Reduction of Hull-Radiated Noise Using Vibroacoustic Optimization of the Propulsion System

Abstract

Vibration modes of a submarine are excited by fluctuating forces generated at the propeller and transmitted to the hull via the propeller-shafting system. The low frequency vibrational modes of the hull can result in significant sound radiation. This work investigates reduction of the far-field radiated sound pressure from a submarine using a resonance changer implemented in the propulsion system as well as design modifications to the propeller-shafting system attachment to the hull. The submarine hull is modeled as a fluid-loaded ring-stiffened cylindrical shell with truncated conical end caps. The propeller-shafting system is modeled in a modular approach using a combination of mass-spring-damper elements, beams, and shells. The stern end plate of the hull, to which the foundation of the propeller-shafting system is attached, is modeled as a circular plate coupled to an annular plate. The connection radius of the foundation to the stern end plate is shown to have a great influence on the structural and acoustic responses and is optimized in a given frequency range to reduce the radiated noise. Optimum connection radii for a range of cost functions based on the maximum radiated sound pressure are obtained for both simple support and clamped attachments of the foundation to the hull stern end plate. A hydraulic vibration attenuation device known as a resonance changer is implemented in the dynamic model of the propeller-shafting system. A combined genetic and pattern search algorithm was used to find the optimum virtual mass, stiffness, and damping parameters of the resonance changer. The use of a resonance changer in conjunction with an optimized connection radius is shown to give a significant reduction in the low frequency structure-borne radiated sound.