偶极子模型在介质混合体中的适用范围

对于颗粒相互靠近、两相介电系数比较大的介质混合体来说,采用偶极子模型(Dipole approximation)计算局部场强将会引起很大误差.为此,分别采用有限元方法和偶极子模型计算混合体中颗粒球表面的电场分布,由此计算出在球面各点偶极子模型与有限元结果之间的相对误差.结果表明,最大误差总是发生在沿电场方向颗粒球的顶点或非常靠近该点的某处.在此基础上,本文提出以这个最大误差不超过容许误差作为评判偶极子模型是否成立的标准,由此确定其适用范围,并绘制出对应于三种不同容许误差的计算曲线.与前人研究结果的对比表明,这种确定偶极子模型适用范围的方法是可行的,由其计算所得的曲线是可信的.     

偶极子模型计算混合体局部场强的误差分析

针对偶极子模型近似计算较高占空比混合体局部场强时误差较大的问题,以有限元法的数值计算结果作为电场的真实值,得到了偶极子模型在近似计算混合体中球形颗粒表面各点场强时的相对误差。结果表明,若占空比<20%,则对于所有介质颗粒,最大误差总是出现在最大场强点;若占空比>20%,则颗粒与环境介电常数差异达到一定值时,最大相对误差将会转移到球面上另外一点,并随介电常数差异增大而逐渐靠近最小场强点。对不同占空比的混合体,考察了最大误差点随介电常数差异的变化而移动的规律,并据此绘制出了一条计算曲线。     

电流变液颗粒间局部电场分析及相互作用力计算

电流变(electrorheo logical,ER)液可用于直接驱动电动机、离合器、无级变速、机械装置的电控等领域,如何准确计算电流变液体成链过程中的颗粒间相互作用成为研究热点。介绍了计算电流变液中多颗粒间局部电场及相互作用力的新模型—偏心电偶极子模型,分析了偏心电偶极子模型的理论基础,研究将其用于计算电流变液体中多颗粒间局部电场及相互作用力的方法。将颗粒间局部电场计算结果与点电偶极子及有限元方法的计算结果进行对比。通过比较可知,偏心电偶极子模型计算结果与有限元计算结果最为接近,优于点电偶极子模型。同时给出用于计算三颗粒间局部电场及相互作用力的公式,并与同等条件下的两颗粒间相互作用力进行对比,结果表明,在一定条件下两颗粒的相互作用力高于三颗粒的相互作用力,这说明颗粒在聚集成链的过程中初期的相互作用力可能要高于后期。     

均匀场中两无限长介质圆柱的柱心线电偶极子模型

针对两无限长的介质圆柱在均匀外电场中的电场计算问题,提出一种考虑了圆柱相互作用的偶极子模型,该偶极子为线电偶极子,且位于圆柱中心。用该方法计算的偶极矩和镜像方法计算的结果作了比较、计算的圆柱表面的电场分布和有限元计算的结果也作了比较,结果表明该方法在柱体表面间距大于0.1倍圆柱半径时是可行的。     

计算混合体在均匀场中最大场强的近似公式

针对混合体在均匀场中的起晕电场问题,提出了近似计算最大畸变场强的公式,它随颗粒占空比、介电常数变化。和点偶极子模型和有限元法的计算结果比较表明该公式计算精度较好。     

剪切模式下磁流变液层间传力理论模型建立及误差分析

为了建立更加准确的磁流变液颗粒间作用力的理论计算模型,分别运用经典偶极子理论模型和局部场偶极子理论模型计算了铁磁性颗粒的磁偶极矩,并根据结果分析了两种理论模型的局限性。分别对弱磁场和强磁场环境下颗粒间作用力进行分析,建立偶极子边界理论计算模型,并且研制了剪切模式下磁流变液层间传力特性实验装置,通过实验验证偶极子边界理论模型的准确性。结果表明,偶极子边界理论模型计算结果更加接近实验值。     

