基于稀薄效应的微气体径向轴承稳态性能

针对微气体轴承给出参考努森数的定义,根据空气不同温度时的黏度,得到参考努森数的分布范围;考虑气体稀薄效应,给出基于Burgdorfer一阶滑移速度边界的微气体径向轴承润滑Reynolds方程的修正形式; 采用有限差分法求解修正的Reynolds方程,得到不同参考努森数$Kn_0$, 轴承数以及轴颈偏心率情况下轴承的压力分布、无量纲承载能力及偏位角. 数值分析表明:随气体稀薄程度的增强,气体径向轴承的压力明显降低,无量纲承载力降低,而轴承偏位角增大. 当偏心率小于0.6时,轴承偏位角变化平缓,受$Kn_0$数的影响不明显. 当轴承数较小时,气体稀薄程度对轴承的无量纲承载力、偏位角影响较小.      

Performance of hydrodynamic journal bearing under the combined influence of textured surface and journal misalignment: A numerical survey

A wisely chosen geometry of micro textures with the favorable relative motion of lubricated surfaces in contacts can enhance tribological characteristics. In this paper, a computational investigation related to the combined influence of bearing surface texturing and journal misalignment on the performances of hydrodynamic journal bearings is reported. To this end, a numerical analysis is performed to test three texture shapes: square “SQ”, cylindrical “CY”, and triangular “TR”, and shaft misalignment variation in angle and degree. The Reynolds equation of a thin viscous film is solved using a finite differences scheme and a mass conservation algorithm (JFO boundary conditions), taking into account the presence of textures on both full film and cavitation regions. Preliminary results are compared with benchmark data and are consistent with a positive enhancement in misaligned bearing performances (load carrying capacity and friction). The results suggest that the micro-step bearing mechanism is a key parameter, where the micro-pressure recovery action present in dimples located at the second angular part of the bearing (from 180° to 360°) can compensate for the loss on performances caused by shaft misalignment, while the micro-pressure drop effect at the full film region causes poor performances. Considering the right arrangement of textures on the contact surface, their contours geometries can have a significant impact on the performance of misaligned journal bearings, particularly at high eccentricity ratios, high misalignment degrees and when the misalignment angle α approaches to $0\mathrm{°}$ or $180\mathrm{°}$.     

复合表面径向滑动轴承的概念和性能预报

近年来的研究发现固液界面的滑移可以减小表面摩擦,但也会造成流体动力效应下降甚至消失.本文提出了复合表面滑动轴承的概念,轴套表面由具有不同吸附和滑移特性的复合表面组成,发现复合表面轴承比普通轴承有许多优点.通过改变轴套表面的滑移特性可以改变和优化轴承的各种性能,例如摩擦系数、承载力、润滑剂流量、承载角等.数值解表明,在轴承高压区改变轴套表面滑移特性,轴承的整体性能会有大幅度提高.例如,本文给出的初步优化设计方案使得摩擦系数降低50%以上,同时承载力可提高20%,并且承载角可以降低33%.本文提出的设计理念不但可用于设计出具有更优异特性的径向滑动轴承,而且可以设计出具有复合表面的轴向滑动轴承或滑块轴承.复合表面滑动轴承在降低轴承摩擦、提高承载能力方面有很大的空间可以探索.     

利用有限元法计算径向磁轴承性能

利用非线性有限元方法(FEM)计算了一种径向磁轴承(定子具有8磁极常规结构)的转子在无偏心以及偏置电流分别为0.5 A、1.0 A和1.5 A下的电磁力及其电流刚度与位置刚度,预测了径向磁轴承的承载力,给出了其磁场分布图,并与磁轴承的线性化模型参数进行了比较.结果表明,基于有限元方法得到的计算值同试验结果一致,可以为径向磁轴承的设计和分析提供依据.     

