Donald B. Bliss
Dept. of Mech. Eng. and Mater. Sci., School of Eng., Duke Univ., Durham, NC 27706
A solution to the low-frequency noise reduction problem associated with panel/frame structures is proposed by way of tailoring the structural mode shapes associated with individual panels. The panel is shown to be a poor acoustic radiator when the panel dynamics are altered by tailoring the structural mode shapes. This is achieved by choosing appropriate panel stiffness and mass distributions. Noise reduction is achieved in a frequency band between the resonances of the first and third panel modes, when their out-of-phase motions result in acoustic cut-off. Normally, in a homogeneous panel this effect is very small and is in a very narrow bandwidth; but, by suitably tailoring the third mode in such a way as to increase its volumetric flow this effect is shown to increase in magnitude and bandwidth. The present work investigates this effect in a two-dimensional panel model, and the results obtained compare favorably to results from similar techniques such as alternate resonance tuning.