Dynamic Characteristics and Stability Analysis of a Wavy Thrust Bearing

A numerical procedure to analyze wavy thrust bearings is described. The numerical model is developed by assuming that two circular plates rotate relative to each other. The upper plate is assumed to be flat and rotating, whereas the lower plate is assumed to be stationary and wavy in surface geometry. A Reynolds-equation-based procedure is used to simulate the dynamics engendered by various wavy geometries and loading conditions. The equilibrium position of the journal results from the equilibrium between the forces generated by the fluid-film pressures and the externally applied loads. A numerical small perturbation technique is applied to calculate the linear stiffness and damping characteristics of the bearing at the equilibrium position. Using a three-degrees-of-freedom system with one axial and two rotational displacements, nine linear stiffness coefficients (three principal and six cross-coupled coefficients) and nine linear damping coefficients are calculated. These linear coefficients are then used to calculate the eigenvalues of the system by solving the homogeneous equations of motion. The stability of the bearing system is then expressed using the lowest logarithmic decrement obtained from these eigenvalues. Using this procedure, a parametric study is carried out to examine the effects of external load, location of the applied load, bearing number, and bearing wave amplitude on journal equilibrium position, bearing linear stiffness, damping characteristics, and bearing stability.     

非线性转子系统碰摩的分岔与混沌研究

以线性项和立方项之和来表示转轴材料的物理非线性因素,建立了具有非线性刚度轴支撑的转子系统局部碰摩的动力学模型,利用数值积分和Poincaré映射方法,对转子系统由于局部碰摩故障导致的非线性动力学行为进行了研究,给出了系统响应随转子转动频率比和偏心量变化的分岔图和最大Lyapunov指数图,以及一些典型的Poincaré截面图、相平面图、轴心轨迹和幅值谱图等,从中发现此类非线性振动系统具有周期、拟周期和混沌等复杂的动力学行为,研究结果为此类系统的安全运行和有效识别转子故障提供了理论参考。     

弹性金属塑料瓦推力轴承的滑移问题研究

本文对流体力学的经典雷诺方程中固液界面无滑移假设对于弹性金属塑料瓦的适用性提出疑问，从理论上论证在一些表面能低的聚合物表面存在滑移的可能性，并进行对比实验，实验证明在聚四氟乙烯与润滑油的界面上存在滑移现象，发现滑移是在剪切速率和油膜厚度达到一定值才出现的，滑移速度随着转速的提高和膜厚的减小而增大。在分析以聚四氟乙烯为表面的弹性金属塑料轴瓦的润滑机理时，应当对雷诺方程进行修正，计入滑移因素的影响。     

动静压推力轴承动特性分析

本文利用有限差分法,对一个高速外圆磨床主轴上的一浅腔动静压推力轴承的动特性进行了理论分析,其结果对提高主轴的性能是非常有益的。     

线支承扇形瓦推力轴承热动力润滑性能分析

建立了线支承扇形瓦推力轴承中油膜压力、油膜厚度、能量方程和粘温方程等的无量纲表达式,研究了各种刮瓦形式和支承线的倾斜度对推力轴承的油有膜厚度分布和温度分布的影响,研究表明,对于可倾瓦来说,各种刮瓦形式并不能有效降低润滑油的温升,不会明显改善推力轴承的润滑性能;推力轴承在经过长期运行后,推力瓦块支承线因受压缩将会向内倾斜,瓦块外半径处沿圆周方向上的油膜厚度显著减小,从而使润滑油温升大大提高,明显降低了推力轴承的润滑性能。     

Hydrodynamic Performance of a Thrust Bearing with Micropatterned Pads

The primary objective of this study was to investigate the influence of surface texturing on hydrodynamic lubrication of tilting-pad thrust bearings in terms of bearing power loss, operating temperature, and oil-film thickness. For this purpose, the working faces of six thrust pads from a 228.6-mm-outer-diameter bearing were textured. The textured surface consisted of a system of crossing channels of less than 10 μm in depth. Tests were conducted with a VG68 mineral turbine oil supplied to the bearings at a constant temperature of 50°C and flow rate of 15 L/min. The following parameters were measured: frictional torque, pad and collar temperatures, oil-film thickness, and pressure profiles along two circumferential lines. No significant change in collar and pad temperature could be observed when the patterned bearing was used. However, the textured bearing showed a tendency to exhibit lower power loss especially when an optimum oil flow supply rate was used. At the same time, inlet and outlet film thicknesses for the patterned bearing showed larger values than those obtained during tests on the plain babbitt pads.     

