Semi Analytical Calculation Method For Wind-Induced Response Of Megawatt Wind Turbine Tower Under Parked Condition

China is rich in wind energy resources,so the development and utilization of wind energy resources for wind power generation has great prospects.When the wind speed exceeds the cut-out wind speed,the wind turbine is in the shutdown state,which requires the accurate estimation of the response extremum of the wind turbine in the shutdown state in the structural design.Based on the numerical simulation software,the time history analysis can be carried out to determine the dynamic response extremum,but the numerical simulation calculation is large and the efficiency is low,so it is difficult to adapt to the design requirements of fast and fine wind turbine selection.Therefore,it is urgent to develop an efficient method to calculate the response extremum of wind turbine tower.Based on the frequency domain method often used in building structure design,this paper studies the extreme value response of megawatt wind turbine under wind load in shutdown state,and puts forward a semi analytical method to quickly estimate the extreme value of tower wind-induced response.The main work and conclusions are as follows:The current research status and existing problems of time domain and frequency domain algorithms in extreme value response calculation method of large wind turbine are summarized.Based on the quasi steady assumption,the wind speed decomposition mode of the blade section of the variable pitch control wind turbine under the shutdown condition is defined.Based on the frequency domain analysis method of random vibration of wind-induced response,an analytical method for calculating the base moment response of variable pitch controlled wind turbine is proposed.Then,based on several different types of large-scale wind turbine,the accurate solutions of average response and pulsating response are obtained by time domain method,and the accuracy of the analytical expression is verified.In view of the problems existing in the analytical method,the corresponding correction method is proposed.For the average response,this paper takes 5MW wind turbine as an example to compare the average response of tower base bending moment calculated by numerical analysis software openfast and analytical method based on quasi steady theory.The results are as follows.With the increase of structural flexibility,the eccentric bending moment caused by the uneven distribution of blade mass changes.At the same time,because the analytical expression can not accurately calculate the force arm change,the results of the two methods are different.The mean value of the analytic expression is always less than the response mean value calculated by openfast,so it may be dangerous to apply the analytic expression directly.Therefore,this paper proposes a semi empirical correction method for the analytical expression of the base moment mean value of 5MW wind turbine by analyzing the calculation results,and verifies the effect of the proposed semi analytical method through the response calculation results of 1.5MW and 15 MW wind turbines.For the fluctuating response,the power spectra of the response in the downwind and crosswind directions are compared by numerical simulation and analytical method based on quasi steady theory.The results show that in the low frequency part which is lower than the natural frequency of the structure,the power spectra calculated by the two methods are in good agreement with each other in the downwind and crosswind directions;in the resonance part near the natural frequency of the structure,the power spectra calculated by the two methods are in good agreement with each other in the downwind direction,while the power spectra calculated by the two methods are quite different in the crosswind direction.Therefore,the main reason for the error is that the calculation of aerodynamic damping in cross wind direction is not accurate.It is found that the aerodynamic damping is almost not affected by the change of turbulence degree.When the average wind speed at hub height is 25 m / s to 50 m / s,the identification results of aerodynamic damping along the wind direction agree well with the results of analytical expression,while the aerodynamic damping value tends to be a stable constant.Finally,the extreme value of tower response is analyzed,and the probability distribution characteristics of the bending moment along the wind direction and across the wind direction are studied respectively.It is shown that the downwind response can be estimated conservatively by the peak factor of Gaussian process,and the crosswind response shows narrow bandwidth and weak hardening non Gaussian characteristics due to the negative aerodynamic damping,which leads to a slightly smaller peak factor of the crosswind base bending moment than that of Gaussian process and tends to be conservative.Therefore,it is suggested that the influence of the narrow band characteristics caused by negative aerodynamic damping should be considered when estimating the extreme moment of the base in cross wind direction.