Papers by Keyword: Periodic Structure

Abstract: In this paper, we construct a second-order two-scale (SOTS) asymptotic expansions for thermopiezoelectric problems in periodic structure by means of construction way. A set of numerical results are demonstrated for predicting the temperature, mechanical displacement and electric potential in periodic structures. It shows that SOTS's asymptotic expansions can capture the 3-D local behaviors caused by 3-D micro-structures well.

Abstract: In this study, we conducted water hammer experiments in the tube which was periodically supported by various numbers of clamps, named periodic structure, initiated by a projectile impact. The parts of the polycarbonate (PC) tube supported by 1-7 steel clamps make the tube stiffer and heavier than the original PC tube and are expected to cause a filtering effect of the frontal frequency components in the water hammer. According to our experimental observations, we confirmed that higher frequency components more than 1 kHz in the wave front were attenuated and the peak strains in circumferential direction of the tube were decreased 20% from the original PC tube. Moreover, we conducted numerical simulations of the water hammer wave similar to the experimental setup. Numerical results also revealed that frontal peak is attenuated 22% through periodic structure.

Abstract: In this paper, the stability analysis of the unconditionally stable one-step leapfrog alternating direction implicit (ADI) finite-difference time-domain (FDTD) method for periodic structures is presented. The amplification matrix of the proposed leap-frog ADI-FDTD method is obtained through the spatial domain with Fourier method and eigenvalues of the Fourier amplification matrix are obtained analytically to prove the unconditional stability of the periodic leapfrog ADI-FDTD method. Numerical verification is proposed to confirm the theoretical result.

Abstract: The periodic structure is common used in engineering to improve the sound diffusion in room acoustics. It usually has large dimensions and it is difficult to calculate the scattering coefficient based on its original scale. In order to represent the scattering coefficients of a large scale periodic structure by those of a smaller one, the relations of the scattering coefficients of the periodic structures with different dimensions are analyzed in this paper. At first, a BMM (Boundary Meshless Method) for calculating the scattering coefficient is derived. The scattering coefficients of the periodic structures which have different numbers of sub-structures are calculated and compared. The computation results of different sub-structure numbers show that the periodic structure with 15 sub-structures can represent the samples which have more sub-structures. In addition, it can be proved that the square samples can be represented by those of the small and rectangular ones which have the same numbers of sub-periods. These conclusions not only greatly enhance the computational efficiency, but also show good prospect for fast evaluation of the periodic structures in engineering applications.

Abstract: This paper investigates the suppression of vibration and noise radiation in a flexible isolation system through the use of periodic layered structures. A single-stage vibration isolation model is developed first. Then, the isolation performance of the periodic structure is studied. Furthermore, the influence of the isolator location and the phase difference on the radiated sound power of the foundation is investigated. The numerical results show that the vibration and noise can be greatly attenuated in the band gaps.

Abstract: The wave propagation in plate covered by periodic damping layers is analyzed and controlled. A theoretical model is developed to describe the wave propagation characteristics and the vibrations of a plate covered by periodic damping structures with simply supported boundary condition along its longitudinal edges. The wave propagation characteristics are estimated by analyzing the transfer matrix of each cell of the resulting periodic structure. The numerical model is used to predict the dynamic response of the plates and to study their propagation and attenuation characteristics for various configurations. The presented numerical results demonstrate the simplicity and the effectiveness of the proposed treatment, which reduces the transmission of waves and the plate vibrations over specified, especially low frequency bands.

Abstract: The mistuning of periodic structure was generally considered to be natural parameter mistuning, such as stiffness mistuning, damping mistuning and mass mistuning. However, in engineering practice, there was another kind of mistuning—force mistuning. Based on a typical concentrated parameter model of periodic structure, the vibration characteristics, such as natural characteristic, vibration mode and vibration localization of periodic structure with different mistuning forms, were compared and analyzed. The results show that, as a new mistuning form, force mistuning won’t bring mode localization, while it could lead to vibration response localization. The results are very important for periodic structure design and manufacture.

Abstract: By using the finite element method, the band structures of the periodic hollow cylinder sandwich panels are investigated, and the influences of the material and geometrical parameters on the band gap are discussed in detail. The results show that The Young's modulus of panel and the coated layer have the greatest influences on the band gap of binary periodic hollow steel cylinder sandwich panels. The smaller the Young's modulus, the lower the frequency band gap. The material and geometrical parameters of the core have important influences on the lower edges of the band gap. Thicker and higher hollow steel cylinder with large density is favorable to gain a wide low-frequency band gap. The work presented will provide a theoretical guidance in the vibration isolation research.

Abstract: The mistuning of periodic structure was generally considered to be natural parameter mistuning, such as stiffness mistuning, damping mistuning and mass mistuning. However, in engineering practice, there was another kind of mistuning——force mistuning, which has not been studied yet. Based on a typical concentrated parameter model of periodic structure, the vibration characteristics, such as natural characteristic, vibration mode and vibration localization of periodic structure with different mistuning forms, were compared and analyzed. The results show that, as a new mistuning form, force mistuning won’t bring mode localization, while it could lead to vibration response localization

Abstract: Sonic crystals are periodic structures made of sound hard scatterers which attenuate sound in a range of frequencies. For an infinite periodic structure, this range of frequencies is known as band gap, and is determined by the geometric arrangement of the scatterers. In this paper, a parametric study on rectangular sonic crystal is presented. It is found that geometric spacing between the scatterers in the direction of sound propagation affects the center frequency of the band gap. Reducing the geometric spacing between the scatterers in the direction perpendicular to the sound propagation helps in better sound attenuation. Such rectangular arrangement of scatterers gives better sound attenuation than the regular square arrangement of scatterers. The model for parametric study is also supported by some experimental results.