FEM System Development for Dynamic Response Analysis of Acoustic Trim

The multilayer vehicle trim is well known for its effective influence upon noise and vibration characteristics not only in the high-frequency range but also in the low and mid-frequency ranges. FEM technologies which represent the accurate stiffness, mass and damping of trim parts such as the dash silencer and the floor carpet are essential in order to extend current body FEM capability to the road noise and the engine noise issues generated in the mid-frequency range. Conventional modeling methodologies such as local impedance and/or spring-mass modeling that express absorption and insulation properties of acoustic trim contain limitations in the mid-frequency range. There are few reliable FEM technologies to create practical vehicle models that represent the precise characteristics of the trim. In this paper, poroelastic modeling of acoustic multilayer trim was established by employing Biot theory. The trim model effectiveness proposed in this paper was confirmed by applying it to various types of trim; for example conventional isolative type trim and absorptive one. But the trim model usually demands direct frequency response analysis that consumes excessive computation time. Therefore an FEM system was developed to reduce this computation time by using reduction of degree of freedom (DOF) of trim model, modal decomposition of structure attached to trim model, and parallel processing. The system was applied to a conventional vehicle model and a vehicle body cut out panel and showed good correlation with experimental data.