一种评估自由场隔声测试中边缘衍射影响的数值分析模型

A Numerical Evaluating Model for Edge Diffraction Effect on Sound Insulation Measurement in Free-Field

水声工程中,改善和提高自由场材料声学测试精度和可靠程度对水下航行器的声隐身设计具有非常重要的工程应用价值和现实意义。本文基于边界元和有限元方法对自由场材料隔声测试中存在的边缘衍射影响进行了数值评估模型研究,理论评估模型、分析条件和分析步骤均以实际测试为基础,并以水下钢板法向隔声测试为例计算分析了边缘衍射对轴向接收和偏轴向接收的影响程度和特点。研究表明,边缘衍射对自由场隔声测试的影响与样板几何尺寸和测试频率波长相对大小以及样板、声源和接收场点的空间几何配置等因素关系密切;与轴向接收相比,小角度偏轴向接收对抑制半波长与样板几何尺寸相当或远大于样板几何尺寸频段的边缘衍射影响较为有效,抑制效果与偏轴向距离及其相关轴向距离的选取有关。研究结果表明,该模型对更好地开展自由场材料隔声测试具有指导意义。

In underwater acoustic engineering, improving precision of acoustic measurement for materials in free-field is very important in design of acoustic stealthy of underwater vehicle. In this paper, a numerical method to evaluate the edge diffraction effect on sound insulation measurement in free-field was investigated using finite element method （FEM） and boundary element method （BEM） based on the commercial sound and vibration analysis software LMS-SYSNOISE. The theoretical analysis model, analysis condition and analysis procedure are on the basis of real measurement. Numerical calculation and analysis were carried out for the influence of edge diffraction on both axial and off-axial receives in a underwater normal sound insulation measurement of a steel plate. The results show that edge diffraction effect is strongly dependent on the ratio of plate dimension to measured fre- quency wavelength, and the geometrical configuration of sound sources, plate and receiving field point. In addition, compared with axial receiving, off-axial receiving with small angle is in favor of restraining edge diffraction effect with certain frequency ranges, and the restraining efficiency is associated with off-axial distance and relative axial distance.