A classical iteration procedure valid for certain strongly nonlinear oscillators

A classical iteration procedure is applied to nonlinear oscillations of conservative single-degree-of-freedom systems with odd nonlinearity. With the procedure, the analytical approximate frequency and the corresponding periodic solution, valid for small as well as large amplitudes of oscillation, can be obtained. Two examples are given to illustrate the accuracy and effectiveness of the method. Another advantage of this classical iteration approach is that it also works if the linear part of restoring force is zero.     

Asymptotic stability with probability one of MDOF nonlinear oscillators with fractional derivative damping

In this paper, the asymptotic stability with probability one of multi-degree-of-freedom (MDOF) nonlinear oscillators with fractional derivative damping parametrically excited by Gaussian white noises is investigated. A stochastic averaging method and the Khasminskii’s procedure are employed to evaluate the largest Lyapunov exponent, whose sign determines the stability of the system. As an example, two coupled nonlinear oscillators with fractional derivative damping is worked out to demonstrate the proposed procedure and to examine the effect of fractional order on the stochastic stability of system. In particular, the case of factional order more than 1 is studied for the first time.     

Response of SDOF nonlinear oscillators with lightly fractional derivative damping under real noise excitations

This paper deals with the response of single-degree-of-freedom (SDOF) strongly nonlinear oscillator with lightly fractional derivative damping to external and (or) parametric real noise excitations. First, the state vector of the displacement and the velocity is approximated by one-dimensional time-homogeneous diffusive Markov process of amplitude through using the stochastic averaging method. Then, the stationary probability density of amplitude is obtained by solving the Fokker-Planck-Kolmogorov (FPK) equation associated with the averaged It? equation of amplitude, in which the Fourier series expansions are used to obtain the explicit expressions of the drift and diffusion coefficients. Finally, the response of a Duffing oscillator with lightly fractional derivative damping under external and parametric real noise excitations is evaluated by using the proposed procedure and compared with that from the Monte Carlo simulation of original system.     

Frequency analysis with coupled nonlinear oscillators

We present a method to obtain the frequency spectrum of a signal with a nonlinear dynamical system. The dynamical system is composed of a pool of adaptive frequency oscillators with negative mean-field coupling. For the frequency analysis, the synchronization and adaptation properties of the component oscillators are exploited. The frequency spectrum of the signal is reflected in the statistics of the intrinsic frequencies of the oscillators. The frequency analysis is completely embedded in the dynamics of the system. Thus, no pre-processing or additional parameters, such as time windows, are needed. Representative results of the numerical integration of the system are presented. It is shown, that the oscillators tune to the correct frequencies for both discrete and continuous spectra. Due to its dynamic nature the system is also capable to track non-stationary spectra. Further, we show that the system can be modeled in a probabilistic manner by means of a nonlinear Fokker-Planck equation. The probabilistic treatment is in good agreement with the numerical results, and provides a useful tool to understand the underlying mechanisms leading to convergence.     

Dynamics of nonlinear oscillators with fluctuating parameters

We derive the (integro-differential) master equation of an oscillator in a thermal environment which is driven by a non-linear randomly varying force. The thermal noise is assumed to be δ-correlated gaussian noise and the parameter fluctuations are assumed to be multiplicative white Poisson noise. For the case of a large viscosity we derive a generalized Smoluchowski equation and sketch the modification of Kramers' reaction rate. The rate is shown to contain a temperature-independent “tunneling” contribution.     

Squeezed field generation by nonlinear bounded quantum oscillators

A new, effective method of squeezing is presented, based on the parametric resonance excitation of nonlinear bounded oscillators as vibration modes of multiatomic molecules.Presented at the International Workshop on Squeezed and Correlated States in Quantum Optics, Moscow, December 3–7, 1990.     

Norm inequalities for fractional powers of positive operators

It is shown that ifA, B andX are operators on a Hilbert space such thatA andB are positive andX belongs to a norm ideal associated with some unitarily invariant norm |·|, then for 0 r 1 we have |A ^r XB ^r | |X|^1-r |AXB| ^r . This is an extension of the classical Heinz-Kato inequality which was originally proved for the usual operator norm. Other related inequalities are also discussed.     

