基于有限元方法的圆筒直线感应电机变化气隙场瞬态特性分析

本文将电机的三维场问题转化为二维场问题,运用有限元法对圆筒直线感应电动机的二维电磁场进行了数值计算。在此理论分析的基础上,采用电磁场分析的专用软件Ansoft Maxwell 2D对样机的瞬态特性进行仿真分析,得到电机运行过程中某一时刻的磁感应强度分布、磁力线、电流密度及气隙磁密等曲线;并在加额定电压条件下,研究了不同气隙下电机磁场及力特性的变化,将分析结果用来指导直线感应电机的理论研究以及本体和其控制系统的设计。     

圆筒直线感应电机电磁场的有限元分析

本文首先介绍圆筒直线感应电机结构，应用ANSOFT公司的Maxwell2D的仿真环境建立圆筒直线感应电机（LIM）的仿真模型。在所建立的模型基础上，对圆筒直线感应电机的电磁场分析，并绘制了磁场分布图。分析结果用来指导直线感应电机的理论研究以及本体和其控制系统的设计。     

圆筒直线感应电机研究综述

圆筒型直线感应电动机与普通电动机的区别在于圆筒型直线电动机存在纵向端部效应.在这篇文章中,简要介绍圆筒直线感应电机的发展与结构后,分析了国内外直线电机特别是圆筒直线电机的研究现状,根据分析得出圆筒直线感应电机需要进一步研究的方向.     

基于有限元方法的圆筒直线感应电机边端效应分析

本文采用基于有限元方法的Maxwell 2D软件对圆筒直线感应电机进行磁场研究和运动仿真。仿真结果表明电机推力随速度的增加出现明显下降,验证了边端效应对电机性能影响的理论分析。     

环形槽孔钻铤随钻感应测井场分布的解析解

针对环形槽孔钻铤随钻感应测井仪结构特点,利用金属钻铤及开槽处地层电磁场边界条件首先给出了电磁场纵向分量Ez和Hz,然后由Ez和Hz导出了扇环区内外（径向）电磁场各分量的解析表示,还给出了无槽孔区段地层中电磁场计算公式,获得了环形槽孔式钻铤随钻感应测井仪场分布的全空间解,分析了环形槽孔式钻铤随钻感应测井系统的电磁场分布特点,给出了在钻铤非开孔区确定地层内电磁场系数的新方法（变系数法）.为环形槽孔式钻铤随钻感应测井仪的场分布研究和仪器设计提供了重要的理论依据.     

基于异步感应发电机的风电场中桨距角控制研究

为了研究基于异步感应发电机的风电场对电力系统稳定性的影响,建立了异步感应电机发电机小信号模型;并通过对异步感应电机状态方程的线性化,分析异步感应发电机对电力系统小干扰稳定性及阻尼特性的影响；提出了改进的桨距角控制系统；并将发电机转速偏差信号引入桨距角控制系统.通过对系统进行特征根分析和时域仿真来验证其有效性.结果表明,改进的桨距角控制环节能够改善系统阻尼、提高系统动态稳定性.     

点群10mm十次对称二维准晶平面弹性的复变解法及孔口问题

研究了点群10mm十次对称二维准晶平面弹性问题的复变函数解法. 首先将二维准晶平面弹性问题的位移势函数F用4个解析函数表示出来, 利用解析函数的性质, 经过大量的推导, 给出了准晶声子场和相位子场的位移、应力及边界条件的复变函数表示, 从而建立了点群10mm十次对称二维准晶平面弹性问题的复变解法的理论基础. 应用这一理论, 借助于复变函数中的保角变换, 解决了椭圆孔口问题. 当椭圆的短半轴趋于零时, 可得裂纹问题的解．计算结果表明, 当声子场-相位子场耦合时, 即使受自平衡力的作用, 对椭圆孔口问题, 声子场应力仍与材料常数有关, 这一性质表现出了准晶弹性与经典弹性的又一不同. 而当声子场-相位子场解耦时, 退化为经典弹性理论．另一方面, 本文是Muskhelishvili创立的经典弹性理论的复变解法在二维准晶平面弹性问题中的推广, 像经典弹性理论一样, 只要能找到点群10mm十次对称二维准晶平面弹性区域到单位圆的保角变换, 就可解决各种孔口和裂纹问题.     

非正弦供电多相感应电机稳态性能分析

性能分析是电机优化设计的基础,由于非正弦供电多相感应电机稳态性能分析计算远比传统三相感应电机复杂,进行相关研究则具有理论意义与实用价值.在3次谐波注入的非正弦供电多相感应电机中,以基波等值电路与3次谐波等值电路为计算工具,考虑气隙磁场的非对称分布性并用拓展分布磁路法计算基波与3次谐波感应电动势,通过3层迭代计算出给定稳态运行工况下的基波与3次谐波电流等变量进而得到电机的性能指标,分析中强调了对节点气隙磁密的内层迭代过程与对激磁电流的中间层迭代过程不同于传统三相感应电机相应迭代过程的特点.以非正弦供电十五相感应电机原理样机为例,分析了不同稳态工况下的运行性能,计算结果与实验结果相互吻合说明了分析计算方法具有高的准确度.     

