Research Of The Absorbing Mechanism Of The Underwater Anechoic Coatings

Underwater anechoic coatings is the main equipment enhancing submarine's concealing ability, which is the only comprehensive key technique for effectively controling the submarine's radiated noise and reducing its active target echo intensity. The technique of the acoustical design of anechoic coatings is one of the most important parts. The design of anechoic coatings which are effective anechoic at low frequency and broad band is an especially difficult problem. Anechoic coatings with single cylindrical cavities are used traditionally whose effective frequency band is very narrow. The types of impedance transition and of composite resonant are now widely used, but the research in this area is not perfect. In this paper analytical means is used to study absorption coefficient's prediction models. Diversified cavity structures and material parameters are analyzed in detail in order to the anechoic coalings' acoustical design.The analytical mode is based on the theory of sound propagation in layered media. The concept of equivalent parameters is established. The absorption of sound energy by damping layer's is represented by use of complex sound impedance. Anechoic coatings' efficiency is getted from its front and back many layer's transfer loss compared. First, absorptive characteristic of homogeneous material is analyzed thoroughly. Then WKB perturbation means are used to calculate absorption coefficient of the impedance transition structure in this paper. The model based on the theory of sound propagation in varying cross section wave-guide, the equivalent impedance model in layered medium, the sound propagation model in viscous cylindrical tubes, foaming material equivalent parameter's model and resonant cavity theory are researched in succession. The great deal of simulation has been finished.In this paper MATLAB and VB are used to build a software which can predict absorption coefficient's of the underwater anechoic coatings from these analytical models. Finally, some algorithm of the single parameter minimization,nonrestraint nonlinear minimization and restraint minimization in the optimization design theory are studied. The formulas of absorption coefficient of these analytical models are object functions. The material parameters are primaryly optimized. Based on the analytical models of underwater anechoic coatings and the simulation research, the absorptive characteristics of some structures are analysed. Some advice are provided on improving absorptive characteristic of anechoic coatings, and enhancing submarine's concealing ability.