Research On Structural Damage Diagnosis And Fatigue Life Prediction Of Large Wind Turbine Blade

Wind turbine blade is an extremely important part of the wind turbine,its main body is made of composite,and it is subjected to fluctuating wind load,centrifugal inertial force load and gravity load during operation.The fatigue crack on the blade will gradually extend to fatigue fracture under the action of multiple loads,which will cause the whole generator unit to stop running or even scrap.Therefore,damage detection and fatigue life calculation of blades are helpful for timely preventive maintenance to ensure the safe operation of the unit.This paper takes 1.5MW wind turbine blades as the research object for transient dynamic analysis,modal analysis and fatigue analysis,and conducts in-depth research on the analysis results,which provides a certain reference for the design,manufacture and damage diagnosis of the blade.The main research contents of this paper are as follows:Firstly,it analyzes the load that the blade bears during operation,analyzes the aerodynamic load,gravity load and inertial force load that affect the fatigue performance of the blade.With the help of special software GH Blade,the load distribution of each blade element section is calculated from the cut-in wind speed to the cut-out wind speed under the action of turbulent wind.Secondly,the geometric shape of the blade is generated by using the surface function in Solid Works software,and the model is imported into Workbench to set the relevant material parameters,and the different parts are layered and meshed to obtain the finite element model of the blade.Then,combined with the load distribution under the different wind speeds mentioned above,the transient dynamic analysis of the blades is carried out to determine the maximum stress position of the fan blades.Then,different damage conditions are simulated at the maximum stress position,and the displacement and strain modal analysis of the blade is carried out.By comparing the diagnosis effect of natural frequency,displacement modal parameters and strain modal parameters as damage indexes,it is proved that the strain modal parameters are more effective for blade damage identification.It is found that using the strain modal variable ratio and direct index based on difference theory of strain modal shapes as damage indicator can further improve the accuracy of identification and reduce the probability of damage misjudgment caused by damage identification error.Finally,the result of stress-time history of the blade obtained from the transient dynamic analysis is used to compile stress spectrum by rain flow counting method.The stress-life curve(S-N curve)of glass fiber Reinforced Plastics(GFRP)is analyzed,and the fatigue life of the wind turbine blade is calculated by the traditional Miner’s rule and the fuzzy life estimation method respectively.The comparison shows that the calculation result by the fuzzy life estimation method is more accurate.