A Model for Intra-Articular Heat Exchange in a Knee Joint

A mathematical model has been developed for the understanding of temperature distribution in knee joint. Temperature rises in knee joint as a result of frictional energy. This heated synovial fluid enters into the articular cartilage by the process of filtration and supplies heat to cartilage and bone. This cooled fluid again mixes well with the lubricant in the joint cavity. The problem is formulated as a two-region flow and diffusion model: flow and thermal diffusion within the intra-articular gap; and within the porous matrix covering the approaching bones at the joint. The solution of the coupled mixed boundary value problem is solved by using perturbation method. It has been observed that, in certain diseased and or old synovial joints, the movement of the fluid into or out of the cartilage resisted, and therefore, the temperature does rise. The temperature does rise in old and diseased joints as observed by varying the values of parameters from its normal values. These values refer to old age and/or diseases affecting degeneration of synovial fluid and or cartilage.     

A study on temperature regulation in synovialjoints

This paper deals with studies of the temperature regulation insynovial joints. During articulation, a certain amount ofintra-articular heat is generated due to joint activity andfrictional resistance. The movement of the interstitial fluidwithin the intra-articular gap and the exchange of fluid to andfrom the cartilage plays an important role in joint functionsincluding the regulation of heat. Analytically, the problem isformulated as a two-region flow and diffusion model: flow andthermal diffusion within the intra-articular gap and within theporous matrices covering the approaching bones at the joint. Thecoupled governing equations are solved as a two-region mixedboundary value problem with suitable boundary and matchingconditions and using perturbation technique. It has been observedthat the rise in temperature is more in the osteo-arthriticsynovial fluid as compared to normal and young synovial fluids.In normal subjects, there is hardly any rise intemperature.     

The influence of couple stresses in squeeze films

A theoretical study of non-Newtonian flow effects in a squeeze film configuration is carried out with special reference to synovial joints. The material model taken is that of the Stokes' couple stress fluid. It is found that the bearings with couple stresss fluid as lubricant provide significant load supporting capacities which result in longer bearing life. The squeeze film time is found to be considerably longer for couple stress fluid than in the case of Newtonian fluid of the same viscosity. These are the most desirable advantages which render the model close to the natural characteristics of synovial joints.     

转炉环缝洗涤器磨损问题研究

针对转炉除尘系统中环缝洗涤器使用时磨损严重问题进行了研究。利用CFD软件,模拟了环缝洗涤器内部流场,原因是内部流场紊乱造成磨损问题,并提出了相应解决办法。     

光刻机浸没单元结构参数对流动状态的影响

不同的浸没单元结构会影响缝隙流场的流动状态,为了研究浸没单元结构参数对缝隙流场流动的影响规律,通过计算流体动力学(CFD)仿真,对浸没流场的流动进行了数值模拟,开展了不同的浸没单元的注液口形状和流场高度所形成的缝隙流场的流动状态分析.研究结果表明:90°～150°的注液口和0.7mm～1 mm的缝隙高度为理想的结构参数...     

Tribological role of synovial fluid compositions on artificial joints — a systematic review of the last 10 years

Biological components of synovial fluid and their concentration play a crucial role in the lubrication mechanism of artificial joints, particularly boundary lubrication. The purpose of this review was to summarise and critically analyse the lubrication mechanism and their tribological outcomes to artificial joints. Thirteen papers published between 01/01/2003 and 28/02/2013 met the inclusion criteria for the review. Four major biological components of synovial fluid (albumin, globulin, hyaluronic acid and lubricin) were found to have an influence on film thickness, friction coefficient and wear rate. The role of these components was reported to be varied, depending on not only their composition and concentration but also surface material properties, wettability, temperature and pressure. The findings suggest that an appropriate synovial fluid composition should be represented in a simulated body fluid in order to evaluate an implant material and subsequently to conduct biotribology tests. Copyright © 2014 John Wiley & Sons, Ltd.     

