矩形截面电容式微加速度计气膜阻尼研究

基于滑流修正的气体压膜雷诺方程,分析了矩形截面电容式微加速度计的敏感质量块在轴向运动中受到的气膜阻尼;指出了质量块受到的气膜阻尼力不仅与尺寸和速度有关,还与动量协调系数有关;得到了阻尼力和阻尼系数的简化解析解.     

简单孔节流静压气体轴承优化设计的一种解析解法

静压气体轴承在工程中应用广泛,但其设计工作涉及的计算繁琐,工程中多采用图表法或数值计算法。为简化工程计算过程,也为研究气体轴承中各参数间的关系提供直观的分析依据,从解析角度研究了静压气体轴承的优化设计问题。以简单孔节流圆盘静压气体止推轴承为研究对象,以轴承刚度最大为优化准则,首先利用数值计算求出与供气压比对应的最佳节流压比,再利用最小二乘法拟合得到它们的解析关系式,以此为基础,进而求出最佳气膜厚度、最佳承载力、最大刚度和最佳气体流量的解析解,并与精确数值解进行了比较验证。得到的解析解,使气体轴承的工程设计简便、有效。     

基于Workbench的高压圆盘气体轴承三维流场分析

为了取得高压圆盘气体轴承的完整三维流场,基于Workbench仿真软件对高压圆盘气体轴承进行三维建模仿真,得到整个流道及圆盘缝隙射流区的流场参数分布;将三维模型的气膜对称面与轴承圆盘、稳流管的轴对称面相交,截得气膜对称线;分析气膜对称线上的流场参数分布,并将其与二维简化模型流场计算结果进行对比,同时验证2种建模分析方法的有效性。结果表明：2种建模分析方法得到的气膜内马赫数和静压分布的变化规律一致,即在绝大部分气膜区域能保持高压,仅在气膜出口处很窄的范围内压力快速下降,同时在气膜出口附近形成超音速圆盘缝隙射流,使上游气膜内高压不受下游环境低压的影响;不同湍流强度对高压圆盘气体轴承内流场的静压无明显影响,但对缝隙射流区及气流远场区域的马赫数有着小幅影响。     

MEMS微平面构件的空气阻尼效应研究

对垂直于衬底表面运动的微平面构件产生的空气挤压阻尼进行研究。从非线性修正雷诺方程出发,计入稀薄气体效应,建立微平面空气挤压理论模型,用有限差分法进行求解。研究揭示了在谐振挤压运动周期内挤压膜的性能变化。研究发现,气体稀薄效应必须在理论分析模型中计入,否则,将高估空气阻尼的影响。微构件平面尺寸增大将增大挤压阻尼力,且阻尼力的增大速度大于微构件面积的增大速度。谐振频率的提高将显著增强空气阻尼效应。     

基于集总参数宏模型的微机械陀螺多域耦合分析

对微机械陀螺中静电、结构、空气阻尼等物理域进行有效分离，在分别对各域进行数值模拟的基础上提取相应的物理参数，建立集总参数模型。在考虑边缘效应的情况下，提取了微结构电容与位移的解析表达式；根据热一流体类似方法，提取了阻尼孔结构的阻尼系数和压膜刚度；根据结构动力学理论，由模态分析提取结构的有效刚度和有效质量。将这些物理参数综合在系统仿真器中与外围电路共同进行仿真，准确地评估不同条件下微机械陀螺的行为特性。     

油膜润滑径向轴承的全域解模拟计算-宽轴承解

雷诺方程的适用范围一般是在微米级膜厚，对纳米级膜厚由于粘度随油膜厚度的改变而改变，粘度成为更重要的润滑剂性能指标，本文采用粘度修正广义雷诺方程求解轴承的性能，对无限宽轴承来说，可得出全域的解析解，其公式可用于任意工作条件，从而为其它轴承的计算提供依据。     

油气弹簧圆盘形缝隙节流分析与特性试验

运用边界层理论推导了紊流状态下缝隙的积分流量表达式,提出了油气弹簧阀片圆盘形缝隙节流的一种研究方法。根据自主研发油气弹簧的结构形式,给出了阀片等效厚度的求解方式以及阻尼阀流量分配示意图,通过上述推导公式以及实际气体状态方程,建立了单气室油气弹簧的数学模型,并对特性进行了仿真和试验。结果表明所建立的油气弹簧圆盘缝隙紊流流量公式和特性数学模型是正确的,对阻尼阀的精确设计具有参考价值。     

