无磁场下磁流变液的温度特性及其幂律模型参数识别

磁流变液稳定工作的温度范围为-50~150℃,磁流变器件在工作过程中会发热,特别是连续高冲击工作情况下会严重发热,从而超出磁流变液稳定工作温度范围,影响磁流变器件工作的可靠性。针对美国Load公司的MRF132磁流变液,研究了不同温度下剪切应力与表观粘度随剪切速率的变化,并利用Origin软件分别对不同温度下磁流变液剪切速率与剪切应力进行幂律模型曲线拟合和参数识别。研究表明,幂率模型能够较好地描述零磁场下磁流变液的力学特性,不同温度下对于所有的流动指数n都满足n<1,表明不同温度下磁流变液具有剪切稀化特性,此特性符合粘度特性曲线,该工作对磁流变液温度特性的深入研究提供理论依据。     

磁流变液离合器离心力特性研究

以圆盘式磁流变液离合器为例,介绍了磁流变液离合器的工作原理,用Bingham模型描述了磁流变液随外加磁场变化的流变特性;对离心力进行模型描述,由于离心力的作用引入无量纲的特性参数,分析了特性参数与其它变量间的关系,在此基础上分析了不同变量参数对磁流变液稳定性的影响;建立了磁流变液离合器转矩与体积分数分布曲线斜率关系的数学模型,指出提高输出转矩的方法,为磁流变液离合器的设计提供理论参考.     

磁流变液的可控电气特性研究

为了研究磁流变液的可控电气特性,以微米级羰基铁粉为分散相、油酸为表面活性剂制备了一种磁流变液。将自制磁流变液电阻器置于可控磁场中,研究了磁流变液电阻随磁场及时间的变化。结果表明,当没有外加磁场时,电阻器电阻大于500M?,表现为绝缘体的特性。随外加磁场逐渐变大,电阻值开始迅速减小至200?以下后趋于稳定。随着外磁场的变化,电阻值可实现可控调节。磁流变液的这种高阻态到低阻态的转变类似电路开关的开启与断开状态,为研究磁流变液的可控电气特性提供了依据。     

多环槽式磁流变阻尼器阻尼力建模及实验分析

介绍了自行设计的多环槽式磁流变阻尼器的结构和工作原理,提出了关于磁流变液的线性粘滞环阻尼力模型,并给出模型中参数的确定方法。通过液压激励试验台系统测试了磁流变阻尼器在不同电流、输入激励下的阻尼力-速度、阻尼力-位移特性。结果表明,在不同的输入电流及输入激励下,该模型都能较好地反映磁流变液的滞回特性,与阻尼器实验数据有较好的拟合精度。线性的力学模型方便计算与控制研究,为磁流变液阻尼器在半主动控制中的应用研究提供指导。     

磁流变液的耐久性及其影响因素研究进展

磁流变液的耐久性是影响磁流变智能减振技术商业化应用的关键因素。对近年国外磁流变液的耐久性研究概况进行了简要综述,主要包括磁流变液的耐久性及失效形式、耐久性研究方法及机理分析、铁磁相和添加剂对耐久性的影响、耐久性磁流变液在高能环境的应用。     

非均匀磁场下磁流变液剪切屈服应力的温度特性

利用自行研制的非均匀复合场(温度、磁场)下磁流变液剪切屈服应力实验装置,测试、研究了非均匀磁场、不同剪切速率下磁流变液剪切屈服应力的温度特性。结果表明,磁流变液在17~150℃温度范围内粘度温度性能稳定,剪切屈服应力-温度特性曲线在17℃和150℃时发生突变:在低于17℃时剪切屈服应力随着温度的上升而下降,17~150℃温度范围内剪切屈服应力近似不变,温度超过150℃时,磁流变液的剪切屈服应力随温度的升高而下降。     

