Parameter variation methods for cell mapping

In the study of nonlinear dynamic systems, the influence of system parameters on the long term behaviour plays an important role. In this paper, parameter variation methods are presented which can be used when investigating a nonlinear dynamic system by means of simple or interpolated cell mapping. In the case of coexisting attractors, the proposed methods determine the evolution of the basin boundaries when a system parameter is varied. Application of the methods to a modified Duffing equation is performed. It is concluded that the proposed methods are very efficient and accurate.     

Basin boundaries and robustness of nonlinear dynamic systems

Summary We present a method of computing a series of sets that approximates the basin of attraction for a given solution of a nonlinear dynamic system. The construction technique uses the general cell-mapping method in conjunction with an adaptive subdivision of the initial cell space. Our method provides a series of sets that contains the basin of attraction. Thus, we can approximate the robustness of a given solution from below. Received 22 April 1999; accepted for publication 3 June 1999     

Comparison of hybrid and standard discontinuous Galerkin methods in a mesh-optimisation setting

This paper assesses the benefits of hybridization on the accuracy and efficiency of high-order discontinuous Galerkin (DG) discretizations. Two hybridized methods are considered in addition to DG: hybridized DG (HDG) and embedded DG (EDG). These methods offer memory and computational time savings by introducing trace degrees of freedom on faces that become the only globally-coupled unknowns. To mitigate the effects of solution singularities on accuracy, the methods are compared in an adaptive setting on meshes optimised for the accurate prediction of chosen scalar outputs. Compressible flow results for the Euler and Reynolds-averaged Navier-Stokes equations demonstrate that the hybridized methods offer cost savings relative to DG in memory and computational time. In addition, for the cases tested, EDG yields the lowest error levels for a given number of degrees of freedom. These benefits disappear on uniformly-refined meshes, indicating the importance of using order-optimised meshes when comparing the discretizations.     

系泊海洋平台周期运动倍周期分岔的胞映射分析

应用胞映射方法研究了系泊海洋生产平台的周期运动及其倍周期分岔。系泊运动的数学模型是一个具有指数回复力特性的非线性强迫振子 ,以波浪作用力为外激励。将波浪激励周期作为分岔控制参数 ,研究了周期系泊运动的倍周期分岔。胞映射方法用于寻找系统的稳定吸引子并确定其吸引域。时间历程、相图、功率谱和Poincar啨映射用于确定吸引子的具体类型芯糠⑾?,分岔参数处于不同的区域时 ,系统存在着相异的倍周期分岔特性。观察到了倍周期分岔的产生和突然消失 ,也找到了一个趋于吸引子的倍周期分岔序列。根据吸引域的胞映射分析结果解释了上述不同的倍周期分岔特征。发现其原因在于倍周期序列中的每个吸引子是否具有全局吸引性。     

Basins of Attraction of Periodic Oscillations in Suspension Bridges

We consider the dynamics of the lowest order transversal vibration mode of a suspension bridge, for which the hangers are treated as one-sided springs, according to the model of Lazer and McKeena [SIAM Review 58, 1990, 537]. We analyze in particular the multi-stability of periodic attractors and the basin of attraction structure in phase space and its dependence with the model parameters. The parameter values used in numerical simulations have been estimated from a number of bridges built in the United States and in the United Kingdom, thus taking into account realistic, yet sometimes simplified, structural, aerodynamical, and physical considerations.     

The behaviour of nonlinear oscillators subjected to ramped forcing

This paper considers the behaviour of a mechanical oscillator with cubic non-linearity subjected to a forcing excitation whose frequency remains constant while the amplitude is ramped, growing until it reaches a predetermined value. We concentrate on the nature of the basins of attraction whose size indicates the stability of the system, in a structural sense. The reduced level of forecing at the initial stages of ramping produces a delay in bifurcational events when compared to the constant sinusoidally forced counterpart. Preliminary results show that for some parameter values the area of basin does not increase monotonically as the length of ramping is varied. A preliminary version was presented at BIFCHAOS '92, Workshop held at L'Aquila, Italy, on 20–21 May 1992.     

