Numerical simulation and experimental research on passive hydrodynamic bearing in a blood pump

The current research of hydrodynamic bearing in blood pump mainly focuses on the bearing structure design.Compared with the typical plane slider bearing and Rayleigh step bearing,spiral groove bearing has excellent performance in load-carrying capacity.However,the load-carrying capacity would decrease significantly with increasing flow rate in conventional designs.In this paper,the special treatment is made to the upper spiral groove bearing to make sure that both the circulatory flowing and load-carrying capacity are high.Three-dimensional computational fluid dynamics(CFD) models in the space between rotor and shaft are developed by using FLUENT software.Effects of groove number,film height and groove depth on load-carrying capacity of the spiral groove bearings are investigated by orthogonal experiment design.The experimental results show that film height is the most remarkable factor to the load-carrying capacity.The variation tendency of load-carrying capacity reveals that the best combination of geometry is the one with groove number of 8,film height 0.03 mm and groove depth 0.08 mm.The velocity and pressure distributions in spiral groove bearings are also analyzed,and the analysis result shows that the distributions are in conformity with the design of the blood pump based on the principle of hydrodynamic bearing.The displacement of the rotor with the best combination parameters is tested by using laser displacement sensors,the testing result shows that the suspending performance is satisfactory both in axial and radial directions.This research proposes a bearing design method which has sufficient load-carrying capacity to support rotor as an effective passive hydrodynamic bearing.     

Theoretical analysis and experimental investigation of a porous metal bearing

To improve the tribological behaviour of porous bearings a new type of self-lubricated porous metal bearing is introduced with special non-uniform distribution of permeability. It has been manufactured using a practical production process, its local permeability varying regularly along its circumference. Theoretical analysis and experimental investigation show that: the new bearing has lower friction and higher load capacity than that of ordinary porous bearings, and there is no initial temperature rise and friction increase with the new bearing. The limiting pV(tested) value of the new bearing is about 200% that of an ordinary porous bearing. Considering non-uniform permeability and the effects of curvature, cavitation and velocity slip, a modified Reynolds equation for the oil film and lubrication equation for the porous matrix are derived. A numerical solution for the equations is obtained. Some aspects of the lubrication mechanism in porous bearings and ways of improving load capacity are also discussed.     

滑动轴承等效刚度阻尼的计算分析方法

为获得更精确的滑动轴承等效油膜支承,针对滑动轴承沿轴向方向存在不同的刚度阻尼,将滑动轴承沿轴向方向等分为多个截面,探索了滑动轴承多截面等效刚度阻尼的计算分析方法。基于N-S方程,结合FLUENT中的动网格方法,建立了多截面、多工况的滑动轴承仿真分析模型,计算得到沿轴向方向的多截面和不同转速下单一截面的径向等效刚度阻尼的变化规律,为进一步考虑滑动轴承等效结合部参数的转子系统动力学研究提供了参考依据。     

Comparison of an optimum‐profile hydrodynamic thrust bearing with a typical tilting‐pad thrust bearing

The oil gap profile in a hydrodynamic thrust bearing exerts a great influence on the bearing properties, and hence the optimisation of the oil gap profile is one method for improving the bearing properties. In the present work, the properties of two hydrodynamic thrust bearings have been experimentally compared under realistic load/ speed conditions. One was a typical tilting‐pad bearing and the other was an unconventional bearing with an elastic thrust plate. The latter was designed using oil gap profile optimisation and design parameter selection. Owing to the design method used, the oil gap profile was close to optimum for the assumed load/speed conditions. The results show a substantial increase in the minimum oil film thickness and lower temperature in the bearing with the elastic thrust plate. This improvement of properties is thought to be because of the optimised oil gap profile in the bearing.     

角接触球轴承动特性的数值与试验研究

角接触球轴承的动特性对机床主轴的回转精度、可靠性及寿命等有重要影响。以弹性力学理论、滚动轴承动力学和沟道控制理论为基础,研究角接触球轴承的动特性。推导了计及过盈配合量和预紧力影响的高速角接触球轴承动刚度计算方法,并对轴承动刚度的影响因素进行了理论分析和试验验证。结果表明:随着过盈量的增大,轴向刚度逐渐减小,径向刚度则逐渐增大,外圈过盈量影响更显著;预紧力过小时,刚度会出现明显的波动现象,适当的预紧力对角接触球轴承刚度的稳定至关重要。     

Theoretical characteristics of hydrodynamic journal bearings lubricated with soybean‐based oil

