tsunamis. Several simplifying assumptions used for the design of previous generations of wind turbines can no longer be applied and new critical factors and uncertainties linked to power-generation efficiency and structural safety will emerge, affecting their resilience and life-cycle. The particular area of focus of this research is the traditional transition piece of a wind turbine, which is a structural element that connects the tower with its foundation and will have to tolerate extreme stresses induced by dynamic loading during extreme natural events. The aim is to replace the traditional connector with a novel mechanical joint of hourglass shape, termed an Hourglass Lattice Structure (HLS). This innovation will combine the unique features of two proven technologies extremely effective in seismic engineering, namely the "reduced beam section" approach and the "rocking foundation" design. In particular, the proposed HLS device, because of its hourglass shape, will facilitate the rocking behaviour in order to create a highly dissipating "fuse" which will protect the wind tower and foundation. Performance of the novel proposed device on the structural life-cycle risk will be assessed through analytical, numerical, and experimental investigation by using, as a measure of efficiency, the levelized cost of energy (LCOE), namely the cost per unit of energy based on amortized capital cost over the project life. In addition, experimental testing of offshore small-scale wind turbines will be carried out by means of an innovative test rig, the first-ever underwater shake-table hosted in a hydraulic flume that will be deployed, calibrated, and used to simulate multi-hazard scenarios such as those recently discovered and dubbed "stormquakes". The successful outcome of this timely project will allow next-generation wind turbines to be more resilient and cost effective so that wind energy can develop as a competitive renewable energy resource with less need for government subsidy. The inclusion of industrial partners in all stages of the project ensures that the technical developments will be included in commercial devices for a medium-long term impact.