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1
Olde, Scheper Tjeerd. "Chaos and information in dynamic neural networks." Thesis, Oxford Brookes University, 2002. https://radar.brookes.ac.uk/radar/items/e2a920c8-ff78-4ad6-adf3-8217d18c3b96/1/.
Повний текст джерелаАнотація:
This research attempts to identify and model ways to store information in dynamic, chaotic neural networks. The justification for this research is given by both biological as well as theoretical motivations [2, 27, 29, 46, 60, 107]. Firstly, there seems to be substantial support for the use of dynamic networks to study more complex and interesting behaviour. The artificial neural networks (ANN) have specific properties that define its order, such as size, type and function. Simply extending the ANN with complex non linear dynamics does not improve the memory performance of the network, it modifies the rate at which a global minimum may be located, if such .a state exists. Using non-linear differential equations may add more com plexity to the system and thereby increase the possible memory states. Secondly, even though chaos is generally undesirable, it has important properties that may be exploited to store and retrieve information [98]. These are the space filling, the possibility of control via delayed feedback, synchronization and the sensitive dependence on initial conditions. It is demonstrated in this thesis that by using delayed feedback, Unsta ble Periodic Orbits (UPO) may be stabilized to reduce the complexity of a chaotic system to n-periodic behaviour. This is a well known effect of de layed control in many types of chaotic models (e.g. Rossler equation), and the periodicity of the resulting orbit is determined by the model parameter as well as the delay (T) and the feedback strength (K) of the control func tion (F). Even though a theoretical infinite number of UPOs exist within a chaotic attractor only some can practically be stabilized. Furthermore, it is shown that input added to the delayed feedback controlled system allows different orbits to be stabilized. The addition of multiple delays changes the number and types of orbits that are available for stabilization. The use of synchronization between similar sets of chaotic systems may be used to target specific orbits.
2
Ruiter, Julia. "Practical Chaos: Using Dynamical Systems to Encrypt Audio and Visual Data." Scholarship @ Claremont, 2019. https://scholarship.claremont.edu/scripps_theses/1389.
Повний текст джерелаАнотація:
Although dynamical systems have a multitude of classical uses in physics and applied mathematics, new research in theoretical computer science shows that dynamical systems can also be used as a highly secure method of encrypting data. Properties of Lorenz and similar systems of equations yield chaotic outputs that are good at masking the underlying data both physically and mathematically. This paper aims to show how Lorenz systems may be used to encrypt text and image data, as well as provide a framework for how physical mechanisms may be built using these properties to transmit encrypted wave signals.
3
Gilbert, Francis Bertrand. "A culture of chaos: The politics of dynamic space." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187356.
Повний текст джерелаАнотація:
This discussion of chaos theory is concerned with two major issues. On the one hand, I explore what kind of knowledge is linked to chaos theory, and more specifically how as a science it informs the cultural discourses created by postindustrial societies. On the other hand, I probe chaos theory's potential as a model for challenging the existing conception of our world within the prevailing epistemologies of order and predictability. Both of these issues are addressed with in mind the broader framework and question concerning social relations, especially to the extent that those relations, in their spatial dimension, have become an object of scientific discourse. My approach to chaos theory is purposefully eclectic, conjoining the scientific with the social and the political. I believe that chaos theory points to a dynamic, intertextual, and multidimensional universe, and therefore, my interest lies in these connections, in bridging the various elements working together to create our contemporary, postmodern world. Science creates theories and images of nature that have been used to subordinate and control segments of the population through theories of race and sexuality. Thus, to recognize the existence of complexity and instability is to give away powerful conceptual means of political and social control, a strategy in which Western science has been an active participant.
4
Pérez, Alepuz Javier. "Dynamic visual servoing of robot manipulators: optimal framework with dynamic perceptibility and chaos compensation." Doctoral thesis, Universidad de Alicante, 2017. http://hdl.handle.net/10045/72433.
Повний текст джерелаАнотація:
This Thesis presents an optimal framework with dynamic perceptibility and chaos compensation for the control of robot manipulators. The fundamental objective of this framework is to obtain a variety of control laws for implementing dynamic visual servoing systems. In addition, this Thesis presents different contributions like the concept of dynamic perceptibility that is used to avoid image and robot singularities, the framework itself, that implements a delayed feedback controller for chaos compensation, and the extension of the framework for space robotic systems. Most of the image-based visual servoing systems implemented to date are indirect visual controllers in which the control action is joint or end-effector velocities to be applied to the robot in order to achieve a given desired location with respect to an observed object. The direct control of the motors for each joint of the robot is performed by the internal controller of the robot, which translates these velocities into joint torques. This Thesis mainly addresses the direct image-based visual servoing systems for trajectory tracking. In this case, in order to follow a given trajectory previously specified in the image space, the control action is defined as a vector of joint torques. The framework detailed in the Thesis allows for obtaining different kind of control laws for direct image-based visual servoing systems. It also integrates the dynamic perceptibility concept into the framework for avoiding image and robot singularities. Furthermore, a delayed feedback controller is also integrated so the chaotic behavior of redundant systems is compensated and thus, obtaining a smoother and efficient movement of the system. As an extension of the framework, the dynamics of free-based space systems is considered when determining the control laws, being able to determine trajectories for systems that do not have the base attached to anything. All these different steps are described throughout the Thesis. This Thesis describes in detail all the calculations for developing the visual servoing framework and the integration of the described optimization techniques. Simulation and experimental results are shown for each step, developing the controllers in an FPGA for further optimization, since this architecture allows to reduce latency and can be easily adapted for controlling of any joint robot by simply modifying certain modules that are hardware dependents. This architecture is modular and can be adapted to possible changes that may occur as a consequence of the incorporation or modification of a control driver, or even changes in the configuration of the data acquisition system or its control. This implementation, however, is not a contribution of this Thesis, but is necessary to briefly describe the architecture to understand the framework’s potential. These are the main objectives of the Thesis, and two robots where used for experimental results. A commercial industrial seven-degrees-of-freedom robot: Mitsubishi PA10, and another three-degrees-of-freedom robot. This last one’s design and implementation has been developed in the research group where the Thesis is written.
5
Zhang, Xiaoyan. "The dynamic behaviour of road traffic flow : stability or chaos?" Thesis, Middlesex University, 1995. http://eprints.mdx.ac.uk/10685/.
Повний текст джерелаАнотація:
The objective of this thesis is to investigate the dynamic behaviour of road traffic flow based on theoretical traffic models. Three traffic models are examined: the classical car-following model which describes the variations of speeds of cars and distances between the cars on a road link, the logit-based trip assignment model which describes the variations of traffic flows on road links in a road network, and the dynamic gravity trip distribution model which describes the variations of flows between O-D pairs in an O-D network. Some dynamic analyses have been made of the car-following model in the literature (Chandler et al., 1958, Herman et al., 1959, Disbro & Frame, 1990, and Kirby and Smith, 1991). The dynamic gravity model and the logit-based trip assignment model are both suggested by Dendrinos and Sonis (1990) without detailed analysis. There is virtually no previous dynamic analysis of trip distribution, although there are some dynamic considerations of trip assignment based on other assignment models (Smith, 1984 and Horowitz, 1984). In this thesis, the three traffic models are considered as dynamical systems. The variations of traffic characteristics are investigated in the context of nonlinear dynamics. Equilibria and oscillatory behaviour are found in all three traffic models; complicated behaviour including period doubling and chaos is found in the gravity model. Values of parameters for different types of behaviour in the models are given. Conditions for the stability of equilibria in the models are established. The stability analysis of the equilibrium in the car-following model is more general here than that in the literature (Chandler et al., 1958, Herman et al., 1959). Chaotic attractors found in the gravity model are characterized by Liapunov exponents and fractal dimension. The research in this thesis aims at understanding and predicting traffic behaviour under various conditions. Traffic systems may be monitored, based on these results, to achieve a stable equilibrium and to avoid instabilities and chaos.
6
Machekhin, Yu P. "Uncertainty measurement and dynamic system chaotical behaviour." Thesis, France, 2008. http://openarchive.nure.ua/handle/document/8734.
Повний текст джерелаАнотація:
Chaotic behaviour of nonlinear dynamic system as a mechanism of influence on uncertainty measurement are discussed. Based on the logistic equation as a mathematical models of measeurement uncertainty investigated as a function of state of dynamic system. In the case when dynamic chaos take place in system, uncertainty measurement are increasing and has anormal distribution.
7
Fisher, James Robert. "Stability analysis and control of stochastic dynamic systems using polynomial chaos." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2853.
Повний текст джерела
8
Taylor, Imogen T. F. "Control and synchronisation of coupled map lattices : interdisciplinary modelling of synchronised dynamic behaviour (insects in particular)." Thesis, University of Derby, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275687.
Повний текст джерела
9
Lee, Hyunwook. "A Polynomial Chaos Approach for Stochastic Modeling of Dynamic Wheel-Rail Friction." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/77195.
Повний текст джерелаАнотація:
Accurate estimation of the coefficient of friction (CoF) is essential to accurately modeling railroad dynamics, reducing maintenance costs, and increasing safety factors in rail operations. The assumption of a constant CoF is popularly used in simulation studies for ease of implementation, however many evidences demonstrated that CoF depends on various dynamic parameters and instantaneous conditions. In the real world, accurately estimating the CoF is difficult due to effects of various uncertain parameters, such as wheel and rail materials, rail roughness, contact patch, and so on. In this study, the newly developed 3-D nonlinear CoF model for the dry rail condition is introduced and the CoF variation is tested using this model with dynamic parameters estimated from the wheel-rail simulation model. In order to account for uncertain parameters, a stochastic analysis using the polynomial chaos (poly-chaos) theory is performed using the CoF and wheel-rail dynamics models.
