考虑密封的悬臂转子系统的裂纹故障分析

以双盘悬臂立式转子-轴承系统为研究对象，建立了系统运动微分方程，并用数值方法分析了在非线性密封力和非线性油膜力作用下的裂纹转子的动力学特性。分析表明，在一定深度裂纹下，转子系统响应随不同角频率比表现出复杂的非线性现象，出现了周期k运动、拟周期运动和混沌运动等多种运动形式。在一定角速度时，工作在远离临界角速度区的转子系统对裂纹非常敏感，而工作在近临界角速度区的转子系统对裂纹不是特别敏感，但是裂纹对它的运动状态影响较大。该研究结果为该类转子-轴承系统的安全运行与故障诊断提供了一定的理论参考。     

具有裂纹-碰摩耦合故障转子-轴承系统的动力学研究

以非线性动力学和转子动力学理论为基础，分析了带有碰摩和裂纹耦合故障的弹性转子系统的复杂运动，在考虑轴承油膜力的同时构造了含有裂纹和碰摩故障转子系统的动力学模型。针对短轴承油膜力和碰摩-裂纹转子系统的强非线性特点，采用Runge-Kutta法对该系统由碰摩和裂纹耦合故障导致的非线性动力学行为进行了数值仿真研究，发现该类碰摩转子系统在运行过程中存在周期运动、拟周期运动和混沌运动等丰富的非线性现象，该研究结果为转子-轴承系统故障诊断、动态设计和安全运行提供理论参考。     

磁摩转子系统中的碰擦分岔现象

对于旋转机械中的常见故障这一－－转子与定子碰摩，应用非线性动力学理论分析了一个简单碰摩转子系统的碰擦分岔现象。通过对运动微分方程的数值积分。研究了转速比变化时系统具有的各种形式的分岔。结果表明：系统的运动具有周期与混沌运动交替、周期递增现象，倍周期分岔，以及随控制参数的减小运动从的周期轨道分岔为混沌吸引了。系统的这非线性特征对于准确地诊断这一故障具有重要意义。     

裂纹转子分叉、混沌行为研究中的映射延拓综合法

介绍一种能全面计算周期激励下非线性系统周期响应，拟周期响应和混沌响应的新算法－映射延拓综合法，它可方便地确定拟周期响应和混沌响应对应的系统参数区间。应用此算法对具有非线性刚度的裂纹转子系统裂纹扩展故障特征问题进行了研究，得到了以裂纹深度为分叉参数的系统稳态响应分叉解图。     

非稳态非线性油膜力作用下柔性轴裂纹转子的动力特性分析

分析了在动载轴承非稳态非线性油膜力作用下，具有横向裂纹柔性轴Jeffcott转子在非线性涡动影响下的动力特性。通过数值计算表明，在油膜失稳转速前，随着裂纹轴刚度变化比的增大，系统在低转速区域内具有丰富的非线性动力行为，出现倍周期分叉及混沌现象，涡动振幅随转速升高而减小，直到非稳态非线性油膜失稳，在无裂纹转子油膜临界失稳点处发现了类Hopf分叉现象，系统运动由平衡变为拟周期运动；裂纹转子在油膜临界失稳时的系统运动亦为拟周期运动，裂纹转子轴刚度变化对油膜失稳点及油膜失稳之后转子的运动影响不大，转子系统作拟周期运动。     

非线性刚度不平衡转子径向碰摩动力学研究

以线性项和立方项之和来表示转轴材料的物理非线性因素,建立了考虑非线性油膜力和非线性刚度的轴转子系统的动力学模型,利用数值积分法对转子系统由于局部碰摩故障导致的非线性动力学行为进行了研究,发现此类非线性振动系统具有倍周期分岔、拟周期和混沌等复杂的动力学行为,为此类系统的安全运行和有效识别转子故障提供了理论参考。     

