Dynamic identification of wind turbine system under operational conditions using FBG transducers

The development of an identification procedure of the dynamic properties of a composite horizontal axis wind turbine blade using data recorded during its operative working conditions is reported in this article. The operational modal analysis method based on the properties of the Hilbert Transform applied to response signals, represented in the frequency domain, has been extended to deal with systems characterized by harmonic component excitations blended with white noise spectra loading. The unknown harmonic contributions are identified and their effects on the time responses removed for a clearer estimate of the modal parameters. The considered data are gained from a Fiber Bragg Grating (FBG) integrated with the wind turbine blade. The FBG transducers have many advantages over other conventional sensors. Providing real-time information about structural integrity and operational load can be used in conjunction with appropriate methods to decrease the overall energy cost of wind turbines by optimizing the maintenance, yielding maximum service life of the wind turbine at minimum maintenance cost. This paper discusses the capabilities of the proposed operational modal analysis procedure, included in the Natural Input Modal Analysis, NIMA, jointly used with data from FBG transducers to track the changes in the natural frequencies, damping ratios and mode shapes of the rotating wind turbine blade for a possible use in structural health monitoring. Experimental data are provided by the wind tunnel test campaign carried out at the Mechanical and Aeronautical Engineering Department of Clarkson University. © 2012 by P. Marzocca, G. Coppotelli. Published by the American Institute of Aeronautics and Astronautics, Inc.