The wheel-rail system at a right traction wheel is modeled as a mass-spring-damper system to simulate the basic wheel-rail dynamics and the CoF variation. The wheel-rail model accounts for wheel-rail contact, creepage effect, and creep force, among others. Simulations are performed at train speed of 20 m/s for 4 sec using rail roughness as a unique excitation source. The dynamic simulation has been performed for the deterministic model and for the stochastic model. The dynamics results of the deterministic model provide the starting point for the uncertainty analysis. Six uncertain parameters have been studied with an assumption of 50% uncertainty, intentionally imposed for testing extreme conditions. These parameters are: the maximum amplitude of rail roughness (MARR), the wheel lateral displacement, the track stiffness and damping coefficient, the sleeper distance, and semi-elliptical contact lengths. A symmetric beta distribution is assumed for these six uncertain parameters. The PDF of the CoF has been obtained for each uncertain parameter study, for combinations of two different uncertain parameters, and also for combinations of three different uncertain parameters.
The results from the deterministic model show acceptable vibration results for the body, the wheel, and the rail. The introduced CoF model demonstrates the nonlinear variation of the total CoF, the stick component, and the slip component. In addition, it captures the maximum CoF value (initial peak) successfully. The stochastic analysis results show that the total CoF PDF before 1 sec is dominantly affected by the stick phenomenon, while the slip dominantly influences the total CoF PDF after 1 sec. Although a symmetric distribution has been used for the uncertain parameters considered, the uncertainty in the response obtained displayed a skewed distribution for some of the situations investigated. The CoF PDFs obtained from simulations with combinations of two and three uncertain parameters have wider PDF ranges than those obtained for only one uncertain parameter.
FFT analysis using the rail displacement has been performed for the qualitative validation of the stochastic simulation result due to the absence of the experimental data. The FFT analysis of the deterministic rail displacement and of the stochastic rail displacement with uncertainties demonstrates consistent trends commensurate with loss of tractive efficiency, such as the bandwidth broadening, peak frequency shifts, and side band occurrence. Thus, the FFT analysis validates qualitatively that the stochastic modeling with various uncertainties is well executed and is reflecting observable, real-world results.
In conclusions, the development of an effective model which helps to understand the nonlinear nature of wheel-rail friction is critical to the progress of railroad component technology and rail safety. In the real world, accurate estimation of the CoF at the wheel-rail interface is very difficult since it is influenced by several uncertain parameters as illustrated in this study. Using the deterministic CoF value can cause underestimation or overestimation of CoF values leading to inaccurate decisions in the design of the wheel-rail system. Thus, the possible PDF ranges of the CoF according to key uncertain parameters must be considered in the design of the wheel-rail system.Ph. D.
10
ELPHICK, CHRISTIAN. "Formes normales, defauts topologiques et chaos spatial." Nice, 1987. http://www.theses.fr/1987NICE4160.
Повний текст джерелаАнотація:
La 1ere partie de cette these regroupe des travaux sur la reduction a la forme normale des equations differentielles ordinaires. Dans le 1er travail de cette partie une simple caracterisation globale des formes normales des champs vectoriels singuliers est donnee. Les autres travaux sont consacres a l'etude de la reduction a la forme normale quand on ajoute des perturbations periodiques ou stochastiques a nos sequations differentielles et dans le cas ou le systeme physique est decrit par un ensemble des variables de grassmann(systeme de fermi classique). Dans la 2eme partie on regroupe des travaux sur les formes normales dans un systeme etendu. En particulier on etudie la linearisation de l'equation non-lineaire de schroedinger pour un champ bosonique et le cas de la convection du type rayleigh-benard soumis a une modulation spatiale exterieure. Enfin, la 3eme partie est constituee par des travaux sur les defauts topologiques, les mecanismes de chaos spatial dans des systemes macroscopiques et sur une version de la theorie de melnikov utilisee pour trouver la dynamique de ces defauts
11
Smuts, Leon. "Relasies in die chaosteorie / Leon Smuts." Thesis, North-West University, 2005. http://hdl.handle.net/10394/778.
Повний текст джерелаАнотація:
The central purpose of this study is the integration of modem philosophical
thinking with different chaos theory principles and definitions to form relational
perspectives. Relations are used in different contexts to base the causes of
deterministic chaos (chaost) in the laws of nature which constitutes order. The
chaost-attractor is used as subjective conception to investigate the possibilities of
hidden order in a seemingly chaotic state of the objective reality.
Relevant definitions of the chaos theory were analysed methodically and
transcendentally with the aid of concepts of order and relations. Attention is given
to the broad associations and analogies from philosophy and other disciplines
which relate to the connectivity of objects to form systems. Subjective model
development was done which is used to consequentially analyse some
statements from published research which applied principles of chaost.
It is argued that: the intrinsic properties of objects determine the causality of
forces which bind objects to compose systems; a web of interactive bonds
functions subjective to laws of nature which determine whether a system is in a
state of order, chaost or real chaos; a dynamical transfer of many intrinsic and
asymmetric properties via internal bonds constitutes non-linear connectivity which
causes a sensitivity for initial conditions.
It is found that the chaost of the chaos theory is not the same as real, objective
chaos. The random-like evolution of a dynamic system is determined by the
occurrence of irregularities and uncertainties in its internal order. A web of
interactive bonds distribute small changes self-similar and scale-relevant. The
difficulty in describing and explaining the complex behaviour of composed entities
is simplified by the proposed web-chaost model.Thesis (M.A. (Philosophy))--North-West University, Potchefstroom Campus, 2006.
12
Yamasue, Kohei. "Studies on time-delayed feedback control of chaos and its application to dynamic force microscopy." 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136231.
Повний текст джерела
13
Tufaile, Alberto. "Estudo da formação de bolhas em líquidos viscosos (uma abordagem usando a teoria do caos)." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-02122013-190512/.
Повний текст джерелаАнотація:
Construímos um aparato experimental para estudar a dinâmica da formação de bolhas de ar em um bico submerso em uma solução de água/glicerina dentro de um tubo cilíndrico. O tempo entre bolhas sucessivas foi medido com um sistema laser/fotodiodo. Os resultados experimentais foram interpretados usando a Teoria do Caos. Foram observados bifurcações, comportamento caótico e saltos no regime periódico, em função da diminuição da vazão do ar soprado no bico. Além das transições dos regimes do borbulhamento, nós também observamos efeitos na dinâmica do borbulhamento quando aplicamos uma onda sonora sintonizada na frequência fundamental da coluna de ar acima do líquido onde as bolhas eram formadas. Em função da amplitude da onda sonora, nós obtivemos ciclo limite, bifurcação flip, comportamento caótico e sincronização do borbulhamento com a frequência da onda sonora. Utilizando caracterizações métrica e topológica em alguns atratores, pudemos relacioná-los com uma dinâmica tipo-Hénon cujo comportamento é um caso particular da dinâmica do mapa do círculo bidimensional. Observamos características presentes na dinâmica do mapa do círculo na formação das bolhas variando a amplitude da onda sonora, tais como transição para o Caos via quase-periodicidade, cascata de duplicações de período e Caos.We have constructed an experimental apparatus to study the dynamics of the formation of air bubbles in a nozzle submerged in a water/glycerin solution inside a cy1indrical tube. The time delay between successive bubbles was measured with a laser/photodiode system. The results were interpreted by means of Chaos Theory, and it was observed bífurcations, chaotic behavior, and sudden changes in a periodic regime as a function of decreasing air flow rate issued through the nozzle. Besides bubbling regime transitions, we also observed dynamical effects by applying a sound wave tuned to the fundamental frequency of the air column above the liquid of the bubble formation, As a function of the sound wave amplitude. we obtained limit cycle, flip bifurcation, chaotic behavior, and synchronization of the bubbling with the sound wave frequency. Applying metrical as well as topological characterization to some chaotic attractors, we could establish relation with a Hénon-like dynamics. The Hénon-like behavior is a particular case of the dissipative two-dimenslonal circle-rnap dynamics, and by varying the amplitude of a sound wave, we have observed featutes present in the circle map dynamics, such as transition from quasiperiodic to chaotic behavior, period doubling cascade, and Chaos.
14
Mercier, Emeric. "High-frequency nonlinear dynamics of a laser diode with phase-conjugate feedback." Thesis, CentraleSupélec, 2016. http://www.theses.fr/2016SUPL0010/document.
Повний текст джерелаАнотація:
Nous étudions l’influence d’une rétroaction optique à conjugaison de phase dans une diode laser. Ce type de rétroaction a été peu étudié et nous montrons ici qu’il donne des résultats intéressants, permettant de débloquer du contenu à haute fréquence. Cela pourrait mener à de meilleures performances dans des systèmes de génération de nombres aléatoires utilisant du chaos optiqueWe study the influence of phase-conjugate feedback in a laser diode. This type of feedback has not been studied a lot and yet we show here that it can give interesting results. It unlocks oscillations at high frequencies. This could lead to an improvement in the performance of random number generators based on optical chaos
15
Piassi, Viviane da Silva Mendes. "Comportamento complexo na formação de bolhas de ar em líquidos." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-05052008-173305/.
Повний текст джерелаАнотація:
Investigamos a dinâmica da formação de bolhas de ar em líquidos viscosos utilizando diferentes parâmetros de controle. Caracterizamos o sistema tomando o fluxo de ar injetado no sistema e o comprimento da mangueira que conecta o sistema de controle de fluxo com o bico injetor como parâmetros de controle. A mangueira corresponde a um elemento dissipativo do sistema. Identificamos rotas de adição de período com e sem a presença de comportamento caótico, regiões de travamento de freqüência e evidências de caos homoclínico. Construímos modelos matemáticos que descrevem bem os resultados experimentais. Com o mapa cúbico explicamos a forma de atratores observados em uma rota de adição de períodos. Com o modelo de mapa descontínuo explicitamos algumas propriedades da dinâmica da formação de bolhas como a biestabilidade de atratores. Desenvolvemos também um modelo baseado na dinâmica integra-edispara que nos levou a resultados condizentes com as propriedades dos mapas da família de Arnold. Desenvolvemos também uma nova técnica experimental para estudar o comportamento do sistema medindo a onda de pressão, gerada pelo borbulhamento na mangueira conectora.We have investigated the air bubble formation in viscous fluid with some control parameters. We have characterized the sistem using the air flow and the length of the hose that connects the air flow control system and the injector nozzle as control parameters. The hose corresponds to a system dissipative element. We have found period adding routes with and without chaotic behavior, frequency locking, and evidences of homoclinic chaos. We have elaborated mathematic models that emule the experimental data. With cubic model we have explained atractors observerd in a period adding route. With a discontinous model we have elucidated some bubble formation dynamic properties as bistability. We have also developed intergrate-and-fire like model that have led us to results in accordance with the maps properties of Arnold family. We also developed a new experimental technique to study the sistem behavior by measuring the bubbling pressure wave inside the hose.
