Browsing by Subject "Lyapunov methods"
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Item Open Access Adaptive human pilot model for uncertain systems(IEEE, 2019-06) Tohidi, Shahab; Yıldız, YıldırayInspired by humans' ability to adapt to changing environments, this paper proposes an adaptive human model that mimics the crossover model despite input bandwidth deviations and plant uncertainties. The proposed human pilot model structure is based on the model reference adaptive control, and the adaptive laws are obtained using the Lyapunov-Krasovskii stability criteria applied to the overall closed loop system including the human pilot and the plant. The proposed model can be employed for human-in-the-Ioop stability and performance analyses with different controllers and plant types. A numerical example is used to demonstrate the effectiveness of the presented method.Item Open Access Chaotic behavior of gas bubble in non-Newtonian fluid: A numerical study(2013) Behnia, S.; Mobadersani F.; Yahyavi, M.; Rezavand, A.In the present paper, the nonlinear behavior of bubble growth under the excitation of an acoustic pressure pulse in non-Newtonian fluid domain has been investigated. Due to the importance of the bubble in the medical applications such as drug, protein or gene delivery, blood is assumed to be the reference fluid. Effects of viscoelasticity term, Deborah number, amplitude and frequency of the acoustic pulse are studied. We have studied the dynamic behavior of the radial response of bubble using Lyapunov exponent spectra, bifurcation diagrams, time series and phase diagram. A period-doubling bifurcation structure is predicted to occur for certain values of the effects of parameters. The results show that by increasing the elasticity of the fluid, the growth phenomenon will be unstable. On the other hand, when the frequency of the external pulse increases the bubble growth experiences more stable condition. It is shown that the results are in good agreement with the previous studies. © 2013 Springer Science+Business Media Dordrecht.Item Open Access Comment on "modeling the electrical conduction in DNA nanowires: Charge transfer and lattice fluctuation theories"(American Physical Society, 2016) Panahi, M.; Chitsazanmoghaddam, M.In a recent paper [S. Behnia and S. Fathizadeh, Phys. Rev. E 91, 022719 (2015)10.1103/PhysRevE.91.022719] an analytical approach is proposed for the investigation of the conductivity properties of DNA. The authors use mean Lyapunov exponent methods as the backbone of their approach and try to interpret properties of the system based on its behavior. Their interpretation regarding the change in nature of the mean Lyapunov exponent at the denaturation temperatures and discussions of stability and instability based on the mean Lyapunov exponent method are questioned. Moreover there is misunderstanding between mean Lyapunov exponent and Lyapunov exponent. © 2016 American Physical Society.Item Open Access Control and stabilization of a rotating flexible structure(Elsevier, 1994) Morgül, Ö.We consider a flexible beam clamped to a rigid base at one end and free at the other end. We assume that the rigid base rotates with a constant angular velocity and that the motion of the flexible beam takes place on a plane. To suppress the beam vibrations, we propose dynamic control laws for boundary control force and torque, both applied to the free end of the beam. We show that, under some conditions, one of which is the strict positive realness of the actuator transfer functions which generate the boundary control force and torque, the beam vibrations asymptotically decay to zero if the rigid base angular frequency is sufficiently small. Moreover, if the transfer functions are proper but not strictly proper, we show that the decay is exponential. We also give a bound on the constant angular velocity above which the system becomes unstable.Item Open Access Differential entropy analysis of the IDEA block cipher(Elsevier, 2014) Biryukov, A.; Nakahara, Jr. J.; Yıldırım H. M.This paper describes a new cryptanalytic technique that combines differential cryptanalysis with Shannon entropy. We call it differential entropy (DE). The objective is to exploit the non-uniform distribution of output differences from a given mapping as a distinguishing tool in cryptanalysis. Our preferred target is the IDEA block cipher, since we detected significantly low entropy at the output of its multiplication operation. We looked to further extend this entropy analysis to larger components and for a number of