Vegetable‐based oils are not only biodegradable but also environmentally advantageous, and the range of lubrication applications offered by them continues to grow. Recently, vegetable‐based oils have been combined with synthetic esters to produce modified vegetable‐based oils. This paper presents an investigation of the theoretical characteristics of hydrodynamic journal bearings lubricated with non‐Newtonian soybean‐based oil. The soybean‐based oil was mixed with synthetic esters and silicone oil. The relationship between the shear stress and shear strain rate of the oil was obtained experimentally. The time‐dependent modified Reynolds equation including non‐Newtonian effects was formulated for short circular journal bearings. The perturbation technique was applied to the Reynolds equation to obtain zero‐ and first‐order pressure equations. The finite difference method was used to calculate the pressure distribution numerically. The static and dynamic characteristics, such as pressure distribution, Sommerfeld number, attitude angle, and spring and damping coefficients, were obtained numerically. It was found that the nonlinear factors of the non‐Newtonian soybean‐based oil strongly affected the performance characteristics of the journal bearings.     

Rigidity and damping characteristics of hydrodynamic sliding bearing with deformable working surfaces

The model of a hydrodynamic sliding bearing has been developed that takes into consideration the effect of the deformation of sliding surfaces on the bearing characteristics. The deformations of the sliding surfaces are determined when solving the problem of elastohydrodynamic contact of the journal and bearing with account for the pressure in the lubricating film. Variation in the clearance size at the deformation of the bearing and shaft surfaces is found by iterations when solving jointly the problems of lubricant flow and working surface deformation. Elastic deformations of the working surfaces are calculated using a two-dimensional boundary element model and a three-dimensional finite element model of the shaft and bearing. The method of finite elements is applied to calculate the parameters of lubricant flow in the bearing based on the solution of Reynolds equation in the disturbed form. The rigidity and damping characteristics of the sliding bearing with the deformable surfaces are compared to those of the bearing with the rigid surfaces; the results of the two-dimensional model of bearing deformation are compared to those of the three-dimensional one.     

Effect of surface roughness on static and dynamic characteristics of MHD couple stress lubrication of parabolic slider bearing

The effect of surface roughness on static and dynamic characteristics of parabolic slider bearing lubricated with couple stress fluid in the presence of magnetic field is theoretically analysed in this paper. The modified stochastic MHD couple stress Reynolds-type equation is derived on the basis of Christensen stochastic theory and considered two types of roughness pattern namely longitudinal and transverse. Expressions for steady pressure and load, dynamic stiffness and damping coefficients are obtained for both roughness patterns. Compared to smooth surface, transverse roughness pattern provides larger load-carrying capacity, dynamic stiffness and damping coefficients, whereas longitudinal roughness pattern has adverse effects. The presence of couple stress and applied magnetic field improves the bearing performance.     

Dynamic responses of rotor drops onto double-decker catcher bearing

In an active magnetic bearing(AMB) system,the catcher bearings(CBs) are indispensable to protect the rotor and stator in case the magnetic bearings fail.Most of the former researches associated with CBs are mainly focused on the dynamic responses of the rotor drops onto traditional single-decker catcher bearings(SDCBs).But because of the lower limited speed of SDCB,it cannot withstand the ultra high speed rotation after rotor drop.In this paper,based on the analysis of the disadvantages of SDCBs,a new type of double-decker catcher bearings(DDCBs) is proposed to enhance the CB work performance in AMB system.In order to obtain the accurate rotor movements before AMB failure,the dynamic characteristics of AMB are theoretically derived.Detailed simulation models containing rigid rotor model,contact model between rotor and inner race,DDCB force model as well as heating model after rotor drop are established.Then,using those established models the dynamic responses of rotor drops onto DDCBs and SDCBs are respectively simulated.The rotor orbits,contact forces,spin speeds of various parts and heat energies after AMB failure are mainly analyzed.The simulation results show that DDCBs can effectively improve the CBs limit rotational speed and reduce the following vibrations,impacts and heating.Finally,rotor drop experiments choosing different types of CBs are carried out on the established AMB test bench.Rotor orbits,inner race temperatures as well as the rotating speeds of both inner race and intermediate races after rotor drop are synchronously measured.The experiment results verify the advantages of DDCB and the correctness of theoretical analysis.The studies provide certain theoretical and experimental references for the application of DDCBs in AMB system.     

