Measuring coercive force in local domains of a sample

A method has been proposed for determining the coercive force in local domains of bulk samples magnetized normally to the surface. The method is based on local measurement of the normal magnetic-field component at the sample surface, in the gap between the sample and the pole of a magnetizing device. The coercive force is determined by the magnetic field for which local magnetization in the measured domain becomes zero. Conditions for the correctness of coercive-force measurements have been established.     

An attachable electromagnet of a coercimeter with an indicating system between the electromagnet’s poles

The dependence of the readings of a coercimeter on the gap width between an article and the poles of an attachable electromagnet (AEM) at different magnetizing and magnetization-reversing currents is studied in the case when the indicator of the magnetic state of an article is removed from the electromagnet’s magnetic circuit and placed between the electromagnet’s poles on the surface of the article. It is shown that, during coercive-force measurements, such an indicator cannot be used for determining the demagnetized state of the article in the case of substantial fluctuations of the gap between the AEM poles and the article, although it can be used for assessing the gap width.     

Resonant enhancement of natural convection in a cubic enclosure under time-periodic magnetizing force

A numerical investigation was carried out for natural convection of air (paramagnetic fluid) in a cubic enclosure subjected to constant gravity and time-periodic magnetizing force. Since the magnetizing force expressed as the gradient of magnetic induction squared in each direction, has three-dimensional characteristics, three-dimensional modeling of system would be required to investigate the effect of magnetizing force more accurately. In this study as a sequent research, the basic analysis of Kang and Hyun [16] was extended to the case of three-dimensional and to cases when the magnitude of magnetizing force is varied. Two geometrical configurations for the location of electrical coils, were considered. The amplification characteristics of heat transfer rate in the cube according to the change of the magnitude of magnetizing force, were investigated especially when the resonance occurs. The numerical results showed that the heat transfer is enhanced appreciably by application of large magnitude of magnetizing force. In addition, the results for two- and three-dimensional cases were also compared.

     

Dynamic model of a continuity flaw during normal magnetization of a ferromagnetic article: II. Magnetostatic field of a continuity flaw during magnetization of the article with a finite-sized magnetizing instrument

A dynamic model of a finite-sized continuity flaw that is present in a ferromagnetic half-space during normal magnetization with a magnetic field produced by a bar magnetizing instrument is obtained. The model takes into account the relative position of the flaw and magnetizing system during the model’s motion along the surface of an article. During normal magnetization of the flaw with the field produced by the finite-sized bar magnet, the longitudinal component of the magnetizing field is shown to exist. The longitudinal component distorts the magnetic-field distribution of the continuity flaw and decreases its detectability.     

A magnetizing device of a scanning coercimeter

We describe a device that is designed for magnetizing articles during the testing of ferromagnetic objects with a scanning coercimeter. The problem of magnetizing an article at high velocities of movement of a magnetizing device and measuring the residual magnetic field above the article surface was solved. The results of experimental studies of the operation of a scanning coercimeter in a range of velocities of motion of the magnetizing device of up to 4 m/s are presented.     

基于子域法的双励磁双调制轴向式磁场调制永磁齿轮磁场分析

轴向式磁场调制永磁齿轮(AFMPMG)存在轴向及切向漏磁严重及转矩密度偏低等问题。在AFMPMG基础上引入了一个外调磁环,使之构成一种双励磁、双调制的AFMPMG(DEM-AFMPMG)结构,由于DEM-AFMPMG低速永磁转子夹在内、外两个调磁环之间,因此可将AFMPMG轴向及切向漏磁通转化成有用谐波,从而增大DEM-AFMPMG输出转矩及转矩密度。虽然3D有限元法计及了永磁齿轮端部漏磁,具有计算精度高等优点,但同时也使计算机资源占用率过高且结构参数优化周期较长,针对此,提出了一种基于子域法的计算DEM-AFMPMG气隙磁场及电磁转矩数学模型,该方法可将3D模型等效为2D模型,但包括了3D模型的所有因素。算例计算结果表明,基于子域法模型的计算精度与3D有限元法的计算精度相当(气隙磁通密度及电磁转矩的计算误差均不大于5%,转矩密度的计算误差不大于1.5%),但子域法模型计算速度更快,且易于实现计算机程序化,更有利于DEM-AFMPMG的结构参数分析与优化。     

Hydroelastic oscillations of submerged constructions and their damping

This paper presents a practical method for calculating damping forces per unit length acting during the submerging of elongated wedge-like bodies into a fluid. Allowance is made for the hydrodynamic warp of the surface, for the inclinations of the keel and bow lines, and for other factors characterizing the geometry of a submerging body.     