16
Mulani, Sameer B. "Uncertainty Quantification in Dynamic Problems With Large Uncertainties." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/28617.
Повний текст джерелаАнотація:
This dissertation investigates uncertainty quantification in dynamic problems. The Advanced Mean Value (AMV) method is used to calculate probabilistic sound power and the sensitivity of elastically supported panels with small uncertainty (coefficient of variation). Sound power calculations are done using Finite Element Method (FEM) and Boundary Element Method (BEM). The sensitivities of the sound power are calculated through direct differentiation of the FEM/BEM/AMV equations. The results are compared with Monte Carlo simulation (MCS). An improved method is developed using AMV, metamodel, and MCS. This new technique is applied to calculate sound power of a composite panel using FEM and Rayleigh Integral. The proposed methodology shows considerable improvement both in terms of accuracy and computational efficiency.
In systems with large uncertainties, the above approach does not work. Two Spectral Stochastic Finite Element Method (SSFEM) algorithms are developed to solve stochastic eigenvalue problems using Polynomial chaos. Presently, the approaches are restricted to problems with real and distinct eigenvalues. In both the approaches, the system uncertainties are modeled by Wiener-Askey orthogonal polynomial functions. Galerkin projection is applied in the probability space to minimize the weighted residual of the error of the governing equation. First algorithm is based on inverse iteration method. A modification is suggested to calculate higher eigenvalues and eigenvectors. The above algorithm is applied to both discrete and continuous systems. In continuous systems, the uncertainties are modeled as Gaussian processes using Karhunen-Loeve (KL) expansion. Second algorithm is based on implicit polynomial iteration method. This algorithm is found to be more efficient when applied to discrete systems. However, the application of the algorithm to continuous systems results in ill-conditioned system matrices, which seriously limit its application.
Lastly, an algorithm to find the basis random variables of KL expansion for non-Gaussian processes, is developed. The basis random variables are obtained via nonlinear transformation of marginal cumulative distribution function using standard deviation. Results are obtained for three known skewed distributions, Log-Normal, Beta, and Exponential. In all the cases, it is found that the proposed algorithm matches very well with the known solutions and can be applied to solve non-Gaussian process using SSFEM.Ph. D.
17
Xu, Yijun. "Uncertainty Quantification, State and Parameter Estimation in Power Systems Using Polynomial Chaos Based Methods." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/97876.
Повний текст джерелаАнотація:
It is a well-known fact that a power system contains many sources of uncertainties. These uncertainties coming from the loads, the renewables, the model and the measurement, etc, are influencing the steady state and dynamic response of the power system.
Facing this problem, traditional methods, such as the Monte Carlo method and the Perturbation method, are either too time consuming or suffering from the strong nonlinearity in the system.
To solve these, this Dissertation will mainly focus on developing the polynomial chaos based method to replace the traditional ones. Using it, the uncertainties from the
model and the measurement are propagated through the polynomial chaos bases at a set of collocation points. The approximated polynomial chaos coefficients contain the statistical information. The method can greatly accelerate the calculation efficiency while not losing the accuracy, even when the system is highly stressed.
In this dissertation, both the forward problem and the inverse problem of uncertainty quantification will be discussed. The forward problems will include the probabilistic power flow problem and statistical power system dynamic simulations. The generalized polynomial chaos method, the adaptive polynomial chaos-ANOVA method and the multi-element polynomial chaos method will be introduced and compared. The case studies show that the proposed methods have great performances in the statistical analysis of the large-scale power systems. The inverse problems will include the state and parameter estimation problem. A novel polynomial-chaos-based Kalman filter will be proposed. The comparison studies with other traditional Kalman filter demonstrate the good performances of the proposed Kalman filter. We further explored the area dynamic parameter estimation problem under the Bayesian inference framework. The polynomial-chaos-expansions are treated as the response surface of the full dynamic solver. Combing with hybrid Markov chain Monte Carlo method, the proposed method yields very high estimation accuracy while greatly reducing the computing time.
For both the forward problem and the inverse problems, the polynomial chaos based methods haven shown great advantages over the traditional methods. These computational techniques can improve the efficiency and accuracy in power system planning, guarantee the rationality and reliability in power system operations, and, finally, speed up the power system dynamic security assessment.PHD
18
Norin, Anna. "Worker Safety and Market Dynamics." Licentiate thesis, Umeå universitet, Nationalekonomi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-83039.
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19
Kaygisiz, Huseyin Burak. "Intelligent Methods For Dynamic Analysis And Navigation Of Autonomous Land Vehicles." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/2/12605112/index.pdf.
Повний текст джерелаАнотація:
Autonomous land vehicles (ALVs) have received considerable attention after their introduction into military and commercial applications. ALVs still stand as a challenging research topic. One of the main problems arising in ALV operations is the navigation accuracy while the other is the dynamic effects of road irregularities which may prevent the vehicle and its cargo to function properly. In this thesis, we propose intelligent solutions to these two basic problems of ALV. First, an intelligent method is proposed to enhance the performance of a coupled global positioning/inertial navigation system (GPS/INS) for land navigation applications during the GPS signal loss. Our method is based on using an artificial neural network (ANN) to intelligently aid the GPS/INS coupled navigation system in the absence of GPS signals. The proposed enhanced GPS/INS is used in the dynamic environment of a tour of an autonomous van and we provide the results here. GPS/INS+ANN system performance is thus demonstrated with the land trials. Secondly, our work focuses on the identification and enlargement of the stability region of the ALV. In this thesis, the domain of attraction of the ALV is found to be patched by chaotic and regular regions with chaotic boundaries which are extracted using novel technique of cell mapping equipped with measures of fractal dimension and rough sets. All image cells in the cellular state space, with their individual fractal dimension are classified as being members of lower approximation (surely stable), upper approximation (possibly stable) or boundary region using rough set theory. The obtained rough set with fractal dimension as its attribute is used to model the uncertainty of the regular regions. This uncertainty is then smoothed by a reinforcement learning algorithm in order to enlarge regular regions that are used for chassis control, critical in ALV in preventing vibration damages that can harm the payload. Hence, we will make ALV work in the largest safe area in dynamical sense and prevent the vehicle and its cargo.
20
Pinto, Rafael Soares 1986. "Caos quântico relativístico." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/278472.
Повний текст джерелаАнотація:
Orientadores: Patrício Aníbal Letelier Sotomayor, Marcus Aloízio Martinez de AguiarDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin
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Resumo: Nesta dissertação analisamos bilhares usando a teoria da relatividade especial, tanto classicamente quanto quanticamente. Inicialmente revisamos a teoria de bilhares clássicos, com ênfase em como se dá sua evolução no tempo. Então estudamos a existência (ou não) de aceleração de Fermi em bilhares forçados: bilhares onde a parede se move e, quando a partícula colide, ela pode ganhar ou perder energia. Estudamos alguns exemplos de bilhares, regulares e caóticos, na dinâmica relativística procurando quais condições são necessárias para que exista aceleração de Fermi relativística Concentramos-nos então no estudo de bilhares quânticos. Após uma revisão dos conceitos básicos, estudamos o método da integral de contorno para o cálculo do espectro do bilhar e analisamos suas propriedades estatísticas, tanto para o caso não relativístico (a equação de Schroedinger) quanto para o caso relativístico, o bilhar de Dirac, introduzido por Berry e Mondragon
Abstract: In this dissertation we analyze billiards using the theory of special relativity, both in the classical and quantum versions. First we review classical billiards, with emphasis in its time evolution. Then we study the existence (or lack of) Fermi acceleration in driven billiards, billiards where the walls are moving and, when the particle collides, it can gain or lose energy. We studied some examples, regular and chaotic ones, in the relativistic dynamics, and analyzed the necessary conditions for the existence of relativistic Fermi acceleration. We focus then on quantum billiards. After a brief review of basic concepts, we study the boundary integral method for numerical evaluation of the billiard spectra and analyze its statistical properties, for the non-relativistic case (the Schroedinger equation) and the relativistic, the Dirac billiards introduced by Berry and Mondragon
Mestrado
Física Geral
Mestre em Física
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Nechak, Lyes. "Approches robustes du comportement dynamique des systèmes non linéaires : Application aux systèmes frottants." Phd thesis, Université de Haute Alsace - Mulhouse, 2011. http://tel.archives-ouvertes.fr/tel-00708215.
Повний текст джерелаАнотація:
Cette thèse traite de l'analyse robuste du comportement dynamique des systèmes frottants. Ces derniers constituent une classe particulière des systèmes non linéaires et sont caractérisés par des comportements dynamiques très sensibles aux variations des paramètres de conception en particulier aux dispersions des lois de frottement. Cette sensibilité se traduit par des variations qualitatives importantes du comportement dynamique (stabilité, niveaux vibratoire) qui peuvent alors affecter négativement les performances des systèmes frottants. Il est ainsi important, voire indispensable, de pouvoir tenir compte de la dispersion des lois de frottement dans l'étude et l'analyse du comportement dynamique des systèmes frottants afin d'en garantir la robustesse et, dans une perspective plus générale, d'asseoir une démarche de conception robuste des systèmes frottants. Des méthodes spectrales basées sur le concept du chaos polynomial sont proposées dans cette thèse pour traiter de l'analyse robuste du comportement dynamique des systèmes frottants. Pouvant modéliser les fonctions et processus stochastiques, ces méthodes sont adaptées au problème en particulier à l'analyse de la stabilité et à la prédiction des niveaux vibratoires en tenant compte de la dispersion des lois de frottement. Différentes procédures sont proposées et développées pour traiter de ces deux questions. Une efficacité importante a été illustrée à travers l'évaluation des différentes méthodes proposées (chaos polynomial généralisé, chaos polynomial multi-éléments, chaos de Wiener-Haar) en les appliquant sur un exemple de système frottant. En effet, il est montré que ces méthodes offrent une alternative très intéressante à la méthode prohibitive, mais référentielle, de Monte Carlo puisque, pour des niveaux de précision et de confiance similaires, le coût en nombre, en volume et nécessairement en temps de calcul occasionné par les méthodes spectrales sur les différentes analyses (de la stabilité et des niveaux vibratoire) est largement inférieur à celui requis par la technique de Monte Carlo.
