Magnetohydrodynamic roller bearing with inertia effect

A theoretical investigation of the effect of inertia in the hydromagnetic roller bearing in the presence of a uniform transverse magnetic field is presented. It is shown that the inertia term makes a positive contribution to the load capacity. The time of approach of a given load increases as the magnetic field increases. The effect of inertia also is to increase the time of approach.     

Pressure distribution in a fluid film between two axially oscillating parallel circular plates in the presence of a transverse magnetic field

A study of a viscous incompressible electrically conducting fluid between two parallel circular plates, one of which is oscillating axially, in the presence of a transverse magnetic field shows that the pressure in the fluid film increases with both the Hartmann number and the Reynolds number. The increase in pressure due to inertia is not significant for a large Hartmann number. The effects of inertia and of the magnetic field on the pressure distribution when the plate is in its downwards motion are qualitatively similar to those effects in a hydromagnetic squeeze film bearing.     

Effects of fluid inertia in magneto-hydrodynamic annular squeeze films

The effects of fluid inertia on the squeeze film behaviors between two parallel annular disks with an electrically conducting fluid in the presence of a transverse magnetic field are analyzed. The local inertia and the convective inertia of the magneto-hydrodynamic fluid flow are considered in the study. Analytical expressions for the magneto-hydrodynamic squeeze film characteristics are obtained using the momentum approximation method. The results are compared with those based upon the assumption of non-inertial flow. It is found that the inertia correction factor in the magneto-hydrodynamic load-carrying capacity is more pronounced with large Hartmann numbers.     

Effect of Magnetic Field in Lubrication of Synovial Joints

A two region flow model has been developed in this paper in the presence of external magnetic field for the better understanding of synovial joint lubrication mechanism. The model consists of two parallel porous cartilageous surfaces separated by a thin film of non newtonian lubricant representing the synovial fluid which is assumed to behave like a paramagnetic fluid system. In this paper, we have represented the cartilage by a mixture of two interacting continua and synovial fluid by viscoelastic fluid. A transverse magnetic field is applied to the system. We have used the modified form of Darcy’s law given by Zahn and Rosenweig; to describe the penetration dynamics of magnetic fluids through porous media. Because of exact solution not being possible for the governing non-linear partial differential equations, the perturbation method has been used to obtain approximate solutions. The results have been obtained by computational techniques and compared by results available in the literature. In this paper, the possibility of increased efficiency of joint lubrication, particularly in diseased states by the application of applied magnetic fields has been explored. The applied magnetic field increases the load carrying capacity. Which helps in sustaining greater loads. Similarly, the viscoelastic parameter describes the increase in the concentration of the suspended hyaluronic acid molecules which, in turn, increases the overall viscosity of the lubricant, which also helps in sustaining greater loads.     

The load capacity of a squeeze film between curved porous rotating circular plates

The squeeze film between rotating circular plates is analysed. The curved upper plate approaches the flat non-porous plate normally. The Reynolds equations are uncoupled by using the Morgan—Cameron approximation and closed-form solutions are obtained. Expressions for the pressure and load capacity of the bearing are given. The effect of rotating fluid inertia is to reduce the load capacity of the bearing.     

The magnetohydrodynamic thrust bearing with variable film thickness

Thrust bearings with converging and diverging film thicknesses under external azimuthal magnetic fields are analysed. With constant flow rate and positive terminal potential difference load capacity diminishes to a minimum then increases with increase of Hartmann number. With negative terminal potential difference load capacity increases with increase of Hartmann number. Under short circuit conditions the load capacity increases with increase of Hartmann number. Load capacity is unaffected by magnetic field under an open circuit condition. For constant flow rate and Hartmann number load capacity increases with increase of current; current increases as the terminal potential difference diminishes.     

Squeeze film in the magnetostatic full journal bearing — Inertia effects

A theoretical investigation of the effect of inertia in the full journal bearing in presence of a radial magnetic field is presented. Viscosity and inertia contribute to the load capacity. The time of approach is increased due to the effect of inertia. The effect of inertia is considerable for all physically possible except for exceedingly large values of the magnetic field.     

Analysis of squeeze film performance between rough porous infinitely long parallel plates with porous matrix of non-uniform thickness under presence of magnetic fluid lubricant

Abstract

The performance of a magnetic fluid based squeeze film between infinitely long porous rough parallel plates with porous matrix of non-uniform thickness has been investigated. The bearing surfaces are considered to be transversely rough. The stochastic film thickness characterising the random roughness is assumed to be asymmetric with non-zero mean and variance. A magnetic fluid is used as a lubricant and the external magnetic field is oblique to the lower plate. With usual assumptions of hydrodynamic lubrication the associated Reynolds' equation is solved with suitable boundary conditions. Then expressions for pressure distribution, load carrying capacity and response time are obtained. It is observed that the load carrying capacity increases nominally due to magnetic fluid lubricant resulting in improved performance. But it is also seen that the composite roughness of the bearing surfaces introduces an adverse effect which gets more compounded due to the thickness ratio. However, the negative effect can be compensated to certain extent by the magnetic fluid lubricant in the case of negatively skewed roughness. This compensation further enhances when negative variance is involved. This study tends to suggest that the thickness ratio may play a crucial role for a better performance of the magnetic fluid based bearing system besides providing an additional degree of freedom.     

