Spontaneous growth of the reconnection electric field during magnetic reconnection with a guide field:A theoretical model and particle-in-cell simulations

Reconnection electric field is a key element of magnetic reconnection.It quantifies the change of magnetic topology and the dissipation of magnetic energy.In this work,two-dimensional(2D)particle-in-cell(PIC)simulations are performed to study the growth of the reconnection electric field in the electron diffusion region(EDR)during magnetic reconnection with a guide field.At first,a seed electric field is produced due to the excitation of the tearing-mode instability.Then,the reconnection electric field in the EDR,which is dominated by the electron pressure tensor term,suffers a spontaneous growth stage and grows exponentially until it saturates.A theoretical model is also proposed to explain such a kind of growth.The reconnection electric field in the EDR is found to be directly proportional to the electron outflow speed.The time derivative of electron outflow speed is proportional to the reconnection electric field in the EDR because the outflow is formed after the inflow electrons are accelerated by the reconnection electric field in the EDR and then directed away along the outflow direction.This kind of reinforcing process at last leads to the exponential growth of the reconnection electric field in the EDR.

SOLIDIFICATION OF Zn－Pb ALLOY UNDER SIMULANT MICROGRAVITY CONDITION OF ORTHOGONAL ELECTRIC AND MAGNETIC FIELDS

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Response laws of rock electrical property and saturation evaluation method of tight sandstone

To solve the problem that the law of rock electrical response under low and medium water saturation in tight sandstone reservoirs is not clear, an experimental method of high-speed centrifugal displacement rock electricity and nuclear magnetic resonance T2 spectrometry under different water saturation was proposed, which can drive the tight sandstone cores with the permeability less than 0.1×10^-3 μm^2, and provide a reliable experimental means for the study of tight sandstone electrical property. By carrying out supporting experiments such as high-resolution CT scan, MAPS and Qemscan, a multi-mineral component fine three-dimensional digital core based on multi-source information fusion was constructed. The finite element numerical simulation method was used to obtain the electrical response of tight sandstone core with low water saturation which cannot be obtained in laboratory conditions. By combining experiment and numerical simulation, the electrical response laws have been clear of tight sandstone with complex pore structure, and the saturation evaluation method of variable rock electrical parameters based on pore structure has been developed. The processing of logging data of multiple wells in tight sandstone reservoir of Chang 7 Member in the Ordos Basin shows that this method can obtain more accurate oil saturation, and provides a new idea and method for fine logging evaluation of tight sandstone reservoir.

In-Situ Analysis of Bulk Solidifying the Hyper-Monotectic Alloy Under a Compound Electric-Magnetic Field by Physical Simulation

A physical simulation was carried out to investigate the realistic experiment of bulk solidifying the Zn-Bi hyper-monotectic alloy under various compound electric-magnetic fields(CEMF).For this experiment,two crucial parameters determinate the cast microstructure,the one is electric-magnetic force(EMF)and the other is the frequency of AC current.Results show that the minor phase could be mixed in the other phase from the initial layered structure when the EMF above a specific value under fixed frequency,and the average diameter of minor phase droplet decreases with increasing EMF.The evolution of the liquid phases structure is reasonable agree with the realistic experiment of Zn-Bi hyper-monotectic alloy,which suggests that the mechanism revealed by the physical simulation could represent the one in the realistic experiment.

基于MATLAB/SIMULINK永磁同步电动机变结构调速系统的建模与仿真

研究如何利用变结构控制理论设计永磁同步电动机的调速控制系统 ,这种控制系统基于同步电动机的转子磁链定向控制理论 ;论文中还对该系统进行数学建模 ,并通过MATLAB

Microstructure evolution of immiscible alloy solidified under the effect of composite electric and magnetic fields

