覆膜指状结构声学特性研究

There has been a diversity of studies on low frequency passive noise control. The principle of this project is to make use of the coupling between resonators and periodicity to realize broadband low frequency noise control. Finger-like structures are proposed by introducing semi-closed cavity covered with membrane to side-branch tubes with varying length, and furthermore, periodicity is adopted through which working band expansion occurs to achieve broadband low frequency noise control in duct. Theoretic studies, numerical simulation and experimental validation are conducted to analyze the frequency characteristic of tubes with vary length. The coupling mechanism between tubes and cavity covered by membrane will be studied; also the “matching” mechanism when periodicity is introduced to the structure will be discussed; finger-like structures array will be realized to achieve broadband low frequency noise control. Meanwhile, experiments will be carried out to verify its practical noise reduction effect. The project may pave the way for the related application on acoustical materials development, and industry noise control, etc..

低频宽带的无源噪声控制是声学研究热点之一。本项目提出通过短管组与覆膜空腔耦合作用实现低频特性可调的覆膜指状结构，进一步通过特定条件下指状结构个体特征与结构周期化“匹配”时的拓频现象实现低频宽带管道噪声控制。研究拟通过理论建模、数值仿真、实验分析相互结合的方法，研究深度渐变管组的频带特性；分析指状结构中短管组和覆膜空腔的耦合作用机理；探讨指状结构在特定周期化条件下“匹配”现象；最终实现具备可调制的低频宽阻带指状结构序列设计；并通过实验测量其在管道中的实际降噪效果。研究结果将在我国声学材料研发、工业噪声控制上有一定的应用价值。

本项目在先前工作的基础上首先对深度渐变管进一步深入的研究，探讨了粘滞阻尼以及短管间隔对系统性能的影响，针对后者发现深度渐变管的工作下限频率受制于管长，因此本项目进一步讨论了有限空间内的结构改善，即引入了卷曲空间结构的讨论。进一步地，研究了覆膜指状结构。通过建立求解覆膜的振动方程，将覆膜振动模态、覆膜背腔声场与主管道的声场分布建立关联。研究发现多模块的耦合可以实现较单一模块更为宽频的噪声控制效果，而在此结构中，通过将背腔后壁设置为深度渐变管，可以实现阻抗分布界面，从而影响背腔声场分布，最终实现对主管道内声场的调控，实现更为宽频的工作效果。研究进一步深入考虑了结构阵列化，通过单元阵列化，调节个体间隔，实现结构单元性能与周期间隔匹配的现象，实现工作频域的拓展。以此为基础，我们将该结构以及结构单元应用于管道噪声控制以及声屏障设计，通过多模块耦合以及短管组阻抗分布特征的设计，用以实现低频且宽频噪声控制目标。