The field of a finite defect in a plate

An equation for determining the magnetic field of a plate inside which there is a cavity of finite dimensions with a smooth boundary has been obtained on the basis of the integro-differential equation of magnetostatics. A particular problem has been solved for a spherical cavity and an external uniform magnetizing field directed parallel to the plate surface.     

On new possibilities for making local measurements of the coercive force of ferromagnetic objects

The possibility of reducing the influence of both the gap in a transducer-object combined circuit and the shape of tested objects on the results of local measurements of their coercive force is investigated. It is shown that additional measurements of the maximum magnetic flux in the circuit and the tangential component of the magnetic field on the surface of the tested area of the object, which is retained after the magnetizing current is turned off, allow a substantial decrease in the corresponding errors.     

大位移角振动台的气隙磁场动静态特性分析

针对电机驱动式角振动台气隙磁场不均匀和输出大位移时波形失真大的问题,提出了一种径向磁通磁路结构的大位移角振动台,对其气隙磁场动静态特性进行优化分析。基于等效磁化强度法,在极坐标系下建立气隙磁感应强度的解析表达式,通过有限元法验证该方法的有效性,进一步分析了永磁体厚度、永磁体扇形角及气隙厚度对静态气隙磁场的影响规律;通过瞬态有限元法仿真分析了0.01、0.1和1 Hz 3个频率点上外磁环固定不动而永磁体和内磁芯转动的气隙磁场动态特性,定量分析了相对运动对气隙磁感应强度的影响规律;将优化后的磁路参数用于大位移角振动台样机中,测试结果表明,气隙平均磁感应强度及其分布规律和理论计算结果相吻合;研究方法对角振动台径向磁通磁路的理论分析与优化设计具有重要意义。     

基于OpenGL的复杂异形弹簧实体造型

对复杂异形弹簧的实体造型技术进行了研究,着重阐述了弹簧实体表面的三维离散技术,提出了一种针对螺旋体与异形弹簧末端连接部分进行光滑处理的方法,避免了实体造型时出现缝隙,并在C++Bu ilder环境下,以OpenGL为工具,实现了异形弹簧的造型和显示。该方法显示效果逼真,实用性强,为异形弹簧的设计和制造提供了新途径。     

一种抗灰尘的近场承载微工作台设计

为满足近场光存储的高密度、高速度和集成化的要求,提高近场界面耦合效率,消除灰尘对固体浸没透镜(SIL)的磨损,设计了一种新型的承载微工作台,并建立了系统动力学模型.微工作台正负压力并存的结构极大地提高了承载刚度及工作稳定性;气垫面的V形轨道设计及独特的负压力布局有效减少了流入SIL底面的灰尘颗粒;SIL底面刻饰的凸台有利于获得较高的近场耦合效率,同时减小了与盘面碰撞的概率.理论分析和计算表明,微工作台的近场间距小于50nm,承载力可达88mN,SIL底面灰尘颗粒明显减少,微工作台具有良好的工作姿态,满足了近场光存储的需要.     

基于气流黏性牵引原理的无接触输运建模仿真与试验研究

目前众多行业需要使用无接触的方式输运清洁、易损的产品。介绍了一种完全无接触的气浮输运平台,通过在物体下方产生气膜及可控气流实现牵引输送。建立了间隙内气流简化模型并针对黏性力进行了理论和实验研究,结果表明,气流在平台表面凹槽区和边缘区域内提供牵引力,且在一定流量条件下黏性力随气膜高度增加而降低。提出了一种基于有效驱动单元列数作为被控量的控制方法,设计PID控制器并对物体在一维方向上的输运与定位进行研究,结果验证了理论模型和控制方法的有效性。     

基于气隙磁场分层耦合的直线时栅位移传感器研究

针对前期研制的电磁式直线时栅位移传感器高信噪比和高时间插补分辨力难以兼顾的问题,设计了一种提高传感器信噪 比的新传感器结构,另外提出了一种高信噪比、高时间插补分辨力的测量新方法,并研制了基于气隙磁场分层耦合的直线时栅位 移传感器。 建立传感器气隙磁场数学模型,分析气隙磁场空间分布特性,研究平面线圈气隙磁场分层耦合的原理;根据气隙磁场 分层耦合原理,建立传感器气隙磁场分层耦合位移测量模型;对传感器测量模型进行电磁场仿真和误差分析;最后,搭建实验平台 进行对传感器的性能进行测试。 实验结果表明,采用气隙磁场分层耦合的结构提高了传感器的信噪比,传感器的测量精度在原有 的基础上提高了 31. 4% ;采用的高信噪比和高时间插补分辨力测量方法,传感器的测量精度在原有的基础上提高了 37. 3% 。     

Vertical attractive force generated in a noncontact chuck using ultrasonic vibration