Solidification experiments were performed with Lead-Aluminum immiscible alloy under the effect of composite electric and magnetic fields(CEMFs).The results demonstrate that CEMFs not only decrease the size of minority phase particles(MPPs)but also promote a more uniform distribution of the MPPs.A theoretical model was built to describe the microstructure evolution during cooling the immiscible alloy.The solidification process of Pb-0.4 wt.%Al alloy under the effect of the CEMFs was simulated.The numerical results are well consistent with the experimental data.These results demonstrate that CEMFs affect the solidification process through changing melt convection and the nucleation behavior of minority phase droplets(MPDs).On one hand,the CEMFs can inhibit the convection and lead to the homogeneous distribution of MPPs along the radial direction of the sample.On the other hand,the CEMFs can increase the nucleation driving force for the MPDs,which decreases the average radius of MPDs and boosts the formation of dispersed solidification structures.This research indicates that the application of CEMFs is a promising strategy for controlling the microstructure of immiscible alloys.

复杂地形瞬变电磁三维正演模拟与地形效应分析

目前,地面瞬变电磁法凭借其优势已被广泛用于煤矿水文地质勘查中,然而,在野外实际勘探中,复杂地形环境常导致发射源几何形状的改变与信号接收偏差,降低了勘探精度。为此,采用理论分析、数值模拟和实际地形数据分析相结合的方式,系统研究了复杂地形条件下电性源与磁性源瞬变电磁场的响应特征。首先,基于二阶后退欧拉离散的矢量有限元正演模拟技术,详细探讨了山峰和山谷地形位于接收点和发射源位置时,对两种源系统的影响规律。结果表明:电性源系统会出现响应变号现象,源导线位置高于周围地形时响应增强,反之则被削弱;而磁性源无变号现象,但响应变化规律与电性源类似。其次,利用实测地形数据,采用四面体网格建立与实际地形高度吻合的三维正演模型。模拟结果显示:早期响应曲线能够清晰反映地形细节,曲线形态与地形特征一致;而晚期响应则逐渐趋于平缓,体现了深部背景的影响。研究成果可为复杂地形条件下瞬变电磁法的勘探装置布设、数据采集、处理和解释提供理论指导,对提高煤矿水文地质勘探精度具有重要意义。

电火花加工用磁悬浮驱动器控制系统

针对传统电火花加工时,主轴不能及时调整极间间隙导致加工效率低下的问题,提出了一种多自由度磁悬浮驱动器代替传统电火花主轴运动。分析了该磁悬浮驱动器的结构及原理并建立了磁悬浮驱动器的动力学模型,运用有限元仿真软件对该驱动器所产生的电磁力进行仿真分析,通过设计传统PID控制系统及模糊PID控制系统对磁悬浮驱动器的控制效果进行仿真与实验验证。结果表明,该磁悬浮驱动器具有较好的跟随特性和快速的响应速度及符合要求的电磁力,满足微细电火花加工要求。

不同石墨化度阳极炭块铝电解槽物理场模拟对比

利用SOLIDWORKS建模软件及COMSOL仿真软件对某厂家350 kA铝电解槽进行电场磁场模拟,对比传统普通阳极炭块电解槽和不同石墨化度阳极炭块电解槽电场磁场的差异。笔者根据不同石墨化度炭块理化性质的不同,探索不同石墨化度阳极炭块对电解槽电场磁场的影响差异,发现阳极炭块石墨化处理可降低电解槽整体电压降,降低铝液中水平电流密度,减小垂直于铝液方向的磁通密度。基于此,认为阳极炭块的最优石墨化度为10%。

大型矿用电铲永磁外转子提升系统动力学特性研究

针对传统电铲提升系统存在传动效率低、能量损耗高、维护工作量大等问题,基于永磁外转子滚筒直接驱动提升装置,提出了一种电铲提升设计方案,并对永磁外转子提升系统的动力学特性进行了研究。首先,分析了电铲挖掘轨迹,建立了以时间为历程的挖掘轨迹函数表达式,确定了齿尖载荷、挖掘体积的计算方法,从而对挖掘过程中铲斗的受力进行了分析;然后,利用SolidWorks建立了电铲三维模型,将其导入SimulationX的CAD模块,建立了电铲多体动力学模型,并加载了外部载荷曲线以模拟铲斗挖掘过程中的受力情况;之后,将电铲多体动力学模型封装成MATLAB子系统,连接到Simulink的永磁外转子滚筒控制模块,采用了比例积分(PI)调节器和永磁同步电机(PMSM)矢量控制方法提高了滚筒的动态性能和抗扰动能力;最后,利用Simulink中的联合仿真模型对电铲挖掘过程进行了仿真分析,得到了提升力、推压力和电机功率等变化曲线。研究结果表明:与传统提升系统相比,永磁外转子滚筒提升系统节能降耗约27%,而电铲挖掘过程整体节能约18%,并在1∶30模拟样机试验台对提升推压力进行了对比验证。永磁外转子滚筒提升方案大大降低了挖掘能耗,为电铲绿色装备转型提供了参考。

