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1
Tang, Xiafei. "Periodic disturbance rejection of nonlinear systems". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/periodic-disturbance-rejection-of-nonlinear-systems(0bddefd9-2750-47fd-8c92-c90a01b8e1ef).html.
Testo completoAbstract (sommario):
Disturbance rejection is an important topic in control design since disturbances are inevitable in practical systems. To realise this target for nonlinear systems, this thesis brings in an assumption about the existence of a controlled invariant mani- fold and a Desired Feedforward Control (DFC) which is contained in the input to compensate the influence of disturbances. According to the approximation property of Neural Networks (NN) that any periodic signals defined in a compact set can be approximated by NN, the NN-based disturbance approximator is applied to approximate the DFC. Algorithmically, two important types of NN approximators that are Multi-layer Neural Networks (MNN) and Radial Basis Function Neural Networks (RBFNN) are presented in detail.In this thesis, a variety of nonlinear systems in standard canonical form are looked into. These forms are the output feedback form, the extended output feedback form, the decentralised output feedback form and the partial state feedback form. For these systems, four types of uncertainties are mainly considered. The first one is the disturbance that can be eliminated by the DFC. Secondly, the parameter uncertainty is taken into account. To get rid of this uncertainty, the adaptive control technique is employed for the estimation of unknown parameters, e.g. the NN gain matrix. The third one is the nonlinear uncertainty. For the case that nonlinear uncertainties are polynomials, it has a bound consisting of an unknown constant and a function of the regulated error such that this uncertainty can be also treated as the parameter uncertainty. Delay is the last type of uncertainty. Particularly, the delay is supposed to appear in output only. This uncertainty can be eliminated together with the nonlinear uncertainty. To establish the closed- loop stability, a Lyapunov-Krasovskii function is invoked. In addition, due to the requirement of the system structure or the stability analysis, some general control techniques are also involved such like the backstepping control and the high gain control.Throughout the results are illustrated by simulations.
2
Abd-Elrady, Emad. "Nonlinear Approaches to Periodic Signal Modeling". Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4644.
Testo completo
3
Groves, James O. "Small signal analysis of nonlinear systems with periodic operating trajectories". Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-06062008-162614/.
Testo completo
4
Zhang, Zhen. "Adaptive robust periodic output regulation". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1187118803.
Testo completo
5
Khames, Imene. "Nonlinear network wave equations : periodic solutions and graph characterizations". Thesis, Normandie, 2018. http://www.theses.fr/2018NORMIR04/document.
Testo completoAbstract (sommario):
Dans cette thèse, nous étudions les équations d’ondes non-linéaires discrètes dans des réseaux finis arbitraires. C’est un modèle général, où le Laplacien continu est remplacé par le Laplacien de graphe. Nous considérons une telle équation d’onde avec une non-linéarité cubique sur les nœuds du graphe, qui est le modèle φ4 discret, décrivant un réseau mécanique d’oscillateurs non-linéaires couplés ou un réseau électrique où les composantes sont des diodes ou des jonctions Josephson. L’équation d’onde linéaire est bien comprise en termes de modes normaux, ce sont des solutions périodiques associées aux vecteurs propres du Laplacien de graphe. Notre premier objectif est d’étudier la continuation des modes normaux dans le régime non-linéaire et le couplage des modes en présence de la non-linéarité. En inspectant les modes normaux du Laplacien de graphe, nous identifions ceux qui peuvent être étendus à des orbites périodiques non-linéaires. Il s’agit des modes normaux dont les vecteurs propres du Laplacien sont composés uniquement de {1}, {-1,+1} ou {-1,0,+1}. Nous effectuons systématiquement une analyse de stabilité linéaire (Floquet) de ces orbites et montrons le couplage des modes lorsque l’orbite est instable. Ensuite, nous caractérisons tous les graphes pour lesquels il existe des vecteurs propres du Laplacien ayant tous leurs composantes dans {-1,+1} ou {-1,0,+1}, en utilisant la théorie spectrale des graphes. Dans la deuxième partie, nous étudions des solutions périodiques localisées spatialement. En supposant une condition initiale de grande amplitude localisée sur un nœud du graphe, nous approchons l’évolution du système par l’équation de Duffing pour le nœud excité et un système linéaire forcé pour le reste du réseau. Cette approximation est validée en réduisant l’équation φ4 discrète à l’équation de Schrödinger non-linéaire de graphes et par l’analyse de Fourier de la solution numérique. Les résultats de cette thèse relient la dynamique non-linéaire à la théorie spectrale des graphesIn this thesis, we study the discrete nonlinear wave equations in arbitrary finite networks. This is a general model, where the usual continuum Laplacian is replaced by the graph Laplacian. We consider such a wave equation with a cubic on-site nonlinearity which is the discrete φ4 model, describing a mechanical network of coupled nonlinear oscillators or an electrical network where the components are diodes or Josephson junctions. The linear graph wave equation is well understood in terms of normal modes, these are periodic solutions associated to the eigenvectors of the graph Laplacian. Our first goal is to investigate the continuation of normal modes in the nonlinear regime and the modes coupling in the presence of nonlinearity. By inspecting the normal modes of the graph Laplacian, we identify which ones can be extended into nonlinear periodic orbits. They are normal modes whose Laplacian eigenvectors are composed uniquely of {1}, {-1,+1} or {-1,0,+1}. We perform a systematic linear stability (Floquet) analysis of these orbits and show the modes coupling when the orbit is unstable. Then, we characterize all graphs for which there are eigenvectors of the graph Laplacian having all their components in {-1,+1} or {-1,0,+1}, using graph spectral theory. In the second part, we investigate periodic solutions that are spatially localized. Assuming a large amplitude localized initial condition on one node of the graph, we approximate its evolution by the Duffing equation. The rest of the network satisfies a linear system forced by the excited node. This approximation is validated by reducing the discrete φ4 equation to the graph nonlinear Schrödinger equation and by Fourier analysis. The results of this thesis relate nonlinear dynamics to graph spectral theory
6
Warkomski, Edward Joseph 1958. "Nonlinear structures subject to periodic and random vibration with applications to optical systems". Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277811.
