The effect of the guide field on energy conversion during collisionless magnetic reconnection

Magnetic reconnection is well known as an efficient mechanism for transferring magnetic energy into plasma energy.However,how the energy conversion and partition between different species is influenced by the shear angle of the reconnecting magnetic component(i.e.,the guide field strength)is not well understood.Using 2.5-dimensional particle-in-cell simulations,we investigated the energy conversion in reconnection with different guide fields.We found that the overall energy conversion first decreases steeply and then increases slowly when the guide field increases fromB_(g)=0 toB_(g)=4.The increase in energy conversion in the large guide field regime is due to the electron energy gain through the perpendicular channelJ_(⊥)·E_(⊥).The overall energy conversion is predominantly contributed byJ_(⊥)·E_(⊥) rather thanJ||E||.We further find that energy conversion mainly occurs within the reconnection front and the flux pileup region.However,the contribution from the fore reconnection front becomes important in large guide field regimes(3<B_(g)≤4)because of the enhanced electron energy gain.

Three-Dimensional Study of the Effect of the Angle of Incidence of a Magnetic Field on the Electrical Power and Conversion Efficiency of a Polycrystalline Silicon Solar Cell under Multispectral Illumination

A three-dimensional approach to the effect of magnetic field incidence angle on electrical power and conversion efficiency is performed on a front-illuminated polycrystalline silicon bifacial solar cell. A solution of the continuity equation allowed us to present the equations of photocurrent density, photovoltage and electric power. The influence of the angle of incidence of the magnetic field on the photocurrent density, the photovoltage and the electric power has been studied. The curves of electrical power versus dynamic junction velocity were used to extract the values of maximum electrical power and dynamic junction velocity and to calculate those of conversion efficiency. From this study, it is found that the conversion efficiency values increase with the angle of incidence of the magnetic field.

Effect of Incidence Angle of Magnetic Field on the Performance of a Polycrystalline Silicon Solar Cell under Multispectral Illumination

The aim of this work is to investigate, with a three-dimensional steady-state approach, the effect of the incidence angle of a magnetic field on the performance of a polycrystalline silicon solar cell under multispectral illumination. The magneto-transport and continuity equations of excess minority carriers are solved to find the expression of the density of excess minority carriers and the related electrical parameters, such as the photocurrent density, the photovoltage and the electric power, of a grain of the polycrystalline silicon solar cell. The influence of the incidence angle of the magnetic field on the diffusion coefficient, the short-circuit photocurrent density, the open-circuit photovoltage and the electric power-photovoltage is studied. Then, the curves of the electric power-photovoltage is used to find the maximum electric power allowing to calculate, according to the incidence angle of the magnetic field, the fill factor and the conversion efficiency. The study has shown that the increase of the incidence angle of the magnetic field from 0 rad to π/2 rad, can reduce the degradation of the performance of solar cells.

Modelling Study of Magnetic Field Effect on the Performance of a Silicon Photovoltaic Module

Solar Photovoltaic is a very promising solution that can greatly contribute in solving the increasing global energy demand. In both rural and urban areas, photovoltaic modules are in some instances installed close to telecommunication antennas or voltage transformers which generate important magnetic fields in their vicinity. The question is whether or not these magnetic fields affect the performances of the photovoltaic installations. This article presents a modelling study of external magnetic field effect on the electrical parameters of a photovoltaic module. The photocurrent, the photovoltage, the electric power, the series and the shunt resistances of the photovoltaic module, made up of ideal cells, are deduced from those of a silicon solar cell. Then, the I-V and P-V curves are plotted and the theoretical values of the electrical parameters of the photovoltaic module are deduced. The series and shunt resistances of the photovoltaic module are calculated using well known equations and the previous electrical parameters. The results show the negative effect of magnetic field on the performance of a solar photovoltaic module.

