Offshore wind energy is becoming a major electricity provider with future expansion in deep water. Floating platforms can access water depths typically greater than 30 m, but have the disadvantage of platform motions due to combined waves and time varying thrust from turbine motion. Platform stabilisation is critically important for improving performance, reducing downtime and enabling safe access. Lost electrical output alone for a proposed 15 MW machine can be £20k per day at today's prices. Moreover, misalignment of the turbine axis with wind direction due to yaw and pitch causes power loss and undesirable blade stresses. In addition to pitch and surge in the wave direction, roll and yaw cross wave may occur due to multi-directional wave fields. Thus this project has two distinct aims both impacting on through life cost: Aim 1: to optimally minimise platform motion during power production by integrated (holistic) preview control of wave and wind effects on platform and turbines. A key reliability goal is to ensure acceleration at the nacelle due to pitch and surge is less than the recommended 0.2-0.3g, and to minimise damaging electrical surges and fatigue of structural components. Aim 2: to absolutely minimise platform motion for safe maintenance during personnel and material transfers by boat or helicopter and minimise debilitating motion effects on personnel during maintenance work. The illustrative case employed is the popular semi-sub floater concept which has comparatively shallow draft and simple deployment. Platform stabilisation will be achieved by combining: (i) pumped tank control between semi-sub columns to minimise pitch and roll as employed in ships, (ii) blade pitch control, already used in wind turbine control and (iii) yaw control for alignment with the wind direction. This multi-objective non-causal control problem requires future knowledge of both wave and wind forcing functions to achieve optimality.

Wave energy convertors (WECs) offer opportunities for niche (powering aquaculture and offshore stations) and grid-scale applications. However, disruptive innovation is essential to unlock the potential of wave energy, achieve step change reduction in cost of energy, and prove competitiveness against other renewable energy options. Here we investigate the opportunity to transform the development of WEC systems by utilising intelligent design concepts that exploit novel use of deformable materials. WECs based on deformable materials may offer improved performance, survivability, reliability, and reduced cost compared with steel or concrete alternatives for the following reasons: 1. To achieve a given resonant frequency, a flexible fabric device can be smaller and lighter. 2. Hydrodynamic characteristics of such a device can be modified by controlling its internal fluid pressure, enabling it to be tuned to suit incident wave conditions. These adjustments can be made by an on-board intelligent responsive system. 3. Controlled non-linear changes of geometry would enable a deformable fabric structure to accommodate or shed high loads without reaching critical stress concentrations, improving survivability and reducing installation and lifetime costs. 4. Flexibility opens up the possibility to use a range of PTOs, such as novel distributed embedded energy converters (DEECs) utilising distributed bellows action, electro active polymers, electric double layer capacitors or micro-hydraulic displacement machines. 5. A lightweight flexible structure with largely elastic polymer construction is unlikely to cause collision damage, and so is therefore a low risk option for niche applications, such as co-location with offshore wind devices. The performance of flexible responsive systems in wave energy, their optimisation in operating conditions, and their ability to survive storm waves, will be assessed through a programme of wave basin experiments and numerical modelling of different flexible WEC concepts. Survivability is a critical hurdle for all WEC concepts as by their nature they need to respond in energetic sea states while avoiding critical stresses in extreme seas. For a flexible responsive structure, this means avoiding concentration of stress (naturally avoided by collapse/folding) or of strain (avoided by use of a distributed PTO during operational conditions). Numerical models will be developed that account for complex interactions between wave action, deforming membrane structure, and internal fluid. The models will be informed, calibrated, and validated using results from materials testing and fundamental hydro-elastic experiments. Advantages and disadvantages of rubber-based, polyurethane and other reinforced polymer materials will be assessed in terms of manufacturing cost, join, bonding, and fatigue performance in the marine environment. The research will draw on origami theory and the technology of deployable structures to avoid problems with wrinkling, folding, or aneurysm formation, and an entirely new design may emerge through this innovative approach. We aim to demonstrate a pathway to cost reduction for flexible fabric WECs optimising for performance, structural design and manufacture for both utility scale and niche applications.