Operational Modal Analysis and Wavelet Transformation for Damage Identification in Wind Turbine Blades

Abstract : The presented study demonstrates an application of a previously proposed modal and wavelet analysis-based damage identification method to a wind turbine blade. A trailing edge debonding was introduced to a SSP 34m blade mounted on a test rig. Operational modal analysis (OMA) was conducted to obtain mode shapes for undamaged and damaged states of the blade. Subsequently, the mode shapes were analyzed with one-dimensional continuous wavelet transformations (CWTs) for damage identification. The basic idea of the method is that structural damage will introduce local mode shape irregularities which are captured in the CWT by significantly magnified transform coefficients, thus providing combined damage detection, localization, and size assessment. It was found that due to the nature of the proposed method, the value of the identification results highly depends on the number of employed measurement points. Since only a limited number of measurement points were utilized in the experiments, valid damage identification can only be obtained when employing high-frequency modes.