Shear Stress in MR Fluid with Small Shear Deformation in Bctlattic Structure

A theoretical model based on BCT lattice structure was developed. Resultant force in the BCT lattice structure was deduced, following the interaction force of two kinds of magnetic particles. According to empirical FroHlich-Kermelly law, the relationship between the magnetic induction and the magnetic field was discussed, and a predictive formula of shear stresses of the BCT lattice structure model was established for the case of small shear deformation. Compared with the experimental data for different particle volume fractions, the theoretical results of the shear stress indicate the effects of the saturation magnetization and the external magnetic field on the shear stress.

一种新型剪切阀式旋转MR制动器的开发与评估

基于磁流变(Magnetorheological,MR)液的流变特性,MR制动器具有的高转矩-体积比(Torque-to-Volume Ratio,TVR)和低功耗优点使其成为一种应用前景广泛的被动力输出装置。为了提高旋转型MR制动器在单位空间内的输出制动转矩,基于凸轮结构提出了一种在剪切阀模式下工作的旋转型MR制动器。首先,介绍了这种新型MR制动器的总体结构,并基于Bingham塑性模型和凸轮模型对MR制动器的输出制动转矩进行了理论推导。然后,利用ANSYS软件和多目标优化设计方法,对制动器的结构进行有限元分析,得到最优的几何参数。在自主搭建的实验平台上对制动器进行了性能测试实验,结果表明,该制动器具有较高的TVR、较低的初始制动转矩和良好的动态特性。该制动器在较小的体积下能够实现最大42.4 kN/m^(2)的TVR,可以很好地满足力触觉交互、康复训练、可穿戴设备等需要小体积和大输出转矩的应用场景。

Acoustic Modeling of a 3-Layered Panel Incorporating Electro-Rheological/ Magneto-Rheological (EMR) Fluids

Applications of Electro-Rheological (ER) or Magneto-Rheological (MR) fluids as typical smart materials have been widely investigated over the past decades (since their introduction in 40’s). The special applications of these materials as a means of noise suppression are not yet investigated. Constrained Layer Damping (CLD) sheets can be realized by incorporating EMR (ER/MR) materials. In this way, a multilayered damping sheet is obtained with adaptive (tunable) stiffness and damping characteristics. These properties are easily changed in proportion to the electric (magnetic) field applied upon the EMR layer. This notion has been introduced for semi-active vibration control problems. Herein, such panels incorporating EMR material are proposed for adaptive acoustic treatments. Modeling (simulation) of a 3-layered panel with the middle layer being EMR with adjustable properties is carried out in this paper. The tunability of transmission/absorption characteristics of these composite sheets enables us making smart panels for adaptive noise and acoustic treatments. An adaptive performance can be achieved via changing the properties of such panels, on line, according to some sensor outputs. The main objective is to develop proper models to predict the Transmission Loss (TL) of such panels. Also, the TL of this panel is compared with the middle layer of a Newtonian fluid.

基于磁流变阻尼器的滚珠丝杠进给系统主动抑振研究

针对滚珠丝杠进给系统轴向振动影响工件的加工质量和精度保持性的问题,将磁流变阻尼器应用于机床滚珠丝杠进给系统轴向抑振。设计磁流变阻尼器,进行磁流变阻尼器阻尼特性试验,采用最小二乘法和BP神经网络对阻尼力进行了辨识。建立带有磁流变阻尼器的机床滚珠丝杠进给系统单自由度振动模型,基于Runge-Kutta法计算了系统的动态响应。通过数值计算发现:阻尼器输入电流由零逐渐增大时,系统能够快速趋向于稳定;由幅频曲线可以看出,磁流变阻尼器抑制滚珠丝杠进给系统的振动是可行的。最后试验验证了磁流变阻尼器能够很好地抑制滚珠丝杠进给系统的振动。

MR阻尼器控制与滞环特性相分离的F-v模型

提出了一种基于对称和不对称Sigmoid函数,描述半主动可控磁流变液(MR)阻尼器阻尼力一相对速度(F-v)数学模型。该模型准确地描述了MR阻尼器非线性饱和的直流电流控制和对称滞环F-v的工作特性,以及激励频率和幅度对阻尼力的强影响特性,具有精度高和电流控制增益与滞环算子相分离的特点。将该模型与车辆悬架动力学模型结合分析,仿真结果表明MR阻尼器对实现新一代智能车辆悬架系统设计有潜在的意义,所提出的模型对进一步推动车辆悬架减振控制器设计研究有重要作用。