Dynamics of a multi-DOF beam system with discontinuous support

This paper deals with the long term behaviour of periodically excited mechanical systems consisting of linear components and local nonlinearities. The particular system investigated is a 2D pinned-pinned beam, which halfway its length is supported by a one-sided spring and excited by a periodic transversal force. The linear part of this system is modelled by means of the finite element method and subse1uently reduced using a Component Mode Synthesis method. Periodic solutions are computed by solving a two-point boundary value problem using finite differences or, alternatively, by using the shooting method. Branches of periodic solutions are followed at a changing design variable by applying a path following technique. Floquet multipliers are calculated to determine the local stability of these solutions and to identify local bifurcation points. Also stable and unstable manifolds are calculated. The long term behaviour is also investigated by means of standard numerical time integration, in particular for determining chaotic motions. In addition, the Cell Mapping technique is applied to identify periodic and chaotic solutions and their basins of attraction. An extension of the existing cell mapping methods enables to investigate systems with many degress of freedom. By means of the above methods very rich complex dynamic behaviour is demonstrated for the beam system with one-sided spring support. This behaviour is confirmed by experimental results.     

胞映射搜索最优控制路径的新策略

在胞映射求解最优控制问题的现有方法的基础上，提出了一种利用胞映射搜索最优控制路径的新策略。该策略基于负步长逆向数值积分技巧，采用了一种新的搜索过程，使得求解问题的效率大为提高。同现有的方法相比，新策略节省了几倍，甚至十几倍的时间。而且计算结果可靠，有很强的工程应用价值，为求解高维的最优控制问题可能会提供一定的基础。     

Control of an Adaptive Refinement Technique of Generalized Cell Mapping by System Dynamics

Generalized cell mapping is an efficient and powerful numerical tool for the prediction of the long-term behavior and global analysis of nonlinear dynamic systems. The only drawback of this method is the enormous computational effort it requires for high-dimensional systems. We overcome this problem by adaptively refining a very rough starting cell grid, where the adaptation is controlled by the long-term dynamics of the system. We illustrate the efficiency of our approach by examples.     

Solution of Fixed Final State Optimal Control Problems via Simple Cell Mapping

A strategy is proposed to solve the fixed final state optimalcontrol problem using the simple cell mapping method. A non-uniform timestep simple cell mapping is developed to create a general database fromwhich solutions of various optimal control problems can be obtained. Atwo-stage backward search algorithm is proposed to eliminate degeneratedpaths often associated with the simple cell mapping. The proposed methodcan accurately delineate the switching curves and eliminate false limitcycles in the solution. The method is applied to two optimal controlproblems with bang-bang control. The well-known minimum time controlproblem of moving a point mass from any initial condition to the originof the phase plane is studied first. This example has exact solutionsavailable which provide a yardstick to examine the accuracy of themethod. The cell size dependence of the solution accuracy is studiednumerically. The second example is a variable stiffness feedback controlproblem with tuning range saturation. The strategy proposed is able toprovide the switching curves in the phase plane. This result has notbeen obtained before.     

Fixed Final Time Optimal Control via Simple Cell Mapping

A cell mapping strategy based on Bellman'sPrinciple of optimality (BP) is proposed to solve the fixed final time optimalcontrol of strongly nonlinear systems with state and control bounds. Thefixed final time problem is transformed into a fixed final time-fixed finalstate optimal control problem by reversing the time. This transformationallows to solve the problem in the framework of the BP. Backward searchingalgorithms within the cell mapping context are used to obtain the solution ofthe new problem. This approach reduces considerably the computational effortrequired for the original problem when it is solved by a forward searchingapproach. The vibration control problem of damped and undamped variablestiffness oscillators with bounded stiffness tuning range is studied todemonstrate the effectiveness of the approach. A numerical study on theconvergence of the method is also presented.     

Chaos and instability in a power system: Subharmonic-resonant case

The response of a single-machine quasi-infinite busbar system to the simultaneous occurrence of principal parametric resonance and subharmonic resonance of order one-half is investigated. By numerical simulations we show the existence of oscillatory solutions (limit cycles), period-doubling bifurcations, chaos, and unbounded motions (loss of synchronism). The method of multiple scales is used to derive a second-order analytical solution that predicts (a) the onset of period-doubling bifurcations, which is a precursor to chaos and unbounded motions (loss of synchronism), and (b) saddle-node bifurcations, which may be precursors to loss of synchronism.     

Stochastic Optimal Control of Nonlinear Systems via Short-Time Gaussian Approximation and Cell Mapping

A novel strategy to obtain global solutions of stochasticoptimal control problems with fixed state terminal conditions and controlbounds is proposed in this paper. The solution is global in the sense that theoptimal control solutions for all the initial conditions in a region of thestate space are obtained. The method makes use of Bellman's principle ofoptimality, the cumulant neglect closure method and the short-time Gaussianapproximation. A Markov chain with a control dependent transition probabilitymatrix is built using the generalized cell mapping method. This allows toevaluate the transient and steady state response of the controlled system. Themethod is applied to several linear and nonlinear systems leading to excellentcontrol performances.     

