Numerical study of bifurcation solutions of spherical Taylor-Couette flow

The steady bifurcation flows in a spherical gap (gap ratio sigma=0.18) with rotating inner and stationary outer spheres are simulated numerically for Re(c1)less than or equal to Re less than or equal to 1 500 by solving steady axisymmetric incompressible Navier-Stokes equations using a finite difference method. The simulation shows that there exist two steady stable flows with 1 or 2 vortices per hemisphere for 775 less than or equal to Re less than or equal to 1 220 and three steady stable flows with 0, 1, or 2 vortices for 1 220

Numerical simulation of axisymmetric unsteady incompressible flow by a vorticity-velocity method

A new numerical method for solving the axisymmetric unsteady incompressible Navier-Stokes equations using vorticity-velocity variables and a staggered grid is presented. The solution is advanced in time with an explicit two-stage Runge-Kutta method. At each stage a vector Poisson equation for velocity is solved. Some important aspects of staggering of the variable location, divergence-free correction to the velocity held by means of a suitably chosen scalar potential and numerical treatment of the vorticity boundary condition are examined. The axisymmetric spherical Couette flow between two concentric differentially rotating spheres is computed as an initial value problem. Comparison of the computational results using a staggered grid with those using a non-staggered grid shows that the staggered grid is superior to the non-staggered grid. The computed scenario of the transition from zero-vortex to two-vortex flow at moderate Reynolds number agrees with that simulated using a pseudospectral method, thus validating the temporal accuracy of our method.

The motion of solid particles in a liquid with vertical temperature-gradient

A ground-experiment study on the motions of solid particles in liquid media with vertical temperature gradient is performed in this paper. The movement of solid spheres toward the heating end of a close cell is observed. The behavior and features of the motions examined are quite similar to thermocapillary migration of bubbles and drops in a liquid. The motion velocities of particles measured are about 10(-3) to 10(-4) mm\s. The velocity is compared with the velocity of particles floated in two liquid media. The physical mechanism of motion is explored.

Effects of contact resistance on thermal-conductivity of composite media with a periodic structure

The thermal conductivity of periodic composite media with spherical or cylindrical inclusions embedded in a homogeneous matrix is discussed. Using Green functions, we show that the Rayleigh identity can be generalized to deal with thermal properties ot these systems. A new calculating method for effective conductivity of composite media is proposed. Useful formulae for effective thermal conductivity are derived, and meanings of contact resistance in engineering problems are explained.

Thermal-conductivity of periodic composite media with spherical inclusions

The thermal conductivity of periodic composite media with spherical inclusions embedded in a homogeneous matrix is discussed. Using Green's function, we show that the Rayleigh identity can be generalized to deal with the thermal properties of these systems. A technique for calculating effective thermal conductivities is proposed. Systems with cubic symmetries (including simple cubic, body centered cubic and face centered cubic symmetry) are investigated in detail, and useful formulae for evaluating effective thermal conductivities are derived.

Ballistic impact of ceramics

The impact behaviour of a range of glass and ceramic materials has been studied using high-speed photography. A gas gun was used to project hardened spheres at plate specimens in the velocity range 30 to 1000m s-1. The target materials included soda-lime glass, boron carbide and various glass ceramics and aluminas. The performance of a particular ceramic was found to depend on a combination of parameters but of key importance was the relative hardness of the projectile and target materials. The fracture toughness, K(IC), had only a secondary effect.

沉降对不同粒径聚苯乙烯胶乳球异向聚集的影响

R.Folkersma等报道了在微重力环境下2μm聚苯乙烯（PS）胶乳球的异向聚集速率有明显增大的结果,本文作者之一孙祉伟等的实验结果却与此有很大差异.为此作者在孙祉伟等的实验基础上对1,2,3μm以及1μm+2μm PS胶乳球混和体系的相对聚集速率进行了研究.作者对原有实验装置进行了改进,并验证了改进后的实验装置的可行性.用密度匹配法实现模拟微重力条件,用快聚集过程中浊度随时间的变化表示相对聚集速率.结果表明,重力引起的沉降对所研究体系聚集速率的影响是很小的,在实验误差范围内可以忽略.作者认为与Stein等结果显著不同的原因是二者使用的样品表面性质不同以及实验方法的差异.

