The investigation of the methods for predicting the sound field in a non-anechoic tank with elastic boundary

Abstract

The non-anechoic tank with elastic boundary is a widely used experimental apparatus, and mastering the sound field characteristics is very important for acoustical testing. But the predicting methods still need to improve to ensure a better fit with sound field testing. Considering the enormous differences of the characteristic impedance between air and water, the analytical model of a non-anechoic tank with elastic boundary in previous works was always based on the absolute soft approximation to simulate the boundary of the sound field. However, the boundary effects on the sound field which are caused either by the absolute soft or the elastic are very different, and that may be the real reason why there are obvious differences between analytical calculations and experimental results. Because of the complex coupling mechanism among boundary, sound field and sound source, the numerical methods relevant to analysis of sound field in a tank are somewhat limited. In order accurately to forecast the sound field in a non-anechoic water tank with elastic boundary, both the analytical method and numerical analysis method are established in this study. The analytical method is based on normal-wave theory, in which the general velocity potential function is constructed by considering the boundary influence. The numerical method is based on finite element theory, in which the acoustics finite element software Actran is used for computing, and the convergence validity of the numerical method is verified by the established analytical method. Differences between the effects to the sound field caused by the absolute soft boundary and the elastic boundary are further analyzed. Finally, verification tests are carried out in a glass tank. By comparing the normalized amplitude of sound pressure, we found that the calculation and experimental results matches well, especially in the low frequency range.