Loading...
Search for:
chaos-theory
0.007 seconds
Total 87 records
Cryptoanalysis of CPSS Cryptosystem
, M.Sc. Thesis Sharif University of Technology ; Daneshgar, Amir (Supervisor)
Abstract
In this thesis we will present some aspects of discrete chaos and their usage in cryptography.We discuss a couple of regular attacks to chaotic cryptosystems. We will use this information to analyze the chaotic part of the CPSS cryptosystem(Daneshgar, Farzad, Khadem) and will show that the system has weak keys. Finally, we will show that how these weak keys can be generated in an algorithmic way
Prediction and Control of Chaos in Permanent Magnet Synchronous Machines
, M.Sc. Thesis Sharif University of Technology ; Tavazoei, Mohammad Saleh (Supervisor)
Abstract
Synchronous machines is one of the most popular machines in industry and in power plants. Because the dynamic of this machine is nonlinear, it can exhibit complex behaviors. In this project we have studied a special case in Permanent Magnet Synchronous Machines. A case in which speed of rotor, frequency, currents amplitude and voltages amplitude change in an irregular manner. This special case is called chaos. Chaos occurs for some specific values of parameters and inputs. In this study in the first step, we have tried to find the chaotic area of parameters of system (Prediction of chaos). Then in the next step, we have designed some controllers which can eliminate chaos in the system. The...
Studying of Chaotic Behavior in Some Classical and Quantum Systems
,
M.Sc. Thesis
Sharif University of Technology
;
Shafiee, Afshin
(Supervisor)
Abstract
Chaos is defined as an unpredictable and unrepeatable motion which has been observed in many classical systems such as unharmonic oscillators and turbulent currents in fluids. The common aspect of these types of motions is the deterministic nonlinear equation. On the other hand, quantum mechanics is a stochastic theory which is based on probabilistic description of quantum systems. These approaches lead to quantum chaos phenomenon which has been a controversial issue in the recent years. In the thesis, by studying the classical chaotic models such as kicked rotor, billiard model, excited hydrogen atom under microwave field and etc, we examine the existence of chaotic behavior in quantum...
Chaos control in continuous mode of T-AFM systems using nonlinear delayed feedback via sliding mode control
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings ; Volume 11 PART A , 2008 , Pages 201-208 ; ISBN: 079184305X ; Salaried, H ; Alasty, A ; Sharif University of Technology
Abstract
The taping mode Atomic Force Microscopic (T-AFM) can be assumed as a cantilever beam which its base is excited by a sinusoidal force and nonlinear potential interaction with sample. Thus the cantilever may cause chaotic behavior which decreases the performance of the sample topography. In order to modeling, using the galerkin method, the PDE equation is reduced to a single ODE equation which properly describing the continuous beam. In this paper a nonlinear delayed feedback control.is proposed to control.chaos in T-AFM system. Assuming model parameters uncertainties, the first order Unstable Periodic Orbits (UPOs) of the system is stabilized using the sliding nonlinear delayed feedback...
Unreliability of frequency-domain approximation in recognising chaos in fractional-order systems
, Article IET Signal Processing ; Volume 1, Issue 4 , December , 2007 , Pages 171-181 ; 17519675 (ISSN) ; Haeri, M ; Sharif University of Technology
2007
Abstract
The effects of using frequency-domain approximation in numerical simulation of fractional-order systems are analytically studied. The main aim in the study is to determine the number, location and stability property of the equilibriums in a fractional-order system and its frequency-based approximating counterpart. The comparison shows that the original fractional-order system and its frequency-based approximation may differ from each other in some or all issues considered in the study. Unfortunately, these differences can lead to wrong consequences in some special cases such as detecting chaos in the fractional-order systems. It is shown that using the frequency-domain approximation methods...
Chaotic motions and fractal basin boundaries in spring-pendulum system
, Article Nonlinear Analysis: Real World Applications ; Volume 7, Issue 1 , 2006 , Pages 81-95 ; 14681218 (ISSN) ; Shabani, R ; Sharif University of Technology
2006
Abstract
This study investigates the chaotic response of the spring-pendulum system. In this system besides of strange attractors, multiple regular attractors may co-exist for some values of system parameters, and it is important to study the global behavior of the system using the basin boundaries of the attractors. Here multiple scales method is used to distinguish the regions of stable and unstable attractors. Early studies show that there are unstable regions for the spring-pendulum system. In this study using bifurcation diagrams and Poincaré maps, it is shown that in some cases the response becomes quasi-periodic or chaotic for some deviations from external and internal resonance frequencies....
