Effects of alternating current imposition and alkaline earth elements on modification of primary Mg_2Si crystals in hypereutectic Mg-Si alloy

The effects of alternating current imposition and/or alkaline earth elements on modification of the primary Mg2Si crystals in the hypereutectic Mg-Si alloy were investigated.An alternating current of 60 A with frequency of 1 kHz was applied into the hypereutectic Mg-Si melt which was alloyed with alkaline earth elements or not in the fixed temperature range from 700 to 630℃. The results show that the primary Mg2Si crystals could be refined by imposing alternating current or adding alkaline elements. Compared with the samples treated by adding 0.4%Ca or 0.4%Sr,higher modification efficiency could be obtained for the samples treated by imposing alternating current.No further modification efficiency could be obtained for the samples treated by imposing alternating current combined with 0.4%Ca or 0.4%Sr addition.

Finite Element Method Based on Equivalent Magnetic Energy Method for Computation of 2D Nonlinear Eddy Current Field

In this paper, the finite element method using vector potential in applications to 2D nonlinear eddy current field is discussed. The authors use the equivalent magnetic energy method to deal with magnetization curve of ferromagnetic material,and present the formulation of 2D nonlinear eddy current field.With this method the authors analyze the eddy current field in an induction ladle furnace and the force distribution in the charge (molten metal),and plot the corresponding curves.

DIRECT SOLUTION BY 2-D AND 3-D FINITE ELEMENT METHOD ON FORWARD PROBLEM OF LOW FREQUENCY CURRENT FIELDS IN INHOMOGENEOUS MEDIA

The paper adopts finite element method to analyze the forward problem of low-frequency current fields in inhomogeneous media. Firstly, the direct solution of 2-D and 3-D scalar potential is given. Secondly, the technique of covering finite elements for problems with movement has been presented; namely, when the place of testing point moved, the meshing data will be produced automatically to avoid re-meshing and distortion of the mesh. Thirdly the free and prescribed potential method is used to make the finite element coefficient matrices. Then this paper provides the result of a validity test obtained by simulating the laterolog-3 logging, compared with the numerical model-matching method. Finally, the MLL response is calculated.

An Introductory Note on Finite Element Problems Based on the Eddy Current Testing Approach

The paper addresses the first eddy current benchmark problem proposed by the World Federation of Nondestructive Evaluation Centers (WFNDEC). The problem simulates the eddy current response to the presence of an axisymmetric circumferential defect in an Inconel-600 tube. All simulations employ the axisymmetric code of the electromagnetic field simulator Finite Element Method Magnetics. For three different frequencies of excitation, it is explained how the displacement of the detecting coil inside the tube leads to a variation in the impedance of the eddy current coil. Variations of the resistive and inductive components of the impedance with distance from the defect region are used to build the impedance trajectory for each frequency of analysis.

Novel Minimum Passive Element Realization of All-Pass Network Using A Modified Current Conveyor

1. IntroductionA large number of networks for realizing first and second order transfer functions using a currentconveyor have been reported in the literature. Especially, the networks that can offer highinput impedance attract attention, for high input impedance has the advantage that the networksmay be used in cascade without requiring impedance matching device. In the Higashimura and

Penalty-Finite Element Analysis of the Eddy Current Loss in a Fully-Stabilized Multifilamentary Superconducting Wire

The paper is mainly concerned with the penalty incurred in finite element analysis of the eddy-current loss problem in a fully established multi-filamentary superconducting wire. A finite element model with 4-node quadrilateral isoparametric elements is formulated for the present problem. Unlike the conventional vector potential scheme in use for electromagnetic field problem, the present work features a direct computational approach to eddy current loss. Simplicity and remarkable enhancement in computational accuracy can be obtained with the proposed method.

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTA-TION (Ⅰ)-THE CONTINUOUS-TIME CASE

An initial-boundary value problem for shallow equation system consisting of water dynamics equations,silt transport equation, the equation of bottom topography change,and of some boundary and initial conditions is studied, the existence of its generalized solution and semidiscrete mixed finite element(MFE) solution was discussed, and the error estimates of the semidiscrete MFE solution was derived.The error estimates are optimal.

基于多频涡流技术的燃料棒包壳管氧化膜厚度测量方法

核燃料棒包壳管表面的氧化膜会影响其导热性能,使燃料棒的温度上升,加快燃料包壳的腐蚀速度,给反应堆带来潜在安全风险。故有必要对氧化膜厚度进行精确测量。为此,构建了燃料棒包壳管的三维有限元仿真模型,对燃料包壳多频检测进行了分析,总结了激励频率、包壳管电导率和金属涂层厚度对氧化膜测量结果的影响规律;提出了融合多频测量数据,抑制干扰因素影响,精确计算氧化膜厚度的方法,并进行了试验验证。结果表明,该方法的氧化膜厚度计算误差小于1μm,可用于燃料包壳管氧化膜厚度的量化表征。

MIXED FINITE ELEMENT METHODS FOR THE SHALLOW WATER EQUATIONS INCLUDING CURRENT AND SILT SEDIMENTATION (Ⅱ)——THE DISCRETE-TIME CASE ALONG CHARACTERISTICS

The mixed finite element(MFE) methods for a shallow water equation system consisting of water dynamics equations,silt transport equation,and the equation of bottom topography change were derived.A fully discrete MFE scheme for the discrete_time along characteristics is presented and error estimates are established.The existence and convergence of MFE solution of the discrete current velocity,elevation of the bottom topography,thickness of fluid column,and mass rate of sediment is demonstrated.

