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.

Optimum Position of Electromagnetic Brake on Slab Caster

Three-dimensional mathematical models were developed for studying the molten steel flow and the trajectories of inclusions and bubbles in continuous casting mold with electromagnetic brake.The results show that the effect of the electromagnetic brake on the molten steel flow and the movement of inclusions and bubbles depends on the position of electromagnetic brake.While EMBR Ruler is installed at the exit of the submerged entry nozzle,the velocity of the main jet of molten steel from the nozzle can be decreased effectively,the velocity of the molten steel streams near the free surface and the narrow face is reduced obviously;Meantime more inclusions and bubbles could float up to the slag layer.

Numerical optimisation and experimental validation of divided rail freight brake disc crown

In this study, numerical optimisation and experimental validation of a divided rail freight brake disc crown made of grey cast iron EN-GJL-250 is presented.The analysed brake disc is used in rail freight wagons and possesses a load capacity of 22.5 tons per axle. Two of the divided rail freight brake discs are mounted on each axle.With the aid of numerical analysis, the thermal dissipation properties of the brake disc were optimised and ventilation losses were reduced, and the numerical results were compared with experimental results. A one-way fluid–structure interaction analysis was performed. A computational fluid dynamic model of a divided rail freight brake disc, used to predict air flow properties and heat convection, was incorporated into a finite element model of the disc and used to evaluate the temperature of the disc. A numerical parametrical optimisation of cooling ribs of the brake disc was also performed, and novel optimised cooling ribs were developed. A transient thermal numerical analysis of the brake disc was validated using temperature measurements obtained during a braking test on a test bench. The ventilation losses of the brake disc were measured on a test bench specifically designed for the task, and the losses were compared to the simulation results. The experimentally obtained ventilation losses and temperature measurements compared favourably with the simulation results, confirming that this type of simulation process may be confidently applied in the future. Through systematic optimisation of the divided rail freight brake disc, ventilation losses were reduced by 37% and the mass was reduced by 21%, resulting in better thermal performance that will bring with it substantial energy savings.

Squeeze-Strengthening Effect of Silicone Oil-based Magnetorheological Fluid

In order to study the squeeze-strengthening effect of silicone oil-based magnetorheological fluid （MRF）, theoretical basis of disc squeezing brake was presented and a squeezing braking characteristics test-bed for MRF was designed. Moreover, relevant experiments were carded out and the relationship between squeezing pressure and braking torque was proposed. Experiments results showed that the yield stress of MRF improved linearly with the increasing of external squeezing pressure and the braking torque increased three times when external squeezing pressure achieved 2 MPa.

Aerodynamic Brake for Formula Cars

In the last years, in formula racing cars championships, the aerodynamic had reached an ever more important stance as a performance parameter. In the last four seasons, Red Bull Racing Technical Officer had designed their Formula 1 car with the specific aim to generate the optimal downforce, in relation to the car instantaneous setup. However, this extreme research of higher downforce brings some negative effects when a car is within the wake of another car;indeed, it is well known that under these condition the aerodynamic is disturbed, and it makes difficult to overtake the leading car. To partially remedy this problem, Formula 1 regulations introduced the Drag Reduction System (DRS) in 2011, which was an adjustable flap located on the rear wing;if it is flattened, allowing to reduce the downforce, increasing significantly the velocity and, therefore, the chances to overtake the leading car. Vice versa, when the flap is closed, it ensures a higher grip, which is very useful especially in medium-slow speed turns. Keeping the focus on the rear wing, but by shifting attention from the increased top speed to increase the grip in the middle and slow speed curves, we decided to study a similar device to the DRS, but with the opposite effect. The aim is to design an aerodynamic brake integrated with the rear wing. In particular, the project idea was to sculpt, on the upper surface of the wing (pressure side), a series of 'C' shaped cavity, normally covered by adequate sliding panels. These cavities, when they are discovered, at the beginning of the braking phase, produce a turbulence and additional increase downforce, lightening the load on the braking system and allowing the pilot to substantially reduce slippage and to delay the braking. Since it seems that the regulations adopted by the FIA Formula 1 Championship do not allow such a device, it has been decided to apply the concept on a Formula 4 vehicle. This paper describes the design and analyzes the effects of these details on a standard wing cavity, using a commercial CFD software.

