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  • Articles  (80)
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  • 1
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    Annals of operations research 37 (1992), S. 185-215 
    ISSN: 1572-9338
    Keywords: Nonlinear economics ; mode-locking ; devil's staircase ; period doubling ; chaos ; fractal basin boundaries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Notes: Abstract A central problem for a dynamic formulation of macroeconomic theory is how to explain the occurrence of different, relatively well-defined economic modes such as the short term business cycle, the construction (or Kuznets) cycle, and the economic long wave (or Kondratiev cycle). Equally important is a description of the various phenomena that can arise through interaction between these cycles. Modern nonlinear theory suggests that different cyclical modes may be entrained through the process of mode-locking, where the periods of the interacting modes adjust to one another, so as to attain a rational ratio. This type of interaction is well documented in physical and biological systems. However, despite the importance of the problem and abundant evidence for nonlinearity in the economy, modern concepts of nonlinear mode-interaction have not yet been applied to the problem of entrainment between economic cycles. We show how mode-locking and other highly nonlinear dynamic phenomena arise in a model of the economic long wave. The behavior of the model is mapped as a function of the frequency and amplitude of an external forcing, producing both a devil's staircase and a detailed Arnol'd tongue diagram. Two different routes to chaos are identified. The Lyapunov exponents are calculated, allowing the strength of the chaos to be assessed, and the fractal nature of the basins of attraction for two simultaneously existing periodic solutions is illustrated. The paper concludes with a discussion of the implications for economic theory.
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  • 2
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    Journal of dynamics and differential equations 5 (1993), S. 219-240 
    ISSN: 1572-9222
    Keywords: Arnold diffusion ; n-body problem ; celestial mechanics ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, we show the existence of the Arnold diffusion in the elliptic restricted three-body problem. This gives one of the very few examples of Arnold diffusion in real physical systems. The construction is based on the transversal homoclinic orbits in the circular restricted three-body problem ([6, 7, 14]). We prove that the small perturbations to the horseshoe maps in the neighborhood of the homoclinic orbits creates the Arnold diffusion. The existence of the Arnold diffusion also shows that the elliptic restricted three-body problem is non-integrable.
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  • 3
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    Journal of theoretical probability 7 (1994), S. 339-349 
    ISSN: 1572-9230
    Keywords: U-statistics ; chaos ; type 2 ; decoupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract It is shown that the limite law of canonicalU-process is the law of a chaos process which has a versio with bounded and ‖·‖2 continuous paths. This is also true forB-valued canonicalU-statistics with values in a separable Banach space. Some properties of Banach spaces of type 2 related withU-statistics are presented.
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  • 4
    ISSN: 1572-9036
    Keywords: partial differential equations ; potentials ; chaos ; control
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The present study is a follow-up to previous recent publications in the field of theoretical economic geography and spatial economics. Earlier results are generalised and simulated in higher dimensions (in terms of variables and topological dimensions), and given possible undesirable outcomes of the process (which can behave chaotically), application of control methods to it is being studied.
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  • 5
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    Acta applicandae mathematicae 40 (1995), S. 179-243 
    ISSN: 1572-9036
    Keywords: 58F10 ; 58F13 ; Lyapunov stability ; orbital stability ; Zhukovskij stability ; instability ; system in variations ; Lyapunov characteristic exponent ; Lyapunov function ; positive invariant set ; frequency-domain theorem ; strange attractor ; chaos ; nonlocal reduction method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper discusses the connection between various instability definitions (namely, Lyapunov instability, Poincaré or orbital instability, Zhukovskij instability) and chaotic movements. It is demonstrated that the notion of Zhukovskij instability is the most adequate for describing chaotic movements. In order to investigate this instability, a new type of linearization is offered and the connection between that and the theorems of Borg, Hartman-Olech, and Leonov is established. By means of new linearization, analytical conditions of the existence of strange attractors for impulse stochastic generators are obtained. The assumption is expressed that an analogous analytical tool may be elaborated for continuous dynamical systems describing Chua's circuits. The paper makes a first step in this direction and establishes a frequency criterion of the existence of positive invariant sets with positive Lebesgue measure for piecewise linear systems, which are unstable in every region of phase space where they are linear.
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  • 6
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    OR spectrum 16 (1994), S. 101-111 
    ISSN: 1436-6304
    Keywords: Advertising model ; nonlinear dynamics ; chaos ; threshold rule ; marketing ; Werbemodell ; nichtlineare Dynamik ; Chaos ; Schwellenregel ; Marketing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Economics
    Description / Table of Contents: Zusammenfassung Im Laufe des letzten Jahrzehnts wurden mit Hilfe der Theorie nichtlinearer dynamischer Systeme ökonomische Modelle unterschiedlicher Komplexität untersucht. Der Zweck der vorliegenden Arbeit ist es, ein Model zu analysieren, das so einfach wie möglich ist, aber genügend Nichtlinearität aufweist, um chaotische Orbits zu ermöglichen. Es wird angenommen, daß der Marktanteil eines Unternehmens nur von einer einfachen „Alles oder Nichts“-Werbestrategie beeinflußt wird. Es stellt sich heraus, daß eine derart einfache Strategie komplexes Verhalten erzeugen kann, d. h. periodische Orbits jeder Länge und sogar chaotische, scheinbar zufällige Zeitpfade. Mit Hilfe des Progammpakets LOCBIF sind wir in der Lage zu untersuchen, für welche Parameter Chaos entsteht und wie der Übergang von einem stabilen Gleichgewicht zu Chaos erfolgt.
    Notes: Abstract During the last decade economic models of varying complexity have been studied by using the qualitative theory of nonlinear dynamical systems theory. The purpose of the present paper is to analyze an economic model which is as simple as possible but exhibits sufficient nonlinearity to admit chaotic orbits. A firm's market share is assumed to be influenced only by a simple threshold advertising rule. It turns out that such a simple rule may create complex behavioural patterns, i.e., periodic orbits of any length and even chaotic, seemingly unpredictable time paths. By using the package LOCBIF we are able to investigate for which model parameters chaos arises and how the transition from stable equilibrium to chaos occurs.
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  • 7
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    Journal of nonlinear science 3 (1993), S. 445-458 
    ISSN: 1432-1467
    Keywords: random number ; chaos ; chaotic circuit
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary A simple method to generate pseudorandom numbers is presented. The basic part of the circuit consists of two identical nonautonomous chaotic oscillators, which are driven by an external clock signal. The well-known chaotic circuits are extremely simple, as they are composed only of an inductor and a capacitance diode, and thus it is easy to get the generator to work reliably. The output of the oscillators is discretized by a comparator, and these signals are mixed together using a D flip-flop. The distribution, the spectrum, the return map, and the autocorrelation of random numbers obtained by this circuit are shown. We have studied the system also using the correlation integral method and the local prediction technique. The results of these analyses demonstrate that the number sequence is highly random.
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  • 8
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    Journal of nonlinear science 4 (1994), S. 59-68 
    ISSN: 1432-1467
    Keywords: chaos ; invariant measure ; computer simulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary Whenf(x)=2x (mod 1) is simulated in a finite discretized space, with random round-off error, the dynamical states can be modeled as belonging to a family of Markov chains. We completely characterize the invariant measure of the discretized dynamics in terms of easily computable stationary measures of the chains.
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  • 9
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    Journal of nonlinear science 1 (1991), S. 175-199 
    ISSN: 1432-1467
    Keywords: finite time Lyapunov exponents ; strange attractor ; chaos ; predictability ; invariant density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary We introduce the idea of local Lyapunov exponents which govern the way small perturbations to the orbit of a dynamical system grow or contract after afinite number of steps,L, along the orbit. The distributions of these exponents over the attractor is an invariant of the dynamical system; namely, they are independent of the orbit or initial conditions. They tell us the variation of predictability over the attractor. They allow the estimation of extreme excursions of perturbations to an orbit once we know the mean and moments about the mean of these distributions. We show that the variations about the mean of the Lyapunov exponents approach zero asL → ∞ and argue from our numerical work on several chaotic systems that this approach is asL −v. In our examplesv ≈ 0.5–1.0. The exponents themselves approach the familiar Lyapunov spectrum in this same fashion.
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  • 10
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    Journal of nonlinear science 2 (1992), S. 417-452 
    ISSN: 1432-1467
    Keywords: chaos ; hysteresis ; dynamical system ; ergodicity ; strange attractors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Summary Hysteresis-type nonlinearities often appear in engineering systems such as electric circuits, mechanical systems, and control systems. In this paper, we study a family of two-dimensional nonlinear dynamical systems that can be regarded as models for an active linear network or a linear control system with a hysteresis-type feedback. A complete analysis of the complicated chaotic behavior exhibited by such a system is presented in this paper. The Poincaré return map is determined analytically, and a complete bifurcation study is completed in terms of two canonical parameters. The associated asymptotic behavior of the system is also discussed. Using tools from dynamical system and ergodic theory, a probabilistic description of the chaotic motion is obtained. We show that the chaotic system is isometric, from an ergodic point of view, to a time homogeneous Markov chain, for a certain set of canonical parameters.
