Crack detection on wind turbine blades using a vibro-acoustic modulation technique
As the wind power industry has grown rapidly over the last decade, maintenance costs have become a significant concern. Due to the high repair costs for wind turbine blades, it is especially important to detect initial blade defects before they become structural failures which could lead to other more costly failures in the tower or nacelle. This research presents a technique for identifying cracks in wind turbine blades undergoing operational load using the Vibo-Acoustic Modulation technique. The Vibro-Acoustic modulation technique utilizes a low frequency pumping excitation signal in conjunction with a high frequency excitation signal to create the modulation that is used to identify cracks. Wind turbines provide the ideal conditions in which to utilize Vibro-Acoustic Modulation because wind turbines experience large low frequency structural vibrations during operation which can serve as the low frequency pumping excitation signal and the other probing excitation signal can be generated using a PZT exciter/transducer. The theory underlying the Vibro-Acoutstic technique is described in the document. The proposed crack detection technique was demonstrated with Vibro-Acoustic Modulation experiments performed on a small Whisper 100 wind turbine in operation and the results were compared with two other conventional Vibro-Acoustic Modulation tests. Spatio-temporal response analysis was also performed along with the Vibro-Acoustic Modulation tests using a 3D laser vibrometer. Finally, a finite element model of the cracked blade was developed for numerical simulation of Vibro-Acoustic Modulation tests which enables the design of Vibro-Acoustic Modulation tests to maximize the sensitivity of the technique for detecting cracks in these small-scale wind turbine blades.
Adams, Purdue University.
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