Simplified model for predicting acoustic performance of an underwater sound absorption coating

A simplified analytical model for predicting the acoustic performance of an underwater sound absorption coating is presented in this paper. The sound absorption coating contains hexagonally arrayed cylindrical cavities, so the unit cell of sound absorption coating could be approximated as a cylindrical tube. When the plane wave normally impinges on the sound absorption coating, the axisymmetric wave which propagates in the viscoelastic cylindrical tube will be excited. According to the two-dimensional analytic model, only the first mode (the lowest) should be taken into account in the acoustic performance estimation at low frequencies, because the attenuation of the first propagating mode is much lower than the others. Based on this conclusion, the simplified analytical approach has been given as follows: to solve the characteristic equation, the wavenumber of axisymmetric wave will be obtained firstly; then, the effective impedance of viscoelastic cylindrical tube can be calculated after the axial stress and the axial displacement are averaged, and the reflection coefficient and the transmission coefficient of sound absorption coating can be easily calculated by using the transfer matrix. Comparisons of the simplified analytical model to the finite element method and to the experiment data validate that the present model is a workable and satisfactory approach to predict the acoustic performance of sound absorption coating. In the final section, the effects of several parameters such as the cavity geometry and the acoustical termination on the performance of sound absorption coating have been discussed using the present model.