Testo completoAbstract (sommario):
The methods for analysis of a three degree-of-freedom nonlinear optical support system, subject to periodic and random vibration, are presented. The analysis models were taken from those generated for the dynamic problems related to the NASA Space Infrared Telescope Facility (SIRTF). The models treat the one meter, 116 kilogram (258 pound) primary mirror of the SIRTF as a rigid mass, with elastic elements representing the mirror support structure. Both linear and nonlinear elastic supports are evaluated for the SIRTF. Advanced Continuous Simulation Language (ACSL), a commercially available software package for numerical solution of nonlinear, time-dependent differential equations, was used for all models. The methods presented for handling the nonlinear differential equations can be readily adapted for handling other similar dynamics problems.
7
Zhang, Xiaohong. "Optimal feedback control for nonlinear discrete systems and applications to optimal control of nonlinear periodic ordinary differential equations". Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40185.
Testo completo
8
Myers, Owen Dale. "Spatiotemporally Periodic Driven System with Long-Range Interactions". ScholarWorks @ UVM, 2015. http://scholarworks.uvm.edu/graddis/524.
Testo completoAbstract (sommario):
It is well known that some driven systems undergo transitions when a system parameter is changed adiabatically around a critical value. This transition can be the result of a fundamental change in the structure of the phase space, called a bifurcation. Most of these transitions are well classified in the theory of bifurcations. Among the driven systems, spatiotemporally periodic (STP) potentials are noteworthy due to the intimate coupling between their time and spatial components. A paradigmatic example of such a system is the Kapitza pendulum, which is a pendulum with an oscillating suspension point. The Kapitza pendulum has the strange property that it will stand stably in the inverted position for certain driving frequencies and amplitudes. A particularly interesting and useful STP system is an array of parallel electrodes driven with an AC electrical potential such that adjacent electrodes are 180 degrees out of phase. Such an electrode array embedded in a surface is called an Electric Curtain (EC). As we will show, by using two ECs and a quadrupole trap it is posible to produce an electric potential simular in form to that of the Kapitza pendulum.
Here I will present the results of four related pieces of work, each focused on understanding the behaviors STP systems, long-range interacting particles, and long-range interacting particles in STP systems. I will begin with a discussion on the experimental results of the EC as applied to the cleaning of solar panels in extraterrestrial environments, and as a way to produce a novel one-dimensional multiparticle STP potential. Then I will present a numerical investigation and dynamical systems analysis of the dynamics that may be possible in an EC. Moving to a simpler model in order to explore the rudimentary physics of coulomb interactions in a STP potential, I will show that the tools of statistical mechanics may be important to the study of such systems to understand transitions that fall outside of bifurcation theory. Though the Coulomb and, similarly, gravitational interactions of particles are prevalent in nature, these long-range interactions are not well understood from a statistical mechanics perspective because they are not extensive or additive. Finally, I will present a simple model for understanding long-range interacting pendula, finding interesting non-equilibrium behavior of the pendula angles. Namely, that a quasistationary clustered state can exist when the angles are initially ordered by their index.
9
Hayward, Peter J. "On the computation of periodic responses for nonlinear dynamic systems with multi-harmonic forcing". Thesis, University of Sussex, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429733.
Testo completo
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Royston, Thomas James. "Computational and Experimental Analyses of Passive and Active, Nonlinear Vibration Mounting Systems Under Periodic Excitation /". The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487928649987553.
Testo completo
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Fiedler, Robert [Verfasser]. "Numerical analysis of invariant manifolds characterized by quasi-periodic oscillations of nonlinear systems / Robert Fiedler". Kassel : kassel university press c/o Universität Kassel - Universitätsbibliothek, 2021. http://d-nb.info/1239061412/34.
Testo completo
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Xu, Yeyin. "STABILITY AND BIFURCATION DYNAMICS OF JOURNAL BEARING ROTOR SYSTEMS". OpenSIUC, 2020. https://opensiuc.lib.siu.edu/dissertations/1835.
Testo completoAbstract (sommario):
In this dissertation, the mechanical models of 2-DOF and 4-DOF nonlinear journal bearing rotor systems are established. A more accurate model of oil film forces is derived from Reynolds equations. The periodic motions in such nonlinear journal bearing systems are obtained through discrete mapping method. Such a semi-analytical method constructs an implicit discrete mapping structure for periodic motions by discretization of the continuous journal bearing rotor differential equations. Stable and unstable periodic solutions of periodic motions are obtained with prescribed accuracy. The bifurcation tree of periodic motions in rotor system without oil film forces is demonstrated through the route from period-1 motion to period-8 motion. Stable period-2 and unstable period-1 motion are presented for 2 DOF journal bearing rotor system. Possibly infinite periodic solutions are found in 4 DOF journal bearing rotor system. For the rotor systems, the stability and bifurcations of periodic motions are analyzed through eigenvalue analysis of the corresponding Jacobian matrix of the discretized nonlinear systems. The frequency amplitude characteristics of periodic motions in 2 DOF journal bearing system are presented for a good understanding of the nonlinear dynamics of journal bearing rotor system in frequency domain . The rich dynamics of the journal bearing systems are discovered. The numerical illustrations of stable periodic motions are brought out with the initial conditions from analytical prediction.
