Wen Xi-sen

Improved modeling of rods with periodic arrays of shunted piezoelectric patches

This work improves the modeling of rods with periodic arrays of shunted piezoelectric patches. The modeling method abandons the previous incorrect assumptions and leads to a more precise result. A numerical investigation is based on an epoxy host rod with a periodic array of resistive–inductive shunted piezoelectric patches. The bandgaps are predicted by the application of Bloch theorem and transfer-matrix method. The results show that the boundary frequencies and attenuation extents both have some difference between the predications of the two models. In particular, the maximum attenuation in the locally resonant gap is much smaller in the result of the improved model.

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.

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.

Locally Resonant Gaps of Phononic Beams Induced by Periodic Arrays of Resonant Shunts

Periodic arrays of shunted piezoelectric patches are employed to control the propagation of elastic waves in phononic beams. Each piezo-patch is connected to a single resistance-inductance-capacitance shunting circuit. Therefore, the resonances of the shunting circuits will produce locally resonant gaps in the phononic beam. However, the existence of locally resonant gaps induced by resonant shunts has not been clearly proved by experiment so far. In this work, the locally resonant gap in a piezo-shunted phononic beam is investigated theoretically and verified by experiment. The results prove that resonances of shunting circuits can produce locally resonant gaps in phononic beams.

Flexural wave band-gaps in phononic metamaterial beam with hybrid shunting circuits*

Periodic arrays of hybrid-shunted piezoelectric patches are used to control the band-gaps of phononic metamaterial beams. Passive resistive-inductive (RL) shunting circuits can produce a narrow resonant band-gap (RG), and active negative capacitive (NC) shunting circuits can broaden the Bragg band-gaps (BGs). In this article, active NC shunting circuits and passive resonant RL shunting circuits are connected to the same piezoelectric patches in parallel, which are usually called hybrid shunting circuits, to control the location and the extent of the band-gaps. A super-wide coupled band-gap is generated when the coupling between RG and the BG occurs. The attenuation constant of the infinite periodic structure is predicted by the transfer matrix method, which is compared with the vibration transmittance of a finite periodic structure calculated by the finite element method. Numerical results show that the hybrid-shunting circuits can make the band-gaps wider by appropriately selecting the inductances, negative capacitances, and resistances.

Tunable band gaps in acoustic metamaterials with periodic arrays of resonant shunted piezos

Periodic arrays of resonant shunted piezoelectric patches are employed to control the wave propagation in a two-dimensional (2D) acoustic metamaterial. The performance is characterized by the finite element method. More importantly, we propose an approach to solving the conventional issue of the nonlinear eigenvalue problem, and give a convenient solution to the dispersion properties of 2D metamaterials with periodic arrays of resonant shunts in this article. Based on this modeling method, the dispersion relations of a 2D metamaterial with periodic arrays of resonant shunted piezos are calculated. The results show that the internal resonances of the shunting system split the dispersion curves, thereby forming a locally resonant band gap. However, unlike the conventional locally resonant gap, the vibrations in this locally resonant gap are unable to be completely localized in oscillators consisting of shunting inductors and piezo-patches.Periodic arrays of resonant shunted piezoelectric patches are employed to control the wave propagation in a two-dimensional (2D) acoustic metamaterial. The performance is characterized by the finite element method. More importantly, we propose an approach to solving the conventional issue of the nonlinear eigenvalue problem, and give a convenient solution to the dispersion properties of 2D metamaterials with periodic arrays of resonant shunts in this article. Based on this modeling method, the dispersion relations of a 2D metamaterial with periodic arrays of resonant shunted piezos are calculated. The results show that the internal resonances of the shunting system split the dispersion curves, thereby forming a locally resonant band gap. However, unlike the conventional locally resonant gap, the vibrations in this locally resonant gap are unable to be completely localized in oscillators consisting of shunting inductors and piezo-patches.

Directional Propagation Characteristics of Flexural Waves in Two-Dimensional Thin-Plate Phononic Crystals

The propagation characteristics of flexural waves in two-dimensional thin-plate phononic crystals (PCs) are analysed with the plane wave expansion (PWE) method to yield phase constant surfaces, which predict high directivity of flexural wave propagation for certain frequencies outside the band gap. The prediction is validated through the computation of the harmonic responses of a finite structure with 9×9 unit cells. The results indicate that directional propagation of flexural waves is an inherent characteristic of two-dimensional thin-plate PCs while specific effects of the directional propagation in a finite structure vary with the positions of excitations.

Study on the vibration band gap and vibration attenuation property of phononic crystals

Phononic crystals (PCs) are functional materials with periodic structures and elastic wave (vibration) band gaps, where propagation of vibrations with frequencies within band gaps is forbidden. PCs with finite periods can restrain the propagation of vibrations with frequencies in band gaps and thus has vibration attenuation property. Worldwide, many institutions and researchers are engaged in the research of PCs, however, studies on the vibration attenuation property of PCs are still limited. In this paper, we report our study of band gaps and vibration attenuation properties of 1) a simplified PC—periodic mass-spring structures, 2) longitudinal vibration of one-dimensional (1D-), 2D-, 3D-PCs, and 3) the flexural vibration of 1D-and 2D-PCs. These studies provide a foundation for the applications of PCs in vibration attenuation.

Modeling and Simulation of Complex Maintenance System Dynamics

Equipment maintenance system is naturally a complex dynamical system. The effective maintenance management must be based on the knowledge of the systems intrinsic dynamics. This paper analyzes the basic structure and elements of maintenance system for complex multi-components equipment. The maintenance system is considered as a dynamic system whose behavior is influenced by its structures feedback and interaction, and available resources. Building the dynamical model with Simulink, we show some results about the maintenance systems nonlinear dynamics, which are never given by stochastic process methods. The model can be used for understanding and determining maintenance system behaviors, towards which operational adjustments of maintenance infrastructure, precise prediction of maintenance requirements and timely supply of maintenance resources can be made in a more informed way.

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 10 kHz for normal incidence, and the influence of the incident angle is also discussed.