An improved approach for the fatigue calculation of rotor blades based on sector loads

Abstract

In the design and calculation of rotor blades for wind turbines, a sector representation of the loads is often used. The investigation proposed in this paper indicates that, depending on the loading direction, the evaluated sector and the considered location on the rotor blade, the sector approach can result in a significant overestimation of the acting stresses. This translates in a higher calculated fatigue stress exposure (up to 101% in the considered example). However, under particular conditions, the stresses and therefore the stress exposure are correctly assessed. Based on the observation, an improvement of the current method is suggested. The improved method, called invariant-sector method, relies on the appropriate selection of the sector(s) to be evaluated. The method allows for an accuracy equal to the one of the direct method but with a computational effort that is orders of magnitude lower.