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  • 11
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    Acta applicandae mathematicae 32 (1993), S. 123-156 
    ISSN: 1572-9036
    Keywords: 49M99 ; 58F13 ; 90B50 ; Golden Section ; Fibonacci ; optimization ; dynamic process ; chaos ; fractal ; Lyapunov ; exponent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Certain search algorithms produce a sequence of decreasing regions converging to a pointx *. After renormalizing to a standard region at each iteration, the renormalized location ofx *, sayx x, may obey a dynamic process. In this case, simple ergodic theory might be used to compute asymptotic rates. The family of ‘second-order’ line search algorithms which contains the Golden Section (GS) method have this property. The paper exhibits several alternatives to GS which have better almost sure ergodic rates of convergence for symmetric functions despite the fact that GS is asymptotically minimax. The discussion in the last section includes weakening of the symmetry conditions and announces a backtracking bifurcation algorithm with optimum asymptotic rate.
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  • 12
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    Bulletin of the Brazilian Mathematical Society 29 (1998), S. 197-228 
    ISSN: 1678-7714
    Keywords: time series ; (deterministic) ; chaos ; correlation integral ; predictability ; extremal index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we first give an overview of the methods of analysis of time series in terms of correlation integrals, which were developed for time series generated by deterministic systems. From the extremal value theory one obtains asymptotic information on the behaviour of the correlation integrals of time series generated by non-deterministic (mixing) systems. This leads to an analysis in terms of correlation integrals which is complementary to the estimation of dimension and entropy.
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  • 13
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    Numerical algorithms 14 (1997), S. 25-53 
    ISSN: 1572-9265
    Keywords: dynamical systems ; numerical methods ; homoclinic points for maps ; multihumped homoclinic orbits ; chaos ; 58F13 ; 58F15 ; 58F08
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract Transversal homoclinic orbits of maps are known to generate a Cantor set on which a power of the map conjugates to the Bernoulli shift on two symbols. This conjugacy may be regarded as a coding map, which for example assigns to a homoclinic symbol sequence a point in the Cantor set that lies on a homoclinic orbit of the map with a prescribed number of humps. In this paper we develop a numerical method for evaluating the conjugacy at periodic and homoclinic symbol sequences in a systematic way. The approach combines our previous method for computing the primary homoclinic orbit with the constructive proof of Smale's theorem given by Palmer. It is shown that the resulting nonlinear systems are well conditioned uniformly with respect to the characteristic length of the symbol sequence and that Newton's method converges uniformly too when started at a proper pseudo orbit. For the homoclinic symbol sequences an error analysis is given. The method works in arbitrary dimensions and it is illustrated by examples.
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  • 14
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    Applied mathematics and mechanics 13 (1992), S. 117-123 
    ISSN: 1573-2754
    Keywords: symbolic dynamics ; chaos ; shift-invariant set
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper extends symbolic dynamics to general cases. Some chaotic properties and applications of the general symbolic dynamics (Σ (X), σ) and its special cases are discussed, where Xis a separable metric space.
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  • 15
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    Applied mathematics and mechanics 19 (1998), S. 625-635 
    ISSN: 1573-2754
    Keywords: shallow arch ; internal resonance ; steady state motion ; bifurcation ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract The bifurcation dynamics of shallow arch which possesses initial deflection under periodic excitation for the case of 1∶2 internal resonance is studied in this paper. The whole parametric plane is divided into several different regions according to the types of motions; then the distribution of steady state motions of shallow arch on the plane of physical parameters is obtained. Combining with numerical method, the dynamics of the system in different regions, especially in the Hopf bifurcation region, is studied in detail. The rule of the mode interaction and the route to chaos of the system is also analysed at the end.
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  • 16
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    Applied mathematics and mechanics 20 (1999), S. 830-836 
    ISSN: 1573-2754
    Keywords: chaos ; Melnikov method ; Poincaré map ; phase portrait ; time-displacement diagram ; O343.5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, the system of the forced vibration $$\ddot T - \lambda _1 T + \lambda _2 T^2 + \lambda _3 T^3 = \varepsilon \left( {g\cos \omega t - \varepsilon '\dot T} \right)$$ is discussed, which contains square and cubic items. The critical condition that the system enters chaotic states is given by the Melnikov method. By Poincaré map, phase portrait and time-displacement history diagram, whether the chaos occurs is determined.
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  • 17
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    Applied mathematics and mechanics 13 (1992), S. 51-59 
    ISSN: 1573-2754
    Keywords: conservative compound pendulum ; non-integrability ; chaos ; canonical transformation ; numerical simulation ; Birkhoff's series ; normal form ; nth-fold resonance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract By using a series of canonical transformations (Birkhoff's series), an approximate integral of a conservative compound pendulum is evaluated. Level lines of this approximate integral are compared with the numerical simulation results. It is seen clearly that with a raised energy level, the nearly integrable system becomes non-integrable, i.e. the regular motion pattern changes to the chaotic one. Experiments with such a pendulum device display the behavior mentioned above.
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  • 18
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    Applied mathematics and mechanics 19 (1998), S. 67-73 
    ISSN: 1573-2754
    Keywords: Reyleigh number ; Lorenz system ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract Controlling chaos in the Lorenz system with a controllable Rayleigh number is investigated by the state space exact linearization method. Based on proving the exact linearizability, the nonlinear feedback is utilized to design the transformation changing the original chaotic system into a linear controllable one so that the control is realized. Numerical examples of control are presented.
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  • 19
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    Applied mathematics and mechanics 20 (1999), S. 360-364 
    ISSN: 1573-2754
    Keywords: buckled plate ; chaos ; Poincaré section
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract The primary aim of this paper is to study the chaotic motion of a large deflection plate. Considered here is a buckled plate, which is simply supported and subjected to a lateral harmonic excitation. At first, the partial differential equation governing the transverse vibration of the plate is derived. Then, by means of the Galerkin approach, the partial differential equation is simplified into a set of two ordinary differential equations. It is proved that the double mode model is identical with the single mode model. The Melnikov method is used to give the approximate excitation thresholds for the occurrence of the chaotic vibration. Finally numerical computation is carried out.
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  • 20
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    Acta applicandae mathematicae 20 (1990), S. 177-188 
    ISSN: 1572-9036
    Keywords: 92 (30E) ; Psychophysics ; chaos ; Julia sets ; nonlinear modelling ; sensory processes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Julia sets for the map z→a(z−ie)(1−z)(z+ie) are illustrated for some attractors of interest. This work extends previous analyses of the cubic complex polynomial and considers dynamics in regions which may be associated with the modelling of the results of overload in sensory inputs.
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  • 21
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    Acta applicandae mathematicae 26 (1992), S. 1-60 
    ISSN: 1572-9036
    Keywords: 58F13 ; Hausdorff measure ; Hausdorff dimension ; strange attractor ; Lorenz system ; Rössler system ; Lyapunov function ; stability ; chaos ; weakly contracting system ; monostability ; frequency theorem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract This paper surveys results of the authors and others conceming estimates for the Hausdorff dimension of strange attractors, particularly in the case of (generalized) Lorenz systems and Rössler systems. A key idea is the interpretation of Hausdorff measure as an analogue of a Lyapunov function.
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  • 22
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    Acta applicandae mathematicae 26 (1992), S. 271-291 
    ISSN: 1572-9036
    Keywords: 34C35 ; 58F10 ; 58F13 ; 58F14 ; 58F21 ; Bifurcation ; chaos ; dynamical systems ; nonlinearity ; simple and strange attractors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract These are notes of the lectures presented by the author at the 1991 International Workshop on Application of Statistical Methods in Theoretical Physics and Fluid Dynamics, Indian Statistical Institute, Calcutta. After a very short introduction to the terminology, mathematical description, and geometrical view on nonlinear dynamical systems, a series of examples are presented. They illustrate some specific properties of such systems. Some of the examples have been published in local journals and are little known.
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  • 23
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    Applied mathematics and mechanics 12 (1991), S. 1135-1142 
    ISSN: 1573-2754
    Keywords: chaos ; bifurcation ; transverse ; heteroclinic cycle ; homoclinic orbit ; cat's eye flow ; vortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract This paper discusses the dynamic behavior of the Kelvin-Stuart cat's eye flow under periodic perturbations. By means of the Melnikov method the conditions to have bifurcations to subharmonics of even order for the oscillating orbits and to have bifurcations to subharmonics of any order for the rotating orbits are given, and further, the coexistence phenomena of the chaotic motions and periodic solutions are presented.
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  • 24
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    Applied mathematics and mechanics 12 (1991), S. 1149-1152 
    ISSN: 1573-2754
    Keywords: chaos ; bifurcation ; homoclinic orbit ; heteroclinic orbit ; simple zeros ; the Melnikov function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In this paper, we use the Melnikov function method to study a kind of soft Duffing equations[1] $$\dot x + Af\left( {\dot x,x} \right) + x - x^{2k + 1} = r\left[ {M\left( {x,\dot x} \right)\cos \omega t + N\left( {x,\dot x} \right)\sin \omega t} \right]\left( {k = 1,2,3, \cdots } \right)$$ and give the condition that the equations have chaotic motion and bifurcation. The method used in this paper is effective for dealing with the Melnikov function integral of the system whose explict expression of the homoclinic or heteroclinic orbit cannot be given.
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  • 25
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    Applied mathematics and mechanics 19 (1998), S. 121-128 
    ISSN: 1573-2754
    Keywords: nonlinear frequency ; Floquet theory ; bifurcation ; chaos ; Duffing system with multi-frequency external periodic forces
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    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract By introducing nonlinear freqyency, using Floquet theory and referring to the characteristics of the solution when it passes through the transition boundaries, all kinds of bifurcation modes and their transition boundaries of Duffing equation with two periodic excitations as well as the possible ways to chaos are studied in this paper.
