Nonlinear Quadratic Systems Research Articles

Reduced-order observer design with unknown input for fractional order descriptor nonlinear systems

This paper investigates the observer design issues for the quadratic inner-bounded nonlinear descriptor fractional order systems. Considering the disturbances or inaccessible partial inputs, the order reduction of observer with unknown input is firstly implemented for effectively estimating the system state vectors. Then, for the purpose of the system conservatism reduction, the matrix [Formula: see text] and the matrix generalized inverse technique are applied to design the reduced-order observer, which can deal with unknown input with less restrictions of coefficient matrices. By using fractional order Lyapunov direct method, sufficient conditions can be obtained to ensure the existence of the designed observer. Finally, a fractional order electrical circuit is applied to demonstrate the applicability of the proposed approach.

Global Stabilization of Lotka–Volterra Systems With Interval Uncertainty

This paper deals with the stabilization of the feasible equilibrium point of a special class of nonlinear quadratic systems known as Lotka-Volterra (LV) systems, in the presence of interval uncertainty via a fixed linear state feedback (FLSF). It is well known that for a linear time-invariant system with interval uncertainty, stability at the vertices of a polytope implies stability in the interior of the whole polytope. It has been shown that this idea can be extended to examine the stability of LV systems in the presence of interval uncertainty, recently. In fact, it has been proved that in spite of nonlinear nature of the system, stability at a special vertex guarantees stability at all other vertices, which makes it easier to check the stability of the whole uncertain system. A subtle use of this fact in stabilization of interval LV systems via FLSF leads to a sufficient condition in terms of linear matrix inequalities. Also, the proposed approach is extended to a wider class of LV systems with time-varying and state-dependent system matrices. The efficiency of the proposed scheme is shown through numerical examples and simulations.

Methods of Linear Algebra in the Analysis of Certain Classes of Nonlinear Discretely Transformative Systems. I. Multiplicative Nonlinear Systems

The ideas and methods of pseudo-inversion of linear algebraic systems are propagated to problems of constructing the best root mean square approximation to solutions of nonlinear discretely transformative systems. The cases are considered where the form of nonlinearity is defined by a Cartesian product or iterative specification of linearly transformed input. Pseudo-solutions of quadratic nonlinear systems and systems of arbitrary order of nonlinearity are constructed and analyzed for accuracy and uniqueness.

Approximate nonlinear multiparameter inversion for multicomponent single and double P-wave scattering in isotropic elastic media

An asymptotic quadratic true-amplitude inversion method for isotropic elastic P waves is proposed to invert medium parameters. The multicomponent P-wave scattered wavefield is computed based on a forward relationship using second-order Born approximation and corresponding high-frequency ray theoretical methods. Within the local double scattering mechanism, the P-wave transmission factors are elaborately calculated, which results in the radiation pattern for P-wave scattering being a quadratic combination of the density and Lamé’s moduli perturbation parameters. We further express the elastic P-wave scattered wavefield in a form of generalized Radon transform. After introducing classical backprojection operators, we obtain an approximate solution of the inverse problem by solving a quadratic nonlinear system. Numerical tests with synthetic data computed by finite-differences scheme demonstrate that our quadratic inversion can accurately invert perturbation parameters for strong perturbations, compared with the P-wave single-scattering linear inversion method. Although our inversion strategy here is only syncretized with P-wave scattering, it can be extended to invert multicomponent elastic data containing both P- and S-wave information.

Optimal control of uncertain nonlinear quadratic systems

This paper addresses the problem of robust and optimal control for the class of nonlinear quadratic systems subject to norm-bounded parametric uncertainties and disturbances. By using an approach based on the guaranteed cost control theory, a technique is proposed to design a state feedback controller ensuring for the closed-loop system: (i) the local exponential stability of the zero equilibrium point; (ii) the inclusion of a given region into the domain of exponential stability of the equilibrium point; (iii) the satisfaction of a guaranteed level of performance, in terms of boundedness of some optimality indexes. In particular, a sufficient condition for the existence of a state feedback controller satisfying a prescribed integral–quadratic index is provided, followed by a sufficient condition for the existence of a state feedback controller satisfying a given L2-gain disturbance rejection constraint. By the proposed design procedures, the optimal control problems dealt with here can be efficiently solved as Linear Matrix Inequality (LMI) optimization problems.

Extending HOC-based methods for identifying the diagonal parameters of quadratic systems

In this paper, methods developed for the linear case of identifying the diagonal parameters of quadratic systems are extended to nonlinear case. Firstly, nonlinear relationships between model kernels and output cumulants are presented. Secondly, the relationship linking output cumulants and the coefficients of systems presented in the linear case, is extended to the general case of nonlinear quadratic systems identification. According to this concept, two nonlinear approaches are developed, the first use the fourth-order cumulants, and the second combined the third- and fourth-order cumulants. The numerical simulation results, for various signal to noise ratio (SNR) and 200 Monte Carlo runs, show that the proposed approaches achieve better accuracy, as compared with the related algorithm in the literature. Furthermore, the second algorithm is more precise in high noise environment (smallest \(\mathrm{SNR}=0\) dB), but the first algorithm more efficient in the weak noise environment case (highest SNR \(\ge \) 8 dB) comparing to using others methods.

