基于动网格模型的液体动静压轴承刚度阻尼计算方法

针对雷诺方程不能反映高速油流周向惯性效应、轴颈周向动压效应和静压扩散效应之间的非线性耦合关系及其对三维流场特性的影响,进而导致动静压轴承刚度阻尼的计算精度难以满足高转速精密轴承设计需要之现状,提出基于纳维-斯托克斯方程的动网格计算轴承刚度阻尼新方法。该方法采用自定义程序实现轴颈的旋转速度、位移扰动和速度扰动以及扰动过程中油膜力的计算等功能,成功将轴颈的旋转动边界转换为静边界,有效避免因轴颈旋转引起的网格畸变,并利用弹簧光顺模型更新轴颈受速度扰动和位移扰动引起的油膜网格挤压变形。通过对比研究瞬态和稳态条件下油膜力的变化,界定计算刚度阻尼系数时速度扰动和位移扰动的合理取值范围。利用所提出的方法计算典型轴承的刚度阻尼系数,再现动静压轴承油膜厚度和三维流场压力分布的动态发展过程,并采用影响系数法对该轴承的刚度系数进行试验测试。通过对比试验数据和动网格计算结果发现两者基本吻合,表明所提出的计算方法是有效可行的。     

流固耦合对静压溜板承载性能影响分析

对重型机床静压溜板承载部位进行流固耦合分析,通过建立以雷诺方程和有限元计算为基础的流固耦合模型,分析了开式定量静压油垫的油膜刚度受供油流量、负载和材料特性的影响规律。将计算结果与不考虑流固耦合特性的分析结果进行对比,结果表明:在供油流量相同条件下,考虑流固耦合特性的油膜刚度相对不考虑流固耦合特性的油膜刚度下降更严重,所以,流固耦合特性对油膜刚度的影响不可忽视。     

齿轮动力学与弹性流体动力润滑耦合研究

为探究齿轮的动力学特性与弹流润滑耦合效应,综合考虑齿轮啮合刚度的时变效应和表面粗糙度对齿轮动力学行为的影响,基于动力学理论,建立了6自由度摩擦动力学模型。采用解耦方法求解该模型,将求解获得的轮齿动态啮合力和表面波动速度用于弹流润滑分析中。通过实例研究了动、静两种载荷模型下齿轮的弹流润滑特性。研究表明,与平稳载荷相比,基于动载荷模型的齿轮弹流润滑研究更能准确反映齿轮的瞬态润滑特性,在啮合刚度的激励下,润滑时油膜压力和油膜厚度均表现出一定的振荡效应。啮入点、单齿啮入点以及单齿啮出点存在较大的冲击,是齿轮弹流润滑的危险点。     

磨床用液体静压轴承径向承载特性分析

以磨床用液体静压轴承为例,利用计算流体动力学软件CFX,对动静压轴承的油膜进行稳态分析,得到油膜上的压力场分布,通过流固耦合技术把油膜压力添加到磨床主轴,对静压轴承进行结构静力分析,得到了轴承的径向承载力随偏心距的分布,通过换算求导得到油膜的刚度随着偏心率的分布。研究结果为静压轴承及磨床的转子动力学及静压轴承的优化提供理论依据。     

喷嘴挡板伺服阀前置级流固耦合特性研究

伺服阀前置级流固耦合特性与伺服阀的稳定性、快速性、气穴和自激噪声的产生密切相关。为研究喷嘴挡板伺服阀前置级流场的瞬态气穴分布特性以及流场作用下挡板的位移特性,提出了伺服阀前置级流固耦合分析方法,采用STAR-CCM+软件对伺服阀前置级流固耦合特性进行仿真分析,并通过流场分布规律实验观测对仿真方法进行了验证。结果表明,伺服阀前置级的流固耦合作用会引起流场周期性的瞬态分布和挡板谐振。     

