空间弯折多孔超结构低频宽带水声吸收特性及实验测试研究

The sound absorbent property of conventional anechoic coatings, based on viscoelastic materials, is easily affected by high hydraulic-pressure and low water-temperature, which impairs the stealth of submarines. Concerning these shortcomings, a kind of space-coiled meta-structures based on open-cellular porous materials is proposed in this project. The meta-structures fully take advantages of the low-frequency waterborne sound absorption of sintered metal fiber materials with pore diameter of micrometer scale, and the thickness reduction of space-coiled structures, as well as the impedance matching and sound wave propagation guidance of gradient varying structures. Employing theoretical, numerical and experimental methods, this project is designed to carry out by three steps. Firstly, the rule of waterborne sound wave propagation and attenuation thorough complicated porous materials is studied, for developing an efficient model to predict the waterborne impedance of porous materials. By utilizing the abovementioned model and numerical simulations, the influence of the geometrical parameters of space-coiled structures and the impedance distributions of porous materials on the sound absorbent properties of the meta-structures is investigated, and a relevant design theory is consequently built. Finally, the arrangement of spiral unit cells with different absorbent characteristics is analyzed, to further broadened the absorbent band width of the meta-structures. The significance of this project is to explore a new mechanism of waterborne sound absorption, other than that of viscoelastic materials, and to develop the related design theory of the meta-structures. The resulted models, theories and samples will support the research and development of new type of anechoic coatings in our country.

基于粘弹性材料的传统声学覆盖层吸声性能易受高水压、低水温影响，直接降低了潜艇的隐身性能。为此，本项目提出一种基于通孔型多孔材料的空间弯折超结构，充分发挥微米孔径烧结金属纤维毡低频水声吸收特性和弯折空间减薄结构整体厚度的优势，结合梯度变化结构的阻抗匹配和声波传播引导的优点，开展新型水声吸收结构设计方法研究。本项目拟采用理论分析和数值模拟手段，结合实验测试，揭示复杂多孔材料中水声声波传播与衰减规律，建立复杂多孔材料水声阻抗高效模型；进而研究弯折结构几何形貌和多孔材料阻抗分布对超结构水声吸收特性的影响机理，形成空间弯折多孔超结构水声吸收的设计理论；最终通过组合不同吸声特性的螺旋单胞，进一步拓宽超结构水声吸收频带。本项目研究意义在于探究全新水声吸收机理，建立新型水声吸收结构设计理论，支持我国抗高水压、低水温新型潜艇声学覆盖层研发。

基于粘弹性材料的传统声学覆盖层吸声性能易受高水压、低水温影响，直接降低了潜艇的隐身性能。为此，本项目提出一种基于通孔型多孔材料的空间弯折超结构，充分发挥微米孔径烧结金属纤维毡低频水声吸收特性和弯折空间减薄结构整体厚度的优势，结合梯度变化结构的阻抗匹配和声波传播引导的优点，开展新型水声吸收结构设计方法研究。本项目拟采用理论分析和数值模拟手段，结合实验测试，取得以下重要结果。.1）通过截面为圆形的长直管和包含复杂孔隙的烧结金属纤维毡展示了多孔介质在水下的有效吸声能力，基于Biot理论，发展了预测多孔材料水声吸收系数的理论模型和数值仿真模型，分析表明多孔材料需要大得多的厚度才能达到与空气声吸收系数相当的水声吸收系数。2）提出了一种基于微穿孔板和阻抗匹配弯折空腔的低频宽带吸声超结构，通过对阻抗匹配的研究，弯折空腔截面积的梯度设计可以有效拓宽吸声频带，在共振频率是410Hz时，相对带宽是69.51%，和传统的等截面弯折空腔吸声体相比，将相对带宽拓展了2.34倍。3）基于切槽波纹芯层设计了一种独特的空间弯折吸声超材料，与文献中的已有吸声结构相比，该吸声体在133Hz实现仿真强吸声，而其厚度只有11mm（~λ/234，λ为133Hz对应的波长），显示出深亚波长的吸声能力，同时，夹芯板优良的力学特性充分移植到该超材料夹芯板，使其具有非凡的弯曲刚度，更适合于工程应用。.本项目科学意义在于探究全新水声吸收机理，建立新型水声吸收结构设计理论，支持我国抗高水压、低水温新型潜艇声学覆盖层研发。