复合场下磁流变液层间剪切屈服特性研究

为了研究磁流变液在磁场、温度场共同作用下层间剪切屈服特性,考虑磁化饱和程度以及局部磁场聚集效应的影响,结合经典偶极子和局部场偶极子理论模型,建立了新型颗粒间作用力计算模型—偶极子边界理论模型,理论分析了偶极子边界中颗粒链之间的相互作用力以及同一链中两相邻颗粒间作用力,并给出作用力的数学表达式,搭建了基于线圈外置的圆盘式传动结构的测量装置,通过实验研究验证理论的正确性。结果表明偶极子边界模型计算误差比经典偶极子理论模型和局部场偶极子理论模型小,弱磁场作用下,偶极子边界理论模型计算所得剪切屈服应力结果与实验值的偏差最小,在-1.5%~1%之间;在强磁场作用下,由偶极子边界理论模型计算所得结果与实验值的偏差最小,在-0.4%~0.2%之间。     

改进型偶极子模型的静电放电相关电场计算

分析了静电放电 (ESD)过程中电磁场偶极子模型存在的缺陷及其产生原因。提出了改进型偶极子模型 ,并根据实测 ESD放电电流波形 ,对 ESD在不同空间距离处产生的电场进行了计算 ,结果与有关文献的数据基本吻合     

偏心电偶极子模型在计算颗粒间相互作用力中的应用

介绍了一种新的电流变效应研究中用来计算颗粒间相互作用力的模型--偏心电偶极子模型.分析了偏心电偶极子模型的理论基础,研究了将其应用于计算电流变液体中颗粒间相互作用力的方法,并给出了用于计算相邻颗粒间作用力的公式,最后将所得结果与经典点电偶极子模型、交互点电偶极子模型及用有限元方法得出的计算结果进行了对比.结果表明:偏心电偶极子模型优于经典点电偶极子模型及交互点电偶极子模型.     

偶极子模型在颗粒链中的使用范围

针对偶极子近似模型认为球体内是均匀电场的条件 ,利用电场唯一性定理 ,设定球体边界不受周围偶极子影响的最低限制值 ,提出了统一的条件 ;分别讨论了在纵向和横向电场中 ,两个球体和无限多球体的颗粒链使用偶极子模型时 ,不同的球体间距与不同介电常数的使用要求 ,超出此范围 ,偶极子模型不再有效。     

A displaced dipole model for a two-cylinder system

In this paper, a displaced dipole model for two infinitely long dielectric cylinders in an applied uniform field is proposed. The displaced dipole moment and its displacement can be approximately obtained from the applied field values at the two poles of a cylinder. The electric potential distributions near the surface of cylinder calculated using the displaced dipole method are compared with those obtained with the finite-element method. The electric field distributions around the surfaces of cylinder calculated using the displaced dipole method are compared with those obtained with the finite-element method and the dipole-at-the-center approximation. The displaced dipole method is a good approximation, especially in the area between two cylinders when the displacement is less than 0.2 R.     

空间介质颗粒对交流导线电晕特性影响规律

为了研究空间介质颗粒对导线交流电晕特性的影响,基于小电晕笼,应用Fi Lin?6紫外成像仪记录存在介质颗粒时模拟导线交流电晕放电发生、发展的过程,实验结果表明:空间介质颗粒会对导线交流电晕发生、发展过程产生影响,球径越大、距离导线越近则导线的起晕电压越低;存在多球时,由于颗粒间的相互影响,导线的起晕电压和放电过程会受到影响,其中垂直排列的颗粒之间对放电发展过程和起晕电压影响相对较大。将偏心偶极子模型应用到存在介质颗粒时电场计算中,结合模拟电荷法对导线周围存在颗粒时空间电场分布进行分析,仿真结果表明:导线表面的最大场强以及导线和颗粒间场强的均值随着颗粒尺寸的增大、颗粒导线距离的降低和颗粒相对介电常数的增大而增大;空间存在多个颗粒时,由于球间的相互影响使导线表面场强进一步增大,其中球间连线和电场方向一致时的影响更大。     