圆盘气足的工程计算方法

气足是气体静压止推轴承的一种,是气浮导轨中最常见的部件。气足根据其形状又分为矩形气足与圆盘气足。圆盘气足广泛应用于三坐标测量机中。本文利用线性气源假设,将气膜中的气体二维流动化为一维流动,使雷诺方程得到简单的解析解,推导出了圆盘气足承载能力的工程计算方法,从而为气浮导轨中圆盘气足的设计找到了一条有效、快捷的途径。     

带硬涂层圆盘构件的固有振动特性的精确解法

研究了在广义弹性简支边界条件下的具有硬涂层的圆盘构件的自由振动的量纲一固有频率的精确解.首先利用多铁性多层圆盘的解析分析的多层板弹性理论,导出带硬涂层的圆盘结构的状态方程,其中以位移、电势、磁势、应力、电位移和磁感应强度为状态变量.利用有限Hankel变换和传播矩阵法,得到考虑压电和压磁效应的带硬涂层的圆盘的量纲一固有频率的精确解.根据算例结果,比较了压电、压磁两类硬涂层材料在单面涂层、双面涂层和不同涂层厚度的结构配置下的固有频率变化规律.     

无限短径向轴承动态雷诺方程考虑润滑油压粘效应时的解析解

在无限短径向轴承理论中,引入了线性化的压粘方程式,结合在动态情况下的雷诺方程,用富利叶正弦变换方法,得到油膜压强及油膜力的解析解。作为第一个特例,得到了转子失稳后油膜压强及油膜力的解析解。作为第二个特例,得到了静态时的解析解,算例的数值结果与文献中的叙述一致。为了检查所导出的公式的可信度,取压粘系数α等于０,使问题退化成为具有恒粘度的有关公式,其数值结果与有关文献的相应数值结果作了广泛比较,两者吻合度甚好。     

Experimental Analysis of the Gas Film Damping Effect in an Aerostatic Guideway under Microscale

This article studies the mechanism of gas film damping on the aerostatic guideway system at a microscale with the modified Reynolds equation. The slide film damping force due to the fluid viscous effect is calculated, and the squeeze damping force caused by the gas compression and escape between two plates is analyzed. The damping ratio in the calculation model for the slide film damping is compared with the calculated results from the experiment and the finite element analysis results. Using the results of the study, the optimal supply pressure is designed. The method applied in this article provides the theoretical basis for the analysis and solution of the dynamic performance of an aerostatic guideway.     

Dynamic coupling correlation of gas film in dry gas seal with spiral groove

In working state, the dynamic performance of dry gas seal, generated by the rotating end face with spiral grooves, is determined by the open force of gas film and leakage flow rate. Generally, the open force and the leakage flow rate can be obtained by finite element method, computational fluid dynamics method and experimental measurement method. However, it will take much time to carry out the above measurements and calculations. In this paper, the approximate model of parallel grooves based on the narrow groove theory is used to establish the dynamic equations of the gas film for the purpose of obtaining the dynamic parameters of gas film. The nonlinear differential equations of gas film model are solved by Runge-Kutta method and shooting method. The numerical values of the pressure profiles, leakage flux and opening force on the seal surface are integrated, and then compared to experimental data for the reliability of the numerical simulation. The results show that the numerical simulation curves are in good agreement with experimental values. Furthermore, the opening force and the leakage flux are proved to be strongly correlated with the operating parameters. Then, the function-coupling method is introduced to analyze the numerical results to obtain the correlation formulae of the opening force and leakage flux respectively with the operating parameters, i.e., the inlet pressure and the rotating speed. This study intends to provide an effective way to predict the aerodynamic performance for designing and optimizing the groove styles in dry gas seal rapidly and accurately.     