Electrokinetic energy conversion of electro-magneto-hydro-dynamic nanofluids through a microannulus under the time-periodic excitation

In this work,the effects of externally applied axial pressure gradients and transverse magnetic fields on the electrokinetic energy conversion(EKEC)efficiency and the streaming potential of nanofluids through a microannulus are studied.The analytical solution for electro-magneto-hydro-dynamic(EMHD)flow is obtained under the condition of the Debye-Huuckel linearization.Especially,Green’s function method is used to obtain the analytical solutions of the velocity field.The result shows that the velocity distribution is characterized by the dimensionless frequency?,the Hartmann number Ha,the volume fraction of the nanoparticlesφ,the geometric radius ratio a,and the wallζpotential ratio b.Moreover,the effects of three kinds of periodic excitations are compared and discussed.The results also show that the periodic excitation of the square waveform is more effective in increasing the streaming potential and the EKEC efficiency.It is worth noting that adjusting the wallζpotential ratio and the geometric radius ratio can affect the streaming potential and the EKEC efficiency.

基于均匀磁场标定的微动力测试平台研究

针对微纳卫星的微动力测量问题,设计了一种可对mN级微动力进行测试与分析的扭摆型微动力测试平台;基于电磁力法,采用通电导线和电磁铁组合的方式设计了该测试平台的关键装置--微小标定力产生装置。利用高精度电子天平和激光位移传感器对微动力测试平台进行了静态标定,并通过对导线在磁场中不同位置进行标定实验,得到重复性误差为0.264%,验证了均匀磁场标定的可行性;采用阶跃响应法对测试平台的系统参数进行了标定,最后对微动力测试平台的不确定度和标定方法带来的误差进行了分析。结果表明,该测试平台的测量范围为1~400 mN,分辨率约为1 mN,静态标定的不确定度为8.41 mN,标定方法误差为0.84%,误差较小,能为微动力测量提供一定的技术参考。

变频磁场对工业循环冷却水的杀菌性能研究

通过自制的变频磁场发生器与线圈绕组相连产生变频磁场,对工业循环冷却水进行杀菌处理,分别考察了作用时间、温度、pH和处理管径等因素对杀菌效果的影响。结果表明,变频磁场具有明显的杀菌作用。其杀菌效果随作用时间、温度的增加而增加。在温度为45℃,作用时间60min,pH为9,处理管径为2.61cm时,变频磁场的杀菌效果最好,CODCr去除率为70%,BOD5去除率为84.62%,细菌总数去除率为88.64%,铁细菌的去除率为92%。

地磁辅助导航中的潜艇干扰磁场

为了实现高精度的地磁辅助导航,必须从磁场传感器的测量数据中补偿潜艇干扰磁场,分离出准确的地磁场。分析了潜艇干扰磁场的来源,针对最主要的磁化磁场进行研究。建立了潜艇磁化磁场的方程和边界条件,采用有限元软件ANSYS进行仿真计算和分析。仿真结果表明,在地磁场作用下,潜艇下方距轴线1.25倍艇身半径处,磁化磁场强度为104nT;距轴线20倍艇身半径处,磁化磁场已减弱至50nT左右。重点分析了潜艇下方距轴线1.5倍艇身半径处,磁化磁场的分布特性。分析表明,潜艇磁化场与地磁场之间存在线性转换关系;建立了线性转换矩阵,其中转换矩阵各元素只与空间点坐标、潜艇几何结构、材料特性有关。

偏心式谐波磁力齿轮气隙磁场解析模型

偏心式谐波磁力齿轮利用转子偏心引起气隙磁导的变化,从而实现高速比变速和转矩传递。该文应用边界摄动法,建立了偏心式谐波磁力齿轮气隙磁场二维解析模型。首先分别计算偏心转子和定子永磁体单独作用时的偏心气隙磁场,再根据叠加原理合成谐波齿轮气隙磁场。气隙磁通密度和电磁转矩的解析结果与有限元分析结果相比较,验证了解析模型的正确性和有效性。

