轴向摩擦双盘转子的振动分析

为研究轴向摩擦对转子运动的影响,利用弯曲变形和微小角位移矢量合成理论,推导出圆盘与封严圈之间的轴向碰撞力和摩擦力计算公式.根据力矩相等原则,将轴向碰撞力转化为作用于盘心的横向力.建立简支单跨双盘转、静子轴向碰摩的弯扭耦合振动方程,并数值模拟分析弯曲共振时,不同的转、静子轴向间隙对转子运动的影响.结果表明,随着间隙改变,转子横向和扭转运动特征都会发生相应变化,且扭转运动更能反映轴向摩擦的程度.     

轴向超声振动辅助磨削的磨削力建模

以单颗磨粒为对象,分析轴向超声振动下磨粒的运动特性。在此基础上,将磨削力分为切屑变形力和摩擦力两部分,分别分析了轴向超声振动对切屑变形力和摩擦力的影响。在切屑变形力方面,轴向超声振动改变了磨粒运动方向与主切削方向间的夹角;在摩擦力方面,轴向超声振动降低了磨粒与工件间的摩擦因数。基于此建立了轴向超声振动辅助磨削的磨削力模型。通过对21Ni Cr Mo5H进行了轴向超声振动辅助磨削的磨削力试验,确定了模型中的常数,并验证了所建模型的正确性。建立的磨削力模型是轴向超声振动辅助磨削的磨削力预测的一种有效方法,对轴向超声振动辅助磨削机理的认识具有较大意义。     

定速试验机摩擦振动原因及消除办法

定速试验机的摩擦盘与试块之间存在摩擦振动,往往会影响该试验机的正常使用。对该摩擦振动产生的机理进行了理论分析,并分析了定速试验机产生振动的原因,给出了减小该振动的具体措施,得出摩擦振动是由摩擦力的不断变化这一主要原因引起的。由系统振动位移响应公式得出,当摩擦力变化频率与系统固有振动频率非常接近时就会出现共振。摩擦力的变化主要是由电机的振动,摩擦盘的端面跳动以及外界环境的影响引起的,基于这些方面,经过一系列措施之后,我们重新进行试验,结果表明定速试验机的振动明显减弱,试验机的端面跳动误差也完全符合要求,我们采取的措施取得了良好的效果。     

轴向柱塞泵柱塞副与配流副摩擦性能研究

柱塞副是斜盘式轴向柱塞泵重要的摩擦副之一,在原有柱塞副受力分析基础上考虑了套筒的影响,建立了柱塞受力分析的数学模型,将柱塞副摩擦润滑状态看做边界摩擦,分析了柱塞转动时轴向摩擦力的变化,并得到了[P]、[PV]值得变化。针对配流副的摩擦性能采用剩余压紧力的方法计算分析了剩余压紧力、剩余压紧力系数和[P]的变化规律,以及发生磨损和"烧盘"的位置和原因。结果表明,柱塞各位置受力不均,前端大于后端,配流盘边缘易发生磨损和"烧盘"。     

摩擦摆中的摩擦激励特性研究

介绍一种摩擦摆实验装置,建立摩擦摆稳定摆动状态下系统的运动微分方程,计算并讨论摩擦副间相对角速度和相对角加速度对摩擦摆自激振动稳定性的影响。结果表明:与相对加速度有关的交变摩擦力是系统自激振动的主要原因,因此有效控制工程实践中各种摩擦自激振动的途径在于,力求使摩擦副间摩擦力既不随相对速度变化,更不随相对加速度波动。     

基于齿面摩擦的直齿轮副动力学特性分析

建立了考虑齿面摩擦、时变啮合刚度、齿侧间隙和综合传递误差的直齿轮副6自由度弯曲-扭转耦合的非线性动力学模型,应用牛顿第二运动定律,建立了系统的振动微分方程。依据接触线的位置,推导了齿面摩擦和摩擦力矩的数学表达形式。分析了齿面摩擦对系统周期振动状态、混动运动状态及分岔特性的影响。结果表明,齿面摩擦加剧了齿轮副的振动,且对垂直于啮合线方向的振动影响最为明显;齿面摩擦导致系统的混沌程度降低,且在一定情况下,系统的混沌吸引子可能转化为周期吸引子;齿面摩擦导致系统的分岔变得模糊,且导致系统提前进入混沌运动状态。     

