换向持续时间和换向点位置对往复运动齿轮齿条弹流润滑的影响

往复运动齿轮齿条的润滑失效通常发生在换向死点位置附近,因此研究齿轮齿条换向点位置和换向持续时间对换向过程中润滑油膜的影响具有重要的实际意义。根据齿轮齿条换向瞬间的运动几何关系,建立了换向过程齿轮齿条弹流润滑的瞬态数值模型。采用Ree-Eyring润滑流体,应用多重网格法和多重网格积分法等数值方法,计算得到了齿轮齿条往复运动过程中换向点位置附近一对啮合轮齿间的压力、膜厚和温度,并与前人的实验结果进行了对比验证。分析了不同换向持续时间和换向点位置对一对啮合轮齿间压力、膜厚和温度的影响。齿轮齿条换向过程中油膜厚度明显降低,缩短换向持续时间虽然可以增大齿轮齿条的润滑膜厚,但会导致瞬间油温升高,因此换向持续时间存在最优值。通过比较不同换向死点位置的膜厚发现,当换向死点在单齿啮合后的双齿啮合区时,啮合轮齿间具有较理想的润滑膜厚。无论换向持续时间长短,润滑膜厚的最小值都在换向死点位置,换向死点位置是往复运动齿轮齿条润滑失效的危险点。研究结果为往复运动齿轮齿条的润滑设计提供了理论依据。     

换向持续时间和换向点位置对往复运动齿轮齿条弹流润滑的影响

往复运动齿轮齿条的润滑失效通常发生在换向死点位置附近,因此研究齿轮齿条换向点位置和换向持续时间对换向过程中润滑油膜的影响具有重要的实际意义。根据齿轮齿条换向瞬间的运动几何关系,建立了换向过程齿轮齿条弹流润滑的瞬态数值模型。采用Ree-Eyring润滑流体,应用多重网格法和多重网格积分法等数值方法,计算得到了齿轮齿条往复运动过程中换向点位置附近一对啮合轮齿间的压力、膜厚和温度,并与前人的实验结果进行了对比验证。分析了不同换向持续时间和换向点位置对一对啮合轮齿间压力、膜厚和温度的影响。齿轮齿条换向过程中油膜厚度明显降低,缩短换向持续时间虽然可以增大齿轮齿条的润滑膜厚,但会导致瞬间油温升高,因此换向持续时间存在最优值。通过比较不同换向死点位置的膜厚发现,当换向死点在单齿啮合后的双齿啮合区时,啮合轮齿间具有较理想的润滑膜厚。无论换向持续时间长短,润滑膜厚的最小值都在换向死点位置,换向死点位置是往复运动齿轮齿条润滑失效的危险点。研究结果为往复运动齿轮齿条的润滑设计提供了理论依据。     

计及短周期误差的直齿轮副近周期运动及其辨识

齿轮副中的齿距偏差等短周期误差使系统出现复杂的周期运动, 影响齿轮传动的平稳性. 将该类复杂周期运动定义为近周期运动, 采用多时间尺度Poincaré映射截面对其进行辨识. 为研究齿轮副的近周期运动, 引入含齿距偏差的直齿轮副非线性动力学模型, 并计入齿侧间隙与时变重合度等参数. 采用变步长4阶Runge-Kutta法数值求解动力学方程, 由所提出的辨识方法分析不同参数影响下系统的近周期运动. 根据改进胞映射法计算系统的吸引域, 结合多初值分岔图、吸引域图与分岔树状图等研究了系统随扭矩与啮合频率变化的多稳态近周期运动. 研究结果表明, 齿轮副中的短周期误差导致系统的周期运动变复杂, 在微观时间尺度内, 系统的Poincaré映射点数呈现为点簇形式, 系统的点簇数与实际运动周期数为宏观时间尺度的Poincaré映射点数. 短周期误差导致系统在微观时间尺度内的吸引子数量增多, 使系统运动转迁过程变复杂. 合理的参数范围及初值范围可提高齿轮传动的平稳性. 该辨识与分析方法可为非线性系统中的近周期运动研究奠定理论基础.      

非牛顿流体固粒悬浮流的若干问题

非牛顿流体固粒悬浮流具有广泛的应用背景,其特殊的流动属性使其成为一些新兴技术领域的核心突破点.同时,该流动又比较复杂,即便是在低固粒浓度的情况下,非牛顿流体特性也会对整个系统的微结构产生重要的影响,从而进一步影响固粒的运动.本文给出了非牛顿流体方程、固粒运动方程和非牛顿流体固粒悬浮流的特征参数,分析了这些参数的作用;阐述了单个固粒在管道中的径向移动、多固粒的相互作用和聚集、多固粒形成的链状结构以及非圆球固粒运动等方面的研究成果、结果分析以及尚未解决的问题,并对以上问题进行了总结和展望,给出了需要深入研究的具体问题和内容,旨在为进一步的研究提供参考和依据.     