Gas film disturbance characteristics analysis of high-speed and high-pressure dry gas seal

The dry gas seal(DGS) has been widely used in high parameters centrifugal compressor, but the intense vibrations of shafting,especially in high-speed condition, usually result in DGS's failure. So the DGS's ability of resisting outside interference has become a determining factor of the further development of centrifugal compressor. However, the systematic researches of which about gas film disturbance characteristics of high parameters DGS are very little. In order to study gas film disturbance characteristics of high-speed and high-pressure spiral groove dry gas seal(S-DGS) with a flexibly mounted stator, rotor axial runout and misalignment are taken into consideration, and the finite difference method and analytical method are used to analyze the influence of gas film thickness disturbance on sealing performance parameters, what's more, the effects of many key factors on gas film thickness disturbance are systematically investigated. The results show that, when sealed pressure is 10.1MPa and seal face average linear velocity is 107.3 m/s, gas film thickness disturbance has a significant effect on leakage rate, but has relatively litter effect on open force; Excessively large excitation amplitude or excessively high excitation frequency can lead to severe gas film thickness disturbance; And it is beneficial to assure a smaller gas film thickness disturbance when the stator material density is between 3.1 g/cm~3 to 8.4 g/cm~3; Ensuring sealing performance while minimizing support axial stiffness and support axial damping can help to improve dynamic tracking property of dry gas seal. The proposed research provides the instruction to optimize dynamic tracking property of the DGS.     

A numerical model of an oscillating squeeze film between a rubber surface and a rigid surface

A numerical model for the hydrodynamic behavior of an oscillating squeeze film between a rubber surface and a rigid surface is presented. The effects of roughness of the rubber surface on the hydrodynamic force and the leakage flow rate in the squeeze film are analyzed. A modified Reynolds equation, Laplace equation and a three-parameter viscoelastic constitutive equation are solved simultaneously to obtain the pressure distribution in the squeeze film and the deformation of the rubber surface. Equations are discretized into finite difference equations and solved by Gauss-Siedel iteration method. It is found that increasing roughness of the surface profile significantly increases the hydrodynamic force accompanied by a small decrease in the leakage flow rate. Spatial distribution of the roughness of the rubber surface has no significant effect on the leakage flow rate or hydrodynamic force. The results obtained from the presented simple model are compared with the experimental results available in the literature and a very good agreement is found.     

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。     

多重网格法求解微机械谐振器的挤压膜阻尼

针对求解MEMS挤压膜阻尼过程中存在的问题,采用了多重网格方法进行求解,与传统方法相比,应用于挤压膜中流体问题的求解具有收敛速度快,数值稳定性好的优点,求得了谐振器平板间的压力分布函数以及微谐振器的各个性能指标的值,研究了挤压膜中流体阻尼力的特性以及与谐振器件幅—频特性的关系。     

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.     

LUBRICATION FILM FORMATION MECHANISM OF SLIPPER PAIRS IN LOW SPEED HIGH TORQUE HYDRAULIC MOTORS

Pressure-flow analytical formulas of lubrication film of slipper pairs on camshaft connect- ing rod type low speed high torque (LSHT) hydraulic motors are put forward. The bottom surface of slipper pairs is rectangle, and the effect of squeeze flow and pressure differential flow is considered. The dynamic process of lubrication film formation through squeezing is numerically studied by com- puter simulation. Effects of supply pressure, initial lubrication film thickness, velocity damping coef- ficient, loading impact and gravity, etc are studied. Advantages of novel slipper pairs with large oil cavity area are pointed out.     

Squeezing flow between rigid tilted surfaces: A general solution and case study for MEMS

Squeeze film flow occurs when two surfaces move in a normal direction relative to each other and is a phenomenon of importance to many engineering systems, from macro to microscale. Squeeze film damping is widely used in large‐scale rotating machinery but even more so presently in microsystems. In the latter case, for modelling purposes, the two surfaces producing the squeeze film flow are typically assumed perfectly parallel, which is often not the case in practice. This paper presents a general formula for squeezing flow between two rigid surfaces for both parallel and tilted configurations in the 1‐dimensional case (2‐dimensional flow). The solution is derived from the Reynolds equation. The results in the parallel case compare favorably to previous literature data. A case study is presented for plates with dimensions characteristic of microelectromechanical systems. The important contribution of this paper is to isolate and study this “tilt effect” which can contribute to discrepancies and confusion in interpreting squeeze film behaviour, particularly at the microscale.