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Simonis, Joseph P. "Inexact Newton methods applied to under-determined systems". Link to electronic dissertation, 2006. http://www.wpi.edu/Pubs/ETD/Available/etd-050406-103442/.
Testo completoAbstract (sommario):
Dissertation (Ph.D.)--Worcester Polytechnic Institute.Keywords: Periodic Solutions, Under-Determined Systems, Continuation, Nonlinear Eigenvalue, Inexact Newton Methods, Newton's Method, Trust Region Methods Includes bibliographical references (p.93-95).
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Reichelt, Sina. "Two-scale homogenization of systems of nonlinear parabolic equations". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17385.
Testo completoAbstract (sommario):
Ziel dieser Arbeit ist es zwei verschiedene Klassen von Systemen nichtlinearer parabolischer Gleichungen zu homogenisieren, und zwar Reaktions-Diffusions-Systeme mit verschiedenen Diffusionslängenskalen und Gleichungen vom Typ Cahn-Hilliard. Wir betrachten parabolische Gleichungen mit periodischen Koeffizienten, wobei die Periode dem Verhältnis der charakteristischen mikroskopischen zu der makroskopische Längenskala entspricht. Unser Ziel ist es, effektive Gleichungen rigoros herzuleiten, um die betrachteten Systeme besser zu verstehen und den Simulationsaufwand zu minimieren. Wir suchen also einen Konvergenzbegriff, mit dem die Lösung des Ausgangsmodells im Limes der Periode gegen Null gegen die Lösung des effektiven Modells konvergiert. Um die periodische Mikrostruktur und die verschiedenen Diffusivitäten zu erfassen, verwenden wir die Zwei-Skalen Konvergenz mittels periodischer Auffaltung. Der erste Teil der Arbeit handelt von Reaktions-Diffusions-Systemen, in denen einige Spezies mit der charakteristischen Diffusionslänge der makroskopischen Skala und andere mit der mikroskopischen diffundieren. Die verschiedenen Diffusivitäten führen zu einem Verlust der Kompaktheit, sodass wir nicht direkt den Grenzwert der nichtlinearen Terme bestimmen können. Wir beweisen mittels starker Zwei-Skalen Konvergenz, dass das effektive Modell ein zwei-skaliges Modell ist, welches von der makroskopischen und der mikroskopischen Skale abhängt. Unsere Methode erlaubt es uns, explizite Raten für die Konvergenz der Lösungen zu bestimmen. Im zweiten Teil betrachten wir Gleichungen vom Typ Cahn-Hilliard, welche ortsabhängige Mobilitätskoeffizienten und allgemeine Potentiale beinhalten. Wir beweisen evolutionäre Gamma-Konvergenz der zugehörigen Gradientensysteme basierend auf der Gamma-Konvergenz der Energien und der Dissipationspotentiale.The aim of this thesis is to derive homogenization results for two different types of systems of nonlinear parabolic equations, namely reaction-diffusion systems involving different diffusion length scales and Cahn-Hilliard-type equations. The coefficient functions of the considered parabolic equations are periodically oscillating with a period which is proportional to the ratio between the charactersitic microscopic and macroscopic length scales. In view of greater structural insight and less computational effort, it is our aim to rigorously derive effective equations as the period tends to zero such that solutions of the original model converge to solutions of the effective model. To account for the periodic microstructure as well as for the different diffusion length scales, we employ the method of two-scale convergence via periodic unfolding. In the first part of the thesis, we consider reaction-diffusion systems, where for some species the diffusion length scale is of order of the macroscopic length scale and for other species it is of order of the microscopic one. Based on the notion of strong two-scale convergence, we prove that the effective model is a two-scale reaction-diffusion system depending on the macroscopic and the microscopic scale. Our approach supplies explicit rates for the convergence of the solution. In the second part, we consider Cahn-Hilliard-type equations with position-dependent mobilities and general potentials. It is well-known that the classical Cahn-Hilliard equation admits a gradient structure. Based on the Gamma-convergence of the energies and the dissipation potentials, we prove evolutionary Gamma-convergence, for the associated gradient system such that we obtain in the limit of vanishing periods a Cahn-Hilliard equation with homogenized coefficients.
15
Garrione, Maurizio. "Existence and multiplicity of solutions to boundary value problems associated with nonlinear first order planar systems". Doctoral thesis, SISSA, 2012. http://hdl.handle.net/20.500.11767/4930.
