Structure–Acoustic Interaction Between Vehicle Floor Panels and Carpets – Numerical Simulations and Measurements

Sammanfattning: An attribute that is highly valued amongst vehicle customers is low interior-noise levels when a vehicle is in use. Much of the interior-noise is believed to stem from the vibrations of floor panels in vehicles. Sources to these vibrations can be, for instance, e-motors, engines and road–tire interaction, which in turn is translated into disturbing noise inside the cabin. Interior carpets placed on the floor panels dampen the vibrations and reduce the noise transmission and radiation from the floor panels. The interior carpets in vehicles are usually composed of a light foam material covered by a heavy rubber layer on top, called heavy layer. Due to the different material layers and mechanical properties in such floor panel–carpet setups, the dynamic interaction and structure–acoustic interaction between the layers is complex. The layers vibrate with different, and sometimes conflicting, amplitudes and patterns at different frequencies. This dissertation investigates the structure–acoustic interaction in floor panel–carpet setups, with the dynamic interaction as a starting point, in order to increase the knowledge regarding noise radiation from the setups. Different modelling approaches with increasing complexity for the carpet are considered in order to give guidelines and recommendations for finite element modelling that is able to accurately represent the true behaviour of floor panel–carpet setups at different frequencies. This dissertation also presents an experimental testing that was conducted on a real floor panel–carpet to verify the findings. It was found that a simplified model in which only the mass of the carpet was considered, and distributed evenly on the floor panel, was sufficient to represent the vibration response and acoustic radiation of the floor panel–carpet setup at low frequencies. It was further established that at higher frequencies, geometrical and structural aspects of the carpet are essential to define in order to predict the behaviour with sufficient accuracy. When evaluating the vibration response of the floor panel–carpet setup at higher frequencies, it was found that a model in which the carpet was assigned linear elastic material properties gave satisfactory results in relation to a more advanced model in which the carpet was assigned porous elastic material properties based on Biot's theory. Further, when evaluating the acoustic radiation from the floor panel–carpet setup at higher frequencies, it was deemed necessary to acknowledge the air within the pores of the foam material of the carpet. Lastly, it was concluded that the main contributor to the disturbing interior-noise stemming from the floor panel–carpet setup, can be summarized as follows; • Low frequencies: Floor panel and carpet radiate noise as a solid unit • Mid frequencies: Heavy layer of the carpet dominates the radiation • High frequencies: Floor panel dominates the radiation