滚动轴承动力特性测试方法

轴承的动力特性对转子－轴承系统的动力特性有重要的影响。但至今，滚动轴承的动力特性仍缺乏系统的资料，在许多情况下，将滚动轴承简化为无阻尼的定常弹性元件。本文分析了滚动轴承动力特性的主要影响因素，介绍了滚动轴承动力特性的两种测试方法，并以某航空轴承为例作了具体测试，取得了比较一致的结果。本文提出的方法可作为建立滚动轴承动力特性数据库的基本手段。     

高速精密陶瓷球轴承与钢质球轴承的性能比较研究

角接触球轴承作为高速主轴的核心部件，其动力学特性对整机的切削性能和加工精度有重要的影响。本文根据Jones的套圈控制理论建立的动静分析法，建立了高速球轴承的拟动力学模型，基于该模型采用定量方法比较研究了陶瓷球轴承与钢质球轴承的性能差异，得到了若干有实用价值的研究结果。     

浮环轴承内油膜变偏心率与恒偏心率润滑特性对比分析*

目前对浮环轴承油膜特性的研究,主要基于偏心率对油膜压力及最小油膜厚度的影响,未能反映真实的油膜边界运动。利用计算流体力学的方法,实现浮环与轴颈之间的内油膜边界运动;建立轴颈-浮环之间内油膜润滑部位的流体域模型,研究多相流变偏心率下浮环轴承的油膜特性。结果表明：考虑变偏心率下的仿真计算结果更能反映真实的油膜润滑特性;最大油膜压力在恒定偏心率与变偏心率下均随着转速的升高而增大,最小油膜厚度在恒定偏心率下随着转速的增加保持不变,在变偏心率下随着转速的增加而减小;最大油膜压力与最小油膜厚度在变偏心率影响下变化更明显,为浮环轴承的优化设计提供了理论依据。     

Design and experimental study of a passive power-source-free stiffness-self-adjustable mechanism

Passive variable stiffness joints have unique advantages over active variable stiffness joints and are currently eliciting increased attention. Existing passive variable stiffness joints rely mainly on sensors and special control algorithms, resulting in a bandwidth-limited response speed of the joint. We propose a new passive power-source-free stiffness-self-adjustable mechanism that can be used as the elbow joint of a robot arm. The new mechanism does not require special stiffness regulating motors or sensors and can realize large-range self-adaptive adjustment of stiffness in a purely mechanical manner. The variable stiffness mechanism can automatically adjust joint stiffness in accordance with the magnitude of the payload, and this adjustment is a successful imitation of the stiffness adjustment characteristics of the human elbow. The response speed is high because sensors and control algorithms are not needed. The variable stiffness principle is explained, and the design of the variable stiffness mechanism is analyzed. A prototype is fabricated, and the associated hardware is set up to validate the analytical stiffness model and design experimentally.     

磁流变支座剪切刚度与热损功耗的能效分析

研究不同材料配比下的热损功耗和可调刚度的复杂关系,对提升叠层型磁流变支座(MRB)的隔减振性能具有重要意义。基于力磁耦合理论,构造分析支座的宏微观力磁耦合模型,进而计算支座磁场分布和水平剪切刚度,并考虑热损功耗的影响,得出支座刚度变化与磁流变橡胶(MRR)颗粒体积比的关系。通过MTS测试机对支座进行剪切测试,所得实验数据与理论计算的结果进行对比分析。结果表明,该支座最大可承受的热损功耗限制在38. 7 W时,支座剪切刚度变化为最大且可达42. 8%,其最优颗粒体积比为12%,且最优颗粒体积比随热损功耗的变化而发生偏移。该宏微观模型寻找到支座热损功耗与剪切刚度变化率的一种平衡规律,为磁流变橡胶支座进行结构和性能的优化设计提供了新思路。     

润滑油黏度对液体静压导轨性能的影响

为了提高液体静压导轨的性能,采用5种牌号润滑油,定量分析了润滑油黏度对导轨性能的影响。首先,根据现场工况确定了导轨系统的初始设计参数,计算了不同温度、不同牌号润滑油的动力黏度;接着,基于导轨的力平衡方程及流量方程,建立了导轨系统总功率损失、静态性能、动态性能的线性化数学模型,以总功率损失、承载能力、静刚度、固有频率、调整时间和动刚度作为导轨系统的性能指标;最后,利用MATLAB软件分析了润滑油黏度对导轨性能的影响。研究表明：增大润滑油牌号(VG22→VG100),降低工作温度(60℃→10℃),润滑油黏度增大,导轨系统总功率损失由507.58W (VG22,60℃)降低至33.93W (VG100,10℃),承载能力、静刚度、固有频率恒定不变,调整时间由29.84μs (VG22,60℃)缩短至0.46 μs (VG100,10℃),动刚度由173kN/μm (VG22,60℃)增大至10 369kN/μm (VG100,10℃)。因此,增大润滑油的动力黏度,能降低导轨系统的功率损失,静态性能不受其影响,动态性能大大提高。     

