Science Letters: A current-differential-based method for improving dynamic characteristics of electromagnetic actuators

ontrol method is applied to a real gravure system which verifies the control performance.     

Discussion on dynamic reliability tolerance design technology of electromagnetic relay

Reliability tolerance design of electromagnetic relay during its design period plays an essential role in guaranteeing the consistencies of reliability and output characteristic. The reliability tolerance design can ensure that the products would work well under the influence of disturbing factors (including internal interference, external interference, and machining dispersion). Com- pared with static characteristic, dynamic characteristic of electromagnetic relay can describe its operating process better. This article researches influence of the three kinds of disturbing factors on the dynamic characteristic of electromagnetic relay based on calculating dynamic characteristic. Then, the dynamic reliability tolerance design method of electromagnetic relay is discussed considering three kinds of disturbing factors. Conclusions reached can help to assure the reliability of electromagnetic relay from the beginning of design.     

单层压电弯曲微执行器的非线性静态特性

采用偶应力理论对单层压电悬臂梁式微执行器在强外加电场作用下的非线性静态特征进行了研究.悬臂式执行器包括压电层、被动（弹性）层和2个电极层.首先,采用瑞利-里兹方法分析了在强外加电场作用下由于压电层电致伸缩效应引起的执行器非线性静态特性.其次,由于悬臂执行器的厚度在μm量级,存在变形尺度效应,采用偶应力理论对变形的尺度效应进行了分析.分析结果表明：悬臂执行器的非线性随着外加电场强度的增大而增大,当外加电场很大时,出现刚度软化现象;而且,执行器被动层和压电层厚度比的最优值不是通常采用的1.0.在微尺度下,由于微梁变形存在尺度效应,该厚度比的最优值应比1.0大.     

A novel dynamic equivalence method for grid-connected wind farm

Dynamic equivalence of the wind farm is a fundamental problem in the simulation of a power system connected with wind farms because it is unpractical to model every generator in a wind farm in detail. In this paper, an Equivalence Method based on the Output Characteristics （EMOC） is proposed, with which the wind farm composed of Squirrel-Cage Induction Generators （SCIGs） can be equivalent to one generator. By considering the diversity of wind generators and special operating characteristics of a wind farm, the equivalent generator based on EMOC responds accurately in various faults. No matter whether the wind farm is integrated in grid or just programmed, EMOC can be used to acquire an accurate equivalent generator. Simulation of the dynamic equivalence of an SCIG wind farm validated the method.     

Parameter effects on the dynamic characteristics of a super-long-span triple-tower suspension bridge

A 3D finite element model for the Taizhou Yangtze River Bridge, the first triple-tower long-span suspension bridge in China, is established based on the nonlinear finite element software ABAQUS, and the dynamic characteristics of the bridge are analyzed using the LANCZOS eigenvalue solution method. The study focuses on the effects of the vertical, lateral and torsional stiffness of the steel box girder, the rigid central buckle and the elastic restraints connecting the towers and the steel box girder on the dynamic characteristics of the triple-tower suspension bridge. Our results show that, in general, the dynamic characteristics of the triple-tower suspension bridge are similar to those of two-tower suspension bridges. The vertical, lateral and torsional stiffness of the steel box girder have different effects on the dynamic characteristics of triple-tower suspension bridges. The elastic restraints have a more significant effect on the dynamic characteristics than the central buckle, and decreasing the stiffness of the elastic restraints results in the appearance of a longitudinal floating vibration mode of the bridge. Also, rigid central buckles have a greater influence on the dynamic characteristics of triple-tower suspension bridges than on those of two-tower suspension bridges. The results obtained could serve as a valuable numerical reference for analyzing and designing super-long-span triple- tower suspension bridges.     

调心球轴承动态特性参数分析

基于Jones-Harris方法建立了调心球轴承的动力学模型,应用Newton-Raphson方法对轴承动力学方程组进行了求解,开发了相应的计算程序.完成了该轴承的离心力、陀螺力矩、接触载荷、接触角、径向变形与径向刚度等动态特性参数分析.分析结果表明：转速与载荷是影响接触角大小与接触载荷分布最主要的2个因素;滚子的离心力与陀螺力矩随着转速的上升而增大,在此影响下外圈接触载荷增大而内圈接触载荷减小;受离心力的影响,外圈的接触角减小而内圈的接触角增大,且随着转速的增加,内外圈接触角的差值越来越大;轴承的径向刚度随着转速的上升而下降,而滚道沟曲率系数也对轴承径向刚度有一定程度的影响.     

