Sound Absorption Of The Underwater Absorption Materials Based On The Finite Element Method

The acoustic concealing performance is significant for navy submarines and has arisen a great deal of interest for a long time. It generally adds a layer of anechoic tile on a submarine's surface to improve its concealing ability, which is an important technique and has been widely used. The key part of the anechoic tile is the underwater acoustic absorption material, which is generally a type of viscoelastic polymer containing various particles and/or macro acoustic structures. In this area, to improve the absorption characters, various newly advanced polymers and macro acoustic structures are generally developed in practical applications.Motivated by the insistent demands of the excellent underwater acoustic absorption material, based on the finite element method, the influences of different parameters on absorption performance of the underwater acoustic absorption materials are investigated systemically. Then, the simple means to optimize the absorption performance on the underwater acoustic absorption material is investigated. The main work and achievements are as follows:1. Based on the Bloch's theorem, a unit-cell model which contains fluid and backing is built because of the cavities arranged periodically in underwater acoustic absorption materials, which simplifies the computation of the acoustic properties. Then a finite element method is developed to calculate the acoustic characteristics (including reflection, transmission, and absorption coefficients).2. The effects of various parameters, such as the backing, the structure and array of cavities and material parameters, on the absorption properties of the underwater acoustic absorption materials are investigated systemically. Further, the deformations and movements of the inner nodes in absorption materials are analyzed in detail and the reasons that how the various parameters affect the absorption characters are found out.3. Based on what concluded in section 2, absorption characters of absorption materials are optimized using the assembled cavities and changing the material on the inner surface of the cavities. The results are showed that the assembled cavities by other two cavities with different shape can realize the effective absorption in different frequency domain. And the effective absorption moves to lower frequency domain by adding a layer of soft silicon rubber on the inner surface of the cavities.In summary, using the finite element method, the absorption performance of the underwater acoustic absorption materials are investigated systemically, and absorption characters of absorption materials is optimized initially using the assembled cavities and changing the material on the inner surface of the cavities. What investigated can help one to design an excellent absorption material both in theoretical and practical applications.