碰摩裂纹转子轴承系统的周期运动稳定性及实验研究

根据碰摩裂纹耦合故障转子轴承系统的非线性动力学方程，利用求解非线性非自治系统周期解的延拓打靶法，研究了系统周期运动的稳定性。研究发现，小偏心量下系统周期运动发生Hopf分岔，大偏心量下系统周期运动发生倍周期分岔，偏心量的加大使周期解的稳定性明显降低；系统碰摩间隙变小，碰摩影响了油膜涡动的形成，使失稳转速有所提高；裂纹深度的加大降低了系统周期运动的稳定性。本文的研究为转子轴承系统的安全稳定运行提供了理论参考。     

亚临界情形下非线性裂纹转子的分叉与浑沌

分析非线性涡动裂纹转子中刚度变化比ΔＫ，裂纹角β，不平衡参数Ｕ对系统分叉及浑沌行为的影响。在转速区Ω＝２Ωｃ／３附近，当ΔＫ较大时，会出现分叉及浑沌现象，β对这些行为有很大影响，在Ω＝Ωｃ／２附近，当ΔＫ很大时，无论β为何值，将由拟周期通向浑沌，Ｕ作为一种外部因素，将使系统的非线性行为得到激发或抑制。     

叶片-转子-轴承系统的非线性动力学问题研究

以非线性动力学和转子动力学理论为基础,研究了在油膜力作用下,叶片和转轴耦合振动系统的动力学行为。为分析叶片的惯性影响,将叶片模化为单摆模型。采用Runge-Kutta数值方法求解了耦合系统的振动方程,并利用分岔图、Lyapunov指数图、Poincar啨映射图和频谱图等分析了系统的稳定性。分析结果表明,当转速变化时,系统响应会出现倍周期、拟周期和混沌运动等现象,在此基础上分析了叶片长度的变化对该系统非线性动力学行为的影响。     

时滞非线性悬架系统的混沌动力学特性研究

针对时滞减振控制的非线性悬架系统,建立其二自由度系统的动力学方程。首先,对动力系统进行了数值模拟,通过不同控制参数下系统的动力学行为的分岔图、相轨迹、庞加莱截面、功率谱图来研究时滞非线性悬架系统的混沌动力学行为。研究表明,基于系统参数和外在激励,选择适当的时滞控制参数,可避免系统在运行过程中出现混沌现象,改善系统的运行品质。然后,以主系统幅值均方根为目标函数,对系统进行优化得出减振效果最优时的时滞和反馈增益系数,并与无时滞时非线性悬架系统的主振幅响应进行比较。结果表明,时滞对非线性悬架系统减振和系统品质的改善是能够同时实现的。最后,研究了时滞控制参数变化对系统动力学行为的影响,研究发现,同一系统在不同时滞参数下其分岔形式以及通往混沌的形式具有着多样性,会出现倍周期分岔、Hopf分岔、阵发性分岔以及它们各自通往混沌的不同演化模式,这为实现悬架参数的优化控制提供了理论依据。     

Preface: Current research progress on mechanics of high speed rail

The construction and operation of high-speed rail（HSR）grid within the past two decades in China,in terms of the scale,may be possibly comparable to any national-wide construction in the history of China,even the Great Wall.By counting railways with commercial train service at the speed of200 km/h,China has the world’s longest HSR network with over 19 369.8 km of track in service today and this number     

ACTA MECHANICA SINICA 2014 ANNUAL SUBJECT INDEX

正~~     

人造地震动合成中的位移误差分析

三角函数级数法是合成人工地震动常用算法之一,但是通过对加速度积分求取位移时,却存在与零线漂移相类似的位移漂移现象。     

Rainwater rivulets on a cable subject to windFilets d'eau de pluie sur un câble soumis au vent

Rainwater rivulets appear on inclined cables of cable-stayed bridges when wind and rain occur simultaneously. In a restricted range of parameters this is known to cause vibrations of high amplitudes on the cable. The mechanism underlying this effect is still under debate but the role of rainwater rivulets is certain. We use a standard lubrication model to analyse the dynamics of a water film on a cylinder under the effect of gravity and wind load. A simple criterion is then proposed for the appearance and position of rivulets, where the Froude number is the control parameter. Experiments with several geometries of cylinder covered with water in a wind tunnel show the evolution of the rivulets with the Froude number. Comparison of the prediction by the model with these experimental data shows that the main mechanism of rivulet formation and positioning is captured. To cite this article: C. Lemaitre et al., C. R. Mecanique 334 (2006).     

