冲击载荷作用下滑动轴承油膜压力与应力研究

对动载滑动轴承雷诺方程进行推导,基于有限差分法求解雷诺方程,得到油膜压力分布,并由接触力学分析求得轴承应力。将计算结果与有关研究结论进行对比分析,验证了计算模型的有效性和合理性,并对比分析了阶跃、正弦、孤峰波形冲击作用下滑动轴承油膜压力分布特征。进而对计算方法工程化,研究某舰用齿轮箱滑动轴承在冲击载荷作用下的油膜压力与轴承应力分布,计算结果表明:冲击作用下油膜压力三维分布近似为一连续的抛物面分布,轴承与轴颈接触表层的最大应力逐渐向内表层移动,越靠近接触表面,轴承与轴颈接触表层的最大应力越大,且最大应力产生于最大流体动压力区域。     

磁盘机流体轴承计算机仿真

以二维度平均的雷诺方程作为流体动压轴承的控制方程，通过用有很元方法求解做扰动方程求取轴承刚度系数和阻尼系数，所取单元为三节点的三角形单元。     

陀螺仪进动与章动运动分析

为了分析阻尼条件下陀螺仪章动与进动关系,从陀螺仪动力学模型出发,利用动静法建立运动方程,推导出理想条件下和阻尼条件下的进动与章动模型,指出章动方向上角度的变化中包含重力矩引起的章动和铅垂轴方向阻尼力矩引起的转子轴进动2个方面的影响,并通过实验得到进动和章动摆动曲线,同时证明阻尼能有效消除章动,为以后研究陀螺仪章动提供理论依据。     

PZT微驱动器磁头的动特性研究

采用摄动法对描述超薄气体润滑理论的修正雷诺方程进行处理,建立了气体润滑的静动态方程,求解得到磁头气膜的无量纲刚度系数和阻尼系数,并讨论了磁头线速度对空气膜刚度系数和阻尼系数的影响.采用的磁头模型是一种PZT微驱动器磁头,其主体部分飞高为20 nm,读写头处飞高可达5 nm.模拟结果表明,磁头末端下降15 nm后,其动态特性和稳定性明显提高;磁头线速度在8.0 m/s～11.2 m/s变化时,气膜刚度系数线性增加,阻尼系数却线性减小.     

不同载荷工况下机床主轴预紧力选取的数值分析方法

为研究预紧力对机床主轴的影响,提出在不同载荷工况下机床主轴预紧力选取的数值分析方法.计算得到预紧力与轴承刚度的关系,在轴系结构有限元模型中设置不同预紧力下的轴承刚度值,通过静力学分析求解轴系变形和刚度;计算得到预紧力与轴承发热量的关系,在轴系热分析有限元模型中设置轴承热源,通过传热分析求解主轴温升.计算结果表明,该方法...     

面向二维零质量射流的动网格数值模拟方法

为了研究零质量射流的作用机理和流场结构,发展了一套面向二维零质量射流的非结构化动网格模拟方法:采用控制容积法,引入动网格控制方程,并与任意曲线坐标系下矩阵形式的时均可压缩N-S方程组联合求解,迭代过程中采用弹性类推法进行动态网格更新.基于此方法,对二维零质量射流进行数值模拟,对计算获得的流场涡线和流线分布进行了分析和讨论,并与其他学者类似算例进行了比较,表明该方法能够合理揭示零质量射流的流场结构和作用机理,可实现二维零质量射流的数值模拟.     

弹性环挤压油膜阻尼器支撑下的柔性转子系统动力学分析

弹性环挤压油膜阻尼器(Elastic ring squeeze film damper, ERSFD)具有良好的支撑作用和减振效果,但由于其结构和流场耦合行为极为复杂,使得已有的物理模型难以完整表现出ERSFD的力学特性.为了进一步探究ERSFD的力学机理,本文借助有限元仿真平台,采用双向流固耦合的计算方法,剖析弹性环与油膜之间的相互作用,获取ERSFD中油膜压力的分布规律.在此基础上,利用最小二乘法进一步拟合出ERSFD等效刚度、等效阻尼与转子轴颈扰动位移的映射关系,并将其分别引入柔性转子系统动力学模型中.通过数值计算研究了ERSFD支撑下柔性转子系统的振动响应,分别给出了不同转速下转子系统的响应分岔图、轴心轨迹等.同时,通过对比分析,进一步揭示了ERSFD所诱发出的转子系统丰富的非线性动力学行为,有助于对ERSFD轴承支撑特性的理解.     