Squeeze-film chucks using ultrasonic vibration are attracting considerable attention because of their ability to vertically and horizontally support an object placed on their vibrating surface without any contact. In addition, it has been shown experimentally that an attractive force is exerted on an object set under the vibrating surface. Although the cause of the vertical and horizontal forces has been determined using computational fluid dynamics (CFD) calculations, the cause of the attractive force generated by the vibrating surface has not yet been clarified in detail. This paper investigates numerically and experimentally the cause of this attractive force generation. In the numerical calculations, CFD was used to obtain the pressure distribution both in the air gap between the object and the vibrating plate and in the space surrounding the object. The attractive force acting on the object was found to be generated by the inflow resistance at the outer edge of the object when the air flows into the narrow air gap from the outside, which lowers the pressure in the air gap around the outer edge of the object to below ambient.     

Studying the dependence of flaw-induced magnetic field on the parameters of magnetizing device

The topography of magnetic fields has been studied for different magnetizing conditions. Recommendations are given for the placement of electromagnet poles with respect to the test object. The relationship between magnetic-field strength and the gap between electromagnet poles and the test object is estimated. The distribution of magnetic-field strength above a flaw is given; the possibility of its use in matrix transducers is shown.     

基于杂散磁场感知与NBCNN-LSTM-Attention深度回归建模的永磁直线电机气隙磁密测量研究

本文提出一种基于隧道磁阻(TMR)传感器和噪声注入卷积神经网络(NBCNN)、长短期记忆网络(LSTM)、注意力机制动态集成神经网络预测模型(NBCNN-LSTM-Attention)的双边永磁同步直线电机气隙磁密新型非侵入式测量方法。首先，建立直线电机气隙磁场的解析模型和有限元模型作为数据基础，探寻直线电机的外部空间杂散磁场和内部中心气隙磁场存在非线性映射关系。其次，引入TMR传感器测量直线电机外部杂散磁场信号，并对传感器的安装位置进行优化，将内外一维磁密信号进行相似度特征匹配，以获取传感器最优测量位置。然后，将电机外部杂散磁场数据作为输入，内部气隙磁场数据作为输出，建立NBCNN-LSTM-Attention网络的内外磁场高精度映射模型，实现“用外代内”的非侵入式气隙磁密高精密测量。最后，搭建直线电机气隙磁密测量实验平台和高斯计对比测量实验平台，验证了本文所提方法的先进性和优越性。     

Nonuniform magnetization of an article around a flaw during magnetic inspection

Measurements of the induction in a ferromagnetic article directly around a surface flaw in the form of a rectangular slot have shown that there is a substantial magnetization nonuniformity of the article owing to the discontinuity. The nonuniformity smooths out as magnetizing field H ₀ increases. The increase in magnetizing field H ₀ increases the nonuniformity of the field distribution over the article surface, thereby changing the topography of the flaw field. In particular, in low magnetizing fields, this change leads to the absence of negative extrema in the curve of the tangential component of the flaw field, H _x (x). The discrepancy between the calculated and experimental values of the fields of flaws characterized by different geometric parameters is indicative of a considerable effect of the flaw opening on calculated data. These data should be improved through proper corrections obtained experimentally.     

Air Injection as a Thermal Management Technique for Radial Foil Air Bearings

A thermal management technique for radial foil air bearings was experimentally evaluated. The technique is based on injecting air directly into the internal circulating fluid-film to reduce bulk temperatures and axial thermal gradients. The tests were performed on a single top foil, Generation III, radial foil bearing instrumented with three thermocouples to monitor internal temperatures. A through hole in the bearing shell coincident with the gap between the top foil's fixed and free ends provided entry for the injection air. The tests were conducted at room temperature with the bearing operating at speeds from 20 to 40 krpm while supporting 222 N. Two different mass flow rates of injection air were evaluated for this method, 0.017 and 0.051 kg/min. Test results suggest that the air injection approach is a viable thermal management technique capable of controlling bulk temperatures and axial thermal gradients in radial foil air bearings.     

Microtribological investigations of stick/slip phenomena using a novel oscillatory friction and adhesion tester

A novel friction and adhesion tester bridging the gap between macro- and nanotribology is introduced. A friction and/or adhesion induced deflection of a spring is detected using a high-resolution laser interferometer. Unlike force microscopes, where a sharp tip interacts with the surface, this approach allows two plane substrates to be brought into contact. In this way, the exact tribological analysis of microtechnological devices is possible. Since the tester can be operated in air as well as under high vacuum conditions, the environment can be controlled over a wide range. Using this tester, micro-stick/slip phenomena have been investigated as a function of sliding velocity, surface morphology, normal force and contact area. All experiments presented in this paper were carried out on air. This revised version was published online in June 2006 with corrections to the Cover Date.