arXiv subjects

O. V. Gendelman

Publications and source records attributed to O. V. Gendelman.

At least 19 recordsLinked to original sources

arXiv2024

Modal and wave synchronization in coupled self-excited oscillators

In addition to a common synchronization and/or localization behavior, a system of linearly coupled identical bistable Van der Pol (BVdP) oscillators can exhibit a "non-conventional" or "modal" synchronization. In two-DOF case, one can observe stable beatings attractor with synchronized amplitudes of the symmetric and antisymmetric modes. Current study demonstrates that this unusual behavior is generic and quite ubiquitous, if the system is explored in appropriate parametric regime. Indeed, in the absence of the self - excitation the system of coupled linear oscillators possesses a complete set of non-interacting eigenmodes. If the system is symmetric and the coupling is weak enough, appropriate initial conditions will result in a continuous multi-parametric family of stationary beatings or beat waves. If the self-excitation terms are small enough, i.e. even weaker than the weak coupling, one can expect that, generically, some special stationary or wave beatings will turn into the stable attractors. We demonstrate this phenomenon in systems of ring-coupled BVdP oscillators. In particular, we observe simple two-wave synchronization for $N=2,3,5,6,7$ coupled oscillators; for $N=2$ it corresponds to the "modal" synchronization observed previously. The case $N=4$ is special: due to internal resonances in the slow flow, the two-wave synchronization turns unstable, and more complicated patterns of the multi-wave synchronization are revealed. Analytic models manage to capture the shapes of the observed beat waves. All results are verified by direct numeric simulations.

nlin.PS↗

arXiv2021

Kapitza resistance at a domain boundary in linear and nonlinear chains

We explore Kapitza thermal resistance on the boundary between two homogeneous chain fragments with different characteristics. For a linear model, an exact expression for the resistance is derived, and well-defined in the thermodynamic limit. However, the resistance in this case depends on the thermostat properties and therefore is not a local property of the considered domain boundary. If the domains are nonlinear, but integrable - Toda lattice, elastically colliding particles - the anomalies are similar to the case of the linear chain, besides well-articulated thermal dependence of the resistance. For the case of elastically colliding particles, this dependence follows a simple scaling law - the resistance is proportional to the inverse square root of the temperature. For Fermi-Pasta-Ulam domains, both the temperature drop and the heat flux decrease with the chain length, but with different exponents, so the resistance vanishes in the thermodynamic limit. For the domains comprised of rotators, the thermal resistance exhibits the expected normal behavior.

cond-mat.soft↗

arXiv2021

Kapitza thermal resistance in linear and nonlinear chain models: isotopic defect

Kapitza resistance in the chain models with internal defects is considered. For the case of the linear chain, the exact analytic solution for the boundary resistance is derived for arbitrary linear time-independent conservative inclusion or defect. A simple case of isolated isotopic defects is explored in more detail. Contrary to the bulk conductivity in the linear chain, the Kapitza resistance is finite. However, the universal thermodynamic limit does not exist in this case. In other terms, the exact value of the resistance is not uniquely defined and depends on the way of approaching the infinite lengths of the chain fragments. For this reason, and also due to the explicit dependence on the parameters of the thermostats, the resistance cannot be considered as a local property of the defect. Asymptotic scaling behavior of the heat flux in the case of very heavy defect is explored and compared to the nonlinear counterparts; similarities in the scaling behavior are revealed. For the lightweight isotopic defect in the linear chain, one encounters a typical dip of the temperature profile, related to weak excitation of the localized mode in the attenuation zone. If the nonlinear interactions are included, this dip can still appear at a relatively short time scale, with subsequent elimination due to the nonlinear interactions. This observation implies that even in the nonlinear chains, the linear dynamics can predict the main features of the short-time evolution of the thermal profile if the temperature is low enough.

