Theoretical and experimental investigations of flexural wave propagation in periodic grid structures designed with the idea of phononic crystals

The propagation characteristics of flexural waves in periodic grid structures designed with the idea of phononic crystals are investigated by combining the Bloch theorem with the finite element method. This combined analysis yields phase constant surfaces, which predict the location and the extension of band gaps, as well as the directions and the regions of wave propagation at assigned frequencies. The predictions are validated by computation and experimental analysis of the harmonic responses of a finite structure with 11× 11 unit cells. The flexural wave is localized at the point of excitation in band gaps, while the directional behaviour occurs at particular frequencies in pass bands. These studies provide guidelines to designing periodic structures for vibration attenuation.     

基于集中质量法的一维声子晶体弹性波带隙计算

通过将一维声子晶体中的原胞简化为有限多个自由度的弹簧振子结构，引入了一种基于集中 质量法的一维声子晶体弹性波带隙计算方法.与传统平面波展开法相比，该方法的计算结果 与之相符合，而且在收敛性方面较之有很大改善.通过使用集中质量法，可在得到同样计算 精度的条件下，显著降低计算量，提高计算速度. 关键词： 声子晶体 弹性波带隙 集中质量法 平面波展开法     

表面局域态对一维声子晶体中水平剪切波传输特性的影响

利用传递矩阵法，研究了一维声子晶体表面存在的表面局域态对水平剪切波传输特性的影响。由于表面局域态的存在，声波的透过率出现共振峰。共振峰的极值与入射角度和声子晶体层数有关，合适的入射角度和层数可以使声波完全透射。当入射角在一定范围内连续变化时，在较宽频率范围内均出现较大透过率。声子晶体的这一特性可以应用于高性能的阻抗匹配材料和声波滤波器中。     

内插扩张室声子晶体管路带隙特性研究

声子晶体管路的带隙特性,可以实现管路系统在特定频率下的噪声控制.利用二维模态匹配法推导出单个内插扩张室元胞的传递矩阵,结合Bloch定理,得到声子晶体管路的能带结构计算方法;验证了二维方法在计算能带结构时的准确性.研究发现,内插扩张室声子晶体管路存在布拉格带隙和局域共振带隙.进一步研究了晶格常数以及内插管长度对能带结构的影响,结果表明,晶格常数主要控制布拉格带隙,而内插管长度对局域共振带隙有较大的影响,并研究了两种参数变化下的带隙耦合.研究结果可以为管路降噪设计提供新的思路.     

Experimental and Theoretical Research on the Vibrational Gaps in Two-Dimensional Three-Component Composite Thin Plates

We investigate the vibrational band gaps in a thin plate of two-dimensional phononic crystals with the locally resonant structure in theory and experiment. The experimental sample is optimized based on the simple analytical model. The experimental results are in good agreement with the theoretical calculation by the finite element method. The findings will be significant for applications of phononic crystals in the field of vibration isolation.     

基于Timoshenko梁模型的周期充液管路弯曲振动带隙特性和传输特性

充液管路的固液耦合振动广泛存在于各种工程领域中,对其弯曲振动控制进行研究具有重要意义.将声子晶体的周期性思想引入到管路结构设计中,将管壁设计成沿轴向交替排列的周期性复合结构.基于Timoshenko梁模型,采用传递矩阵法计算了固液耦合条件下周期管路结构的弯曲振动能带结构及其传输特性,同时分析了材料阻尼系数、周期和非周期支撑对带隙特性的影响.充液周期管路结构的弯曲振动带隙特性为管路的振动控制提供了一条新的技术途径. 关键词： 声子晶体 充液管路 振动带隙     

Propagation of acoustic waves in a fluid-filled pipe with periodic elastic Helmholtz resonators

Helmholtz resonators are widely used to reduce noise in a fluid-filled pipe system. It is a challenge to obtain lowfrequency and broadband attenuation with a small sized cavity. In this paper, the propagation of acoustic waves in a fluid-filled pipe system with periodic elastic Helmholtz resonators is studied theoretically. The resonance frequency and sound transmission loss of one unit are analyzed to validate the correctness of simplified acoustic impedance. The band structure of infinite periodic cells and sound transmission loss of finite periodic cells are calculated by the transfer matrix method and finite element software. The effects of several parameters on band gap and sound transmission loss are probed.Further, the negative bulk modulus of periodic cells with elastic Helmholtz resonators is analyzed. Numerical results show that the acoustic propagation properties in the periodic pipe, such as low frequency, broadband sound transmission, can be improved.     

基于非对称吸声器的发动机声学超表面声衬

为了解决发动机低频噪声问题,基于双端口非对称吸声器原理,设计了一种尺寸渐变的吸声超表面,用于发动机声衬降噪设计.首先,建立了非对称共振吸声器的理论分析模型和仿真分析模型,揭示了降噪机理,并分析了其降噪效果的影响因素.然后基于非对称共振吸声器设计了一种声学超表面声衬,用全模型理论计算、等效阻抗理论计算和COMSOL有限元仿真三种方法深入分析了声衬的降噪效果,并用全模型理论计算和等效阻抗理论计算方法考虑了流速对降噪效果的影响,然后对此结构进行了参数优化.研究结果表明,所设计的基于非对称吸声器的声学超表面声衬在厚度仅为2.5 cm (仅为252 Hz对应波长的1/54)的情况下,可实现252—692 Hz的频带范围内3 dB以上的降噪效果,为发动机降噪设计提供了一种新的设计思路.