浅埋桩基的高密度电法数值模拟与探测

在已拆除建筑的地块上重新拟建新建筑时,为方便基桩施工和基坑的开挖需要对地块内遗留的建筑基础进行清除,在缺失相关资料的情况下,对地块内基桩的探查一直是个难题。该文采用有限差分技术建立相应的数学模型,并进行高密度电法的正演模拟。在正演模拟的基础上采用高密度电法对地下基桩进行探测,对判定的基桩位置采用钻孔磁梯度法进行验证,通过磁梯度验证,表明在无基础资料的条件下高密度电法探测浅埋桩基础是可行的。

Electric field induced magnetization reversal in magnet/insulator nanoheterostructure

Electric-field control of magnetization reversal is promising for lowpower spintronics.Here in a magnet/insulator nanoheterostructure which is the fundamental unit of magnetic tunneling junction in spintronics,we demonstrate the electric field induced 180°magne-tization switching through a multiscale study combining firstprinciples calculations and finite-temperature magnetization dynamics.In the model nanoheterostructure MgO/Fe/Cu with insu-lator MgO,soft nanomagnet Fe and capping layer Cu,through firstprinciples calculations we find its magnetocrystalline anisotropy linearly varying with the electric field.Using finite-temperature magnetization dynamics which is informed by the first-principles results,we disclose that a room-temperature 180°magnetization switching with switching probability higher than 90%is achievable by controlling the electric-field pulse and the nanoheterostructure size.The 180°switching could be fast realized within 5 ns.This study is useful for the design of low-power,fast,and miniaturized nanoscale electric-field-controlled spintronics.

变压器和应涌流的理论探讨

在线性化简化的基础上,建立了两台单相变压器并联和级联运行模型,推导了当一台变压器 正常运行,另外一台并联或级联变压器空投充电时,两台变压器的磁链解析表达形式,定性分析了 正在运行的变压器可能发生饱和现象以及和应涌流产生及影响的机理。同时,在利用分段线性特 性考虑磁化特性的情况下,通过数值仿真进一步分析了空投充电变压器的剩磁与合闸角、系统阻抗 参数对运行变压器和应涌流幅值及饱和速度的影响,仿真结果验证了分析结论,为和应涌流导致变 压器差动保护误动的分析以及认识和应涌流的本质奠定了基础。

基于基波磁通补偿的三相有源电力滤波器

电力系统中的谐波源大多为三相结构。根据基波磁通补偿的滤波新原理研制了一套三相有源电力滤波装置 ,该装置采用 3个独立的串联变压器和 3套独立的逆变器 ,以便应用于实际中可能出现不对称的三相负载。通过 MATLAB仿真确定了串联变压器和无源滤波器参数 ,根据自动控制原理和滞环电流控制的特点推导了控制器参数的选择原则 ,研究了有源电力滤波器投入和切除时的过渡过程。

考虑变频器特性的变速恒频双馈风力发电机组控制策略的研究与仿真

以并网型变速恒频风电机组中双馈发电机的运行特性及连接于发电机转子部分的脉宽调制(PWM)控制的电压源型交—直—交变频器的结构和机理为基础,在假设变频器采用理想开关器件,即忽略电子器件的换相重叠、损耗,并只考虑变频器直流电容充放电的动态过程而不计频率调节的动态变化过程的前提下,提出了基于定子磁场旋转坐标系统下的变速恒频风电机组电气控制部分的控制策略并设计了相应的 PI控制器。同时基于 MATLAB 软件建立了变速恒频双馈风力发电机组的仿真模型,并以渐变风和随机风模式为例,针对提出的控制策略对变速恒频双馈风力发电机组的并网运行特性进行了仿真研究,仿真结果表明了该控制策略的合理性及控制器设计的有效性,同时也说明了双馈发电机在保证有功输出的情况下能够有效地调节无功功率,保证变速恒频风电机组的稳定运行。