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  • 26
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    Applied mathematics and mechanics 20 (1999), S. 960-966 
    ISSN: 1573-2754
    Keywords: thermoelasticity ; chaos ; Melnikov function ; Poincaré mapping ; O343.5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Mathematics , Physics
    Notes: Abstract In the paper the nonlinear dynamic equation of a harmonically forced elliptic plate is derived, with the effects of large deflection of plate and thermoelasticity taken into account. The Melnikov function method is used to give the critical condition for chaotic motion. A demonstrative example is discussed through the Poincaré mapping, phase portrait and time history. Finally the path to chaotic motion is also discussed. Through the theoretical analysis and numerical computation some beneficial conclusions are obtained.
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    Journal of optimization theory and applications 80 (1994), S. 385-406 
    ISSN: 1573-2878
    Keywords: Infinite-horizon concave problems ; optimal policies ; discount factors ; strong concavity ; dynamical systems ; chaos ; sensitivity to initial conditions ; topological entropy ; Lipschitz dependence
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    Topics: Mathematics
    Notes: Abstract We study the relationship between the dynamical complexity of optimal paths and the discount factor in general infinite-horizon discrete-time concave problems. Given a dynamic systemx t+1=h(x t ), defined on the state space, we find two discount factors 0 〈 δ* ≤** 〈 1 having the following properties. For any fixed discount factor 0 〈 δ 〈 δ*, the dynamic system is the solution to some concave problem. For any discount factor δ** 〈 δ 〈 1, the dynamic system is not the solution to any strongly concave problem. We prove that the upper bound δ** is a decreasing function of the topological entropy of the dynamic system. Different upper bounds are also discussed.
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    Nonlinear dynamics 1 (1990), S. 1-21 
    ISSN: 1573-269X
    Keywords: bifurcation theory ; chaos ; parametric vibrations ; quadratic nonlinearity ; cubic nonlinearity ; fractal basin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The behavior of single-degree-of-freedom systems possessing quadratic and cubic nonlinearities subject to parametric excitation is investigated. Both fundamental and principal parametric resonances are considered. A global bifurcation diagram in the excitation amplitude and excitation frequency domain is presented showing different possible stable steady-state solutions (attractors). Fractal basin maps for fundamental and principal parametric resonances when three attractors coexist are presented in color. An enlargement of one region of the map for principal parametric resonance reveals a Cantor-like set of fractal boundaries. For some cases, both periodic and chaotic attractors coexist.
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    Nonlinear dynamics 1 (1990), S. 313-339 
    ISSN: 1573-269X
    Keywords: Power systems ; chaos ; bifurcations ; loss of synchronism
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    Topics: Mathematics
    Notes: Abstract We investigate some of the instabilities in a single-machine quasi-infinite busbar system. The system's behavior is described by the so-called swing equation, which is a nonlinear second-order ordinary-differential equation with additive and multiplicative harmonic terms having the frequency Ω. When Ω≈ω0, where ω0 is the linear natural frequency of the machine, we use digital-computer simulations to exhibit some of the complicated responses of the machine, including period-doubling bifurcations, chaotic motions, and unbounded motions (loss of synchronism). To predict the onset of these complicated behaviors, we use the method of multiple scales to develop an approximate first-order closed-form expression for the period-one responses of the machine. Then, we use various techniques to determine the stability of the analytical solutions. The analytically predicted period-one solutions and conditions for its instability are in good agreement with the digital-computer results.
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    Nonlinear dynamics 1 (1990), S. 221-241 
    ISSN: 1573-269X
    Keywords: Nonlinear ; rotor ; clearance ; chaos
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    Topics: Mathematics
    Notes: Abstract A HB (Harmonic Balance)/AFT (Alternating Frequency/Time) technique is developed to obtain synchronous and subsynchronous whirling motions of a horizontal Jeffcott rotor with bearing clearances. The method utilizes an explicit Jacobian form for the iterative process which guarantees convergence at all parameter values. The method is shown to constitute a robust and accurate numerical scheme for the analysis of two dimensional nonlinear rotor problems. The stability analysis of the steady-state motions is obtained using perturbed equations about the periodic motions. The Floquet multipliers of the associated Monodromy matrix are determined using a new discrete HB/AFT method. Flip bifurcation boundaries were obtained which facilitated detection of possible rotor chaotic (irregular) motion as parameters of the system are changed. Quasi-periodic motion is also shown to occur as a result of a secondary Hopf bifurcation due to increase of the destabilizing cross-coupling stiffness coefficients in the rotor model.
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    Nonlinear dynamics 10 (1996), S. 333-357 
    ISSN: 1573-269X
    Keywords: Pipes ; parametric excitation ; nonlinearity ; chaos ; multiple time scales ; harmonic balancing ; stability
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    Topics: Mathematics
    Notes: Abstract Chaotic motions of a simply supported nonlinear pipe conveying fluid with harmonie velocity fluetuations are investigated. The motions are investigated in two flow velocity regimes, one below and above the critical velocity for divergence. Analyses are carried out taking into account single mode and two mode approximations in the neighbourhood of fundamental resonance. The amplitude of the harmonic velocity perturbation is considered as the control parameter. Both period doubling sequence and a sudden transition to chaos of an asymmetric period 2 motion are observed. Above the critical velocity chaos is explained in terms of periodic motion about the equilibrium point shifting to another equilibrium point through a saddle point. Phase plane trajectories, Poincaré maps and time histories are plotted giving the nature of motion. Both single and two mode approximations essentially give the same qualitative behaviour. The stability limits of trivial and nontrivial solutions are obtained by the multiple time scale method and harmonic balance method which are in very good agreement with the numerical results.
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    Nonlinear dynamics 12 (1997), S. 57-68 
    ISSN: 1573-269X
    Keywords: Saddle form cable-suspended roofs ; truncated spectral model ; bifurcation ; chaos
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    Topics: Mathematics
    Notes: Abstract The purpose of this paper is to investigate the dynamic behaviour of saddle form cable-suspended roofs under vertical excitation action. The governing equations of this problem are system of nonlinear partial differential and integral equations. We first establish a spectral equation, and then consider a model with one coefficient, i.e., a perturbed Duffing equation. The analytical solution is derived for the Duffing equation. Successive approximation solutions can be obtained in likely way for each time to only one new unknown function of time. Numerical results are given for our analytical solution. By using the Melnikov method, it is shown that the spectral system has chaotic solutions and subharmonic solutions under determined parametric conditions.
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    Nonlinear dynamics 13 (1997), S. 99-115 
    ISSN: 1573-269X
    Keywords: Stick-slip vibrations ; one-dimensional maps ; reconstruction ; chaos
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    Topics: Mathematics
    Notes: Abstract This paper describes a one-dimensional map generated by a two degree-of-freedom mechanical system that undergoes self-sustained oscillations induced by dry friction. The iterated map allows a much simpler representation and a better understanding of some dynamic features of the system. Some applications of the map are illustrated and its behaviour is simulated by means of an analytically defined one-dimensional map. A method of reconstructing one-dimensional maps from experimental data from the system is introduced. The method uses cubic splines to approximate the iterated mappings. From a sequence of such time series the parameter dependent bifurcation behaviour is analysed by interpolating between the defined mappings. Similarities and differences between the bifurcation behaviour of the exact iterated mapping and the reconstructed mapping are discussed.
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    Nonlinear dynamics 13 (1997), S. 279-305 
    ISSN: 1573-269X
    Keywords: Nonlinear shell dynamics ; integration schemes ; chaos ; finite elements
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    Topics: Mathematics
    Notes: Abstract The paper is concerned with a dynamical formulation of a recently established shell theory capable to catch finite deformations and falls within the class of geometrically exact shell theories. A basic aspect is the design of time integration schemes which preserve specific features of the continuous system such as conservation of momentum, angular momentum, and energy when the applied forces allow to. The integration method differs from the one recently proposed by Simo and Tarnow in being applicable without modifications to shell formulations with linear as well as nonlinear configuration spaces and in being independent of the nonlinearities involved in the strain-displacement relations. A finite element formulation is presented and various examples of nonlinear shell dynamics including large overall and chaotic motions are considered.
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    Nonlinear dynamics 12 (1997), S. 251-262 
    ISSN: 1573-269X
    Keywords: Bifurcation ; chaos ; Duffingoscillator ; fractal basin boundary ; PIDcontroller
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    Topics: Mathematics
    Notes: Abstract We discuss in this paper the bifurcation, stability and chaos of the non-linear Duffing oscillator with a PID controller. Hopf bifurcation can occur and we show that there is a global stable fixed point. The PID controller works well in some fields of the parameter space, but in other fields of the parameter space, or if the reference input is not equal to zero, chaos is common for hard spring type system and so is fractal basin boundary for soft spring system. The Melnikov method is used to obtain the criterion of fractal basin boundary.
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    Nonlinear dynamics 14 (1997), S. 211-229 
    ISSN: 1573-269X
    Keywords: Spring-pendulum system ; chaos ; Lyapunovexponent
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    Topics: Mathematics
    Notes: Abstract An investigation into chaotic responses of a weakly nonlinear multi-degree-of-freedom system is made. The specific system examined is a harmonically excited spring pendulum system, which is known to be a good model for a variety of engineering systems, including ship motions with nonlinear coupling between pitching and rolling motions. By the method of multiple scales the original nonautonomous system is reduced to an approximate autonomous system of amplitude and phase variables. The approximate system is shown to have Hopf bifurcation and a sequence of period-doubling bifurcations leading to chaotic motions. In order to examine what happens in the original system when the approximate system exhibits chaos, we compare the largest Lyapunov exponents for both systems.
