Sound radiation of a thin infinite plate in light and heavy fluids subject to multi-point excitation

Abstract

This paper presents the mathematical expressions for sound radiation from a thin infinite isotropic plate coupled with light and heavy fluids and subject to multi-point excitation. The force at each point is phase dependent. Two typical cases are investigated theoretically; one is the two-point excitation with forces in phase and out of phase (moment). The other one is multi-point excitation with two rows of forces in phase and out of phase. The second one can be used to simulate the sound radiation from a rigid body mounting system with multi-point mounts on a thin infinite plate. It is found that the calculation of total sound pressure in the far field for the above cases cannot be simply considered as the superposition from a single point force excitation as is normally done for the sound pressure calculation from multiple point sound sources. Examples are presented to show the radiation patterns of the above two cases based on the derived equations. The results unveil that, as the plate is coupled with water, the sound radiation is stronger and much more dependent of the excitation frequency, especially as the plate is excited by a moment. It implies that the force excitations at high-order harmonic frequencies may contribute more structure-borne noise than that at basic excitation frequency even though their amplitudes are much smaller.