核阀流体动力学及流固耦合特性数值模拟

以研究高压核电闸阀内流场特性及流固耦合问题为目的,分别建立了稳态、瞬态流体动力学模型和流固耦合作用下的结构动力学模型。通过分析模拟过程中流体的压力和速度分布可知,在稳态和瞬态流动状态下,流体在流经阀体中腔部位时均会产生压力波动,并在底部形成涡流。在流固耦合作用下闸阀的静力学结构变形和应力分布满足刚度和强度要求。然而,在流固耦合作用下,闸阀的动力学结构变形和应力较大,并在阀体与导轨部位产生局部应力集中。可通过加大应力集中部位的圆角以减小应力集中的程度。     

高速大功率电机转子通风孔散热效率优化研究

采用将转子与冷却气体流场实行分离的传统分析方法难以反映转子与冷却气流的热耦合作用,难以实现转子散热效率优化。提出基于流固耦合的高速大功率电机转子系统动态传热特性的分析方法,建立转子系统的流固耦合传热模型。利用建立的模型研究转速、冷却气流入口压力和速度,以及转子冷却孔分布、孔径和轴心距对转子温度场和散热效率的影响规律,提出了优化散热效率的具体途径。结果证明了所提出的计算方法和优化散热效率的具体措施的有效性。     

计入气穴影响的径推联合动静压浮环轴承稳定性研究

研究了计入气穴影响的径推联合动静压浮环轴承的动态性能和稳定性.给出了控制径推联合浮环动静压轴承内、外膜的气油两相流变密度、变黏度无量纲动态Reynolds方程及压力边界条件和深腔流量平衡方程;用有限元法对不同转速、不同偏心率下含气率为0和0.1的内外油膜进行了有限元计算,得到各部分的刚度系数和阻尼系数;计算了该径推浮环轴承的稳定性参数.结果表明:气穴使得径向、推力内外层油膜的刚度系数和阻尼系数均有所下降,随着偏心率的增大及转速的提高,气穴的影响程度减小;气穴使得轴承的无量纲临界转子质量降低,因此在供油压力急剧变化时必须考虑气穴的影响.     

流固耦合对油静压导轨动静特性的影响

油静压导轨被广泛应用于超精密机床,在设计和计算时往往都是将结构件作为刚体,即在工作过程中结构件不影响静压支承油膜厚度以及油压的分布。针对环形缝隙节流闭式油静压导轨,以封油面上动态雷诺方程和导轨的弹性变形方程为基础,再结合导轨工作台动力平衡方程,建立静压导轨的流固耦合模型。分析流固耦合对静压导轨压板变形量、动静刚度以及阶跃响应的影响。研究表明,导轨压板的变形随油腔压力的增加而线性增加;导轨压板的变形会导致动静刚度减小,也会导致阶跃响应的过渡时间变长;动静刚度的实测值与导轨压板有变形时的理论计算值吻合较好。     

渐开线斜齿轮传动摩擦动力学耦合研究

综合考虑时变啮合刚度、轴承刚度以及摩擦力等对动力学行为的影响,基于载荷分担理论和动力学、弹流润滑理论,建立12自由度斜齿轮摩擦动力学模型。采用解耦方法求解该摩擦动力学模型,将动力学求解获得的动态轮齿作用力用于润滑分析中,而润滑分析获得的摩擦因数再次用于动力学分析计算中。通过实例研究了齿面摩擦学特性和动力学行为以及两者之间的耦合关系。研究表明:考虑耦合效应后的斜齿轮动态响应与定摩擦因数下的动态响应相比有较大不同,且时变摩擦力对垂直于啮合线方向的动态响应影响尤为显著;动态载荷等对斜齿轮润滑特性影响较大,转速接近共振转速时,动态载荷作用下的油膜厚度、油膜承载比例、油膜温升和摩擦因数分布规律与幅值与稳态载荷相比差异明显。动态载荷对斜齿轮润滑特性以及时变滑动摩擦力对动态响应的影响不可忽略。     