钨球打钢靶数值仿真研究

通过对钨球垂直撞击钢靶的数值仿真，获得了模拟钨球撞击钢板的整个物理图象，并给出了多种人们所关心的侵彻过程和物理场的演化数据，仿真结果与试验数据有较好的一致性。

An algorithm for coarse particle sedimentation simulation by Stokesian dynamics

Coarse Particle sedimentation is studied by using an algorithm with no adjustable parameters based on stokesian dynamics. Only inter-particle interactions of hydrodynamic force and gravity are considered. The sedimentation of a simple cubic array of spheres is used to verify the computational results. The scaling and parallelism with OpenMP of the method are presented. Random suspension sedimentation is investigated with Mont Carlo simulation. The computational results are shown in good agreement with experimental fitting at the lower computational cost of O(N In N).

On the contact width in generalized plain strain JKR model for isotropic solids

Adhesive contact model between an elastic cylinder and an elastic half space is studied in the present paper, in which an external pulling force is acted on the above cylinder with an arbitrary direction and the contact width is assumed to be asymmetric with respect to the structure. Solutions to the asymmetric model are obtained and the effect of the asymmetric contact width on the whole pulling process is mainly discussed. It is found that the smaller the absolute value of Dundurs' parameter beta or the larger the pulling angle theta, the more reasonable the symmetric model would be to approximate the asymmetric one.

Influence Of Gravity On Structure Of Colloidal Crystal Using Simulated Microgravity

Liquid mixtures of water and deuterium oxide as the liquid phase, were used to match the density of charged colloidal particles. Kossel diffraction method was used to detect the crystal structures. The experiments under the density-matched (g=0) and unmatched (g=1) conditions are compared to examine the influence of gravity on the crystal structures formed by self-assembly of 110 nm (in diameter) polystyrene microspheres. The result shows that die gravity tends to make the lattice constants of colloidal crystals smaller at lower positions, which indicates that the effect of gravity should be taken into account in the study of the colloidal crystals.

Small angle X-ray scattering of the colloidal crystal

The monodisperse polystyrene spheres are assembled into the colloidal crystal on the glass substrate by vertical deposition method, which is aimed at the so-called photonic crystal applications. The structural information of the bulk colloidal crystal is crucial for understanding the crystal growth mechanism and developing the various applications of colloidal crystal. Small-angle X-ray scattering (SAXS) technique was used to obtain the bulk structure of the colloidal crystal at Beamline 1W2A of BSRF. It is found that the SAXS pattern is sensitive to the relative orientation between the colloidal sample and the incident X-ray direction. The crystal lattice was well distinguished and determined by the SAXS data.

Liquid phase epitaxy of Al0.3Ga0.7As islands

Self-organized Al0.3Ga0.7As islands generated on the (100) facet are achieved by liquid phase epitaxy. Three particularly designed experimental conditions-partial oxidation, deficient solute and air quenching-result in defect-free nucleation. Micron-sized frustums and pyramids are observed by a scanning electron microscope. The sharp end of the tip has a radius of curvature less than 50 nm. It is proposed that such Al0.3Ga0.7As islands may be potentially serviceable in microscale and nanoscale fabrication and related spheres. (C) 2004 Elsevier B.V. All rights reserved.

Silica and alumina thin films grown by liquid phase deposition

This work demonstrates the condition optimization during liquid phase deposition (LPD) Of SiO2/GaAs films. LPD method is further applied to form Al2O3 films on semiconductors with poison-free materials. Proceeding at room temperature with inexpensive equipment, LPD of silica and alumina films is potentially serviceable in microelectronics and related spheres.

Changing planar thin film growth into self-assembled island formation by adjusting experimental conditions

Illustrated in this paper are two examples of altering planar growth into self-assembled island formation by adapting experimental conditions. Partial oxidation, undersaturated solution and high temperature change Frank-Van der Merwe (FM) growth of Al0.3Ga0.7As in liquid phase epitaxy (LPE) into isolated island deposition. Low growth speed, high temperature and in situ annealing in molecular beam epitaxy (MBE) cause the origination of InAs/GaAs quantum dots (QDs) to happen while the film is still below critical thickness in Stranski-Krastanow (SK) mode. Sample morphologies are characterized by scanning electron microscopy (SEM) or atomic force microscopy (AFM). It is suggested that such achievements are of value not only to fundamental researches but also to spheres of device applications as well. (c) 2004 Elsevier B.V. All rights reserved.