Viscoelastic Multi-layer Composite Structure Of Sound Absorption Properties

Noise produced by underwater aircraft is an increasingly very important ocean environmental pollution.The technique of anechoic coating is crucial to underwater structure stealth technology. In this thesis, one-dimensional and two-dimensional approximate theoretical model of an incidence plane wave on anechoic coating are established and studied theoretically. Theoretical research is helpful to understand the acoustical characteristics of anechoic coating, and has important guiding significance for the design of anechoic coating and the choice of rubber material.Introducing the complex visco-elastic modulus, visco-elastic wave equation has the similar form with elastic wave equation for harmonic wave motion, in case of linear visco-elastic. The anechoic coating is assumed to be planar multi-layered system in the theoretical analysis. Simultaneously, absorption characteristic of anechoic coating on underwater structure is studied. Various cavity size, cavity shape, perforation ratio and material parameter concerns are analyzed. And the absorption performance of oblique plane wave on multi-layered structure is studied elementarily.Some very useful results are obtained through the analysis of anechoic coating of underwater structure. Material parameter, various cavity size, cavity shape etc are greatly contribute to absorption characteristic.As can be seen from the above conclusions , which are helpful to comprehend the mechanism of sound absorption better. The theoretical compute about absorption coefficient have good adaptability to various structures and different function of the sound-absorbing material and can provide greater theoretical guidance and engineering guidance for the design of the anechoic coating.