Structural dynamic responses analysis applying differential quadrature method

INTRODUCTION The differential quadrature method (DQM) was proposed by Bellman and Casti as an analogous ex- tension of the quadrature method for integrals (Bellman and Casti, 1971; Bellman et al., 1972). It can be essentially expressed as the values of the de- rivatives at each grid point as weighted linear sums approximately of the function values at all grid points within the domain under consideration. As a distinct numerical solution technique to obtain the initial and/or boundary …     

Three-step damage identification method based on dynamic characteristics

A three-step damage identification method based on dynamic characteristics is proposed to improve the structure reliability and security and avoid serious accident. In the proposed method, the frequency and difference of modal curvature （DMC） are used as damage indexes. Firstly, the detection of the occurrence of damage is addressed by the frequency or the square of frequency change. Then the damage location inside the structure is measured by the DMC. Finally, with the stiffness reduction rate as a damage factor, the amount of damage is estimated by the optimization algorithm. The three-step damage identification method has been validated by conducting the simulation on a cantilever beam and the shaking table test on a submerged bridge. The results show that the method proposed in this paper can effectively solve the damage identification problem in theory and engineering practice.     

Birkhoff系统积分的新方法

将Vujanovi(c)提出的用于积分完整非保守系统动力学方程的梯度法思想移植到Bitkho行系统,给出了Birkhoff系统积分的一种新方法.首先,列写出Birkhoff系统的运动微分方程;其次,将2n个Birkhoff变量分成2部分,并假设其中一部分变量是其余变量及时间的函数,由此建立拟线性的基本偏微分方程组;如果...     

Method of analyzing vibration characteristics of armature system of hermetically sealed electromagnetic relay

Published research is minimal on vibration characteristics of hermetically sealed electromagnetic relay (EMR) ex- posed to mechanical environment. The vibration characteristics of armature system, link contact system with electromagnetic system will cause EMR malfunction. The nonlinear dynamics model of armature systems was studied by considering electro- magnetic attraction force and opposite mechanical force in this paper. Angular displacements of armature under different sinu- soidal vibration conditions are solved in order to obtain the failure mode result from armature system. Vibration tests showed the presented analyzing method is suitable for EMR. The conclusions are instructive for increasing vibration resistance of armature systems of EMR, and are significant for reliability design of switch apparatus.     

关于两电流元相互作用不满足牛顿第三定律的解释

本文论证了两个电流元之间相互作用不满足牛顿第三定律只是电流元的机械动量不守恒,若将电磁动量的变化考虑进去,则两电流元体系的总动量守恒。     

Research on electromagnetic relay＇s dynamic characteristics disturbed by uniform static magnetic field

Electromagnetic relay is a widely used apparatus which usually works in a magnetic disturbance environment. To evaluate its electromagnetic compatibility （EMC） in a static magnetic field, dynamic characteristics of a clapper relay in a uniform static magnetic field situation based on the finite element method （FEM） is studied. Influences of the magnetic field on dynamic parameters （delay time, pick-up time, end pressure, and final velocity） as well as a situation in which the relay cannot function normally are analyzed. Simulation reveals that the external magnetic field which weakens the relay＇s air-gap field has a greater influence on the relay＇s dynamic parameters than the one strengthening the field. The validity of the simulation is verified by measured results of coil current and armature displacement.     

表面棱边单元法求解三维电磁场问题

提出了表面棱边单元方法并应用它求解任意形状物体的三维电磁场散色问题.首先根据物体剖分得出表面区域的几何特性,推导出表面棱边单元法的基本公式.该方法保持了普通棱边单元法的基本特性,维持变量的切向分量连续.然后用复合积分方程来模拟普通介质的电磁场散色问题,应用所提出的方法离散积分方程,并且对奇点问题采用特殊的处理方法.最后用该方法计算圆柱体以及四方体的在不同介质条件下的电磁场散色问题,对所得的数值解进行测试,并与其他数值方法解相比较,结果表明该方法行之有效.     

