基于传递函数法的水下消声层声学性能研究

潜艇在水下潜航时,为防止敌方声呐的探测,需要采用各种主被动手段来降低自身的噪声,其中主要手段就是在潜艇外壳覆盖黏弹性消声瓦结构.针对潜艇消声瓦结构降噪问题,考虑结构两侧的流体负载,建立了潜艇壁面水下消声覆盖层的消声理论模型.将潜艇壁面结构简化为无曲率的无限大薄板,基于基尔霍夫(Kirchhoff)薄板理论和声波方程,应用传递函数法导出了消声覆盖层的声压插入损失.利用所建理论模型进行了数值计算,讨论了不同的内侧流体介质、艇壳厚度、消声层厚度和孔腔形状对壁面结构振动与声学性能的影响.研究发现,内侧介质为空气时,在低频段,消声层对结构振动的削弱量小于消声层加入后艇壳振动的增强量,故消声层的加入反而使壁面结构的振动增大;在高频段,覆盖消声层后壁面结构的振动明显减小.内侧介质为水时,覆盖消声层后,壁面结构的振动在全频段均减小,且减小量随频率的增加而增加.增大艇壳厚度及消声层厚度有利于潜艇壁面结构的减振降噪.当消声层孔腔内径沿潜艇内侧至外侧的方向先减小再增大时,消声层在高频段减振降噪效果较佳;当孔腔内径沿潜艇内侧至外侧的方向先增大再减小时,消声层在中频段的减振降噪效果更好.

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 e ect at high frequencies; when the hole diameter first increases and then decreases, the best attenuation is achieved at medium frequencies.