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Candido, Renato. "A questão da equalização em sistemas de comunicação que utilizam sinais caóticos." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-16112015-160224/.
Повний текст джерелаАнотація:
Nas últimas décadas, vários sistemas de comunicação baseados em sincronismo caótico têm sido propostos na literatura como alternativa a sistemas de espalhamento espectral que melhoram o nível de privacidade na transmissão da mensagem. No entanto, devido à falta de robustez do sincronismo caótico, um pequeno nível de ruído ou uma simples imperfeição no canal é suficiente para impedir a comunicação. Neste trabalho, equalizadores adaptativos são utilizados para permitir a comunicação em um sistema de comunicação baseado em caos quando a resposta em frequência do canal não é ideal. São propostos algoritmos de equalização baseados em versões modificadas do algoritmo normalized least-mean-squares para a versão de tempo discreto do sistema de comunicação baseado no modelo de sincronismo de Wu e Chua. Para esses algoritmos, é calculado o intervalo para a escolha do passo de adaptação para evitar a divergência. Como geradores de sinais caóticos (GSC), são utilizados os mapas de Hénon e de Ikeda e, para a codificação da mensagem, são consideradas duas funções, sendo uma baseada na multiplicação da mensagem por um dos estados do GSC e a outra baseada na soma da mensagem com um dos estados do GSC. Os resultados de simulação indicam que os algoritmos propostos são capazes de equalizar o canal de comunicação e permitir o sincronismo caótico em diferente cenários.In the last decades, many communication systems applying synchronism of chaotic systems have been proposed as an alternative spread spectrum modulation that improves the level of privacy in data transmission. However, due to the lack of robustness of chaos synchronization, even a low level of noise or minor channel imperfections are enough to hinder communication. In this work, adaptive equalizers are used to enable chaotic synchronization when the communication channel is not ideal. Adaptive equalization algorithms are proposed based on a modified version of the normalized least-mean-squares algorithm, considering the discrete-time version of the communication system based on Wu and Chuas synchronization model. For these algorithms, the interval for the choice of the step-size is computed, in order to avoid divergence. The Hénon and the Ikeda maps are used as chaotic signal generators (CSG) and two functions are considered to encode the message, one based on the multiplication of the message by one of the states of the CSG and the other based on the addition of the message to one of the states of the CSG. Simulation results show that the proposed algorithms can successfully equalize the channel in different scenarios.
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Vallgren, Andreas. "Dynamic properties of two-dimensional and quasi-geostrophic turbulence." Doctoral thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25712.
Повний текст джерелаАнотація:
Two codes have been developed and implemented for use on massively parallelsuper computers to simulate two-dimensional and quasi-geostrophic turbulence.The codes have been found to scale well with increasing resolution and width ofthe simulations. This has allowed for the highest resolution simulations of twodimensionaland quasi-geostrophic turbulence so far reported in the literature.The direct numerical simulations have focused on the statistical characteristicsof turbulent cascades of energy and enstrophy, the role of coherent vorticesand departures from universal scaling laws, theoretized more than 40 yearsago. In particular, the investigations have concerned the enstrophy and energycascades in forced and decaying two-dimensional turbulence. Furthermore, theapplicability of Charney’s hypotheses on quasi-geostrophic turbulence has beentested. The results have shed light on the flow evolution at very large Reynoldsnumbers. The most important results are the robustness of the enstrophycascade in forced and decaying two-dimensional turbulence, the sensitivity toan infrared Reynolds number in the spectral scaling of the energy spectrumin the inverse energy cascade range, and the validation of Charney’s predictionson the dynamics of quasi-geostrophic turbulence. It has also been shownthat the scaling of the energy spectrum in the enstrophy cascade is insensitiveto intermittency in higher order statistics, but that corrections apply to the”universal” Batchelor-Kraichnan constant, as a consequence of large-scale dissipationanomalies following a classical remark by Landau (Landau & Lifshitz1987). Another finding is that the inverse energy cascade is maintained bynonlocal triad interactions, which is in contradiction with the classical localityassumption.QC 20101029
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Erasmus, Gert Botha. "Stochastic models of steady state and dynamic operation of systems of congestion." Thesis, Pretoria : [s.n.], 2006. http://hdl.handle.net/2263/28814.
Повний текст джерелаАнотація:
(i) The thesis sets out to address the problematic phenomenon of Systems of Congestion via Basic Queueing Theory. The theory, and its application in practice, appears to be a field of study which is the common domain of “theorists” and “practitioners”. (ii) This professional dichotomy has come about due to diverging interests in that one group is mainly interested in the purity of mathematical modelling, and the other group is motivated to use modelling, which conveniently employs applications oriented solutions. (iii) The schism between the groups has been accentuated by the “practitioners” who in addition to having an interest in steady state system behaviour make use of methods of modelling of the transient operation of complex Systems of Congestion. (iv) At the outset the thesis demonstrates how closed form solutions are obtained for steady state and transient state operation of a selection of Systems of Congestion. The attendant mathematical derivations are elegant and intricate. (v) Having revealed the limited utility of closed-form solutions the thesis proceeds to investigate the feasibility of using dynamical systems theory to study the transient behaviour of complex Systems of Congestion. (vi) The creation of Chaos Theory in recent decades suggests that it may be employed as a useful tool in analysing Systems of Congestion. Iterative Chaos Theory methods of orbit generation for complete Systems of Congestion are therefore examined. The use of such orbit generation methods is found to be satisfactory for simple Systems of Congestion. More than a perfunctory knowledge of chaos mapping is however required. The simplicity of modelling is emphasized. (vii) Based on the results of benchmarking the creation of dynamic system orbits against an existing simulation method, the research advances to modelling of the transient operation of complex systems. Once again the iterative method of orbit generation displays the ease of modelling while simultaneously unfolding system dynamics graphically. (viii) One may hopefully contend that a tool of eminent utility has been developed to aid practitioners in studying and optimizing Systems of Congestion.Thesis (PhD (Industrial Engineering))--University of Pretoria, 2006.
Industrial and Systems Engineering
Unrestricted
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Ferro, Luciano [UNESP]. "Modelo do bulbo olfativo baseado em redes neurais recorrentes." Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/91938.
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ferro_l_me_rcla.pdf: 3692564 bytes, checksum: d242c88fdfc24677645cf32fa498c692 (MD5)Neste trabalho construímos modelos de redes neurais artificiais recorrentes com dois, com quatro, com seis e com oito neurônios na tentativa de simular computacionalmente como os neurônios receptores olfativos dos vertebrados, em especial dos seres humanos, conseguem identificar e reconhecer as diferentes moléculas odoríferas (ou odorantes) transportadas pelo ar. Para isso, usamos uma rede que evolui de um sistema dinâmico caótico, na ausência de odorantes, para o não-caótico, quando do reconhecimento de um odor constituído, no máximo, de até três odorantes.
We built models of recurrent artificial neural networks with two, four, six and eight neurons in order to simulate, using computational simulation, the way vertebrate s olfactory neurons, in special the humans, identify and recognize different odoriferous molecules (or odorants) in the air. For that purpose, we used a network that evolves from a chaotic dynamic system, in the absence of odorants, to the non-chaotic, when it recognizes an odor that is made of, at most, three odorants.
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Коваль, О. В. "Моделювання процесу пригнічення хаосу у нелінійних системах". Master's thesis, Сумський державний університет, 2019. http://essuir.sumdu.edu.ua/handle/123456789/75664.
Повний текст джерелаАнотація:
Розроблено та практично застосувано метод математичного моделювання для дослідження та керування хаотичними коливаннями в детермінованих динамічних системах, а також одержано істотно нові результати при яких можливе перетворення хаотичного руху в стабільний. Розроблену математична модель реалізовано у формі програмного забезпечення.
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Garms, Marco Antonio. "Modelagem fuzzy para fixação de trajetórias em sistemas caóticos." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3141/tde-10012008-100351/.
