جستجوی مقالات مرتبط با کلیدواژه "boundary condition" در نشریات گروه "مکانیک"

Lattice Boltzmann method is one of computational fluid dynamic subdivisions. Despite complicated mathematics involved in its background, end simple relations dominate on it; so in comparison to the conventional computational fluid dynamic methods, simpler computer programs are needed. Due to its characteristics for parallel programming, this method is considered efficient for the simulation of complex geometry flows, in which a large amount of computational memories is needed. Because of the curved boundaries in the complex geometries, detecting the proper curved boundary condition is unavoidable for the lattice Boltzmann method. For this purpose, more works have been done, and different curved boundary conditions have been proposed. At the present work, first, some curved boundary conditions have been reviewed; then a simplified curved boundary condition is proposed. A computer program based on the lattice Boltzmann method, in FORTRAN language, has been prepared; in this program, the boundary condition along with some others applied on it is proposed. To verify the accuracy and correctness of the proposed boundary condition, 2D cavity flow has been simulated and compared to the available numerical results. Adaptation of the achieved results with those of previous researchers verifies the prepared program correctness. Also, two fluid flows have been simulated, a flow around a stationary cylinder in a 2D channel and one between two stationary and moving cylinders. The results of simulations with the proposed boundary condition, along with the previous boundary conditions, have been compared to the available results. Comparisons demonstrate that solutions with proper accuracy could be obtained by the proposed boundary condition.

In this study, effects of various boundary conditions on the free vibration of double layer graphene nanoribbons (DLGNRs) are investigated by considering both of tensile-compressive and shear effects of van der Waals (vdWs) interactions. Sandwich beam theory is used to model the DLGNRs. In the references, only one of tensile-compressive or shear effects of vdWs interactions have been considered. Based on sandwich beams theory, vdWs interactions are equivalent to the sandwich core and are modeled in a way that they can withstand the tensile-compressive and shear forces simultaneously. Hamilton’s principle is employed to extract governing equations of motion and boundary conditions. Harmonic differential quadrature method is utilized to investigate natural frequencies and related mode shapes of DLGNRs. In order to verify, results are compared to other literatures in a condition that one of the vdWs effects to be neglected. The effect of boundary condition and interlayer shear direction on the mode shape, sequence and value of DLGNRs natural frequencies are investigated.

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In this paper, the acoustical treatment of double-panel structures lined with poroelatic materials is predicted using analytical method in order to study the effective usage of the various boundary conditions of porous layer and to identify the effective parameters on the transmission loss of the multilayer systems. Therefore, inertia and viscous coupling along with thermal and elastic coupling should be considered in transfer stress dynamic and stress-strain relationships for an elastic porous material based on Biot theory. Then, the governing equations of the wave propagation in an elastic porous material are briefly considered and the general forms for the stresses and displacements within the porous material are given. Applying various boundary conditions and solving these equations with Matlab code simultaneously, the transmission loss of these structures is calculated. The results from the analytical method are compared with the SEA madel and the experimental data with excellent agreement is observed. Finally, the influence of effective parameters of this structure with various boundary conditions on the transmission loss of the multilayer systems is studied. The results have been shown that the transmission loss of double-panel structures lined with a layer of porous material can depend critically on the method of mounting the porous layer to the facing panel.