高性能磁流变液及其在阻尼器上的应用

磁流变液(Magneto Rheological Fluid, MRF)是近半个世纪前出现并发展至今的一种新型智能材料，通常由微米级磁性颗粒、基载液、添加剂三部分组成，未施加磁场时呈现出液体的自由流动状态，施加磁场时可在毫秒级时间内转换为具有类固态相的结构。目前众多磁流变液的流变特性、分散稳定性等较差，直接影响磁流变装置的应用效果。总结了磁流变液各组成成分对其流变特性、分散稳定性的影响，并讨论了磁流变液在阻尼器上的应用，从而为优化磁流变液的性能及其在阻尼方面的应用提供指导。     

纳米Fe3O4对装甲车辆用磁流变液性能的影响

针对装甲车辆对磁流变液的特殊使用要求,制备了添加纳米Fe3O4的磁流变液。研究了纳米Fe3O4磁性颗粒含量对磁流变液性能的影响。结果表明,加入适量的纳米Fe3O4(如1%)不但可以提高磁流变液的剪切应力,降低磁流变液的零场粘度,同时可提高磁流变液的沉降稳定性。选取加入纳米Fe3O4量为5%的磁流变液进行试验研究,结果表明:低温条件下,磁流变液粘度变大,剪切应力增大;高温条件下,磁流变液粘度变小,剪切应力减小。耐久性试验表明经过6000km的工况后磁流变减振器阻尼力衰减不大,证明制备的磁流变液能较好满足装甲车辆的要求。     

表面改性对磁流变液稳定性和磁流变性能的影响

分别以CH-1D超分散剂和油酸为表面改性剂,以羰基铁粉为磁性颗粒,制备了硅油基磁流变液.通过沉降率和磁致剪切应力的测试,比较了磁性颗粒表面改性对磁流变液磁流变性能及沉降稳定性的影响.在磁性颗粒含量及制备工艺相同的情况下,发现以CH-1D超分散剂为表面改性剂制备的磁流变液的磁流变性能和沉降稳定性均明显优于以油酸为表面改性剂的磁流变液.     

磁流变液沉降稳定性研究现状与趋势

磁流变液的稳定性至关重要.对影响弥散粒子沉降稳定性的因素进行了讨论,指出并评述了表征磁流变液沉降稳定性的方法,综合介绍了提高磁流变液弥散粒子沉降稳定性的措施,包括表面活性剂和稳定剂的引入、纳米级物质的加入,用复合磁性响应粒子、轻质磁性材料作弥散粒子.最后展望了磁流变液的应用前景.     

小型轿车磁流变减振器设计与仿真

基于磁流变的基本理论和磁流变液的工作特性,分析磁流变减振器的工作原理与力学模型,确定活塞阻尼力与磁流变液的粘度阻力、剪切力和摩擦阻力之间的数学关系;设计车辆磁流变减振器的结构,计算、选择其结构参数,并建立仿真模型。仿真结果表明,设计是可行与合理的,符合车辆减振器的设计要求,其控制简单且响应迅速。     

Against the flow - Smart fluids that can change their viscosity in real time

An interesting feature of Audi's new TT vehicle is its semi-active primary suspension system enabled by magneto-rheological (MR) fluid technology that allows continuously variable real-time suspension damping control. The suspension system is supplied by Delphi Corp. and is based on technology from Lord Corp. Although it can be used for other applications including seismic damping in buildings, damping of bridges against strong winds, and controlled dampers in prosthetic devices designed to provide users with tactile feedback, MR fluid technology's main market is the auto suspension system. MR-based components are now operating in hundreds of thousands of vehicles all over the world     

The dynamic characteristics of a multizone regulator with frequency–width–pulse modulation at harmonic modulation of a relay element’s switching thresholds

Results of analysis of dynamic characteristics of a multizone integrating frequency–width–pulse regulator (MR) under the influence of a harmonic interference signal over a wide frequency range for thresholds of the leading relay element are considered in this article. A block diagram of the MR and time diagrams of its signals and amplitude and modulation characteristics, as well as basic relations for their construction, are given. Analysis of the MR behavior with harmonic modulation of switching thresholds of relay element is carried on the basis of the character of the behavior of the MR transmission coefficient and the deviation of the sampling interval of its output pulses from the value by a predetermined control signal. The results of the analysis are presented in the form of the dynamic state space of the MR and logarithmic amplitude–frequency characteristics in the investigated frequency range of harmonic signal interference.     