输电走廊工频电磁场的测量和解决方案

随着超高压电网的迅速发展,输电线路走廊的电磁辐射问题引起越来越多的关注。结合工程实例—某500 kV交流线路靠近小学校园引起师生身体不适,运用模拟电荷法和模拟电流法,分别分析了该线路走廊的工频电场和工频磁场的空间分布特性。同时,现场测量数据表明:在晴朗天气条件下,教学楼顶部分区域的电场强度接近国标限值;在阴雨(湿度较大)天气条件下,电场强度确已超标。针对电场超标问题,通过架设3根LGJ-50/30接地屏蔽线将电场强度最大值由3.75 kV/m降至1.35 kV/m,阴雨天气条件下亦满足国家标准要求。

基于MATLAB的磁饱和式可控电抗器的仿真模型参数及过渡时间分析

建模仿真方法和过渡时间计算是磁饱和式可控电抗器研究中值得关注的2个重要问题。根据磁饱和式可控电抗器的饱和特性,通过对小斜率磁化特性的分析,找到了电抗器额定容量、额定电压、自耦比和绕组电阻之间的定量关系,明确了基于MATLAB的磁饱和式可控电抗器仿真模型参数的设置方法。通过对小斜率磁化特性的分段线性化,把从空载到满载的过渡过程分为直流磁链随时间线性增加和控制电流根据线性RL电路充电规律变化这2个过程,得到了比较准确的过渡时间计算公式。实例仿真结果说明所提分析方法简捷有效。

全局优化算法在Preisach磁滞模型参数辨识问题中的应用与性能对比

Preisach模型参数的快速辨识对实现考虑磁滞特性的电工装备有限元计算具有重要意义。该文结合显式Everett函数Preisach磁滞模型,提出一种基于改进速度可控粒子群算法的Preisach模型参数辨识方法,并对比分析全局优化算法在该问题应用的效率问题。首先,为了解决传统离散型Preisach模型因存储庞大Everett矩阵造成的计算效率低下问题,构建Everett函数的参数化显式表达式;其次,提出一种基于改进速度可控粒子群算法的Preisach模型参数辨识方法,并基于测量的硅钢片准静态磁滞回线,实现模型的参数辨识;最后,对比分析模拟退火算法、遗传算法与该文所提算法在模型迭代次数与计算时间、磁滞回线模拟准确度、参数辨识成功率三个方面的应用效率。结果表明,该文所提出的改进速度可控粒子群算法在Preisach模型辨识上同时兼具辨识精度高、收敛速度快、成功率高的特点。

基于变压器模型的新型变压器保护原理和判据

现有的基于变压器模型的保护原理摆脱了励磁涌流的影响,但由于没有全面考虑各种因素而引起的误差可能会使保护误动。文章以双绕组单相变压器为对象讨论了各种误差因素对保护动作特性的影响,进而提出了基于变压器模型的新型保护原理和判据,并指出了参数整定的指导原则。通过对变压器的多种运行状态进行仿真计算验证了该保护原理和整定原则的正确性。

空气开关电弧的磁流体动力学建模及特性仿真

考虑电弧的物理参数以及电磁、热和辐射等现象,通过对商用计算流体力学软件FLUENT进行二次开发,建立了空气开关电弧等离子体的二维磁流体动力学(MHD)数学模型。然后仿真分析了电弧半径、电场强度与电流之间的关系,以及外部磁场对电弧运动过程的影响。同时完成了相关的实验研究。结果表明随着电流的增大,电弧半径将受到器壁宽度的限制;电流对电场强度的影响很小;外部磁场在加速电弧运动的同时,产生的"磁压"会导致电弧高温区不断被压缩以及局部压力的升高。