cond-mat.stat-mech↗

arXiv2020

Modal synchronization of coupled bistable Van der Pol oscillators

The paper revisits recently revealed regimes of the "nonconventional synchronization" in systems of coupled bi-stable Van der Pol oscillators. These regimes are characterized by periodic (or quasiperiodic) almost complete energy exchanges between the coupled oscillators. In the paper it is demonstrated that such responses correspond to synchronization of the modulation amplitudes between symmetric and antisymmetric modes of the system, with persistent phase drift. This observation substantially simplifies the treatment, reduces the dynamics to simple phase cylinder and allows to reveal a rich set of global and local bifurcations of limit cycles and tori in the system. Among other findings, one encounters an unexpected regime of nonstationary asymmetric synchronization.

nlin.PS↗

arXiv2020

Stability of compact breathers in translationally-invariant nonlinear chains with flat dispersion bands

The paper addresses compact oscillatory states (compact breathers) in translationally-invariant lattices with flat dispersion bands. The compact breathers appear in such systems even in the linear approximation. If the interactions are nonlinear, but comply with the flat-band symmetry, the compact breather solutions exist, but can lose their stability for certain parameter values. As benchmark nonlinear potentials, we use the $β$-FPU (Fermi-Pasta-Ulam) and vibro-impact models. Loss of stability is numerically observed to occur through either pitchfork or Hopf bifurcations. The loss of stability can occur through two qualitatively different mechanisms -- through internal instability in the basic lattice elements, or through interaction of the compact breather with the linear passband of the lattice. The former scenario is more typical for high-amplitude breathers, and the latter -- for low amplitudes. For the high-amplitude case, insights into the nature of compact-mode loss-of-stability are obtained by resorting to the limit of a piecewise-linear system, where interactions are represented by conservative impacts. This issue calls for detailed introspection into integrability of piecewise-linear (impacting) systems and their relation to the smooth system. An idea for a sensor based on the studied mechanisms is suggested.

nlin.PS↗

arXiv2019

Breather arrest in a chain of damped oscillators with Hertzian contact

We explore breather propagation in the damped oscillatory chain with essentially nonlinear (non-linearizable) nearest-neighbour coupling. Combination of the damping and the substantially nonlinear coupling leads to rather unusual two-stage pattern of the breather propagation. The first stage occurs at finite fragment of the chain and is characterized by power-law decay of the breather amplitude. The second stage is characterized by extremely small breather amplitudes that decay hyper-exponentially with the site number. Thus, practically, one can speak about finite penetration depth of the breather. This phenomenon is referred to as breather arrest (BA). As particular example, we explore the chain with Hertzian contacts. Dependencies of the breather penetration depth on the initial excitation and on the damping coefficient on the breather penetration depth obey power laws. The results are rationalized by considering beating responses in a system of two damped linear oscillators with strongly nonlinear (non-linearizable) coupling. Initial excitation of one of these oscillators leads to strictly finite number of beating cycles. Then, the beating cycle in this simplified system is associated with the passage of the discrete breather between the neighbouring sites in the chain. Somewhat surprisingly, this simplified model reliably predicts main quantitative features of the breather arrest in the chain, including the exponents in numerically observed power laws.

nlin.PS↗

arXiv2019

Kapitza resistance in basic chain models with isolated defects

Kapitza thermal resistance is a common feature of material interfaces. It is defined as the ratio of the thermal drop at the interface to the heat flux flowing across the interface. One expects that this resistance will depend on the structure of the interface and on the temperature. We address the heat conduction in one-dimensional chain models with isotopic and/or coupling defects and explore the relationship between the interaction potentials and simulated properties of the Kapitza resistance. It is revealed that in linear models the Kapitza resistance is well-defined and size-independent (contrary to the bulk heat conduction coefficient), but depends on the parameters of thermostats used in the simulation. For $β$-FPU model one also encounters the dependence on the thermostats; in addition, the simulated boundary resistance strongly depends on the total system size. Finally, in the models characterized by convergent bulk heat conductivity (chain of rotators, Frenkel-Kontorova model) the boundary resistance is thermostat- and size-independent, as one expects. In linear chains, the Kapitza resistance is temperature-independent; thus, its temperature dependence allows one to judge on significance of the nonlinear interactions in the phonon scattering processes at the interface.