进口防旋板对汽轮机交错齿迷宫密封泄漏特性和动力学特性影响研究

为提高汽轮机高压缸和中压缸之间过桥汽封的气流激振动力学性能、抑制汽轮机轴系振动失稳,针对交错齿迷宫密封,开展了进口防旋板结构方案设计和动力学性能评估研究。首先,建立了具有“虚拟旁路边界”的交错齿迷宫密封动力学计算模型,实现了对动密封进口压力场和高预旋速度场的精准模拟;然后,采用基于多频椭圆轨迹涡动模型的非定常计算流体动力学(CFD)摄动数值方法,对比分析了进口预旋(预旋比为0、0.3、0.5)对无防旋板结构的迷宫密封的动力特性系数的影响规律;最后,详细评估了不同进口防旋板结构方案的止旋抑振性能,比较分析了防旋板倾角和数量对迷宫密封的泄漏量、动力特性系数和周向旋流比分布的影响规律。研究结果表明:迷宫密封泄漏量对防旋板倾角和数量变化不敏感(泄漏量变化小于0.5%);进口预旋会导致迷宫密封交叉刚度和有效阻尼穿越频率增大、有效阻尼减小,易诱发轴系失稳;进口防旋板能够显著减小迷宫密封的交叉刚度(约为53%)和有效阻尼穿越频率(约为24 Hz)、增大有效阻尼,使密封泄漏量略有增加(约为4.5%);相较于直防旋板,45°倾角斜防旋板使密封交叉刚度进一步降低约14%,有效阻尼穿越频率变化较小;当防旋板数由36增加到72时,密封交叉刚度降低约24%,有效阻尼穿越频率减小约5 Hz;而当防旋板数由72增加到144时,密封的转子动力特性对防旋板数变化不敏感;综合考虑加工成本和止旋抑振性能,具有72个直防旋板的迷宫密封进口防旋板结构方案最优。研究结果可为交错齿迷宫密封防旋板设计提供参考。

列车制动作用下悬索桥纵向运动及其黏滞阻尼器控制研究

列车的制动行为会对悬索桥的纵向运动产生影响,因此有必要对千米级大跨度铁路悬索桥在列车制动下的纵向运动进行研究。以一座主跨1060 m的大跨度铁路悬索桥为研究对象,采用数值模拟的方式探讨了列车制动作用下其梁端纵向运动的响应特性,并研究了黏滞阻尼器在控制纵向运动中的效果。首先介绍了该千米级大跨径铁路悬索桥的工程背景,以及基于ANSYS软件建立的有限元模型;然后介绍了大跨径铁路悬索桥纵向运动的加载求解方式,支座摩阻和黏滞阻尼器的有限元模拟方式,以及制动力的模拟方式;接着探究了不同制动位置、是否考虑支座摩阻力对悬索桥梁端纵向运动响应的影响;最后,研究了黏滞阻尼器的纵向运动控制效果,并进行了参数分析。研究结果表明:随着制动位置越接近下桥位置,纵向位移变化曲线形状越接近正弦函数形式;支座摩阻对列车制动作用下的梁端位移响应有一定的控制作用,对梁端速度响应控制效果不佳;采用黏滞阻尼器可以有效控制列车制动下的悬索桥梁端位移和速度响应;当采用阻尼系数为2500 kN(m/s)^(-α),阻尼指数为0.1的黏滞阻尼器时,控制效果最佳。

