Fast modal rotation measurement using a dual sinusoidal-scan continuously scanning laser Doppler vibrometer

Abstract

Rotational degrees of freedom (DOF) are usually indirectly derived from the measured translational DOF in structural dynamic tests by using the finite difference method. However, the noise of translational DOF measurement is easily propagated and further amplified when the finite difference method is employed to obtain the rotational DOF. Therefore, the accuracy of the obtained rotational DOF was rather poor. In order to overcome this disadvantage, a novel approach of using a dual sinusoidal-scan continuously scanning laser Doppler vibrometer (CSLDV) with the objective of obtaining the structural modal rotational DOFs is put forward in this paper. For plate structures, the operational deformation shape of the normal translational DOFs can be measured and described with polynomial functions through the modulation of CSLDV output signals. Then, rotational out-of-plane DOFs can be achieved with respect to the first derivatives of the polynomial functions along orthogonal directions. In such a way, the measurement noise that considerably affects the rotational out-of-plane DOFs derived from normal translational DOF can be significantly eliminated. The approach is validated experimentally with a cantilever plate structure, and a comparison with the results obtained from discrete point measurement is given. The results demonstrate the noticeable improvement in accuracy and spatial resolution of the proposed technique.

Removing speckle noise from the signals of a laser Doppler vibrometer on moving platforms (LDVom) by ensemble empirical mode decomposition

“…However, it requires long-time acquisition at each point, which is timeconsuming. A CSLDV continuously scans the vibrating surface, but it requires multiple reciprocating or cyclical scans for modal analysis [19][20][21][22][23]. In addition, SLDV and CSLDV need cyclical excitation, and thus the mode would not change during measurement.…”

Diagnostics Based on Continuous Scanning LDV Measurements and RASTAR Analysis Method

“…CSLDV techniques well-suit structural integrity analysis for damage detection and identification and, in fact, several papers are available to this account. CSLDV techniques were attempted to either cracked beams or plates embedding damages, and these researches can be read in [15][16][17][18][19][20][21][22][23][24][25][26][27]. One of the most distinctive features of all the CSLDV papers, cited in here, is the recovery of the ODS(s) as means for further investigation of damage detection and identification.…”