Solidification structure of eutectic Al-Si alloy under a high magnetic field-aid-electromagnetic vibration

An electromagnetic vibration was generated by simultaneously imposing a strong static magnetic field （up to 10 T） and an alternative electricity current to the metal. Its effects on the solidification structure of eutectic Al-Si alloy have been investigated experimentally. It is found that the eutectic structure has been refined by solely imposing high magnetic field while it is coarsened under the electromagnetic vibration. Furthermore, polyhedral Si grains and non-dendritic α-Al appeared when the electromagnetic vibration strength was strong enough. The refining of eutectic structure is attributed to the decrease of diffusion coefficient caused by the strong magnetic field. The coarseness of eutectic structure may be attributed to the convection caused by electromagnetic vibration. Strong convection may break co-operative growth of eutectic phases to form polyhedral Si grains and non-dendritic α-Al.

Influence of magnetic field on free vibrations in elastodynamic problem of orthotropic hollow sphere

The effect of magnetic field on the plane vibrations for an elastodynamic orthotropic sphere is studied. Equations of elastodynamic problems of the orthotropic hollow sphere in terms of displacement are solved. The numerical results of the frequency equations in the presence of magnetic field are discussed and shown graphically. Compar-isons are made with the result in the presence and absence of magnetic field in the case of orthotropic sphere. The results show that the effect of magnetic field is very pronounced.

Magnetic field effects on the nonlinear vibration of a rotor

The nonlinear vibration of a rotor operated in a magnetic field with geometric and inertia nonlinearity is investigated. An asymmetric magnetic flux density is generated,resulting in the production of a load on the rotor since the air-gap distribution between the rotor and the stator is not uniform. This electromagnetic load is a nonlinear function of the distance between the geometric centers of the rotor and the stator. The nonlinear equation of motion is obtained by the inclusion of the nonlinearity in the inertia, the curvature, and the electromagnetic load. After discretization of the governing partial differential equations by the Galerkin method, the multiple-scale perturbation method is used to derive the approximate solutions to the equations. In the numerical results, the effects of the electromagnetic parameter load, the damping coefficient, the amplitude of the initial displacement, the mass moment of inertia, and the rotation speed on the linear and nonlinear backward and forward frequencies are investigated. The results show that the magnetic field has significant effects on the nonlinear frequency of oscillation.

Resonance frequencies and stability of a current-carrying suspended nanobeam in a longitudinal magnetic field

The resonance frequencies and stability of a nanobeam in a longitudinal magnetic field are investigated.To this aim,a three dimensional beam model is used in which the small-scale effect is taken into account based on the nonlocal elasticity theory.The Lorentz forces are obtained in terms of the local elastic rotations of the beam and the thermal stress due to current is modeled as an axial compressive force.Using the Galerkin method,the governing equations of motion are solved and the stability boundary of the nanobeam is determined.

Effect of Rotation and Initial Magnetic Field in Fibre-Reinforced Anisotropic Elastic Media

In this work, we study an analytical procedure for evaluation of the displacement and stresses in fibre-reinforced anisotropic elastic media under effects of rotation and initial magnetic field, and due to the application of the rotation and initial magnetic field. Effects of rotation and initial magnetic field are analyzed theoretically and computed numerically. Numerical results have been given and illustrated graphically. Comparison was made with the results obtained in the presence of rotation and initial magnetic field in fibre-reinforced anisotropic and isotropic elastic media. The results indicate the effect of rotation and initial magnetic field.

Fabrication of Grain-oriented (Bi,Pb)_2Sr_2Ca_2Cu_3O_x Superconducting Tapes Using Magnetic Field and Vibration Technique

Highly textured (Bi,Pb)2Sr2Ca2Cu3Ox superconducting tapes have been fabricated by means of magnetic-field and vibration technique. This method is an effective way of improving the degree of grain alignment and density of oxide core in tapes after heat treatment and pressing cycles.Jc of above 20% was increased than that without treatment.

