Vibration-based damage detection in a wind turbine blade through operational modal analysis under wind excitation

Abstract

In the present study, a vibration-based structural health monitoring (SHM) method for wind turbine blades using Operational Modal Analysis (OMA) is presented. To simulate the dynamic response of the wind turbine, the NREL FAST tool implemented in QBlade was used to calculate the forces in the time domain along the blade in response to the stochastic excitation of the rotating blade by means of the rotationally sampled turbulence spectrum of the wind. These force time series are used as input to the transient analysis in ANSYS Workbench. The acceleration time series extracted along the blade are used for Operational Modal Analysis, and the modal parameters are obtained with the Frequency Domain Decomposition (FDD) algorithm. The comparison between the modal properties of an undamaged and a damaged blade is used for the detection of longitudinal crack-type damage features in the upper part of the blade. The proposed method is shown to be capable of correctly detecting and locating the damage with blade accelerations occurring due to the stochastic excitation by the wind only. This approach could pave the way to low-cost structural health monitoring of wind turbine blades and rotors.