Testo completoAbstract (sommario):
The monograph is devoted to the study of nonlinear first order systems in the plane where the principal term is the gradient of a positive and positively 2-homogeneous Hamiltonian (or the convex combination of two of such gradients). After some preliminaries about positively 2-homogeneous autonomous systems, some results of existence and multiplicity of T-periodic solutions are presented in case of bounded or sublinear nonlinear perturbations. Our attention is mainly focused on the occurrence of resonance phenomena, and the corresponding results rely essentially on conditions of Landesman-Lazer or Ahmad-Lazer-Paul type. The techniques used are predominantly topological, exploiting the theory of coincidence degree and the use of the Poincaré-Birkhoff fixed point theorem. At the end, other boundary conditions, including the Sturm-Liouville ones, are taken into account, giving the corresponding existence and multiplicity results in a nonresonant situation via the shooting method and topological arguments.
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Taha, Haithem Ezzat Mohammed. "Mechanics of Flapping Flight: Analytical Formulations of Unsteady Aerodynamics, Kinematic Optimization, Flight Dynamics and Control". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/24428.
Testo completoAbstract (sommario):
A flapping-wing micro-air-vehicle (FWMAV) represents a complex multi-disciplinary system whose analysis invokes the frontiers of the aerospace engineering disciplines. From the aerodynamic point of view, a nonlinear, unsteady flow is created by the flapping motion. In addition, non-conventional contributors, such as the leading edge vortex, to the aerodynamic loads become dominant in flight. On the other hand, the flight dynamics of a FWMAV constitutes a nonlinear, non-autonomous dynamical system. Furthermore, the stringent weight and size constraints that are always imposed on FWMAVs invoke design with minimal actuation. In addition to the numerous motivating applications, all these features of FWMAVs make it an interesting research point for engineers.
In this Dissertation, some challenging points related to FWMAVs are considered. First, an analytical unsteady aerodynamic model that accounts for the leading edge vortex contribution by a feasible computational burden is developed to enable sensitivity and optimization analyses, flight dynamics analysis, and control synthesis. Second, wing kinematics optimization is considered for both aerodynamic performance and maneuverability. For each case, an infinite-dimensional optimization problem is formulated using the calculus of variations to relax any unnecessary constraints induced by approximating the problem as a finite-dimensional one. As such, theoretical upper bounds for the aerodynamic performance and maneuverability are obtained. Third, a design methodology for the actuation mechanism is developed. The proposed actuation mechanism is able to provide the required kinematics for both of hovering and forward flight using only one actuator. This is achieved by exploiting the nonlinearities of the wing dynamics to induce the saturation phenomenon to transfer energy from one mode to another. Fourth, the nonlinear, time-periodic flight dynamics of FWMAVs is analyzed using direct and higher-order averaging. The region of applicability of direct averaging is determined and the effects of the aerodynamic-induced parametric excitation are assessed. Finally, tools combining geometric control theory and averaging are used to derive analytic expressions for the textit{Symmetric Products}, which are vector fields that directly affect the acceleration of the averaged dynamics. A design optimization problem is then formulated to bring the maneuverability index/criterion early in the design process to maximize the FWMAV maneuverability near hover.Ph. D.
17
Demiquel, Antoine. "Control of nonlinear modulated waves in flexible mechanical metamaterials". Electronic Thesis or Diss., Le Mans, 2024. https://cyberdoc-int.univ-lemans.fr/Theses/2024/2024LEMA1015.pdf.
Testo completoAbstract (sommario):
Ce travail est consacré à l'étude des ondes modulées se propageant le long de métamatériaux mécaniques flexibles nonlinéaires (FlexMM). Ces structures sont des matériaux architecturés constitués d'éléments souples très déformables connectés à des éléments plus rigides. Leur capacité à subir de grandes déformations locales favorise l'apparition de phénomènes d'ondes non linéaires. En utilisant une approche par éléments discrets, nous formulons des équations discrètes non linéaires qui décrivent les déplacements longitudinaux et rotationnels de chaque cellule unitaire et leur couplage mutuel. Une analyse multi-échelles est employée afin d'obtenir une équation de Schrödinger non linéaire (NLS) effective décrivant les ondes modulées pour le degré de liberté rotationnel du FlexMM. En nous appuyant sur l'équation NLS, nous identifions divers types de phénomènes d'ondes non linéaires dans le FlexMM. En particulier, nous avons observé que des ondes planes faiblement non linéaires peuvent être modulationellement stables ou instables en fonction des paramètres du système et de l'excitation utilisée. De plus, nous avons trouvé que les FlexMMs supportent des solitons-enveloppe vectoriels où le degré de liberté rotationnel des unités peut prendre la forme de solitons dits "bright" ou "dark" et, en raison du couplage, le degré de liberté de déplacement longitudinal présente un comportement de type "kink". Enfin, nous abordons le phénomène de "catastrophe de gradient", qui prédit l'émergence de structures similaires aux solitons de Peregrine dans la limite semi-classique de l'équation NLS, dans la structure FlexMM. Grâce à nos prédictions analytiques et à l'utilisation de simulations numériques, nous pouvons déterminer les conditions requises et les valeurs des paramètres physiques pour observer ces phénomènes dans les FlexMMsThis work is dedicated to the investigation of modulated waves propagating along nonlinear flexible mechanical metamaterials (FlexMM). These structures are architected materials consisting of highly deformable soft elements connected to stiffer ones. Their capacity to undergo large local deformations promotes the occurrence of nonlinear wave phenomena. Using a lump element approach, we formulate nonlinear discrete equations that describe the longitudinal land rotational displacements of each unit cell and their mutual coupling. A multiple scales analysis is employed in order to derive an effective nonlinear Schrödinger (NLS) equation describing envelope waves for the rotational degree of freedom of FlexMM. Leveraging on the NLS equation we identify various type of nonlinear waves phenomena in FlexMM. In particular we observed that weakly nonlinear plane waves can be modulationally stable or unstable depending of the system and excitation parameters. Moreover we have found that the FlexMMs support envelope vector solitons where the units rotational degree of freedom might take the form of bright or dark soliton and due to coupling, the longitudinal displacement degree of freedom has a kink-like behavior. Finally, we address the phenomenon of "gradient catastrophe", which predicts the emergence of Peregrine soliton-like structures in the semiclassical limit of the NLS equation, in FlexMM. Through our analytical predictions and by using numerical simulations, we can determine the required conditions and the values of the physical parameters in order to observe these phenomena in FlexMMs
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Moussi, El hadi. "Analyse de structures vibrantes dotées de non-linéarités localisées à jeu à l'aide des modes non-linéaires". Thesis, Aix-Marseille, 2013. http://www.theses.fr/2013AIXM4792/document.