Nonlinear vibration analysis of an embedded branched nanofluid-conveying carbon nanotube:Influence of downstream angle,temperature change and two dimensional external magnetic field

In this study,non-linear thermal-mechanical stability and vibration analyses of different end-shaped single-walled carbon nanotube conveying viscous nano-magnetic fluid embedded in non-linear visco-elastic foundation under the influence of magnetic fields are presented.The development of the equation of motion was based on Euler-Bernoulli theory,Hamilton principle and nonlocal elasticity theory.The results of the analytical solutions using Galerkin decomposition differential transform method(GDDTM)were validated with existing experimental results.From the parametric studies,it was shown that decreasing the temperature difference as well as increasing the downstream angle decreased the system's stability for pre-bifurcation analysis but increased stability of the system for post bifurcation analysis.Also,the results obtained from the dynamic behaviour of the system indicated that the magnetic effect had an attenuating impact of about 45%on the system's response at any mode and for any boundary condition considered.It is hoped that this work will enhance the design and optimization of nano-devices with I,V,Y,L,K and T-shaped junctions under the influence of thermal-magneto-mechanical flow induced vibration.

Effect of Transverse Static Magnetic Field on Droplets Transient and Inclusions Evolution During the Electroslag Remelting Process of GCr15 Ingots

The voltage was recorded to investigate the influence of the static magnetic field on droplet evolution during the mag-netically controlled electroslag remelting （MC-ESR） process. MC-ESR experiments were carried out under differentremelting current, and transverse static magnetic fields （TSMF） of 85 mT, 130 mT and 160 mT were superimposed.Statistical work was performed to obtain the quantitative data of the droplets. The ASPEX Explorer was utilized toinvestigate the inclusions evolution of GCr15 ingots. The number of the droplets was 31 in 20 s during the traditional ESRprocess and reached 50 and 51 under the MC-ESR process with the TSMF of 85 mT and 130 mT, respectively. Whencompared the traditional ESR process with the MC-ESR process, the inclusions amount reduced 67%.

Effect of compound field on horizontal continuous casting of Al-1wt.%Si alloy

A travel ing magnetic field, a power ultrasonic field, and a compound field were used separately during the horizontal continuous casting process of Al-1wt.%Si al oy. The samples obtained were characterized using an optical microscope, a scanning electron microscope, a tensile testing machine, and an electron probe microscopic analyzer to test the microstructures, properties, and element distribution of the samples. The results show that the application of a single ifeld can enhance the mechanical properties and reduce the segregation of Si element in Al-1wt.%Si alloy to some extent. The application of a compound field can obtain the best reifnement and homogeneity of the Si element in the al oy, leading to the highest increase of tensile strength and elongation among the three applied ifelds. The mechanism of the action of external ifelds on the reifnement of microstructures and homogeneity of the Si element is discussed and the compound ifeld is considered to be an effective method to achieve high quality Al alloys.

Study on the Electroslag Remelting of Bearing Steel in Static Magnetic Field

The Electroslag Remelting(ESR)Process has been developed quickly in recent years for its productions of excellent metal ingots with high purity,compact structure,homogeneous composition and clean surface.However,some problems in traditional ESR process still exist,for example the nonmetallic inclusions,coarse dendrite crystal and solute segregation in large-scale ESR etc.In this study we combine the ESR process with electromagnetic processing of materials(EPM)process in GCr15 steel under conditions of 400-700 amps current.The microstructure and inclusions analysis showed that,the inner structure of ingots is compact and homogeneous and no remarkable inclusions appear when superimposing static magnetic field simultaneously.Refined branch grain size,homogeneous distribution of solute, decreased concentration of inclusions and impurities and elevated hardness also could be achieved.ESR process under steady magnetic field makes melt pool planer when compared with that without magnetic field,which would be explained by the electromagnetic vibration refined metal melting drops and the temperature field in the pool is uniformity.

Effect of Longitudinal Magnetic Field on Vibration Response of Double-Walled Carbon Nanotubes Embedded in Viscoelastic Medium

