导体椭球的面电荷密度和曲率的关系

通过求解拉普拉斯方程,得到导体椭球的电势分布情况,进一步分析了导体表面的面电荷密度和曲率的关系,得到面电荷密度不是和曲率成正比,而是和曲率的1/3次方成正比的.     

导体旋转椭球电学量的一种计算方法

用一种新方法，计算了孤立导体旋转椭球的面电荷密度、电容、电势和电场强度，并得出相应的解析表达式。     

氩气微腔放电中特性参数的数值模拟研究

本文采用二维自洽完全流体模型,针对阳极为通孔的高气压微腔放电结构,研究了微腔放电的参数特性.数值计算得到了氩气压强为100 Torr,放电稳态时的电势分布、电子数密度分布和电子温度分布等重要参数.模拟结果表明放电区存在显著的阴极鞘层结构,电子数密度的峰值达到10²⁰ m^-3,电子温度的量级为几个eV至十几eV,该结论与实验结果相一致.数值模拟合理的解释了微腔放电的基本原理. 关键词： 微腔放电 等离子体模拟 流体模型     

电荷投影法在研究无限长导体薄板电荷分布规律中的应用

利用无限长均匀带电圆柱面的电荷分布规律和无限长带电直线的场强公式,采用电荷投影法推导了有限宽无限长带电导体的面电荷分布规律.根据电势叠加原理推导了电势积分式,利用场强与电势之间的关系推导了电场强度两个分量的积分式.将公式无量纲化,通过数值积分计算了电势和场强的分量之值.通过作图,显示了有限宽无限长带电导体薄板的电势和场强,画出了二维等势线和电场线,充分显示了场强的分布规律.     

氢吸附金刚石（001）表面的第一性原理研究

采用第一性原理方法研究氢吸附的金刚石（001）表面，计算了氢吸附金刚石表面构型.通过分析吸附前后空间电荷分布的变化，发现吸附H原子的金刚石（001）表面电荷向H原子转移，即表明氢吸附的金刚石表面带负电.分析了这种现象的微观机制，以及它对金刚石表面电学性质的影响. 关键词： 第一性原理计算 金刚石（001）面 表面吸附 电荷密度分布     

电介质/半导体结构样品电子束感生电流瞬态特性

电子束照射下电介质/半导体样品的电子束感生电流(electron beam induced current,EBIC)是其电子显微检测的重要手段.结合数值模拟和实验测量,研究了高能电子束辐照下SiO2/Si薄膜的瞬态EBIC特性.基于Rutherford模型和快二次电子模型研究电子的散射过程,基于电流连续性方程计算电荷的输运、俘获和复合过程,获得了电荷分布、EBIC和透射电流瞬态特性以及束能和束流对它们的影响.结果表明,由于电子散射效应,自由电子密度沿入射方向逐渐减小.由于二次电子出射,净电荷密度呈现近表面为正、内部为负的特性,空间电场在表面附近为正而在样品内部为负,导致一些电子输运到基底以及一些出射二次电子返回表面.SiO2与Si界面处俘获电子导致界面附近负电荷密度高于周围区域.随电子束照射样品内部净电荷密度逐渐降低,带电强度减弱.同时,负电荷逐渐向基底输运,EBIC和样品电流逐渐增大,电场强度逐渐减小.由于样品带电强度较弱,表面出射电流和透射电流随照射基本保持恒定.EBIC、透射电流及表面出射电流均随束流呈现近似正比例关系.对于本文SiO2/Si薄膜,透射电流随束能的升高逐渐增大并接近于束流值,EBIC在束能约15 keV时呈现极大值.     

基于MATLAB的点电荷系电场分布的用户图形界面设计

电场强度与电势是描述静电场性质的重要物理量,利用电场线与等势面可以形象地描述静电场的分布,对其进行数值计算和模拟显示,可以使教学内容更加直观,提高教学效率.本文利用MATLAB编程和MATLAB的GUIDE开发了点电荷系所形成的电场场强分布及电势分布的用户图形界面(GUI),实现了二维平面内任意点电荷系电场的电场线和等势面分布的可视化,并可以方便地调整电荷数目、电量及位置并实时显示,在教学中能起到很好的演示作用.     

匀强电场作用下液滴撞击壁面的动态行为

基于Open FOAM开源软件平台,采用VOF方法耦合电场方程组,数值模拟匀强电场作用下液滴撞击壁面的动态行为,研究电场强度、壁面浸润性对液滴行为的影响,获得电场、流场相互耦合作用下液滴周围电荷密度、电势的分布,重点关注电场力、电荷密度和壁面润湿性对液滴拉伸、撕裂的影响。研究结果表明:电场对液滴运动影响显著,电场力促使液滴拉伸高度增加;随着电场强度增强,电荷集中在液滴尖端,导致液滴喷射现象发生。液滴撞击亲水壁面,底部形成泰勒锥,内部出现涡流,随着壁面浸润性的提高,液滴喷射时间提前,液滴底部不会在疏水壁面上黏接。     

