Operational modal analysis using lifted continuously scanning laser Doppler vibrometer measurements and its application to baseline-free structural damage identification

Abstract

A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of efficient and spatially dense vibration measurements by sweeping its laser spot along a scan path assigned on a structure. This paper proposes a new operational modal analysis (OMA) method based on a data processing method for CSLDV measurements of a structure, called the lifting method, under white-noise excitation and applies a baseline-free method to identify structural damage using estimated mode shapes from the OMA method. The lifting method enables transformation of raw CSLDV measurements into measurements at individual virtual measurement points, as if the latter were made by use of an ordinary scanning laser Doppler vibrometer in a step-wise manner. It is shown that a correlation function with nonnegative time delays between lifted CSLDV measurements at two virtual measurement points on a structure under white-noise excitation and its power spectrum contain modal parameters of the structure, that is, natural frequencies, modal damping ratios, and mode shapes. The modal parameters can be estimated by using a standard OMA algorithm. A major advantage of the proposed OMA method is that curvature mode shapes associated with mode shapes estimated by the method can reflect local anomaly caused by small-sized structural damage, while those estimated by other existing OMA methods that use CSLDV measurements cannot. Numerical and experimental investigations are conducted to study the OMA method and baseline-free structural damage identification method. In the experimental investigation, effects of the scan frequency of a CSLDV system on the two methods were studied. It is shown in both the numerical and experimental investigations that modal parameters can be accurately estimated by the OMA method and structural damage can be successfully identified in neighborhoods with consistently high values of curvature damage indices.

Experimental Detection and Measurement of Crack-Type Damage Features in Composite Thin-Wall Beams Using Modal Analysis

“…The composite plate analyzed had dimensions of 150 × 300 × 1 mm , and the scanning area measured with a SLDV was 140 mm × 280 mm at a spatial resolution of 0.5 mm. An SLDV was also used in [ 15 ], where the lifting method and the curvature mode shape (CMS) metric were applied to identify structural damage in an aluminum cantilever beam. In another work, Katunin presented an approach for damage identification in beams and plates based on the S-transform [ 16 ].…”

Application of scaled boundary finite element method for vibration-based structural health monitoring of breathing cracks

“…Vibration response of structures that is typically used for their health monitoring has some superiority over methods based on frequency response. The damage effects better emerge in the frequency content of the dynamic response and open a category of monitoring methods called frequency methods (Giurgiutiu, 2007;Sepehry et al, 2014;Xu et al, 2019;Zhang et al, 2016). Increasing the excitation frequency decreases the wavelength to a comparable size with tiny damages and makes them detectable.…”

Moving sensors for improved estimation of dynamic structures: Experimental validation

“…A few inspection robots have been developed so far for structural health monitoring purposes, for example, a robot able to crawl on twodimensional surfaces for the inspection of aircraft panels (Backes et al, 1997) and future space stations (Swei et al, 2020), magnet-wheeled robots that can maneuver over structures made with ferromagnetic/steel materials (Zhu et al, 2010(Zhu et al, , 2009, as well as pipe inspectors (Fischer et al, 2008). On the other side, continuous-scan laser Doppler vibrometry (CSLDV) techniques measure the response of a structure by continuously sweeping a laser beam over the surface of a structure as a measurement is acquired (Allen and Sracic, 2010;Xu et al, 2019). A natural application of CSLDV is the continuous monitoring of the response of an entire structure during its operations.…”