This paper aims to study the effect of externally applied longitudinal magnetic field on the transverse vibration of viscoelastic double-walled carbon nanotubes （visco-DWCNTs） embedded in a viscoelastic medium. The analyses are carried out based on the nonlocal viscoelastic model and Euler-Bernoulli beam theory. Governing equations are derived for the vibration of the embedded visco-DWCNT subjected to a magnetic field, where the Lorentz magnetic force, the surrounding viscoelastic medium, the intertube van der Waals forces and viscoelasticity of the DWCNT are taken into consideration. In this study, the transfer function method is employed to solve the governing equations, which enables one to obtain the natural frequencies and the corresponding mode shapes in closed form for the DWCNTs with arbitrary boundary conditions. Here the developed mechanics model is first compared with the existing techniques available in the literature in a few particular cases, where excellent agreement is achieved. The validation of the model is followed by a detailed parametric study of the effects of longitudinal magnetic field, nonlocal parameter, boundary conditions, structural damping coefficient and aspect ratio of the DWCNTs on their vibration. The study demonstrates the efficiency of the present technique designed for vibration analysis of a complicated multi-physics system comprising DWCNTs, the viscoelastic medium and a magnetic field in longitudinal direction.

高场超导磁体剩余磁场对低场磁测量的影响及对策

常用作磁测量的综合物性测量系统中,为其提供强磁场的超导磁体是非理想的第二类超导体.人为引入的“缺陷”可以有效提高超导体的磁场耐受性,使超导磁体能够承载更大的电流并产生更高的磁场.然而,高场超导磁体在退磁过程中会产生剩余磁场,严重影响小磁场条件下的测试结果.通过理论分析和实际试验,对比振荡模式和线性模式在磁场归零时对剩余磁场产生的影响,发现振荡模式可以显著减少剩余磁场,这有利于在小磁场条件下进行磁性测试.

基于多场耦合提升逸散性颗粒与磁种碰撞系数动力学研究

以多场耦合提升逸散性颗粒与磁种碰撞系数为研究对象,基于计算流体力学-离散相模型(DPM),通过用户自定义函数(UDF)添加逸散性颗粒与磁种之间的库仑力和磁偶极子力,数值计算电场和磁场构成的多场中逸散性颗粒与磁种之间的碰撞系数,获得提升磁凝并程度的方法.结果表明,当流体速度u=0.5m/s,颗粒粒径0.5μm≤d_(p)<2.0μm,库仑力和磁偶极子力均可提高逸散性颗粒与磁种之间的碰撞系数,且库仑力可弥补弱磁性颗粒与磁种之间磁偶极子力较小的问题.若荷电场强E_(0)=0.5kV/cm,逸散性颗粒饱和磁化强度M_(j)=500A/m,磁种饱和磁化强度M_(i)=40000A/m,逸散性颗粒与磁种之间的碰撞系数比未荷电时提高了13.50%,若荷电场强E_(0)=1.0kV/cm,碰撞系数提高了23.60%.

一种应用于精密隔振平台的双曲线磁通磁轴承设计

针对精密隔振系统磁轴承存在悬浮力密度小、波动大以及耦合力大问题,设计了一种双曲线磁通结构的磁轴承(MBHFM)。首先利用等效电流法和永磁体镜像法推导了带有磁轭的双曲线磁通的磁轴承的气隙磁场和悬浮力的表达式,并分析了磁轴承悬浮力波动对隔振性能的影响。其次根据双曲线磁通的磁轴承悬浮力线性分布特点,采用电流前馈补偿方法使磁轴承获取更低悬浮力波动的恒定悬浮力。最后,对双曲线磁通的磁轴承与常见的双边Halbach结构磁轴承(MBBH)进行了仿真分析与测试。仿真结果表明所设计双曲线磁通的磁轴承样机静态悬浮力平均值为153.75 N,静态耦合力系数为0.42%,电流前馈补偿后合成悬浮力波动系数为0.15%,较双边Halbach结构磁轴承静态悬浮力密度提高了20%,静态耦合力系数减小了72.2%,合成悬浮力波动系数减小了89.3%。测试结果进一步验证了所设计样机的高性能。

基于有限元法的油浸式变压器振动特性分析及优化设计

根据油浸式变压器的电气和结构参数,基于有限元仿真软件建立电路-磁场仿真模型;根据材料磁特性实验测量结果,结合J-A磁滞模型辨识得到的特征参数,获得材料的磁特性模型。建立变压器磁场-结构力场仿真模型,获得变压器周围磁场和应力分布;将计算得到的铁心麦克斯韦力和磁致伸缩力、绕组洛仑兹力作为激励,计算得到考虑材料磁特性的变压器振动位移;提取铁心不同位置的振动位移,获得铁心振动特性分布规律。在此基础上,为降低油浸式变压器的铁心振动,将有限元法与实验设计方法相结合,通过调整变压器绕组参数获得最佳的参数,结果表明优化前后变压器最大振动位移分别为6.12μm和5.71μm,优化方法显著降低了变压器的振动,对油浸式变压器减振降噪具有重要的指导意义。