精密离心机主轴回转误差对加速度计输入精度的影响

介绍了用4个位移传感器法测试精密离心机主轴径向回转误差和倾角回转误差的方法，计算了主轴回转误差中一次谐波，它包括圆锥运动和一次谐振运动，对一次谐波如何影响精密离心机中的向心加速度及其在加速度计坐标系下的分配作了详细分析，同时对重力加速度分配的影响也作了详细的分析。最后得出了被测加速度计的输入加速度的平均值的补偿方法，进一步提高了加速度计的输入精度。通过对离心机主轴回转误差运动的检测和测试，定量分析了对加速度计输入精度的影响，有助于提高加速度计的标定精度。     

受支架支撑的血管管壁变形及应力分析

为了计算动脉粥样硬化和局部斑块形成的堵塞对血管壁工作状态的影响,论文根据血液流动的连续性方程、运动方程,管壁的运动方程,在给定了血压波形函数的基础上,求得了狭窄血管管壁的径向位移及环向应力.分析了不同狭窄程度对血管壁变形及应力的影响;给出了不同狭窄情况下和局部斑块硬化程度不同时,血管植入支架所需的作用力;计算出植入支架后血管壁的径向位移及应力状态.论文的研究结果可供临床上对狭窄血管植入支架后的变形与受力分析及支架的正确安放参考;可避免发生堵塞严重或血管钙化时,由于安放支架不当而发生血管破裂的医疗事故.     

硅微陀螺正交误差及其对信号检测的影响

分析了硅微陀螺正交误差在运动方程中的表现,利用Simulink仿真研究了正交误差对信号检测的影响。文中先推导了不等弹性存在的情况下正交误差等效角速度的表达式,随后分析了某型硅微陀螺在角速度输入为0（°）/s和80（°）/s时敏感振动的频谱图,最后仿真分析了正交误差对模拟和数字检测电路的影响。经分析,对于模拟解调电路,正交误差会导致陀螺的零偏和温漂;对于数字解调电路,由于正交误差大大减小了敏感振动的电压幅值对角速度的标度因数,在AD量化噪声及其它电路噪声一定的情况下,会使陀螺零偏稳定性变差,从而限制了数字解调的优势。     

杆状弯曲行波型超声电机运动机理研究

为了深入研究杆状弯曲行波型超声电机的运动机理，本文分析了定子表面质点椭圆运动轨迹的形成，并将椭圆运动分解为产生驱动力的有效椭圆运动与使定、转子产生径向滑动的径向直线运动；然后基于有效椭圆运动变化情况，分析了在两相振幅不平衡和任意相位差情况下对转子运动平稳性的影响，为这类电机的设计和性能控制提供理论依据。     

环形浅池内硅熔体中的热流体波

为了了解工业Czochralski炉内硅熔体表面轮型的基本特征,对环形浅池内硅熔体的热毛细-浮力对流进行了三维数值模拟,硅熔池内径为15 mm,外径为50 mm,深度为3 mm,熔池外壁被加热,内壁被冷却,底部固壁和顶部自由表面均绝热或者允许一个垂直方向的传热。模拟结果表明,当径向温差较小时,熔池内会产生稳定的单胞热毛细-浮力流动,随着温差的增大,流动将转变为三维振荡流动,在熔体自由表面会出现沿周向运动的轮型,小的垂直方向的热流密度(3W/cm2)对这种振荡流动没有大的影响。同时,讨论了流动和温度波动的特征,并确定了振荡流动的临界条件。     

转子轴承系统振动响应谱的仿真研究

在转子轴承系统振动信号处理中,针对平稳信号的传统傅里叶变换精度较低、快变启动过程的非平稳信号频谱分析方法较复杂的问题,本文仿真构造了两类响应信号。通过对比给定信号参数与信号识别参数的误差研究了几种谱分析方法或过程的简便性和准确性。对转子系统振动平稳信号离散频谱分析时存在的误差进行了定量分析,利用比例插值法对误差进行校正,开发了高精度谱分析测试软件;分析了转子轴承系统快变过程非平稳振动信号的特征,探索了一种将t时空域非平稳信号转变为tn时空间域平稳信号的办法或过程,然后结合比例插值校正法对其进行频谱分析,再返回到t时空域获得某时刻的谱特征参数;构造了转子系统振动仿真信号检验了上述过程的准确性。研究结果表明:比例插值法提取的谱特征数据近乎与仿真信号设定值相等;针对本文构造的快变过程非平稳仿真信号,利用本文给出的谱分析过程产生的频率误差最大值为0.47%,幅值误差最大值为0.2%。本文的仿真研究为提出和考证新的谱分析方法提供了手段。     

