Transfer function method for acoustic property study of underwater anechoic layer

This paper investigates theoretically the noise reduction property of a submarine wall structure consisting of submarine hull and underwater anechoic layers that contain inner holes. The case that both sides of the submarine wall structure are excited by fluids is considered. Built upon the transfer function method, an analytical anechoic model is developed to determine the pressure insertion loss induced by the anechoic layer. Numerical calculations are subsequently carried out to investigate the influence of fluid medium type, thickness of submarine hull, thickness of anechoic layer as well as shape of inner holes upon the vibro-acoustic properties of the structure. When the fluid medium inside is air, at low frequencies, the reduced vibration due to the anechoic layer is smaller than the increased vibration of submarine hull caused by the anechoic layer, and hence the vibration of the whole structure is increased; at high frequencies, however, the anechoic layer leads to significant attenuation in vibration of the whole structure. When the fluid inside is water, the anechoic layer attenuates the vibration of the whole structure at all frequencies, with the attenuation increasing with increasing frequency. Increasing the thickness of submarine hull or anechoic layer reduces the vibration of the whole structure. When the hole diameter first decreases and then increases in the direction from inside to outside the submarine, the anechoic layer exhibits the best attenuation effect at high frequencies; when the hole diameter first increases and then decreases, the best attenuation is achieved at medium frequencies.