Повний текст джерелаАнотація:
Neste trabalho foi realizado um mapeamento de ferramentas analíticas para representação e tratamento computacional de Sistemas Fuzzy. Este mapeamento evidenciou a existência de relações e a adequação do uso da Teoria Fuzzy na construção de modelos para a solução de problemas envolvendo Sistemas Dinâmicos e, em particular, de Sistemas Dinâmicos Caóticos. Propôs-se uma diferenciação entre dois tipos de Sistemas Dinâmicos Fuzzy (SDF\'s) - os Sistemas Dinâmicos Fuzzy Intrínsecos (SDFI\'s) e os Sistemas Dinâmicos Fuzzy Extrínsecos (SDFE\'s). Foram utilizados SDFE\'s na modelagem Fuzzy para a solução de problemas de fixação de trajetórias em sistemas caóticos. Foram desenvolvidos Estudos de Caso que permitiram verificar, por meio de simulações em bilhares e testes em circuito de Chua (este último implementado em protótipo físico) a adequação do uso desta técnica na solução destes problemas. No desenvolvimento da Tese foram obtidas as seguintes realizações relacionadas ao circuito de Chua (CCH): Tratamento computacional sobre circuito real; Utilização de um conversor analógico-digital de oito bits seguido por filtro passa-baixas para compensar a baixa resolução na leitura dos sinais; Utilização de circuito girador para implementar o indutor do CCH; Proposta e realização de um circuito inédito para definir o resistor de controle, via porta paralela do PC, de modo simples e de fácil reprodução. Com relação aos bilhares foram obtidas as seguintes realizações: Definição de um novo tipo de bilhar (Bilhar Newtoniano de Garms & Andrade); Desenvolvimento da análise detalhada das equações de simulação dos bilhares empregados nos Estudos de Caso. Ao rediscutir-se a Lógica Seqüencial Fuzzy definiu-se e desenvolveu-se, por meio da aplicação de realimentação em Circuitos Seqüenciais Fuzzy nos Sistemas Dinâmicos, um Astável Fuzzy (oscilações não-periódicas), o qual exemplifica um SDFI. Finalmente realizaram-se algumas interpretações da Física pela Teoria Fuzzy, utilizando-se o conceito de SDFI\'s.A mapping of analytical tools for representation and computational treatment of Fuzzy Systems was made in this thesis. This mapping evidenced the existence of relations and the adequacy of the use of the Fuzzy Theory in the models construction for the problems solution involving dynamic systems e, in particular, of chaotic systems. A differentiation was considered about two types of Fuzzy Dynamic Systems - the Intrinsic Fuzzy Dynamic Systems (IFDS) and the Extrinsic Fuzzy Dynamic Systems (EFDS). The EFDS in the Fuzzy modeling is used for the problems solution of trajectories setting in chaotic systems. Case Studies had been developed that allow to verify, by means of simulation in billiards and tests in circuit of Chua (implemented in physical prototype), the adequacy of the use of this strategy in the solution of these problems. Related with Chua circuit, can be mentioned the following achievements: Computational treatment on real circuit; Use of a 8-bits AD converter followed by lowpass filter to compensate this low resolution signals reading; Use of gyrator circuit to implement the inductor used in this circuit; Proposal and accomplishment of a circuit to define the control resistor, via PC parallel port, of simple reproduction. Related with billiards, the following achievements are mentioned: Definition of a new billiard - Garms & Andrade Newtonian Billiard; Development of detailed equations of the simulations billiards analysis. When discussing again the Sequential Logic Fuzzy, is defined and developed, by means of the application of feedback in Sequential Circuits Fuzzy in the Dynamic Systems, an Astable Fuzzy (non-periodic oscillations), which exemplifies an IFDS. Finally, some interpretations of the Physics for the Fuzzy Theory are also presented with the use of the IFDS concept.
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Outa, Roberto. "Supressão do movimento caótico de um rotor dinâmico utilizando o controle linear ótimo." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152241.
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O objetivo deste trabalho é a elaboração de um controlador linear ótimo, que possa reduzir um sinal caótico do rotor dinâmico, em um sinal controlado. Para se obter o resultado esperado foi necessário desenvolver atividades ligadas à caracterização do experimento; análise de estabilidade pelo método de Lyapunov; aplicação da função de Lyapunov; análise da sensibilidade das condições iniciais utilizando o expoente de Lyapunov; desenvolvimento do projeto do controle ótimo linear. O resultado final mostra o desempenho da aplicação do controle linear ótimo no sinal caótico, cujo sinal foi reduzido para um comportamento estável e controlado.
The aim of this work is the elaboration of an optimal linear controller that can reduce a chaotic dynamic rotor signal in a controlled signal. To obtain the expected result, it was necessary to develop activities related to the characterization of the experiment; stability analysis by the Lyapunov method; application of the Lyapunov function; sensitivity analysis of the initial conditions by the Lyapunov exponent; development of linear optimum control. The result shows the performance of the optimal linear control in the chaotic signal, whose signal was reduced to a stable and controlled behavior.
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Wilson, Mark M. J. "Supply chains behaving badly : a dynamic model of inter-organisational supply chain exchange behaviour under rational, relational and chaotic paradigms." Phd thesis, Lincoln University. Commerce Division, 2006. http://theses.lincoln.ac.nz/public/adt-NZLIU20080229.095848/.
Повний текст джерелаАнотація:
Supply chain exchange relationships are complex and sometimes chaotic sociological and organisational phenomena. This complexity is compounded by the boundary spanning necessity of forming supply chain partnerships that are further exacerbated by goal divergence and asymmetric information. One of the main questions for consideration is how these dyadic exchange relationships are maintained and develop over time in response to the various channel behaviours of the actors (the buyer and seller)? In particular, exchange relationships are theorised to be sensitive in some degree to attempts at economic appropriation, and conversely coordinative efforts. Such efforts manifest themselves into the mutually opposing forces broadly labelled as opportunistic and collaborative behavioural paradigms. Drawing from the concepts of Systems and Chaos/Complexity theories, it is theorised that the movement from one form of relational arrangement to another is enacted in a non-linear and dynamic manner with periods of relational equilibrium disrupted by bifurcations resulting in the emergence of new levels of relationship. However, not all exchange relationships are susceptible to constant change, rather, there should be some threshold barrier or relationship inertia that must be overcome before a bifurcation occurs. Yet what is not known is how strong these bonds are to the enactment of opportunistic and collaborative partner behaviours. Hence, 189 manufacturing supply chain relationships were survey-interviewed in order to determine the impact that collaborative and opportunistic behaviours have on supply chain relational movement. The results show that generally exchange relationships do in fact change in response to these enacted behaviours, and that actual levels of supply chain behaviour over a range of 12 variables could be measured. Indeed, the level of opportunistic behaviour experienced by the sample was disturbing. In addition, the level of tolerance (zone of tolerance) for specific behaviours was measured for the first time in the field. Overall, it was found that supply chain exchange relationships do indeed evolve in a non-linear dynamic manner in response to opportunistic and collaborative manoeuvres by the dyadic actors. Finally, these ideas were summarised in the Dynamic Relational Development (DRD) concept that explains how supply chain relationships dynamically change. In addition, the dualistic nature of the collaborative versus opportunistic behaviour choice for exchange actors is tentatively reconciled by the deontological approach of the Supply Chain Citizen theory offered in this research.
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Hamza, Sabra. "Contribution à l'analyse de sensibilité des systèmes complexes : application à la dynamique du véhicule." Thesis, Mulhouse, 2015. http://www.theses.fr/2015MULH1599/document.
Повний текст джерелаАнотація:
Le véhicule est un système dynamique complexe, composé de différents sous-systèmes de nature différente (moteur, système de freinage, suspension ...). Chaque sous-système est décrit par un modèle mathématique dépendant d’un nombre important de paramètres, très souvent incertains (méconnaissance, manque de mesures,…). L’incertitude sur les paramètres se propage à travers le modèle et se retrouve sur la sortie. Cette dernière représente les forces et moments mis en jeu dans le véhicule. L’incertitude sur la sortie n’est pas toujours tolérable pour des raisons de sécurité, précision,…Situé dans ce contexte, les travaux de la thèse consistent à proposer des méthodes d’analyse de sensibilité permettant de déterminer les paramètres dont les incertitudes ont un effet significatif sur le comportement d’un système donné, en particulier le véhicule. Dans une première partie, le cas des modèles à paramètres dépendants et suivant une distribution arbitraire est étudié. Une méthode, basée sur la décorrélation des paramètres par la décomposition de Cholesky, a été proposée. Pour résoudre le problème de la distribution arbitraire, l’approximation par polynôme du chaos arbitraire est adoptée, en construisant une base orthonormale en termes de moments statistiques non centrés des paramètres. Les indices de sensibilité, permettant de quantifier la contribution de chaque paramètre à la variance de la sortie, sont obtenus directement à partir des coefficients des polynômes du chaos ainsi obtenus. La méthode proposée est appliquée et validée sur un modèle de pneumatique. Dans la deuxième partie, le cas des modèles dynamiques est traité. Une méthode basée sur les dérivées partielles est explorée, puis une approche alternative est proposée. Elle utilise de façon originale des outils de l’Automatique, les grammiens d’atteignabilité et d’observabilité. L’influence des paramètres sur l’énergie consommée en entrée et restituée par le système en sortie est ainsi déterminée. L’avantage de cette technique est que les paramètres peuvent être classifiés selon leurs influences sur l’énergie consommée ou restituée, tout au long de la dynamique du système. D’autre part, l’étude de la sensibilité des paramètres sur les échanges de l’énergie, permet de déterminer un placement optimal des paramètres pour une optimisation de l’énergie consommée et restituée en sortie. Les deux méthodes proposées sont appliquées et validées sur un modèle bicyclette décrivant le comportement dynamique d’un véhicule. Dans la dernière partie, des tests sur véhicule d’essais ont été réalisés sur circuit. Les différentes approches d’analyse de sensibilité ont été appliquées sur les résultats d’essais, afin de recaler des modèles de pneumatiqueThe vehicle is a complex dynamic system, composed of various subsystems of different kind (engine, braking system, suspension, etc.). Each subsystem is described by a mathematical model depending on a significant number of parameters, very often uncertain (unknown, lack of measures, etc.). The uncertainty on the parameters is propagated through the model and takes place on the model output. The model output represents the forces and moments involved in the vehicle. The uncertainty on the model output is not always tolerable for safety reasons, precision, etc. In this context, the aim of the thesis is to propose sensitivity analysis methods allowing to determine parameters whose uncertainties have a significant effect on the behavior of a given system. In the first part, the case of models with dependent parameters which follow an arbitrary distribution is studied. A method based on the decorrelation of the parameters using the decomposition of Cholesky, is proposed. To solve the problem of the arbitrary distribution, an approximation using arbitrary polynomial chaos is adopted and an orthonormal data basis is constructed in terms of non central statistical moments of parameters. Sensitivity indices, allowing to quantify the contribution of every parameter to the model output variance, is directly obtained from the polynomial chaos coefficients.The proposed method is applied and validated on a tyre model. In the second part, the case of the dynamic models is studied. A method based on partial derivative is explored. Then a new alternative approach is proposed. This method uses in an original way the control theory tools, the reachability and observability Gramians. The influence of the parameters is formulated in terms the energy consumed and restored by the system. The advantage of this technique is that the parameters can be classified according to their influences on the consumed or restored energy throughout the system dynamics. On the other hand, the study of the parameters sensitivity based on ratio energy exchanged, allows to determine an optimal placement of the parameters for an optimization of consumed and/or restored energy. Both proposed methods are applied and validated using bicycle model describing vehicle dynamic behavior. Finally, the various sensitivity approaches are applied to adjust tyre model parameters using vehicle measurements acquired during a steady-state maneuver
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Caputo, Jean-Guy. "Dimension et entropie des attracteurs associés à des écoulements réels : estimation et analyse de la méthode." Grenoble 1, 1986. http://www.theses.fr/1986GRE10057.
