Load Modeling And Reliability Analysis Of Critical Structure Loads For Megawatt Wind Turbines

With the large-scale and scale-up of wind turbines and the frequent occurrence of wind power accidents at home and abroad,the reliability and safety of key structures such as wind turbine towers and blades have received more and more attention.Therefore,this paper selects a megawatt-level wind turbine supported by a fixed foundation on land for research,and establishes a correct wind field by using the spectral representation based on random functions;Then,based on the probabilistic extrapolation model of the ultimate load of the tower and blade of the megawatt wind turbine,the probability distributions of the long-term service loads of the key components of the wind turbines under different working conditions were obtained by combining the independent identical distribution assumption of the dynamic load response peak and the three-parameter Weibull model;Further define the structural reliability state function of the system failure through the dimensionless extreme value statistics,and combine the fractional moment and maximum entropy optimization methods based on multiplicative dimensionality reduction to perform reliability analysis on the key structural components and systems of megawatt wind turbines;Finally,the crack propagation simulation is performed on the welding joint at the bottom of the tower,the time-varying reliability of the corresponding structure is calculated according to the failure criterion,and the failure probability is updated according to the inspection and maintenance decision.The main research contents of this paper include:(1)Numerical simulation of three-dimensional wind field of the wind turbineThe random function-based spectrum representation method is used to numerically simulate the given Kaimal wind spectrum and related functions in the pulsating wind field area,compare the self-power spectrum and cross power spectrum at different locations in the wind field area,and analyze that the simulated spectrum is consistent with the target spectrum better;Compared with the wind field simulation software TurbSim in frequency domain and time domain.The results show that they are in good agreement,proving that the method is accurate and effective in simulating random wind field.(2)Load probability modeling of tower and blade structureThe equidistant integration point method(LRS)is used to estimate the structural load distribution through univariate and three-variable examples;The Gauss-quadrature scheme(GQ)is proposed to estimate the wind load of the structure and compared it with the traditional equidistant dispersion method.The result shows Gauss-quadrature scheme is more accurate than that of the conventional isometric discrete method.Then,the extreme value of the load is obtained by using the peak over threshold(POT)method,which is fitted to the three-parameter Weibull distribution.Based on the GQ method and LRS method,the probability modeling of the limit load of the key components of the wind turbine is carried out,and the load of the key components such as the blade and tower of the wind turbine is extrapolated under the return cycle of 20 years and 50 years.Finally,the extrapolation results and the annual limit load distribution results in four different situations based on the GQ method and the LRS method are compared to verify the superiority of the Gauss-quadrature scheme in calculating the wind load of the structure.(3)Structural components and system reliability analysisAccording to the failure mode of bending strength of the wind turbine blade and tower.the limit state equation of wind turbine structural system failure is established through dimensionless transformation,and the fractional moment and maximum entropy optimization methods based on multiplicative dimensionality reduction(MDRM)is proposed to calculate the key components structure and system reliability of the wind turbine;The probability distribution of reliability state function based on different structural limit load modeling methods and different turbulence models is studied,and the corresponding failure probability is calculated,and the reliability level of structural components and systems in r years is summarized.(4)Crack propagation simulation and failure probability updating of welded jointsThe crack propagation of the welded joint at the bottom of the wind turbine tower under cyclic load is simulated,and the failure assessment diagram is used as the structural failure criterion.Then,the structural reliability under different limit state functions is compared,and the influence of various parameters on the reliability index is studied.The fatigue reliability based on the design life is updated by using the detection and maintenance strategy based on reliability and risk.