Stability of periodic motion on the rotor-bearing system with coupling faults of crack and rub-impact

A dynamic model was set up for the rotor-bearing system with coupling faults of crack and rub-impact. Using the continuation-shooting algorithm for periodic solution of nonlinear non-autonomous system, the stability of the system periodic motion was studied by the Floquet theory. The saddle-node bifurcation, periodic-doubling bifurcation and the Hopf bifurcation were found. There are peculiar dynamic characteristics of the rotor-bearing system with coupling faults of crack and rub-impact that differs from single fault. The conclusions provide theoretic basis reference for the failure diagnosis of the rotor-bearing system with coupling faults of crack and rub-impact fault.     

Hopf bifurcation to a short porous journal-bearing system using the Brinkman model: weakly nonlinear stability

On the basis of the Brinkman model, the weakly nonlinear stability characteristics of short porous journal-bearing systems are presented. By applying the Hopf bifurcation theory, the weakly nonlinear behaviors near the critical stability boundary are predicted. According to results, the onset of oil whirl for porous bearings is a bifurcation phenomenon; it can exhibit supercritical limit cycles or subcritical limit cycles for journal speeds in the vicinity of the bifurcation point. With a fixed permeability parameter, such supercritical limit cycles for journal speeds in excess of the threshold speed are confined to a specific region in the (ω, ε_s) plane; and outside this region subcritical limit cycles exist for journal speeds below the threshold speed. In addition, increasing the value of system parameter, S_p, may change supercritical bifurcation into the more complicated subcritical bifurcation.     

轴承-转子系统自激振动及迟滞、跳跃现象

采用长轴承解析模型研究滑动轴承支承的平衡单盘柔性转子-轴承系统的自激振动,把结合打靶法的延续算法应用于柔性平衡转子-轴承系统Hopf分叉后周期解的追踪和求解上,基于Floquet理论对极限环的稳定性加以分析,研究了不同系统参数下产生极限环的Hopf分叉的不同过程及特性,分别对超临界及亚临界Hopf分叉进行了描述和分析,结果表明亚临界Hopf分叉会引起突跳、迟滞现象,并可引发转子系统难以预测的振动故障,在设计中应避免这种参数条件。     

Bifurcation analysis of flexible rotor supported by couple-stress fluid film bearings with non-linear suspension systems

This study analyzes the dynamic behavior of a flexible rotor supported by two couple-stress fluid film journal bearings with non-linear suspension systems. The analysis employs a short journal bearing assumption and considers the respective effects on the dynamic response of the system of the lubricant type (i.e. Newtonian or non-Newtonian), the bearing housing suspension system (i.e. linear or non-linear), the rotor speed and the degree of rotor unbalance. The behavior of the system is analyzed by reference to bifurcation diagrams, dynamic trajectory diagrams and Poincaré maps, respectively. In general, the results show that the dynamics of the system are significantly dependent on the rotor speed and the degree of rotor unbalance. Furthermore, it is found that the use of a couple-stress fluid lubricant enhances the dynamic stability of the rotor-bearing system considerably compared to that obtained when using a traditional Newtonian lubricant. Finally, the results show that the common assumption of a linear journal housing suspension system results in a significant underestimation of the vibrational amplitudes of both the rotor and the bearing and should therefore be replaced by a non-linear assumption.     

控制理论在电液控制系统中的应用综述

简单介绍了控制理论的形成和发展、电液控制系统的组成,详细地阐述了电液控制系统的控制方法,控制理论广泛应用于电液控制系统中,是自动化技术发展水平的重要标志,它对电液控制系统性能的改善起着举足轻重的作用。     

Lyapunov theory based robust control of complicated nonlinear mechanical systems with uncertainty

This paper presents a robust control approach for nonlinear uncertain crane systems with a three DOF framework. We deal with an overhead crane in which a trolley located on the top is moved to x- and y-axes independently. We first approximate the nonlinear system model through feedback linearization transformation to simply construct a PD control and then design a robust control system for compensating control deviation feasibly occurring due to modeling error or system perturbation in practice. An adaptive control rule is analytically derived by using Lyapunov stability theory given bounds of system perturbation. We accomplish numerical simulation for evaluating the proposed methodology and demonstrate its superiority by comparing with the traditional control strategy. This paper was recommended for publication in revised form by Associate Editor Dong Hwan Kim Hyun Cheol Cho received a B.S. from the Pukyong National University in 1997, a M.S. from the Dong-A University, Korea in 1999, and a Ph.D. from University of Nevada-Reno, USA in 2006. He is currently a post-doc researcher in the Dept. of Electrical Engineering, Dong-A University. His research interests are in the areas of control systems, neural networks, stochastic process, and signal processing.     

随机服务系统理论在威胁估计中的应用

利用防空武器与空袭目标的对抗过程分析武器系统的作战效能,对武器系统的设计和使用者来说都是不可缺少的环节.随机服务系统理论或称排队论是一种解析分析计算武器系统作战效能的有效工具.用随机服务系统理论方法建立评价武器系统的作战效能的线性解析模型,通过线性解析模型计算空袭目标的突防概率,从而得到用于对敌空袭目标威胁估计的重要参数,根据突防概率可以提供敌空袭目标对我保卫目标或区域所构成的威胁等级,从而使指挥员做出快速、准确的应对措施.     

