Existence and stability of limit cycles in a delayed dry-friction oscillator

Periodic, chaotic, chattering, and bifurcation behavior are fundamental consequences of the nonsmooth nature of systems with dry friction. This work is concerned with the analysis of a single degree of freedom system which is additionally damped by a delayed dry friction device. We get a complete set of closed-form expressions to describe the dynamics of the delay-induced phenomena exhibited by the system. The conditions to determine the existence and stability of limit cycles are clearly defined. This analysis is addressed in the context of both classic stability theory for nonlinear systems and the qualitative theory of Piecewise Smooth Dynamical Systems. Through exhaustive numerical simulations the effectiveness of the set of closed-form expressions is confirmed. Excellent agreement was found between the numerical and analytical results.     

Non-linear behavior in a discretely forced oscillator

The simulated and experimental responses of a rigid-arm pendulum driven by an external impactor are considered. Here, impact occurs if the trajectory of a rotating impactor intersects that of the pendulum. Using the rotation rate of the impactor as the control parameter, experimental trials have demonstrated much of the dynamic behavior predicted by numerical simulations. The system exhibits chatter (i.e., multiple impacts within a single forcing period), sticking (i.e., contact between the pendulum and the impactor for non-negligible amounts of time), high-order periodicity, and behavior suggestive of chaos. A new convention for classifying periodic motions as well as insights regarding the nature of the coefficient of restitution (COR) in an experimental impacting system are also presented.     

Bifurcations in a forced softening duffing oscillator

The response of a damped Duffing oscillator of the softening type to a harmonic excitation is analyzed in a two-parameter space consisting of the frequency and amplitude of the excitation. An approximate procedure is developed for the generation of the bifurcation diagram in the parameter space of interest. It is a combination of second-order perturbation solutions of the system in the neighborhood of its non-linear resonances and Floquet analysis. The results show that the proposed scheme is capable of predicting symmetry-breaking and period-doubling bifurcations as well as Jumps to either bounded or unbounded motions. The results obtained are validated using analogand digital-computer simulations, which show chaos and unbounded motions, among other behaviors.     

Bifurcation and chaos in discrete-time BVP oscillator

In this paper, we investigate the discrete-time Bohöffer-Van der Pol (BVP) oscillator obtained by Euler method. We provide the sufficient conditions of existence, asymptotic stability of the fixed points, then give theoretical analysis for local bifurcations of the fixed points, and derive the conditions under which the local bifurcations such as pitchfork, saddle-node, flip and Hopf occur at the fixed points. Furthermore, we prove that the fixed point eventually evolves into a snap-back repeller which generates chaotic behavior in the sense of Marotto's chaos when certain conditions are satisfied. Finally, several numerical simulations are provided to demonstrate the theoretical results of the previous and to show the new complex dynamical behaviors of the system.     

Periodically forced delay limit cycle oscillator

This paper investigates the dynamics of a delay limit cycle oscillator under periodic external forcing. The system exhibits quasiperiodic motion outside of a resonance region where it has periodic motion at the frequency of the forcer for strong enough forcing. By perturbation methods and bifurcation theory, we show that this resonance region is asymmetric in the frequency detuning, and that there are regions where stable periodic and quasiperiodic motions coexist.     

Experimental demonstration of 1.5 GHz chaos generation using an improved Colpitts oscillator

Experimental study of the ultrahigh-frequency chaotic dynamics generated in an improved Colpitts oscillator is performed. Reliable and reproducible chaos can be generated at the fundamental frequency up to 1.5 GHz using the microwave BFG520 type transistors with the threshold frequency of 9 GHz. By the tuning of the supply voltages, we observe complex nonlinear dynamics like period-one oscillation, period-two oscillation, multiple-period oscillation, and chaotic oscillation. Typical time series, autocorrelation, and broadband continuous power spectrum are presented. Furthermore, compared with the corresponding classical Colpitts oscillator, the main advantage of the improved circuit is in the fact that by operating in a chaotic mode it exhibits higher fundamental frequencies and a lower peak side-lobe level.     

The refined approximate criterion for chaos in a two-state mechanical oscillator

Summary In the two-state mechanical oscillator, a mathematical model of a buckled beam, the refined criterion for the system parameter critical values where chaotic motion can be expected is derived. The derivation is based on the assumption of the second approximate solution for the small orbit. It is shown that a simple approximate analysis of the Hill's type variational equation gives the sought stability loss of the resonant solution as the period doubling bifurcation. The stability limits of the resonant and non-resonant solutions are proposed as the boundary of the region where strange phenomena can appear and the refined criterion thus derived is compared to computer simulation results and to other approximate criteria.