Testo completoAbstract (sommario):
Le travail de cette thèse a été réalisé dans le cadre d'une collaboration entre EDF R&D et le LMA de Marseille (CNRS). Le but était de développer des outils théoriques et numériques pour le calcul de modes non-linéaires de structures industrielles possédant des non-linéarités localisées à jeu. La méthode de calcul utilisée est une combinaison de la méthode d'équilibrage harmonique (EH) et de la méthode asymptotique numérique (MAN), appelée EHMAN. Elle est réputée pour sa robustesse sur les problèmes réguliers. L'enjeu de ce travail de thèse est de l'appliquer sur des problèmes non-réguliers régularisés de type butée à jeu pour lequel un grand nombre d'harmonique est nécessaire. Des améliorations ont été apportées à la méthode de base pour rendre effectif le traitement de modèles à "grand" nombre de degrés de liberté (DDL). Les développements réalisés pendant la thèse ont été capitalisés par la création de nouveaux opérateurs dans Code_Aster.Une étude approfondie d'un système à 2 degrés de liberté a permis de faire émerger quelques caractéristiques des systèmes non-linéaires à jeu. Celles-ci ont servi entre autre à établir une méthodologie pour l'étude de systèmes à grand nombre de DDL. Pour finir, la potentialité des modes non-linéaires comme outil de diagnostic vibratoire est démontrée avec l'étude d'un tube cintré de générateur de vapeur. Le calcul des modes non-linéaires a monté l'existence d'une interaction entre un mode hors-plan (basse fréquence) et un mode plan (haute fréquence) expliquant des régimes vibratoires non-standards. Ce résultat, impossible à obtenir avec les outils de l'analyse modale linéaire, est confirmé expérimentalementThis work is a collaboration between EDF R&D and the Laboratory of Mechanics and Acoustics. The objective is to develop theoretical and numerical tools to compute nonlinear normal modes (NNMs) of structures with localized nonlinearities.We use an approach combining the harmonic balance and the asymptotic numerical methods, known for its robustness principally for smooth systems. Regularization techniques are used to apply this approach for the study of nonsmooth problems. Moreover, several aspects of the method are improved to allow the computation of NNMs for systems with a high number of degrees of freedom (DOF). Finally, the method is implemented in Code_Aster, an open-source finite element solver developed by EDF R&D.The nonlinear normal modes of a two degrees-of-freedom system are studied and some original characteristics are observed. These observations are then used to develop a methodology for the study of systems with a high number of DOFs. The developed method is finally used to compute the NNMs for a model U-tube of a nuclear plant steam generator. The analysis of the NNMs reveals the presence of an interaction between an out-of-plane (low frequency) and an in-plane (high frequency) modes, a result also confirmed by the experiment. This modal interaction is not possible using linear modal analysis and confirms the interest of NNMs as a diagnostic tool in structural dynamics
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Karkar, Sami. "Méthodes numériques pour les systèmes dynamiques non linéaires : application aux instruments de musique auto-oscillants". Phd thesis, Aix-Marseille Université, 2012. http://tel.archives-ouvertes.fr/tel-00742651.
Testo completoAbstract (sommario):
Ces travaux s'articulent autour du calcul des solutions périodiques dans les systèmes dynamiques non linéaires, au moyen de méthodes numériques de continuation. La recherche de solutions périodiques se traduit par un problème avec conditions aux limites périodiques, pour lequel nous avons implémenté deux méthodes d'approximation : - Une méthode spectrale dans le domaine fréquentiel : l'équilibrage harmonique d'ordre élevé, qui repose sur une formulation quadratique des équations. Nous proposons en outre une formulation originale permettant d'étendre cette méthode aux cas de non-linéarités non rationnelles. - Une méthode pseudo-spectrale par éléments dans le domaine temporel : la collocation à l'aide fonctions polynômiales par morceaux. Ces méthodes transforment le problème continu en un système d'équations algébriques non linéaires, dont les solutions sont calculées par continuation à l'aide de la méthode asymptotique numérique. L'ensemble de ces outils, intégrés au code de calcul MANLAB et complétés d'une analyse linéaire de stabilité, sont alors utilisés pour l'étude des régimes périodiques d'une classe particulière de systèmes dynamiques non linéaires : les instruments de musique auto-oscillants. Un modèle physique non-régulier de clarinette est étudié en détail : à partir de la branche de solutions statiques et ses bifurcations, on calcule les différentes branches de solutions périodiques, ainsi que leur stabilité et leurs bifurcations. Ce modèle est ensuite adapté au cas du saxophone, pour lequel on intègre une caractérisation acoustique expérimentale, afin de mieux tenir compte de la géométrie complexe de l'instrument. Enfin, nous étudions un modèle physique simplifié de violon, avec une non-régularité liée frottement de Coulomb. Cette dernière application illustre ainsi la polyvalence des outils développés face aux différents types de non-régularité.
