Time-domain Coupled Analysis Of Dynamic Response Of Floating Offshore Wind Turbine

Floating offshore wind turbine (FOWT) is a major way for development of offshore wind turbine in the future. With extremely complicated stresses in actual sea environment, it is easy to cause danger. FOWT will suffer effects from wind, wave and mooring lines at the same time during operation, and these loads will form a coupled effect with motions of the floating body. So it is very important to do coupled analysis for its dynamic responses.A coupled time-domain calculation model for dynamic response of FOWT is established in this paper. Mainly includes aerodynamic, hydrodynamic, mooring and system motion modules. In aerodynamic module, blade element method is used to calculate the force and power on turbine. In hydrodynamic module, boundary element method is used based on the first-order potential theory to calculate the wave force on floating body. In mooring module, catenary model is used to calculate the mooring force. In system motion module, it connects with other modules by the time-domain floating motion equation, and calculates motion responses of floating body in every moment.OC3-Hywind spar FOWT is chosen as a calculation example. Through single validation for module and coupled calculation among modules, the accuracy of this coupled calculation model has been verified.Dynamic response of FOWT is analyzed. Frequency-domain method is used to analyze coupled relationship among surge, heave and pitch. Time-domain method is used to analyze the difference of motion responses between wind-wave and wave-only condition with regular and irregular wave. Motion response’s influence on power of FOWT is analyzed at the same time. The changes of force of mooring lines are analyzed between different incidences of wind and wave.The parameters of structure which will affect motion responses are studied. The influence of restoring force and mass on nature frequency of structure is calculated and studied. With the added heave plate, the influence of damping in different wave frequencies on motion response is studied. Through changing the top locations mooring lines, the influence of mooring on motion response is studied.