多个磁悬浮轴承转子系统动力学特性研究

多个磁悬浮轴承支承的转子系统,由于支承位置的不对中会造成各个轴承的支承载荷变化。针对某一转子模型,分析采用不同个数的磁悬浮轴承支承时,各个支承载荷随着支承位置不对中的变化情况,并在三个磁悬浮轴承转子系统中得到验证。针对转子动力学特性,分析了支承高度不同时,转子固有频率的变化。此外,采用传递矩阵法,分析转子随着支承个数的增加,其不平衡响应变化情况,并实验对比了采用三支承和两支承时,转子的振幅。三支承较两支承,转子振幅有所减小。     

基于最小二乘法的转子不平衡振动信号的提取

不平衡振动是旋转机械失效的重要原因,实现精确平衡必须从强噪声中提取出与主轴转速同频的不平衡量振动信号,因此,不平衡振动信号的准确提取是进行转子动平衡的前提。基于最小二乘法的原理,通过建立提取转子振动不平衡信号的数学模型,提出了一种准确提取转子不平衡振动信号的方法。基于该方法,并通过Matlab仿真分析,有效提取了转子振动不平衡信号。研究表明,基于最小二乘法的转子振动不平衡信号提取方法能够准确提取转子不平衡振动的幅值和相位信息,该方法可用于转子不平衡振动监测及动平衡等方面。     

Effectiveness of Impact-Synchronous Time Averaging in determination of dynamic characteristics of a rotor dynamic system

Dynamic characteristics of rotor dynamic systems, namely natural frequencies, damping and mode shape, vary with rotation speed due to gyroscopic effect. To consider such effect, modal analysis is required to be performed while in operation. However, to generate the frequency response functions, it is not viable to perform data reduction in frequency domain as noise and harmonics excited by rotating forces dominate the spectrum and hide the natural frequencies. The full set of dynamic characteristics is difficult to obtain. A novel technique, referred to as Impact-Synchronous Time Averaging (ISTA), is developed in this study to screen out the noise and harmonics.     

基于ROMAX的球轴承转子系统动态性能分析

滚动轴承转子系统在旋转机械系统中得到广泛应用,其动态性能对旋转机械有着重要的影响。基于Romax软件建立球轴承转子系统的动力学分析模型,通过算例分析了工况参数和结构参数对球轴承转子系统动态特性的影响规律,并通过实验结果验证了Romax对轴承性能预测的准确性。研究发现球轴承的接触角、内外圈沟曲率系数与安装位置对轴承的刚度、寿命与转子系统临界转速等动态性能有较大影响。工程中需要选择合适的结构与工况参数以满足转子系统的性能要求。     

The dynamic behavior of a rotor system with a slant crack on the shaft

For a Jeffcott rotor system with a 45° slant crack on the shaft, the motion equations are established with four directions, i.e. two transversal directions, one torsional direction and one longitudinal direction. It can be seen from the deducing process of the stiffness with the strain energy release approach that there are coupling stiffnesses of bending–torsion, bending–tension and torsion–tension for the slant-cracked shaft and only bending–tension for the transverse-cracked one. The paper shows that besides the coupling stiffnesses, there is bending–torsion coupling caused by the eccentricity. All these couplings affect the responses of the slant-cracked shaft and the transverse-cracked one. Comparing responses of a cracked shaft with an open crack model and those with a breathing crack model finds that there are the same prominent characteristic frequencies for these two kinds of shafts, even though the cracked shaft with a breathing crack model behaves much more non-linear than that with an open crack model. Therefore, almost all studies in this paper adopt the open crack model since it needs taking much longer time to compute responses of a breathing cracked shaft than that of an open cracked shaft. Analyses of steady responses indicate that the combined frequencies of the rotating speed and the torsional excitation in the transversal response and the frequency of the torsional excitation in the longitudinal response can be used to detect the slant crack on the shaft of the rotor system.     

Compensation of tool axis misalignment in active magnetic bearing spindle system

The tool axis misalignment, which causes machining inaccuracies in an active magnetic bearing (AMB)-spindle system, can be compensated by tracking control of the rotor-spindle. The pseudo-derivative feedback (PDF) control scheme alone does not correct the tool axis misalignment since the integral action results in the narrow bandwidth and large phase lag in the controlled system. To improve the tracking performance, the feedback and feedforward controllers are combined with the existing proportional-derivative controller, which stabilizes the inherently unstable AMB-spindle system dynamics. The theoretical and experimental results show that proposed control scheme efficiently compensates the tool axis misalignment compared with the conventional PDF control scheme.     

