Analysis Of The Fatigue Life Assessment Of Large-scale Wind Turbine Blade

Blade is a key component of the wind turbine. In the past decade, the wind power electricity has been developing rapidly, with a total installed capacity rising dramatically, and unit capacity increasing.1-2MW has been the main model in market, and 3MW-5MW has been put into operation.The size of wind turbine rotors has increased in the past decade from 40 m to more than 120 m diameter. More than 108 load cycles will happen in the prospected lifetime of 20 years of a turbine. As the blades exposed to various harsh environment, and the effects of various loads, it's prone to damage, and the fatigue damage is the most important failure modes. It's of great significance to assess the fatigue of the blade, and the fatigue life assessment is the ultimate aim of fatigue analysis.The complex load conditions on the blades has been analyzed in this paper. The calculation methods of the three main load were summarized in detail. Using the dynamic simulation functions of GH Bladed software, selecting the von Karman turbulent wind model, the normal operating conditions were simulated, and the fatigue load of blade was output. At the same time, the FAST software was used to calculate the fatigue loads of the same wind turbine, the two results are basically similar.The stress analysis function of ANSYS were applied to calculate the stress of the root of blade. Some common S-N curves and empirical models which estimate fatigue limit were introduced, and we selected the exponential function S-N curve as the fatigue life assessment performance curve.Combined the wind speed distribution data determined by Weibull distribution function, the cycles of each of sress determined by the hypothesis that the percentage of wind speed distribution corresponding with the stress cycle, and the cycle life corresponding to each of the stress defined by S-N curve, with Palmgren-Miner linear cumulative injury rules, we calculate the lifetime of the 1.5MW wind turbine blade. The result is 23 years which is similar with design life.The calculation example shows that the lifetime calculation method summarized in this paper is a feasible method.