Periodic and Chaotic Motion of a Time-Delayed Nonlinear System Under Two Coexisting Families of Additive Resonances

A time-delayed quadratic nonlinear mechanical system can exhibit two coexisting stable bifurcating solutions (SBSs) after two-to-one resonant Hopf bifurcations occur in the corresponding autonomous time-delayed system. One SBS is of small-amplitude and has the Hopf bifurcation frequencies (HBFs), while the other is of large-amplitude and contains the shifted Hopf bifurcation frequencies (the shifted HBFs). When the forcing frequency is tuned to be the sum of two HBFs or the sum of two shifted HBFs, two families of additive resonances can be induced in the forced response. The forced response under the additive resonance related to the HBFs can demonstrate periodic, quasi-periodic and chaotic motion. On the contrary, the forced response under the additive resonance associated with the shifted HBFs may exhibit period-three periodic motion and quasi-periodic motion. Bifurcation diagrams, time trajectories, frequency spectra, phase portraits and Poincaré sections are presented to show periodic, quasi-periodic, and chaotic motion of the time-delayed nonlinear system under the two families of additive resonances.

Results on finite‐time boundedness and finite‐time control of non‐linear quadratic systems subject to norm‐bounded disturbances

The present study investigates the synthesis of sufficient conditions for finite-time boundedness and stabilisation of non-linear quadratic systems with exogenous disturbances. For this purpose, the usefulness of combining the notion of annihilator with a version of Finsler's lemma has been investigated. The obtained design conditions are expressed in terms of a set of state-dependent linear matrix inequalities. Several numerical examples are given to show the effectiveness of the authors' approach.

State feedback design for nonlinear quadratic systems with randomly occurring actuator saturation

This paper is concerned with the problem of state feedback control for nonlinear quadratic systems with randomly occurring actuator saturation. The considered actuator saturation is assumed to occur in a random way, and the randomly occurring rates of the saturation are time-varying with known upper and lower bounds. By using the Lyapunov approach, a sufficient condition is given to guarantee that the closed-loop system is locally asymptotically stable in mean-square sense. The desired controller gain can be obtained in terms of the solutions to certain linear matrix inequalities. Finally, a simulation example is provided to show the effectiveness of the proposed control scheme.

On the stabilization of quadratic nonlinear systems

The aim of this paper is to study the problem of stabilization of nonlinear systems with a quadratic control. Under the assumption that a control Lyapunov function (CLF) is known, we derive necessary and sufficient conditions for the stabilization by continuous feedback controls explicitly computed. Illustrative examples are presented.

On frequency responses of period-1 motions to chaos in a periodically forced, time-delayed quadratic nonlinear system

In this paper, frequency responses of periodic motions to chaos in a periodically forced, damped, quadratic nonlinear oscillator are investigated through the finite Fourier series analysis of discrete solutions of periodic motions. The discrete solutions of periodic motions are obtained from mapping structures of discrete nodes, and the corresponding stability and bifurcation analysis of periodic motions are completed by the eigenvalue analysis of fixed points in discrete nonlinear dynamical systems. The frequency–amplitude characteristics for bifurcation trees of periodic motions to chaos are discussed, and the quantity levels of harmonic amplitudes for different harmonic orders are illustrated clearly. Numerical results of periodic motions are illustrated to show harmonic frequency responses effects on periodic motions.

Analytical Predictions of Period-1 motions to Chaos in a Periodically Driven Quadratic Nonlinear Oscillator with a Time-delay

In this paper, periodic motions in a periodically forced, damped, quadratic nonlinear oscillator with time-delayed displacement are analytically predicted through implicit discrete mappings of the corresponding differential equation. From mapping structures, bifurcation trees of periodic motions are achieved analytically, and the corresponding stability and bifurcation analysis are carried out through eigenvalue analysis. From the analytical prediction, numerical results of periodic motions are illustrated to verify such an analytical prediction. The semianalytical method gives the analytical prediction of the periodic motions matching very well with the approximate analytical solution for the time-delayed, quadratic nonlinear system. The method can also be applied to other time-delayed nonlinear systems.

Forced response of quadratic nonlinear oscillator: comparison of various approaches

The primary resonances of a quadratic nonlinear system under weak and strong external excitations are investigated with the emphasis on the comparison of different analytical approximate approaches. The forced vibration of snap-through mechanism is treated as a quadratic nonlinear oscillator. The Lindstedt-Poincare method, the multiple-scale method, the averaging method, and the harmonic balance method are used to determine the amplitude-frequency response relationships of the steady-state responses. It is demonstrated that the zeroth-order harmonic components should be accounted in the application of the harmonic balance method. The analytical approximations are compared with the numerical integrations in terms of the frequency response curves and the phase portraits. Supported by the numerical results, the harmonic balance method predicts that the quadratic nonlinearity bends the frequency response curves to the left. If the excitation amplitude is a second-order small quantity of the bookkeeping parameter, the steady-state responses predicted by the second-order approximation of the LindstedtPoincare method and the multiple-scale method agree qualitatively with the numerical results. It is demonstrated that the quadratic nonlinear system implies softening type nonlinearity for any quadratic nonlinear coefficients.

