Noise Reduction Analysis of an Underwater Decoupling Layer

Based on the vibro-acoustic coupled model of an infinite bare plate, using the impedance transfer matrix, the analytical model predicting the noise reduction performance of a void decoupling layer covered on an infinite plate under mechanical excitation is presented. The void decoupling layer, especially containing periodically distributed cylindrical or conical holes, can be approximated as a homogenous material described by several parameters, including the effective density, the effective propagation constant, and the effective attenuation. Analysis shows that (1) the primary mechanism of noise reduction is the vibration attenuation of the decoupling layer from the “front” interface between the decoupling layer and the plate to the “back” interface between the decoupling layer and the water, rather than the plate vibration reduction, (2) the plate vibration is increased with the decoupling layer at low frequencies and the increased amount of plate vibration is more than the attenuated amount of the decoupling layer vibration, so the radiated pressure is increased at low frequencies, and (3) at high frequencies, the pressure insertion loss, which quantitatively describes the noise reduction performance of the decoupling layer is estimated by the general sound transmission loss through a simple expression. Finally, good agreement between analytical calculations and experimental results validates that the developed model is useful to predict the noise reduction performance of the void decoupling layer.