Bubble Motion near a Wall Under Microgravity: Existence of Attractive and Repulsive Forces

A numerical simulation for a bubble motion near a wall under microgravity, relevant to material processing such as crystal growth in space, is presented based on a mass conservation level set algorithm to predict the bubble behavior affected by the near wall. The simulation for the wall effect on the bubble driven by an external acceleration parallel with the near wall referred to as g-jitter confirms for the first time the existence of the wall attractive force to the bubble near the wall under certain conditions such as the initial distance between the bubble and the wall, density and viscosity ratios between the bubble and surrounding liquid under microgravity. The wall effect mechanism is explained, and the results show that the wall attractive force increases with the increasing of density ratio. Moreover, the simulation for the wall repulsive effect on the bubble near the wall under microgravity has been carried out as well.     

Flow Structure and Surface Deformation of High Prandtl Number Fluid Under Reduced Gravity and Microgravity

The numerical simulation has been conducted to investigate the flow structure and surface deformation in a liquid bridge of high Prandtl number fluid under reduced gravity and microgravity. The Navier–Stokes equations coupled with the energy conservation equation are solved on a staggered grid, and the mass conserving level set approach is used to capture the free surface deformation of the liquid bridge. The effect of reduced gravity and thermocapillary convection on the surface deformation of the liquid bridge is investigated, and the results show that the amplitude of the surface horizontal vibration decreases gradually, and the thermocapillary convection inside the liquid bridge starts to turn into a steady state after the initial period. Moreover, the shift of the center of the recirculating flow inside the liquid bridge under horizontal external acceleration and zero gravity is also studied, and the results indicate that the vortex centers move initially toward the cold disk and reach an equilibrium position, and then the vortex centers vibrate around the equilibrium position periodically.     

Totally Asymmetric Simple Exclusion Process under Exit Control Feedback Policy

出口控制反馈策略下的完全非对称简单排他过程

崔晓玲¹, 陈晓瑜², 肖松¹

（1. 临沂大学 机械与车辆工程学院, 山东 临沂 276000;

2．东北大学 材料电磁过程实验室,沈阳 110004)

摘要：

本文研究了出口控制反馈策略对交通流的影响。出口速率(β)定义为跳变速率(p)、电流(J)和体积密度(ρbulk)的函数,并改写为β = p - J/ρbulk。采用平均场法对基于完全不对称简单排他过程(TASEP)的模型进行了分析。相图中存在一个相变点,由p决定。此外,除低密度(LD)相外,其他各相出口率保持在β = p/2时,系统流量达到最大电流。结果表明,当交通系统处于交通堵塞状态时,可以采用控制反馈策略使交通流量达到最大值。

关键词：完全非对称简单排他过程;出口控制反馈;相图

     

Moving behavior of pellets in a pellet shaft furnace

The downward moving behavior of pellets in a 8 m2 pellet shaft furnace with an internal vertical air channel and a drying bed was studied by means of a visualized model(1-15) and a top model(1-1).The visualized model experiment shows that the downward movement of pellets can be regarded as plug flow approximately inside the furnace except for the lower region of cooling zone due to the influence of the drained hopper.The top model experiment reveals that the pellet sizes increase along the moving direction because of the percolation phenomenon,which results in a decrease of the resistance coefficient and an increase of the gas flow rate from the furnace wall toward the furnace center.     

Non-Lyapunov Type Stability in a Model of the Dewetted Bridgman Crystal Growth Under Zero Gravity Conditions

A numerical model has been developed based on a mass conservation level set algorithm considering a wall adhesion to predict the surface motion for a single and double dam break problems. The simulation for the single dam break shows that the wall adhesion force can be introduced through contact angle by modifying the level set function on the boundary in the level set method, and the magnitude of the contact angle has an effect on the moving location of the leading front of water–gas system. Moreover, the simulation for the double dam break presents clearly the processes of coalescence and break up of the free surface.     

Experimental research and numerical simulation of the dynamic cylinder upsetting

In order to study the dynamic effects under impulsive load, experimental and numerical investigations on the dynamic upsetting process of lead cylinder were conducted. Experiments were carried out on a drop hammer impact test machine. The results show that the dynamic effects on the forming load is related to the hammer velocity, radius–height ratio of specimen and drop mass. The forming load increases with the increase of the hammer velocity or radius-to-height ratio. The fluctuation of load–displacement curve becomes obvious with the increase of the hammer velocity and drop mass. The deformation processes were simulated by the finite element program ANSYS/LS-DYNA. The deformed configuration, velocity vector field and equivalent strain distribution were obtained. The results show that the deformed geometry exhibits mushroom, the material points in the upper region flow faster than that in the lower region, and a strain concentration zone appears in the upper center region.     