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    Nonlinear dynamics 7 (1995), S. 217-229 
    ISSN: 1573-269X
    Keywords: Nonlinear dynamics ; chaos ; elastic-plastic material ; Euler arch
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    Topics: Mathematics
    Notes: Abstract This paper deals with the dynamics of a truss structure, the Euler arch. The bars are made of elastic-plastic material, and the structure can exhibit large displacements. The aim of this paper is to give evidence of the possible chaotic behavior of this structure, even in the presence of a hardening plastic branch. The tools used are the diagrams of bifurcation, the measure of the dimension of the attractor, the Kolmogorov entropy, and the maximum Lyapunov exponent. This study emphasizes the sensitivity to the initial conditions by means of generalized basins of attraction.
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    Nonlinear dynamics 7 (1995), S. 273-284 
    ISSN: 1573-269X
    Keywords: Cell mapping ; continuation ; basins of attraction ; chaos
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    Notes: Abstract 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.
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    Nonlinear dynamics 7 (1995), S. 403-428 
    ISSN: 1573-269X
    Keywords: Lie transformation (perturbation method) ; dynamical systems ; small divisors ; chaos
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    Topics: Mathematics
    Notes: Abstract The paper persents recent developments in a singular perturbation method, known as the “Lie transformation method” for the analysis of nonlinear dynamical systems having chaotic behavior. A general approximate solution for a system of first-order differential equations having algebraic nonlinearities is introduced. Past applications to simple dynamical nonlinear models have shown that this method yields highly accurate solutions of the systems. In the present paper the capability of this method is extended to the analysis of dynamical systems having chaotic behavior: indeed, the presence of “small divisors” in the general expression of the solution suggests a modification of the method that is necessary in order to analyze nonlinear systems having chaotic behavior (indeed, even non-simple-harmonic behavior). For the case of Hamiltonian systems this is consistent with the KAM (Kolmogorov-Arnold-Moser) theory, which gives the limits of integrability for such systems; in contrast to the KAM theory, the present formulation is not limited to conservative systems. Applications to a classic aeroelastic problem (panel flutter) are also included.
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    Nonlinear dynamics 8 (1995), S. 111-139 
    ISSN: 1573-269X
    Keywords: Elastoplastic oscillator ; piecewise linear map ; chaos ; Smale horseshoe ; symbolic dynamics
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    Topics: Mathematics
    Notes: Abstract We study the local and global dynamical behavior of a two dimensional piecewise linear map which describes the asymptotic motions of a single degree of freedom, parametrically excited, elastoplastic oscillator after it has settled down to purely elastic oscillations. We give existence and stability conditions for periodic orbits and prove that chaos, in the form of a Smale horseshoe, exists at specific, but representative, parameter values. We interpret simulations of the elastoplastic oscillator itself in the light of these results.
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    Nonlinear dynamics 2 (1991), S. 53-72 
    ISSN: 1573-269X
    Keywords: Power systems ; loss of synchronism ; chaos ; bifurcations
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    Topics: Mathematics
    Notes: Abstract 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.
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    Nonlinear dynamics 2 (1991), S. 389-404 
    ISSN: 1573-269X
    Keywords: Railway dynamics ; limit-cycles ; bifurcations ; chaos
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    Topics: Mathematics
    Notes: Abstract A dicone moving on a pair of cylindrical rails can be considered as a simplified model of a railway wheelset. Taking into account the non-linear friction laws of rolling contact, the equations of motion for this non-linear mechanical system result in a set of differential-algebraic equations. Previous simulations performed with the differential-algebraic solver DASSL, [2], and experiments, [7], indicated non-linear phenomena such as limit-cycles, bifurcations as well as chaotic behaviour. In this paper the non-linear phenomena are investigated in more detail with the aid of special in-house software and the path-following algorithm PATH [10]. We apply Poincaré sections and Poincaré maps to describe the structure of periodic, quasiperiodic and chaotic motions. The analyses show that part of the chaotic behaviour of the non-linear system can be fully understood as a non-linear iterative process. The resulting stretching and folding processes are illustrated by series of Poincaré sections.
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    Nonlinear dynamics 20 (1999), S. 309-317 
    ISSN: 1573-269X
    Keywords: nonlinear oscillations ; chaos ; control ; input-output linearization
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    Topics: Mathematics
    Notes: Abstract The control of chaotic oscillations is investigated in this paper. A control methodology, termed input-output linearization, is modified by locally linearizing the nonlinear control law in the small neighborhood of the control goal. Its suitability for controlling chaotic oscillators is analyzed. The forced Duffing oscillator is treated as a numerical example of controlling chaotic motion to a given fixed point and a given period-2 motion. The control signals and time needed to achieve the desired goals of the modified method are compared with those of the original method. The robustness of the control law is demonstrated.
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    Nonlinear dynamics 19 (1999), S. 387-397 
    ISSN: 1573-269X
    Keywords: rotor dynamics ; chaos ; conical whirl ; restoring forces
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    Topics: Mathematics
    Notes: Abstract In Part I, theoretical analysis of the dynamic behaviour of a rigid rotor with nonlinear elastic restoring forces was carried out. In this part (Part II), an experimental confirmation of the theoretical data from that analysis was sought. With this aim, an experimental model was set up consisting mainly of a practically rigid rotor clamped onto a small diameter piano wire symmetrical to the wire supports. These supports were rigid and equipped with roller bearings and a device that made it possible to adjust the initial tension in the wire so as to make the elastic restoring forces less or more linear. The rotor was dynamically unbalanced and was driven by an asynchronous motor regulated by means of an inverter in order to adjust the rotor speed. A series of tests was performed on this rig with different values of the initial tension in the wire, and the trajectories of two points on the rotor axis were recorded in the course of the tests. These trajectories were obtained, under the hypothesis of similarity, from the orbits covered by two given sections of the wire and detected with two pairs of capacitive transducers. The collected data was compared with the theoretical results from Part I of the present investigation. Comparison of the collected data with the corresponding theoretical results made it possible to infer that system nonlinearity in the presence of small damping can give rise to motions that are periodic, whether synchronous or not, or quasi-periodic, but never chaotic.
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    Nonlinear dynamics 2 (1991), S. 77-117 
    ISSN: 1573-269X
    Keywords: Internal resonances ; bifurcations ; quasiperiodic motions ; chaos
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    Topics: Mathematics
    Notes: Abstract We present a collection of experimental results on the influence of modal interactions (i.e., internal or autoparametric resonances) on the nonlinear response of flexible metallic and composite structures subjected to a range of resonant excitations. The experimental results are provided in the form of frequency spectra, Poincaré sections, pseudo-phase planes, dimension calculations, and response curves. Experimental observations of transitions from periodic to chaotically modulated motions are also presented. We also discuss relevant analytical results. The current study is also relevant to other internally resonant structural systems.
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    Nonlinear dynamics 2 (1991), S. 1-34 
    ISSN: 1573-269X
    Keywords: Autoparametric resonance ; composite beams ; flapwise excitations ; chaos
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    Topics: Mathematics
    Notes: Abstract The nonlinear equations of motion derived in Part I are used to investigate the response of an inextensional, symmetric angle-ply graphite-epoxy beam to a harmonic base-excitation along the flapwise direction. The equations contain bending-twisting couplings and quadratic and cubic nonlinearities due to curvature and inertia. The analysis focuses on the case of primary resonance of the first flexural-torsional (flapwise-torsional) mode when its frequency is approximately one-half the frequency of the first out-of-plane flexural (chordwide) mode. A combination of the fundamental-matrix method and the method of multiple scales is used to derive four first-order ordinary-differential equations to describe the time variation of the amplitudes and phases of the interacting modes with damping, nonlinearity, and resonances. The eigenvalues of the Jacobian matrix of the modulation equations are used to determine the stability and bifurcations of their constant solutions, and Floquet theory is used to determine the stability and bifurcations of their limit-cycle solutions. Hopf bifurcations, symmetry-breaking bifurcations, period-multiplying sequences, and chaotic solutions of the modulation equations are studied. Chaotic solutions are identified from their frequency spectra, Poincaré sections, and Lyapunov's exponents. The results show that the beam motion may be nonplanar although the input force is planar. Nonplanar responses may be periodic, periodically modulated, or chaotically modulated motions.
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    Nonlinear dynamics 3 (1992), S. 183-198 
    ISSN: 1573-269X
    Keywords: Mechanical oscillator ; clearance nonlinearity ; period-doubling bifurcations ; chaos
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    Topics: Mathematics
    Notes: Abstract The dynamic behavior of a harmonically excited, preloaded mechanical oscillator with dead-zone nonlinearity is described quantiatively. The governing strongly nonlinear differential equation is solved numerically. Damping coefficient-force ratio maps for two different values of the excitation frequency have been formed and the boundaries of the regions of different motion types are determined. The results have been compared with the results of the forced Duffing's equation available in the literature in order to identify the differences between cubic and dead-zone nonlinearities. Period-doubling bifurcations, which take place with a change of any of the system parameters, have been found to be the most common route to chaos. Such bifurcations follow the scaling rule of Feigenbaum. b half length of the clearance. c viscous damping coefficient. f nonlinear displacement function. % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabiqaaiaacaGaaeqabaWaaeaaeaaakeaaceqGgbGbaKaaaa% a!3332!\[{\rm{\hat F}}\] alternating force to mean force ratio. Faalternating force amplitude. Fmmean force (preload). j period-doubling index. k stiffness coefficient. m mass. n period number. t dimensionless time. x dimensionless displacement. α variable system parameter in period-doubling bifurcation. δ Feigenbaum number. λ a point on the ζ-% MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabiqaaiaacaGaaeqabaWaaeaaeaaakeaaceqGgbGbaKaaaa% a!3332!\[{\rm{\hat F}}\] map. ω dimensionless excitation frequency. ω nnatural frequency of the corresponding linear system. ζ damping ratio. Superscripts: (−) dimensional quantity. (.) differentiation with respect to t.
