ESTIMATION OF MODAL PARAMETERS OF A BEAM UNDER RANDOM EXCITATION USING A NOVEL 3D CONTINUOUSLY SCANNING LASER DOPPLER VIBROMETER SYSTEM AND AN EXTENDED DEMODULATION METHOD
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A novel three-dimensional (3D) continuously scanning laser Doppler vibrometer (CSLDV) system that contains three CSLDVs and an external controller is developed to measure 3D vibration of a structure under random excitation, and a new operational modal analysis method is proposed to estimate its 3D modal parameters, by extending the conventional demodulation method. Calibration among three CSLDVs in the 3D CSLDV system is conducted to ensure that three laser spots can continuously and synchronously move along the same scan path on the structure. The extended demodulation method can estimate undamped mode shapes of the structure under random excitation by filtering raw response with a bandpass filter and demodulating the filtered response. Experimental investigation on one-dimensional (1D) and 3D CSLDV measurements for modal parameter estimation is conducted on a beam under white-noise excitation to validate the extended demodulation method and examine the accuracy of the 3D CSLDV system.