柱塞泵组件球面缝隙流动特性分析

球面缝隙流动常见于多种机械结构,如柱塞泵中的球面配流副、球铰副等,然而针对球面副半径不等及存在偏心的缝隙流动特性研究较少。针对2个半径不相等的球面元件形成球面缝隙且其球心存在一定偏心时,根据球坐标系下的N-S方程对其缝隙中流体的速度分布、压力分布、泄漏流量及流体的承载量进行了分析,得到了相应的解析表达式,依此可知,半径相等且球心存在一定偏心时球面缝隙中流体的相关解析表达式;同时,得到了仅与球面缝隙流动自身结构有关的球面支撑泄漏系数和球面支撑承载系数,进一步为形成球面缝隙的机械结构(如柱塞泵中的球面配流副、球铰副等)相关设计提供理论参考;最后以柱塞泵中球铰副形成的球面缝隙为例,对其缝隙中流体的压力分布、速度分布等参数进行了分析。     

屏蔽套形变对环形间隙轴向流阻的影响研究

针对核主泵屏蔽电机中内冷回路上下支路流量分配的预测问题,研究了屏蔽电机定子屏蔽套变形规律及其对间隙环流轴向流阻的影响规律。采用有限元方法计算了内冷介质高压作用下定子屏蔽套轮廓的圆角沟槽状变形特征,并进行了实验验证。采用计算流体动力学方法研究了界面非圆轮廓形变对间隙流场的影响,通过变参数分析与数学拟合,建立了核主泵屏蔽电机定子屏蔽套形变后的间隙环流轴向流动阻力系数修正模型。该模型的计算结果表明,在屏蔽式核主泵的额定工作状态,驱动电机定子界面轮廓相较于理想状态存在11%的变形,这种变形会导致电机定转子间隙流动轴向沿程压降值下降到无形变间隙的83%左右。     

间隙宽度对类迷宫密封性能的影响

类迷宫密封由于其结构的特殊性,内部流体流动也有别于迷宫密封。利用FLUENT软件分析密封间隙对类迷宫密封性能的影响,并与传统迷宫密封内部流场进行对比。结果表明：在同等尺寸条件下,类迷宫密封湍流流体流动在槽向上比迷宫密封明显,在研究类迷宫密封时槽向流动不可忽略;间隙宽度对泄漏特性影响较大,随着间隙宽度的增大,流体速度降低,节流效应减弱,泄漏量增大。     

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.     

Expressions for coefficients of electrorheological fluid dampers

Useful expressions are developed for the damping coefficient of two types of viscous dampers that contain electrorheological (ER) fluids. The damping action in the first type occurs in flow between stationary parallel plates; the second type has annular flow between two stationary concentric cylinders. For ER fluid control, an electric field is applied across the gap in which the fluid flow occurs. The solution for the concentric cylinder damper is based on a thin gap approximation. These solutions may facilitate solving mechanical systems problems, using ER fluids, and demonstrate the controllability of ER dampers.     

Approximate closed-form solution of the synovial fluid film force in the human ankle joint with non-Newtonian lubricant

The aim of this paper is to propose an approximate closed form lubrication model of the human ankle joint by taking into account the porosity of the cartilage matrix and the non-Newtonian behaviour of the synovial fluid. The model is based on the theory of squeeze lubrication and introduce an original modified Reynolds equation obtained modelling the synovial fluid as a couple-stress fluid and the synovial fluid transport across the articular cartilage by using a modified Darcy's equation. This approach gives the advantage to obtain an analytical expression of the synovial pressure field and of the non-stationary fluid film force acting in the synovial joint during the squeeze motion in terms of couple-stress parameter, film thickness, and porosity parameter.     

A nonlinear analytical model for the squeeze-film dynamics of parallel plates subjected to axial flow

In this paper, we develop a theoretical model to predict the nonlinear fluid-structure interaction forces and the dynamics of parallel vibrating plates subjected to an axial gap flow. The gap is assumed small, when compared to the plate dimensions, the plate width being much larger than the length, so that the simplifying assumptions of 1D bulk-flow models are adequate. We thus develop a simplified theoretical squeeze-film formulation, which includes both the distributed and singular dissipative flow terms. This model is suitable for performing effective time-domain numerical simulations of vibrating systems which are coupled by the nonlinear unsteady flow forces, for instance the vibro-impact dynamics of plates with fluid gap interfaces. A linearized version of the flow model is also presented and discussed, which is appropriate for studying the complex modes and linear stability of flow/structure coupled systems as a function of the average axial gap velocity. Two applications of our formulation are presented: (1) first we study how an axial flow modifies the rigid-body motion of immersed plates falling under gravity; (2) then we compute the dynamical behavior of an immersed oscillating plate as a function of the axial gap flow velocity. Linear stability plots of oscillating plates are shown, as a function of the average fluid gap and of the axial flow velocity, for various scenarios of the loss terms. These results highlight the conditions leading to either the divergence or flutter instabilities. Numerical simulations of the nonlinear flow/structure dynamical responses are also presented, for both stable and unstable regimes. This work is of interest to a large body of real-life problems, for instance the dynamics of nuclear spent fuel racks immersed in a pool when subjected to seismic excitations, or the self-excited vibro-impact motions of valve-like components under axial flows.     