瓦块弹性对大型水轮发电机组径向可倾瓦轴承润滑性能的影响

用有限元素法和有限差分法建立了可倾瓦轴承瓦块三维弹为形及热效应的计算模型。分析了由瓦面油膜压力引起的三维瓦块弹性变形对采用小包角径向可倾瓦及瓦块支点非均匀密集布置方式下滑动轴承热动力润滑性能的影响。结果表明：在大型低速重载条件下,瓦块三维弹性变形及热效应对小包角瓦块非均匀布置的径向可倾轴承后静态特性和动力特性均有较大影响。     

Investigation of surface texture influence on hydrodynamic performance of parallel slider bearing under transient condition

Although surface texture has been becoming an attractive technique for improving hydrodynamic performance in lubrication system, the study of surface texture mainly focus on the steady-state load conditions. This investigation evaluates the effect of surface texture on hydrodynamic performance under transient lubrication in parallel bearing. In the case, considering cavitation phenomena in liquid lubricating film, a mass conserving formulation based on Elrod–Adams model with JFO conditions is then employed. The implementation of numerical simulation is discretized in spatial and time domain for calculating the pressure distribution. The effect of different geometrical configurations of lubricated contact on hydrodynamic performance is evaluated. The results show that surface texture in parallel bearing yields a great improvement in terms of friction force and friction coefficient.     

四瓦可倾瓦径向滑动轴承动力特性的实验研究

采用在线分析方法考察了300MW汽轮发电机可倾瓦轴承的静、动力特性,探讨了载荷、轴颈转速以及动态激振力频率等参数变化对可倾瓦轴承的静、动态性能的影响,比较试验结果与理论计算结果发现,在不同频率激振力作用下,理论计算所得到的可倾瓦轴承动特性参数与试验结果有较大的差异。     

On the Development of Negative Pressure in Oil Film and the Characteristics of Journal Bearing

The stability and vibration characteristics of turbo-rotors running in journal bearings depend strongly on the characteristics of journal bearing determined by the oil film pressure and negative pressure developed in journal bearings. This paper is concerned with clarifying the development of this negative pressure and its influences by taking into account air bubbles in oil film, especially the surface dilatational viscosity, which decelerates the compression and expansion of air bubbles. Deceleration of the bubble expansion under negative pressure helps the bubbles to withstand greater negative pressure. When the negative pressure is developed in the oil film, the locus of center of journal running in bearing deviates from the well-known semi-circle like shape, and the journal center is pushed outwards and horizontally under vertical static load. This means that the stability of a turbo-rotor will be reduced when negative pressure is developed.     

仿生猪笼草结构的水润滑轴承摩擦学性能有限元分析研究

水润滑轴承的轴瓦结构设计对其摩擦磨损和润滑性能有着重要影响. 为提升其摩擦学性能,设计一种轴瓦布置有仿生猪笼草结构的水润滑轴承,主要为蜡质区的月牙形结构和唇部的径向脊形结构两类. 利用ANSYS Fluent对简化后的轴承润滑水膜模型进行流场分析,改变不同转速、载荷和不同织构形状、尺寸,探究水膜承载能力和减摩性能的优化情况并进行机理分析. 结果表明:通过比较不同织构形状、尺寸下的轴承水膜最大压力与摩擦系数,发现型号CC1006的月牙形织构和型号DR0102的径向脊形织构的水膜承载能力和减摩性能综合优化最佳. 通过改变不同载荷,发现轴瓦布置有仿生猪笼草结构的水润滑轴承更适合应用于中速中载的条件下,此时其拥有优异的水膜承载能力与减摩性能. 该研究为仿生表面结构的水润滑轴承设计及摩擦学性能提升等提供了分析方法和理论依据.      

随动耦合变阶梯径向滑动轴承动力特征及稳定性的研究

用有限差分法循环迭代求解了随动耦合变阶梯结构径向滑动轴承油膜压力的雷诺方程和两阶段油膜耦合变阶梯结构的流量控制方程。在分析轴承油膜压力形成机量及静力特性的基础上,采用对位移和速度的小扰动法计算了轴承的动力特性系数,考察了运转参数对这种轴承承载特性、动力特性系数、等效刚度、界限涡动比以界限失稳转速的影响,结果发现合理地选择设计参数可以使这种轴承具有较好的静力特性、动力特性和稳定性。     

Experimental Study of the Influence of Changes in Load Direction on the Performance of a Crown Bearing

Laboratory tests have been carried out in order to investigate the influence of small changes in load direction on the performance of a steadily loaded hydrodynamic crown journal bearing. Hydrodynamic pressures, temperature distribution on the bush internal surface, shaft temperature, oil flow rate and bush torque were measured for fixed sets of operating conditions, at three different groove locations () with respect to the line of load ( = 0, –30, and +30 degrees). For each groove location quantitative information is provided concerning to the influence of applied load and shaft rotational speed on the performance characteristics. Changing the location of the groove around the load line did affect flow rate, bush torque and maximum hydrodynamic pressure, but only had a slight effect on bush maximum temperature.     