Magnetohydrodynamic externally pressurized porous thrust bearings

The characteristics of externally pressurized porous thrust bearings in the presence of a transverse applied magnetic field have been studied. It was found that the load capacity increases as the supply pressure, permeability and strength of the magnetic field increase. The time of approach also increases as the strength of the magnetic field increases for a prescribed porosity parameter.     

Effect of deformation in magnetic fluid based transversely rough short bearing

Abstract

This investigation aims to analyse the performance of a magnetic fluid based rough short bearing incorporating a deformation effect. The associated stochastically averaged Reynolds equation is solved with suitable boundary conditions to obtain the expression for pressure distribution, which results in the calculation of the load carrying capacity. The expression for the friction is obtained for both plates. It is seen that the load carrying capacity increases nominally as a result of the magnetic fluid lubricant. Furthermore, the film thickness ratio increases the load carrying capacity. It is found that the load carrying capacity increases as the ratio of the length/outlet film thickness increases, while this trend is reversed in the case of magnetisation. Moreover, it is noticed that friction remains unaltered because of the magnetic fluid lubricant. Furthermore, it is interesting to note that the deformation also unalters the friction. This article suggests that the negative effect of the standard deviation can be neutralised up to a certain extent by the combined positive effect of the magnetisation parameter, the film thickness ratio and the ratio of the length/outlet film thickness, especially when the deformation is relatively less. Therefore, this study offers some scopes for extending the bearing’s life. Finally, the bearing can support a load even in the absence of flow, unlike in the case of conventional lubricant.     

绕赤道直径旋转的球形静压推力轴承考虑流体惯性效应的性能分析与计算

本文推导出绕赤道直径旋转的球形静压推力轴承考虑流体惯性效应的广义雷诺方程,并求其数值解,研究了流体惯性效应对该轴承的压力分布、承载能力和流量等工作性能的影响。     

外加磁场对高速GMAW电弧和熔池行为的主动调控效应

在熔化极气体保护焊(Gas metal arc welding,GMAW)过程中,当焊接速度超过临界值后,焊缝成形变差,出现咬边和驼峰焊道,无法满足生产要求。研究证明,熔池中动量很大的后向液体流是产生驼峰焊道的主要原因。自主研发外加磁场发生装置,向熔池施加横向电磁力,对后向液体流进行主动干预,并调控熔池流态,从而抑制驼峰焊道的形成。在Q235低碳钢板上开展焊接工艺试验,获得了不同磁感应强度下的焊缝表面成形;采用高速摄像技术,拍摄焊接过程中的电弧和熔池图像,分析外加磁场对电弧形态、熔池流场和焊缝成形的影响规律,初步揭示外加磁场抑制驼峰焊道的机理。试验结果表明,外加横向磁场能明显调控熔池流态,减小后向液体流的动量,并能有效抑制驼峰焊道和咬边等缺陷,显著改善焊缝成形,提高临界焊接速度。     

Inertia effects due to lubricant compressibility in a sliding externally pressurized gas bearing

The sliding externally pressurized gas bearing with parallel surfaces was theoretically investigated taking inertia effects due to lubricant compressibility into account. The ratio of film thickness to bearing width was assumed to be small. An approximate solution of the Navier-Stokes equation for a compressible viscous fluid obeying the barotropic relation was analytically sought to first order in the ratio of film thickness to bearing width. It was found that fluid motion in the directions both perpendicular and parallel to the bearing surface are important in the inertia terms of the equation of motion. The characteristics of the bearing are elucidated by determinations of the load capacity, the mass flow rate, the pressure profile and the stream line. In most cases inertia effects due to compressibility enhance the load capacity irrespective of the direction and the magnitude of the relative velocity.     

Modified Reynolds Equation for Different Types of Finite Plates with the Combined Effect of MHD and Couple Stresses

We make an effort to analyze the behavior of squeeze film characteristics of different finite plates with couple stress fluid in the presence of a transverse magnetic field. On the basis of the Stokes couple stress fluid model and hydromagnetic flow model, a modified Reynold's equation is derived, which is solved by using appropriate boundary conditions to obtain squeeze film pressure, load-carrying capacity, and squeeze film time. The graphical representation of the results suggests that the different bearing systems register an enhanced performance with couple stresses compared to that of a bearing system working with a conventional lubricant in the presence of a transverse magnetic field. It is observed that the effect of applied magnetic field on the squeeze film lubrication between different finite plates with conducting couple stress fluids is to increase the load-carrying capacity significantly and to delay the time of approach compared to the corresponding nonconducting Newtonian case. It is seen that for all of the finite plates of different shapes, the circular shape gives the maximum load and time.     

