Acoustic excitation of hull surfaces by propeller sources

Abstract

Acoustic boundary element models are used to solve the Helmholtz equation in order to explore the nature of fluctuating hull pressures due to propeller sources when the wavelength of the underwater sound is comparable to the hull dimensions. Sources are represented by stationary monopoles and dipoles near a rigid hull. The results for submerged and floating bodies are described. A simple ellipsoidal representation of submerged and floating bodies is used first to aid understanding of how hull pressure distributions are affected by the location and frequency of propeller sources. The sea surface is represented using image techniques, to ensure zero pressure there when the body is floating. Solid boundary factors are used to indicate the principal effects of source location, frequency, and the sea surface. Finally, the results from an independent model of a cruise liner hull are used to illustrate the combined effects of diffraction, interference, and flotation on hull forces, with explicit modeling of the free surface.