轴承预紧力对转子系统静动态特性的影响

轴承预紧力的大小直接影响到滚动轴承-转子系统的静动态特性. 综合考虑离心力和陀螺力矩效应,在Romax软件中建立了5自由度轴承-转子系统动力学模型,分析了预紧力对轴承刚度、工作接触角以及工作寿命的影响,并搭建了轴承 转子系统试验台做验证试验. 在不同轴承预紧力下,分别研究了轴承刚度、工作接触角、工作寿命、静载荷作用下轴承 转子系统的静变形以及动不平衡载荷作用下主轴系统的振动响应等,并在轴承-转子试验台上进行试验验证,得到了轴承预紧力与这些因素的关系曲线. 在此基础上,研究了预紧力对转子系统固有频率的影响,结果表明加大预紧力有助于提高系统的固有频率. 研究结果可为轴承-转子系统的设计与分析提供理论参考.     

可倾瓦推力滑动轴承静动特性的实验研究

在近些年中涡轮机组的轴向振动引起了越来越多的关注。可倾瓦推力滑动轴承被广泛应用于涡轮汽轮机组来承受轴向力。润滑油膜的动特性因素对于转子及其轴承的轴向振动有很大影响。因此建立一种方法来测试推力轴承的动特性是十分有必要的。设计了一种测试一个测试推力轴承性能的实验装置,其采用了倒置式结构,可同时测量采集轴瓦的温度,油压及油膜厚度。实验结果显示出了试验工况的选择对推力滑动轴承的静动特性影响巨大。     

飞艇动力学仿真

刚体假设条件下,飞艇动力学行为的核心问题之一是如何获取气动导数和推进系统螺旋桨的性能参数.针对静导数,采用分块粘结技术和O型网格,生成结构化贴体网格单元,利用SST(Shear Stress Transport)湍流模型进行CFD仿真,动导数采用半经验的方法,附加质量采用边条理论计算.螺旋桨性能参数采用结构化网格与非结构化网格相结合的方法,利用旋转机械CFD软件计算.在此基础上给出了飞艇纵向静稳定性的判别方法,建立飞艇非线性动力学方程和小扰动方程.为验证上述方程,给出了纵向阶跃响应,仿真结果表明该方法是有效的,可用于飞艇后续的飞行控制研究.     

空间杆系结构回传波射分析及程序实现

为有效地进行杆系结构应力波响应分析,基于传统的空间杆系结构回传波射矩阵法,考虑黏滞阻尼、复刚度阻尼及节点集中质量的影响,采用VC+ +编制通用回传波射矩阵法分析程序. 该程序可以计算空间杆系结构在任意动力集中载荷作用下任意位置的动力瞬态响应. 针对某刚架结构,比较运用该程序与运用有限元法得到的结果,验证该方法的精确度.     

Design sensitivity analysis of multi-span non-linear elastic beam–columns with elastic supports

The incremental problem arising from the design perturbation of a materially non-linear elastic beam–column with intermediate supports and elastic end supports is formulated via a second variation of the potential energy functional, augmented with constraint conditions. Design variables are distributed parameters (bending stiffness and transverse load), discrete (compression force, end points dead loads and elasticity of supports) and domain (length and intermediate support points). The state variables perturbations are the solution of an incremental BVP (equilibrium differential equation, static, kinematic and jump conditions) derived from an incremental virtual work equation. A sensitivity formula is obtained by the adjoint method.     

Forced vibration of a curved beam with viscous damping

A generalization of the dynamic solution for an arbitrary plane curved beam with viscous damping, under arbitrary load, is presented. The equation of motion, based on the linear theory, admits proportionality of the damping to the mass and stiffness matrices (Raleigh damping). The numerical solution is obtained by direct time-integration, using backward differences (Houbolt's method). A general computer program (CURBEAM) was written for this purpose and a numerical example is presented.     

Dynamic characteristics of a coupled journal and thrust hydrodynamic bearing in a HDD spindle system due to its groove location

 This research numerically analyzes the dynamic characteristics of a coupled journal and thrust hydrodynamic bearing due to its groove location which has the static load due to the weight of a rotor in the axial direction and the dynamic load due to its mass unbalance in the radial direction. The Reynolds equation is transformed to solve a plain member rotating type of journal bearing (PMRJ), a grooved member rotating type of journal bearing (GMRJ), a plain member rotating type of thrust bearing (PMRT), and a grooved member rotating type of thrust bearing (GMRT). FEM is used to solve the Reynolds equations in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or axial displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge–Kutta method. This research shows that the groove location affects the pressure distribution in the fluid film and consequently the dynamic performance of a HDD spindle system. Received: 5 July 2001/Accepted: 17 October 2001     

Prediction of dynamic properties of rotor supported by hydrodynamic bearings using the finite element method

The purpose of this paper is to present general programs for rotor bearing analysis using the Finite Element Method. A consistent representation of both mass and stiffness is used for the rotor shaft, while hydrodynamic bearings are calculated by solving Reynolds equation. Dynamic characteristics of these bearings are then obtained with a perturbation method.These programs are first compared with both numerical and experimental results from literature. We also study the influence of bearing characteristics on stability threshold and unbalance response of a rotor.     