一种可以预设定输出电流的开关电源设计

目前,绝大多数开关电源的共性通常是具有恒压输出功能,也就是人们常说的稳压电源．然而,对一些大功率的设备,不但要求有稳定的输出电压,还要求有稳定的输出电流．同时这个稳定的输出电流值还要求能预先设定．这一种可以预设定输出电流的开关电源,在现有开关电源的基础上增加了单片机闭环控制系统,使得它可以应用在一些既需要稳定的输出电压,又需要稳定的输出电流的系统上．解决目前大部分开关电源因负载变化,造成开关电源停止工作,影响用电设备正常工作的问题．     

Effect of concrete cracks on dynamic characteristics of powerhouse for giant-scale hydrostation

With the increase of capacity and size of the hydro-generator unit, the spiral case becomes a more super-giant hydraulic structure with very high HD value, where H and D denote water head and maximum intake diameter of spiral case, respectively. Due to the induced lower stiffness by the more giant size and adverse operation conditions, dynamic performances of the powerhouse and the supporting structure for the giant units have become more important and attracted much attention. If the manner of steel spiral case embedded directly in concrete is adopted, on some locations of the concrete surrounding the spiral case, distributed and concentrated cracks will emerge due to high tensile stress. Although the concrete is reinforced well to control the maximum crack width, definitely these cracks will reduce the local and entire stiffness of the powerhouse. Under dynamic loads such as hydraulic forces including water pressure pulsation in flow passage acting on the structure, effect of the cracks on the dynamic characteristics of the local members and entire structure needs to be evaluated. However, research on this subject is few in hydroelectric engineering. In this paper, Three-Gorge Project was taken as an example to evaluate effect of such cracks on natural frequencies and the vibration responses of the powerhouse under hydraulic and earthquake forces in detail. Results show that cracks only reduce the local structural stiffness greatly but have little effect on the entire powerhouse especially the superstructure; vibrations of powerhouse with cracks in concrete surrounding the spiral case are still under the design limits. Results in this paper have been verified by practice of Three-Gorge Project. Supported by National Natural Science Foundation of China (No.50679009) and Foundations for Young Teachers in Dalian University of Technology(No.893219). TIAN Ziqin, born in 1965, male, doctoral student, senior engineer.     

负反馈放大电路活动态特性的两种计算法

本文介绍两种变换法即电路等效变换法、方块图变换法,用以计算负反馈放大电路的动态特性,并举例说明.     

A framework of region-based dynamic image fusion

INTRODUCTION Image fusion is a sub-area of more general topics of Information Fusion and Data Fusion and deals with static images and dynamic images (image sequences or video data) (Maitre and Bloch, 1997). By com-bining the information from a range of image data obtained by different sensors or the same sensor with different imaging schemes, the composite image al-ways presents the complementary information of different input images at the same time and provides us the integrated descr…     

质子交换膜燃料电池的动态特性仿真实验方法的研究

该文发展了一种基于MATLAB和VB软件包的质子交换膜燃料电池（PEMFC）的动态特性仿真实验方法。主要介绍了动态仿真实验方法的建模、软件设计方法和人机界面构成。仿真实验结果表明，该仿真实验方法可以满足PEMFC动态特性参数仿真实验的要求，为PEMFC动态特性的实验教学与演示提供了一种有效而廉价的实验方法。     

一类均匀介质腔体模型电磁散射问题的快速求解算法

针对矩形腔体模型的散射问题,基于双线性元离散,提出了一种有效的快速求解算法.通过傅里叶变换和高斯消去法将离散方程简化为维数较低的界面方程,对界面方程给出了一个有效的预处理子空间迭代法,数值试验说明了算法的有效性.     

二阶延迟微分方程Runge-Kutta方法的稳定性

研究二阶延迟微分方程Runge-Kutta方法的稳定性.首先,引入新变量,将二阶延迟微分方程化为一阶方程组.然后,应用Runge-Kuta 方法于一阶方程组,给出了Runge-Kutta稳定的充分条件,进而得到了二阶延迟微分方程Runge-Kutta方法稳定的充分条件.最后,通过数值试验验证所得结论的正确性.