Dynamic cable motion characterisation for FOWT

Project Description:

This Research Project is part of the Aura CDT’s dynamic cable motion prediction and monitoring for floating offshore wind turbines Cluster.

Wind power stands as one of the swiftly expanding technologies within the realm of renewable energy. As noted in the quarterly report from Drax Electric Insights, it has now ascended to become the foremost contributor to power generation capacity in the UK. Nevertheless, the present landscape sees approximately 90% of offshore wind energy harnessed through stationary bottom-mounted wind turbines. This has led to a scarcity of available space for fresh installations. Floating Offshore Wind Turbines (FOWT) represent a unique opportunity for the Northeast and Scotland, since deep (>100m) offshore areas represent 80% of the offshore wind potential. However, the sector faces two main challenges: high costs for installation and maintenance, as well as a lack of skilled human resources.

Given the harsh environmental conditions prevailing in distant offshore regions, the floating structure of FOWTs is subjected to immensely dynamic forces arising from the interaction of tides, waves, and winds. Consequently, the design of the floater necessitates a flexible attachment through the employment of a mooring system. For instance, the range of the excursion motion alone on Spar or semi-submersible type of floater can reach an order of magnitude of 10 meters. This requires that the electrical cables, which transmit power form FOWT to the substation inland, need to be sufficiently dynamic to withstand the motion of the floater. This is usually realised by buoyancy modules installed in the middle part of the cable length (lazy wave type) so that the entire cable is neutrally buoyant in seawater. These long and flexible cables however are continuously subjected to bending and twisting forces, etc., caused by the tidal current and floater behaviour; therefore, they are likely to suffer mechanical damage in various sections, according to the mounting method and the modes of the induced motion on the cables.

In order to enhance the efficiency of cable installation strategies and reduce maintenance expenses, a profound understanding of cable dynamics within the local underwater environment is essential. However, comprehending their motion is a highly intricate endeavour due to the multifaceted influence of wave and tidal forces, as well as their intricate interaction with both the continuously moving six-degree-of-freedom floater structure and the seabed. Presently, cable installation follows the established standards of the Oil & Gas industry. However, the current landscape lacks a dedicated industry standard tailored for FOWTs or any functional model that can furnish the sector with insights into the intricate behaviour of dynamic cables. Therefore, development of a high-accuracy model to predict the cable motion and curvatures, specific to FOWT and for a variety of hydrodynamic and environmental loadings, becomes imperative to inform applications like cable ancillary hardware designs.

Within this PhD project, we aim to perform high-fidelity computational simulations to characterise highly dynamic motion of the dynamic cable, starting from the lazy wave type, for a single Spar and a semi-submersible type FOWT installation, properly verified by available observation data, working for simplified but realistic hydrodynamic loading conditions. We will then derive a low-order model based on the simulation results suitable for multiple turbine applications. From these, we will equip the PhD student with state-of-the-art subject knowledge and research skills, as well as sufficient research training, for them to contribute to the offshore wind sector for their future career.