Numerical simulations of floating offshore wind turbines with shared mooring under current-only conditions

Abstract

In recent years, with the continuous development of offshore wind power, reducing construction costs has become one of the key issues. Among them, the mooring system cost accounts for about 20%–30 % of the entire floating offshore wind turbine investment. The concept of shared mooring systems can potentially reduce the cost of floating offshore wind farms (FOWF). In this paper, research is carried out on the dynamic response of an FOWF under representative current conditions of the South China Sea. The comparative analysis focuses on the motion response of a single-spar Floating Offshore Wind Turbine (FOWT)and a dual-spar FOWF. A sensitivity analysis was performed on the length of the shared mooring line. The NREL 5-MW wind turbine with a spar platform is taken as a basis FOWT model for this work. The frequency-domain hydrodynamics is computed based on potential flow theory. The time domain analysis was simulated in a software for marine operations: SIMA(DNV). The viscous effect on the floater is modeled by the drag term in Morison's equation and the hydrodynamic force acting on the mooring line is computed using Morison's equation. Based on the finite element method, the mooring line is defined by a sequence of segments with homogeneous cross-sectional properties. The result shows that with the increase of the current return period, the two platforms move synchronously, and the movement increases almost linearly. Moreover, the motion response of the shared mooring platform is smaller than that of the single mooring platform under the same conditions, especially in the vertical direction. This paper contributes to improved fundamental understanding of shared mooring systems under complex marine environmental loads.