Повний текст джерелаАнотація:
On s'interesse a la caracterisation des regimes chaotiques par lesquels un ecoulement atteint la turbulence. On montre qu'un regime chaotique de convection de rayleigh-benard est decrit par un attracteur dont on determine la dimension et l'entropie. En vue de caracteriser des attracteurs de dimension plus elevee on determine les conditions d'obtention de resultats corrects sur des exemples precis
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Krcelic, Khristine M. "Chaos and Dynamical Systems." Youngstown State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1364545282.
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Tesař, Lukáš. "Nelineární dynamické systémy a chaos." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-392844.
Повний текст джерелаАнотація:
The diploma thesis deals with nonlinear dynamical systems with emphasis on typical phenomena like bifurcation or chaotic behavior. The basic theoretical knowledge is applied to analysis of selected (chaotic) models, namely, Lorenz, Rössler and Chen system. The practical part of the work is then focused on a numerical simulation to confirm the correctness of the theoretical results. In particular, an algorithm for calculating the largest Lyapunov exponent is created (under the MATLAB environment). It represents the main tool for indicating chaos in a system.
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Öster, Michael. "Stability and Mobility of Localized and Extended Excitations in Nonlinear Schrödinger Models." Doctoral thesis, Linköpings universitet, Teoretisk Fysik, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8091.
Повний текст джерелаАнотація:
This thesis is mainly concerned with the properties of some discrete nonlinear Schrödinger equations. These naturally arise in many different physical contexts as the limiting form of general dynamical lattice equations that incorporate nonlinearity and coupling. Interest is focused on theoretical models of coupled optical waveguides constructed from materials with a nonlinear index of refraction. In arrays of waveguides the overlap of the evanescent electric field of the modes in neighbouring waveguides provides a coupling and the nonlinearity of the material provides a mechanism to halt the discrete diffraction that otherwise would spread localized energy across the array. In particular, waveguide structures where also a nonlinear coupling is taken into account are studied. It is noted that the equation for the evolution of the complex amplitudes of the electric field along an array of waveguides also can be used to describe the dynamics of Bose-Einstein condensates trapped in a periodic optical potential. Possible excitations in arrays in both one and two dimensions are considered, with emphasis on the effects of the nonlinear coupling. Localized excitations are considered from the viewpoint of the theory of discrete breathers, or intrinsic localized modes, i.e., solutions of the dynamical equations that are periodic in time and have a spatial localization. The general theory of such solutions, that appear under very general circumstances in nonlinear lattice equations, is reviewed. In an array of waveguides this means that light can propagate along the array confined essentially to one or a few waveguides. In general a distinction is made between excitations that are centred on a waveguide, or site in the lattice, and excitations that are centred inbetween waveguides. Usually only the former give stable propagation. When the localized beam can be displaced to neighbouring waveguides the array can operate as an optical switch. With the inclusion of nonlinear coupling between the sites, as in the model derived in this thesis, the stability of the site-centred and bond-centred solutions can be exchanged. It is shown how this leads to the existence of highly localized mobile solutions that can propagate transversely in the one-dimensional array of waveguides. The inversion of stability of stationary solutions occurs also in the two-dimensional array, but in this setting it fails to give good mobility of localized excitations. The reason for this is also explained. In a two-dimensional lattice a discrete breather can have the form of a vortex. This means that the phase of the complex amplitude will vary on a contour around the excitation, such that the phase is increased by 2πS, where S is the topological charge, on the completion of one turn. Some ring-like vortex excitations are considered and in particular a stable vortex with S=2 is found. It is also noted that the effect of charge flipping, i.e., when the topological charge periodically changes between -S and S, is connected to the existence of quasiperiodic solutions. The nonlinear coupling of the waveguide model will also give rise to some more exotic and novel properties of localized solutions, e.g., discrete breathers with a nontrivial phase. When the linear coupling and the nonlinear coupling have opposite signs, there can be a decoupling in the lattice that allows for compact solutions. These localized excitations will have no decaying tail. Of interest is also the flexibility in controlling the transport of power across the array when it is excited with a nonlinear plane wave. It is shown how a change of the amplitude of a plane wave can affect the magnitude and direction of power flow in the array. Also the continuum limit of the one-dimensional discrete waveguide model is considered with an equation incorporating both nonlocal and nonlinear dispersion. In general continuum equations the balance between nonlinearity and dispersion can lead to the formation of localized travelling waves, or solitons. With nonlinear dispersion it is seen that these solitons can be nonanalytic and have discontinuous spatial derivatives. The emergence of short-wavelength instabilities due to the simultaneous presence of nonlocal and nonlinear dispersion is also explained.
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Abu-Mahfouz, Issam Abdullah. "Routes to chaos in rotor dynamics." Case Western Reserve University School of Graduate Studies / OhioLINK, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=case1060787527.
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Wahlstrand, Björn. "Wave Transport and Chaos in Two-Dimensional Cavities." Thesis, Linköping University, Linköping University, The Swedish Institute for Disability Research, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-16492.
Повний текст джерелаАнотація:
This thesis focuses on chaotic stationary waves, both quantum mechanical and classical. In particular we study different statistical properties regarding thesewaves, such as energy transport, intensity (or density) and stress tensor components. Also, the methods used to model these waves are investigated, and somelimitations and specialities are pointed out.
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Bird, C. M. "The control of chaos." Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/804952/.
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Alhajj, Chehade Hicham. "Geosynthetic-Reinforced Retaining Walls-Deterministic And Probabilistic Approaches." Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALI010.
Повний текст джерелаАнотація:
L'objectif de cette thèse est de développer, dans le cadre de la mécanique des sols, des méthodes d’analyse de la stabilité interne des murs de soutènement renforcés par géosynthétiques sous chargement sismique. Le travail porte d'abord sur des analyses déterministes, puis est étendu à des analyses probabilistes. Dans la première partie de cette thèse, un modèle déterministe, basé sur le théorème cinématique de l'analyse limite, est proposé pour évaluer le facteur de sécurité d’un mur en sol renforcé ou la résistance nécessaire du renforcement pour stabiliser la structure. Une technique de discrétisation spatiale est utilisée pour générer une surface de rupture rotationnelle, afin de pouvoir considérer des remblais hétérogènes et/ou de représenter le chargement sismique par une approche de type pseudo-dynamique. Les cas de sols secs, non saturés et saturés sont étudiés. La présence de fissures dans le sol est également prise en compte. Ce modèle déterministe permet d’obtenir des résultats rigoureux et est validé par confrontation avec des résultats existants dans la littérature. Dans la deuxième partie du mémoire de thèse, ce modèle déterministe est utilisé dans un cadre probabiliste. Tout d'abord, l’approche en variables aléatoires est utilisée. Les incertitudes considérées concernent les paramètres de résistance au cisaillement du sol, la charge sismique et la résistance des renforcements. L'expansion du chaos polynomial qui consiste à remplacer le modèle déterministe coûteux par un modèle analytique, combinée avec la technique de simulation de Monte Carlo est la méthode fiabiliste considérée pour effectuer l'analyse probabiliste. L'approche en variables aléatoires néglige la variabilité spatiale du sol puisque les propriétés du sol et les autres paramètres modélisés par des variables aléatoires, sont considérés comme constants dans chaque simulation déterministe. Pour cette raison, dans la dernière partie du manuscrit, la variabilité spatiale du sol est considérée en utilisant la théorie des champs aléatoires. La méthode SIR/A-bSPCE, une combinaison entre la technique de réduction dimensionnelle SIR (Sliced Inverse Regression) et une expansion de chaos polynomial adaptative (A-bSPCE), est la méthode fiabiliste considérée pour effectuer l'analyse probabiliste. Le temps de calcul total de l'analyse probabiliste, effectuée à l'aide de la méthode SIR-SPCE, est considérablement réduit par rapport à l'exécution directe des méthode probabilistes classiques. Seuls les paramètres de résistance du sol sont modélisés à l'aide de champs aléatoires, afin de se concentrer sur l'effet de la variabilité spatiale sur les résultats fiabilistesThe aim of this thesis is to assess the seismic internal stability of geosynthetic reinforced soil retaining walls. The work first deals with deterministic analyses and then focus on probabilistic ones. In the first part of this thesis, a deterministic model, based on the upper bound theorem of limit analysis, is proposed for assessing the reinforced soil wall safety factor or the required reinforcement strength to stabilize the structure. A spatial discretization technique is used to generate the rotational failure surface and give the possibility of considering heterogeneous backfills and/or to represent the seismic loading by the pseudo-dynamic approach. The cases of dry, unsaturated and saturated soils are investigated. Additionally, the crack presence in the backfill soils is considered. This deterministic model gives rigorous results and is validated by confrontation with existing results from the literature. Then, in the second part of the thesis, this deterministic model is used in a probabilistic framework. First, the uncertain input parameters are modeled using random variables. The considered uncertainties involve the soil shear strength parameters, seismic loading and reinforcement strength parameters. The Sparse Polynomial Chaos Expansion that consists of replacing the time expensive deterministic model by a meta-model, combined with Monte Carlo Simulations is considered as the reliability method to carry out the probabilistic analysis. Random variables approach neglects the soil spatial variability since the soil properties and the other uncertain input parameters, are considered constant in each deterministic simulation. Therefore, in the last part of the manuscript, the soil spatial variability is considered using the random field theory. The SIR/A-bSPCE method, a combination between the dimension reduction technique, Sliced Inverse Regression (SIR) and an active learning sparse polynomial chaos expansion (A-bSPCE), is implemented to carry out the probabilistic analysis. The total computational time of the probabilistic analysis, performed using SIR-SPCE, is significantly reduced compared to directly running classical probabilistic methods. Only the soil strength parameters are modeled using random fields, in order to focus on the effect of the spatial variability on the reliability results
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Banks, Jess M. "Chaos and Learning in Discrete-Time Neural Networks." Oberlin College Honors Theses / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1445945609.
