CRACK DETECTION OF WIND TURBINE BLADES BY USING DYNAMIC ANALYSIS

Abstract

This work presents a new technique for detecting the cracks in the wind turbine blades (WTBs) during rotation without the need to stop the turbine. This method considers both the centrifugal stiffening effect and stiffness reduction due to cracks presence in the rotating blade. The centrifugal stiffening effect increases the values of eigenfrequencies during rotation. By contrast, the presence of cracks in the WTBs minimizes the values of eigenfrequencies due to stiffness reduction. Therefore, the mode of deformation of the rotating WTBs is expected to be a good indicator for the cracks presence during rotation. MSC/Adams software was used to verify the analytical solutions of previous publications related to the centrifugal stiffening effect in rotating beams. The first model to be verified was a uniform rotating beam that was developed by using Euler-Bernoulli beam principle. While, the other models were uniform and tapered twisted rotating beams that were developed by using Timoshenko beam approach. The WTB model was designed by using the blade element momentum (BEM) theory. The finite element model was generated by using MSC/Adams. Parametric study was then applied to the WTB model to study the effect of crack direction on the modal parameters of the WTB. Besides, different cracks sizes were investigated. The effect of crack location was studied by using the same crack size but at different locations. Dynamic analysis was then applied to check the centrifugal stiffening effect on the modal parameters of the WTB. Finally, the effect of cracks presence and rotational speeds on the modal parameters of the WTB during rotation were investigated.