Fatigue damage assessment of wind turbine composite blades using corrected blade element momentum theory

This paper presents a method for estimating the fatigue life of composite blades of horizontal axis wind turbines, and a real blade example of the NREL 5 MW reference wind turbine is employed to verify this proposed method. First, the distributions of aerodynamic loads are analysed by new corrected blade element momentum theory, and then the aerodynamic performance of the blade under various wind speeds is assessed. The time-history of the wind speed is generated by using the Weibull distribution based on the offshore wind parameters available. The maximum stress caused by the aerodynamic loads due to wind is then calculated through the finite element analyses. The fatigue cycle during the certain time period is estimated by fast Fourier transform for the load spectrum, which converts the time-stress spectrum to stress cycles. The fatigue damage and remaining service life of wind turbine composite blades are estimated by the Goodman diagram and S-N curve for stress cycles during the service time. Finally, the remaining service life is predicted by utilising the Miner's law for linear fatigue damage accumulation. The results of the real wind turbine composite blade show that the proposed approach can provide an effective tool for evaluating the fatigue damage and assessing the structural performance of the wind turbine composite blades during the service life.