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    Keywords: Articulated cylinder ; chaos ; period-doubling ; intermittency ; quasi-periodicity
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    Topics: Mathematics
    Notes: Abstract In this paper, the dynamics of a cantilevered articulated system of rigid cylinders interconnected by rotational springs, within a pipe containing fluid flow is studied. Although the formulation is generalized to any number of degrees-of-freedom (articulations), the present work is restricted to three-degree-of-freedom systems. The motions are considered to be planar, and the equations of motion, apart from impacting terms, are linearized. Impacting of the articulated cylinder system on the outer pipe is modelled by either a cubic spring (for analytical convenience) or, more realistically, by a trilinear spring model. The critical flow velocities, for which the system loses stability, by flutter (Hopf bifurcation) or divergence (pitchfork bifurcation) are determined by an eigenvalue analysis. Beyond these first bifurcations, it is shown that, for different values of the system parameters, chaos is obtained through three different routes as the flow is incremented: a period-doubling cascade, the quasiperiodic route, and type III intermittency. The dynamical behaviour of the system and differing routes to chaos are illustrated by phase-plane portraits, bifurcation diagrams, power spectra, Poincaré sections, and Lyapunov exponent calculations.
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    Nonlinear dynamics 9 (1996), S. 391-417 
    ISSN: 1573-269X
    Keywords: Bifurcation ; chaos ; pendulum ; feedback control ; second-order averaging ; Melnikov method ; experiment
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    Topics: Mathematics
    Notes: Abstract We consider a pendulum subjected to linear feedback control with periodic desired motions. The pendulum is assumed to be driven by a servo-motor with small time constant, so that the feedback control system can be approximated by a periodically forced oscillator. It was previously shown by Melnikov's method that transverse homoclinic and heteroclinic orbits exist and chaos may occur in certain parameter regions. Here we study local bifurcations of harmonics and subharmonics using the second-order averaging method and Melnikov's method. The Melnikov analysis was performed by numerically computing the Melnikov functions. Numerical simulations and experimental measurements are also given and are compared with the previous and present theoretical predictions. Sustained chaotic motions which result from homoclinic and heteroclinic tangles for not only single but also multiple hyperbolic periodic orbits are observed. Fairly good agreement is found between numerical simulation and experimental results.
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    ISSN: 1573-269X
    Keywords: Experimental ; bifurcation ; chaos ; fractal dimension ; parametric excitation
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    Topics: Mathematics
    Notes: Abstract An experimental study of a system that is parametrically excited through a bifurcation parameter is presented. The system consits of a lightly-damped, flexible beam which is buckled and unbuckled magnetically: it is parametrically excited by driving an electromagnet with a low-frequency sine wave. For voltage amplitudes in excess of the static bifurcation value, the beam slowly switches between the one-and two-well configurations. Experimental static and dynamic bifurcation results are presented. Static bifurcatons for the system are shown to involve a butterfly catastrophe. The dynamic bifurcation diagram, obtained with an automated data acquisition system, shows several period-doubling sequences, jump phenomena, and a chaotic region. Poincaré sections of a chaotic steady-state are obtained for various values of the driving phase, and the correlation dimension of the chaotic attractor is estimated over a large scaling region. Singular system analysis is used to demonstrate the effect of delay time on the noise level in delay-reconstructions, and to provide an independent check on the dimension estimate by directly estimating the number of independent coordinates from time series data. The correlation dimension is also estimated using the delay-reconstructed data and shown to be in good agrement with the value obtained from the Poincaré sections. The bifurcation and dimension results are used together with physical sonsiderations to derive the general form of a single-degree-of-freedom model for the experimental system.
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    Nonlinear dynamics 1 (1990), S. 23-38 
    ISSN: 1573-269X
    Keywords: numerical simulation ; chaos ; cable ; resonances ; bifurcations
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    Topics: Mathematics
    Notes: Abstract The finite motions of a suspended elastic cable subjected to a planar harmonic excitation can be studied accurately enough through a single ordinary-differential equation with quadratic and cubic nonlinearities. The possible onset of chaotic motion for the cable in the region between the one-half subharmonic resonance condition and the primary one is analysed via numerical simulations. Chaotic charts in the parameter space of the excitation are obtained and the transition from periodic to chaotic regimes is analysed in detail by using phase-plane portraits, Poincaré maps, frequency-power spectra, Lyapunov exponents and fractal dimensions as chaotic measures. Period-doubling, sudden changes and intermittency bifurcations are observed.
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    Nonlinear dynamics 6 (1994), S. 215-236 
    ISSN: 1573-269X
    Keywords: Bifurcations ; symmetry breaking ; chaos ; Lyapunov exponents
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    Topics: Mathematics
    Notes: Abstract In this paper we continue a numerical study of the dynamical behavior of a model of a suspended railway wheelset. We investigate the effect of speed and suspension and flange stiffnesses on the dynamics. Numerical bifurcation analysis is applied and one- and two-dimensional bifurcation diagrams are constructed. The onset of chaos as a function of speed, spring stiffness, and flange forces is investigated through the calculation of Lyapunov exponents with adiabatically varying parameters. The different transitions to chaos in the system are discussed and analyzed using symbolic dynamics. Finally, we discuss the change in orbit structure as stochastic perturbations are taken into account.
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    Nonlinear dynamics 6 (1994), S. 247-263 
    ISSN: 1573-269X
    Keywords: Stable and unstable limit cycles ; chaos
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    Topics: Mathematics
    Notes: Abstract Two alternative criteria for predicting the onset of chaos are presented. Both are based on the notion that it is the interaction between a stable and nearby unstable limit cycle pair in the phase space that disrupts the stable motion, thereby producing chaotic behavior. The first criterion is based upon an intersection of the unstable and stable limit cycle orbits in the phase plane. The second criterion proposes that an energy equivalence between the stable and unstable limitcycles may be responsible for the loss of periodicity of the stable motion. Both criteria are tested numerically using three distinct softening spring oscillators and their predictive capabilities are discussed. The results of this study, particularly for the energy criterion, are encouraging.
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    Nonlinear dynamics 7 (1995), S. 129-147 
    ISSN: 1573-269X
    Keywords: Nonlinear oscillations ; chaos ; escape ; predictive criteria
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    Topics: Mathematics
    Notes: Abstract The purpose of this paper is to provide a brief summary of the various analytical predictive criteria in order for “strange phenomena” to occur in a class of softening nonlinear oscillators, oscillators which may exhibit escape from a potential well. Implications of Melnikov's criteria are discussed first and transient chaos in the twin-well potential oscillator is illustrated. Three different heuristic criteria for steady state chaos or escape solution, proposes by F. Moon, G. Schmidt and W. Szemplińskia-Stupnicka, are then presented and compared to computer simulation results.
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    Nonlinear dynamics 7 (1995), S. 195-216 
    ISSN: 1573-269X
    Keywords: Energy transfer ; bifurcations ; chaos ; crises
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    Topics: Mathematics
    Notes: Abstract An investigation is presented into the transfer of energy from high- to low-frequency modes. The method of averaging is used to analyze the response of a two-degree-of-freedom system with widely spaced frequencies and cubic nonlinearities to a principal parametric resonance of the high-frequency mode. The conditions under which energy can be transferred from high- to low-frequency modes, as observed in the experiments, are determined. The interactions between the widely separated modes result in various bifurcations, the coexistence of multiple attractors, and chaotic attractors. The results show that damping may be destabilizing. The analytical results are validated by numerically solving the original system.
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    Nonlinear dynamics 15 (1998), S. 83-102 
    ISSN: 1573-269X
    Keywords: Bifurcation ; chaos ; Lyapunov exponents ; stable and unstable manifolds ; Latté's method ; convective flow
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    Topics: Mathematics
    Notes: Abstract The results of the study of the global behaviour of the convective flow of a binary mixture in a porous medium are presented. Bifurcation diagram, fixed points, periodic, chaotic solutions, stable and unstable manifolds, and basins of attraction have been calculated. Different behaviours (chaos, undecidable behaviour, etc.) have been found.
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    Nonlinear dynamics 15 (1998), S. 31-61 
    ISSN: 1573-269X
    Keywords: Beams ; internal resonance ; parametric resonance ; bifurcations ; chaos
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    Topics: Mathematics
    Notes: Abstract The nonlinear nonplanar response of cantilever inextensional metallic beams to a principal parametric excitation of two of its flexural modes, one in each plane, is investigated. The lowest torsional frequencies of the beams considered are much larger than the frequencies of the excited modes so that the torsional inertia can be neglected. Using this condition as well as the inextensionality condition, we develop a Lagrangian whose variation leads to two integro-partial-differential equations governing the motions of the beams. The method of time-averaged Lagrangian is used to derive four first-order nonlinear ordinary-differential equations governing the modulation of the amplitudes and phases of the two interacting modes. These modulation equations exhibit symmetry properties. A pseudo arclength scheme is used to trace the branches of the equilibrium solutions and an investigation of the eigenvalues of the Jacobian matrix is used to assess their stability. The equilibrium solutions experience pitchfork, saddle-node, Hopf, and codimension-2 bifurcations. A detailed bifurcation analysis of the dynamic solutions of the modulation equations is presented. Five branches of dynamic (periodic and chaotic) solutions were found. Two of these branches emerge from two Hopf bifurcations and the other three are isolated. The limit cycles undergo symmetry-breaking, cyclic-fold, and period-doubling bifurcations, whereas the chaotic attractors undergo attractor-merging and boundary crises.
