Numerical modelling and field testing of a pneumatic mooring damper for application in floating offshore wind

Abstract

The cost associated to mooring systems of floating offshore wind (FOW) turbines can be reduced by introducing innovative components that lower the design load requirements. An ideal FOW mooring system must possess sufficient stiffness to maintain station-keeping whilst providing the necessary compliance to dampen peak loads. The Intelligent Mooring System (IMS) is a component that provides this combination of desirable stiffness characteristics; it demonstrates a nonlinear stiffness response that not only reduces mooring loads but also loads transferred to other components and subsystems of the turbine. This results in providing an opportunity to reduce the load capacity and associated cost of the mooring system.

The key innovation, performance and reliability aspects of the IMS have been physically proven in previous experimental work. This paper presents the results of a numerical modelling study to develop the IMS to Technology Readiness Level (TRL) 6, that is, a demonstration in relevant environment. The IMS is integrated into the mooring system of the IEA 15-MW FOW reference turbine in OrcaFlex using a stiffness profile based on physical lab testing. Coupled hydro-aerodynamic simulations are used to highlight the load reduction potential offered by various configurations of the IMS in different water depths. The results of this study confirm that the load reduction potential of the IMS is larger in shallow water at rated wind speeds relative to deep water sites or extreme weather conditions. The IMS demonstrates a maximum reduction of up to 20%, indicating the possibility of lowering the design requirements for other mooring components leading to cost saving benefits. The paper will be of interest to practitioners and researchers tasked with the design, analysis and installation of mooring systems for floating wind.