机械设备润滑故障的预防

１．润滑故障的早期预防 润滑故障在即将发生或刚开始发生之时，机械零部件会在温度、噪声、振动、金属磨粒等方面表现出与正常时不同的状态，因此采用监控、测量仪器检测设备，及时了解异常状态，能有效预防润滑故障。 （１）温度。设备摩擦部位在润滑良好时运动，摩擦力小，发热量少，温度低。当润滑不良时，摩擦力、发热量增大，高温会直接造成烧结、粘咬，因此，测量摩擦部位及其附近的温度具有重要意义。可使用单玻璃棒温度计、红外非接触式温度计或带自动监控装置的温度计测量温度。 （２）噪声与振动。机械设备运动摩擦副在使用中发…     

圆盘摩擦损失降阻新方法实验研究

采用在封闭空腔间隙流场内插入一自由旋转圆盘的方法降低圆盘摩擦损失.在圆盘旋转雷诺数为2×10~5～9.5×10~5条件下,对空腔轴向间距比S/D_2为0.0435～0.1087、插入盘的无量纲轴向位置L/S及其半径不同情况分别进行实验研究,结果表明:采用插入盘方法可以降低圆盘摩擦损失;插入盘半径减小使圆盘磨擦损失增大;随轴向间距、圆盘旋转雷诺数增大降阻效果增强;插入盘位于不同轴向位置对降阻效果有不同影响.最后,对减阻的机理进行初步分析.     

复杂接触运动下非线性摩擦力的求解

提出了复杂接触运动下求解接触非线性摩擦力的数值轨迹跟踪方法,利用该方法对几种复杂接触运动下的非线性摩擦力进行了计算。计算结果表明:数值方法在分析二维接触椭圆运动时可以得到更准确的结果;计算接触面摩擦力时不能忽略法向运动与切向运动之间的相位差,该相位差对接触状态的转变、摩擦力的大小以及迟滞回线的形状都有很大的影响;对于接触面的三维运动,必须同时考虑法向运动与接触面内两个方向切向运动之间的耦合;数值轨迹跟踪方法可以方便地求解一维、二维以及三维接触运动下的非线性摩擦力,为求解带干摩擦阻尼结构的动态响应提供了一种实用算法。     

基于无矩理论的凹版印刷机运动薄膜横向振动特性及稳定性

研究了运动薄膜横向振动特性及其稳定性,以无矩理论为基础,建立了多色组印刷情况下具有中间刚性支承运动薄膜的横向振动模型。根据D'Alembert原理,建立了振动系统的运动微分方程。数值分析了薄膜的振动频率与运动速度、张力、支承位置之间的关系,结果表明中间单刚性支承薄膜振动发散失稳的临界速度为35.855 m/s。对于具有中间两刚性支承的印刷运动薄膜,薄膜轴向运动速度越低,支撑位置的变化对薄膜振动频率影响越明显。     

Characteristics analysis of aero-engine whole vibration response with rolling bearing radial clearance

For the influence of rolling bearing radial clearance on the whole vibration in the aero-engine whole system, a real engine rotorbearing- casing whole model is established. The rotor and casing systems are modeled by means of FEM; the support systems are modeled by lumped-mass model; rolling bearing radial clearance and strong-nonlinearity of Hertz contact force at four different supports are considered. The coupled system response is obtained by the numerical integral method. The characteristics of the whole vibration response are analyzed. For rolling bearing at a typical support, the rotor, outer ring of rolling bearing and casing response characteristics at different rotating speeds are analyzed. The changing law of contact forces for each ball and the global contact forces at different speeds are analyzed. The influence of the radical clearance on the contact forces on the whole vibration is analyzed. The results show that the contact forces will be larger and the acceleration amplitude jumps obviously when the radial clearance is increased, and due to the variable stiffness of the rolling bearing, the natural frequency will appear when the stiffness changes fiercely, that is frequency-locked phenomenon. When the radical clearance is larger and the rotating speed is between two critical speeds, the rotor squeezes the outer ring now and then. Reducing the radical clearance can reduce the whole vibration and increase the rotor’s stability.     