Dynamic and static characteristics of a hydrostatic spindle for machine tools

The objective of this work is to study the static and dynamic behavior of a shaft supported by hydrostatic bearings. The hydrostatic bearing consists of a thrust bearing and a radial bearing fed by orifice restrictors. The radial bearing consists of six rectangular symmetry oil pockets that have the same depth; the thrust bearing consists of eight fan-shaped oil pockets. Static and dynamic modeling was performed in order to investigate the effect of the eccentricity ratio on the film thickness, stiffness and deformation of a spindle system. In the first step, the deformation of the spindle caused by the parameter change is studied according to a static model. In the second step, the vibration response caused by the eccentricity is analyzed with a dynamic model. In the third step, the effect of imbalanced vibration on the machining accuracy is analyzed; the imbalance-induced force in two directions is derived from the dynamic results. This research shows that the location and stiffness of the bearing affect the machining accuracy to a high degree.     

Customized Dynamic Load Balancing for a Network of Workstations

Load balancing involves assigning to each processor work proportional to its performance, thereby minimizing the execution time of a program. Although static load balancing can solve many problems (e.g., those caused by processor heterogeneity and nonuniform loops) for most regular applications, the transient external load due to multiple users on a network of workstations necessitates a dynamic approach to load balancing. In this paper we show that different load balancing schemes are best for different applications under varying program and system parameters. Therefore, application-driven customized dynamic load balancing becomes essential for good performance. We present a hybrid compile-time and run-time modeling and decision process which selects (customizes) the best scheme, along with automatic generation of parallel code with calls to a run-time library for load balancing.     

Buckling of pressure loaded rings and shells by the finite element method

The correct formulations for solving nonlinear structural problems by the finite element method have now been established. Numerous investigators have given the derivation for the solution of problems by the incremental tangent stiffness method and total formulation methods. These derivations have been applied to many problems and the results have been shown to be quite accurate for the problems that have been selected. However there is one area of application that has received practically no attention. This is in the investigation of the buckling strength of pressure loaded rings and shells. The effect of pressure loading where the loading changes direction as the structure deforms has been included in several previous derivations, by what is known as the load stiffness matrix, but to the author's knowledge no one has investigated problems where this effect has been included in the solution procedure. For rings and some buckling modes of shells, the results can be in error by as much as 50%.This paper will describe an iterative process for solving the nonlinear equilibrium equations and correcting the loads to include the effect of changing geometry at each load level. This approach is different from the classical eigenvalue or bifurcation method. Several case studies will be described which were performed on ring and shell problems. The geometry of these example problems were axisymmetric and in order to apply a nonlinear collapse analysis, the structure had to be perturbed out of its axisymmetric pattern into a buckling pattern. Imperfect geometry and very small concentrated loads were used to cause this perturbation and this will be described in the paper. The sensitivity of the computed collapse pressure to the finite element mesh gradation will be discussed. A comparison will be made between results obtained by including the effect of following pressure load and those obtained by not including this effect.     

Dynamic response of a torsional micromirror to electrostatic force and mechanical shock

In this paper dynamic characteristics of a capacitive torsional micromirror under electrostatic forces and mechanical shocks have been investigated. A 2DOF model considering the torsion and bending stiffness of the micromirror structure has been presented. A set of nonlinear equations have been derived and solved by Runge–Kutta method. The Static pull-in voltage has been calculated by frequency analyzing method, and the dynamic pull-in voltage of the micromirror imposed to a step DC voltage has been derived for different damping ratios. It has been shown that by increasing the damping ratio the dynamic pull-in voltage converges to static one. The effects of linear and torsional shock forces on the mechanical behavior of the electrostatically deflected and undeflected micromirror have been studied. The results have shown that the combined effect of a shock load and an electrostatic actuation makes the instability threshold much lower than the threshold predicted, considering the effect of shock force or electrostatic actuation alone. It has been shown that the torsional shock force has negligible influence on dynamic response of the micromirror in comparison with the linear one. The results have been calculated for linear shocks with different durations, amplitudes, and input times.