Output-only Modal Analysis using Continuous-Scan Laser Doppler Vibrometry and application to a 20 kW wind turbine

Abstract

Abstract:Continuous-scan laser Doppler vibrometry (CSLDV) is a method whereby one continuously sweeps the laser measurement point over a structure while measuring, in contrast to the conventional scanning LDV approach where the laser spot remains stationary while the response is collected at each point. The continuousscan approach can greatly accelerate measurements, allowing one to capture spatially detailed mode shapes along a scan path in the same amount of time that is typically required to measure the response at a single point. The method is especially beneficial when testing large structures, such as wind turbines, whose natural frequencies are very low and hence require very long time records. Several CSLDV methods have been presented that employ harmonic excitation or impulse excitation, but no prior work has performed CSLDV with an unmeasured, broadband random input. This work extends CSLDV to that class of input, developing an outputonly CSLDV method (OMA-CSLDV). This is accomplished by adapting a recently developed algorithm for linear time-periodic systems to the CSLDV measurements, which makes use of harmonic power spectra and the harmonic transfer function concept developed by Wereley. The proposed method is validated on a randomly excited free-free beam, where one-dimensional mode shapes are captured by scanning the laser along the length of the beam. The natural frequencies and mode shapes are extracted from the harmonic power spectrum of the vibrometer signal and show good agreement with the first seven analytically-derived modes of the beam. The method is then applied to identify the shapes of several modes of a 20kW wind turbine using a ground based laser and with only a light breeze providing excitation.

Periodic stability analysis of wind turbines operating in turbulent wind conditions

“…26, it appears that the amplitudes picked from the th column at frequency ω j + w are equivalent to those picked from the central column at ω j + (w + ) . This also means that computing the central column could be sufficient for having an estimation of frequencies, damping, and participation factors, as already noted in Shifei and Allen (2012). The POMA technique can then be summarized as follows:…”

Çok Katli Yapilarda Roboti̇k Lazer Tarayici Si̇stemlerle Yapisal Sağlik Taki̇bi̇

“…Kaynaktan çıkan ve ölçülecek olan hedef cisme yönlendirilen lazer ışınları yüzeyden yansıdıktan sonra yine aynı sensör tarafından algılanmakta ve Doppler prensibine göre işlenmektedir. Hedefe gönderilen ve geri yansıyan ışın demetleri arasında oluşan dalga boyu ve faz farklarının analiz edilmesi sayesinde hedef cismin hızı ve ötelenmesi hesaplanabilmektedir (Yang ve Allen, 2012).…”

Heartbeat Detection by Laser Doppler Vibrometry and Machine Learning

“…LDV uses a laser beam and exploits an interferometric optical scheme to detect the velocity, along the direction of the optical beam, of a point on a surface [13]. Originally, LDV was mainly used for testing mechanical vibration in structures (e.g., wind turbine [14], washing machine [15], structural analysis [16], propeller [17]) or detecting defects in construction while avoiding direct contact with surfaces [18]. More recently, LDV has found application when a non-contact approach is required for evaluating cardiovascular function [19,20].…”