塑料类高分子聚合物材料水中目标声学参数反演

Inversion for acoustic parameters of plastic polymer target in water

塑料类高分子聚合物材料作为3D打印领域的一类主要材料,在水下声学模型和结构成型中的应用越来越广泛,这类新材料的声学参数直接影响着3D打印的水下声学模型和结构的声学性能.基于水中目标声散射的Rayleigh简正级数解及塑料类高分子聚合物材料实心球中亚音速Rayleigh波低频共振机理分析,获取了亚音速Rayleigh波在低频情况下共振峰频率和幅度分别对材料的波速和衰减系数敏感的特征.在此特征基础上建立了一种以亚音速Rayleigh波反向散射共振峰频率和幅度为代价函数的塑料类高分子聚合物材料声学参数反演方法.最后通过典型塑料类高分子聚合物材料PMMA(甲基丙烯酸甲酯-亚克力)实心球反向声散射特性水池试验,测量了亚音速Rayleigh波反向散射共振特性,并反演得到了此类PMMA材料的纵波、剪切波声速及其声衰减系数,与理论预报结果基本吻合,为3D打印的塑料类高分子聚合物材料模型声学性能测试和评估提供了一种新方法.

The high-precision molding capability of complex surfaces and structures makes three-dimensional(3 D)printing technology more widely used in underwater acoustic models and structural molding. The plastic polymer material, as the main material in the field of 3 D printing, possesses the acoustic parameters that are directly related to the acoustic properties of 3 D printed underwater acoustic models and structures. Based on the Rayleigh normal series solution for the acoustic scattering of underwater target and the mechanism analysis of the low-frequency resonance which is associated with subsonic Rayleigh waves on the solid plastic polymer spheres, the sensitivity characteristics of the resonance frequency and amplitude to the wave velocity and attenuation coefficient are obtained at low frequencies. It is shown that the transverse wave velocity and the transverse wave attenuation coefficient both have high inversion accuracy at low values of ka, where a is the radius of elastic sphere, as they are quite sensitive to the backscattering resonance frequency and amplitude,respectively. In the frequency band of interest, the backscattering resonance frequency is almost independent of attenuation coefficient. Considering the inversion accuracy, the longitudinal wave velocity and transverse wave velocity are inverted by the resonance frequency separately. Based on these characteristics, the cyclic search method is used to establish an acoustic parameter inversion method for plastic polymer materials, in which the frequency and amplitude of backscattering resonance peak are used as cost functions. Finally, the backscattering acoustic scattering experiment on a solid typical plastic polymer PMMA(methyl methacrylate-acrylic) sphere is conducted in the tank. The experimental results about the backscattering target strength varying with the frequency are in good agreement with the simulation results in a frequency range of 5–20 kHz. The simulation parameters such as the longitudinal wave velocity, transverse wave velocity and attenuation coefficient are obtained by the previously established inversion method. Therefore, the acoustic parameter inversion method provides reliable acoustic parameters for 3 D printed underwater acoustic model and structure performance prediction for plastic polymer materials.