Two-phase microstructure selection in peritectic solidification: from island banding to coupled growth

We report the first experimental observation in directionally solidified peritectic Fe–Ni alloys of two-phase island banding microstructures that consist of rows of islands of one solid phase (either peritectic or primary) inside the continuous matrix of the other phase. These microstructures form under predominantly diffusion-limited growth conditions and when both phases are morphologically stable, as recently predicted by numerical simulations of a phase-field model. They are observed either as transients that seed the formation of coupled growth structures, or as the final microstructure. Phase-field simulations are reported that shed light on the relationship of island banding and coupled growth as well as on the growth conditions and nucleation parameters that control the dynamical selection of these two basic microstructures in peritectic alloys.     

Amplitude Equations for Large-Scale Marangoni Convection in a Liquid Layer with Insoluble Surfactant on Deformable Free Surface

The numerical simulation has been carried out to investigate the motion of a droplet initially near a wall under gravity and confirm the existence of the wall repulsive force on the droplet. The numerical model is developed based on a mass conservation level set algorithm to capture the surface deformation of the droplet. The results show that the wall repulsive force on the droplet initially near the wall plays an important role in the droplet falling process, and the viscosity force affects the oscillatory trajectory of the falling droplet. In addition, the mutual repulsive effect between two droplets is also studied by settling symmetrically two droplets, and the oscillatory mechanism of droplet motion is discussed as well.     

Study on the Characteristics of Fluid Flow in Stirring Vessel of New Type Stirring of KR Desulphurization

Aimed at the problem of short life of mixing head in KR mechanical mixing method for desulfurization of hot metal,a new type of mixing stir was proposed.CFD theory was used to simulate the characteristics of the fluid flow for the new type of stirring vessel of water model for KR mechanical desulfurization.Flow characteristics and structures of the flow field were investigated and compared with the traditional cross-flow type.The results show that the new type of impeller can not only improve the defects of the flow caused by stir structure of the traditional type,but also reduce the separation of mixing zone in the stirred tank and make the flow field more uniform to make the desulfurization more fully,thus shortening the mixing time,and improving the life of mixing head.Numerical simulation method has been proven to be sound by comparing with the experimental ones.     

Effect of dissolved organic matter on the stability of magnetite nanoparticles under different pH and ionic strength conditions

Upon release of engineered nanoparticles (NPs) into the subsurface environment, their fate and transport and hence their potential environmental and public health impacts will largely depend on how stable these NPs are as suspended particles in the natural environment. In this study, we systematically examine the effect of humic acid (HA) on surface charge status and aggregation potential of magnetite (Fe₃O₄) NPs, selected as a model for metal oxide NPs, over a wide range of solution pH and ionic strength. Through zeta potential (ZP) measurements, we found that HA can adsorb to magnetite particles hence modifying their surface charge status. At low loadings, the presence of HA can induce a shift in the point zero of charge of due to partial neutralization of the positive charges on magnetite NPs. At high loadings, however, HA is capable of completely cover magnetite particles giving rise to a suspension ZP profile similar to its own (observed in presence of 20 mg L⁻¹ HA). These impacts on surface charge correspond well with the observed aggregation behaviors in the absence and presence of HA. From the dynamic light scattering (DLS) measurements, fast aggregation, which is independent of solution chemistry, took place when the pH is close to the point zero charge (PZC) and the ionic strength is above the critical coagulation concentration (CCC). At high ionic strength, a small dose (2 mg L⁻¹) of HA stabilized the NPs' suspension significantly. This stabilization effect is substantially enhanced with increasing HA concentration. The calculated DLVO (Derjaguin-Landau-Verwey-Overbeek) interaction energy profiles, using experimentally determined values of Hamaker constant, adequately support the experimental observations. The DLVO analysis further reveals the possible presence of secondary energy minima and the possibility of deaggregation of magnetite agglomerates. The complexation of HA-NPs and the HA effects on NPs aggregations were confirmed by atomic force microscope (AFM) observations.