含有周期球腔的黏弹性覆盖层消声性能分析

利用散射矩阵法分析了单个球状空腔在黏弹性橡胶中的Mie散射特性以及振动模式.以此为基础，利用多重散射法分析了不同背衬条件下，含有单层周期球状空腔的橡胶覆盖层(厚度为8mm)的消声性能.结果表明，单个球腔的径向共振对覆盖层的低频消声性能有重要贡献，覆盖薄层在共振区具有良好的消声性能.最后，设计了双层消声覆盖层(厚度为20mm)，有效拓展了消声带宽. 关键词： Mie散射 多重散射法 消声材料 声子晶体     

Acoustic anechoic layers with singly periodic array of scatterers: Computational methods,absorption mechanisms,and optimal design

The acoustic properties of anechoic layers with a singly periodic array of cylindrical scatterers are investigated. A method combined plane wave expansion and finite element analysis is extended for out-of-plane incidence. The reflection characteristics of the anechoic layers with cavities and locally resonant scatterers are discussed. The backing is a steel plate followed by an air half space. Under this approximate zero transmission backing condition, the reflection reduction is induced by the absorption enhancement. The absorption mechanism is explained by the scattering/absorption cross section of the isolated scatterer. Three types of resonant modes which can induce efficient absorption are revealed. Due to the fact that the frequencies of the resonant modes are related to the size of the scatterers, anechoic layers with scatterers of mixed size can broaden the absorption band. A genetic optimization algorithm is adopted to design the anechoic layer with scatterers of mixed size at a desired frequency band from 2 kHz to l0 kHz for normal incidence, and the influence of the incident angle is also discussed.     

力学超材料研究进展与减振降噪应用

力学超材料是一类由人工微结构单元构筑的复合结构或复合材料, 具有天然材料所不具备的静力学/动力学性能. 由于这些超常特性通常取决于微结构单元而非材料组分, 这就为力学性能调控和结构功能材料设计提供了新思路. 本文在简述力学超材料概念的提出、发展及其超常力学性能的基础上, 以装备减振降噪工程需求为牵引, 重点探讨力学超材料在水声调控, 空气声吸隔声降噪, 结构减振抗冲设计等方面的应用探索及发展趋势, 为相关领域的科研及工程人员提供一定参考.      

Sound Absorption of Locally Resonant Sonic Materials

The acoustic properties of locally resonant sonic materials with viscosity are theoretically investigated by using the multiple-scattering approach. We find that the absorption of a two-layer slab dominates the wave attenuation in the resonant frequency region under the condition of moderate or high viscous level. The fundamental mechanism operating in local resonance for absorption is investigated for the viability by the mode translation in the scattering process of a single scatterer. Finally the absorption performance in a multi-layer system is discussed.     

薄板状周期栅格结构中弹性波传播特性研究

相位常数面可以描述特定频率、特定结构中波的传播方向及传播区域.将相位常数面这一分析方法应用于薄板状周期栅格结构中弹性波传播特性的研究，采用集中质量法计算了周期栅格结构的相位常数面，得到了直观的三维能带结构图.相位常数面可以用二维等高线图描述，通过计算等高线上每一点的法线方向，得到了在特定通带频率下弹性波的传播方向及传播区域.这些研究对于通带频率范围内的弹性波传播特性具有重要意义. 关键词： 声子晶体 弹性波带隙 集中质量法 相位常数面     

Comparison of the mechanism of gap formation for tri- and bi-component phononic crystal

Using an exact Mie scattering solution, this paper investigates the mode conversions during the Mie scattering of a single bi- or one-component sphere in unbounded epoxy. Then the formation mechanism of the first complete gap in the corresponding tri- or bi-component phononic crystal is investigated by the multiple-scattering method. It is shown that the heavy density of the scatterer plays an essential role in the Mie resonance and the formation of the gaps for both types of the phononic crystals. For the tri-component phononic crystal, the gap is mainly induced by the Mie resonance of the single scatterer. For the bi-component phononic crystal, the transverse wave （by mode-conversion during the Mie scattering under a longitudinal wave incidence） is modulated by the periodicity and governed by the Bloch theory, which induces the gap cooperatively.     

一种含柱形空腔结构橡胶层的吸声机理及优化

采用有限元法,分析了含单层柱形空腔橡胶层(厚度20 mm)的吸声性能,表明其吸声峰频率比相同尺寸的球形空腔低,这与单个柱形和球形空腔的单极共振频率相对应,通过谐波散射分析证实了空腔单极共振引起的能量耗散增强了声波的吸收。采用能量耗散功率及位移场分布,对柱形空腔结构的吸声机理进行了深入分析.其次,在钢背衬条件下分析了横波损耗因子对橡胶层吸声特性的影响,并采用遗传算法对含不同尺寸柱形空腔橡胶层在1.5—10 kHz频段上的吸声特性进行了优化,获得了较好的宽频吸声效果.     

黏弹性材料的动态力学特性及其对覆盖层吸声性能的影响

本文利用标准化动态力学测量手段获得了某种高分子聚合物的动态杨氏模量,并根据时温等效原理对动态杨氏模量与声学测量在频段上的差异加以分析和转换,得到了500—7500 Hz频率范围内该黏弹性材料杨氏模量随频率变化的特性.基于所测得动态杨氏模量,采用有限元方法分析了均匀黏弹材料的吸声性能,并将仿真结果与样品声管实验数据进行对比,验证了测试所得参数的准确性.进一步仿真分析了含有局域共振结构的声学覆盖层吸声性能,并讨论了黏弹性材料的动态特性对其吸声性能的影响,提出了改进水声覆盖层低频宽带吸声特性的建议.     

基于散射单元的声子晶体振动带隙研究

硬质芯体及其包覆层构成的复合结构称为散射单元，散射单元按照特定的排列方式可以构成声子晶体。文章采用有限元方法分别计算了立方散射单元构成的一维声子晶体及简单立方结构三维声子晶体的振动特性，结果表明，两种声子晶体的振动带隙有较好的一致性，因此，对三维声子晶体振动带隙的研究可以简化为对一维声子晶体振动带隙的研究。叠加层数、芯体材料对一维声子晶体振动带隙的影响在文中进行了讨论。最后，声子晶体的振动特性测试结果验证了文中的结论。     

一种含圆柱形谐振散射体的黏弹材料低频吸声机理研究

利用层多重散射法分析了一种含圆柱形谐振散射体黏弹 材料吸声层在钢背衬条件下的低频吸声特性. 该吸声层由包覆软材料的圆柱空腔周期嵌入橡胶材料中构成, 其中, 散射体轴线与吸声层平行. 结果表明, 20 mm厚吸声层在1000–3000 Hz具有良好的吸声性能. 通过综合分析单个散射体的吸收截面、单层周期散射体的声吸收、 结构内部位移场以及耗散功率密度分布, 揭示了该吸声层的低频吸声机理. 关键词： 水声吸声 吸收截面 耗散功率密度