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Banquet, Brango Carlos Alberto. "Existencia e estabilidade de ondas viajantes periodicas para alguns modelos dispersivos". [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/305952.
Testo completoAbstract (sommario):
Orientadores: Marcia Assumpção Guimarães Scialom, Jaime Angulo PavaTese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica
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Resumo: O objetivo da tese é estudar algumas propriedades de soluções de equações diferenciais dispersivas. Primeiro, estabelecemos uma teoria de boa colocação local e global para a equação de Benjamin-Ono regularizada no contexto peri'odico, depois mostramos que o problema de Cauchy para esta equação (em ambos os casos periódico e não periódico) não pode ser resolvido usando um esquema iterativo baseado na fórmula de Duhamel em espaços de Sobolev com índice negativo. Adicionalmente, apresentamos a prova da existência de uma curva suave de soluções ondas viajantes periódicas, para a equação Benjamin-Ono regularizada, via o Teorema do Somatório de Poisson, com período minimal 2L fixo. Também é mostrado que estas soluções são não linearmente estáveis no espaço de energia H1/2per por perturbações do mesmo período. Como uma extensão da teoria estabelecida para a equação Benjamin-Ono regularizada é provado que as soluções ondas periódicas associadas as equações Benjamin-Bona-Mahony, Benjamin-Bona-Mahony modificada e 4-Benjamin-Bona-Mahony são não linearmente estáveis em H1per. Finalmente, provamos a existência e estabilidade não linear de uma família de soluções ondas dnoidal associadas ao sistema de Zakharov. Neste último caso, para obter as propriedades espectrais requeridas na prova da estabilidade foi usada a teoria de Floquet.
Abstract: The goal of this thesis is to study the properties of solutions of some dispersive differential equations. First, we develop a local and global well-posedness theory for the regularized Benjamin-Ono equation in the periodic setting, then, we show that the Cauchy problem for this equation (in both periodic and nonperiodic cases) cannot be solved by an iteration scheme based on the Duhamel formula for negative Sobolev indices. Additionally, a proof of the existence of a smooth curve of periodic travelling wave solutions, for the regularized Benjamin-Ono equation, with fixed minimal period 2L, is given. It is also shown that these solutions are nonlinearly stable in the energy space H1/2per by perturbations of the same wavelength. An extension of the theory developed for the regularized Benjamin-Ono equation is given and as examples it is proved that the periodic wave solutions associated to the Benjamin-Bona-Mahony, modified Benjamin-Bona-Mahony and 4-Benjamin-Bona- Mahony equations are nonlinearly stable in H1per. Finally, we prove the existence and the nonlinear estability of a family of dnoidal wave solutions associated to the Zakharov system. The Floquet theory is used in the last case to obtain the spectral properties required to prove the stability.
Doutorado
Matematica
Doutor em Matemática
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Kyjovský, Adam. "Periodická okrajová úloha v modelování kmitů nelineárních oscilátorů". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417091.
Testo completoAbstract (sommario):
This master's thesis deals with qualitative analysis of nonlinear differential equations of second order. For autonomous equations some basic notions of Hamiltonian systems (mainly construction of phase portrait) are presented. For non-autonomous equations the method of lower and upper functions for periodic boundary value problem is used. These notions are then applied to a model of mechanical oscillator, a question of existence of solutions to autonomous and non-autonomous nonlinear differential equations is studied.
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Hussein, Ahmed Abd Elmonem Ahmed. "Dynamical System Representation and Analysis of Unsteady Flow and Fluid-Structure Interactions". Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85626.
Testo completoAbstract (sommario):
A dynamical system approach is utilized to reduce the representation order of unsteady fluid flows and fluid-structure interaction systems. This approach allows for significant reduction in the computational cost of their numerical simulations, implementation of optimization and control methodologies and assessment of their dynamic stability. In the first chapter, I present a new Lagrangian function to derive the equations of motion of unsteady point vortices. This representation is a reconciliation between Newtonian and Lagrangian mechanics yielding a new approach to model the dynamics of these vortices. In the second chapter, I investigate the flutter of a helicopter rotor blade using finite-state time approximation of the unsteady aerodynamics. The analysis showed a new stability region that could not be determined under the assumption of a quasi-steady flow. In the third chapter, I implement the unsteady vortex lattice method to quantify the effects of tail flexibility on the propulsive efficiency of a fish. I determine that flexibility enhances the propulsion. In the fourth chapter, I consider the stability of a flapping micro air vehicle and use different approaches to design the transition from hovering to forward flight. I determine that first order averaging is not suitable and that time periodic dynamics are required for the controller to achieve this transition. In the fifth chapter, I derive a mathematical model for the free motion of a two-body planar system representing a fish under the action of coupled dynamics and hydrodynamics loads. I conclude that the psicform fish family are inherently stable under certain conditions that depend on the location of the center of mass.Ph. D.
