Attenuation of the structural and acoustic responses of a submerged hull

As the only true covert naval option, Submarines are in constant demand around the world. Reducing the structure borne noise from the hull is one of the highest priorities associated with Submarine design. The major sources of underwater noise from maritime vessels include onboard machinery, wake from the propeller, flow of fluid over the hull and excitation of the global hull resonances. At low frequencies, rotation of the propeller results in discrete tones at the blade passing frequency and its harmonics. The fluctuating forces at the propeller are transmitted through the propulsion system, resulting in excitation of the low frequency hull vibrational modes, which in turn results in a high level of structure-borne radiated noise. In this thesis, the low frequency vibro-acoustic responses from a submerged hull are determined and then attenuated using control strategies. Analytical and computational models of the submarine are created, allowing the structural responses of the hull and the far field acoustic responses to be obtained. The submarine hull is represented by a thin walled cylindrical shell, with additional complicating effects including ring-stiffeners, bulkheads, external fluid loading and ballast tanks. Novel control methods are utilised to attenuate the structural response of the submerged hull. Passive tuned vibration absorbers, active vibration control, hybrid vibration absorbers and compliant coatings are used to attenuate the breathing and higher order modes of the submerged hull. Attenuation of the higher order hull modes by active and hybrid means has rarely been examined. To the best of the author’s knowledge, the use of compliant coatings in conjunction with active or hybrid technologies has never been investigated. This thesis fills these gaps in the research. The highest level of attenuation is achieved from the use of the hybrid and coating technologies. The hybrid vibration absorbers provide greater attenuation than the passive control with a lower control force requirement than the active treatment. The acoustic coatings provide significant attenuation at the anti resonances. This thesis shows that passive, active, hybrid and coating treatments reduce the structural and acoustic responses of the submerged hull