Study On Dynamic Analysis And Fatigue Assessment Of Wind Turbine Foundation

With the rapid development of our country,the energy shortage has become increasingly prominent.The abundant wind energy is an effective method to solve the problem.The wind turbine foundation suffers from the vibration from the upper tower caused by the complicated load of the external environment during the 20-year service life of the wind turbine.The load-bearing mechanism of wind turbine foundation is quite complex.The foundation is prone to damage which in turn leads to the overall failure of the structure due to the long-term cyclic loading.As an important supporting component of wind turbine,the fatigue assessment of the foundation is the key to ensure long-term safe operation of wind turbine structure based on the natural conditions of wind farms.The following work is carried out based on these problems:1.The dynamic analysis method of wind turbine structure,the theory and method of fatigue assessment of steel structures and concrete are summarized.The widely used S-N curve and Miner's linear cumulative damage theory are also introduced.This paper summarize and compare the modal properties identification theory of the wind turbine under environmental excitation.These theories provide theoretical basis for dynamic analysis and fatigue assessment of the wind turbine foundation.2.Vibration data and strain data are acquired by long-term monitoring of the wind turbine.MATLAB is used to simulate random wind speed and calculate the wind load.The tower-embedded ring-foundation model founded in COMSOL Multiphysics is analyzed in dynamics.And then the correctness of the model is testified by measured data.The results show that the results of numerical simulation are in agreement with the measured data.The model can simulate the actual wind turbine structure accurately.3.Using COMSOL Multiphysics finite element software,the three-dimensional finite element model is established.The dynamic response of the wind turbine foundation is analyzed under different wind speed and different wind direction.The influence of damping on the dynamic response of the foundation is studied.The results show that damping has a great influence on the dynamic response.The greater the damping is,the weaker the transient dynamic response is.Compared with the effect of material damping,the viscous damping of air has a greater influence on the dynamic response of the foundation.The damping of the foundation has a greater effect on the dynamic response than the damping of the steel.4.Based on the S-N curve method and Miner's linear cumulative damage theory and the probability distribution of wind speed and direction,the fatigue assessment of wind turbine is calculated by COMSOL Multiphysics Fatigue Module.The influence of different wind directions on the key points of the embedded ring is considered.The results show that the upper flange of the embedded ring is the most vulnerable point when the wind turbine suffers the north wind in the service life.The fatigue usage factor is 9.81E-2.The fatigue usage factor of the bottom flange of the embedded ring in the service life is 7.34E-4.The fatigue usage factor of the concrete under the bottom flange of the foundation ring is 1.36E-1.When calculating the fatigue usage factor of the vulnerable point of the embedded ring,it should not only consider the damage caused by the the main wind direction but also consider the damage caused by other wind directions.