Stiffness and damping coefficients for journal bearing using the 3D transient flow calculation

The dynamic coefficients of journal bearing are necessary components in the analysis of linear stability and response of rotating dynamic systems. We propose a new method for the numerical identification of bearing support force coefficients in flexible rotor-bearing systems based on the 3D transient flow calculation. The CFD commercial software FLUENT is mainly used in this simulation, which employs a finite volume method for the discretization of the Navier-Stokes equations. To determine the dynamic coefficients, a new mesh movement approach is presented to update the volume mesh when the journal moves during the 3D transient flow calculation of a journal bearing. Existing dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. Measurements and identification are performed on a test rotor supported on a pair of identical two-lobe fluid film bearings, and the results obtained from the CFD methods agree well with experimental results. The results indicate that the methods proposed in this paper can predict the dynamic coefficients of the journal bearing in a rotor-bearing system effectively, and provide a further tool for stability analysis.     

Application of computational fluid dynamics and fluid structure interaction techniques for calculating the 3D transient flow of journal bearings coupled with rotor systems

Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics (CFD)-fluid structure interaction (FSI) techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called ’’dynamic mesh’’ technique. A new mesh movement approach is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the journal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function (UDF). The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.     

Severity Estimation of Cracked Shaft Vibrations within Fluid Film Bearings

The equations of motion, with four degrees of freedom, taking into consideration the flexibility, damping and cross coupling of the fluid film bearings are derived for a cracked Jeffcott rotor supported on fluid film bearings.

Dimensionless equations are developed for dynamic radial load, dynamic pressure developed in the fluid film bearings and coefficient of dissipation considering the journal vibrations in two harmonics; bearing fluid film stiffness and damping coefficients. These are applied to a cracked Jeffcott rotor supported on different types of bearings, i.e., cylindrical journal bearings, offset cylindrical bearings, tilting pad journal bearings and three-lobe bearings. Based on the allowable dynamic pressure developed in the fluid bearings, the severity of cracked shaft and allowable crack depths are estimated in this study. Measurement of dynamic pressure and dissipation for monitoring the crack growth is suggested. However, 2x vibration is the best indicator of cracks in the shafts.     

Stiffness and damping coefficients of an inclined journal bearingSteifigkeit und dämpfungskoeffiziente eines schrägen gleitlagers

In the determination of the dynamic behaviour of a rotating shaft, the fluid film stiffness and damping coefficients of the bearings play an important role. The general practice is to ignore the rotational stiffnesses and damping coefficients due to the tilt of the journal in the bearing. This paper presents the stiffness and damping coefficients of such journal bearings. Using the expression for film thickness, the modified Reynolds' Equation for the tilted finite journal bearing is set up. The solution of this equation for the film pressure is obtained by using Fedor's proportionality hypothesis. The results obtained are presented in the form of non-dimensional charts.     

轴质量对用液体油膜轴承支承转子动特性的影响

本文研究了轴质量对支承于液体油膜轴承上的转子的影响.转子假定是位于弹性轴中部的薄盘,它考虑非零弹性轴质量由液体油膜轴承支承.该径向轴承假定为短简易型,用纵向的和相互作用的刚度及阻尼系数表示,这些系数与系统的角速度有关.假定转于由一电机加速,假定电机速度由一两阶传递函数控制.仿真结果表示质量比的小值,它由轴质量对盘质量比...     

