Field Testing of Wind Turbine Towers with Contact and Noncontact Vibration Measurement Methods

AbstractWind turbine tower vibration parameters are critical for design and maintenance of wind farms. In this paper, measurement campaigns of two in-service 65-m tall wind turbine towers are investigated. Different field vibration measurements with contact and noncontact sensors, including integrated circuits piezoelectric accelerometers, passive servovelocimeters, a laser Doppler vibrometer, and an interferometric radar, were conducted in the campaigns. Frequencies, damping ratios, and mode shapes were identified based on the measurements by use of a stochastic subspace identification method. Performances of the contact and noncontact sensors were compared in time and frequency domains. Also, time-frequency spectra were used to figure out noncontact measurement sections with high quality. Because the superior frequency ranges of contact and noncontact sensors are different, a data fusion method, which can take advantage of both types of sensors, was introduced. The practicality of field vibration measurements for modal parameter identification is discussed, and the results are compared with those from simplified finite-element models of the tested wind turbine towers.