On the nonlinear stability behaviour of distorted plane Couette flow

This paper discusses the nonlinear stability behaviour of distorted plane Couette flowto 2-dimensional disturbances,and compares it with that of distorted plane Poiseuille flow.The results show that plane Couette flow is more unstable than plane Poiseuille flow tofinite-amplitude disturbances.     

Empirical slip and viscosity model performance for microscale gas flow

For the simple geometries of Couette and Poiseuille flows, the velocity profile maintains a similar shape from continuum to free molecular flow. Therefore, modifications to the fluid viscosity and slip boundary conditions can improve the continuum based Navier–Stokes solution in the non‐continuum non‐equilibrium regime. In this investigation, the optimal modifications are found by a linear least‐squares fit of the Navier–Stokes solution to the non‐equilibrium solution obtained using the direct simulation Monte Carlo (DSMC) method. Models are then constructed for the Knudsen number dependence of the viscosity correction and the slip model from a database of DSMC solutions for Couette and Poiseuille flows of argon and nitrogen gas, with Knudsen numbers ranging from 0.01 to 10. Finally, the accuracy of the models is measured for non‐equilibrium cases both in and outside the DSMC database. Flows outside the database include: combined Couette and Poiseuille flow, partial wall accommodation, helium gas, and non‐zero convective acceleration. The models reproduce the velocity profiles in the DSMC database within an L₂ error norm of 3% for Couette flows and 7% for Poiseuille flows. However, the errors in the model predictions outside the database are up to five times larger. Copyright © 2005 John Wiley & Sons, Ltd.     

Stability of plane poiseuille and couette flow of a Maxwell fluid

The classical Orr-Sommerfeld analysis is extended to a Maxwell fluid in fully developed Poiseuille flow between two flat plates and Couette flow between two flat plates. For the Poiseuille flow problem eigenmodes that are anti-symmetric in position are considered to augment the literature results for the symmetric eigenmodes. A shooting method with a stiff integrator, orthonormalization, and Newton-Raphson iterations on the eigenvalue are used to find the eigenvalues. The most dangerous mode is the anti-symmetric one, and both symmetric and anti-symmetric modes are more dangerous when the wave number and the Weissenberg number are large. No unstable eigenvalues are found.     

Axial Couette–Poiseuille flow of Bingham fluids through concentric annuli

In this paper, the axial Couette–Poiseuille flow of Bingham fluids through concentric annuli is studied. Analytical solutions of different types of flow are derived. Compared to previous studies, we emphasize two new types of flow, which have been missed previously, are found in our results. Hence, there are eight different forms of the velocity profile depending on values of three dimensionless parameters, which are the Bingham, axial Couette numbers and the radius ratio. Distributions of these eight forms are specified in the parameter plane of axial Couette number vs. Bingham number for various radius ratios. These new flow regimes are analyzed from both a mathematical and physical perspective.     

Linear stability of plane creeping Couette flow for Burgers fluid

It is well known that plane creeping Couette flow of UCM and Oldroy-B fluids are linearly stable. However, for Burges fluid, which includes UCM and Oldroyd-B fluids as special cases, unstable modes are detected in the present work. The wave speed, critical parameters and perturbation mode are studied for neutral waves. Energy analysis shows that the sustaining of perturbation energy in Poiseuille flow and Couette flow is completely different. At low Reynolds number limit, analytical solutions are obtained for simplified perturbation equations. The essential difference between Burgers fluid and Oldroyd-B fluid is revealed to be the fact that neutral mode exists only in the former.     

Slip effects on shearing flows in a porous medium

This paper deals with the magnetohydrodynamic （MHD） flow of an Oldroyd 8-constant fluid in a porous medium when no-slip condition is no longer valid. Modified Darcy＇s law is used in the flow modelling. The non-linear differential equation with non-linear boundary conditions is solved numerically using finite difference scheme in combination with an iterative technique. Numerical results are obtained for the Couette, Poiseuille and generalized Couette flows. The effects of slip parameters on the velocity profile are discussed.     