励磁绕组与阻尼绕组耦合效应对大型同步调相机转子暂态电流特性的影响

针对大型同步调相机暂态分析时模型精度较低的问题,提出一种考虑励磁绕组与阻尼绕组耦合效应的同步调相机暂态分析精确模型。首先,通过引入特征电抗建立同步调相机考虑励磁绕组与阻尼绕组耦合效应的暂态分析精确模型,并基于励磁电流拟合对特征电抗进行求解。然后,通过三相短路与BC相间短路故障仿真,对比同步调相机传统模型与精确模型的转子暂态电流特性。最后,建立同步调相机机-网暂态仿真模型,分析系统送端交流母线电压波动时同步调相机精确模型的暂态运行特性。研究表明,考虑励磁绕组与阻尼绕组耦合效应时同步调相机转子暂态电流特性的精度更高。三相短路与BC相间短路故障后3个周期内,同步调相机暂态分析精确模型励磁电流峰值平均值的精度分别提高了27.27%和61.53%。

基于多TMR的涡流无损顶锤裂纹检测系统设计

针对碳化钨顶锤的表面及近表面裂纹的快速精准无损检测需求,开发了一套基于多个隧道磁阻的涡流裂纹探伤检测系统。系统设计了电源供电电路、频率可调节的信号发生电路、功率放大电路、检测探头,能检测出微缺陷引起的叠加磁场的变化。有限元仿真与顶锤检测实验的对比分析表明该检测系统可以准确识别顶锤的细微裂纹损伤,实现了基于涡流原理的顶锤钨合金试块近表面微小裂纹的检测。

面向电流信息与模态分析的工业机器人关节振动求解研究

在工业机器人健康监测中,针对需采用振动传感器对机器人各关节逐一检测而引起测试成本剧增问题,提出一种基于电流信息与模态分析的关节振动求解方法,该方法可由关节电流经模态转换直接获取关节振动信息。首先,将关节电流信息引入,建立基于关节电流的工业机器人振动模型。然后,由有限元法进行模态分析获取机器人前6阶振型,便于后续模态试验优化测点布置。接着,在力锤激励试验中,基于优化后的测点,测取工业机器人系统质量、刚度等模态参数。之后,将驱动力矩与模态参数带入该模型进行龙格库塔数值求解,得到机器人各关节振动响应。最后,在指定关节转角运行的关节单动与联动实测振动数据验证了本文提出算法的正确性。

狭窄空间内矩形导体电流测量装置设计与优化

针对狭窄空间内矩形导体电流测量,提出了一种基于霍尔元件椭圆阵列的电流测量装置,通过理论计算和有限元仿真分析确定了相对最优的阵列分布,搭建实验平台并通过实验验证了该方法的可行性,以及导体偏心状态下电流测量的有效性,同时分析了导体偏心状态下的电流测量偏心误差。仿真和实验结果表明,椭圆阵列电流测量装置在行业允许的±1%误差限内,允许导线X轴偏心-4.1~4.1 mm,Y轴无限制;且与传统电流测量装置相比,重量减轻82.9%,安装占用面积减小72.4%,对狭窄空间的适用性更强,为新能源产品轻量化、小型化、持续降本提供了技术支持。

基于直流电位降法的缺陷区域多探针检测

油气管道在服役过程中由于制造过程、环境复杂等因素容易产生缺陷,造成管道破裂等事故,因此对管道的无损检测具有重要意义。通过直流电位降法研究裂纹缺陷对电位场的影响规律,建立了多探针缺陷检测方法。首先采用有限元法对含有缺陷的平板试样进行电位分析,缺陷区域的电位差明显高于无缺陷区域,通过多探针的检测范围对试样区域进行划分后,提出了多探针缺陷区域检测方法。检测到区域存在缺陷后,对缺陷影响因子k进行计算,无缺陷区域k值基本在0.8~1.2之间,而缺陷周围的k值都超过了2,根据k值的分布可以得到缺陷的大致位置和尺寸。并搭建了多探针检测试验平台进行试验,结果表明,缺陷附近的电势差显著高于其他区域,与有限元结果相符。缺陷区域电势差明显高于其他区域,无缺陷区域k值在0.75~1.2之间,缺陷区域k值基本大于1.5。通过k值分布对缺陷位置和尺寸进行分析,与实际尺寸相差在3~5 mm左右。

