Anchor Loads for Shallow Water Mooring of a 15MW Floating Wind Turbine - Part I: Chain Catenary Moorings for Single and Shared Anchor Scenarios

Abstract

Floating offshore wind turbines are characterised by complex coupled dynamics between the floating structure and turbine. These are subjected to a combination of aerodynamic, hydrodynamic and servo-dynamic loads which must be quantified when considering the requirements of a mooring and anchoring system. If suitably engineered, shared anchors enable reduced hardware and installation costs for floating wind turbines. This paper presents the results of coupled dynamic simulations, evaluating single and shared anchor loads for different mooring configurations considering the IEA 15 MW turbine and VolturnUS-S reference platform subjected to environmental loads representative of the Celtic Sea. Simulations highlight that increasing the mooring footprint in shallow waters can reduce loads by up to 56% and through anchor sharing, peak loads can be reduced by 67%. The advent of anchor sharing, however, significantly alters the directionality of the applied loads. Misalignment of wind and wave conditions is also shown to have a considerable impact on anchor loads highlighting the importance of considering operational and parked design load cases, with wind and waves propagating from a range of directions, to adequately design and optimise a mooring and anchoring system. This paper will inform mooring and anchor design optimisation for large-scale floating wind turbines.