最优方案非统计原理在轴承优化设计中的应用

在轴承优化设计中常会碰到不同的实际要求,如何根据这些要求,对设计方案进行评价是轴承设计人员经常面对的问题。本文介绍了一种利用灰色理论进行轴承优化设计的方法。采用灰色关联度来对各设计方案的各项指标进行评价,从而可以根据实际要求,对各设计方案做出正确的排序和评价。     

运用相似理论研究机床导轨爬行问题

文中提出运用相似理论研究导轨爬行问题，通过量纲分析法导出了表征爬行现象的相似准则方程，并通过实例对准则关系曲线进行了验证和推广。     

有回路无根多刚体系统图论描述的优化问题

在求解多刚体系统中任意刚体的绝对角速度等运动量时，需要对指定刚体到零刚体的路径上所有刚体的某一物理量作求和运算。某一刚体到零刚体的路径长度直接影响着该刚体运动学分析计算量的大小。对有回路的无根多刚体系统，寻找最优的派生树系统，恰当选择与零刚体直接相连的刚体，可以使零刚体到所有刚体的路径长度总和为最小，最大限度减小动力分析的计算量。首次就这一优化问题使用图论方法进行了分析，提出了解决办法。结合一个简单实例，阐述了对于有回路无根多刚体系统图论描述的优化处理流程。     

应用像差理论评估镜面热变形对成像的影响

通过多项式拟合法计算由于热变形导致的面形改变量,来修正镜面面形系数;然后应用平面对称光学系统的像差理论,计算它对成像的影响.和以往方法不同的是它通过像差形式解析表达,并能得到光线在像面上的点列图分布.如果热变形导致的镜面改变量分布比较复杂,很难用单个面形精确地拟合,建议进行分区拟合以减小拟合误差.最后,通过一个实例,用...     

Application of a variable flow stress machining theory to helical end milling

A methodology of modeling chip geometry of flat helical end milling based on a variable flow stress machining theory is presented in this article. The proposed model is concerned with the variation of the width of cut thickness. The nonuniform chip thickness geometry is discretized into several segments based on the radial depth of cut. The chip geometry for each segment is considered to be constant by taking the average value of the maximum and minimum chip thickness. The maximum chip thickness for each chip segment is computed based on the current width of cut, feed per tooth and the cutter diameter. The subsequent radial depth of cut is subtracted from the discretized size of the width of cut to obtain the minimum chip thicknesses. The forces for each segment are summed to obtain the total forces acting on the system of the workpiece and the tool. The cutting forces can be predicted from input data of work material properties, cutter configuration and the cutting conditions used. The validation of the proposed model is achieved by correlating experimental results with the predicted results obtained.     

混入逃逸函数的遗传算法优化超大视场光学系统

超大视场光学成像系统在各领域的应用越来越多,但却缺少能够对该类光学系统的像差进行参量化设计的方法。将遗传算法和逃逸函数相结合对超大视场光学系统进行了优化设计。首先,修正了基于平面对称像差理论的超大视场光学系统的评价函数;然后针对遗传算法在优化超多参量光学系统时,其优化解的鲁棒性较差的问题,采用在遗传算法中混入逃逸函数来改善算法的鲁棒性。最后应用改进的算法分别对鱼眼镜头和折反射全景成像系统进行了优化计算,结果表明,优化后光学系统的像质比参考设计有较大的改善。     

生命系统理论在新型制造模式中的应用初探

生命系统理论认为有生命的地方均可分为８个层次，可抽象出２０个关键子系统，构成基本的生命过程。该理论在国外已有应用。阐述生命系统理论与新型制造模式的联系，探讨利用我国传统文化同ＬＳＴ相结合创立一套具有中国特色的现代化管理理论的可能性。     

MMAS与粗糙集在轴承复合故障诊断中的应用

在分析振动加速度信号的基础上,提出了新的粗糙集属性约简算法,并应用于轴承复合故障诊断.将最大一最小蚂蚁系统(max-min ant system,简称MMAS)引入条件属性约简中,以最坏Fisher准则函数作为启发式信息以提高搜索效率,综合考虑分类正确率和条件属性个数两方面因素,利用粗糙集理论约简故障诊断决策表,有效地提高了轴承故障诊断的效率.     

基于PMAC的数控系统在螺纹磨削中的应用

介绍了基于PMAC运动控制器的磨螺纹数控系统的软硬件设计,系统运行于Windows平台或脱机运行,采用COM总线通讯的上下位机模式,有效地保证了数据传输速度和加工的实时性。利用PMAC卡自身提供的强大编程语言,可以很方便地实现对数控系统的精确控制。     

带变异算子的启发式最大最小蚂蚁系统求解流水车间调度问题

针对蚂蚁算法在求解流水车间调度问题(FSP)时易出现停滞以及计算时间较长的缺点,对最大最小蚂蚁系统(MMAS)进行了改进,提出一种带变异算子的启发式最大最小蚂蚁系统,在改进的算法中,指出了启发式信息值的求法,对一些参数作动态性调整并融入了遗传算法中的变异操作,最后,通过仿真结果表明了该算法对求解FSP问题是有效的。     

A novel design strategy for iterative learning and repetitive controllers of systems with a high modal density: Application to active noise control

This paper describes the application of a novel design strategy for iterative learning and repetitive controllers for systems with a high modal density, presented in the companion paper, on two experimental case studies. Both case studies are examples of active structural acoustic control, where the goal is to reduce the radiated noise using structural actuators. In the first case study, ILC is used to control punching noise. An electrodynamic actuator on the frame of the punching machine is driven by the ILC algorithm which takes advantage of the repetitiveness of the consecutive impacts to reduce noise radiation. In the second case study, an RC algorithm is used to control the noise radiated by rotating machinery, which is often mainly periodic. A piezoelectric actuator incorporated in the bearing is driven by the RC algorithm which is capable of reducing harmonics of the rotational frequency of the shaft. Both applications show the practical usefulness of the novel design strategy.