滑动轴承转子系统非线性动力学稳定性研究

采用多尺度法研究了滑动轴承刚性平衡转子系统临界点的稳定性。研究发现，滑动轴承在其线性失稳转速上发生Hopf分岔，系统是发生超临界Hopf分岔还是亚临界Hopf分岔取决于系统参数的设计。给出了通用的公式和程序，为滑动轴承的非线性动力学设计及性能预测提供了有利的工具。     

有初弯的单盘不平衡转子等加速过临界时的瞬态响应分析

以具有初始弯曲横置Jeffcott转子系统为研究对象,建立含有初始弯曲和加速度项的运动微分方程。通过数值分析,就不同初始弯曲、不平衡和外阻尼对转子加速过临界时的动挠度、相位角和进动角速度的变化规律进行了详细的讨论。结果表明:在转子达到临界转速时,转子的动挠度幅值随着初始弯曲的增加或者外阻尼的减小而迅速增加;不平衡对转子在临界转速前后的动挠度影响较为明显,并且近似呈线性关系变化。不同的外阻尼和不平衡对转子系统的相位角和进动角速度变化都有较大的影响。     

磁悬浮转子振动主动控制综述

利用磁悬浮系统的可控性,应用于转子的振动控制,将会进一步提高转子的旋转精度.本文阐述了磁悬浮系统控制转子振动的研究现状,磁悬浮系统的结构,工作原理及磁悬浮系统的优点.并且分析了将磁悬浮系统应用于控制转子振动的两种方法,指出现在这两种方法的缺点.并介绍了点磁悬浮动力吸振器的优点.在文章的最后提出了研究这种系统所要面临的问题.     

Effects of cracks on rotor system instability

The stability threshold of a rotor-bearing system having a transverse crack has been studied by using FEM and considering the various crack parameters and shaft internal damping (viscous and hysteretic damping) and geometric parameters. It has been observed that the instability speed has reduced considerably with increase in crack depth and influenced more with hysteretic damping compared to viscous damping. The stability of the rotor system including shaft with two open cracks has also been carried out and observed the influence of one crack over the other for threshold speed limits.     

一种用于刚性转子动平衡的快速消振法

介绍了一种快速消振法来对转子进行动平衡,使用此方法可以在某些情况下减少设备启动次数.通过实验室模拟实验及现场实际应用,证明了此方法的有效性.     

遗传算法在转子影响系数平衡法中的应用

在详细地论述了转子动平衡影响系数法有关理论的基础上 ,分析了利用遗传算法求解平衡方程的优越性 ,然后讨论了具体应用过程中需要解决的一些问题。通过理论分析和算例 ,证明了应用此方法得到的平衡效果是好的。     

A novel nonlinear model of rotor/bearing/seal system and numerical analysis

A novel nonlinear model of rotor/bearing/seal system based on the Hamilton principle is proposed for steam turbine systems in power plants. The Musznyska model and unsteady bearing oil-film force model were applied to describe the nonlinear steam excitation force and oil-film force. The Runge-Kutta method was used to solve the motion equation of the rotor/seal/bearing system. The dynamic characteristics of the rotor/bearing/seal system were analyzed with bifurcation diagrams, time-history diagrams, trajectory diagrams, Poincare maps and frequency spectrums. The numerical analysis indicates that the seal force and the oil-film force influence the nonlinear dynamic characteristics of the rotor system. With the increase of rotation speed, the rotor system exhibits rich forms of periodic, double-periodic, multi-periodic, quasi-periodic and chaotic motion. The combined impact of steam excitation force and bearing oil-film force may cause a severe vibration which seriously affects the safety and stability of the rotor. The presented model provides a theoretic foundation for further research on the ultra-supercritical steam turbines.     

Nonlinear dynamic characteristics of geared rotor bearing systems with dynamic backlash and friction

Effects of the friction and dynamic backlash on the multi-degree of freedom nonlinear dynamic gear transmission system, which incorporate time varying stiffness, are investigated. Firstly, the relationship between gear central distance error and backlash is deduced and the dynamic backlash is defined, subsequently a multi-degree of freedom nonlinear dynamic gear transmission system is developed with dynamic backlash, friction and time varying stiffness. The nonlinear dynamic system is solved by the Runge-Kutta method. The results show that the friction force may enlarge the displacement magnitude and affect the high frequency parts significantly in frequency domain at low speed. But the RMS of the steady response is reduced on the effect of friction. The difference between the constant backlash and the dynamic backlash models is also discussed. The system may enter into previous chaotic motion due to the effect of dynamic backlash. Finally, no impact motion, single-side impact motion and double-side impact motion are also predicted in the new dynamic backlash model.     

