非线性转子的低频振动失稳机理分析

包括两部分内容：１）材料内阻作用下转子自激振动的局部分岔分析；２）考虑湍流因素的滑动轴承油膜力作用下转子轴承系统油膜失稳机理的全面分析。结果表明，非线性转子的自激振动表现出复杂的动力学现象，这些低频振动现象的揭示，为工程上转子故障的识别和预防提供了理论依据。     

参数激励与强迫激励联合作用下非线性振动系统的分叉

本文利用多尺度法研究了参数激励与强迫激励联合作用下非线性振动系统的分叉问题,给出了分叉集和八种分叉响应曲线。     

汽轮机转子在气流力和油膜力作用下的非线性动力学特性

为了分析转子在油膜力和气流激振力共同作用下的非线性振动特性，本文以短轴承支撑的不平衡刚性对称Jeffcott转子系统为研究对象，首先分析转子在非稳态油膜力作用下的振动特性，然后分析转子在油膜力和气流激振力共同作用下的非线性振动特性。采用数值模拟的方法研究了系统的分岔和混沌特性，计算结果表明，考虑气流激振力和油膜力共同作用下的转子系统与仅考虑油膜力的转子系统相比，在相对进气速度v=30m／s时，随着无量纲转速ω的增加。二者都出现了周期运动和混沌运动多次交替出现的复杂运动特性，但是前者首次出现倍周期分岔和混沌运动时的转运提前，在定转速情况下，随着v的增大，系统最终在经历周期运动之后进入混沌运动，而且圆盘中心的最大振幅随着v的增大而增大。     

非线性转子-机匣系统的分岔行为研究

建立了一类非线性转子-机匣系统的碰摩模型.应用数值分析的方法对其进行研究,得到了不同参数变化下系统响应随转速变化的分岔图,分析了系统参数变化对分岔过程的影响,并作出了在相应参数状态和特定转速下的Poincare截面图,揭示系统参数变化对非线性碰摩转子-机匣系统分岔特性的影响.     

轴承-转子系统在基础运动作用时的非线性分析

轴承-转子系统的非线性特性及其在基础运动作用时的响应,是离心机设备设计阶段必须考虑的。本文使用简化的多自由度转子模型进行模拟分析,运动方程考虑了非线性的油膜润滑轴承模型。应用自适应时间步长的Runge-Kutta-Felburg法求解微分运动方程组,将人造的正弦波加速度作为基础运动输入系统,使用Poincaré图、分岔图和瀑布图分别考察了垂直放置转子在有无基础运动作用时的动力学性质。快速傅里叶变换在频域内揭示了转动频率与基础振动频率之间的组合共振现象。计算的结果不仅给出了泵转子自身的非线性性质,也展示了泵转子在基础运动作用时的组合共振。     

分段线性非线性振动机械周期运动的分岔

对于分段线性非线性振动机械已经进行了一些研究工作，本文利用点映射－胞映射法（简称ＰＣＡＳ）分析了分段线性非线性振动机械的周期运动关于软弹簧刚度的分岔的情况，所得结论对于设计这灯机械有指导意义。     

非线性转子——轴承系统1／2亚谐共振全局分岔研究

本文以采用短轴承模型的具有不平衡质量单园盘非线性刚性转子－－轴承变研究对象，利用中心流形定理和平均法相结合的方法，以及Ｔａｋｅｎｓ又特性值理论方法，在其临界点处对其有１／２亚谱共振情况下的周期振动、调幅和调相振动、以及同窠、异宿轨道的分岔性态进行了研究，给出了控制系统稳定运行的结构参数区域，为大型复杂转子系统的油膜失稳控制提供了某些理论依据。     

转子轴承系统电磁阻尼器的位移反馈振动控制

本文研究在周期激振力作用下转子轴承系统电磁阻尼器的位移反馈振动控制。首先给出受电磁阻尼器控制的一般线性多自由度转子轴承系统的振动方程，控制力和电磁阻尼器结构参数，控制电流等之间的关系式，然后提出在保证系统稳定的前提下，通过位移反馈控制其电流位移增益矩阵应满足的条件；其次以单盘对称转子轴承系统为例，求出转子系统受电磁阻器控制的幅频响应和相频响应；最后给出算例，打印出电磁阻尼器的静态电流，电流位移增益     

参数激励与强迫激励联合作用下非线性振动系统的余维2退化分叉

在本文里我们首先研究了具有Z_2-对称性的范式理论和退化向量场的普适开折理论。然后利用上述理论研究了参数激励与强迫激励联合作用下非线性振动系统的余维2退化分叉,从而解决了当解具有两个零特征值时解的稳定性问题。最后利用Melnikov方法求出了参数平面上的同宿分叉曲线,讨论了全局分叉的存在性。     

一类非线性油膜轴承—转子系统的碰摩数值分析

本文结合非线性油膜力模型和碰摩速度跃迁公式,建立了描述非线性油膜轴承-转子系统碰摩的刚性约束非光滑模型。通过数值模拟,得到了该系统随转动角频率及油膜特性参数变化发生碰摩的分岔特性,并揭示出转子系统的碰摩与油膜振荡的1/2亚谐共振有密切关系。     

A class of bifurcation solutions of almost-periodic parametric vibration systems

A class of bifurcation solutions of almost-periodic (a. p. for short) parametric vibration systems is studied by Liapunov-Schmidt reduction. The bifurcation diagrams and formulas are given. The Project Supported by National Natural Science Foundation of China.     

