高速客车蛇行运动Hopf分叉的研究

建立了高速客车非线性系统数学模型,模型中考虑了轨道的整体弹性和阻尼。基于常微分方程的一次近似理论和Hopf分叉理论,研究了高速客车在直线和大半径曲线轨道上蛇行运动的Hopf分叉情况。借助于DEPAR延续算法解决了圆曲线上车辆系统平衡位置难以确定的难题,分析了轨道整体刚度和阻尼、圆曲线半径和外轨超高及转向架悬挂参数等因素对高速客车Hopf分叉速度的影响。研究表明,高速客车在大半径曲线上也有可能出现Hopf分叉现象,并且曲线半径越大、外轨超高越大,车辆的Hopf分叉速度越高,但最大值不会超过车辆系统在直线上运行时的Hopf分叉速度。车辆系统在弹性轨道条件下的Hopf分叉速度高于刚性轨道条件下车辆系统对应的Hopf分叉速度。不论是刚性轨道还是弹性轨道,转向架悬挂参数对车辆系统Hopf分叉速度的影响趋势是一致的。     

A discrete-integral strength criterion for complicated stress states

The atomic structure behaviour at a crack tip in closely-packed layers of atoms is studied. The deformation of a three-atomic chain for the complicated stress state is analysed. This study includes the analyses of bifurcation and post-bifurcation behaviour as well as the sensitivity of the limit strength to fixing conditions. The numerically obtained values of theoretical strengths are compared with the available experimental results and the theoretical estimates. The discrete-integral strength criterion for complicated stress states is proposed. Contrary to the classical criteria, the proposed criterion allows a limiting transition of the crack length parameter and describes the strength of cracked and crack-free solids.     

Pore bifurcation, growth and pore termination in nanoporous alumina with concave and convex surfaces

The growth of nanoporous alumina on concave or convex aluminium surfaces has been investigated. The number of pores during anodic oxidation increases or decreases almost linearly with the thickness of the oxide which is due to bifurcation or termination of single pores during alumina growth. The anodic oxidation has been constantly conducted in oxalic acid at 40 V. Therefore the average interpore distance has not changed during alumina growth. In earlier papers it has been shown that a bifurcation of pores is the result of the change of voltage and the electrolyte. In this work we have demonstrated that a termination or a bifurcation of pores is also possible by structuring the aluminium to a curved surface with concave or convex properties before oxidation. Those results do not depend on the substrate characteristics or on the alumina preparation techniques.     

Non‐Uniform Distribution of Two‐Phase Flows through Parallel Identical Paths

When a single‐phase fluid splits, passes through identical paths in parallel, and then recombines, the flow distributes itself uniformly among the multiple paths. However, when multi‐phase suspensions travel through identical parallel paths, the flow distribution can be significantly non‐uniform. Although the uniform distribution is a solution of the governing equations, this solution may be an unstable steady‐state solution between two or more stable solutions, or one of an array of possible steady‐state solutions. This multiplicity has arisen in practice for multiple vertical channels within fluidized beds, for cyclones in parallel, and for distributed feed suspension flows. Simple theories are employed to explain the principles involved for two cyclones and for a pair of risers in parallel.     

NONLINEAR DYNAMICAL ANALYSIS OF BIFURCATION AND CONFLUENCE OF THE PACIFIC WESTERN BOUNDARY CURRENTS

In this paper, we analyze the bifurcation and the confluence of the Pacific western boundary currents by an analytical approach. Applying the conservation law, the geostrophic balance relation and the Bernoulli integral to a reduced gravity model, we get a quantitative relation for the outflow and the inflow, and establish the related formulae for the width and the veering angle of offshore currents under the inflow condition. Furthermore, a comparison between the volume transport based on the observation data and the analytical value for the Pacific western boundary currents is presented, which validates the theoretical analysis.     

时滞动力学与控制研究进展

与一般动力系统不同,无穷维时滞系统的研究方法并不成熟,使得时滞系统的分析和控制都很困难.与此同时,时滞广泛存在于包括神经网络、人工智能、机械加工、多智能体、机器人控制等众多领域,使得时滞动力学与控制的研究至关重要.因此,本专刊聚焦时滞引起的稳定性、非线性动力学和控制问题,着重讨论了神经、网络、机械和减振等领域的时滞动力学问题,希望能为相关领域的学者提供一些借鉴和参考.     

梁的强迫振动问题Green函数解及应用研究综述

针对一类周期激励下的广义离散Duffing系统,运用快慢分析方法,对系统状态进行数值模拟,通过分岔图和时间历程图对系统进行分析,得到不同参数下系统所表现出的新型簇发振荡模式,并探讨其与连续Duffing系统之间的联系.系统的簇发振荡模式被分为两类,一类是当慢变量穿过Fold分岔点或混沌激变点,吸引子发生转迁所诱发的各种对称式簇发振荡,另一类则是当慢变量无法穿过Fold分岔点或混沌激变点,由延迟Flip分岔所诱发的各种非对称式簇发振荡.     

Principle of designing slope compensation in PFC Boost converter

Due to wide input fluctuation with line frequency of 50 Hz, power-factor-correction (PFC) Boost converters tend to exhibit fast-scale instability over time domain. The traditional remedy is to impose slope compensation so as to weaken or eliminate this instability. A theoretical principle on the implementation of slope compensation signal is still lacking. Empirical design will induce over compensation frequently, resulting in a large decrease of power factor. In order to tackle this issue, by constructing the discrete-time iterative map of the PFC Boost converter from the viewpoint of bifurcation control theory of nonlinear systems, consequently, the criterion of critical stability for the PFC circuit can be established. Based on this stability criterion, appropriate design of slope compensation can be achieved. Our work indicates that 3 main circuit parameters (i.e. switching cycle, output reference voltage and inductor) determine the effective amplitude design of the slope compensation signal. The results, validated by a large quantity of analytical and numerical studies, show that appropriate slope compensation can be effective in weakening (or controlling) fast-scale bifurcation while maintaining a rather high input power factor.     

含时滞和Ih流的神经元的同步放电行为

本文研究了时滞和超极化激活的阳离子流Ih对抑制耦合的水蛭神经元的同步放电行为的调控.通过数值仿真揭示了时滞、耦合强度和Ih流都能诱发丰富的同步转迁行为,如从同步的周期-6簇放电到同步的周期-1簇放电.借助ISI分岔和快慢变量分离方法获得了Ih流诱导同步转迁行为的动力学原因.研究结果表明,时滞和Ih流都是影响水蛭神经元同步行为的重要因素.     

船舶横摇运动的非线性振动与混沌

本文针对船舶非线性横摇运动模型，以波浪尺度为变参数，运用平均化方法和范德坡变换，一系统的振动解随参数变化的定性情况，然后通过数值积分和胞映射相结合的方法，确定系统的多种开熙熙攘攘夺动解。可以看到胞映地能灵活地处理各种不同形式的上子，如周期解，各阶亚谐解乃至混沌吸引子并能方便快速地求解。横摇运动的大量非线性现象，如吸引子工存，对称性碳缺，倍周期分岔等现象都被观察到，文中还给出了由一系列倍周期分岔导致