Coherence and chaos in the driven,damped sine-Gordon chain

Representative example of preliminary numerical results are presented for solutions of the deterministic sine-Gordon equation under the influence of damping and a sinusoidal uniform driving force. Depending on the choice of (inhomogeneous) initial conditions and values of the amplitude and frequency of the driving force, we find a great variety of possible responses, including: (i) permanent spatial structures riding on an overall background motion which can be temporally chaotic or not, (ii) intermittent transitions between at least two metastable spatial structures which are typically a localized breather-like structure and an extended wave train, in the presence of temporal chaos or not and with large- or small-amplitude background motion. For some parameter values, we find very similar power spectra for different initial conditions, while other cases show considerable dependence on initial conditions. Both the spatial and temporal behavior of the response can exhibit extreme sensitivity to small changes in the parameters.     

Transition to chaos in a driven pendulum with nonlinear dissipation

The Melnikov-Holmes method is used to study the onset of chaos in a driven pendulum with nonlinear dissipation. Detailed numerical studies reveal many interesting features like a chaotic attractor at low frequencies, band formation near escape from the potential well and a sequence of subharmonic bifurcations inside the band that accumulates at the homoclinic bifurcation point.     

Coherence and chaos in the driven damped sine-gordon equation: Measurement of the soliton spectrum

A numerical procedure is developed which measures the sine-Gordon soliton and radiation content of any field (φ, φ_t) which is periodic in space. The procedure is applied to the field generated by a damped, driven sine-Gordon equation. This field can be either temporally periodic (locked to the driver) or chaotic. In either case the numerical measurement shows that the spatial structure can be described by only a few spatially localized (soliton wave-train) modes. The numerical procedure quantitatively identifies the presence, number and properties of these soliton wave-trains. For example, an increase of spatial symmetry is accompanied by the injection of additional solitons into the field.     

有阻尼单摆的冲击波解

研究和分析有阻尼单摆的运动方程,应用近似法方程时发现存在冲击波解并精确求解.同时结合有阻尼单摆的相图分析冲击波解存在的物理意义.     

弱阻尼非线性单摆的周期研究

用平均法研究了弱阻尼条件下非线性单摆的振动,得到周期比随角振幅和阻尼常量变化的表达式.     

Chaos in a damped and driven toda system

We describe our numerical studies of chaos for a damped and driven single Toda particle and in a Toda lattice. Comparisons are made with chaos in other classes of nonlinear potentials.     

Parametrically driven pendulum and exact solutions

The parametrically driven pendulumx +f ₁(t) x +f ₂(t) sinx = 0 cannot be solved in closed form for arbitrary functionvsf ₁,f ₂. We apply the Painlevé test to obtain the constraint on the functionsf ₁, andf ₂ for which the equation passes the test. The constraint onf ₁, andf ₂, a differential equation whichf ₁ andf ₂ obey, is discussed and solutions are given. The third Painlevé transcendent plays a central role.     

单摆系统通向混沌的道路

对受迫非线性单摆系统进入混沌的道路进行了研究,发现单摆系统的运动是极其复杂的.目前在其他系统发现的进入混沌的通道,在该系统中几乎均可找到.这是一个介绍混沌运动的典型系统.     

单摆的振动图像演示装置

用电火花计时器作单摆的高压电源,使单摆的针尖和铜片间产生火花放电,并且在单放机带动而做匀速直线运动的纸带上产生放电点迹,形成单摆的振动图像.根据振动图像探究单摆的振动周期与振幅、摆长和摆的质量是否有关.     

Distinguishing the transition to chaos in a spherical pendulum

Complex responses are studied for a spherical pendulum whose support is excited with a translational periodic motion. Governing equations are studied analytically to allow prediction of responses under various excitation conditions. Stability for certain cases of damping is predicted by means of existing analysis and compared with experimental data. Numerical time-step integration of the governing equations is developed to predict responses for various types of excitation and damping conditions. Predicted results are compared with corresponding motions measured in an experimental spherical pendulum system. A data acquisition system is included whereby detailed digitized time histories of the pendulum motion can be established and various parameters can be computed to characterize the type of motion present. Two new vector spaces are defined for describing complex responses which occur for certain specified excitation conditions. It is shown in these parameter spaces that the transition from quasiperiodic to chaotic motions can be carefully quantified in systems with very light damping. This discovery provides a convenient means for comparison of complex motions in the numerical and experimental air pendulum systems. The implications of the results are important for dynamic response in various applications, including fluid motions in satellite tanks and other nonlinear time-dependent physical processes which include very light damping. (c) 1995 American Institute of Physics.     

倒摆运动的混沌行为

设计一个受周期外力驱动的倒摆实验装置,并建立该系统的动力学方程,用线性稳定性分析方法讨论了平衡点附近邻域的稳定性,利用数值计算并结合多种分析方法求解非线性方程并判断解的性质．通过改变系统参数,画出时域图、相图及分岔图,计算分析和实验发现,这个简单的力学系统存在十分丰富的动力学行为（分岔、混沌）．理论分析、数值模拟和实验结果一致．     

Structure of the stochastic layer in a driven pendulum

An analysis of the stochastic layer in a driven pendulum is extended to the case when the separatrix map contains both single-and double-frequency harmonics. Resonance invariants of the first three orders are found for the double-frequency harmonic. Combined with the previously known single-frequency invariants, they can be used to obtain further information about the layer, in particular, to examine the neighborhoods of zeros of Melnikov integrals.     

Chaos and transient chaos in an experimental nonlinear pendulum

Pendulum is a mechanical device that instigates either technological or scientific studies, being associated with the measure of time, stabilization devices as well as ballistic applications. Nonlinear characteristic of the pendulum attracts a lot of attention being used to describe different phenomena related to oscillations, bifurcation and chaos. The main purpose of this contribution is the analysis of chaos in an experimental nonlinear pendulum. The pendulum consists of a disc with a lumped mass that is connected to a rotary motion sensor. This assembly is driven by a string-spring device that is attached to an electric motor and also provides torsional stiffness to the system. A magnetic device provides an adjustable dissipation of energy. This experimental apparatus is modeled and numerical simulations are carried out. Free and forced vibrations are analyzed showing that numerical results are in close agreement with those obtained from experimental data. This analysis shows that the experimental pendulum has a rich response, presenting periodic response, chaos and transient chaos.     

Stability of the parametrically excited damped inverted pendulum: theory and experiment

The parametrically driven, damped, inverted pendulum can be dynamically stabilized in particular regions of the parameter space. The impact of damping on dynamic stabilization can be stabilizing or destabilizing depending on the location in parameter space (i.e., drive frequency and amplitude). Floquet analysis and numerical simulations were used to determine the stable regions. An experiment was conducted that verifies the model. Physical explanations and simple bounding approximations are provided to summarize findings. The utility of the highly damped pendulum results are illustrated by drawing the analogy to dynamic stabilization of the Rayleigh-Taylor instability: it permits ready demonstration that dynamic stabilization is impossible in that system absent surface tension.     

Chaos in a driven pendulum under asymmetric forcing

An analysis of the stochastic layer in a pendulum driven by an asymmetric high-frequency perturbation of fairly general form is continued. Analytical expressions are found for the amplitudes of secondary harmonics, and their contributions to the amplitude of the separatrix map responsible for onset of dynamical chaos are evaluated. Additional evidence is presented of the previously established fact that the secondary harmonics completely determine the stochasticl-ayer width when the primary frequencies lie in certain intervals. The mechanism of the onset of chaos in the vicinity of zeros of Melnikov integrals is shown to be substantially different as compared to the previously analyzed case of symmetric perturbation.