双稳态结构中的1/2次谐波共振及其对隔振特性的影响

以典型的双稳态系统——屈曲梁结构为例,基于等效模型,结合解析、数值和实验手段,研究了双稳态结构中的1/2次谐波共振特性、演化过程、参数调节规律及其对隔振特性的影响.研究发现,当非线性刚度系数或激励幅值增加到一定程度时,系统会在一定带宽下产生显著的1/2次谐波共振;随着激励幅值增加,阻尼系统的1/2次谐波遵循“产生-增强-衰退-消失”的过程,该过程对峰值频率和峰值传递率有重要影响;适当提高非线性强度能有效改善双稳态结构隔振特性.针对双稳态屈曲梁结构开展的实验验证了1/2次谐波特性和隔振特性变化规律.     

Band gap control of phononic beam with negative capacitance piezoelectric shunt

Periodic arrays of negative capacitance shunted piezoelectric patches are employed to control the band gaps of phononic beams. The location and the extent of induced band gap depend on the mismatch in impedance generated by each patch. The total impedance mismatch is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Therefore, the band gap of the shunted phononic beam can be actively tuned by appropriately selecting the value of negative capacitance. The control of the band gap of phononic beam with negative capacitive shunt is demonstrated numerically by employing transfer matrix method. The result reveals that using negative capacitive shunt to tune the band gap is effective.     

Design of the Coordinate Transformation Function for Cylindrical Acoustic Cloaks with a Quantity of Discrete Layers

Acoustic cloak based on coordinate transformation is of great topical interest and has promise in potential appli- cations such as sound transparency and insulation. The frequency response of acoustic cloaks with a quantity of discrete homogeneous layers is analyzed by the acoustic scattering theory. The effect of coordinate transforma- tion function on the acoustic total scattering cross section is discussed to achieve low scattering with only a few layers of anisotropic metamaterials. Also, the physics of acoustic wave interaction with the interfaces between the discrete layers inside the cloak shell is discussed. These results provide a better way of designing a multilayered acoustic cloak with fewer layers.     

Collision enhanced hyper-damping in nonlinear elastic metamaterial

Nonlinear elastic metamaterial, a topic which has attracted extensive attention in recent years, can enable broadband vibration reduction under relatively large amplitude. The combination of damping and strong nonlinearity in metamaterials may entail extraordinary effects and offer the capability for low-frequency and broadband vibration reduction. However, there exists a clear lack of proper design methods as well as the deficiency in understanding properties arising from this concept. To tackle this problem, this paper numerically demonstrates that the nonlinear elastic metamaterials, consisting of sandwich damping layers and collision resonators, can generate very robust hyper-damping effect, conducive to efficient and broadband vibration suppression. The collision-enhanced hyper damping is persistently presented in a large parameter space, ranging from small to large amplitudes, and for small and large damping coefficients. The achieved robust effects greatly enlarge the application scope of nonlinear metamaterials. We report the design concept, properties and mechanisms of the hyper-damping and its effect on vibration transmission. This paper reveals new properties offered by nonlinear elastic metamaterials, and offers a robust method for achieving efficient low-frequency and broadband vibration suppression.     

一种多频局域共振型声子晶体板的低频带隙与减振特性

设计了一种多频局域共振型声子晶体板结构, 该结构由一薄板上附加周期性排列的多个双悬臂梁式子结构而构成. 由于多个双悬臂梁式子结构的低频振动与薄板振动的相互耦合作用, 这种局域共振型板结构可产生多个低频弯曲波带隙(禁带); 带隙频率范围内的板弯曲波会被禁止传播, 利用带隙可以实现对薄板的多个目标频率处低频减振. 本文针对这种局域共振型板结构进行了简化, 并基于平面波展开法建立了其弯曲波带隙计算理论模型; 基于该模型, 结合具体算例进行了带隙特性理论分析. 设计、制备了一种存在两个低频弯曲波带隙的局域共振型板结构样件, 通过激光扫描测振仪测试证实该结构存在两个低频带隙, 在带隙频率范围的板弯曲振动被显著衰减.     

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     

不同压电分流电路对声子晶体梁带隙的影响

通过在匀质基体梁上周期性对贴连有分流电路的压电片,可以形成一维声子晶体结构.不同分流电路将决定梁的带隙特性.电阻分流电路能够对梁的模态共振有一定的抑制作用,而且可以通过改变压电效应的强弱使Bragg带隙结构发生变化.LC分流电路会使梁产生局域共振带隙,其带隙是由压电片激励LC电路产生电磁振荡形成.引入电阻后会使LC电路的共振作用变弱,使得带隙衰减幅值变小,但可以扩宽带隙频率范围.     

Theoretical and Experimental Investigation of Flexural Wave Propagating in a Periodic Pipe with Fluid-Filled Loading

Based on the Bragg scattering mechanism of phononic crystals （PCs）, a periodic composite material pipe with fluid loading is designed and studied. The band structure of the flexural wave in the periodic pipe is calculated with the transfer matrix （TM） method. A periodic piping experimental system is designed, and the vibration experiment is performed to validate the attenuation ability of the periodic pipe structure. Finally, a finite-element pipe model is constructed using the MSC-Actran software, and the calculated results match well with the vibration experiment. The errors between the theoretical calculation results and the vibration experimental results are analyzed.     

Flexural vibration band gaps in thin plates with two-dimensional binary locally resonant structures

The complete flexural vibration band gaps are studied in the thin plates with two-dimensional binary locally resonant structures, i.e. the composite plate consisting of soft rubber cylindrical inclusions periodically placed in a host material. Numerical simulations show that the low-frequency gaps of flexural wave exist in the thin plates. The width of the first gap decreases monotonically as the matrix density increases. The frequency response of the finite periodic thin plates is simulated by the finite element method, which provides attenuations of over 20dB in the frequency range of the band gaps. The findings will be significant in the application of phononic crystals.     

大弹性常数差二维声子晶体带隙计算中的集中质量法

通过引入振动力学中的连续系统离散化的思想，将一维集中质量法延伸至二维，提出一种二维声子晶体带隙特性计算的集中质量法. 进而采用该算法对两种正方晶格的二维声子晶体的带结构进行了计算，计算结果与传统的平面波展开法相符合. 通过对计算结果以及两种算法收敛性的分析，发现集中质量法的收敛性对组成声子晶体的不同材料弹性参数差不敏感，这使得该算法在计算大弹性常数差二维声子晶体的带隙特性时较平面波展开法收敛速度更快. 此外，集中质量法对二维声子晶体单元形状没有特殊要求，这使得它更加适用于声子晶体带隙特性的计算. 关键词： 声子晶体 声子带隙 集中质量法