Low frequency random excitation of water-loaded rectangular plates

Abstract The response to random excitation of a thin rectangular plate inserted in an infinite baffle is considered. The infinite half space on one side of the baffle is filled with water. Only low frequency (that is, when the wavelength in the acoustic medium is greater than the plate dimensions) excitation is discussed. The analysis is based on the in vacuo modes or characteristic functions of the plate. The inter-modal coupling coefficients are evaluated. An approximate solution of the resulting infinite set of linear simultaneous equations for the plate modal velocity amplitudes is obtained in terms of modal admittances of the plate-fluid system. These admittances describe the important modal coupling due to both fluid inertia and radiation damping effects. The effective coupling depends on both wave-number matching and resonance frequency proximity, and hence on the relative magnitudes of the widths of the resonance peaks and the frequency spacing of the resonances. Expressions are obtained for the spectral density of radiated acoustic power for the particular case of excitation by a turbulent boundary layer.