The goal of the project is to set up a laboratory equipment to measure vibration patterns of structures in view of the improvement to the vibrational and acoustical comfort of automobiles. The basic innovation is to develop an industrial holographic optical bench, enabling in double pulse, to record the three components of the displacement vector thus giving full and rapid access to the vibration pattern.
The project was to set up laboratory equipment to measure vibration patterns of structures in view of the improvement to the vibrational and acoustical comfort of automobiles. The basic innovation was to develop an industrial holographic optical bench, enabling in double pulse, to record the 3 components of the displacement vector, thus giving full and rapid access to the vibration pattern.
As a result of the first phase of the project, a method using 3 directions of illumination and one direction of observation has been retained. This appeared to be the most convenient; giving sensitivity, simplicity and accuracy in terms of optical arrangement.
Laboratory equipment has been developed to measure vibration patterns of structures with high spatial resolution and industrial capability, in view of their modification to improve the vibrational and acoustical comfort of automobiles.
An industrial holographic bench with image processing has been developed. It permits simultaneous measurement of the 3 components of the observed deformation vector. It can be used for periodic phenomena (sinusoidal response), with a reduced processing time for the analysis of the vibrating object by complementary techniques to existing holography, and for random, transient and complex vibratory phenomena (multimode response of a vehicle structure in running condition) using a multiexposure technique, and in particular the possibilities of multipulsed lasers.
It also allows accurate determination of the shape of the object using an optical method or a computer aided design (CAD) data set, the skin mesh file being integrated into the procedure of determination of the displacement vector, taking in account the shape of the object.
Computation and utilization of the optical measurements integrating all theoretical development and relevant software permit:
fringe analysis; 1-dimensional and 3-dimensional vibration analysis; 1-dimensional and 3-dimensional vibration analysis in multiexposure conditions; computation of the acoustical field (sound pressure, sound power, intensity, phase distribution) by a boundary element method; modal decomposition calculation from the recording of 2 consecutive interferograms.
The developed systems have already proved their worth in selected problems in the automotive industry. However, before the system can be distributed further developments are necessary.
The new system will offer the advantage of high spatial resolution and drastic reduction of the digitization time by several orders of magnitude.
As a result of the first phase of the project the following method, using three directions of illumination an one direction of observation, has been retained. This one appeared to be the most convenient : sensitivity, simplicity, accuracy in terms of optical arrangement.
The shape of the object, used as a reference, will obtained by optical measurement made in situ or by interrogating the CAD database. Finally, an automatic procedure will be industrialized for the quantitative evaluation of the resultant vector of the vibrations and air vibration, will be reduced by modification of the vibrational pattern (optimized by computer or trial and error method). New trends could be accompanied by these types of developments in holographic metrology for industrial purpose.
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