非稳态油膜力作用下轴承-转子系统非线性动力学行为研究

以刚性 Jeffcott转子为研究对象 ,借助一种新的油膜力模型和数值积分法研究了非线性油膜力作用下转子的一些非线性动力学行为 .作出了系统运动随某些参数变化的分岔图及部分点的 Poincare映射图。结果表明 ,系统中存在着倍周期分岔、概周期及混沌等复杂的动力学行为     

Three-Dimensional Thermohydrodynamic Analyses of Rayleigh Step Air Foil Thrust Bearing with Radially Arranged Bump Foils

A three-dimensional (3D) thermohydrodynamic (THD) model for air foil thrust bearings (AFTBs) is presented. The nonisothermal Reynolds equation is solved using pressure boundary conditions at the cooling air plenum considering local temperature-dependent viscosity and density. Air film temperature is calculated using the 3D energy equation with thermal boundary conditions at the top foil, thrust runner, and top foil’s leading edge. The cooling air plenum distributes the cooling air to multiple radially arranged cooling channels. The plenum temperature and pressure are found from mass and energy balance equations applied to the plenum. Temperature fields of the top foil, bump foils, thrust disc runner, bearing plate, and cooling air channels are also solved through appropriate energy balance equations with their surroundings. A robust computational algorithm with multiple iteration loops was developed to find all the temperature fields. THD analyses were performed for AFTB with outer radius of 50 mm up to 100,000 rpm. As the cooling air source pressure is increased, the plenum pressure also increases and its temperature decreases due to more cooling capacity. However, cooling effectiveness is not necessarily proportional to the pressure because the flow residence time inside the cooling channels is inversely proportional to the pressure. The analyses show that the thrust disc temperature is a parabolic function with speed, and thermal expansions of the thrust disc and thrust plates contribute to the most significant driving force of thermal instability. Optimum cooling air pressure was found around 12,500 Pa for the proposed AFTB design at the reference simulation condition.     

LEC型推力轴承回油结构与节能效果

本文分析了ＪＨＪ型推力轴承及ＬＥＧ型推力轴承的进回油方式对轴承性能的影响。用ＬＥＧ型推力轴承替代ＪＨＪ型推力轴承时,应该注意改变原轴承的回油结构。ＬＥＧ型推力轴承在氧气透平压缩压上应用时,实测的节能效果。     

行星齿轮系扭转非线性振动建模与运动分岔特性研究

建立行星齿轮系扭转非线性振动模型,模型中考虑了行星齿轮系各齿轮副间的时变啮合刚度、齿侧间隙以及综合传递误差等非线性因素;推导出系统的量纲一振动微分方程,采用数值积分方法研究行星齿轮的运动特性随转速以及齿侧间隙等参数的分岔特性,结合Poincaré图形分析,研究转速、啮合阻尼以及齿侧间隙等参数对系统分岔特性的影响。结果发现,随着转速的逐渐增大,系统会通过激变途径进入到混沌运动,而随着齿侧间隙的逐渐增大,系统会通过倍周期分岔途径进入到混沌。阻尼过小将会导致行星齿轮系统的稳态运动由短周期运动向复杂运动转变。齿侧间隙是影响系统运动分岔特性的重要因素,但是影响范围主要限于量纲一齿侧间隙大于3.5的大间隙区段。     

Thrust Bump Air Foil Bearings with Variable Axial Load: Theoretical Predictions and Experiments

Thrust air foil bearings are critical components in high-efficiency turbomachinery, such as two-stage compressors subjected to large and irregular axial forces. In this article, a model of thrust bump foil bearings that predicts deflection with variable axial load is developed assuming no tilting effect of the thrust collar. To predict the air clearance, deflection of the elastic foundation was used in the air film height equation. Combined Dirichlet and Neumann-type boundary conditions were used for static load performance predictions.

To verify the theoretical model, tests were performed with three different thrust air foil bearings with outer radii of 45, 50, and 55 mm. The rotating speed ranged from 10,000 to 25,000 rpm. From the test results, the model using nonlinear stiffness was in better agreement with the experimental results than the model using linear stiffness.     

水润滑扇形瓦推力轴承润滑性能的边界元分析

用边界元法分析水润滑扇形瓦推力轴承的润滑性能,将雷诺方程转化为类似泊松方程的形式,采用边界元法求解该方程,研制了一套C++计算程序,得到多组轴瓦参数下的水膜厚度、压力分布和相关润滑性能,可以显著降低代数方程组的阶数,从而减少计算所需时间,并可提高计算精度。研究表明瓦块张角和瓦块倾角对最小水膜厚度、最大水膜压力、摩擦功耗、压力中心位置和进水口流量有不同程度的影响,该研究将有助于合理的设计水润滑扇形瓦推力轴承的轴瓦参数。     

汽车悬架动力学建模与仿真分析

建立了基于Sim Mechnics的悬架模型,该模型能更真实的反映悬架特性,并且根据实际工程应用场合的不同,此模型还能方便的进行扩展或缩减,无需复杂的数学推导。应用此模型对汽车悬架在多种工况下进行了仿真,结果表明车身的俯仰或侧倾运动对汽车行驶加速度敏感,且加速度绝对值越大,车身俯仰或侧倾运动越剧烈;在转弯工况下对汽车转向角敏感。基于Sim Mechnics悬架模型的建立和仿真分析,为全车悬架的主动控制研究提供了更贴近工程实际的被控对象模型。     

