Noether symmetries and conserved quantities for Birkhoffian systems with time delay

The Noether symmetries and conserved quantities for Birkhoffian systems with time delay are proposed and studied. First, the Pfaff–Birkhoff principle with time delay is proposed, and Birkhoff’s equations with time delay are obtained. Second, based on the invariance of the Pfaff action with time delay under a group of infinitesimal transformations, the Noether symmetric transformations and the Noether quasisymmetric transformations of the system are defined, and the criteria of the Noether symmetries are established. Finally, the relationship between the symmetries and the conserved quantities are studied, and the Noether theorems for Birkhoffian systems with time delay are established. Some examples are given to illustrate the application of the results.     

Perturbation to Noether symmetries and adiabatic invariants for disturbed Hamiltonian systems based on El-Nabulsi nonconservative dynamics model

This paper focuses on studying the perturbation to the Noether symmetries and the adiabatic invariants for nonconservative dynamic systems in phase space under nonconservative dynamics model presented by El-Nabulsi. First of all, the El-Nabulsi dynamics model for a nonconservative system is introduced and the El-Nabulsi–Hamilton canonical equations are established. Secondly, the basic formulae for the variation of El-Nabulsi–Hamilton action in phase space are deduced, the definition and criterion of the Noether quasi-symmetric transformation are given, and the exact invariant led directly by the Noether symmetry is obtained. Finally, based upon the concept of high-order adiabatic invariant of a mechanical system, the relationship between the perturbation to the Noether symmetry and the adiabatic invariant after the action of a small disturbance is studied and the conditions that the perturbation of symmetry leads to the adiabatic invariant and its formulation are given. At the end of the paper, two examples are given to illustrate the application of the method and results.     

Mei symmetries and conserved quantities for non-conservative Hamiltonian difference systems with irregular lattices

Noether conserved quantities and Mei symmetries for non-conservative Hamiltonian difference systems with irregular lattices are studied. The generalized Hamiltonian equations of the systems are given on the basis of the transformation operators in the space of discrete Hamiltonians. The Lie point transformations acting on the lattice, as well as the difference equations, and the determining equations of Mei symmetries are obtained for the systems. The discrete versions of Noether conserved quantity are constructed by the Mei symmetries. An example is presented to illustrate the results.     

Noether symmetry method for Birkhoffian systems in terms of generalized fractional operators

Compared with the Hamiltonian mechanics and the Lagrangian mechanics, the Birkhoffian mechanics is more general. The Birkhoffian mechanics is discussed on the basis of the generalized fractional operators, which are proposed recently. Therefore, differential equations of motion within generalized fractional operators are established. Then, in order to find the solutions to the differential equations, Noether symmetry, conserved quantity, perturbation to Noether symmetry and adiabatic invariant are investigated. In the end, two applications are given to illustrate the methods and results.     

Nonlinear control for teleoperation systems with time varying delay

In this paper, we introduce delay-dependent control strategies for bilateral teleoperation systems in the presence of passive and constant input forces under time varying delay. We first design teleoperation systems where the local and remote sites are coupled by position signals of the master and slave manipulator. The design also combined undelayed position and velocity signals with nonlinear adaptive control terms to deal with the parametric uncertainties associated with the dynamical model of the master and slave manipulator. Then, we develop teleoperators by delaying position and velocity signals of the master and slave manipulator. Using Lyapunov–Krasovskii function, delay-dependent stability and tracking conditions for both teleoperators are developed in the presence of symmetrical and unsymmetrical time varying delays. The stability conditions are established in the presence of passive and constant human and environment interaction forces with the master and slave manipulators. Finally, simulation results are presented to demonstrate the validity of the theoretical development of the proposed designs for real-time teleoperation applications.     