MR脑脊液成像技术及其对颅内中线病变诊断的作用

目的:探讨MR脑脊液成像技术及其对颅中线病变的诊断作用。材料和方法:对160人次行颅内MR脑脊液成像技术,用3DMIP重建图像。结果:84例正常人MR脑脊液成像显示脑脊液呈均匀高信号,脑实质呈均匀低信号;脑脊液从侧脑室、第三脑室、导水管、第四脑室经正中孔至枕大池,形成一个连续完整的脑室系统造影图像。76例异常患者中,8例显示出常规T2WI图像不易显示的细节。1例阻塞性脑积水患者,MR脑脊液成像清楚显示梗阻原因为中脑导水管的局部粘连闭塞。2例脑室内肿瘤,1例延髓胶质母细胞瘤压迫四脑室,MR脑脊液成像可清楚显示病变的部位和范围。MR脑脊液成像还可帮助鞍区及颅后窝肿瘤进一步定位诊断。结论:MR脑脊液成像是一种新的无创伤,快捷的成像技术。对脑室系统疾病和脑脊液循环异常的疾病给予了直观明确的影像学资料,具有良好的临床应用前景。

Analysis and Design of Cylindrical Magnetorheological Fluid Brake

Magnetorheological (MR) fluids consist of stable suspensions of magnetic particles in a carrying fluid such as water or silicone oils. The magnetorheological response of MR fluids results from the polarization induced in suspended particles by application of an external magnetic field. The interaction between the induced dipoles causes the particles to form columnar structure, parallel to the applied field. These chain-like structures restrict the motion of fluids, thereby increasing the viscosity and yield stress of the MR fluids. These mechanical characteristics allow for the construction of magnetically controlled device such as the MR fluids rotary brakes. However, there has been little information published about the design of MR fluid brakes. In this paper the design of the cylindrical MR fluid brake is investigated theoretically. Bingham model is used to characterize the constitutive behaviors of the MR fluids subject to an external magnetic field. The operational principle of the cylindrical MR fluid brake is presented. The theoretical method is developed to analyze the transmission properties of the torque of the cylindrical MR fluid brake. An engineering expression for the torque is derived to provide the theoretical foundations in the design of the cylindrical MR fluid brake. Based on this equation the volume and thickness of the annular MR fluids within the brake is expressed as functions of the desired ratio of torques with saturated magnetic field and without external field, the controlled mechanical power and the MR fluid material properties. The parameters of the thickness and width of the fluid in the brake can be calculated from the obtained equations when the required mechanical power level, the desired torque ratio are specified.

交通性脑积水脑室分流前后的脑脊液MRI定量研究

目的:运用 MRI cine PC定量研究交通性脑积水脑室分流前后的脑脊液流动情况。材料和方法:在1.5T GEHorizon Signa磁共振机器上利用MRI cine PC程序,在以前实验所得的液体流速与信号强度关系公式的基础上,对16例交通性脑积水的中脑导水管、枕大孔和C2水平脑脊液流速、流量情况进行MRI cine PC检查(1.5TGE Horizon Signa),并对其中10例交通性脑积水脑室引流后的中脑导水管和枕大孔处脑脊液的流速和流量同样进行测量,并与术前进行比较。同时作为对照,对31例正常志愿者颅内中脑导水管、枕大孔和C2水平的脑脊液流速和流量进行测定。结果:交通性脑积水中脑导水管水平脑脊液流速和流量明显增快,与正常者进行统计有明显差异(P<0.05),向下峰速和向上峰速分别为47.57±16.71mm/s和44.48±19.22mm/s,向下流量及向上流量明显增大为3.142±1.055ml/s及3.143±1.055ml/s;脑脊液净流量为0±0.003ml/s。而枕大孔向下峰速和向上峰速分别为1.37±0.44mm/s和1.33±0.41mm/s,向下流量及向上流量分别为0.351±0.125ml/s及0.350±0.12lml/s;脑脊液净流量为0.001±0.007ml/s。C2水平脑脊液向下峰速和向上峰速分别为2.41±1.27mm/s和2.95±1.15mm/s,向下流量及向上流量分别为0.521±0.214ml/s和0.519±0.214ml/s;