Comparison between different synchronization methods of identical chaotic systems
, Article Chaos, Solitons and Fractals ; Volume 29, Issue 4 , 2006 , Pages 1002-1022 ; 09600779 (ISSN) ; Khademian, B ; Sharif University of Technology
2006
Abstract
This paper studies and compares three nonadaptive (bidirectional, unidirectional, and sliding mode) and two adaptive (active control and backstepping) synchronization methods on the synchronizing of four pairs of identical chaotic systems (Chua's circuit, Rössler system, Lorenz system, and Lü system). Results from computer simulations are presented in order to illustrate the effectiveness of the methods and to compare them based on different criteria. © 2005 Elsevier Ltd. All rights reserved
Anti-synchronization of two different chaotic systems via active control
, Article Wec 05: Fourth World Enformatika Conference, Istanbul, 24 June 2005 through 26 June 2005 ; Volume 6 , 2005 , Pages 62-65 ; 9759845857 (ISBN); 9789759845858 (ISBN) ; Haeri, M ; Sharif University of Technology
2005
Abstract
This paper presents anti-synchronization of chaos between two different chaotic systems using active control method. The proposed technique is applied to achieve chaos antisynchronization for the Lu and Rössler dynamical systems. Numerical simulations are implemented to verify the results. COPYRIGHT © ENFORMATIKA
Nonlinear Dynamics of CNTs Conveying Fluid
, M.Sc. Thesis Sharif University of Technology ; Hosseini Kordkheyli, Ali (Supervisor)
Abstract
This dissertation is a survey on linear and nonlinear dynamics of single-walled carbon nanotubes (SWNTs) conveying fluid with different boundary conditions. A detailed review on Some of the most important studies on free vibration and instability of CNTs conveying fluid is done. By employing the nonlocal continuum field theory of Eringen and Von Karman nonlinear strains, an analytical model are developed. In linear analysis the natural frequencies and critical flow velocities are discussed. In nonlinear analysis effect of nonlocal parameter on Nonlinear dynamics of cantilevered SWNTs conveying fluid investigated by bifurcation diagram, phase plane and Poincare map. The numerical results...
Urban Transportation Network Design in Chaotic Conditions and Uncertainty in Travel Demand
, M.Sc. Thesis Sharif University of Technology ; Pourzahedi, Hossein (Supervisor)
Abstract
Transportation systems are dynamic and complex systems due to the interaction between human and non-human factors. In certain circumstances, the dynamics of traffic flow causes the transportation system fail to reach equilibrium and chaos will occur. In such cases, travel times vary daily and travel time reliability decreases. Moreover, these systems are continuously exposed to incidents that cause a high degree of uncertainty. So, it is necessary to enter such dynamics and uncertainty in the decision making models, such as network design. In this study a bilevel network design problem is defined with chaos and uncertainty taken into account. At the higher level problem, the optimization...
Comparison of Switching Stream Cipher Systems
, M.Sc. Thesis Sharif University of Technology ; Daneshgar, Amir (Supervisor)
Abstract
In this thesis, we analyze and compare switching and CPSP cryptography systems. CPSP is a dynamic system which can act as synchronized or self-synchronized stream cipher under specific conditions. To do the comparison, first we have a brief review of cryptography fundamentals like stream cipher systems, synchronized stream ciphers, and self-synchronized ones. Then, we consider chaos systems in general form and then we present their role in cryptography systems, and in continue by introducing switching cryptography systems and also CPSP cryptography systems, and analyzing their relation with self-synchronized stream ciphers, we do our statistical tests on them
Generalized synchronization of non-identical chaotic systems with minimum control effort
, Article 2008 International Conference on Control, Automation and Systems, ICCAS 2008, Seoul, 14 October 2008 through 17 October 2008 ; 2008 , Pages 2330-2333 ; 9788995003893 (ISBN) ; Haeri, M ; Sharif University of Technology
2008
Abstract
In synchronization of identical chaotic systems, the control cost would be optimal in the sense that it would be zero when the synchronization is occurred. Based on this idea, in synchronization of non-identical chaotic systems, we find a signal function added to states of the derive system so that it makes the dynamics of the drive system translated into dynamics of the response system. After synchronizing two systems using this function, states of the response system will be synchronized with the equivalent states and the control cost will be optimal similar to those in the identical synchronization. © ICROS
Chaos control in continuous mode of T-AFM systems using nonlinear delayed feedback via sliding mode control
, Article ASME International Mechanical Engineering Congress and Exposition, IMECE 2007, Seattle, WA, 11 November 2007 through 15 November 2007 ; Volume 11 PART A , 2008 , Pages 201-208 ; 079184305X (ISBN); 9780791843055 (ISBN) ; Salaried, H ; Alasty, A ; Sharif University of Technology
2008
Abstract
The taping mode Atomic Force Microscopic (T-AFM) can be assumed as a cantilever beam which its base is excited by a sinusoidal force and nonlinear potential interaction with sample. Thus the cantilever may cause chaotic behavior which decreases the performance of the sample topography. In order to modeling, using the galerkin method, the PDE equation is reduced to a single ODE equation which properly describing the continuous beam. In this paper a nonlinear delayed feedback control is proposed to control chaos in T-AFM system. Assuming model parameters uncertainties, the first order Unstable Periodic Orbits (UPOs) of the system is stabilized using the sliding nonlinear delayed feedback...
