Structural-acoustic coupling characteristics of a rectangular enclosure with lightweight design considerations

As an effort to reduce energy consumption and hazardous emissions, lightweight design has become more and more important in new vehicle developments. In structural design, substituting conventional steel material with alternative low-density materials is one typical approach for weight reduction. However, the material and weight change often lead to variations in the dynamic characteristics of the structure such as its noise, vibration and harshness (NVH) performance. Based on a structural-acoustic coupled model of a rectangular cavity consisting of 1 or 2 flexible panels, this paper presents detailed parametric studies aiming at reducing the total weight of the structure and simultaneously improving the NVH performance. For the case of a single flexible panel subject to a point force excitation, it is found that substituting the heavier steel panel with a lighter aluminum panel may actually reduce the sound radiation inside the cavity, especially in the low frequency range. On the other hand, at higher frequencies, the radiated noise level seems to be roughly inversely proportional to the material density, making the lightweight design goal difficult to reach without sacrificing the NVH performance. For the case with dual flexible panels, it is shown that the two panels are generally weakly coupled through the acoustic cavity. Thus, their lightweight designs may be treated separately under a geometrically symmetrical load condition, or considered independent of the NVH criterion for the panel that is free of external excitation. However, for the latter case, within certain narrow frequency ranges where the modes from the two panels are sufficiently close and are also coupled well with the nearby acoustic mode, the cavity interior noise level may still be reduced significantly with a proper lightweight design of the panel. (C) 2012 Institute of Noise Control Engineering.