Theoretical investigations on the performance of an externally adjustable fluid-film bearing including misalignment and turbulence effects

An externally adjustable fluid-film bearing has been devised whereby the hydrodynamic conditions can be changed as required in a continuously controlled manner. Principal feature of the externally adjustable pad bearing is the facility to control the bearing clearance and film thickness gradient in circumferential direction, irrespective of the operating conditions. Unlike a tilting pad bearing, this bearing can have both radial and tilt adjustments. A single pad externally adjustable pad bearing will perform as a conventional partial arc bearing when the adjustments are set to zero.The paper deals with the effect of turbulence and misalignment on steady state characteristics of a centrally loaded 120° single pad externally adjustable bearing. The bearing has an aspect ratio of one and operates over a wide range of eccentricity ratios with adjustments and degrees of misalignment. Reynolds equation incorporated with linearized turbulent lubrication model of Ng and Pan is solved using a finite difference method. Static performance characteristics calculated are presented in terms of attitude angle, Sommerfeld number, friction variable, misalignment moment and oil flow. A study with various adjustments predicts that negative radial and negative tilt adjustment configuration results in superior static characteristics as compared to a conventional fluid-film bearing.     

High performance hydrostatic bearing using a variable inherent restrictor with a thin metal plate

Demands for machining of hard-to-cut materials have increased in a variety of industries. In order to meet such demands, high performance guideways are required for machine tools. In this study, in order to realize a bearing with high dynamic and static stiffness, a hydrostatic bearing using a variable inherent restrictor with a thin metal plate is newly proposed. The thin metal plate deforms elastically according to the pressure difference of working oil between both sides of the thin metal plate. Consequently, the deformation compensates the bearing clearance by adjusting the inherent restrictor. Modeling and numerical analysis of the proposed bearing were conducted, and the results confirmed that the bearing stiffness and response characteristics can be improved and then the oil flow can be reduced by applying the inherent restrictor with a thin metal plate. Furthermore, an experimental set-up for evaluating the bearing property was constructed and the load capability, static stiffness, dynamic stiffness, flow characteristic, and response characteristic of the bearing with the thin metal plate were compared with that of the bearing without the thin metal plate. The evaluation results of static performance confirmed that the flow rate of the bearing with the thin metal plate becomes lower as compared with that of the bearing without the thin metal plate, because the thin metal plate is acting as a fluid restrictor. In addition, the evaluation results of dynamic performance confirmed that the dynamic stiffness and the time response of the bearing were greatly improved by applying a variable inherent restrictor. These results confirmed that a high performance hydrostatic bearing can be realized by applying the proposed bearing.     

Effect of textured area on the performances of a hydrodynamic journal bearing

A growing interest is given to the textured hydrodynamic lubricated contacts. The use of textured surfaces with different shapes of microcavities (textures) and at different locations of the texture zone can be an effective approach to improve the performance of bearings. The present study examines the texture location influence on the hydrodynamic journal bearing performance. A numerical modelling is used to analyze the cylindrical texture shape effect on the characteristics of a hydrodynamic journal bearing. The theoretical results show that the most important characteristics can be improved through an appropriate arrangement of the textured area on the contact surface.     

试验台约束对滑动轴承动特性识别精度的影响

在滑动轴承的动特性测试中,试验台参数对动特性测试精度有重要的影响。以某倒置式轴承动特性试验台为研究对象,基于轴承动力学正反问题,提出滑动轴承动特性系数识别精度的仿真评估方法,分析不同激振频率时试验台约束参数对轴承动特性系数识别精度的影响规律,并对激振频率和约束参数的取值范围进行优选。结果表明：在较低激振频率的条件下,当约束刚度和约束阻尼取值较小时,动特性系数的识别精度受测试误差的影响不大,随着约束刚度和约束阻尼取值增大到一定值,动特性系数的识别精度受测试误差的影响迅速增大。针对研究的试验台,选择激振频率在30~300 Hz之间,选择试验台约束刚度小于试验轴承刚度的0.3%,试验台约束阻尼小于试验轴承阻尼的7%时,能够保证较好的轴承动特性系数的测试精度。     

考虑空穴因素的动载滑动轴承动态特性分析研究

基于JFO理论 (Jakobsson,Floberg ,Olsson)提出的质量守恒边界条件 ,对二维动载滑动轴承的线性稳定性在考虑空穴因素影响的条件下进行分析研究 ,建立相应的模型及方程 ,进而求得动力特性系数 ,以便进一步更准确的考察其稳定性。最后 ,对一个 36 0°的普通圆柱动载径向轴承进行实例计算 ,计算结果显示和实验测量数据吻合的较为一致。