Amplitude death in nonlinear oscillators with indirect coupling

We investigate the effect of frequency mismatch in two indirectly coupled Rössler oscillators and Hindmarsh–Rose neuron model systems. While identical systems show in-phase or out-of-phase synchronization states when coupled through a dynamic environment, mismatch in the internal frequencies of the systems drives them to a fixed point state, i.e., amplitude death. There is a region in the parameter space of the frequency mismatch and coupling strength where system shows amplitude death. The numerical results of Rössler system are also experimentally verified using piece-wise Rössler circuits.     

Dynamics of three Toda oscillators with nonlinear unidirectional coupling

We study the dynamics of three unidirectionally coupled Toda oscillators with nonlinear coupling function in the form of first three terms of Taylor power series. We analytically investigate how the coupling influence the stability of steady state. Basing on calculation of the first Lyapunov coefficient, we show that destabilization may occur by the sub- or supercritical Andronov-Hopf bifurcation. Born periodic solutions are calculated using path-following as a function of coupling strength and Taylor series coefficients. We present that initially stable or unstable branch of periodic solutions may undergo a sequence of bifurcations including: period doubling, Neimark-Saker and fold.     

Phase-flip transition in nonlinear oscillators coupled by dynamic environment

We study the dynamics of nonlinear oscillators indirectly coupled through a dynamical environment or a common medium. We observed that this form of indirect coupling leads to synchronization and phase-flip transition in periodic as well as chaotic regime of oscillators. The phase-flip transition from in- to anti-phase synchronization or vise-versa is analyzed in the parameter plane with examples of Landau-Stuart and Ro?ssler oscillators. The dynamical transitions are characterized using various indices such as average phase difference, frequency, and Lyapunov exponents. Experimental evidence of the phase-flip transition is shown using an electronic version of the van der Pol oscillators.     

Dynamics of weakly overdamped nonlinear oscillators

The dynamics of weakly overdamped nonlinear oscillators is studied. Weak overdamping is defined as a slight excess in the value of the damping decrement corresponding to the eigenfrequency of an oscillator. Based on exact solutions to the problem, it is shown that in approaching equilibrium, relaxation dynamics is replaced by a quasi-oscillation process, provided that the initial shift exceeds the threshold value.     

Phase equation with nonlinear excitation for nonlocally coupled oscillators

Some reaction-diffusion systems feature nonlocal interaction and, near the point of Hopf bifurcation, can be represented as a system of nonlocally coupled oscillators. Phase of oscillations satisfies an evolution pde which takes different forms depending on the values of parameters. In the simplest case the equation is effectively a diffusion equation which is excitation-free. However, more complex forms are possible such as the Nikolaevskii equation and the Kuramoto–Sivashinsky equation incorporating linear excitation. We analyse a situation when the phase equation is based on nonlinear excitation. We derive conditions on the values of the parameters leading to the situation and show that the values satisfying the conditions exist.     

Approximate first integrals of nonlinear oscillators with one-degree of freedom

Exact symmetries of the unperturbed (linear) part of the dynamical systems are determined. Resonance conditions which lead to the symmetry-breaking of the symmetries of the unperturbed part are obtained. The second-order approximate symmetries of the one degree of freedom, damped-driven oscillators are found. By employing an approximate version of Noether's theorem, second-order approximate first integrals are obtained for undamped oscillators. The results are discussed on the contour plots of the first integrals.     