变频控制下永磁同步电机温度场分析

在变频控制下的永磁同步电机谐波含量大、发热严重,且散热结构复杂。为研究其温升分布规律,该文以一台50 kW永磁同步电机为例,基于计算流体力学以及传热传质学基本理论,根据共轭传热原理,建立包含形状复杂的散热翅及接线盒等结构部件的三维流动与传热的物理模型。应用有限体积元法,对变频供电情况下的永磁同步驱动电机内各部件温升及流体流动进行了数值求解,并着重分析了电机内主要结构部件的温升空间分布特性。通过与实验数据的对比分析,验证了其计算结果的准确性以及求解方法的合理性,为中小型永磁同步驱动电机的设计提供一定的参考和实际工程价值。

产生匀强磁场的球状线圈设计

根据Biot-Savart定律和磁场叠加原理,提出了一种产生匀强磁场的三维正交球状反馈线圈系统的设计方法。为分析该系统内部的磁场分布,建立了球状线圈内磁场分布的数学模型,并讨论了其磁场分布、分布均匀度与线圈匝数,线圈间距和有关参数之间的关系。分析结果表明球状线圈能在较小的几何尺度内产生较大范围的均匀磁场,可根据磁传感器几何尺寸和对匀强磁场均匀度的需求,利用此设计方法确定球状线圈的线圈匝数和线圈间距等绕制参数,实现磁传感器的磁场反馈。

舰艇磁场磁偶极子阵列数学模型研究

为提高舰艇磁性防护能力,准确反映其磁场特性,舰艇测磁需要使用先进的测磁技术,这就可以用磁偶极子阵列模拟舰艇磁场源;文中根据舰艇测量面上的磁场数据建立了舰艇磁场换算的数学模型,给出一种运用实例评述测磁技术在舰艇磁性防护中的应用;实例结合点阵式大平面测磁法和磁荷模拟算法建立了测磁后舰艇磁场换算的数学模型,简单论述了该模型的数学原理、磁场函数计算方法及具体应用中有关参数的确定方法等,并对计算精度作了分析,仿真结果表明模型精度较高;测磁技术的应用在磁性防护中具有重要的实用价值。

基于AVR单片机的电磁场监测仪设计

设计了一个环境电磁污染监测系统,能够测量环境磁场大小,测量精度可达到6×10-8T。利用磁阻芯片特有的置位/复位功能有效地消除因温度漂移和电路参数漂移等共模信号造成的误差,提高了磁场检测的灵敏度。监测仪器以Atmega16L为控制器,单片集成磁场传感器HMC1052L为检测元件,其输出通过运算放大器LMV358放大,利用Atmega16L单片机模数转换器转换成数字信号,并由LCD显示测量结果。

工频电磁场长期曝露健康风险的预防性政策分析

近年来国内仍有一些质疑现有国际电磁场限值导则或国内限值标准安全性的信息不时出现,并建议通过降低限值的手段来保证公众的健康,这就需要分析该类做法的合理性。为此,调查国际组织对电磁场健康风险预防性政策的制定原则,跟踪以法令形式颁布"预防性限值"的意大利、瑞士等典型国家情况,提出我国企业在该问题做法上的启示及建议。根据调查及跟踪可得到,按世界卫生组织的建议,在建造新设施和设计新设备时,应采取低成本的预防措施来优化线路并降低曝露水平,对拟采取的政策措施进行利益-代价分析。分析后认为,政府与企业应对已确定的危害及未证实的风险做出明确区分,并在政策措施上区别对待。企业需要加强全面、科学地对待电磁场环境健康问题的意识,增强对国际主流观点和研究成果的认知程度,提高电网环保政策风险预控能力。

