Fatigue Life Prediction Of Wind Turbine Blades Based On The Miner Methods

The performance and quality of the blade,one of the key components of the wind turbine,directly affect the operation efficiency of the wind turbine.Fatigue load is the main cause of blade failure.The actual service life of wind turbine blades depends mainly on the fatigue life.At present,the blade fatigue life prediction mainly uses the linear Miner method and the fuzzy Miner method.The former only considers the linear superposition of fatigue damage,while the latter considers the effect of the load below the fatigue limit on fatigue life.Neither method considers the load application sequence.According to the fatigue damage accumulation process of blades,the continuous Miner method comprehensively considers the fuzzyness of the fatigue damage and the randomness of the load.The fatigue life prediction is closer to the actual operation of the wind turbine blades.Taking the NREL 5MW wind turbine blades as the research object,the continuous Miner method is used to predict the fatigue life.The main work is as follows:(1)Load calculation model of the wind turbine and finite element model of the blade are established.The blade section loads under each wind speed are calculated.Analyzing strength of the blade,the model reliability is verified by modal analysis and static analysis.(2)The principal stress-time courses of the dangerous node are extracted by transient dynamics analysis.The stress spectrum is prepared by rain flow counting method.The stress probability model considering the load random variation is established.(3)Based on the S-N curve and the modified fatigue limit of the blade material,the fatigue life of the blade under random cyclic load is comparatively analysed based on the linear Miner method,fuzzy Miner method and continuous Miner method.The results of the study show that the critical pomaximum sition of the blade is located at the root through blade strength analysis.The displacement of the blade tip and maximum Von Mises stress of the blade root are lower than the allowable deformation and allowable stress.The blade structure design meets the strength requirement.Considering the load random variation,the stress spectrum of the blade is statistically analyzed,and the probability distribution of the blade stress obeys a normal distribution in a long period of time.The fatigue life prediction results of the blade based on linear Miner method,fuzzy Miner method and continuous Miner method are more than the design life of 20 years,which proves that the structure and layup of NREL 5MW blades meet the design requirements.The fatigue life prediction result of 21.46 years based on continuous Miner method is the closest to the design life,whose minimum error is 7.3%.The continuous Miner method improves the prediction accuracy of blade fatigue life,which provides a new fatigue life prediction model for wind turbine blades.