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Brandão, Dienes de Lima. "Sobre o caos de Devaney e implicações /." São José do Rio Preto, 2019. http://hdl.handle.net/11449/191142.
Повний текст джерелаАнотація:
Orientador: Weber Flávio PereiraResumo: A Teoria dos Sistemas Dinâmicos pode ser aplicada em diversas áreas da ciência, para, por exemplo, modelar fenômenos e problemas: Biológicos, da Física, Mecânica, Eletrônica, Economia, etc. Um sistema pode ser definido como um conjunto de elementos agrupados que mantêm alguma interação, de modo que existam relações de causa e efeito. Dizemos que é dinâmico quando algumas grandezas que compõem os elementos variam no tempo, sendo o tempo discreto quando a variável tempo é um número inteiro. Na busca de uma compreensão qualitativa e/ou topológica de um sistema, revela-se uma gama muito grande de movimentos que podem ser tanto regulares quanto caóticos. O termo “caos” só foi introduzido por James Yorke e TienYien Li em 1975, num artigo que simplificava um dos resultados da escola russa: o Teorema de Sharkovskii de 1964. Esporadicamente, antes e depois da introdução do termo, os sistemas caóticos apareciam na literatura aplicada, o mais famoso deles foi por Edward Norton Lorenz em 1963, que se propôs a modelar a convecção atmosférica. Em seus estudos ele descobriu que, para o seu modelo matemático, ínfimas modificações nas coordenadas iniciais mudavam de forma significativa os resultados finais, daí originou o termo popular do fenômeno (Efeito Borboleta). Mais tarde, em 1989, Robert Luke Devaney no seu livro: “An Introduction to Chaotic Dynamical Systems” [11], definiu um sistema como caótico se ele tem uma dependência sensível das condições iniciais, é topologicamente transitivo e suas ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Dynamical Systems Theory can be applied in various areas of science, for example, to model phenomena and problems: biology, physics, mechanics, electronics, economics, etc. A system can be defined as a set of grouped elements that maintain someinteraction. Wesaythatitisdynamicwhensomemagnitudesthatmakeupthe elementsvaryintime,beingdiscretetimewhenthevariabletimeisaninteger. Inthe pursuit of a qualitative and/or topological understanding of a system, a wide range of movements that can be both regular or chaotic is revealed. The term “chaos” was only introduced by James Yorke and TienYien Li in 1975, in an article that simplified one of the results of the Russian school: the 1964 Sharkovskii’s Theorem. Sporadically, before and after the introduction of the term, chaotic systems appeared in applied literature, the most famous of which was by Edward Norton Lorenz in 1963, who set out to model atmospheric convection. In his studies he found that for his created system, minor modifications to the initial coordinates significantly changed the final results, hence the popular term of the phenomenon (Butterfly Effect). Later, in 1989, Robert Luke Devaney in his book, “An Introduction to Chaotic Dynamical Systems” [11], defined a system as chaotic if it has a sensitive dependence on initial conditions, is topologically transitive, and its periodic orbits form a dense set. The main objective of this work is to study and present the evolution of the definition of discrete time Chaotic Dynamic Sy... (Complete abstract click electronic access below)
Mestre
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Korb, Mason. "Conceptualizing Chaos: Continuous Flows versus Boolean Dynamics." Ohio University Honors Tutorial College / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1338928594.
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Toufen, Dennis Lozano. "Controle da turbulência em plasmas." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-26032013-154737/.
Повний текст джерелаАнотація:
O Texas Helimak é uma máquina toroidal de confinamento de plasma cujas linhas de campo magnético têm forma helicoidal e no qual parâmetros do plasma (como a densidade e a temperatura) são similares aos da borda e da região externa (scrape-off-layer) de um tokamak. Nesta tese foram analisados o equilíbrio e as flutuações do plasma no Texas Helimak. São apresentadas a análise e a interpretação do controle da turbulência eletrostática e do transporte turbulento de partículas pelo potencial elétrico, bias, aplicado externamente. As alterações na turbulência e no transporte causadas pela mudança do potencial elétrico externo foram investigadas em uma região do plasma com gradientes radiais uniformes. As flutuações em descargas com bias positivo ou nulo apresentam espectros de potência de banda larga e uma PDF com uma cauda acentuada que revela a ocorrência intermitente de eventos extremos. Por outro lado, as flutuações em descargas com bias negativo possuem um espectro de potência mais estreito, uma PDF mais Gaussiana e um diagrama de recorrência com mais estruturas. Um modelo de quatro ondas acopladas foi utilizado para relacionar a largura de banda da turbulência com o tempo de interação entre as ondas do modelo. Perfis radiais do transporte turbulento de partículas na direção radial foram calculados, como função do bias, e comparados com os perfis da velocidade do fluxo de plasma e seu cisalhamento. Foi mostrado que o transporte depende do perfil radial da velocidade de fluxo do plasma. Nas descargas em que essa velocidade apresenta um ponto de máximo em seu perfil radial, o perfil do transporte possui um mínimo que foi interpretado, utilizando um modelo Hamiltoniano de ondas de deriva, como sendo resultado de uma barreira de transporte onde o cisalhamento do fluxo é nulo. Em outras descargas, máximos no perfil radial do transporte foram relacionados a ressonâncias que ocorrem onde a velocidade de fase da onda é igual à velocidade do plasma.The Texas Helimak is a toroidal confinement of plasma device with helically magnetic field lines and which plasma parameters (like the density and temperature) are similar to the edge and the scrape-off-layer of a tokamak. This thesis analyzed the equilibrium and fluctuations in the Helimak Texas plasma. We present the analysis and interpretation of electrostatic control of turbulence and turbulent particle transport by electrical potential, bias, applied externally. Changes in transport and turbulence caused by the change of external electric potential were investigated in a region of uniform radial gradients plasma. Fluctuations in discharges with positive or zero bias have broadband power spectra and a PDF with an accentuated tail that reveals the intermittent occurrence of extreme events. Moreover, fluctuations in discharges with negative bias have narrow power spectra, a more Gaussian PDF and more structures in the recurrence diagram. A four coupled wave model was used to relate the bandwidth of turbulence with the interaction time between the waves in the model. Radial profiles of turbulent transport of particles in the radial direction were calculated as a function of bias and compared to the profiles of the plasma flow velocity and its shear. It was shown that the transport depends on the radial profile of the plasma flow velocity. In that discharges where the velocity radial profile presents a point of maximum, the transport profile has a minimum which was interpreted, using a drift wave model Hamiltonian, as a result of a shearless flow transport barrier. In other discharges, the maxima in the transport radial profiles were related with resonances that occur where the wave phase velocity is equal to the plasma velocity.
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Chygryn, S. A. "Intermittent chaos in Hamiltonian dynamical systems." Thesis, Сумський державний університет, 2014. http://essuir.sumdu.edu.ua/handle/123456789/35109.
Повний текст джерелаАнотація:
The statistical characterization of chaotic trajectories in Hamiltonian dynamical systems attract special interest. Such systems usually show coexistence of regions of chaotic and regular motion in the phase space. When chaotic trajectories approach the regular regions, they stick to their border inducing long periods of almost regular motion. This intermittent behavior determines the main dynamical properties of the system. The fundamental problem is how to quantitatively relate the intermittency of the chaotic dynamics to the distribution and stability properties of the regular regions of the phase space.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35109
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Nixon, Melina S. "Nonlinear dynamics and chaos of tethered satellite systems." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=27246.
Повний текст джерелаАнотація:
The equations of motion of a tethered satellite system are highly nonlinear and should possess many interesting related features; yet its nonlinear dynamics has never been thoroughly investigated in previous works. This thesis analyzes the nonlinear dynamics of two-body tethered satellite systems using numerical tools of analysis such as phase plane plots, power spectral densities (PSD's), Poincare sections and first Lyapunov exponents, as well as approximate analytical methods including the method of Melnikov. Motion in the stationkeeping phase wherein the tethered system is just a gravity gradient pendulum is studied, first considering pitch motion only, and then considering the coupled pitch and roll motions. The deployment/retrieval phases are studied next. For a circular orbit, pitch stability is examined for varying exponential length rates; for the unstable cases, it is compared to an equivalent uniform length rate scheme, which showed better stability behaviour. (Abstract shortened by UMI.)
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Nixon, Melina S. "Nonlinear dynamics and chaos of tethered satellite systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ29619.pdf.
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Hall, Toby Dixon Harold. "Periodicity in chaos : the dynamics of surface automorphisms." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387125.
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Andreev, Anton. "Random matrices, quantum chaos and irreversible classical dynamics." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/36086.
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Huang, Dazhan. "Essays on cycles and chaos in economic dynamics." Thesis, University of Manchester, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.594757.