cond-mat.stat-mech↗

arXiv2019

Nucleation and propagation of excitation fronts in self-excited systems

Frictional interfaces exhibits a very rich dynamical behavior due to frictional interactions. This work focuses on the transition between spatially localized and propagating stick-slip motion. To overcome the difficulties related to the non-smoothness of the friction law we have studied two models: (model I) a friction-excited chain of weakly coupled oscillators excited by a frictional moving belt and (model II) a chain of Van der Pol oscillators. The two models show very similar dynamical features. Both exhibit discrete breathers (i.e. spatially localized periodic solutions) solutions for low coupling and show propagation along the chain of high amplitude limit cycles for stronger elastic coupling between the unit cells. In both models the transition from discrete breathers to propagating limit cycles happens through a nucleation process and, above a certain critical coupling, the velocity of propagation scales linearly with the elastic coupling coefficient. We suggest that dynamical features similar to what was demonstrated in this work are expected for models that are different quantitatively but preserve the same single-unit topology.

nlin.PS↗

arXiv2018

Basic mechanisms of escape of a harmonically forced classical particle from a potential well

In various models and systems involving the escape of periodically forced particle from the potential well, a common pattern is observed. Namely, the minimal forcing amplitude required for the escape exhibits sharp minimum for the excitation frequency below the natural frequency of small oscillations in the well. The paper explains this regularity by exploring the transient escape dynamics in simple benchmark potential wells. In the truncated parabolic well, in absence of the damping the minimal forcing amplitude obviously tends to zero for the natural excitation frequency. Addition of weak symmetric softening nonlinearity to the truncated parabolic well leads to the nonzero forcing minimum below the natural frequency. We explicitly compute this shift in the principal approximation by considering the slow-flow dynamics in conditions of the principal 1:1 resonance. Essentially nonlinear model, analyzed with the help of transformation to action-angle variables, demonstrates very similar qualitative features of the transient escape dynamics.

nlin.CD↗

arXiv2018

Nonlinear dynamics of hidden modes in a system with internal symmetry

We consider a discrete dynamical system with internal degrees of freedom (DOF). Due to the symmetry between the internal DOFs, certain internal modes cannot be excited by external forcing (in a case of linear interactions) and thus are considered "hidden". If such a system is weakly asymmetric, the internal modes remain approximately "hidden" from the external excitation, given that small damping is taken into account. However, already in the case of weak cubic nonlinearity, these hidden modes can be excited, even as the exact symmetry is preserved. This excitation occurs through parametric resonance. Floquet analysis reveals instability patterns for the explored modes. To perform this analysis with the required accuracy, we suggest a special method for obtaining the Fourier series of the unperturbed solution for the nonlinear normal mode. This method does not require explicit integration of the arising quadratures. Instead, it employs expansion of the solution at the stage of the implicit quadrature in terms of Chebyshev polynomials. The emerging implicit equations are solved by using a fixed-point iteration scheme. Poincaré sections help to clarify the correspondence between the loss of stability of the modes and the global structure of the dynamical flow. In particular, the conditions for intensive energy exchange in the system are characterized.

nlin.SI↗

arXiv2018

Transient dynamics in strongly nonlinear systems: optimization of initial conditions on the resonant manifold

We consider a system of two linear and linearly coupled oscillators with ideal impact constraints. Primary resonant energy exchange is investigated by analysis of the slow-flow using the action-angle (AA) formalism. Exact inversion of the action-energy dependence for the linear oscillator with impact constraints is not possible. This difficulty, typical for many models of nonlinear oscillators, is circumvented by matching the asymptotic expansions for the linear and impact limits. The obtained energy-action relation enables the complete analysis of the slow-flow and the accurate description of the critical delocalization transition. The transition from the localization regime to the energy-exchange regime is captured by prediction of the critical coupling value. Accurate prediction of the delocalization transition requires detailed account of the coupling energy with appropriate re-definition and optimization of the limiting phase trajectory on the resonant manifold.