基于BP和HBP流变模型的磁流变阻尼器数值模拟与性能分析

针对传统本构模型表达磁流变液的流变特性精度不高的问题,采用MCR302流变仪对磁流变液的流变特性进行测试,获得了不同磁场下剪切应力与剪切速率之间的关系。利用遗传算法对Bingham-Papanastasiou(BP)模型和Herschel-Bulkley-Papanastasiou(HBP)模型进行参数辨识。利用辨识结果建立了仿真模型,对磁流变阻尼器的动态特性进行数值模拟。设计并加工了磁流变阻尼器,搭建了阻尼力测试平台进行阻尼力测试实验,并将实验结果与仿真结果进行对比。结果表明:HBP模型对磁流变液流变特性的辨识结果与实验结果吻合较好;2个模型对阻尼器动态特性的预测结果相差较大,仅对流速的预测一致性较好;基于HBP模型的阻尼力预测值与实验值较吻合。所提出的HBP模型表达磁流变液流变特性的精度较高,具有良好的实用价值。研究结果可以为振动控制领域磁流变阻尼器力学模型的选择提供参考。

内外液流通道筒式磁流变制动器制动性能分析

针对传统磁流变制动器磁场利用率不高的问题,提出了一种具有内外液通道的筒式磁流变制动器;通过在缸筒和旋转套筒中增设非磁性器件,使得磁力线蜿蜒通过内外轴向液流通道的6段有效阻尼间隙,从而使该制动器在外形尺寸不变的前提下能产生较好的转矩性能;阐述了内外液流通道筒式磁流变制动器的结构和工作原理,并对有效阻尼间隙在磁场作用下的磁路进行分析;同时推导建立了制动转矩和温度场数学模型;基于COMSOL软件对磁流变制动器电磁场和温度场进行了仿真分析。由电磁场仿真可知,在外加电流为2.0 A、转速400 r/min时,制动转矩可达101.96 N·m,转矩动态可调范围由1.00增加至29.69;由温度场仿真可知,在多次紧急制动下最高温度为42.88℃,符合磁流变液正常工作范围。

新型核磁共振测井仪MR Scanner性能及其应用

斯伦贝谢公司2006年新推出了核磁共振测井仪器MR Scanner,该仪器采用偏心梯度设计,具有提供多种探测深度、测量结果不受井眼条件的影响、能进行流体表征等特点。在低阻、低对比度储层的评价中具有较大优势。文章对MR Scanner仪器的结构、特点、规格及技术指标进行了介绍,列举了其优点以及应用效果。

MR阻尼器在振动系统中的最优位置

给出了一个在振动系统中放置磁流变阻尼器的有效方法.利用虚拟阻尼器,放在结构感兴趣的位置,可以计算出虚拟阻尼器所消耗的功率值,根据虚拟阻尼器在振动系统中不同点所消耗的功率数值,讨论了寻找放置阻尼器最佳位置的方法.为了说明这种方法的有效性,用Newmark方法进行数值积分,求得节点的响应,计算了含有MR(magneorheological fluid)阻尼器的车架结构,结果说明所提供的方法和寻找准则是正确的和有效的.

低场MR T2 FLAIR序列在轻微脑外伤中的诊断价值

目的探讨低场MR T2 FLAIR序列在轻微脑外伤中的诊断价值。方法对120例轻微脑外伤患者分别进行CT、常规T2 FRFSE、T1 FLAIR序列扫描并加扫T2 FLAIR序列。结果 CT平扫发现阳性病灶143个,MR常规T2WI+T1WI像发现阳性病灶118个,加扫T2 FLAIR序列后阳性病灶为176个。结论低场MR加扫T2FLAIR序列能清楚显示病灶及其范围和大小,并可增加轻微脑外伤的病灶检出率,减少漏诊。

基于遗传算法的MR减振器多目标优化设计

作为车辆半主动悬架系统中的关键元件,磁流变减振器既需要良好的动力学特性,又需要良好的系统响应和低功耗特性,但目前大多数设计仅仅以其中某一项为目标,很难得到综合性能满足要求的磁流变减振器。笔者综合考虑了MR减振器实车应用中对动力性能、响应速度及能耗的要求,提出了基于遗传算法的多目标优化设计方法,并讨论了MR减振器励磁电流和线圈匝数对响应时间和能耗的影响。参考捷达轿车后减振器的要求,应用多目标设计方法设计、制造了一款MR减振器样品,并进行了台架试验。试验结果与设计目标能较好的吻合,证明该设计方法是正确有效的。

圆盘式MRF离合器的研究

磁流变液离合器是一种利用磁流变液剪切应力来进行离合的一种装置,它传递的力矩随外加磁场的变化迅速变化。本文在理论上给出了盘式磁流变液离合器的设计方法,推出了磁流变液离合器传递力矩的方程,得出了盘式磁流变液离合器中磁流变液体积、厚度等的计算公式。为盘式磁流变液离合器的设计奠定了理论基础。

