| The stealth performance of submarines is usually concerned by people. Acoustic covering layers are usually applied to the surface of the shells that is very effective to improve the stealth performance of underwater moving bodies. In this paper, the finite element method is applied to analyze the sound reflection,transmission and absorption characteristics of layered acoustic structures when the incident plane wave impinges at normal and oblique incidence. Then, the sound insulation of sound-isolating and decoupled tile is studied based on the theory of non-uniform wave guide.Sound character of anechoic coating is studied by the finite element approach, .' and the solution is obtained by the program.The frequency response curves of reflection coefficients,transmission coefficients and absorption coefficients are numerical simulated on different cases of backing conditions .The viscoelastic material is considered as the elastic medium with the certain internal losses, including the shear deformation of the viscoelastic material, and the Young's modulus are expressed as complex numbers. A unit cell is analyzed, and the influences of boundary condition,shape of the cavities and the direction of incident wave to harmonic properties are studied with the help of Bloch—Floquet periodic relations.Sound insulation of sound-isolating and decoupled tiles covered on the outside surface of pressure hull is studied based on the theory of non-uniform wave guide. Shapes of cavities and material parameters are designed by inversion of transfer matrixes and the sound energy relation of inverse transmission. In the end, the shape of cavities of sound-isolating and decoupled tiles which have better sound insulation is obtained. The researches show that the impact of Young's modulus on sound transmission loss is more than density and loss ratio; invertion cavities can improve the low frequency sound insulation character of present sound-isolating and decoupled tiles apparently.
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