Unsteady shrinking sheet with mass transfer in a rotating fluid

In this paper, the problem of unsteady flow induced by a shrinking sheet with mass transfer in a rotating fluid is studied. The transformed boundary layer equations are solved numerically by an implicit finite‐difference scheme known as the Keller‐box method. The influence of rotation, unsteadiness and mass suction parameters on the reduced skin friction coefficients f″(0) and g′(0), as well as the lateral velocity and velocity profiles are presented and discussed in detail. Copyright © 2010 John Wiley & Sons, Ltd.     

配送中心业务流程优化设计——以广州A连锁便利店配送中心为例

分析广州A连锁便利店物流需求,根据设计目标,遵循设计原则,优化配送中心业务流程设计,形成优化设计方案,达到优化设计预期效果.     

A two-phase, two-component model for vertical upward gas-liquid annular flow

In this paper, a new two-fluid two-component computational fluid dynamics (CFD) model is developed to simulate vertical upward two-phase annular flow. The two-phase VOF scheme is utilized to model the roll wave flow, and the gas core is described by a two-component phase consisting of liquid droplets and gas phase. The entrainment and deposition processes are taken into account by source terms of the governing equations. Unlike the previous models, the newly developed model includes the effect of liquid roll waves directly determined from the CFD code, which is able to provide more detailed and, the most important, more self-standing information for both the gas core flow and the film flow as well as their interactions. Predicted results are compared with experimental data, and a good agreement is achieved.     

Disorder structure of free-flow and global jams in the extended BML model

The original BML model is extended by introducing extended sites, which can hold several vehicles at each time-step. Unexpectedly, the flow in the extended model sharply transits from free-flow to global jams, but the transition is not one-order in original BML model. And congestion in the extended model appears more easily. This can ascribe to the mixture of vehicles from different directions in one site, leading to the drop-off of the capacity of the site. Furthermore, the typical configuration of free flowing and global jams in the extended models is disorder, different from the regular structure in the original model.     

Group and phase velocities in the free-surface visco-potential flow: New kind of boundary layer induced instability

Water wave propagation can be attenuated by various physical mechanisms. One of the main sources of wave energy dissipation lies in boundary layers. The present work is entirely devoted to thorough analysis of the dispersion relation of the novel visco-potential formulation. Namely, in this study we relax all assumptions of the weak dependence of the wave frequency on time. As a result, we have to deal with complex integro-differential equations that describe transient behaviour of the phase and group velocities. Using numerical computations, we show several snapshots of these important quantities at different times as functions of the wave number. Good qualitative agreement with previous study [D. Dutykh, Eur. J. Mech. B/Fluids 28 (2009) 430] is obtained. Thus, we validate in some sense approximations made anteriorly. There is an unexpected conclusion of this study. According to our computations, the bottom boundary layer creates disintegrating modes in the group velocity. In the same time, the imaginary part of the phase velocity remains negative for all times. This result can be interpreted as a new kind of instability which is induced by the bottom boundary layer effect.     

高速公路微波车辆检测器的应用解决方案

通过对目前常见的交通检测技术性能的比较,分析了微波车辆检测器的优点,重点介绍了微波车辆检测器在高速公路中的安装和使用方法.     

A ghost fluid Lattice Boltzmann method for complex geometries

A ghost fluid Lattice Boltzmann method (GF‐LBM) is developed in this study to represent complex boundaries in Lattice Boltzmann simulations of fluid flows. Velocity and density values at the ghost points are extrapolated from the fluid interior and domain boundary via obtaining image points along the boundary normal inside the fluid domain. A general bilinear interpolation algorithm is used to obtain values at image points which are then extrapolated to ghost nodes thus satisfying hydrodynamic boundary conditions. The method ensures no‐penetration and no‐slip conditions at the boundaries. Equilibrium distribution functions at the ghost points are computed using the extrapolated values of the hydrodynamic variables, while non‐equilibrium distribution functions are extrapolated from the interior nodes. The method developed is general, and is capable of prescribing Dirichlet as well as Neumann boundary conditions for pressure and velocity. Consistency and second‐order accuracy of the method are established by running three test problems including cylindrical Couette flow, flow between eccentric rotating cylinders and flow over a cylinder in a confined channel. Copyright © 2011 John Wiley & Sons, Ltd.     

Doppler effects of an oscillating line source in shear flow with a free surface

The linearised water-wave radiation problem for the oscillating 2D submerged source in an inviscid shear flow with a free surface is investigated analytically. There is a nonzero surface velocity. The depth is infinite and the vorticity is uniform. The amplitudes radiated from the source are calculated analytically. Due to Doppler effects, there may be up to four different emitted waves, and there is resonance with zero group velocity and infinite amplitude.     

RHEED study on continuously repeated step flow and layer-by-layer growth modes in SrRuO3/SrMnO3 superlattice

Nanolayered superlattices composed of ferromagnetic SrRuO₃ and antiferromagnetic SrMnO₃ layers were grown on SrTiO₃ (100) substrates by pulsed laser deposition. Multilayers were grown under predetermined synthesis conditions resulting in growth of SrRuO₃ and SrMnO₃ by step flow and layer-by-layer modes, respectively. The growth of SrMnO₃ was observed to occur through the layer-by-layer during the entire deposition process despite the expected increase in surface roughness because of the incorporation of SrRuO₃ upper layers. Monitoring by reflection high-energy electron diffraction (RHEED) revealed that the growth of every SrMnO₃ layer consisted of a pre-stage during which the gaps on the relatively rough SrRuO₃ surface were filled before the actual growth of the SrMnO₃ layer, which resulted in incomplete half oscillation and change from spot patterns to streaky patterns. The in-plane lattice constant did not show any considerable change in the case of SrRuO₃ and SrMnO₃ layers, despite the considerable lattice mismatch between the two materials (SrRuO₃, SrMnO₃) and SrTiO₃. On the other hand, the RHEED patterns showed the existence of lattice mismatch effects in the out-of-plane lattice constant, which showed significant strains of opposite signs in the different layers, indicating a strong dependence on the composition of the layers and superlattice periodicity. In this paper, the growth characteristics of a SrRuO₃/SrMnO₃ multilayer along with its magnetic properties will be discussed.     

Free (open) boundary condition: some experiences with viscous flow simulations

The free (or open) boundary condition (FBC, OBC) was proposed by Papanastasiou et al. (A new outflow boundary condition, International Journal for Numerical Methods in Fluids, 1992; 14:587–608) to handle truncated domains with synthetic boundaries where the outflow conditions are unknown. In the present work, implementation of the FBC has been tested in several benchmark problems of viscous flow in fluid mechanics. The FEM is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal or non‐isothermal, steady‐state conditions, for Newtonian fluids. The effects of inertia, gravity, compressibility, pressure dependence of the viscosity, slip at the wall, and surface tension are all considered individually in the extrudate‐swell benchmark problem for a wide range of the relevant parameters. The present results extend previous ones regarding the applicability of the FBC and show cases where the FBC is inappropriate, namely in the extrudate‐swell problem with gravity or surface‐tension effects. Particular emphasis has been given to the pressure at the outflow, which is the most sensitive quantity of the computations. In all cases where FBC is appropriate, excellent agreement has been found in comparisons with results from very long domains. The formulation for Picard‐type iterations is given in some detail, and the differences with the Newton–Raphson formulation are highlighted regarding some computational aspects. Copyright © 2011 John Wiley & Sons, Ltd.