Friction Behavior of Magnetorheological Fluids with Different Material Types and Magnetic Field Strength

Magnetorheological （MR） fluid is a type of a smart material that can control its mechanical properties under a magnetic field. Iron particles in MR fluid form chain structures in the direction of an applied magnetic field, which is known as MR effect, resulting in variation of stiffness, shear modulus, damping and tribological characteristics of MR fluid. As MR effect depends on the density of particles in the fluid or the strength of a magnetic field, the experiments are conducted to evaluate the friction property under reciprocating motion by changing the types of MR fluid and the strength of a magnetic field. The material of aluminum, brass, and steel are chosen for specimen as they are the most common material in mechanical applications. The surfaces of specimen are also observed by optical microscope before and after experiments to compare the surfaces with test conditions. The comparing results show that the friction coefficient increases as the strength of a magnetic field increases in regardless of types of MR fluid or the material. Also the density of particle in MR fluid affects the friction characteristic. The results from this research can be used to improve the performance of mechanical applications using MR fluid.

FLAIR序列在高场强颅脑MR的应用价值

目的 :通过对头颅液体衰减反转恢复序列的应用研究 ,了解其特点及临床价值。方法 :本组 32例经FLAIR序列及常规SE序列扫描的病例进行对比分析 ,并讨论了FLAIR序列的原理、特点及应用价值。结果 :在FLAIR序列显示的 81个病灶中 ,常规SE序列只显示 6 6个病灶 ,FLAIR序列在显示脑室内、脑室旁及脑灰质区病灶方面优于常规SE序列。结论 :FLAIR序列在特定部位病变显示方面更敏感 ,有很高的临床使用价值。

Fractional Modeling and Analysis of Coupled MR Damping System

The coupled magnetorheological (MR) damping system addressed in this paper contains rubber spring and magnetorheological damper. The device inherits the damping merits of both the rubber spring and the magnetorheological damper. Here a fractional-order constitutive equation is introduced to study the viscoelasticity of the combined damper. An introduction to the definitions of fractional calculus, and the transfer function representation of a fractional-order system are given. The fractional-order system model of a magnetorheological vibration platform is set up using fractional calculus, and the function of displacement is presented. It is indicated that the fractional-order constitutive equation and the transfer function are feasible and effective means for investigating of magnetorheological vibration device. © 2014 Chinese Association of Automation.

A Novel Shear Mode MR Damper and Its Mechanical Performance

This paper presents a linear shear mod magneto-rheological(MR) damper which can be applied to vibration control system.The proposed MR damper featured by a small amount of MR fluid,absence of a gas chamber or diaphragm and piston with helix slotted.Because of the absence of a gas chamber or diaphragm,unnecessary damping force caused by gas compression is not generated.Magnitude and damping coefficient of damping force are two important indexes to evaluate performance of MR damper.The piston with helix slotted is developed based on mechanical analysis on rheological characteristics of MR damper,and the damping performance of MR damper with helix slotted piston is investigated through performance experiments and comparison with analytical simulation.The results indicate that helix slot may increase friction coefficient on surface of the piston,and improve the maximum damping force without reducing damping coefficient of the damper.The reflux of MR fluid may be increased by adjusting helix angle suitably,which avoids the settlement of MR fluid.

GENERATION OF ASYMMETRIC F-v CHARACTERISTICS FOR SYMMETRIC MR DAMPERS

An asymmetric damping force generation algorithm is originally proposed to yield the asymmetric force-velocity characteristics for the symmetric magneto-rheological （MR） dampers. The command current is formulated in an asymmetric manner to excite the symmetric MR dampers by employing the “on-off” control law in response to the direction of velocity, and a smooth modulation function is developed without phase shift to suppress strong transients in the damping forces caused by the current-switching discontinuity. The effectiveness of the proposed algorithm is evaluated by analyzing the dynamic responses of a quarter-vehicle suspension system with a symmetric MR-damper by modulating the command current into the asymmetric manner. The simulation results show that the proposed algorithm could achieve a better compromise between the conflicting requirements of the asymmetric damping force ratio and the force-velocity curve smoothness, and the asymmetric damping MR-suspension design can ideally improve the road holding and ride performances of vehicle motion. The proposed algorithm can be generally incorporated with a controller synthesis to realize an intelligent vehicle suspension design with the symmetric MR dampers.