We present modeling approaches of the interaction between flying or swimming bodies and the surrounding fluids. We consider their stability as they perform special maneuvers. The approaches are applied to rotating blades of helicopters, fish-like robots, and micro-air vehicles. We develop and validate a new mathematical representation for the flow generated by moving or deforming elements. We also assess the effects of fast variations in the flow on the stability of a rotating helicopter blade. The results point to a new stable regime for their operation. In other words, the fast flow variations could stabilize the rotating blades. These results can also be applied to the analysis of stability of rotating blades of wind turbines. We consider the effects of flexing a tail on the propulsive force of fish-like robots. The results show that adding flexibility enhances the efficiency of the fish propulsion. Inspired by the ability of some birds and insects to transition from hovering to forward motion, we thoroughly investigate different approaches to model and realize this transition. We determine that no simplification should be applied to the rigorous model representing the flapping flight in order to model transition phenomena correctly. Finally, we model the forward-swim dynamics of psciform and determine the condition on the center of mass for which a robotic fish can maintain its stability. This condition could help in designing fish-like robots that perform stable underwater maneuvers.
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Dias, Elaine Santos. "Caracterização da região de estabilidade de sistemas dinâmicos discretos não lineares". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18153/tde-21112016-110309/.
Testo completoAbstract (sommario):
O estudo da região de estabilidade é de extrema importância nas ciências, aplicações em engenharia e nos sistemas de controle não linear. Neste trabalho, uma caracterização completa da região de estabilidade e da fronteira da região de estabilidade de pontos fixos estáveis de uma classe ampla de sistemas dinâmicos discretos não lineares é desenvolvida. Os resultados deste trabalho estendem a caracterização da região de estabilidade já proposta na literatura para uma ampla classe de sistemas, modelados por difeomorfismos e que admitem a presença de órbitas periódicas e pontos fixos na fronteira da região de estabilidade. Caracterizações dinâmicas e topológicas são propostas para a fronteira da região de estabilidade. Além disso, são dadas condições necessárias e suficientes para que um ponto fixo ou órbita periódica pertença à fronteira da região de estabilidade. Exemplos numéricos, incluindo o modelo de uma rede neural simétrica com 2-neurônios, ilustram os resultados propostos neste trabalho.The study of the stability region is very important in the sciences, engineering applications, and in nonlinear control systems. In this work, a complete characterization for both the stability region and the stability boundary of stable xed points of a nonlinear discrete dynamical systems is developed. The results of this work extend the characterization of the stability region already proposed in the literature for a larger class of systems, which are modeled by dieomorphisms and which admit the presence of periodic orbits and xed points on the stability boundary. Several dynamical and topological characterizations are proposed to the stability boundary. Moreover, several necessary and sucient conditions for xed points and periodic orbits to lie on the stability boundary are derived. Numerical examples, including the model of a symmetric neural network with 2-neurons, illustrate the results proposed in this work.
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Prado, Joaquim Orlando. "Vibrações não lineares em tubulações com fluido em escoamento". Universidade Federal de Goiás, 2013. http://repositorio.bc.ufg.br/tede/handle/tede/6759.
Testo completoAbstract (sommario):
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this work, the linear and nonlinear instability of pipes conveying static and pulsating fluid flow is analyzed. The dynamic equation of motion was derived for cantilevered and clamped-clamped pipes. For this purpose, the Euler Bernoulli beam theory and Hamilton’s principle were applied, resulting in a partial differential equation of second order in time. Thus, a model with four degrees of freedom, which satisfies the boundary condition, is used and, the Galekin method is applied to derive the set of coupled non linear ordinary equations of motion which are, in turn, solved by the fourth order Runge-Kutta method, and then some numerical results were obtained as Argand diagram, stability boudaries, time response, phase plane and, Poincaré section, through computational algorithms modeled in C++. These results revealed the importance of the nonlinear terms in the stability of the system, especially in the post-critical analysis, also revealed the existence of quasi-periodic motions, for the system subjected to a static flow and, chaotic motions for pulsating fluid flow
Nesta dissertação analisa-se a instabilidade linear e não linear de tubos com fluido interno em escoamento estático e pulsante. A equação de movimento dinâmico foi deduzida para tubos em balanço e biengastados. Para tanto, utilizou-se a teoria de vigas de Euler Bernoulli e o princípio variacional de Hamilton, resultado em uma equação diferencial parcial de segunda ordem no tempo. Tal equação foi discretizada, pelo método de Galerkin, em quatro equações diferenciais ordinárias, uma para cada grau de liberdade, em seguida transformadas em um conjunto de equações diferenciais de primeira ordem. Tais equações foram integradas pelo método de Runge-Kutta de quarta ordem e, posteriormente, foram obtidos alguns resultados numéricos como: diagrama de Argand, curvas de escape, diagrama de bifurcação, resposta no tempo, plano fase e, seção de Poincaré, através de algoritmos implementados computacionalmente na linguagem C++. Tais resultados revelaram a importância dos termos não lineares na estabilidade do sistema, especialmente na análise pós-crítica, revelaram também a existência de movimentos quase periódicos, para o sistema submetido a um fluxo estático e, caóticos para fluxo pulsante.
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Van, Zyl Gideon Johannes. "The analysis of nonlinear systems driven by almost periodic inputs". Thesis, 2003. http://wwwlib.umi.com/cr/utexas/fullcit?p3116215.