Looking for systematic approach to select chaos tests
, Article Applied Mathematics and Computation ; Volume 198, Issue 1 , 2008 , Pages 73-91 ; 00963003 (ISSN) ; Esfahani, M. S ; Nojumi, H ; Sharif University of Technology
2008
Abstract
This paper will consider the mathematical definition of chaos (in sense of Devaney) in order to select appropriate chaos tests. The tests chosen according to investigate the properties mentioned in the definition. In fact, these are prerequisites of chaoticity. Either it will be represented that "sensitivity dependence on initial conditions" is not equivalent to chaos, although some researchers considering it. Hence, it is implied that checking all of the properties mentioned in the definition are required to establish chaos. As our case study, some sample stocks were selected from Tehran Stock Exchange (TSE) and the chosen tests implemented on their returns time series. Incoming results...
Determination of active sliding mode controller parameters in synchronizing different chaotic systems
, Article Chaos, Solitons and Fractals ; Volume 32, Issue 2 , 2007 , Pages 583-591 ; 09600779 (ISSN) ; Haeri, M ; Sharif University of Technology
2007
Abstract
In this paper, we propose an algorithm to determine the active sliding mode controller parameters in synchronizing different chaotic systems. The resulted control parameters not only secure stability of the error systems, they can also be adjusted to obtain the desired rate of error convergence. Numerical simulations are presented to evaluate effectiveness of the proposed algorithm where the Lü system is implemented as the response (slave) system. © 2005 Elsevier Ltd. All rights reserved
Synchronizing different chaotic systems using active sliding mode control
, Article Chaos, Solitons and Fractals ; Volume 31, Issue 1 , 2007 , Pages 119-129 ; 09600779 (ISSN) ; Emadzadeh, A. A ; Sharif University of Technology
2007
Abstract
An active sliding mode controller is designed to synchronize three pairs of different chaotic systems (Lorenz-Chen, Chen-Lü, and Lü-Lorenz) in drive-response structure. It is assumed that the system parameters are known. The closed loop error dynamics depend on the linear part of the response systems and parameters of the controller. Therefore, the synchronization rate can be adjusted through these parameters. Analysis of the stability for the proposed method is derived based on the Lyapunov stability theorem. Finally, numerical results are presented to show the effectiveness of the proposed control technique. © 2005 Elsevier Ltd. All rights reserved
Chaos synchronization using sliding mode technique
, Article Wec 05: Fourth World Enformatika Conference, Istanbul, 24 June 2005 through 26 June 2005 ; Volume 6 , 2005 , Pages 159-162 ; 9759845857 (ISBN); 9789759845858 (ISBN) ; Haeri, M ; Sharif University of Technology
2005
Abstract
In this paper, an effective sliding mode design is applied to chaos synchronization. The proposed controller can make the states of two identical modified Chua's circuits globally asymptotically synchronized. Numerical results are provided to show the effectiveness and robustness of the proposed method. COPYRIGHT © ENFORMATIKA
Network Design to Alleviate Chaos in the Transportation Network Flows: Cases of Deterministic and Uncertain Supply
, M.Sc. Thesis Sharif University of Technology ; Pourzahedi, Hossein (Supervisor)
Abstract
Transportation networks are considered as complex systems, and in many cases they behave in such an irregular and unexpected manner. Such complexities cause problems in studying the behavior of these systems. An example of such complexities is chaos in the network flows. On the other hand, the behavior of these networks is highly affected by the incidents like accidents and bad weather. Such events affect the level of service and travel time reliability of the networks. In this research, a dynamical approach to traffic assignment has been chosen to model chaos and uncertainties in the network. By using this approach for modeling flow evolution, edge of chaos and uncertainty in supply and...
Chaotic Network Flows in an Evolutionary Model of Traffic Assignment Based on Speed and Density
, M.Sc. Thesis Sharif University of Technology ; Poorzahedy, Hossein (Supervisor)
Abstract
Chaotic Flow in transportation networks has been the subject of several studies. Evolutionary models have been employed to simulate traffic flows. This study takes advantage of an existing evolutionary model of traffic assignment to show that chaotic phenomena arise when the model’s driving force is speed or density, of traffic flow. It has been observed that drivers show higher sensitivity when the network is more loaded.
Investigation of Chaos in the Relativistic Restricted Three Body Problem
, M.Sc. Thesis Sharif University of Technology ; Pourtakdoust, Hossein (Supervisor)
Abstract
In this dissertation, initial conditions that cause chaotic movement in the relativistic restricted three body problem was obtained by the fast Lyapunov indicator and the time-frequency analysis. With general relativistic model, we can proceed with more accuracy in the design of stable orbit and this chaotic amplification effect could be used as a novel test of general relativity