Research On The Dynamic Response And Fatigue Damage Of Floating Wind Turbine In Combined Wind And Wave

The development of renewable energy is not only a fundamental way to achieve the ‘dual carbon’ goal and solve ecological environment problems,but also a major development strategy for accelerating our country’s energy transition.As one of the most important renewable energy,wind energy is a significant way to achieve low-carbon development.China’s wind energy resources reserves are about 1 billion k W,ranking first in the world,among which offshore wind energy reserves reach 758 million k W,showing huge development potential.Deep sea wind power is one of the mainstream trends in the development of offshore wind power,which is rich in deep sea wind energy resources,stable wind speed and little impact on coastal environment.Floating wind turbine is currently the most effective offshore engineering equipment for developing deep sea wind energy resources.However,in the whole life cycle of 25 years,the floating structure design of floating wind turbine will make it produce complex dynamic response under the combined action of wind and wave,which will easily aggravate the fatigue damage of key structures such as tower and mooring lines,and affect the life of the whole floating wind turbine.In this paper,a 5 MW floating wind turbine is taken as the research object.Based on the measured data of wind and waves in a domestic sea area,considering the dependence structure of wind and wave,the Copula joint probability distribution function of random wind and wave is deduced,and the dynamic model of the floating wind turbine system is established.Based on the maximum dissimilarity algorithm and the radial basis function interpolation method,the long-term dynamic response reconstruction method of the floating wind turbine is carried out.The extreme loads of the floating wind turbine based on the environmental contour method are studied.The short-term fatigue damage and long-term fatigue damage of the floating wind turbine under the combined action of wind and wave are analyzed.The research results are of great significance for evaluating the dynamic service performance of floating wind turbine and improving the design optimization capabilities of floating wind turbine.The main research contents of the thesis are as follows:(1)Based on the joint distribution statistics of wind and wave in a domestic sea area,the marginal distribution functions of wind and wave are constructed by using the three commonly used parameter distributions of Weibull distribution,Gamma distribution and Lognormal distribution.The joint probability density distribution model of wind and wave is established using Copula theory as the carrier,and the correlation between the mean wind speed,the significant wave height and the spectral peak period is explored.Finally,random distribution characteristics of wind and wave are analyzed.(2)Considering the nonlinear coupling factors among subsystems such as aerodynamic model,hydrodynamic model,mooring system and control system,the dynamic model of the floating wind turbine system is established.The selection method of representative sea states based on the maximum dissimilarity algorithm is studied.Combined with the dynamic model of the floating wind turbine system,the radial basis function interpolation method is used to reconstruct the statistical characteristics of dynamic response of floating wind turbine.(3)Combined with the characteristics of the joint probability distribution of wind and wave,as well as considering the exceedance probability,the environmental contour methods based on the inverse first reliability method and the inverse second reliability method are proposed,and the calculation method of long-term extreme load of floating wind turbine based on Gumbel extreme value distribution is studied.The variation law of extreme load of floating wind turbine under different key environmental conditions is analyzed,and the extreme load prediction of 50-year return period of floating wind turbine is realized.(4)Under the combined wind-wave action,the fatigue damage calculation methods of floating wind turbine tower top,tower base and mooring lines are studied.The short-term fatigue damage and long-term fatigue damage of floating wind turbine under the combined wind-wave action are analyzed,and the influences of wind-wave loads and wind-wave misalignment on the fatigue damage of floating wind turbine are discussed.