On the radiation of sound from an immersed cylindrical shell close to the sea surface

Abstract

Numerical methods for the prediction of underwater radiated noise from immersed structures play a key role in the naval and offshore industry to ensure high acoustic performance of systems or to preserve natural habitats. Most of the approaches so far assume that the surrounding fluid is homogeneous and unbounded. However, in many situations the structure can be close to interfaces, namely the sea surface and the sea bottom, such as navigation of underwater vehicles in shallow waters. The Lloyd's mirror effect describes the interference phenomena occurring when a sound source is close to the sea surface. This effect is easily accounted for with a source image approach, while the strong vibro-acoustic coupling between the structure and the interface is more complicated to deal with. In this context, an analytical method has recently been developed to predict the vibro-acoustic behaviour of an infinite length cylindrical shell close to the surface, based on the shell equations and Graf's addition theorem. In the present work, we compare this approach to a simplified one where the strong interactions between the surface and the structure are not considered. Results highlight these effects on a typical underwater structure