Response of regularly ribbed fluid loaded panels

Abstract

The paper largely presents computer estimations of the response of models of mechanically driven regularly ribbed fluid loaded panels. The estimates are presented in terms of the spectral distribution of the acceleration of the panel and the spectral distribution of the pressure in the fluid. The ribs are defined in terms of line and line moment impedances and these may be mass, resistance, and/or stiffness controlled, and of various values and combinations thereof. Typical estimations of the spectral distribution of the magnitudes of the acceleration are displayed as functions of the normalized wavenumber that lies in the plane of the panel and normal to the ribs, and the normalized frequency. It is found that the magnitudes of the acceleration vanish at the sonic loci when fluid loading is included. A sonic gorge, with a nadir at the sonic loci, characterizes the acceleration of the fluid loaded panel, whether it is unribbed or ribbed. If the magnitudes of the line impedances (and, when appropriate, also the line moment impedances) of the ribs are not unusually high, the magnitudes of the acceleration and their patterns elsewhere in the spectral domain remain substantially similar to those obtained in the absence of fluid loading. The dissimilarities are readily accounted for by straightforward arguments relating to the increase in the surface mass and the radiation damping that manifest fluid loading on panels. The corresponding magnitudes of the pressure on the surface of the panel do not vanish at the sonic loci as do the magnitudes of the acceleration. Rather, a moderate sonic peak appears at the sonic loci and a sonic ridge replaces the sonic gorge. The loss of subsonic components in the pressure on a plane as the plane is removed from the surface of the panel, is clearly and dramatically displayed.