Generalized macroscopic traffic model with time delay

The effect of delay or reaction time on traffic flow dynamics has been investigated widely in the literature using microscopic traffic models. Recent studies using second-order Payne-type models have shown analytically that, on a macroscopic scale, time delay does not contribute to whether traffic instabilities occur. This paper will attempt to show that it all depends on the (macroscopic) model used for the analysis that delay does have effect on traffic instabilities or not. To this end, we will formulate a generalized (linear) stability condition for a second-order macroscopic model with delay and investigate analytically the effect of such delay on traffic instabilities in some specific macroscopic models. It is found that the choice of the equilibrium speed function in a (second order) macroscopic model will determine how delay affects such (linear) stability condition     

Arbitrary amplitude periodic solutions for parametrically excited systems with time delay

Periodic solutions for parametrically excited system under state feedback control with a time delay are investigated. Using the asymptotic perturbation method, two slow-flow equations for the amplitude and phase of the parametric resonance response are derived. Their fixed points correspond to limit cycles (phase-locked periodic solutions) for the starting system. In the system without control, periodic solutions (if any) exist only for fixed values of amplitude and phase and depend on the system parameters and excitation amplitude. In many cases, the amplitudes of periodic solutions do not correspond to the technical requirements. On the contrary, it is demonstrated that, if the vibration control terms are added, stable periodic solutions with arbitrarily chosen amplitude and phase can be accomplished. Therefore, an effective vibration control is possible if appropriate time delay and feedback gains are chosen.     

Exact solutions for some non-conservative hyperbolic systems

In this paper, we study initial value problem for some non-conservative hyperbolic systems of partial differential equations of first order. The first one is the Riemann problem for a model in elastodynamics and the second one the initial value problem for a system which is a generalization of the Hopf equation. The non-conservative products which appear in the equations do not make sense in the classical theory of distributions and are understood in the sense of Volpert (Math. USSR Sb. 2 (1967) 225). Following Lax (Comm. Pure Appl. Math. 10 (1957) 537) and Dal Maso et al. (J. Math. Pures Appl. 74 (1995) 483), we give an explicit solution for the Riemann problem for the elastodynamics equation. The coupled Hopf equation is studied using a generalization of the method of Hopf (Comm. Pure Appl. Math. 3 (1950) 201).     

时滞线性系统振动主动控制的滑移模态方法

直接从时滞微分方程求解控制律，对时滞线性系统振动主动控制的滑移模态方法进行了研究，并给出了控制具体实现过程。推导出的切换面和控制律表达式中，除了包含有当前的状态反馈外，还包含有前若干步控制的线性组合。算例结果显示，所提控制方法能够较好地控制系统的峰值响应。且能够保证控制系统的稳定性；若按无时滞控制设计对地滞系统进行振动控制，系统响应有可能出现发散。     

A frequency-domain method for solving linear time delay systems with constant coefficients

In an active control system, time delay will occur due to processes such as signal acquisition and transmission, calculation, and actuation. Time delay systems are usually described by delay differential equations (DDEs). Since it is hard to obtain an analytical solution to a DDE, numerical solution is of necessity. This paper presents a frequency-domain method that uses a truncated transfer function to solve a class of DDEs. The theoretical transfer function is the sum of infinite items expressed in terms of poles and residues. The basic idea is to select the dominant poles and residues to truncate the transfer function, thus ensuring the validity of the solution while improving the efficiency of calculation. Meanwhile, the guideline of selecting these poles and residues is provided. Numerical simulations of both stable and unstable delayed systems are given to verify the proposed method, and the results are presented and analysed in detail.     

Reduced-order fault detection filter design for switched nonlinear systems with time delay

This paper investigates the problem of reduced-order robust fault detection filter (RFDF) design for a class of switched nonlinear systems with time-varying delay. The nonlinearities are assumed to satisfy global Lipschitz conditions. By using a generalized form of observer-based fault detection filter as a residual generator, the problem is formulated in the framework of H _∞ filtering. Based on the average dwell time approach and the Lyapunov functional technique, a sufficient delay-dependent criterion on the existence of the RFDF is derived to ensure the exponential stability and a prescribed L ₂-gain bound of the residual error system. Furthermore, the parameters of an admissible filter are obtained from the solution of a convex optimization problem. A practical example is provided to illustrate the effectiveness of the proposed results.     