定子永磁型混合励磁双凸极电机设计、分析与控制

将"混合励磁"思想引入双凸极永磁电机,提出一种定子永磁型混合励磁双凸极电机,对其进行系统深入的理论分析和实验研究.理论上,建立了电机的数学模型;提出了切实可行的该类电机的一般设计方法,建立了电机的一般功率方程,推导出电机磁场调节能力与最大速度之间关系,为电机的电励磁绕组的安匝数、永磁体用量等关键电磁参数的确定提供理论依据.将2维和3维有限元相结合,提出快速、准确的"一步法"对电机特有的定子外漏磁以及端部漏磁进行研究,并对电机电磁性能进行了分析;提出了该类电机的驱动控制策略和方案,并进行了实验研究.原理样机的实验结果不仅验证了理论分析的正确性,而且表明,该电机在保留双凸极永磁电机优点的同时,能有效拓宽调速范围,在宽调速范围内具有较高的能量效率,在电动汽车等应用领域具有应用前景.     

十字型阵列的互耦自校正算法

针对十字型阵列的互耦校正问题,提出一种信号源的二维角信息与互耦系数联合估计的互耦自校正算法,该方法对线阵内和线阵间的互耦同时进行校正.利用线阵内互耦矩阵及线阵间互耦矩阵的特性,构造重构矩阵,将耦合的二维角与互耦系数联合估计问题转化为级联估计问题,不需要校正源,避免了高维参数的非线性搜索.理论分析和仿真结果均表明,提出的方法可以很好地解决十字型阵列的互耦校正问题,信号的二维角和互耦系数的估计精度高,且计算量小.     

Unipolar induction: a case study of the interaction between science and technology

Unipolar induction, discovered in 1832 by Michael Faraday, is the case of electromagnetic induction in which a conductor and magnet are in relative rotatory motion. Attempts by scientists and engineers in the nineteenth and twentieth centuries to understand unipolar induction by using magnetic lines of force displayed striking national differences that influenced where the first largescale unipolar dynamo was built. This episode is described, as well as the effect of unipolar induction on Albert Einstein's thinking toward the special theory of relativity, in sections 1–6. The analysis of electromagnetic induction in cases where the source of the magnetic field is in motion relative to the conductor is provided in sections 7–9.     

手舟骨的有限元建模及其损伤分析

目的 基于医学DICOM格式的图像,不经过二次转换并快速且准确的建立舟骨有限元模型,从而得到可以用于舟骨应力分析的有限元模型,并通过模拟手舟骨损伤来分析不同的受力特点. 方法 选择健康成年男性志愿者,进行高精度螺旋CT扫描,将得到的DICOM 3.0医学图像数据,导八MIMICS医学影像软件并生成实体模型,然后应用通用有限元分析软件ANSYS 11生成有限元模型.约束边界条件,模拟舟骨轴向压力进行加载,得出舟骨有限元模型上的应力分布与应变结果,并模拟舟骨不同损伤的力学改变. 结果 建立的舟骨三维有限元模型共有节点73588个,单元397344个.所建模型结构完整,空间结构准确,单位划分精细,轴向压力作用下加栽模拟形象、逼真,客观反映舟骨三维解剖形态结构和生物力学特点. 结论 应用高精度螺旋CT成像的DICOM 3.0数据,并与MIMICS和ANSYS相结合的方法快速建立舟骨的三维有限元模型是切实有效和可行的;有限元方法可较好的分析手舟骨及其损伤的生物力学特点.     

基于人工鱼群算法的喷油系统断油电磁阀的优化设计

为合理选择和正确设计柴油自卸车喷油系统的断油电磁阀，根据电磁阀的结构特点，建立了在自卸车出现转速失控时喷油系统断油时间最短的目标函数。利用人工鱼群算法对断油电磁阀的阀芯质量、弹簧刚度、线圈匝数、工作气隙、阀芯举升高度进行优化，得出断油电磁阀的最佳动态响应参数，并利用HYDSIM分析了优化前后喷油系统的响应特性。结果表明：断油电磁阀参数优化后的喷油系统比优化前的系统的响应时间减小了5．59ms，能更有效地控制柴油机自卸车转速失控，明显提高柴油自卸车的运行安全和使用寿命．     

采空区上方边坡稳定性分析

分别根据《三下采煤规程》采动坡体稳定性预测方法和瑞典条分法对采空区上方边坡稳定性进行了验算，并用大型有限元分析软件ADINA进行了二维模拟，得出了预计边坡稳定性系数、条带开采后引起的地表移动和变形最大值等数据，具有一定的工程应用价值。     

Is electromagnetic field momentum due to the flow of field energy?