nlin.CD↗

arXiv2017

Flat bands and compactons in mechanical lattices

Local configurational symmetry in lattice structures may give rise to stationary, compact solutions, even in the absence of disorder and nonlinearity. These compact solutions are related to the existence of flat dispersion curves (bands). Nonlinearity can destabilize such compactons. One common flat-band-generating system is the 1D cross-stitch model, in which compactons were shown to exist for the photonic lattice with Kerr nonlinearity. The compactons exist there already in the linear regime and are not generally destructed by that nonlinearity. Smooth nonlinearity of this kind does not allow doing a complete stability analysis for this chain. We consider a discrete mechanical system with flat dispersion bands, in which the nonlinearity exists due to impact constraints. There, one can use the concept of the saltation matrix for the analytic construction of the monodromy matrix. Besides, we consider a smooth nonlinear lattice with linearly connected massless boxes, each containing two symmetric anharmonic oscillators. In this model, the flat bands and discrete compactons also readily emerge. This system also permits performing comprehensive stability analysis, at least in the anti-continuum limit, due to the reduced number of degrees-of-freedom. In both systems, there exist two types of localization. The first one is the complete localization, and the second one is the more common exponential localization. The latter type is associated with discrete breathers (DBs). Two principal mechanisms for the loss of stability are revealed. The first one is the possible internal instability of the symmetric and/or antisymmetric solution in the individual unit cell of the chain. One can interpret this instability pattern as internal resonance between the compacton and the DB. The other mechanism is global instability related to resonance of the stationary solution with the propagation frequencies.

nlin.PS↗

arXiv2017

Front propagation in lattices with on-site bistable non-degenerate potential: multiplicity, bifurcations and route to chaos

Propagation of transition fronts in models of coupled oscillators with non-degenerate on-site potential is usually considered in terms of travelling waves. We show that the system dynamics can be reformulated as an implicit map structure, and the travelling waves correspond to stable fixed points. Therefore, the loss of stability of such waves should follow well-known generic bifurcation scenarios. Then, one can expect a plethora of qualitatively different propagating-front solutions - multistable, multi-periodic, quasiperiodic and chaotic.

nlin.PS↗

arXiv2017

Escape of harmonically forced classical particle from an infinite-range potential well

The paper considers a process of escape of classical particle from a one-dimensional potential well by virtue of an external harmonic forcing. We address a particular model of the infinite-range potential well that allows independent adjustment of the well depth and of the frequency of small oscillations. The problem can be conveniently reformulated in terms of action-angle variables. Further averaging provides a nontrivial conservation law for the slow flow. Thus, one can consider the problem in terms of averaged dynamics on primary 1:1 resonance manifold. This simplification allows efficient analytic exploration of the escape process, and yields a theoretical prediction for minimal forcing amplitude required for the escape, as a function of the excitation frequency. This function exhibits a single minimum for certain intermediate frequency value. Numeric simulations are in complete qualitative and reasonable quantitative agreement with the theoretical predictions.

physics.class-ph↗

arXiv2017

Propagation of transition fronts in nonlinear chains with non-degenerate on-site potentials