Finite‐time stochastic stabilisation of Markovian jump non‐linear quadratic systems with partially known transition probabilities

This paper studies the problems of the finite-time stochastic boundedness (FTSB) and stabilisation for a class of discrete-time Markovian jump non-linear quadratic systems with incomplete information on transition probabilities. It is shown that the FTSB of the system can be ensured under some sufficient conditions derived. As a corollary, some sufficient conditions of the finite-time stochastic stability for the non-linear quadratic systems without exogenous disturbance are also established. Based on these results, stabilising mode-dependent state feedback controllers are designed for Markovian jump non-linear quadratic systems with/without exogenous disturbance, respectively. Consequently, the finite-time stochastic stabilisation problem is resolved. Finally, a numerical example is presented to demonstrate the effectiveness of the proposed theory.

Modified Lindstedt-Poincaré method for obtaining resonance periodic solutions of nonlinear non-autonomous oscillators

A modified Lindstedt-Poincare (LP) method for obtaining the resonance periodic solutions of nonlinear non-autonomous vibration systems is proposed in this paper. In the modified method, nonlinear non-autonomous equations are converted into a group of linear ordinary differential equations by introducing a set of simple transformations. An approximate resonance solution for the original equation can then be obtained. The periodic solutions of primary, super-harmonic, sub-harmonic, zero-frequency and combination resonances can be solved effectively using the modified method. Some examples, such as damped cubic nonlinear systems under single and double frequency excitation, and damped quadratic nonlinear systems under double frequency excitation, are given to illustrate its convenience and effectiveness. Using the modified LP method, the first-order approximate solutions for each equation are obtained. By comparison, the modified method proposed in this paper produces the same results as the method of multiple scales.

Delay-Dependent Regional Stabilization of Nonlinear Quadratic Time-Delay Systems

This paper addresses the synthesis of delay-dependent local stabilizing controllers for, possibly open-loop unstable, nonlinear quadratic systems with a varying time-delay in the state. We develop methods for designing static nonlinear quadratic state feedback controllers that guarantee the local asymptotic stability of the closed-loop system zero equilibrium point in some polytopic region of the state-space while ensuring a region of stability inside this polytope. Control designs based on either the Razumikhin or the Lyapunov-Krasovskii approaches are considered. The proposed designs are delay-dependent and are formulated in terms of linear matrix inequalities. A numerical example is presented to illustrate the application of the stabilization methods.

Finite-Time Stability and Stabilization of Nonlinear Quadratic Systems with Jumps

This paper investigates the problems of finite-time stability and finite-time stabilization for nonlinear quadratic systems with jumps. The jump time sequences here are assumed to satisfy some given constraints. Based on Lyapunov function and a particular presentation of the quadratic terms, sufficient conditions for finite-time stability and finite-time stabilization are developed to a set containing bilinear matrix inequalities (BLIMs) and linear matrix inequalities (LMIs). Numerical examples are given to illustrate the effectiveness of the proposed methodology.

Local Stabilization of Markov Jump Nonlinear Quadratic Systems

This paper investigates the problem of local stabilization of Markov jump nonlinear quadratic systems. A method is presented for the synthesis of a static nonlinear quadratic state feedback control law that ensures the local exponential mean square stability of the zero equilibrium point of the closed-loop system in some polytopic region of the state-space with a guaranteed region of stability inside this polytope. The proposed control design is tailored in terms of linear matrix inequalities together with convex optimization to achieve an enlarged stability region. A numerical example is presented to illustrate the application of the stabilization method.

Analysis on a class of double-wing chaotic system and its control via linear matrix inequality

This paper presents a class of quadratic nonlinear system by introducing a linear term x of the third equation into the second equation of a chaotic system based on analyzing and studying some chaos. Using nonlinear dynamics method we analyze the steady, quasi-periodic and chaotic transition process when the system parameter varies. Experiment results are in good agreement with the Matlab simulation results. The Lyapunov exponent of the system with absolute value operation is larger than the original system, and the absolute value operation makes the wing of the original system doubled. Based on Takagi-Sugeno (T-S) fuzzy model and linear matrix inequality, a robust fuzzy controller is designed for the double-wing chaotic system being in asymptotical stability. Simulation results are provided to illustrate the effectiveness of the proposed scheme.

Controller design for nonlinear quadratic Markov jumping systems with input saturation

This paper deals with the controller design problem of nonlinear quadratic Markov jumping systems with input saturation. Both mode-dependent and mode-independent state feedback controllers are designed. By using the concept of domain of attraction in mean square sense, sufficient conditions for stochastic stabilisation for nonlinear quadratic systems are derived in terms of linear matrix inequalities. Certain existing results are improved. Simulation examples are presented to illustrate the effectiveness of the proposed technique.