Momentum and energy conservation require electromagnetic field momentum and energy to be treated as physically real, even in static fields. This motivates the conjecture that field momentum might be due to the flow of a relativistic mass density (defined as energy density divided by the square of the speed of light).This article investigates the velocity of such a mass flow and finds a conflict between two different definitions of it, both of which originally seem plausible if the flow is to be taken as real. This investigation is careful to respect the transformation rules of special relativity throughout.The paper demonstrates that the consensus definition of the flow velocity of electromagnetic energy is inconsistent with the transformation rules of special relativity, and hence is incorrect. A replacement flow velocity is derived which is completely consistent with those transformation rules.The conclusion is that these conflicting definitions of flow velocity cannot be resolved in a way that is consistent with special relativity and also allows electromagnetic field momentum density to be the result of relativistic mass flow. Though real, field momentum density cannot be explained as the flow of a relativistic mass density.As a byproduct of the study, it is also shown that there is a comoving system in which the electromagnetic energy-momentum tensor is reduced to a simple diagonal form, with two of its diagonal elements equal to the energy density and the other two diagonal elements equal to plus and minus a single parameter derived from the electromagnetic field values, a result that places constraints on possible fluid models of electromagnetism.     

What's nu? A re-examination of Maxwell's ‘ratio-of-units’ argument,from the mechanical theory of the electromagnetic field to ‘On the elementary relations between electrical measurements’

This re-examination of the earliest version of Maxwell's most important argument for the electromagnetic theory of light—the equality between the speed of wave propagation in the electromagnetic ether and the ratio of electrostatic to electromagnetic measures of electrical quantity—establishes unforeseen connections between Maxwell's theoretical electrical metrology and his mechanical theory of the electromagnetic field. Electrical metrology was not neutral with respect to field-theoretic versus action-at-a-distance conceptions of electro-magnetic interaction. Mutual accommodation between these conceptions was reached by Maxwell on the British Association for the Advancement of Science (BAAS) Committee on Electrical Standards by exploiting the measurement of the medium parameters—electric inductive capacity and magnetic permeability—on an arbitrary scale. While he always worked within this constraint in developing the ‘ratio-of-units’ argument mathematically, I maintain that Maxwell came to conceive of the ratio ‘as a velocity’ by treating the medium parameters as physical quantities that could be measured absolutely, which was only possible via the correspondences between electrical and mechanical quantities established in the mechanical theory. I thereby correct two closely-related misconceptions of the ratio-of-units argument—the counterintuitive but widespread notion that the ratio is naturally a speed, and the supposition that Maxwell either inferred or proved this from its dimensional formula.     

基于自然边界元与有限元耦合的重叠型迭代算法

了更充分地利用有限元与自然边界元各自的优点，并尽量减少由于方法的局限性造成的在计算量及计算精度上的不足，本文引入了有限元与自然边界元耦合的方法。在文中简单介绍了自然边界元法及其与有限元耦合的原理，通过设置含有重叠区域的圆形人工边界，实现自然边界元与有限元的耦合，并把该方法应用到无界区域的实际算例中。从计算结果的比较中可以看出自然边界元与有限元耦合算法的收敛速度更快，充分体现了耦合法在解决无界区域问题上的优越性。     

一种岩石损伤流变模型及数值分析

根据石膏角砾岩的蠕变特性，建立石膏角砾岩的损伤流变模型；推导有限元计算中黏弹塑性损伤流变模型黏性应变的计算公式，结合初应变法的基本原理，分析模型的有限元求解过程；用MATLAB编制了损伤流变模型的平面应变有限元计算程序。利用编制的程序对石膏角砾岩蠕变试验进行有限元分析，有限元计算结果与蠕变试验结果吻合得较好，表明采用统计损伤理论研究岩石的非线性流变是可行、有效的。     

On the time reversal invariance of classical electromagnetic theory

David Albert claims that classical electromagnetic theory is not time reversal invariant. He acknowledges that all physics books say that it is, but claims they are “simply wrong” because they rely on an incorrect account of how the time reversal operator acts on magnetic fields. On that account, electric fields are left intact by the operator, but magnetic fields are inverted. Albert sees no reason for the asymmetric treatment, and insists that neither field should be inverted. I argue, to the contrary, that the inversion of magnetic fields makes good sense and is, in fact, forced by elementary geometric considerations. I also suggest a way of thinking about the time reversal invariance of classical electromagnetic theory—one that makes use of the invariant four-dimensional formulation of the theory—that makes no reference to magnetic fields at all. It is my hope that it will be of interest in its own right, Albert aside. It has the advantage that it allows for arbitrary curvature in the background spacetime structure, and is therefore suitable for the framework of general relativity. The only assumption one needs is temporal orientability.