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。

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。

多盘连续可变工作间隙磁流变制动器仿真与验证

为提高磁流变制动器制动能效,提出一种多盘连续可变磁流变液工作间隙结构的磁流变制动器。在ANSYS workbench环境下完成不同电流、间隙状态下的三维静态磁场仿真,对磁场沿工作间隙分布状况进行分析,通过试验台架对制动器性能进行测试。结果表明,磁流变液工作区域磁矢量分布相对均匀,无明显积聚现象,磁路设计合理。理论与实验结果变化趋势基本吻合,但在电流较大时,两者之间误差呈逐渐增大趋势。制动力矩在0~2.5 A电流变化区间增速较快,而在2.5~4.0 A区间明显放缓,最大力矩达到146.4 N·m,较间隙未改变状态增加25.80%。设计的制动器TVR值达到48.81 kN·m/m^(3),较传统磁流变制动器结构更紧凑,力矩调节范围更广,设计思路及实验结论对磁流变制动器结构的进一步研究具有借鉴意义。

高速列车车下复杂环境碳陶制动盘热散逸分析

高速制动条件下,碳陶制动盘表面温度会急速升高,对制动盘本身及周围环境带来一定的热影响。针对高速制动工况下碳陶制动盘热散逸问题,运用热-流-固耦合仿真方法,建立了包含车下复杂环境的碳陶制动盘热散逸模型,分析碳陶制动盘在紧急/常用制动工况下的热负荷状态以及碳陶制动盘温升对周围环境的影响。结果表明:碳陶制动盘在制动初速度为400 km/h的紧急/常用制动工况下,盘面最高温度均超过了740℃,紧急制动工况下的盘面温升速率更高;制动盘摩擦面与散热筋结构之间的热传导作用使制动盘摩擦面形成了花瓣状温度云图。制动过程中,制动盘内部空气温度上升明显;制动结束后,制动盘正上方空气域温度变化较大。

设计参数对鼓式磁流变液制动器传动性能的影响

针对传统圆筒式磁流变液制动器制动转矩小的缺点,提出了一种鼓形间隙磁流变液制动的方法。鼓式磁流变液制动器的磁流变液工作体积比圆筒式的更大,从而制动性能显著提升。通过有限元法对装置进行磁场分析,得到了两种间隙形状和鼓形张角对磁场的影响以及不同电流下磁感应强度与轴向距离的关系;建立了鼓式磁流变液制动器转矩与磁感应强度、半径、角速度等参数的关系。结果表明,鼓形的张角对磁流变液的工作体积影响显著;制动器转矩随电流增大而增大,在3 A时输出转矩为10.56 N·m,比圆筒式磁流变液制动器提高了23.6%。

基于NSGA-Ⅱ的内外液流通道筒式磁流变制动器优化设计

【目的】针对传统磁流变制动器磁场利用率不高的问题,设计了一种具有内外流道的筒式磁流变制动器。【方法】通过将隔磁环和隔磁盘集成在导磁材料旋转套筒和定子磁缸内,使得磁力线蜿蜒穿过内外液流通道的6段有效阻尼间隙,从而在制动器外形尺寸不变的前提下提高了转矩性能。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,同时建立了制动转矩的数学模型。在电磁场和转矩分析的基础上,通过理论计算和DOE实验正交法预测模型精度,并利用NSGA-Ⅱ算法对内外液流通道筒式磁流变制动器进行多目标优化。【结果】结果表明,当加载电流为2.0 A时,制动器的转矩最大值由36.38 N·m提高到47.35 N·m,相比优化前提升了30.15%;转矩动态可调范围系数由18.28提高到21.31,相比优化前提升了16.58%。【结论】优化后的制动器满足无人配送小车的制动性能需求。