圆筒状DBD放电特性模拟研究

用XOOPIC软件对同轴圆筒状反应装置DBD放电特性进行了二维模拟研究。在频率为20kHz、正弦电压幅值为5kV的大气压氩气放电中,再现了微放电通道形成和发展过程,其微放电的寿命约为4ns。获得了电子、离子、介质表面电荷密度和电场强度随空间和时间的分布,发现在高压线圈的位置附近电子、离子和介质表面电荷密度存在极值。与典型平板介质阻挡放电相比,微放电中的电子密度、场强增加2~3个数量级。     

杂质离子对等离子体边界参量的影响

采用一维流体模型研究了含有杂质离子的等离子体与器壁材料相互作用给边界等离子体参量带来的影响.通过数值模拟,研究了分别选用碳和钨作为器壁材料时,器壁温度不同情形下热发射产生的电子对等离子体器壁电势、电场强度、热发射电子流以及沉积器壁离子动能流的影响.研究结果发现,当面向等离子体材料表面温度升高时,器壁电势和热发射产生的电流将增加,器壁电场强度和离子沉积器壁动能流则会减小,并且钨作为器壁材料要比碳作为器壁材料对于等离子体边界参量影响更明显.此外,研究了钨作为器壁材料时,碳杂质离子（浓度和电荷数）对等离子体器壁参量的影响.     

基于等离子体粒子模拟的喷气Z箍缩过程物理研究

给出了喷气Z箍缩动力学过程在二维柱坐标系下的等离子体粒子模拟物理模型,编写了相应的程序.对低电流驱动下的稀薄喷气Z箍缩动力学过程进行了验证性的等离子体粒子模拟,得到了许多微观的Z箍缩物理信息,如负载中的电流(密度)、电磁场、粒子位置和密度的时空演化,以及总的z箍缩拖尾质量和拖尾电流等信息.发现在Z箍缩过程中,模拟得到的等离子体电流随时间的变化反映出了等离子体箍缩到心和反弹的过程特征,磁场随径向的变化与长直导线电流给出的磁场很接近;电子所受到的电场力和磁场力(洛伦兹力)是相当的,而离子所受到的力主要是电场力;电子首先在z方向加速,然后在自身运动产生电流的磁场的作用下向轴心箍缩,而离子是在电子和离子电荷分离所产生的电场力的作用下向轴心运动;在压缩到轴心附近时,电子首先因静电排斥而飞散,而离子则在惯性的作用下继续向轴心箍缩,而后滞止飞散.Z箍缩等离子体的拖尾质量在20%左右,拖尾电流最大时在7%左右.     

Self-consistent nonlinear resonance and hysteresis of a charged microparticle in a RF sheath

A self-consistent model is proposed to study nonlinear phenomena, such as secondary resonance and hysteresis in the vertical oscillations of a charged microparticle in a radio-frequency sheath. The motion of a single microparticle in the sheath is simulated by solving Newton's equation in which various forces acting on the particle are taken into account. The particle charging and the sheath electric field are described by a self-consistent model of the collisional radio-frequency sheath dynamics. It is found that the nonlinearity is related to the particle's charge, the sheath electric field, and the external excitation force, as well as the ion drag force and neutral-gas friction on the particle.     

洛伦兹力可看作静止电荷所受电场力的相对论效应——兼论洛伦兹力公式具有与库仑定律相同的精确度

从洛伦兹变换出发,利用电磁场张量和四维力的协变性及电荷相对论不变,直接证明:在一个惯性参考系内的静止电荷所受电场力,转换到另一个惯性参考系就是运动电荷受的洛伦兹力.证明洛伦兹力公式具有与库仑定律相同的精确度.     

聚乙烯空间电荷包行为的形成机理与仿真方法研究

聚乙烯中的空间电荷包行为是空间电荷的一种特殊的输运行为.研究表明,空间电荷包行为由于受材料本身特性、外加电场大小以及环境温度等的影响,导致其产生过程及传输特性上存在较大差异,这些因素给空间电荷包行为产生机理研究带来了较大困难.通过对电荷的电极注入过程、载流子的体内迁移规律及空间电荷与体内陷阱的相互作用机制进行分析,探讨了不同外加电场及不同深度陷阱能级对电荷包行为造成的相关影响,在此基础上建立物理模型来描述电荷包的产生和迁移过程.模型中提出了在高于阈值电场时,载流子迁移速度与电场关系存在负微分迁移率的假设.基于此模型对空间包行为的模拟结果与实验结果取得较好的一致. 关键词： 空间电荷包 数值模拟 负微分迁移率     

过热液体中蒸汽泡上升过程的格子Boltzmann三维数值模拟

应用格子Boltzmann相变模型,在三维空间研究蒸汽泡在过热液体中生长、上升和变形等动力学行为.为研究传热传质对蒸汽泡运动的影响,对比模拟相同条件下气泡在等温环境中上升的物理过程.结果表明：蒸汽泡在过热液体中上升发生的变形程度较小,意味着相变对蒸汽泡的影响和表面张力一样使汽泡保持初始的形状.蒸汽泡在过热液体中的上升速度较小,说明随着汽泡生长拖拽力的影响比浮力大.蒸汽泡生长率在初始阶段达到最大值,随后会趋于一个恒定的值.随着汽泡体积增大和上升速度的增加,其对流场的扰动也越来越剧烈.蒸汽泡生长和上升引起的对流运动对温度场的演化造成很大的影响.     

