Reduction of the Sound Pressure Radiated by a Submarine by Isolation of the End Caps

A passive isolation approach to reduce the sound pressure radiated by a submarine is presented. The submerged vessel is modeled as a stiffened cylindrical hull partitioned by bulkheads and with two end caps of conical shape. Fluctuating forces from the propeller are transmitted to the hull through the shaft and a rigid foundation, resulting in axisymmetric excitation of the hull. The hull surface motion is mainly in the axial direction with a small radial component due to the coupling between the two orthogonal shell displacements. The sound pressure resulting from the axial motion is radiated from the end caps of the submarine. This work investigates reduction of the far field sound pressure by passive isolation of the end caps from the main hull. Isolation of the axial motion of the end caps from the cylindrical hull results in significant reduction of the radiated sound at low frequencies. The fluid loading approximation for a finite cylindrical shell in the low frequency range is also discussed.