Influence Of Truncation And Limited Water On Vibro-acoustic Characteristics Of Cylindrical Shell

Vibration and sound radiation of cylindrical shells in water is one of the researchfocus in recent years. This thesis discusses the effect of limited water boundary onvibration and sound radiation. The traditional studies generally assume that the structure isimmersed in an infinite field, without considering the boundary reflection effect. Limitedwaters boundary is treated as free surface and rigid wall, to analyze their impact on theresponse of cylindrical shells.Firstly, the problem of structural truncation is discussed. Based on finite elementmethod (FEM), the modes and harmonic response of cabin modal of different boundaryconstraints are calculated. Comparing with the whole ship model, boundary conditions ofthe cabin truncated are settled, and the applicable frequency range is determined.Secondly, the effects of limited waters boundary on vibration and sound radiation arestudied using analytical method and FEM. When the cylindrical shells are partiallysubmerged, the relationship between submerge state and vibration are studied. When theshells are totally submerged in different immersion depths, the responses of the shells aretaken into compared to figure out the effect of boundary. The thesis also analyzes thecause of the boundary’s effect by computing the added mass of the shells.Finally, as the vibration analyses of cylindrical shells are accomplished by FEM, theboundary element method (BEM) is used to analyze the free surface and rigid wall’s roleon sound radiation, based on the theory of image method. This method requires vibrationaldisplacement distribution to set boundary conditions, then construct a symmetric orantisymmetric virtual source, with considering the role of the real source and virtualsource, the sound radiation of the cylindrical shells in the sound field with boundary arecalculated.The virtual source image method and other numerical methods are introduced tosolve the limited waters acoustic radiation issues. Although the cases are ralativelyidealistic, the study still has some engineering significance for actual complex finite soundfield.