Multipole Corrections to Dielectrophoretic Force

Calculation of the dielectrophoretic (DEP) force on a neutral dielectric partide in a nonuniform electric field is simplified by using the effective dipole method. Once the instantaneous effective dipole moment peff(t) has been correctly identified using Gauss's law, then the expression (peff(t)?)E0(t) is used to determine the force on the particle. Recent work has demonstrated that the effective dipole method produces a result consistent with integration of the Maxwell stress tensor. In the present paper, the issues concerning identification of peff(t) are aired, and an alternate derivation of the DEP force on a conducting dielectric sphere immersed in a conducting dielectric fluid is offered. Then the effective dipole theory is generalized to account for higher order (multipole) contributions. This new effective multipole theory is restricted to spherical particles in a cylindrically symmetric cusped electric field, but the analysis leads to straightforward computation of the quadrupolar correction factor for the DEP force. A quantitative example is provided.     

A finite-element analysis of the electrostatic force on a uniformlycharged dielectric sphere resting on a dielectric-coated electrode in adetaching electric field

In the electrophotographic process, charged toner particles are transferred from one surface to another with an electric field. To enable electric field transfer of toner, the externally applied field strength must be greater than a threshold value, so that the Coulomb force can overcome the toner adhesion force at the supporting surface. In this paper, the threshold field strength to detach a charged dielectric particle is determined efficiently by using the Galerkin finite-element method to simultaneously solve the Laplace equation for the field distribution and an overall constraint equation for the force balance. This computational method also enables calculation of the electrostatic adhesion force and is applicable to various particle-electrode configurations. For illustrative purposes, however, we consider the axisymmetric problem of electric field detachment of a dielectric sphere with uniform surface charge resting on a planar dielectric-coated electrode. The analysis is particularly focused on the dependence of the electrostatic force upon the dielectric overcoating thickness and spacing between parallel plate electrodes. The electrostatic force on a uniformly charged particle in contact with a surface is found to be influenced significantly by the thickness of dielectric overcoating and the spacing between electrodes when either becomes less than five times the particle radius     

混合编程法及其在绝缘子电场和电位分析中的应用

室温硫化硅橡胶防污闪涂料在电力系统外绝缘中有着广泛的应用,有必要分析它对电场和电位分布的影响。分析不同厚度情况下硅橡胶涂层的电阻率和相对介电常数对绝缘子附近最大强场、沿面电场和电位的影响。采用Matlab与ANSYS混合编程的方法实现了绝缘子的自动建模,采用C++Builder(BCB)与ANSYS混合编程的方法实现了自动导出lis文件,节省了工作量和后续处理时间,同时使用Matlab对lis文件处理获得沿面的场强和电位。研究结果表明:瓷支柱绝缘子喷涂硅橡胶后无论是最大场强还是局部细节场强均未见明显变化;随涂层厚度、相对介电常数增加最大场强略有减少,但变化程度非常小,沿面平均场强略有增加;随电阻率的变化最大场强和沿面平均场强基本不变。电阻率、介电常数和厚度正常的取值范围内时硅橡胶涂层对绝缘子及附近电场畸变造成的影响可以忽略。     

Electrode protrusions and particle chaining as factors affectingthe dielectric strength of air

Electrode protrusions and free particles have been demonstrated to reduce dramatically the breakdown voltage of insulating fluids. This paper examines two factors which affect the dielectric strength of gaseous insulators: (1) shape and size of electrode protrusions, and (2) particle chain formation. A computer program, based on the boundary element method, was employed for the computation of the electric field modified by an electrode protrusion and/or a particle chain. The results regarding field enhancement were used as input data of another program that evaluated the dielectric strength of the air-gap. Two types of protrusions were studied: hemispheres and hemispherically ended rods. One to ten conductive spheres were considered to be attracted to such protrusions and chain at the top of them. The computations showed that the large protrusions are more harmful than the small ones and that the dielectric strength of the air-gap decreases with the number of particles in a chain