封闭空间中声源辐射阻抗特性研究

In order to expand the low-frequency applications in a non-anechoic pool, the theoretical and the experimental research, on which the mechanisms of the sound radiation impedance changes are impacted by the boundary of an enclosed chamber, will be carried out in this subject. Currently, how to measure the low-frequency acoustic properties of the large complex structures in a non-anechoic pool becomes an urgent problem to be solved, which is exceeded the application of the method of reverberation. To solve this problem, in an enclosed chamber, the each radiation impedance of the small-scale typical sound source and the large-scale elastic shell structures are selected as investigated subjects. The mechanisms of the radiation impedance changes which are impacted by the boundary will be studied by establishing the theoretical analysis model of the radiation impedances, in further, the free-field correction method of measuring the radiation impedance and sound radiation power in an enclosed chamber are established in the low-frequency ranges. The principle experiments will be done to verify the feasibility of the proposed measuring method, with analyzing the internal relationship between the non-anechoic pool field and the free field, the application limitations will also be given by analyzing the experiment results. All these work can provide a new technique for mastering the low-frequency acoustic properties of the complex underwater structures.

为了拓展非消声水池低频应用范围，本课题将从封闭空间声场边界对声源辐射阻抗的影响机理角度开展理论及试验研究。目前，如何在现有条件下的非消声水池中对大型复杂结构声源进行低频声学特性测量已成为迫切解决的问题，这已超出了混响法的适用条件。针对这一问题，以封闭空间中小尺度典型声源和大尺度弹性壳体结构的辐射阻抗为研究对象，建立封闭空间中声源辐射阻抗的理论分析模型，通过研究不同声场边界对声源辐射阻抗的影响机理，在低频域建立封闭空间中声源辐射阻抗及辐射声功率的自由场校正方法；通过原理验证试验，深入分析非消声水池声场与自由场间的内在联系，验证所建立的在非消声水池中测量声源低频辐射声功率方法的可行性，并分析该测量方法的适用条件，为掌握水下结构声源低频声学特性提供一种新的测量技术手段。

本项目研究了封闭空间边界对声源辐射阻抗的影响规律，从物理本质上掌握了水池中声源辐射声功率相对自由场变化的机理，特别是封闭空间的低频域，研究发现辐射阻抗相比机械阻抗是小量，声源辐射阻抗与声功率存在着对应规律，为在封闭空间中进行低频声功率测量提供了物理依据。项目主要的研究进展及结论如下：.1. 以解析和数值分析手段，通过研究脉动球源、体积声源、弹性球壳和圆柱壳在理想边界、弹性边界以及阻抗边界混响水池中的辐射阻抗变化，明确了声源在封闭空间中发射时声源与声场耦合、边界对声场作用的声振耦合机理。在中高频域，辐射阻抗受封闭空间声场影响剧烈，与声功率变化的关系复杂；但在低频域，声源辐射阻抗与声功率存在着对应规律。.2. 提出了一种基于近场声能流分离的水下声源低频辐射声功率的声强法测量技术，采用近场测量声源辐射声能反演的方式实现，进一步扩展了混响法在低频域测量的应用范围。当混响水槽和自由场中圆柱壳声源辐射阻变化趋势规律相似时，此时辐射阻抗相比机械阻抗是小量，且辐射阻抗的变化不足以改变声源的振动状态时，利用基于近场声能流分离的声强法测量声源的辐射声功率是适用的。.3. 在混响水池中分别开展了球形换能器声源的辐射阻抗测量实验和低频声功率测量实验，试验结果验证了声强法测量技术的有效性。进一步在混响水池中开展了圆柱壳模型辐射阻测量实验和低频声功率测量实验，其声功率窄带测量结果与自由场相比偏差不大于2 dB。.结合项目组已经建立起的混响水池理论以及本项目提出的低频测量方法，将形成在甚低、低、高等不同频段分别采用近场测量、比较法测量和混响法测量的封闭空间测量体系，有望实现复杂声源在非消声水池中全频带测量。本项目成果为国防工业水下、水面的目标声学特性获取提供了水池测量手段的技术支撑。