Vibration And Sound Radiation From Fluid-loaded Orthotropically Reinforced Infinite Cylindrical Shells

With the progressive development of underwater acoustic detection and acoustic-guided weapons, more advanced requirements are imposed upon the acoustic properties of submarines. Provided that the submarine structure strength is met, noise is vital to submarine battle ability. The submarine noise detected by sonar consists of two parts: propeller-generated hydro-dynamical noise, which can be greatly reduced by improving the submarine rear shape; radiated noise from the submarine structure excited by the centrifugal forces (moments) of rotatory machine, which is more complicated and influenced by many factors. This paper is aimed to provide a computational method of sound radiation from the pressure and non-pressure hulls of submarines subjected to harmonious point forces. It is significant for reducing vibration and sound radiation of the submarine hull, guiding the optimization design of submarine and enhancing its battle ability.The submarine structure is simplified to single or double infinite cylindrical shell stiffened with rings, bulkheads and stringers, focusing on underwater sound radiation from the single shell. The shell motion is described by Donnell's theory including excitation forces and reactions of rings, bulkheads, stringers and fluid, which leads to the fluid-structure coupling vibration equation. Expressing displacements by velocities, applying modal expansion circumferentially and Fourier transformation longitudinally result in the shell's modal equations of motion. Then Fourier transformation is employed to solve equations of motion of the rings, bulkheads, stringers and fluid respectively, with their reactions (moments) expanded by the shell's in-vacuo modes. By means of continuity conditions on the interfaces between the shell and the stiffeners as well as the fluid, and inverse Fourier transformation, the modal reactions (moments) are finally expressed by the shell's modal velocities. Substituting the above modal reactions (moments) and excitation forces into the shell's modal vibrationequations, the shell's radial modal velocity are obtained from which the far-fieldsound pressure derived by stationary phase method can be calculated.MATLAB procedure is coded to compute the far-field sound pressure levels of the shell excited by radial point force. The influences of modal truncation, stringers, bulkheads and damping on the shell's far-field sound pressure are analyzed, laying down the basis for accurate analysis of the sound radiation from fluid-loaded reinforced double cylindrical shells.In addition, the sound radiation from fluid-loaded reinforced double cylindrical shells, periodically connected by slabs, is formulated.