A state-of-the-art review on low-frequency nonlinear vibration isolation with electromagnetic mechanisms

Vibration isolation is one of the most efficient approaches to protecting host structures from harmful vibrations, especially in aerospace, mechanical, and architectural engineering, etc. Traditional linear vibration isolation is hard to meet the requirements of the loading capacity and isolation band simultaneously, which limits further engineering application, especially in the low-frequency range. In recent twenty years, the nonlinear vibration isolation technology has been widely investigated to broaden the vibration isolation band by exploiting beneficial nonlinearities. One of the most widely studied objects is the “three-spring” configured quasi-zero-stiffness (QZS) vibration isolator, which can realize the negative stiffness and high-static-low-dynamic stiffness (HSLDS) characteristics. The nonlinear vibration isolation with QZS can overcome the drawbacks of the linear one to achieve a better broadband vibration isolation performance. Due to the characteristics of fast response, strong stroke, nonlinearities, easy control, and low-cost, the nonlinear vibration with electromagnetic mechanisms has attracted attention. In this review, we focus on the basic theory, design methodology, nonlinear damping mechanism, and active control of electromagnetic QZS vibration isolators. Furthermore, we provide perspectives for further studies with electromagnetic devices to realize high-efficiency vibration isolation.

     

Stability and bifurcation of unbalance rotor/labyrinth seal system

The influence of labyrinth seal on the stability of unbalanced rotor system was presented . Under the periodic excitation of rotor unbalance , the whirling vibration of rotor is synchronous if the rotation speed is below stability threshold, whereas the vibration becomes severe and asynchronous which is defined as unstable if the rotation speed exceeds threshold . The. Muszynska model of seal force and shooting method were used to investigate synchronous solution of the dynamic equation of rotor system. Then , based on Floquet theory the stability of synchronous solution and unstable dynamic characteristic of system were analyzed.     

考虑进油压力的滑动轴承非线性油膜力数据库

通过对ReyTlolds方程的非线性变换，提出了考虑进油压力边界条件时径向滑动轴承非线性油膜力数据库的建库方法，扩展了油膜力数据库计算方法的应用，通过引入2个有限数据域的新变量对转子轴心速度项和进油压力边界条件进行有限化处理，得到了更符合实际工况的连续性油膜力数据库及计算模型，同有限元法对比分析了非线性油膜力数据库的适用性．结果表明，非线性油膜力数据库模型的精度较高，所建立的非线性油膜力计算模型可用于对转子系统瞬态运动进行简便和快捷的分析．     

Nonlinear vibration of beamplates with a delamination

The problem of beam-plates with a delamination located at an arbitrary site undergoing non-linear free vibration without damp is investigated. For this problem, nonlinear governing equations as well as the continuity, equilibrium and compatibility conditions are established. The Galerkin method and harmonic balance method are employed to find solutions. Finally, in some examples amplitude-frequency curves of the delaminated structure are presented in order to reveal some special dynamic features. Supported by the National Natural Science Foundation of China (No. 19872024).     

Effects of van der Waals force on nonlinear vibration of electromechanical integrated electrostatic harmonic actuator

An electromechanical integrated electrostatic harmonic actuator is promising for the miniaturization of electromechanical devices. As the dimensions of the actuator decrease, the effects of the van der Waals force become obvious. In this study, by considering the nonlinearity of electrostatic and van der Waals forces, nonlinear vibration equations of the flexible ring of an electrostatic harmonic actuator are deduced. Using these equations, the nonlinear free vibration and nonlinear forced response of the actuator are investigated. The effects of the van der Waals force on the nonlinear vibration of the flexible ring are analyzed. Results show that these effects of the van der Waals force are relatively obvious under some conditions and should be considered.     

On some performance characteristics of base excited vibration isolation systems with a purely nonlinear restoring force

Base excited vibration isolation systems with a purely nonlinear restoring force and a velocity nth power damper are considered. The restoring force has a single-term power form with the exponent that can be any non-negative real number. Approximations for the steady-state response at the frequency of excitation are obtained by using the Jacobi elliptic function with a changeable elliptic parameter and by applying an elliptic averaging method. The relative and absolute displacement transmissibility of this system are analysed. These performance characteristics are expressed in terms of the damping parameters, but they are also determined for an arbitrary non-negative real power of geometric nonlinearity, which represent new and so far unknown results. Some examples illustrating the effect of the system parameters on these performance characteristics are also presented.     

Buckling of a beam subjected to electromagnetic force and its stabilization by controlling the perturbation of the bifurcation

For a beam subjected to electromagnetic force, magnetoelastic buckling due to the increase of such force is theoretically investigated by taking account of the nonlinearity of the electromagnetic force and the elastic force of the beam. Using Liapunov-Schmidt method and center manifold theory, the equilibrium space, the bifurcation set and the bifurcation diagram are theoretically derived. Also, the effect of the higher modes other than the buckling mode on the mode shape of the postbuckling state is discussed. Furthermore, a control method to stabilize the magnetoelastic buckling is proposed, and the unstable equilibrium state of the beam in the postbuckling state, i.e., the straight position of the beam, is stabilized by controlling the perturbation of the bifurcation.