Study On The Fatigue Characteristics Of The Critical Components And Assemblies In The Offshore Wind Turbine Drivetrains

Wind power generation is currently the most developed potential renewable energy,and the development of wind power technology plays a vital role in China’s energy transformation and environmental pollution resolution.Compared with land,offshore wind resources are more abundant,and with the support of national policies,the development of offshore wind turbines has become an inevitable trend.Offshore singlecolumn wind turbines are currently relatively mature offshore wind turbines in China.Compared with onshore wind turbines,the combined effect of wind and waves makes the working environment of the offshore single-column wind turbines more complicated and changeable,the load condition of components is worse,which severely affects their operating life.A complete offshore single-column wind turbine model is established in this paper.Following this,the dynamic loads of critical components of the wind turbine under random wind load are calculated.The fatigue characteristics of components during the entire life cycle are also analyzed,which is of great significance to the optimized design and reliable work of offshore wind turbines.The main contents of the thesis are summarized as follows:(1)The structure and working principle of the 5MW offshore single-column wind turbine of NREL are analyzed,and the system topology diagram is established according to the structure of wind turbine.Comprehensively considering the aerodynamics,hydrodynamics,multi-body dynamics characteristics and component flexibility of the wind turbine,combined with variable speed control and pitch control,the wind turbine’s dynamic model is established based on Simpack software.(2)Turbulent wind models with different average wind speeds are established,and the dynamic loads of critical parts of gears and bearings in the drivetrain are analyzed under different average wind speeds.The results show that the dynamic loads of gears and bearings change significantly when the wind speed is below the rated wind speed,and the dynamic loads of gears and bearings do not change significantly above the rated wind speed.(3)The bending stress,contact stress of gears,and equivalent dynamic load of the bearings are analyzed,and the fatigue load spectrums of gears and bearings are formulated.The short-term fatigue damage of the gears and bearings in the drivetrain at various wind speeds are analyzed,combined with the wind speed frequency distribution of the wind field,the fatigue damage value at different wind speeds accounts for the proportion of the long-term 20-years damage.The result show: The damage value generated in the wind speed range of 3～11m/s accounts for only 21.9% of the total damage value,and the damage value in the wind speed range of 12～25m/s accounts for78.1%.(4)The fatigue characteristics of gears and bearings in the drivetrain during the life cycle are analyzed.The result show: The long-term 20-years damage values of all gears and bearings have not reached the limit of fatigue failure.The damage values of gears and bearings near the main shaft of the low-speed grade and the output shaft of the highspeed grade are large,while the fatigue damages of the intermediate gear and bearing are small.