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Operational Modal Analysis -the technique where modal parameters are estimated without known input forces- has been an accepted tool in advanced mechanical engineering. The technique has its advantages were the modal parameters have to be estimated during the operational conditions as in flight ad on road testing. The paper will discuss the recent state of the art in vibration data acquisition as well as in modal parameter estimation enabling easy use of Operational Modal Analysis. A new data optimisation method, which will enhance the speed of calculation, will be shown Examples from both laboratory set-up and practical examples from automotive applications will be shown.

The non-contact measurement methods used in laser-based vibrometers offer some unique advantages compared to using traditional, surface mounted accelerometers. Applications that were previously difficult or even impossible to perform can now be accomplished. This includes measurements on small lightweight, delicate or hot structures, inaccessible parts and measurements in high-voltage or radioactive environments. Furthermore, the frequency range can be quite high. When using a Scanning Laser Doppler Vibrometer (SLDV), additional benefits are gained. This includes high spatial resolution in the measurement and fast and flexible data acquisition. The paper itself describes the major features of such Scanning laser Doppler Vibrometer in general, but emphasis will be given during the oral presentation to its benefits in the automotive industry specifically.

Near-field Acoustical Holography (NAH) can perform source location with high spatial resolution even at low frequencies by measuring very close to the sound source and by reconstructing part of the evanescent near-field. But a measurement grid with less than half wavelength spacing is required, and the measurement area should cover the main radiating regions to avoid windowing effects. These requirements make the method impractical at higher frequencies, typically above 3-5 kHz. At those higher frequencies, however, Beamforming can provide good resolution with typically 40-90 measurement points, because it is possible to use irregular arrays at intermediate measurement distances. Various array designs exist that can provide good suppression of ghost images up to frequencies, where the average element spacing is much larger than half a wavelength. The problem to be addressed here is that it is not practical to have to use two different arrays to perform the two types of measurement.