Force Distribution Dependence of Sound Radiation From a Doubly Rib-Stiffened Plate

Abstract

Analytical formulae for both the velocity spectrum and the acoustic far-field radiated sound pressure for a doubly rib-stiffened (small frames and bulkheads) fluid-loaded elastic plate, excited by several different force distributions, are derived. The force distributions are (1) a line-force applied at a single point and (2) two Gaussian distributed force intensities whose effective width either spans the small rib spacing or the large rib spacing. The far-field sound pressure as a function of frequency is calculated. The concentrated line force case shows evidence of frame interference effects (sometimes referred to as Bloch waves) in the radiated pressure fields. These arise from coherent interaction of the pressure fields emanating from the frame reaction forces and the applied force pressure field. The frequencies at which these coherence effects are manifest depend on the stiffeners’ spacing as compared to the fluid-loaded flexural wavelength. The Gaussian force distribution eliminates these interaction effects depending on whether or not the effective force width is greater or less than the respective rib spacing.