Lattice Boltzmann Model for The Volume-Averaged Navier-Stokes Equations

A numerical method, based on the discrete lattice Boltzmann equation, is presented for solving the volume-averaged Navier-Stokes equations. With a modified equilibrium distribution and an additional forcing term, the volume-averaged Navier-Stokes equations can be recovered from the lattice Boltzmann equation in the limit of small Mach number by the Chapman-Enskog analysis and Taylor expansion. Due to its advantages such as explicit solver and inherent parallelism, the method appears to be more competitive with traditional numerical techniques. Numerical simulations show that the proposed model can accurately reproduce both the linear and nonlinear drag effects of porosity in the fluid flow through porous media.Comment: 9 pages, 2 figure

Quantum tunneling of magnetization in dipolar spin-1 condensates under external fields

We study the macroscopic quantum tunneling of magnetization of the F=1 spinor condensate interacting through dipole-dipole interaction with an external magnetic field applied along the longitudinal or transverse direction. We show that the ground state energy and the effective magnetic moment of the system exhibit an interesting macroscopic quantum oscillation phenomenon originating from the oscillating dependence of thermodynamic properties of the system on the vacuum angle. Tunneling between two degenerate minima are analyzed by means of an effective potential method and the periodic instanton method.Comment: 2 figures, accepted PR

A stability condition for turbulence model: From EMMS model to EMMS-based turbulence model

The closure problem of turbulence is still a challenging issue in turbulence modeling. In this work, a stability condition is used to close turbulence. Specifically, we regard single-phase flow as a mixture of turbulent and non-turbulent fluids, separating the structure of turbulence. Subsequently, according to the picture of the turbulent eddy cascade, the energy contained in turbulent flow is decomposed into different parts and then quantified. A turbulence stability condition, similar to the principle of the energy-minimization multi-scale (EMMS) model for gas-solid systems, is formulated to close the dynamic constraint equations of turbulence, allowing the heterogeneous structural parameters of turbulence to be optimized. We call this model the `EMMS-based turbulence model', and use it to construct the corresponding turbulent viscosity coefficient. To validate the EMMS-based turbulence model, it is used to simulate two classical benchmark problems, lid-driven cavity flow and turbulent flow with forced convection in an empty room. The numerical results show that the EMMS-based turbulence model improves the accuracy of turbulence modeling due to it considers the principle of compromise in competition between viscosity and inertia.Comment: 26 pages, 13 figures, 2 table

Managing Virtual Team Performance: An Exploratory Study of Social Loafing and Social Comparison

This study investigates the effects of social comparison and social loafing on virtual team performance when teams engage in asynchronous ideation process. The results of the study suggest that the effects of social comparison and social loafing co-exist in virtual teams. Team members may choose to engage in different behaviors (social loafing vs. social comparison) in different team interactions. Furthermore, team members tend to elaborate on the ideas generated by co-workers. As a result, teams with less social loafing will produce richer elaboration on ideas generated

A Numerical Study of the Effects of Wave-Induced Fluid Flow in Porous Media: Linear Solver

In this paper, we present a computational method to simulate wave propagation in porous rocks saturated with Newtonian fluids over a range of frequencies of interest. The method can use a digital representation of a rock sample where distinct material phase and properties at each volume cell are identified and model the dynamic response of the rock to an acoustic excitation mathematically with a coupled equation system: elastic wave equation in solid matrix and viscous wave equation in fluid. The coupled wave equations are solved numerically with a rotated-staggered-grid finite difference scheme. We simulate P-wave propagation through an idealized porous medium of periodically alternating solid and fluid layers where an analytical solution is available and obtain excellent agreements between numerical and analytical solutions. The method models the effect of pore fluid motion on the rock dynamic response more accurately with a linearized Navier-Stokes equation than with the viscoelastic model of the generalized Maxwell body, a low frequency approximation commonly used to overcome the difficulty of modeling frequency-dependent fluid shear modulus in time domain.Schlumberger Doll ResearchMassachusetts Institute of Technology. Earth Resources Laborator

Construction of a complete set of orthogonal Fourier-Mellin moment invariants for pattern recognition applications

International audienceThe completeness property of a set of invariant descriptors is of fundamental importance from the theoretical as well as the practical points of view. In this paper, we propose a general approach to construct a complete set of orthogonal Fourier-Mellin moment (OFMM) invariants. By establishing a relationship between the OFMMs of the original image and those of the image having the same shape but distinct orientation and scale, a complete set of scale and rotation invariants is derived. The efficiency and the robustness to noise of the method for recognition tasks are shown by comparing it with some existing methods on several data sets