Lamb波电磁超声换能器三维仿真研究

为提高电磁超声Lamb波换能器的换能效率,该文以铁磁性材料钢板为检测对象,对换能器进行建模并进行一系列的仿真研究。首先,使用Comsol仿真软件建立电磁超声Lamb波换能器仿真模型,对于换能器中的蛇形线圈激励电流参数、蛇形线圈几何及结构参数、方形永磁体几何参数对换能效率的影响进行仿真研究。结果表明,采用蛇形线圈和方形磁铁组成电磁超声Lamb换能器时,在所选参数范围内:对于线圈,增大激励电流幅值、线圈间距及线圈回折次数,减小线圈截面积、提离距离以及脉冲个数可以提高换能效率;对于永磁体,增大宽度和高度可以提高换能器效率,但是最终会趋于饱和状态。     

矩形凹结构转子磁流变阻尼器的设计与优化EI北大核心CSCD

针对传统盘式磁流变阻尼器(magneto-rheological damper,MRD)力矩密度偏低的问题,提出在转子端面构造凹结构以增加有效工作间隙长度,保持结构尺寸紧凑的同时,提高输出力矩密度。分别建立了传统盘式、矩形凹结构和弧形凹结构力矩模型,通过关键尺寸设计和定量对比分析表明,在同等条件下矩形凹结构对提升力矩密度效果更佳。为充分利用矩形凹结构的力矩增益效应,定量地分析了矩形槽位置、槽宽和槽深等关键参数对力矩密度和力矩波动的影响规律,得到了关键参数合理的优化区间。在满足目标设计力矩、线圈功率及确定的参数取值范围前提下,以体积最小为目标函数,对包括矩形凹结构的磁流变阻尼器结构参数进行了优化设计。结果表明,优化后装置力矩密度增幅达23.39%,为矩形凹结构转子阻尼器的实际设计提供了指导。     

双线圈旁置式新型磁流变制动器的设计与优化

为提高传统单线圈混合式磁流变制动器的制动力矩,提出了一种双线圈旁置式新型磁流变制动器.利用一种新的线圈安装方式,增大了制动盘圆柱面的可控作用面积,从而增大了磁流变制动器的制动力矩.基于Herscher-Bulkley模型,提出了双线圈旁置式磁流变制动器的力矩模型与磁路设计方法,并在特定条件下对其进行了多目标优化.研究结果表明:与单线圈混合式相比,在相同体积条件下,双线圈旁置式能产生更大的制动力矩;而为了充分利用磁流变液的流变性能,获得更紧凑的结构,双线圈旁置式磁流变制动器的宽度应在80~100mm之间,长宽比的合理范围应在0.6~1.2之间;优化后在制动器质量基本维持不变的情况下,制动力矩提高了11%.研究结果可作为磁流变制动器的设计参考.     

飞机螺旋桨发动机桨叶力矩平衡测量方法研究

研究了飞机螺旋桨桨叶力矩平衡的测量方法,分析比较了天平力矩平衡测量法和传感器力矩平衡测量法两种测量方法,给出了桨叶力矩平衡测量的要求及两种测量方法的原理并分析了2种方法的优缺点.重点介绍了根据天平力矩平衡测量方法研制的桨叶力矩平衡机的机构和特点,并通过试验验证了天平力矩平衡测量法的可行性.     

汽车非驱动桥轮毂装置设计改进

轮毂装置的启动力矩是评价轮毂装置运转灵活性及寿命的重要指标。为了提高轮毂装置的使用性能,保证轮毂长期稳定可靠无噪音运转,通过对轮毂装置启动力矩的分析,得到影响启动力矩的主要因素为轮毂装置轴承轴向间隙的大小,进一步分析总结得出影响轴承轴向间隙大小的主要因素,并通过对原有轮毂装置的结构进行重新设计改进,取得了良好的效果。     

自激励式电磁铆接铆钉镦头变形试验研究

目的掌握自激励式电磁铆接驱动力的作用方式,确定合理的工艺参数,探究铆钉变形规律。方法以2A10半圆头铆钉为研究对象,通过试验方法研究放电电压、放电电容及线圈结构对线圈放电电流和铆钉镦头变形的影响。结果自激励式电磁铆接驱动力源于两放电线圈电流的相互作用,两放电电流可分别进行独立控制。随着放电电压升高,线圈放电电流幅值增加,周期略有增加,铆钉镦头的变形量增加,相同放电能量下,放电电容值增加使放电电流幅值降低,周期增大,铆钉镦头变形量存在最大值;放电线圈匝数较多,导线宽度较小时,铆钉镦头变形量更大。结论自激励式电磁铆接是一种动力源可控的连接方法,为铆接驱动力的产生引入新方式,实现了铆接驱动力的主动控制,提高了控制的灵活性,其能量利用率较感应式高,为高强度大直径铆钉的成形提供一种有效的方式。铆钉变形是铆接驱动力幅值在一定时间下的作用效果,要综合考虑放电电流幅值与作用时间的关系。     

