Efficacy of Damping Submerged Cylindrical Shells

Abstract

An experiment has demonstrated that a practical mechanical-damping treatment can significantly reduce the resonant vibration of an end-stiffened cylindrical shell in water. High-Q resonances ranging from about 100 to over 2000 were observed for the undamped shell in both air and water for selected and identified low-order flexural modes of vibration (m=1, 3; n=2, ⋯, 10). A commercial viscoelastic damping layer applied to the interior of the shell reduced these resonances, in both air and water, to Q's of 20 or smaller; some resonant amplitudes were reduced by as much as a factor of 100. The radiation resistance of the water was measurable, but the dissipation was negligible compared with that provided by the damping treatment. The potential usefulness of mechanical damping for the control of resonant behavior of submerged structures is, therefore, established, at least for situations resembling those of this experiment. Moreover, a method of investigation essential to the detailed study of the low-order modal behavior of actual submerged vibrating structures is established. [This work was supported by the U. S. Navy Bureau of Ordnance under direction of the Ordnance Research Laboratory.]