Traditionally in the automotive industry, the acoustic trim has been modelled using a series of spring/mass/dampers added to an FE description of the structure. This simple method has deficiencies in accuracy even in the low frequency domain and could therefore not be used with confidence as a predictive method over 150 Hz. Other approaches literally ignored the effect of trim on the structure and focused at representing the acoustic trim absorption in the interior fluid. In recent years, new developments have shown that the physics of acoustic trim can be well represented when modelling the porous layers using Biot parameters. In fact, since the Biot theory describes the interaction between the acoustic trim, the structure and the fluid using intrinsic properties of the foams and fibers, this modelling approach can be considered predictive over the full audible frequency range. It has been shown for many years now that for high frequency analysis using Statistical Energy Analysis (SEA), Biot parameters play a critical role in the predictive character of a model and therefore its accuracy. Similarly, combining Biot theory with the use of Finite Element Method (FEM) to model acoustic trim in low frequency has shown a significant improvements in the accuracy of predictions and has pushed the upper limit of FE trim simulation over 400 Hz. This paper introduces the Biot theory approach and the interaction between trim, structure and fluid. It also presents a comparison between traditional and Biot theory approach on an academic and industrial case. Sensitivity of the response to Biot parameter values is also presented.
2010 – 1st EAA Euroreggio 2010, Ljubljana, Slovenia
Denis Blanchet (ESI Group, Germany)
Arnaud Caillet (ESI group, Germany)