Hermitian space-time finite elements for estuarine mass transport

Space-time finite element solutions of the convection–dispersion equation using higher-order nodal continuity and Hermitian polynomial shape functions are described. Five separate elements ranging from a complete linear element with C^0,0 nodal continuity to a complete first-order Hermitian element with C^1,1 nodal continuity are subjected to detailed analysis. Wave deformation analyses identify the source of leading or trailing edge oscillations, trailing edge oscillations being the major source of difficulty. These observations are confirmed by numerical experiments which further demonstrate the potential of higher-order nodal continuity. The performance of the complete first-order Hermitian element is quite satisfactory and measurably superior to the linear element.     

Cristallisation par onde acoustique : le cas de l'héliumCrystallization by acoustic waves: the case of helium

We establish a theoretical model to explain the nucleation of a crystal of helium by an acoustic over-pressure. We explain the interfacial laws for this ultra-fast cristallization, close to the sound speed. Assuming spherical symmetry and taking into account the experimental data, we recover the dynamics of the growth and melting during an over-pressure impulse. To cite this article: M. Ben Amar et al., C. R. Mecanique 331 (2003).     

Structure initiale et propriétés de liquéfaction statique d'un sableInitial structure and static liquefaction properties of sand.

Based on the use of two different preparation procedures for reconstituting triaxial samples of sand, i.e. wet tamping and dry pluviation, significant differences in associated mechanical behaviour are observed on a reference sand with respect to the phenomenon of ‘static’ liquefaction. Wet tamping favours the initiation of liquefaction instability, whereas dry pluviation favours a more stable behaviour, less susceptible to liquefaction. Microscopic observation of corresponding sand specimens allows us to identify two well differentiated structures, i.e., for wet tamping, an irregular structure with predominance of aggregates (aggregated grains) and macropores, very contractant and unstable and, for dry pluviation, a more regular structure, without macropores, more dilatant and more stable. These observations show the importance of further characterization, based on the introduction of appropriate parameters, of the initial structure of sandy materials, strongly dependant upon their mode of formation (natural or artificial). To cite this article: N. Benahmed et al., C. R. Mecanique 332 (2004).     

Sources of Complexity in Human Systems

Complex is a special attribute we can give to many kinds of systems. Although it is used often as a synonym of difficult, it has a specific epistemological meaning, which is going to be shared by the incoming science of complexity. Difficult is an object which, by means of an adequate computational power, can be deterministically or stochastically predictable. On the contrary complex is an object which can not be predictable because of logical impossibility or because its predictability would require a computational power far beyond any physical feasibility, now and forever. For complexity refers to some observing system, it is always subjective, and thus it is defined as observed irreducible complexity. Human systems are affected by several sources of complexity, belonging to three classes, in order of descending restrictivity. Systems belonging to the first class are not predictable at all, those belonging to the second class are predictable only through an infinite computational capacity, and those belonging to the third class are predictable only through a trans-computational capacity. The first class has two sources of complexity: logical complexity, directly deriving from self-reference and Gödel's incompleteness theorems, and relational complexity, resulting in a sort of indeterminacy principle occurring in social systems. The second class has three sources of complexity: gnosiological complexity, which consists of the variety of possible perceptions; semiotic complexity, which represents the infinite possible interpretations of signs and facts; and chaotic complexity, which characterizes phenomena of nonlinear dynamic systems. The third class coincides with computational complexity, which basically coincides with the mathematical concept of intractability. Artificial, natural, biological and human systems are characterized by the influence of different sources of complexity, and the latter appear to be the most complex.