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    Nonlinear dynamics 18 (1999), S. 89-103 
    ISSN: 1573-269X
    Keywords: higher order finite elements ; panel flutter ; nonlinear ; postbuckling ; chaos ; dynamic response
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Higher order elements were first design for linear problems where, in certain situations, they present advantages over the lower order elements. A method to efficiently extend their use to geometrical nonlinear problems as panel flutter and postbuckling behavior is presented. The chaotic and limit-cycle oscillations of an isotropic plate are obtained based on direct integration of the discretized equation of motion. The plate is modeled using the von Karman theory and the geometrical nonlinearities are separated in a nonlinear term of the first kind which manifests especially in the prebuckling and buckling regimes, and a nonlinear term of the second kind which is responsible for the postbuckling behavior. A fifth order, fully compatible element has been used to model thin plates while the inplane loads where introduced through a membrane element. The aerodynamics was modeled using the first order 'piston theory’. The method introduces the concept of a deteriorated form of the second geometric matrix which is equivalent to neglecting higher order terms in the strain energy of the plate. This allows for a drastic reduction in the computational effort with no observable loss of accuracy. Well established results in the literature are used to validate the method.
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    Nonlinear dynamics 16 (1998), S. 71-90 
    ISSN: 1573-269X
    Keywords: Oil film journal bearing-rotor system ; power spectrum ; chaos ; fractaldimension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The dynamics of flexible rotors associated with fluid film bearings have been studied since the 1950s. Most of the literature has assumed rigid, undamped bearing support with linear elastic restoring force. For a more precise description of fluid film bearing-rotor systems, a non-linearly supported model is proposed in this paper, where a linear damping force and a non-linear elastic restoring force are assumed. Numerical results show that due to non-linear factors, though the dynamic equations of the bearing center and the rotor center are coupled, the trajectory of the rotor center demonstrates steady-state symmetric motion even when the trajectory of the bearing center is in a state of disorder. Poincaré maps, bifurcation diagrams, and power spectra are used to analyze the behavior of the bearing center in the horizontal and vertical directions under different operating conditions. The fractal dimension concept is used to determine whether the system is in a state of chaotic motion. Numerical results find that the dimension of the bearing center trajectory is fractal and greater than two in some operating conditions, indicating that the system is in a state of chaotic motion. Chaotic behavior was found in an intermediate speed range, disappearing at higher speeds. It is suggested that this is a characteristic of all fluid film systems. It is suggested that a number of existing life-critical fluid film bearing systems are possibly being operated in this chaotic region and that such systems should be reevaluated in terms of this new observation.
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    Nonlinear dynamics 16 (1998), S. 127-151 
    ISSN: 1573-269X
    Keywords: Car-following models ; nonlinear systems ; delay-differential equations ; chaos
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    Topics: Mathematics
    Notes: Abstract In order to describe the dynamics of a group of road vehicles travelling in a single lane, car-following models attempt to mimic the interactions between individual vehicles where the behaviour of each vehicle is dependent upon the motion of the vehicle immediately ahead. In this paper we investigate a modified car-following model which features a new nonlinear term which attempts to adjust the inter-vehicle spacing to a certain desired value. In contrast to our earlier work, a desired time separation between vehicles is used rather than simply being a constant desired distance. In addition, we extend our previous work to include a non-zero driver vehicle reaction time, thus producing a more realistic mathematical model of congested road traffic. Numerical solution of the resulting coupled system of nonlinear delay differential equations is used to analyse the stability of the equilibrium solution to a periodic perturbation. For certain parameter values the post-transient response is a chaotic (non-periodic) oscillations consisting of a broad spectrum of frequency components. Such chaotic motion leads to highly complex dynamical behaviour which is inherently unpredictable. The model is analysed over a range of parameter values and, in each case, the nature of the response is indicated. In the case of a chaotic solution, the degree of chaos is estimated.
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    Nonlinear dynamics 19 (1999), S. 313-332 
    ISSN: 1573-269X
    Keywords: double pendulum system ; double Hopf bifurcation ; stability ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract A double pendulum system is studied for analyzing the dynamic behaviour near a critical point characterized by nonsemisimple 1:1 resonance. Based on normal form theory, it is shown that two phase-locked periodic solutions may bifurcate from an initial equilibrium, one of them is unstable and the other may be stable for certain values of parameters. A secondary bifurcation from the stable periodic solution yields a family of quasi-periodic solutions lying on a two-dimensional torus. Further cascading bifurcations from the quasi-periodic motions lead to two chaoses via a period-doubling route. It is shown that all the solutions and chaotic motions are obtained under positive damping.
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    Nonlinear dynamics 2 (1991), S. 157-170 
    ISSN: 1573-269X
    Keywords: Beams ; chaos ; nonlinear dynamics
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    Topics: Mathematics
    Notes: Abstract The purpose of this paper is to examine a highly nonlinear model of a slender beam which yields chaotic solutions for some forcing amplitudes. The study is unique in that the governing partial differential equations are solved directly, and that the model lends itself to a more physical analysis of the beam than traditional chaotic models. In addition, the analysis will provide proof that a beam experiencing moderate deformations without stops or an initial axial force can exhibit chaotic motion. The model represents a simply-supported. Euler-Bernoulli beam subjected to a transverse load. The forcing function is sinusoidally distributed in space with an amplitude which also varies sinusoidally in time and is assumed to reach a maximum sufficient to allow nonlinearities associated with finite deformations to become important. During motion, even though displacements are large, the beam is assumed to attain only small strain levels and thus is assumed to be linearly elastic. The results indicate that for most levels of the forcing function the response of the beam is periodic. However, the steady state motion is not sinusoidal in time and in fact exhibits some bifurcated motions. At a certain level of the forcing amplitude, an asymmetry is observed and the periodicity of the motion breaks down as the beam experiences a period doubling cascade which culminates in a chaotic motion. The progression from periodic to chaotic motion is presented through a series of phase plane and Poincané plots, and physical variables such as bending moment are examined.
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    Nonlinear dynamics 20 (1999), S. 319-359 
    ISSN: 1573-269X
    Keywords: Melnikov method ; bifurcation ; chaos ; weak coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract We study periodic and homoclinic motions in periodically forced, weakly coupled oscillators with a form of perturbations of two independent planar Hamiltonian systems. First, we extend the subharmonic Melnikov method, and give existence, stability and bifurcation theorems for periodic orbits. Second, we directly apply or modify a version of the homoclinic Melnikov method for orbits homoclinic to two types of periodic orbits. The first type of periodic orbit results from persistence of the unperturbed hyperbolic periodic orbit, and the second type is born out of resonances in the unperturbed invariant manifolds. So we see that some different types of homoclinic motions occur. The relationship between the subharmonic and homoclinic Melnikov theories is also discussed. We apply these theories to the weakly coupled Duffing oscillators.
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    Nonlinear dynamics 2 (1991), S. 137-156 
    ISSN: 1573-269X
    Keywords: Autoparametric resonance ; composite beams ; chordwise excitations ; chaos
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    Topics: Mathematics
    Notes: Abstract Three nonlinear integro-differential equations of motion derived in Part I are used to investigate the forced nonlinear vibration of a symmetrically laminated graphite-epoxy composite beam. The analysis focuses on the case of primary resonance of the first in-plane flexural (chordwise) mode when its frequency is approximately twice the frequency of the first out-of-plane flexural-torsional (flapwise-torsional) mode. A combination of the fundamental-matrix method and the method of multiple scales is used to derive four first-order ordinary-differential equations describing the modulation of the amplitudes and phases of the interacting modes with damping, nonlinearity, and resonances. The eigenvalues of the Jacobian matrix of the modulation equations are used to determine the stability of their constant solutions, and Floquet theory is used to determine the stability and bifurcations of their limit-cycle solutions. Hopf bifurcations, symmetry-breaking bifurcations, period-multiplying sequences, and chaotic motions of the modulation equations are studied. The results show that the motion can be nonplanar although the input force is planar. Nonplanar responses may be periodic, periodically modulated, or chaotically modulated motions.
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    Nonlinear dynamics 4 (1993), S. 389-408 
    ISSN: 1573-269X
    Keywords: Plate ; bifurcation ; chaos ; homoclinic orbit
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    Topics: Mathematics
    Notes: Abstract In this paper we investigate global bifurcations in the motion of parametrically excited, damped thin plates. Using new mathematical results by Kovačič and Wiggins in finding homoclinic and heteroclinic orbits to fixed points that are created in a resonance resulting from perturbation, we are able to obtain explicit conditions under which Silnikov homoclinic orbits occur. Furthermore, we confirm our theoretical predictions by numerical simulations.