超磁致伸缩力传感执行器磁路优化设计与分析

以超磁致伸缩力传感执行器为研究对象,基于磁致伸缩与涡流损耗理论,应用COMSOL有限元软件进行磁场分析,系统地研究了导磁体参数对磁通密度与涡流的影响规律。为增大磁通密度、减小涡流损耗,以超磁致伸缩棒中轴线上磁通密度均匀度为评价标准,优化了导磁体参数,并将导磁体分区绝缘。静、动态磁场下与未优化时实验结果进行对比,结果表明:静磁场中优化后的磁通密度均值提升了0.0161T,均匀度提升了4.5%;动态磁场中,分区绝缘可有效减少涡流损耗,优化后的力传感器灵敏度提升了5.76%。

基于COMSOL仿真软件的电涡流传感器教学探索

为了提升课堂教学效果,辅助学生理解电涡流传感器的检测原理及相关抽象概念,采用COMSOL仿真软件,构建了电涡流传感器探头线圈的仿真模型,并采用有限元的分析方法对其进行求解计算。通过对仿真结果的分析,学生可以直观地看到,当涡流线圈激励频率、提离距离、线圈内径、线圈外径和线圈厚度变化时,电涡流传感器的检测灵敏度将随之发生变化,有助于学生对电涡流传感器相关知识的理解和掌握,提高了学生的学习热情和思考深度。

架空地线临界融冰电流估算方法研究

架空线路覆冰是影响电网正常运行较为严重的灾害之一,尤其地线更易出现覆冰,有必要对架空地线直流融冰电流进行计算,而现有的经验公式及应用较多的布尔斯道尔夫融冰电流计算公式较为复杂,且有些参数测量困难。因此,该文提出一种用于快速估算已知架空地线型号在不同风速、环境温度、覆冰厚度条件下临界融冰电流的方法,通过分析地线融冰物理过程,利用有限元软件搭建仿真模型,经模型计算得到数据集,然后采用多元线性回归拟合得到相关变量的函数表达式,并与计算值进行对比。

电塑性轧制加电装置设计及实验验证

为满足电塑性轧制中高能脉冲电流的高效传输和靶向作用,提出一种电塑性轧制加电装置,并利用ANASYS有限元分析软件对轧辊与轧件的电流场和温度场进行了仿真分析。通过变参数多工况模拟,研究了不同参数对电极与轧辊、轧辊与轧件接触处电流集中的影响、轧件塑性变形区内电流非均匀分布区的影响规律以及轧辊和轧件的温升情况。基于此,搭建了二辊电塑性轧制实验平台,并以AZ31镁合金板材为对象,验证了新的加电方案可以有效遏制AZ31镁合金轧制过程中边裂现象的发生,从而大幅度提升了镁合金板材的成形效率与质量。

脉冲电流条件下同轴电缆温度分析及优化设计

脉冲功率电源系统与耗能装置之间通过同轴电缆连接,在连续快速脉冲大电流工况下同轴电缆会快速升温。针对该问题,在土壤直埋敷设条件下建立同轴电缆有限元电-热耦合模型,对比分析不同数量和不同排列方式下同轴电缆在多循环通、断电时的温升特性,同时考虑敷设深度对电缆温度的影响。在此基础上,提出两种新型电缆排列方式以改善温度分布。结果表明,随着电缆数量的增加,电缆的最高温度呈上升趋势,但并非比例增长;在相同电缆数量和电缆间距的前提下,多层电缆排列方式相较于单层电缆虽然占用空间较小,但温度更高;随着敷设深度的增加,电缆温度呈逐渐升高的趋势,当敷设深度为1237.50 mm时,电缆温度达到最高,而超过该深度时,电缆温度又显著降低。提出的新型电缆排列方式不仅降低了占用空间,同时还实现了电缆温度的降低。

交流励磁直线轨道涡流制动器的多目标优化研究

直线轨道涡流制动技术具有制动力平稳、无摩擦等优势,在连续长大坡道等复杂线路中能维持稳定的制动力输出,是对高速列车制动系统的有力补充。本文针对直线轨道涡流制动器进行多目标优化,首先建立了基于分层模型的交流励磁直线轨道涡流制动器解析计算模型,利用实验测试、有限元仿真模型验证了解析模型的有效性,并分析了制动-速度特性;之后结合基于第二代非支配排序遗传算法NSGA-II的优化方法,对影响制动力的制动器的初级绕组关键结构参数进行优化设计,最终将最大制动力从35.7N提升至46.7 N,增加了30.8%,同时将最大临界速度从40 m/s提升至43.4 m/s,增加了8.5%,提升了交流励磁直线轨道涡流制动器的制动性能,拓宽了制动器的适用速度范围,为交流励磁直线轨道涡流制动器的优化设计和应用奠定了理论基础。