Predicting the vibration response in subcomponent testing of wind turbine blades

Abstract

Currently new wind turbine blade materials are certified by starting with coupon testing for initial strength and fatigue analysis, followed by full-scale blade testing as a final quality control to assess material characteristics. Subcomponent testing has been proposed as a supplement to the structural analysis and material characterization, bridging the gap between coupon and full-scale tests. In this study, similitude theory is applied to a simply-supported rectangular plate that is representative of a wind turbine blade spar cap with the goal of designing a validated scaled-down subcomponent. The vibration of a specially orthotropic rectangular laminated plate is analyzed to extract the scaling laws based on direct use of the field equations. The accuracy of the derived scaling laws is analyzed as a model validation criteria by mapping the first natural frequency of the variant subcomponents to the full-scale plate. The effect of the ply stack up scheme and size of the subcomponents in predicting accuracy of the scaling laws are then investigated by applying partial and complete similarity conditions. According to the results, subcomponents with modified ply stack up could be found that have a good accuracy in predicting the first natural frequency of the full-scale plate. However, picking an appropriate aspect ratio is critical to the success of the prediction of full scale plate response as shown in the cases studied.