基于可见-近红外光谱的制动液品牌鉴别方法研究

提出了一种基于可见-近红外光谱分析技术快速鉴别汽车制动液品牌的新方法。采用美国ASD公司的便携式光谱仪对五种不同品牌的制动液进行光谱分析,各获取60个样本数据。采用平均平滑法和标准归一化方法对样本数据进行预处理,再对光谱数据进行主成分分析,建立第一主成分和第二主成分的二维散点图,表明不同品牌制动液具有较好的聚类特性。将前6个主成分作为输入量,制动液品牌作为输出量,建立了基于逐步判别分析法的鉴别模型。随机抽取225个样本用于建模,余下的75个样本用于模型验证。试验结果表明验证准确率达到94.67%,说明所提出的方法具有很好的分类和鉴别作用,为制动液品牌的快速鉴别提供了一种新方法。

用太赫兹时域光谱技术判别防冻液和刹车油的真伪

太赫兹时域光谱技术可以分辨化合物结构上的微小差异并应用于物质检测与分析,为有机化工产品的鉴别及更宽有效光谱区的测试提供了新的实验方法.本文运用太赫兹时域光谱技术研究了甲醇、防冻液和刹车油在太赫兹波段的光学特性,在室温氮气环境中,得到了样品的时域谱和在0.2～2.5THz波段的吸收谱.甲醇和防冻液、刹车油在此波段的吸收谱存在显著差异,甲醇的吸收峰位于0.35THz、0.72THz处,防冻液和刹车油的主要吸收峰位于0.62THz处.实验表明,用太赫兹时域光谱技术可以检测防冻液和刹车油里是否掺有甲醇,进而判断其质量的优劣.

硼酸酯水解稳定性研究与应用

对硼酸酯水解稳定性的本质及研究现状进行了概括,目前解决硼酸酯水解稳定性差的最佳途径是合成含氮硼酸酯,并对硼酸酯在润滑油添加剂、表面活性剂、汽车制动液、光热引发剂、偶联剂等方面的应用进行了综述。

长大列车空气管系充气特性数值仿真研究

应用现代流体动力学数值计算方法,以长大货物列车空气制动管系的充气特性作为研究对象,研究列车编组辆数、管系组成、管系泄漏等因素对列车管充气压力的影响和沿列车管长度方向的充气压力分布情况。建立了考虑列车管泄漏的连续性方程,给出一种求解压力速度耦合方程的显式有限差分算法。将计算结果和国内外长大列车充气特性的有关试验数据进行对比分析。研究工作为长大列车制动作用的试验研究提供理论参考,并为研制完整的货物列车空气制动系统奠定了基础。

制动液用环状硼酸酯的研制

采用减压装置合成环状硼酸酯,并考察了侧链结构对硼酸酯干沸点的影响,硼酸酯的pH值及结构对其水解稳定性的影响。实验利用IR对产品结构进行表征,并按照国标方法对硼酸酯的性能进行测定。实验结果表明,对于五元环状硼酸酯,一定聚合度的多聚醇醚侧链对硼酸酯的干沸点的影响规律是:侧链的碳氧个数比越大,其干沸点越低;对于大环硼酸酯:侧链中的碳氧个数比越大,其干沸点越高。最终,得到了干平衡回流干沸点在240℃以上的环状硼酸酯产品,并且考察出当硼酸酯产品的pH值至中性或偏碱性时水解稳定性较好,可达到96h以上。

液力减速器动态制动性能预测分析

为了在产品设计时全面预测及评价其制动性能,采用CFD数值模拟分析的方法对液力减速器动态制动性能进行了预测。经过数值仿真计算,得出了制动力矩与充液率、制动时间与制动力矩两条重要关系曲线,为液力减速器产品设计过程中的性能预测提供了较可靠的方法。

全液压制动系统的仿真分析与试验

介绍了全液压制动系统的工作原理。通过分析全液压制动系统各组成模块,建立了全液压制动系统的AMESim模型,并对蓄能器充液阀的充液特性及制动系统的动态响应等特性进行了仿真研究。仿真与试验结果的对比分析证明:液压制动系统的制动性能完全能够满足工程上的制动需求。