基于小型机械平面阵列的水下低频宽带吸声结构的原理和优化设计方法

Enlightened by the excellent design idea of the electromagnetic absorbers which absorbing performance approaches the theroetic limit of milti-layer electromagnetic absorbing structures, a new working priciple of acoustic absorbers is proposed in this project, based on the analogy researches between electromagnetism and acoustics as well as between electrics and mechanics. Meanwhile, a novel broadband design scheme of acoustic absorbers is put forwards, namely, multi-layer absorbing structures imbeded with planar periodic arrays of small mechanical devices. The acoustic absorbers consists of acoustic material layers and planar periodic arrays of small mechanical devices, which are installed alternately before hard walls reflecting sound waves.The working principle proposed here can be utilized to design acoustic absorbers with good performances including low-frequency, broadband and super thin structure etc. The new principles are described as follows: Firstly, the acoustic absorbing structure utilizes two different-type resonances, one is the resonance produced by planar periodic arrays of small mechanical devices excited by acoustic waves, the other is the standing wave resonance formed by incident acoustic waves and reflection acoustic waves propagating in acoustic absorbing structures, and the broadband resonance of acoustic absorbing structures with acoustic waves can be achieved by utilizing the two different resonances, because the phases of the two resonances contrarily vary with frequencies of acoustic waves.Thus, by using broadband matching technique to design parameters of planar periodic array of small mechanical devices and material parameters of acoustic material layer, the two resonance phases can realize phase compensation when frequencies of acoustic waves are away from the resonance point, and the broadband resonance of the acoustic absorbing structure with acoustic waves can be obtained,that is, the broadband absorbing performance is achieved. Secondly, the super-thin acoustic material layer design in absorbers can be implemented by impedance transformation provided by planar periodic array of small mechanical devices which transmission ratios is not equal to one. Thirdly, broadband resonating, vibrating velocity enlarging and dumping elements in small mechanical devices all contribute to enhance the absorption of low-frequency acoustic waves. Here, research works will be carried out mainly on the design theory of the proposed absorbers, including the acoustic property analysis method of planar periodic array of small mechanical devices, the broadband matching design method of multi-layer absorbers, and the low-frequency super-thin design method of multi-layer absorbers etc. Meanwhile, considering the urgent need of our submarines for low-frequency acoustic absorption coating, this research will focus on underwater low-frequency and broadband acoustic absorbers, and the prototype model will be fabricated and tested.

受性能接近理论最优的电磁吸波结构的巧妙设计思想启发，通过电磁与声、机与电之间的模拟和类比，提出了一种新的声波吸收结构设计原理，并构思了声波吸收结构- - 小型机械单元平面阵列的多层吸声结构。它由在反射声波的刚性墙前交替安装声学材料层和小型机械单元平面阵列构成，可实现吸声结构的低频、宽带和超薄设计。原理上综合利用两种谐振：①小型机械单元平面阵列与声波产生的谐振，②声波在声学材料层中形成的驻波谐振。宽带匹配设计能使这两种不同性质的谐振相位随频率的变化互相补偿，实现宽带谐振和宽带吸波；利用小型机械的放大比获得阻抗变换，实现超薄设计；利用小型机械的宽带谐振、振动放大和阻尼元件，实现低频声波吸收。这里研究这种吸声结构的设计理论和方法，包括小型机械平面阵列的声学特性分析设计、吸声结构的宽带匹配设计、超薄设计等方法。考虑我国潜艇隐身对低频吸声覆盖层迫切需求，研究水环境下低频、宽带吸声结构设计方法，研制模型。

针对低频宽带减振降噪这一困难问题，本项目通过电磁与声之间的类比关系，模拟电磁波隐身结构，探索了一种新的声波吸收结构设计原理，并设计了多个具有实用价值的结构和装置。基于本项目的工作，撰写并发表论文13篇，录用1篇；培养毕业研究生21名；申请专利11项，其中授权军工发明专利1项，授权发明专利1项，授权实用新型专利2项，申请国际专利1项，其它处于实质性审查阶段。. 到目前为止，项目已圆满结题。在4年中，主要研究内容包括：①设计了不同类型的小型机械单元，给出了确定其输入输出之间传递函数的方法,并结合数值分析，归纳总结几种小型机械单元的结构参数与其动态特性之间的关系。②将小型机械单元周期排列，构成小型机械单元平面阵列，研究了小型机械单元平面阵列的振动声辐射与单个小型机械单元参数之间的关系，从数值和理论两个方面，分析小型机械单元平面阵列的声阻抗性质，给出了小型机械单元平面阵列的声阻抗解析表达式。③为了获得超宽带隙，以周期安装力型、力偶型振子的无限欧拉伯努利梁为例，研究局部共振型带隙和布拉格散射型带隙的特征，并利用复平面上的特征根轨迹加以分类描述，同时发现了局部共振附近的双波速现象，并给出了力型、力偶型振子的参数调整策略，以获得力偶耦合带隙、力耦合带隙和布拉格带隙拼接成超宽带隙的设计方法。④构造了小型机械单元结构参数优化设计策略，设计了几种多层吸声结构，包括小型机械单元阵列的多层吸声结构、以弱弹性级联的多层吸声结构和一种新型的超薄声波阻抗变换吸声结构等。⑤将小型机械单元阵列和五模材料相结合，设计了一种可承载的隐身结构；⑥针对潜艇隐身，设计了一种适用于水下的新型低频宽带多层吸声结构。. 本项目获得了诸多研究成果，在吸声结构中周期嵌入小型机械单元，相当于增加了吸声结构的设计参数，扩大了设计空间。这种声波吸收结构的设计方法，兼具设计原理上的创新，以及结构和技术手段上的奇思妙想，既有科学价值，也具有实用性。