曲轴轴向运动对粗糙表面曲轴主轴承润滑性能影响的研究

内燃机实际工作中,在多种影响因素综合影响下,曲轴进行旋转运动的同时,还存在沿轴承轴线方向的运动. 以某四缸四冲程内燃机曲轴-轴承系统为研究对象,综合考虑曲轴轴向运动、曲轴变形和摩擦表面粗糙度,基于平均Reynolds方程,建立了耦合曲轴轴向运动的粗糙表面主轴承润滑分析模型,着重研究了倾斜曲轴轴向运动对主轴承润滑特性的影响. 分析中,采用试验法实测曲轴沿轴承轴线方向的运动规律,应用有限单元法求解曲轴受载变形导致轴颈在轴承孔中倾斜状况. 结果表明:曲轴轴向运动对粗糙表面内燃机主轴承润滑特性影响显著;计及曲轴轴向运动时内燃机各主轴承轴颈轴心轨迹均为1条不封闭的三维空间曲线;曲轴轴向运动对主轴承润滑特性的影响程度与摩擦表面粗糙度直接相关;计及曲轴轴向运动时摩擦表面粗糙度对主轴承润滑特性影响趋势及程度均发生明显变化.      

推力轴承对轴承－转子系统的耦合作用研究

研究了推力轴承对轴承－转子系统的耦合作用。在传递矩阵法的基础上，提出一种研究考虑推力轴承影响的轴承－转子系统的动力学的通用方法。研究中考虑了如下几个因素：（１）推力盘的静态倾斜；（２）转子的静变形；（３）径向轴承中负荷的重新分配；（４）偏载对径向轴承性能的影响；（５）推力轴承对系统稳定性的影响。研究结果表明，在某些情况下，推力轴承对径向轴承的动特性、转子的静挠度、系统稳定性等具有显著的影响     

轴同期涡动和轴承座激振对轴承油膜稳定性的影响

在自行设计的轴承试验台上研究了轴颈同期涡动和轴承座激振对油膜层流失稳的影响 .结果表明 :随着轴颈偏心的增大 ,涡动倾向增强 ,流体出现层流失稳 ;当涡动倾向较弱时 ,影响油膜层流失稳的主要因素是轴承激振的强度以及低频激振 ,而高频激振对其影响较小 ;但当涡动倾向较强时 ,轴承激振的强度以及激振频率对油膜层流的失稳几乎没有影响     

The Effect of Bubbly Oil on the THD Lubrication of Tilting-pad Journal Bearings Subjected to Rotating Unbalance Load

Little work has been published on the contribution of entrained air and/or gas bubbles on the lubricant viscosity and hence on the hydrodynamic performance of bearings. In this work, a thermo-hydrodynamic analysis of the performance of dynamically loaded tilting-pad journal bearing lubricated by bubbly oil is carried out. The non-steady Reynolds equation for compressible fluid and the energy equation are solved iteratively using finite difference method to study the effect of air bubbles on the bearing performance characteristics. The effect of bubbles content on the lubricant viscosity is considered.The results showed that the value of maximum pressure slightly increases with increasing the bubble ratio up to 0.2, while the film thickness deteriorates at very high bubble content. The pressure peak moves in the downstream direction with the increase of bubble ratio ₁, which would be of great importance in deciding the pivot location in tilting-pad bearings.     

Analysis of mass transfer effects on the performance of journal bearings using micropolar lubricant

In this paper the static and dynamic characteristics of a finite hydrodynamic journal bearing with micropolar lubricant are analyzed. The effects of mass transfer of solid additives and contaminants in the lubricant oil, on the bearing characteristics are considered in this study. A generalized form of Reynolds equation is derived from the fluid flow equations with the effects of mass transfer across the fluid film considered. The generalized Reynolds equation is solved using Galerkin's weighted-residual finite element method to obtain the fluid pressure distribution in the bearing. The various static and dynamic characteristics are subsequently obtained and presented.     