On a stationarity principle for non-conservative dynamical systems

A stationarity principle for non-conservative, holonomic dynamical systems is formulated. It is based on the notion of Gâteaux directional derivative. Its relation to the classical and variational principle with non-commutative variational rules is discussed.     

Synchrony and lag synchrony on a neuron model coupling with time delay

A neuron model of the Morris and Lecar form is investigated, which is composed of two individuals and is considered to be functioned by the gap junction coupling. When the level of the reversal potential in the calcium ion channel is small, neurons adjust their activities to the common asymptotic states. However, if we increase the level of the reversal voltage in the calcium ion channel, the exact synchrony firing of neurons is produced. Patterns of synchrony activity and the stability are observed to vary with the choice of time delay, which also enhances the multi-variety of the spike bursting firing rhythm. The lag synchrony of time trajectories of the voltage is illustrated near the boundary of the synchrony regime.     

Consensus of second-order multi-agent systems with nonlinear dynamics and time delay

This paper aims at investigating the second-order consensus problem of the multi-agent systems with nonlinear dynamics. Since it is more difficult to obtain the velocity information compared with the position information in practical application, a very simple sufficient condition for updating the coupling gain of the velocity information exchange between each agent is firstly derived to achieve asymptotic consensus. Furthermore, communication delay of each agent is considered for velocity information exchange. The velocity signal from a virtual leader is introduced to reach the second-order consensus. All the above fundamental consensus criteria are guaranteed base on algebraic graph theory, matrix theory, and Lyapunov stability method. Two simulation examples are provided to demonstrate the effectiveness of the analytical results. The results obtained in this paper can be easily applied to various cases, which can facilitate practical designs for the second-order consensus.     

Stability and bifurcation analysis in tri-neuron model with time delay

A simple delayed neural network model with three neurons is considered. By constructing suitable Lyapunov functions, we obtain sufficient delay-dependent criteria to ensure global asymptotical stability of the equilibrium of a tri-neuron network with single time delay. Local stability of the model is investigated by analyzing the associated characteristic equation. It is found that Hopf bifurcation occurs when the time delay varies and passes a sequence of critical values. The stability and direction of bifurcating periodic solution are determined by applying the normal form theory and the center manifold theorem. If the associated characteristic equation of linearized system evaluated at a critical point involves a repeated pair of pure imaginary eigenvalues, then the double Hopf bifurcation is also found to occur in this model. Our main attention will be paid to the double Hopf bifurcation associated with resonance. Some Numerical examples are finally given for justifying the theoretical results.     

Stability indicative function and its application to systems with time delay

Summary For investigating stability of linear systems with time delay, it is not sufficient to know critical values of such a parameter as time delay. In order to determine whether or not the system is stable for a given delay, the stability indicative function is introduced. This function is applied to second- and third-order linear systems with time delay and the stability regions of several cases are obtained. Some examples clearly show that the existence of time delay may make a stable system unstable or an unstable system stable. This phenomenon is explained from a theoretical point of view.

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Übersicht Die Ermittlung kritischer Totzeitwerte ist nicht ausreichend für Stabilitätsuntersuchungen von linearen Systemen mit Totzeiten, die durch Differential-Differenzen-Gleichungen beschrieben werden. Um festzustellen, ob ein System mit vorgegebener Totzeit stabil ist, kann man eine stabilitätsbestimmende Funktion einführen und untersuchen. Diese Funktion wird benutzt, um lineare Systeme zweiter und dritter Ordnung zu studieren und die Stabilitätsgebiete für verschiedene Fälle zu bestimmen. Beispiele zeigen, daß das Auftreten von Totzeiten stabile Systeme unstabil machen kann und umgekehrt unstabile Systeme stabilisieren kann.

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This research was supported by the Air Force Office of Scientific Research, Office of Aerospace Research, under Contract AF 49 (638) 1431.