Application of stroboscopic andpulsed-laser electronic speckle pattern interferometry (ESPI) tomodal analysis problems

Abstract

Accurate structural models are key to the optimization ofthe vibro-acoustic behaviour of panel-like structures. However, atthe frequencies of relevance to the acoustic problem, the structuralmodes are very complex, requiring high-spatial-resolutionmeasurements. The present paper discusses a vibration testingsystem based on pulsed-laser holographic electronic speckle patterninterferometry (ESPI) measurements. It is a characteristic of themethod that time-triggered (and not time-averaged) vibration imagesare obtained.Its integration into a practicable modal testing and analysisprocedure is reviewed. The accumulation of results at multipleexcitation frequencies allows one to build up frequency responsefunctions. A novel parameter extraction approach using spline-baseddata reduction and maximum-likelihood parameter estimation wasdeveloped. Specific extensions have been added in view of theindustrial application of the approach. These include theintegration of geometry and response information, the integration ofmultiple views into one single model, the integration withfinite-element model data and the prior identification of thecritical panels and critical modes. A global procedure was henceestablished. The approach has been applied to several industrialcase studies, including car panels, the firewall of a monovolumecar, a full vehicle, panels of a light truck and a householdproduct. The research was conducted in the context of the EUREKAproject HOLOMODAL and the Brite-Euram project SALOME.