Noise, vibration and harshness (NVH) levels are recognised to be an important selling point for vehicle manufacturers. However, at present it is difficult to design against boom-noise which is essentially high interior noise levels generated in the low-frequency range (40-200 Hz). In this paper, two theoretical models will be used to simulate boom noise with the purpose of understanding its physics and identifying parameters that affect its generation. The first (box) model is based on a simple plate-cavity layout. Acoustic excitation is performed and the plate is randomised to generate Monte-Carlo simulations of the effects of structural uncertainties. The second (hybrid) model is formulated based on a mass-spring-damper system that is connected to a fuzzy plate element. For both models, results indicate a boom noise around the acoustic resonant frequency which is 5-10 decibels higher than the mean noise levels. Physically both models show that boom noise is the result of coupling between plate and acoustic modes where there is more of the former compared to the latter within the frequency range of interest. The acoustic mode is thought to be the dominant component in the generation of boom noise. Variances in panel quality can considerably affect overall responses by up to 10 dB. This demonstrates why identical vehicles may have different noise levels despite being manufactured and assembled on the same production line. An interesting observation from the results obtained from both models with strong coupling is the dip in the relative variance for the plate energies around the acoustic resonant frequency. This is because a highly responsive plate provides damping to the acoustic mode, which reduces the amplitude of the acoustic mode, and hence reduces the acoustic excitation of the plate. Conversely, an unresponsive plate provides little damping and thus feels a greater degree of acoustic forcing. This feedback mechanism means that both 'responsive' and 'unresponsive' plates tend to have the same actual level of response, leading to a low variance.
A hybrid method for modelling in-vehicle boom noise
Hybrides Verfahren zur Simulation niederfrequenter Geräusche im Innenraum von Kraftfahrzeugen
2004
13 Seiten, 12 Bilder, 1 Tabelle, 8 Quellen
Conference paper
English
Overall vehicle system noise: sonic boom
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|Overall vehicle system noise: sonic boom
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|Computer Simulation of In-Vehicle Boom Noise
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