三边简支载流薄板在交变磁场中的稳定性分析

针对三边简支、一边自由的载流矩形薄板,利用马丢方程解的稳定性,研究在交变磁场与机械载荷共同作用下的磁弹性稳定性问题.在导出载流薄板在电磁场与机械载荷共同作用下的磁弹性动力稳定方程的基础上,应用伽辽金原理将方程整理为马丢方程的标准形式.利用马丢方程系数的本征值关系,得出载流薄板磁弹性动力失稳临界状态的判别方程.通过具体算例,给出该矩形薄板在交变磁场中,动力失稳临界状态与相关参量之间的关系曲线及变化规律,并与均匀磁场中情形相比较.研究结果表明:变化电磁场的性质和大小,改变通电电流参数,均可改变电磁力的状态,从而达到控制载流薄板稳定性的目的.     

圆盘式磁流变调速风扇离合器的理论研究

应用B ingham模型来描述磁流变液的本构方程,在理论上分析了盘式磁流变液风扇离合器的调速机理;建立了离合器传递转矩与输出转速的计算模型,并导出了设计计算公式;讨论了动态响应特性、功率损失特性、传递的转矩及调速范围与离合器结构参数等因素的关系。结果表明:影响离合器动态品质的主要因素为其结构参数,减小从动盘的转动惯量可以改善系统的动态特性;离合器的调速范围主要由工作间隙和磁流变液零场粘度决定,减小磁流变液零场粘度和适当增大工作间隙可以减小粘性功率损失,提高效率。     

单相阶段板式多喷嘴阵列喷雾冷却的试验研究

喷雾冷却由于在较小的工质流量下可以实现很高的散热能力,在高热流密度散热、电子元器件热控等领域具有广阔的应用前景。针对较大面积的发热表面的温度控制和热量散出,本文建立闭式喷雾冷却循环系统,并选取板式多喷嘴阵列,对其在单相阶段瞬态和稳态时的换热特性进行研究。系统选取水为工质,冷却30mm×30mm的发热表面。试验中测试了板式多喷嘴阵列的雾化性能,并得出了在单相阶段时瞬态的温度变化曲线和不同体积流量下的喷雾冷却曲线。试验结果表明,板式多喷嘴阵列的雾化特性较为均匀,且喷雾冷却在单相阶段能达到较高换热性能,而流量对换热影响明显,在更大的流量下换热性能更显著。     

磁流体在磁场中的粘度测试研究

针对磁流体在磁场中粘度测试的特殊性,研制了一种新型的旋转法磁流体粘度测试实验台,该实验台可通过测试带动工作气隙内磁流体作旋转剪切运动所需的力矩来推算得出磁流体的粘度,满足磁流体在磁场中的粘度测试要求。利用所设计的实验台对矿物油基Fe3O4磁流体的粘度进行了测试,研究了外加磁场、温度及磁流体中磁性颗粒含量对其粘度的影响规律。结果表明:磁流体的粘度随着外加磁场强度的增加而增大,当磁场强度增大到一定程度时,其粘度变化逐渐趋缓;随着温度的升高,磁流体的粘度呈不断下降趋势,在有外加磁场作用情况下,其粘度下降的幅度要远大于无外加磁场作用的情况;随着磁流体中所含磁性颗粒质量分数的增加,其粘度逐渐增大,当磁性颗粒质量分数小于30%时,粘度增加缓慢,但当质量分数超过30%以后,粘度则急剧增大。     

规则形貌作用下非牛顿流体润滑的数值分析

利用Navier-Stockes方程和有限体积法,求解斜面滑块润滑模型的承载力和摩擦力,研究形貌高度较大时,表面形貌影响下非牛顿介质的润滑效果,获得用传统的包含表面形貌统计模型的雷诺方程方法难以获得的流场的细节信息。数值结果显示：在规则横向条纹形貌的作用下,形貌突变处出现压力突变;当形貌高度大于1%油膜厚度时才对润滑结果有较大影响,承载力和压差阻力随形貌高度的增加而增加,摩擦阻力随之下降,总阻力基本保持不变;当形貌高度大于油膜厚度的10% 时,摩擦阻力随之上升,总阻力迅速增加。非牛顿介质幂律模型参数对润滑结果的影响远大于形貌参数的影响,但其并不影响承载力等结果随形貌高度变化的趋势,选择合适的润滑材料参数是改善润滑的关键因素。     

Magnetic-fluid-based porous inclined slider bearing

A porous inclined slider bearing, lubricated with a magnetic fluid, in the presence of an externally applied magnetic field which is oblique to the lower surface of the bearing is discussed. The load capacity of the magnetic-fluid-based porous inclined slider bearing is found to be greater than that of a viscous porous inclined slider bearing. It is shown that the magnetic-fluid-based porous inclined slider bearing has a performance superior to that of the viscous porous inclined slider bearing.