Floating offshore wind turbine (FOWT) deployments are predicted to increase in the future and the outlook is that globally, 6.2 GW of FOWTs will be built in the next 10 years (https://tinyurl.com/camyybxk). Highly dynamic, free hanging power cables transport power generated by these FOWTs to substations and the onshore grid. Safety critical design of such power cables in order for them to operate in the ocean without failure is of utmost importance, given that these cables are highly expensive to install and replace and any down-time of turbine electrical output results in huge revenue loss. In FOWTs, a large length of the power cable, from the base of the floating foundation to the seabed, is directly exposed to dynamic loading caused by ocean waves, currents, and turbulence. Waves move the floating foundation, and currents produce cable oscillations generated by vortex shedding. In the water column a cable experiences enhanced dynamic loads and undergoes complicated motions. When a dynamic cable is installed in deep water, the upper portion of the cable is exposed to high mechanical load and fatigue, and the lower part to substantial hydrostatic pressure. Motion of the floating foundation in surge, sway, and heave causes the power cable to undergo oscillatory motions that in turn promote vortex-induced vibration (VIV) - which is analogous to the vibration experienced by long marine risers used in offshore oil and gas platforms. As a result, large and complex deflections of the cable occur at various locations along its length, altering its mechanical properties and strength, and eventually leading to fatigue-induced failure. The dynamic forces produce cyclical motions of the cable, and a sharp transition in cable stiffness is expected in cases where these motions and loads concentrate toward a rigid connection point. Repetition of the foregoing process and over-bending can also lead to fatigue damage to the cable. To date, hardly any research has been undertaken to investigate the 3-dimensional nature of VIV, dynamic loads, and motion of power cables subject to combined waves, currents, and turbulence. Moreover, no detailed guidance is given in design standards for the offshore wind industry on how to predict, assess, and suppress fatigue failure of dynamic cables under wave-current-turbulence conditions. Power cable failure is much more likely to occur if the design of such cables is based on poor understanding of the hydrodynamic interactions between cables and the ocean environment. This fundamental scientific research aims to investigate the dynamic loading, motion response, impact of vortex induced vibration and its suppression mechanism, and fatigue failure of subsea power cables subjected to combined 3-dimensional waves, currents, and turbulence. This research will be approached by both numerical and physical modelling of power cable's response. Controlled experimental tests on scale models of power cables will be undertaken in Edinburgh University's FloWave wave-current facility where multi-directional waves and currents of various combinations of amplitudes, frequencies, and directions can be generated. Advanced novel phenomenological wake oscillator models, calibrated and validated with FloWave experimental results, will be used to simulate the hydrodynamic behaviour of power cables. The resulting software tools, experimental data, analysis techniques for characterising cable dynamics and VIV, methodologies established for fatigue analysis, and other outcomes of this research will enhance the design of cost-effective power cables. By reducing uncertainty, our research will lead to increased reliability of offshore power cables, of benefit to the power cable manufacturing industry.

There is a compelling need for well-trained future UK leaders in, the rapidly growing, Offshore Wind (OSW) Energy sector, whose skills extend across boundaries of engineering and environmental sciences. The Aura CDT proposed here unites world-leading expertise and facilities in offshore wind (OSW) engineering and the environment via academic partnerships and links to industry knowledge of key real-world challenges. The CDT will build a unique PhD cohort programme that forges interdisciplinary collaboration between key UK academic institutions, and the major global industry players and will deliver an integrated research programme, tailored to the industry need, that maximises industrial and academic impact across the OSW sector. The most significant OSW industry cluster operates along the coast of north-east England, centred on the Humber Estuary, where Aura is based. The Humber 'Energy Estuary' is located at the centre of ~90% of all UK OSW projects currently in development. Recent estimates suggest that to meet national energy targets, developers need >4,000 offshore wind turbines, worth £120 billion, within 100 km of the Humber. Location, combined with existing infrastructure, has led the OSW industry to invest in the Humber at a transformative scale. This includes: (1) £315M investment by Siemens and ABP in an OSW turbine blade manufacturing plant, and logistics hub, at Greenport Hull, creating over 1,000 direct jobs; (2) £40M in infrastructure in Grimsby, part of a £6BN ongoing investment in the Humber, supporting Orsted, Eon, Centrica, Siemens-Gamesa and MHI Vestas; (3) The £450M Able Marine Energy Park, a bespoke port facility focused on the operations and maintenance of OSW; and (4) Significant growth in local and regional supply chain companies. The Aura cluster (www.aurawindenergy.com) has the critical mass needed to deliver a multidisciplinary CDT on OSW research and innovation, and train future OSW sector leaders effectively. It is led by the University of Hull, in collaboration with the Universities of Durham, Newcastle and Sheffield. Aura has already forged major collaborations between academia and industry (e.g. Siemens-Gamesa Renewable Energy and Orsted). Core members also include the Offshore Renewable Energy Catapult (OREC) and the National Oceanography Centre (NOC), who respectively are the UK government bodies that directly support innovation in the OSW sector and the development of novel marine environment technology and science. The Aura CDT will develop future leaders with urgently needed skills that span Engineering (EPSRC) and Environmental (NERC) Sciences, whose research plays a key role in solving major OSW challenges. Our vision is to ensure the UK capitalises on a world-leading position in offshore wind energy. The CDT will involve 5 annual cohorts of at least 14 students, supported by EPSRC/NERC and the Universities of Hull, Durham, Newcastle and Sheffield, and by industry. In Year 1, the CDT provides students, recruited from disparate backgrounds, with a consistent foundation of learning in OSW and the Environment, after which they will be awarded a University of Hull PG Diploma in Wind Energy. The Hull PG Diploma consists of 6 x 20 credit modules. In Year 1, Trimester 1, three core modules, adapted from current Hull MSc courses and supported by academics across the partner-institutes, will cover: i) an introduction to OSW, with industry guest lectures; ii) a core skills module, in data analysis and visualization; and iii) an industry-directed group research project that utilises resources and supervisors across the Aura partner institutes and industry partners. In Year 1, Trimester 2, Aura students will specialise further in OSW via 3 modules chosen from >24 relevant Hull MSc level courses. This first year at Hull will be followed in Years 2-4 by a PhD by research at one of the partner institutions, together with a range of continued cohort development and training.