Cell mapping methods-beyond global analysis of nonlinear dynamic systems

在20世纪80年代由徐皆苏教授创建的胞映射方法一直受非线性科学界同仁的欢迎.近几年胞映射方法有了许多新的应用和算法.本文介绍了一些控制应用和算法的文献.另外,还介绍和讨论胞映射方法应用与多目标优化问题的研究和方法,多目标优化控制设计和非线性代数方程找零解.文中指出胞映射方法在并行计算的帮助下,现在可以解决中等高维空间中的各类问题,新的应用还会不断出现.     

Poincaré maps modeling and local orbital stability analysis of discontinuous piecewise affine periodically driven systems

This paper presents a methodology to study the local stability of periodic orbits (orbital stability) in switched discontinuous piecewise affine (DPWA) periodically driven multiple-input multiple-output (MIMO) systems. The switched system of interest has a bilinear state space representation where the controller inputs are binary signals taking values in the set {0,1}. These systems are characterized by a set of affine differential equations together with switching rules to commute between them. These switching rules are described by switching functions that are periodic in time and linear in state. The methodology is based on obtaining a discrete time model (Poincaré map), its steady state operation points, and its Jacobian matrix. This provides a powerful tool for studying their stability and to predict some kind of instability phenomena that the system can undergo like subharmonic oscillations. The proposed approach is applied to a power electronic circuit which toggles among six different system equations with five switching boundaries within a switching cycle. This work was supported by the Spanish Ministerio de Educación y Ciencia under Grant TEC-2004-05608-C02-02.     

The behaviour of a mass-spring system provided with a discontinuous dynamic vibration absorber

Summary The influence of a specific discontinuous dynamic vibration absorber on the motion of a vibrating system is investigated. Attention is paid to the effectiveness in the case of free vibrations and of vibrations due to sinusoidal excitations, where structural damping is also taken into account. For certain configurations numerical results are given.Notation M mass of the vibrating system - m mass of the ball - c spring constant - k structural damping coefficient - g acceleration of gravity - F ₀ amplitude of external force - frequency of external force - 2 distance over which the ball may move - x displacement of centre of tube - y displacement of the ball x and y are measured positive downward from the equilibrium position of the system when no gravitational force would act     

The adjoining cell mapping and its recursive unraveling,part II: Application to selected problems

Several applications of the adjoining cell mapping technique are provided here by employing the adaptive mapping unraveling algorithm to analyze smooth and pathological autonomous dynamical systems. The performance of an implementation of recursive unraveling algorithm is also illustrated regarding its low memory requirements for computational purposes when compared with the simple cell mapping method. The applications considered here illustrate the effectiveness of the adjoining cell mapping technique in its ability to determine limit cycles and to unravel nonstandard dynamics. The advantages of this new technique of global analysis over the simple cell mapping method are discussed.     

非线性系统全局动态特性分析的PCM法及其在转子轴承系统中的应用

本文将Ｐｏｉｎｃａｒｅ映射的思想与胞映射法相结合，提出了可用于高维非线性动力系统全局稳定性分析的新型数值方法：ＰＣＭ（Ｐｏｉｎｃａｒｅ－Ｃｅｌｌ－Ｍａｐｐｉｎｇ）法，和胞映射法相比，新方法在实用上具有明显的优点。为说明ＰＣＭ法的有效性，本文应用此方法对平衡转子轴承非线性动力系统进行了全局稳定性分析，同时给出了一确定状态空间中存在的所有周期解及其吸引域。     

PMUCR方法在高维非线性动力学系统中的应用

对现有的若干种胞映射方法应用于高维非线性动力学系统全局分析时存在的局限性进行了分析,在此基础上,提出了胞映射方法应用于高维系统时需遵循的几个原则:选择合适的分析平面;减少数据量;确定吸引子在相空间中的位置。根据这些原则,对胞参考点映射法(PMUCR)进行了改进,并对该改进方法应用于2维系统和4维系统时消耗的相对CPU时间进行了比较,结果表明,该改进方法能有效地应用于高维非线性动力学系统中。最后以船舶机械非线性隔振系统为例,分别分析了该改进方法在系统呈现周期运动和混沌运动时的应用。