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    Nonlinear dynamics 3 (1992), S. 385-410 
    ISSN: 1573-269X
    Keywords: Autoparametric resonance ; torus ; chaos ; Hopf bifurcation
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    Topics: Mathematics
    Notes: Abstract An investigation is presented of the response of a three-degree-of-freedom system with quadratic nonlinearities and the autoparametric resonances ω3≈2ω2 and ω2≈2ω1 to a harmonic excitation of the third mode, where the ω m are the linear natural frequencies of the system. The method of multiple scales is used to determine six first-order nonlinear ordinary differential equations that govern the time variation of the amplitudes and phases of the interacting modes. The fixed points of these equations are obtained and their stability is determined. For certain parameter values, the fixed points are found to lose stability due to Hopf bifurcations and consequently the system exhibits amplitude-and phase-modulated motions. Regions where the amplitudes and phases display periodic, quasiperiodic, and chaotic time variations and hence regions where the overall system motion is periodically, quasiperiodically, and chaotically modulated are determined. Using various numerical simulations, we investigated nonperiodic solutions of the modulation equations using the amplitudeF of the excitation as a control parameter. As the excitation amplitudeF is increased, the fixed points of the modulation equations exhibit an instability due to a Hopf bifurcation, leading to limit-cycle solutions of the modulation equations. AsF is increased further, the limit cycle undergoes a period-doubling bifurcation followed by a secondary Hopf bifurcation, resulting in either a two-period quasiperiodic or a phase-locked solution. AsF is increased further, there is a torus breakdown and the solution of the modulation equations becomes chaotic, resulting in a chaotically modulated motion of the system.
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    Nonlinear dynamics 4 (1993), S. 153-181 
    ISSN: 1573-269X
    Keywords: Dynamics ; rotors ; stability ; chaos
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    Topics: Mathematics
    Notes: Abstract Nonlinear rotors are often considered as potential sources of chaotic vibrations. The aim of the present paper is that of studying in detail the behaviour of a nonlinear isotropic Jeffcott rotor, representing the simplest nonlinear rotor. The restoring and damping forces have been expanded in Taylor series obtaining a ‘Duffing-type’ equation. The isotropic nature of the system allows circular whirling to be a solution at all rotational speeds. However there are ranges of rotational speed in which this solution is unstable and other, more complicated, solutions exist. The conditions for stability of circular whirling are first studied from closed form solutions of the mathematical model and then the conditions for the existence of solutions of other type are studied by numerical experimentation. Although attractors of the limit cycle type are often found, chaotic attractors were identified only in few very particular cases. An attractor supposedly of the last type reported in the literature was found, after a detailed analysis, to be related to a nonchaotic polyharmonic solution. As the typical unbalance response of isotropic nonlinear rotors has been shown to be a synchronous circular whirling motion, the convergence characteristics of Newton-Raphson algorithm applied to the solution of the set of nonlinear algebraic equations obtained from the differential equations of motion are studied in some detail. c damping coefficient i imaginaty unit (i=% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbqfgBHr% xAU9gimLMBVrxEWvgarmWu51MyVXgaruWqVvNCPvMCG4uz3bqefqvA% Tv2CG4uz3bIuV1wyUbqee0evGueE0jxyaibaieYlf9irVeeu0dXdh9% vqqj-hEeeu0xXdbba9frFf0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea% 0dXdar-Jb9hs0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabe% aadaabauaaaOqaamaakaaabaGaeyOeI0IaaGymaaWcbeaaaaa!3E66!\[\sqrt { - 1}\]) k stiffness m mass t time x istate variables i=1, 4 z complex co-ordinate (z=x+iy) [J] Jacobian matrix Oxyz inertial co-ordinate frame Oξηz rotating co-ordinate frame δ perturbation term ε eccentricity ζ complex co-ordinate (ζ=ξ+iη) λ system eigenvalues μ nonlinearity parameter τ nondimensional time ϕ phase ω spin speed u nonrotating t rotating 0 amplitude t nondimensional terms
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    Nonlinear dynamics 8 (1995), S. 85-109 
    ISSN: 1573-269X
    Keywords: Resonance ; global bifurcations ; homoclinic orbits ; Melnikov ; Silnikov ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this study we examine the global dynamics associated with a generic two-degree-of-freedom (2-DOF), coupled nonlinear system that is externally excited. The method of averaging is used to obtain the second order approximation of the response of the system in the presence of one-one internal resonance and subharmonic external resonance. This system can describe a variety of physical phenomena such as the motion of an initially deflected shallow arch, pitching vibrations in a nonlinear vibration absorber, nonlinear response of suspended cables etc. Using a perturbation method developed by Kovačič and Wiggins (1992), we show the existence of Silnikov type homoclinic orbits which may lead to chaotic behavior in this system. Here two different cases are examined and conditions are obtained for the existence of Silnikov type chaos.
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    Nonlinear dynamics 6 (1994), S. 87-99 
    ISSN: 1573-269X
    Keywords: Discontinuous systems ; chaos ; basins of attraction ; cell mapping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The Cell Mapping method is a robust tool for investigating nonlinear dynamic systems. It is capable of finding the attractors and corresponding basins of attraction of a system under investigation. To investigate the applicability of the Cell Mapping method to discontinuous systems, a “forced zero-stiffness impact oscillator” is chosen as an application. The numerical integration algorithm, the basic element in the Cell Mapping method, is adjusted to overcome the discontinuity. Four types of Cell Mapping techniques are applied: Simple Cell Mapping, Generalized Cell Mapping, Interpolated Cell Mapping, and Mixed Cell Mapping. The last type is a new modification to existing types. Each type of Cell Mapping is briefly explained. The results are compared to the exact solutions. The Interpolated Cell Mapping and Mixed Cell Mapping methods are found to produce the most accurate results for this case.
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    Nonlinear dynamics 14 (1997), S. 57-87 
    ISSN: 1573-269X
    Keywords: Rotor dynamics ; rigid rotors ; chaos ; conical whirl ; journal bearings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The dynamic behaviour of a rigid rotor supported on plain journal bearings was studied, focusing particular attention on its nonlinear aspects. Under the hypothesis that the motion of the rotor mass center is plane, the rotor has five Lagrangian co-ordinates which are represented by the co-ordinates of the mass center and the three angular co-ordinates needed to express the rotor's rotation with respect to its center of mass. In such conditions, the system is characterised not only by the nonlinearity of the bearings but also by the nonlinearity due to the trigonometric functions of the three assigned angular co-ordinates. However, if two angular co-ordinates have values that are generally quite small because of the small radial clearances in the bearings, the system is de facto linear in these angular co-ordinates. Moreover, if the third angular co-ordinate is assumed to be cyclic [18], the number of degrees of freedom in the system is reduced to four and nonlinearity depends solely on the presence of the journal bearings, whose reactions were predicted with the π-film, short bearing model. After writing the equations of motion in this way and determining a numerical routine for a Runge–Kutta integration the most significant aspects of the dynamics of a symmetrical rotor were studied, in the presence of either pure static or pure couple unbalance and also when both types of unbalance were present. Two categories of rotors, whose motion is prevailingly a cylindrical whirl or a conical whirl, were put under investigation.
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    ISSN: 1573-269X
    Keywords: Unbalanced shaft ; nonlinear vibrations ; limited power supply ; chaos
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    Notes: Abstract Rotation of an elastically mounted unbalanced shaft may be in general affected by its lateral vibration, due to a “vibrational torque”. This interaction is nonlinear, and can be neglected only in case of an unlimited power supply. Whenever the available power of the drive is comparable with power consumption due to vibration, various nonlinear phenomena may be observed, the most well-known of these being the so called Sommerfeld effect – slowing down or complete capture of the shaft at resonance. The corresponding steady-state motions and their stability can be studied by asymptotic methods, as applied to the governing nonlinear set of two second-order equations. However, study of transient motions in general requires numerical solution. This numerical solution is obtained here, and extensive parametric studies are performed of the Sommerfeld effect. In particular, the influence is evaluated of damping ratio and slope of the torque-speed curve of the drive on a passage/capture threshold. The results of numerical simulation, as well as experiments with a physical model, also demonstrate the effect of smooth passage through resonance with a limited power supply, based on using a “switch” of suspension stiffness from a certain artificially increased value to the design one. A brief description is presented also of time-variant components of the resonant amplitude and rotational frequency responses in the case of capture, as observed both in numerical simulation studies and in experiments. Whilst these components are small compared with the corresponding constant ones, i.e. steady-state vibration amplitude and rotational frequency, the above observations indicate the possibility for periodic or chaotic nonstationarity in the system's response.
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    Nonlinear dynamics 13 (1997), S. 117-129 
    ISSN: 1573-269X
    Keywords: Period-doubling bifurcations ; chaos ; quasiperiodicity ; railway dynamics
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    Topics: Mathematics
    Notes: Abstract Cooperrider's mathematical model of a railway bogie running on a straight track has been thoroughly investigated due to its interesting nonlinear dynamics (see True [1] for a survey). In this article a detailed numerical investigation is made of the dynamics in a speed range, where many solutions exist, but only a couple of which are stable. One of them is a chaotic attractor. Cooperrider's bogie model is described in Section 2, and in Section 3 we explain the method of numerical investigation. In Section 4 the results are shown. The main result is that the chaotic attractor is created through a period-doubling cascade of the secondary period in an asymptotically stable quasiperiodic oscillation at decreasing speed. Several quasiperiodic windows were found in the chaotic motion. This route to chaos was first described by Franceschini [9], who discovered it in a seven-mode truncation of the plane incompressible Navier–Stokes equations. The problem investigated by Franceschini is a smooth dynamical system in contrast to the dynamics of the Cooperrider truck model. The forcing in the Cooperrider model includes a component, which has the form of a very stiff linear spring with a dead band simulating an elastic impact. The dynamics of the Cooperrider truck is therefore “non-smooth”. The quasiperiodic oscillation is created in a supercritical Neimark bifurcation at higher speeds from an asymmetric unstable periodic oscillation, which gains stability in the bifurcation. The bifurcating quasiperiodic solution is initially unstable, but it gains stability in a saddle-node bifurcation when the branch turns back toward lower speeds. The chaotic attractor disappears abruptly in what is conjectured to be a blue sky catastrophe, when the speed decreases further.