大功率电磁装置短时变频磁场辐射测试系统

使用电磁兼容标准中规定的测试系统测量短时变频磁场信号代价过高,为了解决这一问题,论文设计了适用于大功率电磁装置短时变频磁场辐射测量的测试系统,并与电磁兼容标准中规定的测试系统进行了测试对比。所设计的测量系统由三维磁场探头、多通道示波器和虚拟接收机软件三部分组成,测试时,首先使用三维磁场探头和多通道示波器获取被测短时变频磁场信号的时域波形,然后使用基于Matlab的虚拟接收机软件分析被测信号的频谱特性。实验表明,所设计的测试系统能够准确捕捉待测设备在各个频率上的最大发射幅度,且具有测量成本低、测试耗时短的优点。

变压器环流损耗的计算与软件设计

采用数值计算方法得到一台变压器漏磁场沿绕组径向和轴向的分布情况,并与解析方法进行对比,阐述了解析方法及数值解法的优缺点。为计算方便和提高计算精度,本文利用从有限元计算模块导入和解析法两种方式得到变压器漏磁场,自动生成导线排布。基于积分原理,提出一种适用于变压器各种绕组形式的环流损耗计算模型。编制软件对一台31500kVA变压器的低压绕组三种换位方式的损耗进行分析,并与实验结果进行对比和分析。

新型线圈发射器的电磁场仿真分析

电磁发射拥有许多化学发射不可比拟的优点,近年来受到各国的广泛关注。传统发射器需在线圈内部加装位置传感器,这使得线圈磁场分布不均且结构复杂。该文基于电磁感应原理,设计出了新型线圈发射器模型,该模型利用线圈外部的传感器来控制电路放电时间,克服了传统结构的缺陷。借助SIMPLORER和Maxwell仿真软件对发射器的主体电路和线圈磁场进行分析,得到了磁场中弹丸的静态和动态特性曲线。仿真结果验证了该新型发射器的作用机理,并得到了四级发射器模型的结构参数。该新型发射器可把30g弹丸加速到12.00m/s。结果表明该新型发射器结构简单、线圈内部磁场分布均匀,大大提高了模型的发射效率和系统的稳定性。

有限长通电螺线管空间磁场分析

分析比较了两种求解有限长螺线管空间磁场分布的方法。有限长通电螺线管在一些工程问题中有重要的应用,第一种为线圈叠加方法,通过求解多个直流环形线圈磁场叠加求解空间磁场分布;第二种为通电圆柱体方法,把螺线管考虑成一空心表面电流密度均匀分布的通电圆柱体。最后通过两种方法计算有限长通电螺线管空间的磁感应强度分布,推导出了磁场求解公式,并绘出其空间分布图。虽然第二种方法在运算时间上要比第一种方法长,但是第二种方法更具优势,这种方法可以推广到多层螺线圈及任意位置螺线圈空间磁场的分布求解中。经过反复仿真计算,得出结论:管子越长,两种方法结果越接近。

新型电磁齿轮磁力矩计算方法的探讨

电磁齿轮是一种新型磁力传动装置,根据电磁场理论,提出一种电磁齿轮传动磁力矩的计算方法,推导建立了径向多极电磁齿轮传动机构磁力矩的计算表达式,并采用三维有限元法对推导公式进行了理论验证,结果表明了推导公式正确,可用于电磁齿轮机构的设计计算。

肿瘤旋磁治疗机的基本原理与临床初步应用

ZCX-Ⅱ型旋磁治疗机由上下两对磁头组成,下磁头由电动马达驱动,而上磁头则是在下磁头耦合力的作用下而发生同步旋转,以达到人体组织纤维与磁力线发生相对运动,从而产生磁生物学效应的目的,属国际首创。随机选择的32例临床放弃治疗的晚期恶性肿瘤患者,使用ZCX-Ⅱ型肿瘤旋磁治疗机,采用不同的治疗参数进行治疗。结果观察,症状完全缓解率达28.1%,部分缓解率达65.6%,总有效率为93.8%1,年生存率为28.1%。治疗后所有患者的临床症状和体征均可得到不同程度的改善和缓解,且无任何严重地毒副作用。文中介绍了该设备的基本原理、使用方法和临床疗效,并对其临床相关问题进行简要讨论。