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Verfeinertes Kriterium für chaotische Bewegung in einem Schwingungssystem mit zwei stabilen Gleichgewichtslagen

Übersicht Für ein mechanisches Schwingungssystem mit zwei stabilen Gleichgewichtslagen, das ein mathematisches Modell eines Knickstabes darstellt, wird ein verfeinertes Kriterium für die kritischen Systemparameterwerte, bei denen chaotische Bewegung zu erwarten ist, hergeleitet. Die Herleitung geht von der Näherungslösung zweiter Ordnung für kleine Bahnen um das Gleichgewicht aus. Es wird gezeigt, daß eine einfache Näherungsbehandlung der Variationsgleichung vom Hill-Typ den gesuchten Stabilitätsverlust der Resonanzlösung als Verzweigung der Periodenverdopplung liefert. Die Stabilitätsgrenzen der resonanten und nichtresonanten Lösungen werden als Bereichsgrenze, wo chaotische Bewegungen auftreten können, vorgeschlagen. Das derart hergeleitete verfeinerte Kriterium wird mit Computer-Simulationen und anderen Näherungskriterien verglichen.

     

Analytical period-3 motions to chaos in a hardening Duffing oscillator

In this paper, bifurcation trees of period-3 motions to chaos in the periodically forced, hardening Duffing oscillator are investigated analytically. Analytical solutions for period-3 and period-6 motions are used for the bifurcation trees of period-3 motions to chaos. Such bifurcation trees are based on the Hopf bifurcations of asymmetric period-3 motions. In addition, an independent symmetric period-3 motion without imbedding in chaos is discovered, and such a symmetric period-3 motion possesses saddle-node bifurcations only. The switching of symmetric to asymmetric period-3 motions is completed through saddle-node bifurcations, and the onset of asymmetric period-6 motions occurs at the Hopf bifurcations of asymmetric period-3 motions. Continuously, the onset of period-12 motions is at the Hopf bifurcation of asymmetric period-6 motions. With such bifurcation trees, the chaotic motions relative to asymmetric period-3 motions can be determined analytically. This investigation provides a systematic way to study analytical dynamics of chaos relative to period-m motions in nonlinear dynamical systems.     

Suppressing homoclinic chaos for a weak periodically excited non-smooth oscillator

Nonlinear Dynamics - We follow our interest in a nonautonomous (2+1)-dimensional coupled nonlinear Schrödinger equation with partially nonlocal nonlinear effect and a linear potential, and get...     

Analytic evaluation of periodic responses of a forced nonlinear oscillator

The periodic responses of a strongly nonlinear, single-degree-of-freedom forced oscillator with weak excitation and damping are examined. The presented methodology is based on a regular perturbation expansion, whose first term is the solution of the unforced, and undamped nonlinear problem. Higher order approximations are computed by explicitly solving linear differential equations possessing a periodically varying coefficient. The general theory is used for studying the periodic steady state motions of the periodically forced system. Moreover, it is shown that the presented analysis can be used to analytically study the orbital stability of the identified steady state motions. The proposed method can also be used for studying periodic responses due to nonperiodic transient forces, provided that these responses are close to the O(1) periodic generating solution.     

General perturbational solution of a harmonically forced non-linear oscillator equation

An extension of a general perturbational method in the theory of harmonically forced non-linear oscillations has been presented, in which the interplay of two system parameters appears. The method clearly exhibits the entrainment of subharmonic, super-harmonic and other harmonic responses for various interplays of the system parameters.The mathematical insufficiency of the method to predict the behavior of the system in a limiting case of parameter interplay, which is usually attributed to the perturbational method in the Poincaré sense, has been recognized and the method for its removal suggested.     