柔性转子滚动轴承系统混沌行为研究

研究了滚动轴承支承的柔性转子系统的混沌行为。考虑空间Euler-Bernoulli杆单元、刚性圆盘、圆柱滚子轴承非线性接触力、不平衡力,使用有限单元法建立了柔性转子轴承系统的非线性动力学方程组。根据FPA修正法确定求解周期,采用Runge-Kutta法、Newton-Raphson法求解非线性动力学方程组,用获得的系统最大Lyapunov指数判断系统的混沌行为。以某滚子轴承柔性转子系统为例,研究了该类转子系统在径向间隙、不平衡力、转轴刚度比对柔性转子系统混沌特性的影响规律,发现随着轴承径向间隙的增大,系统的混沌区间逐渐增大、变多。不平衡力的存在使得系统混沌的转速及范围变大。随着刚度比增大,振幅峰值及对应的转速均逐渐增大,系统混沌区间也增多,轴承非线性振动对柔性转子系统非线性行为的影响逐渐增强。     

Evaluation of impact dynamics and contact forces in a hydropower rotor due to variations in damping and lateral fluid forces

Damages due to contact between the runner and the discharge ring have been observed in several hydroelectric power units. The damage can cause high repair costs of the runner and the discharge ring as well as considerable production losses.In this paper a rotor model of a 45 MW hydropower unit is used for the analysis of the rotor dynamical phenomena occurring due to contact between the runner and the discharge ring for different grades of lateral force on the turbine and bearing damping. The rotor model consists of a generator rotor and a turbine, which is connected to an elastic shaft supported by three isotropic bearings. The discrete representation of rotor model consists of 32 degrees of freedom; to increase the speed of the analysis, the size of the model was reduced with the IRS method to a system with 8 degrees of freedom.Results are presented in bifurcation diagrams, maximum contact force, Poincaré map and phase portrait. Simulations indicate that the contact forces between the turbine and the discharge ring are large, with considerable risks for serious damage as a consequence. The analysis shows that the risk for contact and damage are large for relatively small lateral turbine loads when the gap between the turbine and the discharge ring is small and the contact stiffness is high.     

Numerical analysis of the dynamic behavior of a rotor-bearing-brush seal system with bristle interference

To minimize leakage and maintain the efficiency of turbomachinery, brush seal can be installed with zero clearance or interference as the flexibility. This leads to contact between the rotor and bristle pack, and may cause self-excited vibration, even instability. In this study, to establishment a mathematical model of the rotor system, a seal force model with bristle interference is proposed and the nonlinear oil-film force is applied in view of short bearing assumption. The influences of main factors containing rotor rotational speed, installing interval, disc mass, and disk eccentricity on the nonlinear characteristics of the rotor-bearing-brush seal system are conducted by adopting bifurcation diagram, spectrum cascade, axis orbit, and Poincaré map. The results indicate that the vibration amplitude of the system with bristle interference is a bit larger than that without interference. The system stability is enhanced with smaller disk mass at a higher rotational speed. The proposed model could provide valuable reference for the design of a rotor-bearing-seal system.

     

Effect of rotational speed fluctuations on the dynamic behaviour of rolling element bearings with radial clearances

The behaviour of rolling element bearings is of major importance to the vast majority of rotating machines. Due to the varying assembly compliance and the internal clearance existing in the bearing in most cases, a highly non-linear behaviour of the rotor bearing system appears. Thus, a dynamic model of a horizontal rotor supported on ball bearings with radial internal clearance is considered, taking into account contact forces between the balls and the races, as well as the effect of varying compliance and of the internal radial clearance. However, since rotational speed fluctuations of various levels practically appear in all rotating equipment, their effect is now additionally considered. Their effect is examined in two characteristic rotor bearing cases. The analysis includes all the characteristic states of the dynamic behaviour of the rotor, such as periodic, unstable periodic and chaotic responses, using methods like frequency spectra, phase spaces, higher-order Poincare maps and Lyapunov exponents. All results presented show a dominant stabilization effect of the speed fluctuations with respect to the system behaviour. From the analysis performed, it is concluded that even a minimum fluctuation of the rotor speed may result in major changes of the system dynamics, indicating that speed fluctuations of the rotor are a governing parameter for the dynamic behaviour of the system.     