Exploring in vivo blood flow dynamics

With the development of improved MR imaging techniques, there has been a resurgence of interest since the early 1980s. Today, MR flow imaging techniques are regarded as important clinical tools for providing detailed in vivo blood flow information. MR phase velocity mapping is a versatile noninvasive flow quantification method that is well suited for analyzing in vivo flow patterns. Since the introduction of quantitative MR velocity imaging methods, clinical and research applications of these techniques have flourished, enabling noninvasive acquisition of detailed quantitative blood flow information. The success of quantitative flow imaging complements recent advances in computational fluid dynamics, which may provide further understanding of cardiovascular mechanics and the genesis and development of cardiovascular disease     

磁流变阻尼器间隙结构对阻尼力的影响

设计一种新型的磁流变阻尼器间隙结构,然后用ANSYS软件,对带有新型间隙结构阻尼器进行磁场有限元分析和流场有限元分析,求得不同电流作用下阻尼器在不同活塞速度下所能提供的阻尼力.通过与原阻尼器进行对比分析,可以发现:间隙结构对阻尼器的性能有显著影响;设计合理的间隙结构对磁流变阻尼器性能的提高具有重大意义.     

Magnetic resonance spectroscopic imaging

Gliomas are infiltrative primary brain tumors that are extremely heterogeneous in terms of both their imaging characteristics and response to therapy. Anatomic magnetic resonance (MR) images are limited in terms of their ability to evaluate the spatial extent of the lesion and to distinguish recurrent tumor from treatment-induced necrosis. An in vivo molecular imaging technique that has shown promising results for assisting in the evaluation of gliomas is MR spectroscopic imaging (MRSI). Examples of these data are presented and compared with results obtained from diffusion-weighted and perfusion-weighted MR images.     

MR imaging of baker cysts—prevalence and relation to internal derangements of the knee

Rationale and objectives: To evaluate the prevalence of popliteal cysts in patients studied with magnetic resonance (MR) imaging. Cyst presence and volume will be related to other internal derangement of the knee.Materials and methods: Three hundred and eighty-two consecutive patients with a MR study of the knee were included. Images were obtained in the three spatial orthogonal planes and evaluated through consensus. Four categories were established for the Baker cyst and synovial fluid (absence, minimum, moderate and massive), and the presence of meniscal, cruciate ligaments and cartilage lesions were recorded. Statistical analysis was carried out with bivariate analysis (χ² of Pearson and Gamma tests).Results: From the 382 patients, 145 had Baker cysts (38.0%). Cyst content was minimum in 99, moderate in 34 and massive in 12. Joint effusion was observed in 269 patients (70.4%), being minimal in 140 patients, moderate in 119 and massive in ten. Meniscal lesions were observed in 195 patients (51%), while 58 patients (15%) had a cruciate ligament lesion. Baker cyst has a statistically significant direct relationship with the presence and quantity of synovial fluid (P=0.002) and with the presence and type of meniscal lesion (P=0.01) but not with cruciate ligaments or cartilage lesions.Conclusions: The prevalence of Baker cysts in MR studies of the knee is high. Its presence and volume are related to the quantity of synovial fluid, and to the presence and severity of meniscal lesions.     

发电机内部流体流动与定子热性能数值分析

大型发电机内部流体流动状态决定了电机内温度分布以及温度极值。在建立大型发电机定子径向通风沟内流体流动二维计算模型以及电机内温度场计算模型的基础上,分别采用有限体积元法和有限元法对电机内的流体场以及温度场进行计算,并对流体流动与定子热性能进行数值分析,指出不同流体流动状态下定子温度的分布特性。     

磁流变弹性体的制备与应用研究进展

磁流变弹性体是一种新型智能材料,力学性能等随外加磁场可控.磁流变弹性体兼有磁流变材料和弹性体的优点,如响应快、可逆性好、可控能力强等,又克服了磁流变液沉降、稳定性差、需要密封装置等缺点,在减振降噪、智能感应等领域具有广阔的应用前景,因而近年来成为磁流变材料研究的一个热点、磁流变弹性体根据基体与磁性颗粒的不同,可以分为很...