松动-裂纹耦合故障转子系统的非线性响应

基于现代非线性动力学和转子动力学理论,采用Newmark-β法和Poincaré映射对裂纹和一端支座松动耦合故障转子系统进行了数值模拟研究,给出了系统响应随转速比、松动质量和裂纹深度变化的分岔图,分析了一些主要参数变化的影响以及典型的Poincaré截面图。研究发现,系统存在拟周期环面破裂、阵发性分岔和多倍T周期运动失稳进入混沌三条混沌道路。这些结论为旋转机械的故障诊断提供了理论基础和参考。     

周向拉杆转子系统非线性动力行为及稳定性

针对周向拉杆转子轴承系统,将拉杆简化为无质量、受预紧的线性弹簧,得到周向拉杆提供的附加刚度矩阵和附加广义力矩;对具有粗糙表面的长方微元体进行有限元接触分析,得到不同载荷作用下的法向和切向界面接触刚度;计入界面接触刚度和周向预紧拉杆的影响,采用受轴向载荷的Timoshenko梁轴有限单元建立周向拉杆转子轴承系统的非线性动力学模型.基于系统的局部非线性特性进行自由度缩减后,运用结合预估-校正机理的Poincaré-Newton-Floquet方法对滑动轴承支承下周向拉杆转子系统的非线性动力特性进行研究,得到不同转速和质量偏心下系统稳态周期解的稳定性边界和分岔形式.结果表明,系统存在同步周期解、准周期解和倍周期解对应的参数区域,随着转速的增加,当质量偏心较小时,周期解发生准周期分岔,当质量偏心较大时,周期解发生倍周期分岔.考虑界面接触刚度后,系统的分岔失稳转速降低;预紧不均时,系统在更低的不平衡量下发生倍周期分岔.     

半挂汽车列车横向失稳的非线性动力学机制

半挂汽车列车载运工况变化较大,横向失稳机制复杂,给整车及稳定性控制系统的开发设计带来困难。应用非线性动力学的相关理论,研究半挂汽车列车在极限操纵工况下的平衡点分岔、相轨迹和Hopf分岔特性以及与载运工况的关系;在此基础上,结合不足转向梯度和系统阻尼特性对不同横向失稳形式的发生机制进行探讨。结果表明,载运工况的变化可能导致系统出现鞍结分岔、Hopf分岔和同宿轨道等非线性动力学现象;牵引车后轴侧滑而导致折叠是半挂汽车列车主要的横向失稳形式,挂车甩尾与折叠密切相关,挂车甩尾会同时加剧牵引车侧滑而加剧折叠,横向摆振与Hopf分岔密切相关,一般仅在载重较大且半挂车质心显著靠后才可能发生,且横向摆振失稳一般都会进一步发展到折叠而完全失控,选择牵引车横摆角速度和挂车侧偏角为控制变量设计稳定性控制系统有望取得较好的效果。     

应用新型可控轴承改善转子系统稳定性的研究

介绍了一种动态特性可在线调整的新型可控径向轴承工作原理,其特征是具有一个由挠性板、控制油腔和流体阻尼器组成的可动部分。给出了转子－轴承系统非线性数学模型,分析了系统的稳定性,并着重研究了阻尼器参数对系统稳定性的影响。计算机仿真结果表明,在较大的转子偏心范围内,应用该轴承可有效地消除或降低系统的自激振荡。     

圆形可倾瓦与扇形瓦推力轴承性能的比较

应用有限元程序分别对圆形瓦和扇形瓦推力轴承在中心支承条件下的性能进行了计算。并根据计算结果对两种瓦形的轴承性能作了比较。其结果和实验结论比较一致。最后得出圆形瓦轴承比扇形瓦轴承在某些方面有一定的优越性。     

不同镜板转速对推力轴承油膜流场的影响

以推力轴承中的油膜层作为控制体系 ,建立了油膜层的非等温三维流场偏微分方程组数学模型 ,通过采用有限差分方法对其所构成的偏微分方程组进行数值求解。在数值计算的基础上 ,详细分析了镜板不同转速对推力轴承油膜层速度场分布的影响、油膜层速度矢量分布和油膜层与层之间速度分布规律。研究结果表明 :油膜层中的速度矢量分布主要由周向速度和径向速度所组成 ,其速度矢量分布是构成油膜层对流换热的主要因素。     

斜齿轮柔性转子轴承系统非线性动力学分析

考虑齿侧间隙、轴承径向间隙、齿轮不平衡力,使用有限元法建立质量矩阵、刚度矩阵、阻尼矩阵并组装成整体参数矩阵,建立了适用于斜齿轮柔性转子滚动轴承系统的非线性动力学模型。采用Runge-Kutta法求解,并分析系统的动力学行为。研究了转速、转轴刚度、不平衡力对斜齿轮系统非线性动力学行为的影响规律。结果表明：随着转速的变化,系统将经历周期、拟周期、混沌等多种运动状态;随着转轴刚度的减小,混沌运动的区间减小,振幅大小发生改变;不平衡力增大后,系统混沌区间增大,混沌运动的区间也发生改变。