半无限基衬上功能梯度材料层结构声学性能研究

Analysis of acoustic characteristics of functionally graded material layer based on a semi-infinite substrate

基于回传射线矩阵法,研究了平面声波入射下半无限弹性基衬上功能梯度材料层的水下声学性能。将功能梯度材料层沿厚度方向上分层,各子层视为均匀材料,并推导了流-固界面处及功能梯度层与基衬界面处的声波局部散射矩阵及各分层的相位偏移矩阵,然后组装得到关于各分层材料波幅的总体矩阵方程,最终求解功能梯度材料层的反射系数及吸声系数。通过数值计算分析了材料参数沿厚度指数型式变化的功能梯度材料层的材料梯度、入射角、基衬材料参数等因素对吸声系数的影响规律。分析结果表明半无限介质上的功能梯度材料层结构实现了由表层材料向基衬材料参数的渐变,对中高频声波具有较宽频的吸声性能;弹性基衬材料主要影响功能梯度层结构的低频吸声性能,基衬材料的特性阻抗与水越接近有利于提高低频段吸声性能。

The underwater acoustic characters of an infinite functionally grade material（FGM） layer with a semi-infinite elastic substrate and subjected to an oblique incident plane wave are investigated based on the extended reverberation-ray matrix method（RMM）. With the treatment to divided FGM layer into sub layers, each sub layer is being treated as a homogeneous layer, the local scattering matrixes at fluid-FGM and FGM-substrate interfaces are deduced, these local scattering and phase matrixes are then stacked to form the global matrix, sound reflection and absorption coefficients are obtained by solving the matrix equation. Reflection and absorption coefficient changing with respect to the material gradient, incident angle,substrate material of the FGM layer with exponential increasing material properties are analyzed by numerical simulation with present method. The results show that the FGM layer based on the semi-infinite substrate with gradually changing from its surface material property to the substrate material enhanced the wide band frequency sound absorption performance; the substrate material mainly affects the sound absorption performance at lower frequency, substrate material with closer impedance with water contributes to higher sound absorption in lower frequency range.