Blade Load Analysis And Fatigue Life Estimation Of MW Grade Direct Driven Wind Turbine

In the case of the load of wind turbine blade is complex, this paper analysisthe load of blade. Thus it could find the calculation method of load and thedistribution of load, and this result could provide the foundation of strengthanalysis and fatigue analysis. Before strength analysis of blade, it shouldestablish the three-dimension of blade, the data of load is come from actualmeasurement data, then could analysis the strength of blade in the finite elementsoftware, thus could get the stress data and these data could prepare forestimation of fatigue life. Combine the data from actual measurement and theS-N curve of the blade material to estimate the fatigue life of blade. At present,there is no method to estimate the fatigue life of blade accurately, which isrestricted by the fatigue stress spectrum is hard to obtain and there is no accurateS-N curve formula of blade material.The research object of this paper is MW grade direct drive wind turbineblades, build the load test system, and measure the load of wind turbine, thenobtain the load data in two weeks, and process the load data into the form thatsubsequent analysis could use. Extract the airfoil data from the professional airfoil database software Profili, according to these airfoil data, use the softwarePro/E to establish the three-dimension model, thus it could solve the problem toestablish the model of blade. Use the software ANSYS Workbench to strengthanalysis of blade, import the handled load data to ANSYS Workbench, thus itcould solve the problem that the amount of actual load data is huge and it isdifficult to load-on the load and so on.This paper study on the blade load distribution, because of the complexityof estimate distribution parameters, then proposed a method that combine thecorrelation coefficient method and the maximum likelihood estimation methodto estimate the parameters of load distribution, and use Kolmogorov test methodto prove that the accuracy of parameters using this method is more than theaccuracy of parameters using alone method, and the parameters value is morepractical.When estimate the fatigue life of wind turbine blades, for the stress dataobtained from ANSYS Workbench strength analysis is same as the original loaddata, they have much randomness. So, at first, the stress data needed statisticalanalysis, then the counting method is used to count the stress data to obtain thestress spectrum. This paper use the improved rainflow counting method to count,this method solve the problem that the original counting method need count twotimes, so this method is convenient, quickly to count and easy to programming,simplify the counting process.The fatigue life was estimated use Palmgren-Miner theory has a problem that the accuracy is not enough and the deviation is big. This paper proposed amethod based on Fuzzy theory to estimate fatigue life, combine with the stressspectrum get from improved rainflow counting method and the S-N curve ofblade material, thus it could estimate the fatigue life of wind turbine blade,compared with traditional method, use this paper’s method could get fatiguelifetime that more close to actual.