电动负载模拟系统自适应控制系统设计

为了有效抑制电动负载模拟系统多余力矩,从而提高系统加载力矩的输出精度,设计了一种自适应抑制位置干扰力矩的控制方法。基于前馈控制与自适应控制原理,使用MATLAB仿真软件对该方法的有效性作了分析,并进行了试验验证。仿真与试验结果表明:该方法能自适应调节系统加载误差,且舵机运动频率越高,系统跟踪误差调节时间越长;当加载力矩和舵机运动幅值相同时,舵机运动频率越高,该控制方法对系统多余力矩的抑制效果越明显;当加载力矩和舵机运动频率相同时,舵机运动幅值越大,抑制效果越明显。该控制方法能够在系统部分参数未知或者渐变的情况下,有效抑制系统多余力矩。研究结果对飞行器电动负载模拟器的设计具有一定参考价值。     

聚变反应堆校正场结构优化及性能分析

针对核聚变反应堆校正场线圈的结构进行了优化,确定了满足物理和工程装配的线圈结构。针对校正场线圈进行电磁分析,并得到线圈磁场和电磁力分布。根据广义胡克定律,利用有限元方法将线圈绕组材料属性等效,以简化结构计算模型。通过建立结构分析模型,计算电磁力载荷下的校正场线圈强度,确定了线圈盒厚度,支撑位置及支撑数目。最后为保证校正场线圈始终处于低温工作环境,根据校正场线圈结构和热负载,提出并确定线圈液氦冷却管方案。     

匝间短路故障对永磁同步电机失磁影响的分析与研究

目的 研究不同相带第1匝发生短路故障对永磁电机失磁的影响。方法 利用有限元法, 在对电机的设计参数及绕组结构进行介绍的基础上, 运用ansoft软件建立了永磁电机模型, 并计算了不同故障类型对永磁电机的失磁影响; 提取了不同故障下, 永磁电机短路线圈的电流变化波形和磁密矢量分布图; 从绕组分布的2个不同方面,讨论了不同相带的第1匝发生短路故障时, 去磁磁场的大小、 失磁区域的大小和失磁区域分布之间的关系。结果 失磁区域的大小和分布与短路线圈的空间位置有关。结论 该研究结果可以作为判断短路线圈与永磁体失磁位置的依据, 也为永磁同步电机的设计提供了技术参考。     

力矩激励器功率输出特性

力矩激励器是一种新型传感器 ,用于研究结构声转动自由度的特性。本文利用互功率谱方法对力矩激励器的最大不失真力矩输出功率和相对应的输入电功率进行了测量 ,并计算了其电 力功率转换效率     

Characterization of noise and vibration sources in interior permanent-magnet brushless DC motors

This work characterizes electromagnetic excitation forces in interior permanent-magnet (IPM) brushless direct current (BLDC) motors and investigates their effects on noise and vibration. First, the electromagnetic excitations are classified into three sources: 1) so-called cogging torque, for which we propose an efficient technique of computation that takes into account saturation effects as a function of rotor position; 2) ripples of mutual and reluctance torque, for which we develop an equation to characterize the combination of space harmonics of inductances and flux linkages related to permanent magnets and time harmonics of current; and 3) fluctuation of attractive forces in the radial direction between the stator and rotor, for which we analyze contributions of electric currents as well as permanent magnets by the finite-element method. Then, the paper reports on an experimental investigation of influences of structural dynamic characteristics such as natural frequencies and mode shapes, as well as electromagnetic excitation forces, on noise and vibration in an IPM motor used in washing machines.     

Three-Dimensional Analytical Modeling of Axial-Flux Permanent Magnet Drivers

In this paper, the axial-flux permanent magnet driver is modeled and analyzed in a simple and novel way under three-dimensional cylindrical coordinates. The inherent three-dimensional characteristics of the device are comprehensively considered, and the governing equations are solved by simplifying the boundary conditions. The axial magnetization of the sector-shaped permanent magnets is accurately described in an algebraic form by the parameters, which makes the physical meaning more explicit than the purely mathematical expression in general series forms. The parameters of the Bessel function are determined simply and the magnetic field distribution of permanent magnets and the air-gap is solved. Furthermore, the field solutions are completely analytical, which provides convenience and satisfactory accuracy for modeling a series of electromagnetic performance parameters, such as the axial electromagnetic force density, axial electromagnetic force, and electromagnetic torque. The correctness and accuracy of the analytical models are fully verified by three-dimensional finite element simulations and a 15 kW prototype and the results of calculations, simulations, and experiments under three methods are highly consistent. The influence of several design parameters on magnetic field distribution and performance is studied and discussed. The results indicate that the modeling method proposed in this paper can calculate the magnetic field distribution and performance accurately and rapidly, which affords an important reference for the design and optimization of axial-flux permanent magnet drivers.     

