Mechanism of mooring line breakage of floating offshore wind turbine under extreme coherent gust with direction change condition

Abstract

With an extreme load condition, the mooring system of a floating offshore wind turbine (FOWT) will be led to failure, such as mooring line breakage. However, the induced FOWT mooring line breakage in extreme gust still requires further study for design optimization in the future. In this paper, an aero-hydro-cable-servo time domain coupled simulation have been carried out of a NREL’s 5 MW OC4-DeepCwind semi-submersible type FOWT for investigate the mooring system response under extreme coherent gust with direction change (ECD) condition. The platform is assumed to be installed at 50 m depth location in the South China Sea. The practical ECD is simulated by a fast conversion between two wind conditions with different mean wind speeds and wind direction. In addition, the gust characteristics that can generate snap tension of mooring lines were identified, and the consequence of the induced ECD accident is investigated. ECD condition with rise time of 10 s is prone to cause a snap tension of the mooring line, and it may eventually lead to cascading mooring line breakage and potential catastrophic collision events.