表面织构动压滑动轴承油膜力解析模型

提出一种求解表面织构动压轴承油膜力的解析模型。基于Sommerfeld油膜边界,通过分离变量的方法,求解表面织构动压滑动轴承二阶偏微分Reynolds方程,得到表面织构动压滑动轴承油膜压力解析式。以圆形凹坑轴承为例,在油膜区域通过积分求得织构轴承的油膜力,分析织构参数对油膜压力的影响,研究发现,表面织构位于收敛区域(升压区)的轴承,其润滑与承载性能优于表面织构位于发散区域(降压区)的轴承、全织构轴承以及光滑轴承。对比了提出的解析模型与FDM和CFD模型在不同长径比和偏心率下的计算结果,结果表明,提出的解析模型能准确地描述表面织构动压滑动轴承的油膜力,且计算结果同FDM和CFD模型计算结果基本一致,验证了该模型的正确性。     

轴承载荷对转子系统各支承的耦合振动分析

以多支承转子 轴承 弹性基础系统为研究对象,对多支承转子系统某支承处轴承载荷变化引起不同支承点处轴及轴承的耦合振动响应进行了研究。首先,建立了多支承转子系统支承间的耦合振动模型,并进行了仿真和试验,耦合振动模型考虑了每个支承处的油膜耦合效应,通过轴承载荷敏感度矩阵得到各支承耦合力;然后,利用龙格库塔法对油膜刚度为定刚度和动刚度两种情况下的转子系统进行了数值分析及仿真;最后,在8支承转子试验台上进行试验,采取改变某一支承处的位移来得到轴承载荷的变化,并提取各支承处的振动信号。结果表明,轴承位置在稳态和瞬态两种情况下改变时振动响应明显不同,油膜刚度为动刚度的分析结果更为合理。     

Identification of unbalance forces by metaheuristic search algorithms

This paper discusses the identification of parameters in rotary systems, namely, the unbalance magnitude, phase and position in the rotor system. These parameters can be identified using the measured orbits in the hydrodynamic bearings. The oil film forces are evaluated in the different positions of the orbit of the journal and are applied to the model of the shaft. The model, integrated in time domain, allows with an assumed unbalance, to simulate the orbits. The objective function is basically the difference between measured and simulated orbits, and its minimum corresponds to the identified unbalance amount, phase and position along the shaft. With respect to traditional model based identification procedures, this approach using oil film forces instead of oil film linearized stiffness and damping coefficients, and unfiltered orbits instead of 1X vibration components is suitable to deal with non-linear behaviour of the system.     

Dynamic behavior of fluid‐structure coupling of hydrostatic spindle under effect of oil film slip

To better understand the dynamic characteristics of a hydrostatic spindle in fluid‐structure coupling, the impact of oil film slip on the 4 dynamic stiffness and damping coefficients of the spindle is studied. On the basis of modified Reynolds equation, which considers the microscale velocity slip effect, rotation error of the spindle is calculated. To solve the rotor axis orbit under the existence of eccentric quality, 4 dynamic stiffness and damping coefficients of the oil film, which describe the dynamics of a rotor axis orbit, are calculated by using load increment method and the pressure perturbation method. The research results show that velocity slip caused a certain impact on dynamics of bearing stiffness and damping performance. The experiment of the measuring path of the shaft verifies the correct and effect of the orbit of shaft center model.     

Approximate closed‐form solution for the dynamical analysis of short bearings with couple stress fluid

The film forces in journal bearings may cause self‐exciting oscillations under particular operating conditions; if the amplitude of these oil‐whirl oscillations becomes too large, it may involve unsafe machinery dynamics. Thus, there is a need to understand the dynamic characteristics of the journal bearings evaluating the performances of the couple stress lubricants used to minimise the friction losses in steady operating conditions. The purpose of this paper was to illustrate a method to formulate with closed‐form solutions the non‐steady fluid film forces, and the stiffness and damping coefficients for ‘short’ liquid‐lubricated couple stress journal bearings, assuming the micro‐continuum Stokes' model. It is shown that the model allows the advantage of minimising the computational time required for the non‐linear dynamic analysis of couple stress journal bearings without any significant loss of accuracy, while the analytical form of the solution involves a better readability of the parameter effects on the system unsteady behaviour. Copyright © 2007 John Wiley & Sons, Ltd.