Vibration response of rigid rotor in unloaded rolling element bearing

Rolling element bearings appear in nearly 90% of all rotating machinery. Their dynamic performance is often the limiting factor in the performance of the machines that use them. The specific construction of a bearing has a decisive influence on its dynamic behaviour. The paper defines a new vibration model of a rigid rotor supported by rolling element bearings. By application of the defined model, the parametric analysis of the influence of internal radial clearance value and number of rolling elements influence on rigid rotor vibrations in unloaded rolling element bearing was performed. The defined vibration model and parametric analysis were verified experimentally. The results of experimental analysis are also presented in this paper.     

Model validation and controller design for vibration suppression of flexible rotor using AMB

This paper discusses the model validation and vibration suppression of an AMB flexible rotor via additional LQG controller. The main difficulty in the vibration suppression of the flexible rotor using AMB is to realize a controller that can minimize resonance without injuring the stabilized rigid modes. In order to solve this problem, simple scheme for system modeling and controller design are developed. Firstly, the AMB flexible rotor is stabilized with a PID controller, which leads to a new stable rotor-bearing system. Then, authors propose the model validation procedure using measured open-loop frequency responses to obtain an accurate model of the AMB flexible rotor system. After that, LQG controller with modal weighting is designed to suppress resonances of the stable rotor-bearing system. Due to the poor controllability and observability of flexible modes compared to rigid ones, balancing of two Gramians is prerequisite for the fair LQG controller design. Simulation with step disturbance and experimental results of unbalance response up to 10,000 rpm verified the effectiveness of the proposed scheme.     

Analytical study on effect of a circumferential feeding groove on unbalance response of a flexible rotor in squeeze film damper

Of recent years, a series of researches have shown that a circumferential feeding groove of squeeze film damper (SFD) has evident effect on fluid film forces in SFD. Therefore, the feeding groove also affects dynamic responses of a rotor in SFD. Present work studies the effect of the feeding groove on unbalance response of a flexible rotor in SFD based on new film force models that include effects of the feeding groove and fluid inertia on dynamic characteristics of the fluid film in SFD. Compared with the published work, unbalance responses predicated under considering effect of the feeding groove on the dynamic characteristics in SFD are small, and rotor speed region for unbalance responses with multiple solutions is different, affecting the stability of a rotor system. And the effect of the feeding groove on the unbalance response is related to action of fluid inertia.     

可变阻抗滑动轴承的动力系数计算

本文讨论了具有两个动力缓冲器的可变阻抗滑动轴承的动力学系数及其计算方法，建立了基于Ｒｅｙｎｏｌｄｓ方程和流量连续性原理的油膜压力分布理论模型，并提出了这种轴承油膜的线性动力学系数计算的压力扰动法。理论分析结果表明这种轴承可以在运行条件下有效地改变其油膜的动力特性，为这种轴承的实际应用提供了必要的理论基础。     

薄膜蒸发器转子系统固有频率及稳态不平衡响应分析

薄膜蒸发器转子系统中的不平衡力易导致转子振幅加大,从而加剧刮板磨损,导致刮板失效.采用VB对ANSYS进行二次开发,对薄膜蒸发器转子系统进行模态分析,并对转子某些位置上的不平衡量进行了稳态不平衡响应分析,初步实现了薄膜蒸发器转子动力学分析,为薄膜蒸发器设计及安全运行提供依据.     

全矢动平衡方法平衡精度的动力学研究

首先依据全矢谱理论,介绍了全矢动平衡方法的基本思想;然后从分析单圆盘转子模型的振动入手,得出转子水平和垂直方向不平衡响应与转子系统特征参数之间的关系;接着从不平衡灵敏度的角度,推导出了全矢动平衡方法与传统动平衡方法各自的不平衡灵敏度表达式,因为不平衡灵敏度高的转子平衡精度较高,通过比较全矢动平衡方法与传统单通道动平衡方法各自的不平衡灵敏度,证明了全矢动平衡方法具有较高的平衡精度,最后通过实验验证了文中理论分析的结论。