| Wind power generation is a new energy generation method with a wide range of applications.Accelerating the development of wind power has become a common consensus in many countries including China.The wind turbine consists of the foundation,the tower and the nacelle,the hub,the blades,the foundation plays a key role in the stability of the wind turbine.The loading mechanism of the foundation is very complicated.Under the action of long-term cyclic load,fatigue damage is easy to occur.Therefore,it is very important to analyze the fatigue damage of the turbine foundation.In order to improve the accuracy of fatigue damage calculation of wind turbine foundation and evaluate the applicability and influence of different calculation methods,this thesis studies the fatigue damage of wind turbine foundation.The main contents are as follows:(1)The current research results of the wind turbine foundation were reviewed,and then the basic theories involved in the research were introduced,including the calculation of environmental load,the simulation of pile-soil interaction and the theory of fatigue damage assessment.According to the spectrum analysis theory,the process of frequency domain fatigue damage analysis based on power spectral density function was established.(2)A 1.5MW onshore wind turbine was taken as an example,the fatigue damage of the weld at the bottom of the tower and the embedded ring flange was evaluated by the frequency domain fatigue damage analysis method.The hot spring stress was applied and the wind speed-direction joint distribution was considered to calculate the flange welding.The fatigue damage of the flange welding was close to the fatigue damage based on the measured data,and the frequency domain fatigue damage analysis method was verified.(3)A 3.3MW offshore wind turbine supported by monopile foundation was taken as an example,an offshore wind turbine tower-foundation finite element model was established,and the influence of damping was considered in the model.Based on the full-time domain dynamic analysis and frequency domain fatigue damage analysis process,the effects of wind and wave combined action,aerodynamic damping ratio and stress amplitude probability distribution model on the underlying fatigue damage were studied.(4)The results of the example of offshore wind turbines show that the results of the combination of wind and wave alone and then the damage value superimposed in the time domain method are 43.3%lower than the combined wind and wave,indicating that the method of superimposing wind and wave-induced fatigue damage is dangerous.Compared the stress time history of the superimposed the stress under the wind and wave alone and combined with the wind and wave,it is found that there is a certain coupling effect between the wind and waves,but the coupling effect is weak.In order to simplify the work,it is possible to approximate the dynamic response analysis of the combined action of wind and waves by superimposing the stress of the wind and wave alone.(5)The stress amplitude probability distribution model has significant influence on the fatigue damage calculated by the frequency domain method.The wind induced fatigue damage is calculated by the Dirlik method to be the closest to the time domain result,and the wave induced fatigue damage is calculated by the IFFT method to be the closest to the time domain result.After the wind and wave damage values calculated by the frequency domain method are superimposed,the total fatigue damage is less than the calculation result when the wind and waves combine.The foundation fatigue damage is very sensitive to the value of the aerodynamic damping ratio.The effect of the aerodynamic damping ratio on the wind-induced dynamic response is more significant than the wave-induced response.The higher the aerodynamic damping ratio,the lower the difference in wind-induced fatigue damage.One should consider the damping ratio reasonably and accurately. |
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