Power spectral density transmissibility-based operational modal parameters identification of a wind turbine under seismic excitations

Operational modal analysis technology has broad application prospects in structural health monitoring owing to the characteristics of no manual measurement of excitation data and analysis of data solely from the outputs. However, the harmonic excitation of wind turbines significantly interferes with the accurate extraction of modal parameters, and the transmissibility measurements-based method provides a feasible way to solve the problem as mentioned above. The transmissibility function at the system poles is equal to the ratio of the modal components of the two measurements and is independent of the excitation conditions, so this method can effectively suppress the interference of harmonic modes. In this paper, an operational modal analysis method based on the power spectral density transmissibility is adopted. First, the power spectral density transmissibility matrix of the multireference measure points is established. Then, singular value decomposition is performed on the transmissibility matrix to calculate the mode indicator function. Finally, the stabilization diagrams and the modal indicator function are combined to determine the final modal identification result. A numerical example of a 5-DOF mass-spring-damping system and an operational modal analysis engineering example of a real-world offshore wind turbine under seismic excitation demonstrate the effectiveness and reliability of the proposed method.