The effect of speed of balanced rotor on nonlinear vibrations associated with ball bearings

The paper deals with the structural dynamic response of rotor supported by ball bearings. The mathematical model takes into account the sources of nonlinearity such as Hertzian contact force, surface waviness, varying compliance and internal radial clearance resulting transition from no contact to contact state between rolling elements and races. In terms of the feature that the nonlinear bearing forces act on the system, a new reduction method and corresponding integration technique is used to increase the numerical stability and decrease computer time for system analysis. The effects of speed of balanced rotor in which ball bearings show periodic, quasi-periodic and chaotic behavior are analyzed. The results are presented in the form of time displacement responses, frequency spectra and Poincarè maps. It is implied from the frequency spectra that peak amplitude of vibrations appear at the varying compliance frequency.     

齿轮联轴器不对中转子系统的稳态振动特征分析

对不对中齿轮联轴器连接的轴承－转子系统进行了动力学分析，讨论了齿轮联轴器不对中力的组成。理论分析表明，齿轮联轴器的不对中而产生的作用力是联轴器内齿套的惯性力和联轴器内阻尼共同作用的结果，转子系统的稳态响应振幅与齿轮联轴器的不对中量、内阻尼、转子的转速和齿轮联轴器的结构参数有关。数值模拟结果显示在弯曲振动中转子系统会产生工频的2，4，6，8，…等偶数倍频分量，而在扭转振动中会产生工频的1，3，5，7，…等奇数倍频分量，并且这些倍频分量在齿轮联轴器附近处表现得非常明显。     

UNBALANCE RESPONSE AND TOUCH-RUBBING THRESHOLD SPEED OF ROTOR SUBJECTED TO NONLINEAR MAGNETIC FORCES

Because of the effect of unbalance excitation and nonlinear magnetic force, the large vibration of the rotor supported by active magnetic bearing（AMB） will go beyond the radial gap of the bearing, even causing mechanical touch-rubbing when the system works at an operational speed closer to the critical speed. In order to investigate this problem, the linear model and nonlinear model of the single mass symmetric rigid rotor system supported by AMB are established respectively and the corresponding transfer functions of close-loop system are given. To pass through the numerical calculation by using MATLAB/Simulink, the effect of both the unbalance response and threshold speed of touch-rubbing of the system subjected to nonlinear magnetic forces and nonlinear output current of power amplifier are studied. Furthermore, threshold speed of touch-rubbing of the rotor-bearing system is defined and the results of numerical simulation are presented. Finally, based on above studies, two methods of increasing the touch-rubbing threshold speed are discussed.     

Nonlinear Dynamic Response of Cylindrical Roller Bearing–Rotor System with 9 Degree of Freedom Model Having a Combined Localized Defect at Inner–Outer Races of Bearing

This article presents a nonlinear dynamic model for a cylindrical roller bearing–rotor system with interaction forces between the inner race, outer race, and roller. Roller–race contacts are modeled predicting nonlinear stiffness (Hertz contact theory) and nonlinear damping for a rotor–cylindrical roller bearing system. Here a shaft–rotor bearing system is modeled with 9 degrees of freedom with one defect on the inner race and one defect on the outer race for a case of combined localized defects. In the mathematical formulation, contacts between rolling elements and inner and outer races are considered as nonlinear springs and nonlinear damping is taken into consideration. Contact force calculations with nonlinearity are solved using the Newton-Raphson method for n unknown nonlinear simultaneous equation. The Newmark-β implicit integration technique coupled with the Newton-Raphson method is used to solve the differential equations. The results are obtained in the form of a time domain plot, frequency domain plot, and phase plot/Poincare map. The validity of the proposed model is compared with experimental results. A bifurcation graph of speed versus peak amplitude predicts the behavior of the system.     

圆柱滚子轴承刚性转子系统周期运动分岔

推导了考虑径向力、力矩联合作用的滚子轴承的非线性轴承力和力矩,建立了圆柱滚子轴承刚性转子系统的四自由度动力学方程,利用求解非线性非自治动力系统周期解的延拓打靶算法进行计算,根据Floquet乘子判断周期运动的分岔.以某滚子轴承刚性转子系统为例,研究了该类转子系统在径向间隙-转速、阻尼-转速、力矩-转速参数域内周期运动的分岔及失稳规律.结果发现:随径向间隙、阻尼和力矩的变化,周期运动将产生倍周期或Hopf分岔,分岔转速随参数变化而改变.其中力矩的存在会明显降低系统的失稳转速,可通过选择合适的结构和工况参数尽量避免滚子轴承转子系统出现非周期运动.