Fatigue Analysis Of The Substructure Of Offshore Wind Turbine Based On Coupled Analysis Model

Offshore wind energy,as an important part of solution to energy and environmentalchallenges and the implementation of low-carbon energy strategy in China,has been strongly supported by the state in recent years.Designing and constructing of offshore wind farms may confront with severe environmental conditions,which are the potential hazards for the offshore wind turbines(OWTs).At present,the semi-integrated method is widely adopted to design and check the safety of the substructure of bottom fixed OWT.The method ignores the coupling effects of the marine environmental loads,operating control strategies and the structural responses such as the effects of aerodynamic damping on the responses of structure,the variation of aerodynamic loads due to the influence of wave loads and responses of the substructure.To research the coupling effects on the structural responses,a fully coupled analysis model of OWT is established in the study.Then,the structural responses and cumulative fatigue of tubular joints under combined wind and waves loads are analyzed.Finally,compared with the results from semi-integrated analysis model,fatigue assessment of OWTs performed by fully coupled is of necessity.Following researches are carried out for the fatigue analysis of bottom fixed OW T in the paper.(1)Reference OWT is designed by combination of the NREL 5MW baseline win d turbine and a practical OWT in the coastal regions of China.(2)Considering the aero-servo-hydro-elastic interactions,a fully coupled analysis model of reference OWT is established in order to research the coupling effects on the structural responses of OWT.(3)Influence of unsteady initial structural responses,simulation intervals and random seeds is studied based on the fatigue of substructure under synthesized wind speeds.(4)Semi-integrated analysis model of reference OWT is established as well.Meanwhile,the comparison of the structural responses and cumulative fatigue of tubular joints by semi-integrated and fully coupled analysis model is carried out.(5)The coupling effects on cumulative fatigue of tubular joints under combined load conditions,and directions of inflow winds and waves are analyzed on the base of the fully coupled model of OWT.