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    Nonlinear dynamics 17 (1998), S. 119-139 
    ISSN: 1573-269X
    Keywords: Phase-locking ; bifurcations ; chaos ; electronic circuits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The dynamic alterations of an electronic circuit in a chaotic regime, described by the Double Scroll attractor, subjected to sinusoidal perturbation are numerically investigated. Parameter diagrams of the circuit phase-locking oscillations in terms of the driving amplitude and frequency are computed. These diagrams have highly interleaved and complex structures, part of them Cantor-like fractals. However, a Cantor-like fractal structure is also observed. In addition, the power spectrum analysis is used to find and characterize three ways of phase-locking the Double Scroll circuit, and to determine how this process depends on the driving parameters. Furthermore, the dynamics of bifurcation phenomena, as chaotic attractor entrainment, Arnold's tongues, coexistence of attractors, and hysteresis are identified in the parameter space.
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    ISSN: 1573-269X
    Keywords: Aeroelasticity ; nonlinear vibration ; panel flutter ; bifurcation ; attractor ; chaos ; attraction basin
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    Topics: Mathematics
    Notes: Abstract The behavior of a nonlinear, non-Hamiltonian system in the postcritical (flutter) domain is studied with special attention to the influence of initial conditions on the properties of attractors situated at a certain point of the control parameter space. As a prototype system, an elastic panel is considered that is subjected to a combination of supersonic gas flow and quasistatic loading in the middle surface. A two natural modes approximation, resulting in a four-dimensional phase space and several control parameters is considered in detail. For two fixed points in the control parameter space, several plane sections of the four-dimensional space of initial conditions are presented and the asymptotic behavior of the final stationary responses are identified. Amongst the latter there are stable periodic orbits, both symmetric and asymmetric with respect to the origin, as well as chaotic attractors. The mosaic structure of the attraction basins is observed. In particular, it is shown that even for neighboring initial conditions can result in distinctly different nonstationary responses asymptotically approach quite different types of attractors. A number of closely neighboring periodic attractors are observed, separated by Hopf bifurcations. Periodic attractors also are observed under special initial conditions in the domains where chaotic behavior is usually expected.
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    Nonlinear dynamics 14 (1997), S. 157-189 
    ISSN: 1573-269X
    Keywords: Rotor dynamics ; rigid rotors ; chaos ; conical whirl ; journal bearings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In the first part of the present investigation [9], the dynamic behaviour of a rigid rotor supported on plain journal bearings was studied, focusing particular attention on its nonlinear aspects. In the present paper an experimental confirmation of the theoretical results is sought. The steel rotor of the experimental rig was given a constant circular cross section in order to fix in an easy way the two distances between supports corresponding, respectively, to the values of the λ parameter assigned in [9]. Two steel rings, each one with a series of holes and a clamping screw, were mounted onto the rotor with a small clearance. This arrangement made it possible to fix the positions of the rings and their holes respect to the rotor, so as to realize a pre-estabilished unbalance. The two bronze journal bearings were characterised by a relatively low length/diameter ratio, and a relatively high value of the radial clearance and were lubricated with oil delivered from a thermostatic tank. In this way, despite the relative lightness of the rotor, the dimensionless static eccentricity εs was given the high values that were apt to realize the operating conditions assumed in the theoretical analysis. The rotor was driven by means of a d.c. motor connected to a toothed belt-drive. Varying the rotor speed in the range 1000 ÷ 10000 r.p.m., made it possible to assign the values of the modified Sommerfeld number assumed in the theoretical analysis. Three pairs of eddy-current probes were mounted in order to detect the trajectories of three points (C1, C and C2) suitably fixed along the rotor axis. These orbits were finally put in comparison with the corresponding ones previously obtained through numerical analysis. The comparison pointed out that the experimental data were in good agreement with the theoretical predictions, despite the approximations that characterise the theoretical model and the unavoidable errors affecting measures in the course of the experimental test.
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    Nonlinear dynamics 19 (1999), S. 359-385 
    ISSN: 1573-269X
    Keywords: rotor dynamics ; chaos ; conical whirl ; restoring forces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In a previous paper, the dynamic behaviour of a Jeffcott rotor was studied in the presence of pure static unbalance and nonlinear elastic restoring forces. The present paper extends the analysis to a rigid rotor with an axial length such as to make the transverse moment of inertia greater than the axial one. As in the previous investigation, the elastic restoring forces are assumed to be nonlinear and the effects of couple unbalance are also included but, unlike the Jeffcott rotor, the system exhibits six degrees-of-freedom. The Lagrangian coordinates were fixed so as to coincide with the three coordinates of the centre of mass of the rotor and the three angular coordinates needed in order to express the rotor's rotations with respect to a reference frame having its origin in the centre of mass. The precession motions of such a rotor turn out to be cylindrical at low angular speeds and exhibit a conical aspect when operating at higher speeds. The motion equations of the rotor were written with reference to a system that was subsequently adopted for the experimental analysis. The particular feature of this system was the use of a steel wire (piano wire) for the rotor shaft, suitably constrained and with the possibility of regulating the tension of the wire itself, in order to increase or reduce the nonlinear character of the system. The numerical analysis performed with integration of the motion equations made it possible to point out that chaotic solutions were manifested only when the tension in the wire was given the lowest values – i.e. when the system was strongly nonlinear – in the presence of considerable damping and rotor unbalance values that were so high as to lose any practical significance. Under conditions commonly shared by analogous real systems characterised by poor damping, where the contribution to nonlinearity is almost entirely due to elastic restoring forces, the analysis pointed out that precession motions may be manifested with a periodic character, whether synchronous or not, or a quasi-periodic character, but in no case is the solution chaotic.
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    Nonlinear dynamics 3 (1992), S. 225-243 
    ISSN: 1573-269X
    Keywords: Nonlinear oscillations ; chaos ; escape ; perturbation methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract The paper is devoted to the study of common features in regular and strange behavior of the three classic dissipative softening type driven oscillators: (a) twin-well potential system, (b) single-well potential unsymmetric system and (c) single-well potential symmetric system. Computer simulations are followed by analytical approximations. It is shown that the mathematical techniques and physical concepts related to the theory of nonlinear oscillations are very useful in predicting bifurcations from regular, periodic responses to cross-well chaotic motions or to escape phenomena. The approximate analysis of periodic, resonant solutions and of period doubling or symmetry breaking instabilities in the Hill's type variational equation provides us with closed-form algebraic simple formulae; that is, the relationship between critical system parameter values, for which strange phenomena can be expected.
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    Nonlinear dynamics 4 (1993), S. 655-670 
    ISSN: 1573-269X
    Keywords: Fluidelasticity ; stability ; nonlinear ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper, the planar dynamics of a nonlinearly constrained pipe conveying fluid is examined numerically, by considering the full nonlinear equation of motions and a refined trilinear-spring model for the impact constraints—completing the circle of several studies on the subject. The effect of varying system parameters is investigated for the two-degree-of-freedom (N=2) model of the system, followed by less extensive similar investigations forN=3 and 4. Phase portraits, bifurcation diagrams, power spectra and Lyapunov exponents are presented for a selected set of system parameters, showing some rather interesting, and sometimes unexpected, results. The numerical results are compared with experimental ones obtained previously. It is found that in the parameter space that includesN, there exists a subspace wherein excellent qualitative, and reasonably good (N=2) to excellent (N=4) quantitative agreement with experiment. In the latter case, excellent agreement is not only obtained in the threshold flow velocities (u) for the key bifurcations, but the inclusion of the nonlinear terms improves agreement with experiment in terms of amplitudes of motion and by capturing features of behaviour not hitherto predicted by theory.
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  • 79
    Electronic Resource
    Electronic Resource
    Springer
    Nonlinear dynamics 4 (1993), S. 25-37 
    ISSN: 1573-269X
    Keywords: Bifurcations ; chaos ; Coulomb friction ; universality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In some parameter ranges, the dynamics of a forced oscillator with Coulomb friction dependent on both displacement and velocity is reducible to the dynamics of a one-dimensional map. In numerical simulations, period-doubling bifurcations are observed for the oscillator. In this bifurcation procedure, the map arising from the Coulomb model may not have ‘standard’ form. The bifurcation sequence of the Coulomb model is compared to that of the standard one-dimensional maps to see if it exhibits ‘universal’ behavior. All observed components of the bifurcation sequence fit the universal sequence, although some universal events are not witnessed.
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  • 80
    ISSN: 1573-269X
    Keywords: Numerical and geometrical techniques ; local and global bifurcations ; chaos
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract An asymmetric nonlinear oscillator representative of the finite forced dynamics of a structural system with initial curvature is used as a model system to show how the combined use of numerical and geometrical analysis allows deep insight into bifurcation phenomena and chaotic behaviour in the light of the system global dynamics. Numerical techniques are used to calculate fixed points of the response and bifurcation diagrams, to identify chaotic attractors, and to obtain basins of attraction of coexisting solutions. Geometrical analysis in control-phase portraits of the invariant manifolds of the direct and inverse saddles corresponding to unstable periodic motions is performed systematically in order to understand the global attractor structure and the attractor and basin bifurcations.
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