Stochastic modeling of tire–snow interaction using a polynomial chaos approach

Developing accurate models to simulate the interaction between pneumatic tires and unprepared terrain is a demanding task. Such tire–terrain contact models are often used to analyze the mobility of a wheeled vehicle on a given type of soil, or to predict the vehicle performance under specified operational conditions (as related to the vehicle and tires, as well as to the running support). Due to the complex nature of the interaction between a tire and off-road environment, one usually needs to make simplifying assumptions when modeling such an interaction. It is often assumed that the tire–terrain interaction can be captured using a deterministic approach, which means that one assumes fixed values for several vehicle or tire parameters, and expects exact responses from the system. While this is rarely the case in real life, it is nevertheless a necessary step in the modeling process of a deterministic framework. In reality, the external excitations affecting the system, as well as the values of the vehicle and terrain parameters, do not have fixed values, but vary in time or space. Thus, although a deterministic model may capture the response of the system given one set of deterministic values for the system parameters, inputs, etc., this is in fact only one possible realization of the multitude of responses that could occur in reality. The goal of our study is to develop a mathematically sound methodology to improve the prediction of the tire–snow interaction by considering the variability of snow depth and snow density, which will lead to a significantly better understanding and a more realistic representation of tire–snow interaction. We constructed stochastic snow models using a polynomial chaos approach developed at Virginia Tech, to account for the variability of snow depth and of snow density. The stochastic tire–snow models developed are based on the extension of two representative deterministic tire–snow interaction models developed at the University of Alaska, including the pressure–stress deterministic model and the hybrid (on-road extended for off-road) deterministic model. Case studies of a select combination of uncertainties were conducted to quantify the uncertainties of the interfacial forces, sinkage, entry angle, and the friction ellipses as a function of wheel load, longitudinal slip, and slip angle. The simulation results of the stochastic pressure–stress model and the stochastic hybrid model are compared and analyzed to identify the most convenient tire design stage for which they are more suitable. The computational efficiency of the two models is also discussed.     

Multistability in a three-dimensional oscillator: tori,resonant cycles and chaos

The emergence of multistability in a simple three-dimensional autonomous oscillator is investigated using numerical simulations, calculations of Lyapunov exponents and bifurcation analysis over a broad area of two-dimensional plane of control parameters. Using Neimark–Sacker bifurcation of 1:1 limit cycle as the starting regime, many parameter islands with the coexisting attractors were detected in the phase diagram, including the coexistence of torus, resonant limit cycles and chaos; and transitions between the regimes were considered in detail. The overlapping between resonant limit cycles of different winding numbers, torus and chaos forms the multistability.     

Control of vibroimpact dynamics of a single-sided Hertzian contact forced oscillator

The control of vibroimpact dynamics of a single-sided Hertzian contact forced oscillator is investigated analytically and numerically in this paper. The control strategy is introduced via a fast excitation and attention is focused on the response near the primary resonance. The fast excitation is added to the basic harmonic force, either through a harmonic force applied from above, or via a harmonic base displacement added from bellow, or by considering the stiffness of the oscillator as a periodically and rapidly varying in time. The results reveal that the threshold of vibroimpact response initiated by jump phenomenon near the primary resonance can be shifted toward lower or higher frequencies of the slow dynamic system depending on the fast excitation taken into consideration. It was also shown that the most realistic and practical way for controlling the vibroimpact dynamics is the introduction of a fast harmonic base displacement.     

Nonstationary effects on safe basins of a forced softening Duffing oscillator

The safe basin of a forced softening Duffing oscillator is studied numerically. The changes of safe basins are observed under both stationary and nonstationary variations of the external excitation frequency. The kind of nonstationary variations of the excitation frequency can greatly change the erosion rate and the shape of the safe basin. The other effects of nonstationary variations on the safe basin are also discussed. Supported by the National Natural Science Foundation, the Aviation Science Foundation and the Doctoral Training Foundation of China.     

Fractional damping enhances chaos in the nonlinear Helmholtz oscillator

Nonlinear Dynamics - The main purpose of this paper is to study both the underdamped and the overdamped dynamics of the nonlinear Helmholtz oscillator with a fractional-order damping. For that...     

Bifurcation trees of period-3 motions to chaos in a time-delayed Duffing oscillator

Nonlinear Dynamics - In this paper, bifurcation trees of period-3 motions to chaos in a periodically forced, time-delayed, hardening Duffing oscillator are investigated by a semi-analytical method....     

Analytical solutions for asymmetric periodic motions to chaos in a hardening Duffing oscillator

In this paper, the analytical dynamics of asymmetric periodic motions in the periodically forced, hardening Duffing oscillator is investigated via the generalized harmonic balance method. For the hardening Duffing oscillator, the symmetric periodic motions were extensively investigated with the aim of a good understanding of solutions with jumping phenomena. However, the asymmetric periodic motions for the hardening Duffing oscillators have not been obtained yet, and such asymmetric periodic motions are very important to find routes of periodic motions to chaos in the hardening Duffing oscillator analytically. Thus, the bifurcation trees from asymmetric period-1 motions to chaos are presented. The corresponding unstable periodic motions in the hardening Duffing oscillator are presented, and numerical illustrations of stable and unstable periodic motions are carried out as well. This investigation provides a comprehensive understanding of chaos mechanism in the hardening Duffing oscillator.