We address the problem of a front propagation in chains with a bi-stable nondegenerate on-site potential and a nonlinear gradient coupling. For a generic nonlinear coupling, one encounters a special regime of transitions, characterized by extremely narrow fronts, far supersonic velocities of propagation and long waves in the oscillatory tail. This regime can be qualitatively associated with a shock wave. The front propagation can be described with the help of a simple reduced-order model; the latter delivers a kinetic law, which is almost not sensitive to fine details of the on-site potential. Besides, it is possible to predict all main characteristics of the transition front, including its shape and frequency and amplitude of the oscillatory tail. The numerical results are in a good agreement with the analytical predictions. The suggested approach allows one to consider the effects of an external pre-load and on-site damping. When the damping is moderate, the analysis remains in the frame of the reduced-order model. It is possible to consider the solution for the front propagating in the damped chain as a perturbation of the undamped dynamics. This approach yield reasonable predictions. When the damping is high, the transition front enters a completely different asymptotic regime. The gradient nonlinearity generically turns negligible, and the propagating front converges to the exact solution obtained from a simple linear continuous model.

nlin.PS↗

arXiv2017

Response Regimes in Equivalent Mechanical Model of Moderately Nonlinear Liquid Sloshing

The paper considers non-stationary responses in reduced-order model of partially liquid-filled tank under external forcing. The model involves one common degree of freedom for the tank and the non-sloshing portion of the liquid, and the other one -- for the sloshing portion of the liquid. The coupling between these degrees of freedom is nonlinear, with the lowest-order potential dictated by symmetry considerations. Since the mass of the sloshing liquid in realistic conditions does not exceed 10% of the total mass of the system, the reduced-order model turns to be formally equivalent to well-studied oscillatory systems with nonlinear energy sinks (NES). Exploiting this analogy, and applying the methodology known from the studies of the systems with the NES, we predict a multitude of possible non-stationary responses in the considered model. These responses conform, at least on the qualitative level, to the responses observed in experimental sloshing settings, multi-modal theoretical models and full-scale numeric simulations.

physics.flu-dyn↗

arXiv2017

Propagation of transition front in bi-stable nondegenerate chains: model dependence and universality

We consider a propagation of transition fronts in one-dimensional chains with bi-stable nondegenerate on-site potential. If one adopts linear coupling in the chain and piecewise linear on-site force, then it is possible to develop well-known exact solutions for the front and accompanying oscillatory tail. We demonstrate that these solutions are essentially non-robust. Various approximations for the on-site potential with the same basic parameters (height and coordinate of the potential barrier, energy effect and distance between the potential wells) lead to substantially different front velocities. Besides, inclusion of even weak nearest neighbor nonlinearity drastically modifies the front structure and parameters. The energy concentration in the front zone leads to a dominance of the nonlinear term. It turns out that the dynamics can be efficiently studied in terms of an equivalent model with a single degree of freedom. This estimation leads to accurate prediction of the front velocity and parameters of the oscillatory tail. Moreover, it turns out that the solution is robust - exact shape of the on-site potential weakly effects the front parameters. This finding also conforms to the simplified model, since the latter invokes only the general shape characteristics of the on-site potential.

nlin.PS↗

arXiv2017

Localization in finite asymmetric vibro-impact chains

We explore the dynamics of strongly localized periodic solutions (discrete solitons, or discrete breathers) in a finite one-dimensional chain of asymmetric vibro-impact oscillators. The model involves a parabolic on-site potential with asymmetric rigid constraints (the displacement domain of each particle is finite), and a linear nearest-neighbor coupling. When the particle approaches the constraint, it undergoes an impact (not necessarily elastic), that satisfies Newton impact law. Nonlinearity of the system stems from the impacts; their possible non-elasticity is the sole source of damping in the system. We demonstrate that this vibro-impact model allows derivation of exact analytic solutions for the asymmetric discrete breathers, both in conservative and forced-damped settings. The asymmetry makes two types of breathers possible: breathers that impact both or only one constraint. Transition between these two types of the breathers corresponds to a grazing bifurcation. Special character of the nonlinearity permits explicit derivation of a monodromy matrix. Therefore, the stability of the obtained breather solutions can be exactly studied in the framework of simple methods of linear algebra, and with rather moderate computational efforts. All three generic scenarios of the loss of stability (pitchfork, Neimark-Sacker and period doubling bifurcations) are observed.

nlin.PS↗