Flow-induced vibrations of long circular cylinders modeled by coupled nonlinear oscillators

The dynamics of long slender cylinders undergoing vortex-induced vibrations (VIV) is studied in this work. Long slender cylinders such as risers or tension legs are widely used in the field of ocean engineering. When the sea current flows past a cylinder, it will be excited due to vortex shedding. A three-dimensional time domain model is formulated to describe the response of the cylinder, in which the in-line (IL) and cross-flow (CF) deflections are coupled. The wake dynamics, including in-line and cross-flow vibrations, is represented using a pair of non-linear oscillators distributed along the cylinder. The wake oscillators are coupled to the dynamics of the long cylinder with the acceleration coupling term. A non-linear fluid force model is accounted for to reflect the relative motion of cylinder to current. The model is validated against the published data from a tank experiment with the free span riser. The comparisons show that some aspects due to VIV of long flexible cylinders can be reproduced by the proposed model, such as vibrating frequency, dominant mode number, occurrence and transition of the standing or traveling waves. In the case study, the simulations show that the IL curvature is not smaller than CF curvature, which indicates that both IL and CF vibrations are important for the structural fatigue damage. Supported by the National Natural Science Foundation of China (Grant No. 10532070), the Knowledge Innovation Program of Chinese Academy of Sciences (Grant No. KJCX2-YW-L07), and the LNM Initial Funding for Young Investigators     

Homoclinic bifurcation sets of driven nonlinear oscillators

Different quasiperiodically and parametrically driven nonlinear oscillators with quadratic and cubic nonlinearities are considered, and the corresponding homoclinic bifurcation sets in a five-dimensional parameter space are explicitly calculated. We classify all these cases into two basic types of homoclinic bifurcation sets: the first one corresponds to quasiperiodically driven oscillators and the second one corresponds to parametrically driven oscillators.     

Spectra of delay-coupled heterogeneous noisy nonlinear oscillators

Complex systems are described by a large number of variables with strong and nonlinear interactions. Such systems frequently undergo regime shifts. Combining insights from bifurcation theory in nonlinear dynamics and the theory of critical transitions in statistical physics, we know that critical slowing down and critical fluctuations occur close to such regime shifts. In this paper, we show how universal precursors expected from such critical transitions can be used to forecast regime shifts in the US housing market. In the housing permit, volume of homes sold and percentage of homes sold for gain data, we detected strong early warning signals associated with a sequence of coupled regime shifts, starting from a Subprime Mortgage Loans transition in 2003–2004 and ending with the Subprime Crisis in 2007–2008. Weaker signals of critical slowing down were also detected in the US housing market data during the 1997–1998 Asian Financial Crisis and the 2000–2001 Technology Bubble Crisis. Backed by various macroeconomic data, we propose a scenario whereby hot money flowing back into the US during the Asian Financial Crisis fueled the Technology Bubble. When the Technology Bubble collapsed in 2000–2001, the hot money then flowed into the US housing market, triggering the Subprime Mortgage Loans transition in 2003–2004 and an ensuing sequence of transitions. We showed how this sequence of couple transitions unfolded in space and in time over the whole of US.     

Global versus local superintegrability of nonlinear oscillators

Liouville (super)integrability of a Hamiltonian system of differential equations is based on the existence of globally well-defined constants of the motion, while Lie point symmetries provide a local approach to conserved integrals. Therefore, it seems natural to investigate in which sense Lie point symmetries can be used to provide information concerning the superintegrability of a given Hamiltonian system. The two-dimensional oscillator and the central force problem are used as benchmark examples to show that the relationship between standard Lie point symmetries and superintegrability is neither straightforward nor universal. In general, it turns out that superintegrability is not related to either the size or the structure of the algebra of variational dynamical symmetries. Nevertheless, all of the first integrals for a given Hamiltonian system can be obtained through an extension of the standard point symmetry method, which is applied to a superintegrable nonlinear oscillator describing the motion of a particle on a space with non-constant curvature and spherical symmetry.     

Self-consistent nonlinear analysis of overmoded gyrotron oscillators

The self-consistent nonlinear analysis is presented for an overmoded gyrotron, in which the gyrotropic beam interacts with more than one cavity eigenmodes. The nonlinear equations are obtained in the slow time scale for the motion of each individual particle and for the evolution of the amplitude and frequency of each individual cavity eigenmode. A numerically efficient algebraic longtime-step algorithm is developed, which includes magnetostatic field tapering and time transients. Numerical examples are presented for the excitation and competition of the cavity eigenmodes.Work supported by the U.S. Naval Research Laboratory, Plasma Physics Division, under Contract No. N00173-79-C-0200.