Повний текст джерелаАнотація:
The topics of this thesis are cycles and chaos in economic dynamics. Endogenous economic fluctuations are discussed in chapter 2 and 3. It is shown that persistent deterministic business cycles, and even chaos, appear in a purely endogenous fashion in an overlapping generations economy with decreasing returns production and profit distribution. To generate such cycles or chaos, the individuals' offer curve need not be backward bending. The origin of the cycles or chaos is sufficient inelasticity of labour demand at high employment levels. Chapter 4 deals with efficiency of competitive equilibrium allocations and monetary policy in overlapping generations models with decreasing return production. All competitive equilibrium allocations are Pareto Optimal. It is argued that monetary policy can not change the set of competitive equilibrium paths, but it is sufficient to "guide" the economy to converge to any competitive equilibrium path in the set. In particular, the government will prefer to lead the economy to converge to the stationary state in order to maximize social welfare. Chapter 5 concerns an allocation problem of renewable resources. The model discussed in this chapter is a non standard dynamic programming model. The existence of cycles and chaos is studied. The focus of this chapter is the relationship between the optimal policy function and the environmental function. Two questions are addressed; whether the optimal control can create chaos when the environment is non chaotic in the absence of control, and conversely, whether the optimal control can bring about a stationary state when the environment is chaotic in the absence of control. The anwser to both is "Yes".
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Bel, Mabrouk Imen. "Etude des effets des charges aérodynamiques sur le comportement dynamique non linéaire des éoliennes à axe vertical." Thesis, Normandie, 2017. http://www.theses.fr/2017NORMIR17.
Повний текст джерелаАнотація:
Ce sujet de thèse s'intéresse à l'étude des effets des charges aérodynamiques sur le comportement dynamique non linéaire d'une éolienne à axe vertical de type Darrieus. Cette dernière présente, comparativement aux autres éoliennes, des profits très importants à exploiter, notamment dans les milieux urbains. Il s'agit d'une technologie fiable caractérisée surtout par son fonctionnement omnidirectionnel ainsi que son adaptation à tout type de vent. Généralement, ces éoliennes, ayant des phénomènes aérodynamiques complexes, sont affectées par des vibrations au niveau de leur système de transmission de puissance. En fait, ces vibrations commencent à se manifester à partir des pales du rotor jusqu'au génératrice. L'écoulement autour de ses pales présente également un fort caractère instationnaire. Cette caractéristique augmente d'avantage les vibrations aérodynamiques, qui sont automatiquement transmise au système d'engrenage d'éolienne. À ce niveau, nous avons développé un code de calcul numérique permettant de simuler la complexité des aspects aérodynamiques instationnaires tout en gardant un compromis entre la fiabilité des prédictions et la rapidité de calcul. Les simulations sont réalisées suivant une méthode de mécanique des fluides numérique (CFD) instationnaire bidimensionnel. Les résultats de simulation comparés avec ceux disponibles dans la littérature sont en bonne concordance, le rendement aérodynamique étant optimisé, qui présente un apport scientifique notable. Cette étude numérique a été l'objectif de l'analyse de l'impact des charges aérodynamiques vis-à-vis le comportement dynamique du système d'engrenage de l'éolienne en régime non-stationnaire. Dans ce contexte, une étude paramétrique a été développée afin d'établir le fonctionnement optimal de l'éolienne, caractérisé par un couple aérodynamique plus performant associé à des niveaux de vibrations dynamiques acceptables. En général, il est difficile d'identifier précisément la réponse dynamique des éoliennes à cause du caractère turbulent et stochastique des charges aérodynamiques. Par conséquent, il est indispensable de tenir en compte la variabilité des paramètres d'entrée pour assurer la robustesse du système étudié. Adoptons l'objectif de dimensionnement robuste. Une méthode d'évaluation basée sur des approches stochastiques, particulièrement la méthode du Chaos Polynomial, est utilisée pour simuler le comportement dynamique non-linéaire du système d'engrenage d'éolienne, en tenant compte des incertitudes. Ces dernières sont au niveau des charges aérodynamiques, inhérentes au calcul des niveaux vibratoires du système d'engrenage. Ce qui implique un apport scientifique important. Les résultats obtenus par l'approximation par Chaos Polynomial démontrent une forte dispersion des charges aérodynamiques aléatoires dans la réponse dynamique du système d'engrenage, contrairement aux études déterministes. Ce qui prouve l'insuffisance de telles études pour une analyse de robustesse. Les résultats mettent également en évidence la forte corrélation entre les phénomènes aérodynamiques complexes et les vibrations dynamiques. Le couplage établi constitue l'originalité de notre travailThis thesis focuses on the study of the aerodynamic loads effects on the nonlinear dynamic behavior of Darrieus--type vertical axis wind turbine. The latter has received more attention due to its efficiency in urban regions compared to other wind turbines. In fact, the wind flow speed in urban regions continuously changes direction and is extremely turbulent. The inherent characteristics of its omni-directionality make it more suitable to harnessing this kind of flow. It is known that Darrieus wind turbine is characterized by an inherently unsteady aerodynamic behavior and a complex flow around rotor blades. The non-stationary behavior of the mentioned turbine increases vibration. These aerodynamic vibrations are transmitted to the gearing mechanism. We have, firstly, developed a numerical simulation, allowing to simulate the complexity of the unsteady aerodynamic phenomena keeping a compromise between the reliability of prediction and the rapidity of calculation. This numerical simulation has been carried out using a two-dimensional unsteady Computational Fluid Dynamics (CFD) method. Simulation results compared to those available in the literature are in good agreement. The Darrieus turbine efficiency is also optimized; thus introducing a significant scientific contribution. The latter is the objective of analyzing the aerodynamic load impact in the dynamic behavior of the Darrieus turbine in non-stationary regime. In this context, a parametric study has been developed in order to find optimal functioning of the studied turbine, which is characterized by the most performing aerodynamic torque associated with acceptable levels of dynamic vibration. In general, it is difficult to predict the dynamic response of the wind turbine with a good level of accuracy due to the aerodynamic loads turbulence and uncertain characteristics. It becomes necessary to take into account the uncertainty in the input parameters to ensure the robustness of the Darrieus turbine geared system. In a robustness study objective, the Polynomial Chaos method is adopted to predict the nonlinear dynamic behavior of the gearing system taking into account uncertainties which are associated to the performance coefficient of the input aerodynamic torque. This leads to an important scientific research contribution. The results have shown a large dispersion of the random parameter in the dynamic response of the gearing system compared to the deterministic study. That proves the insufficiency of that study for a robustness analyses. They have also proved that the Polynomial Chaos method is an efficient probabilistic tool for uncertainty propagation. Finally, the new proposed robust mechanical analysis indicates a good capacity to investigate the dynamic behavior of the Darrieus turbine thanks to its superior predictive capabilities in coupling complex aerodynamic phenomena with a mechanical gearing system vibration. Where the originality of such correlation in our work
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Clodong, Sébastien. "Recurrent outbreaks in ecology : chaotic dynamics in complex networks." Phd thesis, Universität Potsdam, 2004. http://opus.kobv.de/ubp/volltexte/2005/171/.
Повний текст джерелаАнотація:
Gegenstand der Dissertation ist die Untersuchung von wiederkehrenden Ausbrüchen (wie z.B. Epidemien) in der Natur. Dies gelang anhand von Modellen, die die Dynamik von Phytoplankton und die Ausbreitung von Krankheiten zwischen Städten beschreiben. Diese beide Systeme bilden hervorragende Beispiele für solche Phänomene.
Die Frage, ob die in der Zeit wiederkehrenden Ausbrüche ein Ausdruck chaotischer Dynamik sein können, ist aktuell in der Ökologie und fasziniert Wissenschaftler dieser Disziplin. Wir konnten zeigen, dass sich das Plankton-Modell im Falle von periodischem Antreiben über die Nährstoffe in einem chaotischen Regime befindet. Diese Dynamik wurde als die komplexe Wechselwirkung zweier Oszillatoren verstanden.
Ebenfalls wurde die Ausbreitung von Epidemien in Netzwerken wechselwirkender Städte mit unterschiedlichen Grössen untersucht. Dafür wurde zunächst die Kopplung zwischen zwei Städten als Verhältnis der Stadtgrössen eingeführt. Es konnte gezeigt werden, dass das System sich in einem globalen zweijährigen Zyklus, der auch in den realen Daten beobachtet wird, befinden kann.
Der Effekt von Heterogenität in der Grösseverteilung ist durch gewichtete Kopplung von generischen Modellen (Zelt- und Logistische Abbildung) in Netzwerken im Detail untersucht worden. Eine neue Art von Kopplungsfunktion mit nichtlinearer Sättigung wurde eingeführt, um die Stabilität des Systems zu gewährleisten. Diese Kopplung beinhaltet einen Parameter, der es erlaubt, die Netzwerktopologie von globaler Kopplung in gerichtete Netzwerke gleichmässig umzuwandeln. Die Dynamik des Systems wurde anhand von Bifurkationsdiagrammen untersucht. Zum Verständnis dieser Dynamik wurde eine effektive Theorie, die die beobachteten Bifurkationen sehr gut nachahmt, entwickelt.One of the most striking features of ecological systems is their ability to undergo sudden outbreaks in the population numbers of one or a small number of species. The similarity of outbreak characteristics, which is exhibited in totally different and unrelated (ecological) systems naturally leads to the question whether there are universal mechanisms underlying outbreak dynamics in Ecology. It will be shown into two case studies (dynamics of phytoplankton blooms under variable nutrients supply and spread of epidemics in networks of cities) that one explanation for the regular recurrence of outbreaks stems from the interaction of the natural systems with periodical variations of their environment. Natural aquatic systems like lakes offer very good examples for the annual recurrence of outbreaks in Ecology. The idea whether chaos is responsible for the irregular heights of outbreaks is central in the domain of ecological modeling. This question is investigated in the context of phytoplankton blooms. The dynamics of epidemics in networks of cities is a problem which offers many ecological and theoretical aspects. The coupling between the cities is introduced through their sizes and gives rise to a weighted network which topology is generated from the distribution of the city sizes. We examine the dynamics in this network and classified the different possible regimes. It could be shown that a single epidemiological model can be reduced to a one-dimensional map. We analyze in this context the dynamics in networks of weighted maps. The coupling is a saturation function which possess a parameter which can be interpreted as an effective temperature for the network. This parameter allows to vary continously the network topology from global coupling to hierarchical network. We perform bifurcation analysis of the global dynamics and succeed to construct an effective theory explaining very well the behavior of the system.