Research On Method For On-line Predicting The Life Loss Of Coastal Wind Turbine Blades

The load characteristics of coastal wind turbines are complex,and fatigue failure is one of the main causes of failure of wind turbine blades.Due to the complex structure of wind turbine blades,the harsh working environment,and the complex and unpredictable load conditions,it is necessary to establish a on-line monitoring system of wind turbine blades to prevent safety accidents which caused by fatigue loss.The analysis results play an important role on the adjustment of wind turbine operation strategy and the scheduling of maintenance.In this dissertation,the load characteristics of the wind turbine blade during operation are analyzed firstly,and obtained conclusions are as following:fatigue failure is the main cause of blade failure.There are three kinds of loads,such as aerodynamic load,gravity load and inertial load,which have a serious effect on the fatigue life of the blade.The wind conditions of a 2MW blade which located at a coastal wind field were simulated through the principle of statistics and Kaimal spectrum,and the dynamic load data of the blade was calculated.Calculation results show that blade root is the most fragile part of the wind turbine blade.The 2MW wind turbine blade model was established by the ANSYS APDL.At the same time,the dynamic characteristics of the wind turbine blades were calculated.The calculation results show that each of the first three modal frequencies is less than 1.OHz,and the first and second order natural frequency are close to the excitation frequency,which would cause the resonance of the working blades.According to the S-N curve of FRP,the stress-cyclic number of cycles leading to material damage under the action of stress at all levels were calculated,and the miner cumulative damage criterion was used to calculate the life loss of the wind turbine blade.The calculation results show that the life loss rate of wind blades are 0.04,0.08 and 0.12 respectively after 1,2,and 3 years of operation.Based on the mathematical model of the stiffness degradation model and the life loss model,the change of the blade modal frequency and the material stiffness,the quantitative relation between the change of natural frequency and the life loss of the wind turbine blade was established.Based on the above theoretical results,a set of on-line monitoring subsystem of wind turbine blade life loss was developed,which was applied to calculate the life loss of the wind turbine blade in detection test.Application results show that the life loss calculation results obtained from the subsystem is basically consistent with the actual value of life loss.