Excitation of a Submarine Hull by Propeller Forces

Abstract

This paper begins with a review of the unclassified literature relating to the radiated sound-field of a submarine. Only sound generation induced by the propeller is considered. It is of interest to investigate excitation of the submarine hull due to fluctuating forces from the propeller that are transmitted to a submerged hull via both the external pressure field and the propeller shaft. This will assist in predicting the resulting underwater far-field pressure of the submarine due to direct sound radiation from the propeller and its hull vibration. The submarine hull is often modelled as a thin-walled cylinder with appropriate endcaps or, alternatively, as an ellipsoid. The hull deflection shapes excited by the vibratory shaft forces correspond primarily to the accordion modes. There is little unclassified work on the excitation of a submarine hull by the radiated sound field of the propeller. Some work has been done in order to determine the exciting forces acting on the hull without considering its vibrational response and fluid interaction. However, most of this work does not take into account the compressibility of the fluid. Subsequent research requires the development of meaningful models for the investigation of the combined effects and interactions of the exciting forces taking account of fluid compressibility and fluid-structure interaction. For this work, numerical methods such as finite element and boundary element methods (FEM, BEM), computational fluid dynamics (CFD) and their combination are of relevance. A fully coupled FEM/BEM model has been developed to investigate the the excitation of a submarine hull through the fluid and the shaft taking fluid compressibility into account. For a realistic hull, the induced vibration due to fluid forces was found to be between 10% and 50% of the vibration due to the shaft force.