Finite-Amplitude Equilibrium Solutions for Plane Poiseuille–Couette Flow

Two-dimensional nonlinear equilibrium solutions for the plane Poiseuille–Couette flow are computed by directly solving the full Navier–Stokes equations as a nonlinear eigenvalue problem. The equations are solved using the two-point fourth-order compact scheme and the Newton–Raphson iteration technique. The linear eigenvalue computations show that the combined Poiseuille–Couette flow is stable at all Reynolds numbers when the Couette velocity component σ₂ exceeds 0.34552. Starting with the neutral solution for the plane Poiseuille flow, the nonlinear neutral surfaces for the combined Poiseuille–Couette flow were mapped out by gradually increasing the velocity component σ₂. It is found that, for small σ₂, the neutral surfaces stay in the same family as that for the plane Poiseuille flow, and the nonlinear critical Reynolds number gradually increases with increasing σ₂. When the Couette velocity component is increased further, the neutral curve deviates from that for the Poiseuille flow with an appearance of a new loop at low wave numbers and at very low energy. By gradually increasing the σ₂ values at a constant Reynolds number, the nonlinear critical Reynolds numbers were determined as a function of σ₂. The results show that the nonlinear neutral curve is similar in shape to a linear case. The critical Reynolds number increases slowly up to σ₂∼ 0.2 and remains constant until σ₂∼ 0.58. Beyond σ₂ > 0.59, the critical Reynolds number increases sharply. From the computed results it is concluded that two-dimensional nonlinear equilibrium solutions do not exist beyond a critical σ₂ value of about 0.59. Received: 26 November 1996 and accepted 12 May 1997     

Mechanism of flow instability and transition to turbulence

In this paper, a new mechanism of flow instability and turbulence transition is proposed for wall bounded shear flows. It is stated that the total energy gradient in the transverse direction and that in the streamwise direction of the main flow dominate the disturbance amplification or decay. Thus, they determine the critical condition of instability initiation and flow transition under given initial disturbance. A new dimensionless parameter K for characterizing flow instability is proposed which is expressed as the ratio of the energy gradients in the two directions for the flow without energy input or output. It is suggested that flow instability should first occur at the position of K_max which may be the most dangerous position. This speculation is confirmed by Nishioka et al.'s experimental data. Comparison with experimental data for plane Poiseuille flow and pipe Poiseuille flow indicates that the proposed idea is really valid. It is found that the turbulence transition takes place at a critical value of K_max of about 385 for both plane Poiseuille flow and pipe Poiseuille flow, below which no turbulence will occur regardless the disturbance. More studies show that the theory is also valid for plane Couette flows which holds a critical value of K_max of about 370.     

Effect of duct velocity profile and buoyancy‐induced flow on efficiency of transient hydrodynamic removal of a contaminant from a cavity

This paper describes a preliminary numerical analysis of the effect of duct velocity profile and buoyancy‐induced flow generated by the heat source on hydrodynamic removal of contaminants contained in cavities. The process of fluid renewal in a cavity is modelled via a numerical solution of the Navier–Stokes equations coupled with the energy equation for transient flows. The foulant has the same density as the fluid in the duct and the duct velocity profile is considered to be Poiseuille flow and Couette flow, respectively. The results show that the change in Grashof number and duct flow velocity profile causes a dramatic difference in the observed flow patterns and cleaning efficiency. From a cleaning perspective, the results suggest that Couette flow at higher value of Grashof number becomes more effective in further purging of contaminated fluid from a cavity. Copyright © 2004 John Wiley & Sons, Ltd.     

On the steady simple shear flows of the one-mode Giesekus fluid

Analytical solutions for the plane Couette flow and the plane Poiseuille flow of the one-mode Giesekus fluid without any retardation time have been obtained by considering the domain of definition for each of the two branch solutions which arise due to the presence of the quadratic stress terms in the constitutive equations. For each fixed value of the mobility parametera, the limiting value of the Weissenberg number for the upper branch solution, i.e., the physically realistic solution is determined in terms of the corresponding dimensionless shear stress for the plane Couette flow and in terms of the corresponding dimensionless pressure gradient for the plane Poiseuille flow. In the case of the plane Couette flow, it is shown that fora falling in the range 0a1/2 only the physically realistic solution exists while for 1/2<a 1 a nonphysical solution coexists with the realistic one. In the case of the plane Poiseuille flow, it is shown that the non-physical solution cannot even exist around the center plane of the channel, and the effects of the mobility parameter and the dimensionless pressure gradient on the flow variables are investigated. Possible extensions of the present approach to other steady simple shear flows with and without the introduction of the retardation time are also discussed.