rounds. We present key-recovery attacks on up to 2.5-round IDEA in the single-key model and without weak-key assumptions. © 2013 Elsevier B.V. All rights reserved.Item Open Access Dynamic boundary control of the timoshenko beam(Pergamon Press, 1992) Morgül, Ö.We consider a clamped-free Timoshenko beam. To stabilize the beam vibrations, we propose a dynamic boundary control law applied at the free end of the beam. We prove that with the proposed control law, the beam vibrations uniformly and exponentially decay to zero. The proof uses a Lyapunov functional based on the energy of the system. © 1992.Item Open Access A dynamic control law for the wave equation(Elsevier, 1994) Morgül, Ö.We consider a system described by the one-dimensional linear wave equation in a bounded domain with appropriate boundary conditions. To stabilize the system, we propose a dynamic boundary controller applied at the free end of the system. The transfer function of the proposed controller is restricted to be a positive real function which could be strictly proper. We then show that, if the transfer function of the controller is strictly proper, then the resulting closed-loop system is asymptotically stable, and if proper but not strictly proper, then the resulting closed-loop system is exponentially stable.Item Open Access Effect of magnetic field on the radial pulsations of a gas bubble in a non-Newtonian fluid(Elsevier Ltd, 2015) Behnia, S.; Mobadersani F.; Yahyavi, M.; Rezavand, A.; Hoesinpour, N.; Ezzat, A.Dynamics of acoustically driven bubbles' radial oscillations in viscoelastic fluids are known as complex and uncontrollable phenomenon indicative of highly active nonlinear as well as chaotic behavior. In the present paper, the effect of magnetic fields on the non-linear behavior of bubble growth under the excitation of an acoustic pressure pulse in non-Newtonian fluid domain has been investigated. The constitutive equation [Upper-Convective Maxwell (UCM)] was used for modeling the rheological behaviors of the fluid. Due to the importance of the bubble in the medical applications such as drug, protein or gene delivery, blood is assumed to be the reference fluid. It was found that the magnetic field parameter (B) can be used for controlling the nonlinear radial oscillations of a spherical, acoustically forced gas bubble in nonlinear viscoelastic media. The relevance and importance of this control method to biomedical ultrasound applications were highlighted. We have studied the dynamic behavior of the radial response of the bubble before and after applying the magnetic field using Lyapunov exponent spectra, bifurcation diagrams and time series. A period-doubling bifurcation structure was predicted to occur for certain values of the parameters effects. Results indicated its strong impact on reducing the chaotic radial oscillations to regular ones. © 2015 Elsevier Ltd. All rights reserved.Item Open Access A model-based scheme for anticontrol of some chaotic systems(World Scientific Publishing, 2003) Morgül, Ö.We consider a model-based approach for the anticontrol of some continuous time systems. We assume the existence of a chaotic model in an appropriate form. By using a suitable input, we match the dynamics of the controlled system and the chaotic model. We show that controllable systems can be chaotifled with the proposed method. We give a procedure to generate such chaotic models. We also apply an observer-based synchronization scheme to compute the required input.Item Open Access Nonlinear PDE control of two-link flexible arm with nonuniform cross section(IEEE, 2006-06) Dog̃an, M.; Morgül, ÖmerA two-link flexible arm with nonuniform or variable cross-section by design will be considered based on an exact PDE model with boundary conditions. In this research, the nonlinear controller is used to achieve set-point regulation of the rigid modes as well as suppression of elastic vibrations. The control laws are obtained by energy based Lyapunov approach. © 2006 IEEE.Item Open Access Stability analysis of switched systems using Lyapunov-Krasovskii functionals(Elsevier, 2011) Çalişkan, S.Y.; Özbay, Hitay; Niculescu, S.-I.Piecewise Lyapunov-Razumikhin functions are previously used for obtaining a lower bound for the dwell time of the switched time delay systems under the assumption that each candidate system is delay dependently stable. In this work, using Lyapunov-Krasovskii functionals, a less conservative lower bound for the dwell time is obtained. Improvement in the dwell time is illustrated with an example. © 2011 IFAC.