管坯电磁成形时线圈受力的研究

成形线圈设计是电磁成形工艺的关键技术之一,为了有针对性地进行防破设计,提高线圈的使用寿命,采用数值模拟的方法研究了螺线管线圈和阶梯形线圈电磁胀形时的磁场,得到了成形瞬间的磁力线分布和线圈受到的磁压力分布.结果表明:线圈、工件的结构参数和相对安装位置对线圈的磁压力分布影响很大;将受力分布引入成形线圈设计,有效地提高了工艺实验中线圈的使用寿命.     

厚膜永磁阵列微致动器的磁路研究

研究了厚膜永磁阵列微致动器中的磁场分布，并研究了永磁阵列单元几何尺寸对微致动器电磁力的影响。结果表明，厚膜永磁阵列单元高宽比和磁体单元间隔对微致动器电磁力影响较大磁徕单元高宽比为0．7是一个比较合适的尺寸。     

Optimal realization of arbitrary forces in a magnetic stereotaxissystem

Very small implanted permanent magnets guided by large electromagnetic coils have been proposed previously as a method for delivering hyperthermia to or guiding catheters through brain tissue. This procedure is termed “magnetic stereotaxis”. Early efforts employed a single coil on a movable boom, a design that proved logistically difficult to use on human patients. The present work deals instead with a design where several stationary coils are employed to develop a force on the implanted magnet. The coil current-to-force relationship is developed for this type of machine, and several optimal solutions for realizing an arbitrary static force are presented for various constraints on the orientation of the implanted permanent magnet. Costs of the different solutions are compared in several examples using a mathematical model based on the Magnetic Stereotaxis System (MSS) developed by Stereotaxis, Inc., the University of Virginia, and Wang NMR     

Finite element solution of permanent magnetic field

Currently available CAD (computer-aided design) systems on electromagnetics use the technique of shifting a known demagnetization curve of the second quadrant to the origin and introduce a suitable current-carrying coil for modelling permanent magnets. A test of the validity of this technique is reported that was based on the simulation of a rotating magnetobase. The behavior of the torque of a permanent magnet with its rotation has been calculated using the technique and compared to experimental results. The comparison confirms the validity of this technique     

Electromagnetic Analysis of the ITER Upper VS Coil

In order to control the plasma vertical stability of ITER, a novel magnet is developed, that is the vertical stability coil. The coil is located in the vacuum vessel and its safe operation is very important for ITER’s reliable working. During the normal operation, the coil should bear the electromagnetic force caused by the external superconducting magnet and plasma current. The electromagnetic load is one of the important factors to affect the lifetime of the VS coil. Therefore, it is necessary to calculate the magnetic field and evaluate the structural reliability under the electromagnetic load. In this paper, the current at the time “end of burn” was selected to perform the electromagnetic calculation. Based on the Maxwell equation, the magnetic field on the cross section of the upper VS coil was computed and the maximum electromagnetic force corresponding to the magnetic field was also presented. In order to verify the current design model, the finite element model was created by use of ANSYS. The Tresca stress was extracted and classified based on analytical design. The peak stress was compared with the ASME criteria. The analysis has verified the physical model from the perspective of electromagnetic load, and it will offer a guidance for the future optimization.     

Characterization of a magnetic field sensor based on torquemeasuring [for fusion diagnostics application]

A sensor for low-frequency measurements of the magnetic field is presented in the paper. It is based on measurements of an electromagnetic torque. An output directly proportional to the unknown magnetic field is produced. This method has the main advantage of avoiding the drift present in the integration of signals from inductive sensors. The design and construction criteria, aiming at an uncertainty of a few milliteslas in field measuring, are described. The analysis of the sensor linearity is presented in the paper together with the test rig, able to guarantee reproducible conditions. The dynamic behavior of the torque-based sensor is considered. It is studied either on the basis of the coil and load cell characteristics or analyzing the response to an applied known electromagnetic torque     

Magnetic Field Created by Tile Permanent Magnets

This paper presents an analytical calculation of the three components of the magnetic field created by tile permanent magnets whose magnetization is either radial or axial. The calculations are based on the Coulombian model of permanent magnets. The magnetic field is directly calculated, without the magnetic potential. Both axial and radial magnetization of the tiles are considered. The expressions obtained give the magnetic field in all the space. Such analytical expressions are very useful for the design and optimization of many industrial applications.      

Analytical Solution for Electromagnetic Torque in Surface Permanent-Magnet Motors Using Conformal Mapping

We present an analytical method for the calculation of electromagnetic torque in surface permanent-magnet (PM) motors. Our method uses conformal mapping to calculate the electromagnetic torque by integrating the Maxwell stress tensor inside the air gap. It uses the radial and tangential components of the flux density in the slotted air-gap produced by the currents flowing in the three-phase armature winding. We demonstrate our analytical solution on a 7-kW four-pole surface PM motor and compare the results with finite-element solutions. We present the results for various angular spans of permanent magnets and various sizes of the slot opening to confirm the validity of the analytical approach.