Study On Coupled Methods And Performance Of A Spar-type Offshore Floating Wind Turbine System

Wind energy is of significant developing potential as it's renewable and pollution-free.Therefore,International exploitation of wind energy is growing at an accelerative speed.Compared with onshore or near-shore wind resources,offshore wind resource is much faster and more stable,which gradually makes the wind energy industry move to the deep-sea zones.Under this circumstance,offshore floating wind turbine system is becoming an international research focus.Unlike onshore turbines and offshore floating oil production platforms,offshore floating wind turbines' motion and load performance is characterized by non-linearity and instability.Although several numerical computational tools have already been developed both domestically and internationally,there is still no consensus and comprehensive demonstration on topics like how support platform motion affects the aerodynamics of turbine rotor,characteristics of offshore floating wind turbine system's performance under wind and wave conditions etc.Under this background,this thesis focuses on the prediction of overall loads and dynamic response of offshore floating wind turbine system and characteristics of the rotor and the floating turbine system's performance.In respect of rotor aerodynamics,the following aspects have been accomplished.First of all,coordinate system of the floating turbine system is established on the basis of the fixed wind turbine coordinate system and the oceaneering coordinate system.Secondly,the rotor's aerodynamic computational model is established on the integration of the generalized dynamic wake theory,Beddoes-Leishman dynamic stall model and blade element theory and it is validated in terms of accuracy.Using the NREL 5MW offshore wind turbine,research on turbine's aerodynamic performance under yawed conditions is conducted within two different situations,with the rotor control system on or off.Also,research on how rotor aerodynamics is affected by periodic surge motion is conducted.In terms of system hydrodynamics,the non-linear time-domain coupled kinetic equations of the floating turbine system are established on the basis of Euler angles.The computational models of wind environment and aerodynamic loads are established.Considering regular waves,irregular waves and currents,computational model of the water environment is established and the hydrodynamic load computational model is established by using the slender body theory.According to the quasi-static catenary theory,the mooring model is established.Then,how steady wind and regular wave affect the performance of a Spar-type offshore floating wind turbine is analyzed.Besides,analysis on the Spar-type floating turbine system's overall motion response of under random wave condition is conducted.Finally,influences of wind and wave environment on turbine system are summarized.