Modeling a non-linear mooring system for floating offshore wind using a hydraulic cylinder analogy

Abstract

The mooring system for a floating offshore wind turbine is a critical sub-system that ensures the safe station keeping of the platform and has a key influence on hydrodynamic stability. R&D efforts have increasingly explored the benefits of non-linear mooring systems for this application, as they have the potential to reduce the peak mooring loads and fatigue cycling, ultimately reducing the system cost. This paper reports on a hydraulic based mooring component that possesses these characteristics, attributable mostly to the non-linear deformation of a flexible bladder. This is not a typical hydraulic component and, as a consequence, modeling its dynamic performance is non-trivial. This paper addresses this by introducing an analogy to numerically model the system, in which the functionality of the mooring component is compared to that of a hydraulic cylinder. The development of a working model in Simscape Fluids is outlined, and is subsequently used to simulate the IMS in a realistic environment. It is found that the numerical model captures a number of the dynamic performance characteristics observed in a previously tested prototype of the IMS.