The acoustic black hole (ABH) can be utilized to achieve aggregation of flexural wave in structures with the feature that the thickness gradually reduced to zero with a power exponent no less than 2. The above characteristics could be applied in vibration reduction, noise attenuation or improving sound insulation. Previous literatures on vibration and acoustic characteristics of ABH structures mainly focus on the structural response under mechanical force excitation, while the transmission loss (TL) of circular plates embedded with two-dimensional ABHs investigated in this paper is a vibro-acoustic coupling procedure under excitation of diffuse sound field. Series of vibro-acoustic coupling finite element models (FEM) for TL analysis of ABH circular plates were established by automatic matched layer (AML) method in this paper and an experimental platform for measuring TLs of ABH circular plates and uniform plates was constructed. The accuracy of the FEM analysis was verified by experimental measurements. To systematically analyze the influence mechanism of parameters of the ABH on TLs of ABH circular plates, the effects of diameter, orientation, number, and truncation thickness of ABHs on TLs of ABH circular plates were further studied. The effect of the damping layer on TLs of circular plates embedded with 1 and 19 ABHs was also analyzed and it reveals that the influence of damping layer mainly concentrates on the first-order resonance frequency and damping-controlled region of the plate, and at some frequencies, the greater the damping layer thickness, the worse the sound insulation performance, despite that the modal damping loss factor has been increased in the whole frequency domain.

Traditional acoustic black hole (ABH) structure that usually has a wedge-shaped structure with unchanged power-law profile has been studied extensively. Embedding an ABH in a thin-walled structure can help the system to control the flexural wave to realize vibration damping and energy concentration. However, due to the limitations of processing and manufacturing technology, the structural thickness of the ABH region cannot completely reach zero and will always leave a truncation at the tip of the ABH region, which makes ABH structure cannot give full play to the effect of ABH. In this paper, we show that a beam with segmented ABH structure whose baseline is segmented into two portions and they are respectively subjected to different power functions can effectively improve the effect of ABH. A semi-analytical method is adopted to establish the dynamical model of the segmented ABH beam under the clamped-free boundary condition. Finite element method and experimental method are carried out to verify the accuracy of the semi-analytical model. The segmented ABH effect of the beam is analyzed by the comparison of segmented ABH beam, conventional ABH beam, and uniform beam. In addition, the influence of the damping layer location on the dynamic response of the segmented ABH beam is studied as well. The numerical simulation results show that the vibration energy of segmented ABH beam can be more effectively shifted to the ABH area, thus enhancing the energy concentration effect and vibration attenuation. Moreover, the results also reveal that attaching the damping layer to the tip of the segmented ABH structure can effectively improve the system modal loss factor and achieve better vibration attenuation. The research of this paper can give rise to explorations of different innovative ABH structures and broaden the application of ABH beam structures in engineering.

In this study, to improve the vibration isolation performance of a cab seat and the ride comfort of the driver, we propose a mathematical model for a seat suspension system of a construction machinery cab based on a negative stiffness structure (NSS). First, a static analysis of a seat suspension system is conducted and the different parameters and their influences on the dynamic stiffness are discussed. Thereby, the ideal configuration parameter range of the suspension system is obtained. Moreover, the nonlinear dynamic model of the designed seat suspension system is established. The frequency response and the stability are analyzed by using the HBM method and numerical simulation. The vibration transmissibility characteristics and vibration suppression effects of the seat suspension system are presented in detail. The results show that, as compared with a quasi-zero-stiffness system, the QZS-IE system has higher vibration suppression advantages under large excitation and small damping, as well as lower transmissibility and a wider vibration isolation frequency range. In addition, an inerter element with a larger mass ratio and relatively shorter distance ratio is better for vibration isolation performance of the QZS-IE system in a practical engineering application. The results of this study provide a scientific basis for the design and improvement of a seat suspension system.