Automotive machinery cover acoustic radiation with frequency-dependent preloaded gaskets

Acoustic radiation from machinery covers is an important factor in automotive noise and vibration. The magnitude of this radiation is affected by the presence of gasket material in several ways: The compliance of the gasket is affected by bolt preload and nonlinear deformation, and the damping effect of the gasket exhibits strong frequency dependence, which itself is preload dependent. Numerical models for this phenomenon are essential, because the geometry is too complex for analytical methods and the available constitutive and damping data is strongly frequency- dependent. We describe a mechanical model for automotive gasket behavior which is suitable for incorporation into finite element analysis, and which extends from nonlinear static preloading to frequency-domain vibration. In the frequency-domain, both stiffness and damping properties may exhibit frequency-dependence. We present numerical results demonstrating the effect of the gasket damping and the exterior air on the response of the cover. The acoustic radiation is quantified using a fast radiated power method. The latter case, well-suited to steel structures in air, relies on the surface normal velocities of the vibrating structure, only.