Coupled dynamics analysis of floating wind turbine mooring system under extreme operating gust

Abstract

Extreme operational gust (EOG), defined by sudden increases in wind speed, is one of the most hazardous situations for wind turbines and the mooring system. A coupled aero-hydro-servo-elastic simulation model is developed using a dynamic link library and a reserved interface between the upper wind turbine and the platform with the mooring system. The blade element momentum (BEM) theory, potential flow theory and lumped-mass model is used to simulate the aerodynamic loads, hydrodynamic forces and mooring tension. The motion response and mooring tension of the OC4-DeepCwind FOWT under EOG are calculated, and the effects of different gust durations and gust amplitudes on the response of the FOWT system are analyzed. It has also been discovered that when gusts and waves cooperate on the FOWT, impact tension occurs in the mooring line, which can cause line breakage. The 107 s interval preceding the peak mooring tension post-EOG emergence presents an opportune moment for an emergency shutdown, with the potential to mitigate maximum tension by 20–42 %. A mooring line break induced by EOG will result in long-distance drift, and a significant reduction in the safety factors of the remaining mooring lines could lead to subsequent breaks. An emergency shutdown following a mooring line break can prevent successive mooring line breaks and limit long-distance drifting. The above study is intended to serve as a reference for future research into the motion performance of the FOWT mooring systems under extreme sea states.