二阶滑移边界对微型气浮轴承稳态性能的影响

考虑微型气浮轴承的尺寸特征,内部气流不再满足连续流的假设,根据Knudsen数可确定内 部气流为滑移流. 分别利用一阶速度滑移模型和二阶速度滑移模型对连续流的状态方程进行 修改,得到一阶滑移流和二阶滑移流机制下修正的雷诺方程. 利用有限差分法对连续流、一 阶滑移流和二阶滑移流的雷诺方程分别求解,得出相应的承载力和偏位角. 经过对比分析, 发现采用滑移流模型得到的轴承的稳态力学性能与连续流机制的结果存在较大差异,一阶滑 移流与二阶滑移流间的差异随偏心率增加而增加. 说明在MEMS环境下必须考虑滑移流效应 对微型气浮轴承稳态力学性能的影响. 在大偏心率工作状态下,二阶滑移流模型能够得到最 好的结果.     

The effect of misalignment on performance characteristics of engine main crankshaft bearings

The effect of static misalignment on the dynamic behaviour of a main crankshaft bearing is examined in this paper. The mobility method of Booker is used to predict the performance parameters of the bearing such as the minimum oil-film thickness and the journal centre cyclic path under dynamic load conditions. The theoretical results are compared with those of an aligned bearing. The Ruston–Hornsby 6 Veb-X Mk III engine big-end bearing is selected as an example to validate the computer program incorporating the present analysis. It is shown that the misalignment has significant effects on the minimum film thickness and the journal centre trajectories even for the low values of misalignment parameters. It is also found that the presence of circumferential feed grooves can cause metal-to-metal contact in such bearings.     

A methodology for measuring and modeling crystallographic texture gradients in processed alloys

The explicit representation of internal material structure in alloy processing and in-service performance simulations is becoming increasingly prevalent. This paper presents a methodology for characterizing and representing a spatially-varying orientation distribution function (ODF) that can be used in processing and performance simulations for alloys containing texture gradients. We use thick AA 7050 aluminum plate, which is known to contain texture gradients, as a case study to demonstrate the methodology, which employs a finite element representation of the ODF initialized using individual lattice orientation measurements taken using the electron backscatter pattern (EBSP) technique. As expected, we find that the texture varies significantly through the plate thickness. We use the ODF to examine the effect of the varying texture on the resulting yield strength distribution as embodied by the average Taylor factor. We find that the predicted yield strength anisotropy is different at different locations through the thickness of the plate. We examine the optimal number of orientation measurements necessary for determining the ODF in the presence of this texture gradient. We find that as we increase the number of orientations, the ODF quickly becomes stable but eventually starts to change under the influence of the texture gradient. We also investigate spatial interpolation of the ODF using the finite element representation. We find that, as with finite element representations of other fields, interpolation accuracy depends on the variation of the field variable and the discretization of the domain. In this case, gradients in both physical space and orientation space affect the accuracy of the interpolation. Finally, the effects of the texture gradient on the mechanical response of the material is demonstrated by employing the ODFs taken from various locations through the thickness of the plate in polycrystal plasticity simulations of uniaxial tension and plane strain compression.     

承压热冲击下RPV承载力影响因素的数值分析

为研究承压热冲击下含缺陷的核反应堆压力容器(RPV)的极限承载力,借助ABAQUS软件建立含表面裂纹的RPV的3D有限元模型.通过热-力耦合分析,分别得到筒体区和喷嘴区的瞬态温度场和应力场.考虑到实际RPV断裂试验工作具有相当大的危险性,使用扩展有限元法(XFEM)对裂纹的扩展情况进行数值模拟.通过对含有不同位置和尺寸裂纹、具有不同壁厚容器的极限承载力分析,得到满足强度条件的各临界裂纹尺寸.结果表明,当表面裂纹距喷嘴口的距离达到一定程度,其长度对RPV结构的极限承载力不构成影响.在喷嘴区,随裂纹距喷嘴口距离的减小,临界裂纹尺寸迅速减小,喷嘴口上仅允许深长比较小的浅表面裂纹出现.