| The uppermost character of submarine is the flexibility and the stealth, which have decided its advantage of sudden strike and its effects of terrorizing. So that it is the key point of reducing submarine's acoustic for hiding its body in naval battle to ensure the combat effectiveness. The vibration and the sound radiation from the structure have important effect on the stealth of submarine. Reducing the vibration and the sound radiation of a submarine can not only improve its conceal, but also can enhance its sonar properties, improve its undersea antagonism ability thereby greatly. Therefore, the theoretical research of underwater monolayer or bilayer shell structure is very valuable.Based on the sound-vibration radiation theories, numerical analysis of vibration and sound radiation efficiency about three groups including the cylinder, the cone with cap, the ellipsoid of monolayer and bilayer shell structures in the fluid are disused and the FEM(Finite Element Method) and BEM(Boundary Element Method) analysis models are built. The numerical analyses of vibration and acoustic radiation from the three groups of monolayer and bilayer shell structure models are carried out by using FEM software ANSYS and BEM software SYSNOISE. First, the coupled-vibration of the shell and water is calculated and the normal displacement of the nodes is obtained. Then, by transferring the mesh of the shells and the displacement values on the nodes into software SYSNOISE, the sound pressure, the radiated sound power and the radiant efficiency are carried out by SYSNOISE. By use of the two softwares, the response of the sound and vibration of shells are computed, the influence of the light outer covering to the sound radiation are analyzed.In this dissertation, the characteristics of vibration and acoustic radiation from kinds of shell structures are analyzed. The effect of the light outer covering upon the acoustic radiation of bilayer shell structure is also analyzed by comparing the characteristics of vibration and acoustic radiation from monolayer and bilayer shell structures with conditions of changing the outer covering and ribs' thickness.The conclusion of the paper can be useful to predict the acoustic radiation of the submarine, reduce its sound pressure, and also for its development and exploitation. |
