Diagnostics Based on Continuous Scanning LDV Measurements and RASTAR Analysis Method

Abstract

AbstractThis paper presents a technique for rapid diagnostics of structural integrity that exploits spectral sidebands measured by the continuous scanning LDV (CSLDV) measurement method. Structural integrity can be monitored by Operational Deflection Shapes ODSs, which can be quickly measurable at any excitation frequency when a laser continuously scans a vibrating surface. The LDV output time series is an amplitude modulated signal, and its spectral lines are used for recovering polynomial coefficients which build a polynomial function describing a deflection shape. The process of conversion from the time series to a polynomial function can be biased by measurement and analysis uncertainty which eventually will affect the quality of recovered ODS. This paper will show that an effective, rapid and straightforward diagnostics can be yielded by direct analysis of the spectral sidebands without the need to be transformed into polynomial coefficients. The Relative Amplitude of the Sidebands to the Total Amplitude Reference (RASTAR) method is an indicator that exploits the relative amplitude of the sidebands against a datum reference. The relative magnitudes of the sidebands will not change in the absence of any the structural change, and it is independent of the vibration response amplitudes set for the measurements. Such diagnostic method suits maintenance operations of structures which could be quickly scanned by an SLDV system providing an indicative level of structural integrity over the number of duty cycles.