A study on single fuel droplets combustion in vertical direct current electric fields

Both the electric force working on flames and the natural buoyancy are body forces, so there is a possibility to control the natural buoyancy by applying than electric field. It is important to discuss the body force in the flame because it induces the convective flow around flames. In this circumstance, combustion behavior of single droplets in vertical direct current electric fields was investigated. Ethanol, n-octane, and toluene were used as fuels, and the flame shape and the burning rate constants were measured. The distance between electrodes is 50 mm, and the applied voltage ranged between −4 and 6 kV as the bottom electrode is ground. When the direction of the electric field is opposite to the natural buoyancy direction, the applied voltage exists that make the flame symmetrical in the vertical direction, and the burning rate constants have local minima for ethanol and n-octane at the voltage. However, the minimum burning rate constants are larger than those under microgravity. This means that the electric force roughly balances with natural buoyancy, but it does not completely balance with the same. When the direction of the electric field is in the same direction as the natural buoyancy, there exist some experimental results, which cannot be explained by the assumption that electric field induces the body force only through the positive ions. This suggests that the additional body force is induced by the negative ions. The effects of negative charged soot particles on the combustion behavior are also discussed for the sooty flame of toluene.     

基于位相分布限制衍射光学元件的散斑抑制方法

根据散斑产生的机理,利用像素点之间干涉的概念,提出了通过限制光场的位相分布范围来抑制投影图像中散斑对比度的方法.在部分发展散斑的条件下,推导了位相均匀分布情况下的散斑对比度公式,揭示了当相位分布范围在0.6π~2π之间时,散斑对比度随相位分布范围的变化而震荡变化,当把相位分布范围限制在0.6π以下时,散斑对比度会随相位分布范围的减小而迅速下降.建立了理想仿真模型和实际仿真模型来验证该方法的正确性和可行性.在理想仿真模型中,当位相分布范围从2π变到0,所得散斑图样对比度从66.44%降到0;在实际仿真模型中,模拟了实际激光投影系统的光路结构,并运用了两片衍射光学元件,一片用于激光整形匀化,一片用于光场的位相分布范围限制,散斑图样对比度从92.78%降低到2.09%.该方法稳定性高、耗能低、使用元件尺寸小,为全息投影显示的散斑抑制提供了参考.     

Magnetohydrodynamic Natural Convection in a Rotating Enclosure

Magnetohydrodynamic natural convection heat transfer in a rotating, differentially heated enclosure is studied numerically in this article. The governing equations are in velocity, pressure and temperature formulation and solved using the staggered grid arrangement together with MAC method. The governing parameters considered are the Hartmann number, 0≤$Ha$≤70, the inclination angle of the magnetic field, 0$^◦$≤$θ$≤90$^◦$, the Taylor number, 8.9×10$^4$≤$Ta$≤1.1×10$^6$ and the centrifugal force is smaller than the Coriolis force and the both forces were kept below the buoyancy force. It is found that a sufficiently large Lorentz force neutralizes the effect of buoyancy, inertial and Coriolis forces. Horizontal or vertical direction of the magnetic field is the most effective in reducing the global heat transfer.     

Capillary oscillations and stability of a charged drop rotating about the axis of symmetry

The stability of a charged conductive liquid drop rotating about the axis of symmetry against the pressure of the self-charge electric field and inertial force pressure is investigated in an approximation linear in oscillation amplitude and square of the spheroidal drop deformation eccentricity. It is found that the axisymmetric modes of the rotating drop are stable. Only nonaxisymmetric modes with azimuthal numbers maximal for a given mode may be unstable. The Coriolis force plays a stabilizing role.     

Phase field simulation of single bubble behavior under an electric field

Based on the Cahn-Hilliard phase field model, a three-dimensional multiple-field coupling model for simulating the motion characteristics of a rising bubble in a liquid is established in a gas-liquid two-phase flow. The gas-liquid interface motion is simulated by using a phase-field method, and the effect of the electric field intensity on bubble dynamics is studied without electric field, or with vertical electric field or horizontal electric field. Through the coupling effect of electric field and flow field, the deformation of a single rising bubble and the formation of wake vortices under the action of gravity and electric field force are studied in detail. The correctness of the results is verified by mass conservation, and the influences of different electric field directions and different voltages on the movement of bubbles in liquid are considered. The results show that the ratio of the length to axis is proportional to the strength of the electric field when the air bubble is stretched into an ellipsoid along the electric field line under the action of electrostatic gravity and surface tension. In addition, the bubble rising speed is affected by the electric field, the vertical electric field accelerates the bubble rise, and the horizontal direction slows it down.