一种新型四象限洛伦兹力电机的设计及优化方法

为满足六自由度隔振平台(VIP)高定位精度、高动态响应和短运动行程的使用需求,设计了一种应用在六自由度隔振平台的新型四象限洛伦兹力电机,这种电机具有低推力波动和小耦合力的优点。首先介绍了提出的新型四象限洛伦兹力电机的结构和工作原理。然后基于等效电流法和永磁体镜像法推导这种电机磁场分布以及电磁力情况。并且分析不同结构参数对气隙磁场以及电磁力的影响,再基于遗传算法在兼顾推力波动、耦合力的情况下对推力密度进行参数优化。最后,根据提出的电机电磁力模型进行3D有限元仿真和实验验证,实验结果表明,所设计电机在线圈电流为5 A,y、z向位移台运动位移在-1 mm~1 mm时,推力波动小于0.23%,耦合力在19.3 mN以内。

电磁式线-角振动激振器气隙磁场特性分析

针对传统单轴激振器无法复现线-角空间耦合运动的问题,提出了一种可实现复合振动的电磁式线-角振动激振器磁路结构,并对其气隙磁场特性进行分析。首先构建了激振器的磁路和线圈结构,基于等效电流法,建立了气隙磁场的解析模型,与有限元分析结果的最大相对误差为1.25%,验证了解析模型的正确性;接着研究了各磁路参数对气隙磁场分布特性的影响规律,以及线圈电流产生的磁场与原磁场的耦合效应,并分析了线圈在运动过程中的受力情况;最后研制了激振器磁路拓扑结构样机,分别对线、角振动气隙磁场进行了实验测量,测得结果与有限元计算结果的最大相对误差小于5%,进一步验证了所提出磁路结构的有效性。

干式变压器铁芯振动特性的研究分析

干式变压器是电力系统中常用的重要电气设备,对电力系统的稳定运行具有重要的影响作用。干式变压器中的主要组成部分包括铁芯及绕组,由于磁致伸缩效应及电磁力的作用,使得变压器在工作过程中存在一定的振动,不利于变压器的稳定使用。针对干式变压器铁芯的振动特性采用有限元仿真计算的形式进行分析,建立变压器多物理场耦合分析模型,在不同的电压下对变压器的磁场分布及振动位移进行分析。结果表明,变压器空载状态下随着电压的增加,其内部的磁场密度及振动位移随之增加,且呈现一定的周期性,容易引发变压器的故障。

Refinement and migrating behaviors in Al-Si hypereutectic alloys solidified under electromagnetic vibration

The effects of electromagnetic vibration （EMV） on the refinement and migration of primary silicons in the A1-18 wt pct Si alloy were investigated systematically. It was found that EMV could effectively refine primary silicons. The equivalent diameter of primary silicon first decreases slowly with the current increasing from 1 A to 3 A, but then drops rapidly between 3 A and 10 A, next gradually decreases with increasing current intensity. When the EMV intensity was low, the primary silicons were agglomerated and expelled to the top of a sample, the segregation of silicon grains gradually decreased and the agglomerating phenomena disappeared with the increase of EMV intensity, and the star-like coarse primary silicons turned refined flake or square morphology. The refinement and migration of primary silicons depended on the Lorentz force, gravity and the effective viscous force.

磁矩及地磁场水平分量的测量实验设计

制作设计一种简易的测量磁矩及地磁场水平分量的实验装置,采用智能手机内置的磁传感器以及霍尔传感器分别测量处于地磁场和通电线圈总磁场中磁铁的简谐振动周期,通过曲线拟合完成地磁场的水平分量及磁性材料磁矩的测量和计算,地磁场实验结果与中国科学院地质与地球物理研究所网站的实时观测数据相比相对误差范围为1.83%~1.98%,表明该实验装置和实验方法具有较高的准确性。该实验适用于普通物理实验或者设计性实验,有助于激发学生的实验兴趣,提高学生的动手能力与创新思维。