Modeling lubricant flow between thrust-bearing pads

Inlet temperature is one of the main inputs in all models for the analysis of fluid film bearing performance. At the same time, inlet temperature distribution and also oil velocity distribution at the inlet are the result of flow phenomena in the gap between the bearing pads. These phenomena are complex and in many cases further affected by any special arrangements of forced oil supply to the gap between pads. The reason for such arrangements is the more efficient introduction of externally cooled lubricant. Not many details are known about any flow phenomena in the gap between the pads and even less if the bearing is fitted with any kind of directed lubrication system. Contemporary tools of computational fluid dynamics (CFD) enable one to study the flow between bearing pads and even to build models of a whole hydrodynamic bearing. Preliminary results of modeling lubricant flow in the gap, in a bearing with a direct oil supply system will be presented in this paper. The effects of modified inlet oil temperature on some aspects of bearing performance are also presented.     

连续注排式气体离心密封的性能分析

针对普通离心密封用于气体场合下存在的问题,提出一种带有连续注排密封液结构的新型离心密封,介绍该密封的工作原理及特点。基于VOF方法,利用Fluent软件对离心密封内的气液两相流进行数值模拟,求得密封液流量、气液交界面位置以及压力折减系数等密封特性参数,研究操作参数和结构参数对密封性能的影响。结果表明:该密封适用于高转速下的气体密封,在一定的密封间隙范围内,增加转轴转速会减少密封液的流量,而在密封液进口处设置环形积水槽会增加密封液的流量;增加密封液的注入压力,减小密封间隙有助于降低环形漩涡的影响。     

A polar model for synovial fluid with reference to human joints

An analysis of “Boosted Lubrication” between two approaching solids, one of which is porous, is presented with reference to normally loaded living human joints. Micropolar fluid has been considered to represent the synovial fluid in the fluid film region between the approaching surfaces and the flow of viscous fluid in the porous matrix due to filtration through the porous material. Such a situation analysed in two regions separately using the slip flow model introduced by Beavers and Joseph. The effect of concentration, shape and size of the micro molecules on the bearing characteristics is discussed. The results are in accordance with those of Dowson et al.⁸     

基于Navier滑移的油膜缝隙微流动特性数值分析

针对液压系统中微米级油膜缝隙流动内的近壁面滑移微观尺度效应,采用计算流体力学(Computational fluid dynamics,CFD)方法分析壁面滑移作用对微米级油膜缝隙流动规律特性的影响。在对静压支承系统中封油边内油膜缝隙流动进行边界条件处理时,采取了壁面滑移速度与壁面滑移系数和当地局部速度梯度都成正比的Navier滑移模型边界条件。在数值模拟和理论基本吻合的基础上,进一步讨论分析壁面滑移系数对微米级油膜缝隙流动特性的影响,侧重分析考虑壁面表观粘度系数、温粘特性和非牛顿流体属性对微米级油膜缝隙流动特性分布和缝隙壁面滑移速度大小的影响。研究表明在微观尺度下具有界面滑移的油膜缝隙流动区别于无滑移的缝隙流动特性,壁面材料特性系数φ=0.01时,缝隙壁面的滑移速度越大,油膜缝隙流动分布均匀。其温粘特性将最大限度地影响壁面滑移速度大小和缝隙流动特性分布。     

Numerical Analysis of Secondary Flow in the Narrow Gap of Magnetic Fluid Shaft Seal Using a Spectral Finite Difference Method

In the article, attention is focused on a secondary flow in the narrow gap of a magnetic fluid shaft seal, and the secondary flow and circumferential speed of the magnetic fluid are numerically evaluated with variation in magnetic fluid plug shape such as angle of the polar head and seal clearance to be varied, using a spectral finite difference method with a new mapped function. Moreover, the maximum pressure drop is calculated in several patterns of equilibrium magnetic fluid plug, and the influence of the centrifugal force is also discussed.     

Soft layer lubrication of artificial hip joints

An experimental study of the lubrication mechanisms existing in prototype artificial hip joints which have compliant surface linings, has shown that for a lining with a hardness of about 4N/mm², fluid film lubrication can be achieved even with the low viscosity synovial fluid present in diseased joints after surgery. In tests, a synthetic lubricant was used in place of the synovial fluid. The best results seem to be produced with a 2 mm thick layer.