Session: 01-08-01: Vibration and Acoustic Measurements, Signal Processing, and Test Facilities

Paper Number: 71521

Start Time: Wednesday, 01:40 PM

71521 - Operational Modal Analysis of a Rotating Structure Subject to Random Excitation Using a T Modal Analysis of a Rotating Structure Subject to Random Excitation Using a Tracking Continuously Scanning Laser Doppler Vibrometer via a Two-Dimensional Scan Scheme 

A new operational modal analysis (OMA) method is developed for estimation of modal parameters (MPs) of a rotating structure (RS) subject to random excitation using a nonuniform rotating beam model, an image processing method, and an improved demodulation method. The solution to the governing equation of a nonuniform rotating beam is derived, which can be considered as the response of the beam measured by a continuously scanning laser Doppler vibrometer (CSLDV) system. A recently developed tracking CSLDV system can track and scan the RS. The image processing method determines the angular position of the RS so that the tracking CSLDV system can sweep its laser spot along a time-varying path on it. The improved demodulation method obtains undamped mode shapes (UMSs) of the RS by multiplying its measured response by sinusoids whose frequencies are its damped natural frequencies (DNFs) that are obtained from the fast Fourier transform of the measured response. Experimental investigation of the OMA method using the tracking CSLDV system is conducted, and MPs of a rotating fan blade (RFB), including DNFs and UMSs, with different constant speeds and its instantaneous MPs with a non-constant speed are estimated. Estimated first DNFs and UMSs of the stationary fan blade and RFB are compared with those from the lifting method that was previously developed by the authors.

A new OMA method is developed for estimation of DNFs and UMSs of an RS with a constant speed and its instantaneous UMSs in a short time duration for a non-constant speed using a nonuniform rotating beam model, an image processing method, and an improved demodulation method. The improved demodulation method determines UMSs of the RS subject to random excitation by applying a low-pass filter to the measured response multiplied by sinusoids whose DNFs are estimated from the FFT of the measured response. The image processing method is used to track real-time positions of the RS so that the tracking CSLDV system can scan it. DNFs and UMSs of an RFB with a constant speed subject to random excitation and UMSs of the RFB with a non-constant speed in a short time duration were successfully estimated using the new method. Estimated DNFs of the RFB are theoretically and experimentally shown to increase with its constant speed. The first estimated DNF and UMS of the stationary fan blade and RFB are compared with those from the lifting method. The demodulation method can estimate higher modes of an RS using a low frame-rate camera and a low scan frequency, while the lifting method cannot. The lifting method can estimate modal damping ratios and ODSs of an RS subject to random excitation, while the demodulation method cannot.

Presenting Author: Linfeng Lyu University of Maryland

Authors:

Linfeng Lyu University of Maryland
Weidong Zhu University of Maryland