Testo completo
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Su, Wei-Jr, e 蘇偉誌. "An Investigation of Nonlinear Periodic Motions for Frictional Systems". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/72970009240586072896.
Testo completoAbstract (sommario):
碩士國立臺灣科技大學
營建工程系
96
The objective of this thesis is to investigate the nonlinear periodic motions for frictional systems under frequency ratio effects. The Newmark average acceleration method is employed to solve the nonlinear displacement and velocity time histories. Three different frictional restoring force models are considered, restectively the classical friction model,the constant friction model, and the exponential friction model. It is shown that most responses exhibit distinct phase angle differences that are closely related to the ratio of external frequency to the natural frequency. For the the exponential friction model, the displacement and velocity can drift in one direction when the ratio of external frequency to the natural frequency is about 0.5.
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Rudko, Volodymyr. "Nonlinear Periodic Adaptive Control for Linear Time-Varying Plants". Thesis, 2013. http://hdl.handle.net/10012/7775.
Testo completoAbstract (sommario):
In adaptive control the goal is to deal with systems that have unknown and/or time-varying parameters. Adaptive control techniques have been developed since 1950’s and most results were proven in the cases when the time-variations were non-existent or slow. However the results pertaining to systems with fast time-variations are still limited, in particular, when it comes to plants with unstable zero dynamics.
In this work we adopt the controller design technique from the area of gain scheduling, where the time-varying parameter is assumed to be measurable. We propose the design of a nonlinear periodic controller, where in each period the state and parameter values are estimated and an appropriate stabilizing control signal is applied. It is shown that the closed loop system is stable under fast parameter variations with persistent jumps: the trajectory of the closed loop state in response to the initial condition is bounded by a decaying exponential plus a gain times the size of the noise. Our approach imposes several constraints on the plant; however, we show that there exists at least one interesting class of systems, which includes plants with unstable zero dynamics, that can be stabilized by our controller.
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"Stability and Reducibility of Quasi-Periodic Systems". Master's thesis, 2012. http://hdl.handle.net/2286/R.I.15103.
Testo completoAbstract (sommario):
abstract: In this work, we focused on the stability and reducibility of quasi-periodic systems. We examined the quasi-periodic linear Mathieu equation of the form x ̈+(ä+ϵ[cost+cosùt])x=0 The stability of solutions of Mathieu's equation as a function of parameter values (ä,ϵ) had been analyzed in this work. We used the Floquet type theory to generate stability diagrams which were used to determine the bounded regions of stability in the ä-ù plane for fixed ϵ. In the case of reducibility, we first applied the Lyapunov- Floquet (LF) transformation and modal transformation, which converted the linear part of the system into the Jordan form. Very importantly, quasi-periodic near-identity transformation was applied to reduce the system equations to a constant coefficient system by solving homological equations via harmonic balance. In this process we obtained the reducibility/resonance conditions that needed to be satisfied to convert a quasi-periodic system to a constant one.Dissertation/Thesis
M.S.Tech Engineering 2012
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Sukhorukov, Andrey. "Spatial solitons and guided waves in multicomponent and periodic optical systems". Phd thesis, 2002. http://hdl.handle.net/1885/146190.
Testo completo
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Mirus, Kevin A. "Control of nonlinear systems using periodic parametric perturbations with applications to a reversed field pinch". 1998. http://catalog.hathitrust.org/api/volumes/oclc/40806623.html.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of Wisconsin--Madison, 1998.Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 13-154).
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Bick, Christian. "Chaos and Chaos Control in Network Dynamical Systems". Doctoral thesis, 2012. http://hdl.handle.net/11858/00-1735-0000-000D-F0EE-8.
Testo completo
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Chen, Jyong-jhang, e 陳炯彰. "Analysis of nonlinear dynamical system under external periodic drive: synchronization, frequency locking and multi-periodicity". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/f5azjg.
Testo completoAbstract (sommario):
碩士國立中央大學
物理學系
104
We consider two nonlinear dynamical model(FitzHugh-Nagumo model and phase model) under periodic drive. First,external forcing on excitable FitzHugh-Nagumo (FHN) element in the presence of noise and is investigated as a function of the coupling strength.Periodic forcing of triangle, cosine and square waves are considered. The excitable element can exhibit multiple periodicity in certain range of coupling strengths. Histograms of the inter spike intervals are measured to quantify the weights of different multiple periods and the associated system memory. Second, oscillatory or excitable phase element driven by an external uniform rotator is investigated as a function of the coupling strength g. The excitable or oscillator phase element can exhibit frequency locked states in certain range of g. The frequency of the driven element shows a maximum as g increases. Remarkably, the driven element can exhibit a maximal locked frequency several times that of its intrinsic frequency or the driving frequency. Simple model can produce large frequency enhancement, with well-defined integer multiple frequency locked states, the frequency locked at m∙Ω state corresponds to period-m motion.
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Δερμιτζάκης, Ιωάννης. "Βελτιστοποίηση διεργασιών υπό περιοδική λειτουργία". Thesis, 2009. http://nemertes.lis.upatras.gr/jspui/handle/10889/1776.
Testo completoAbstract (sommario):
Το Πι-κριτήριο των Bittanti et al. (1973) έχει χρησιμοποιηθεί εκτενώς σε εφαρμογές με στόχο την πρόβλεψη ενδεχόμενης βελτίωσης της απόδοσης ενός μη γραμμικού συστήματος υπό περιοδική είσοδο. Το κριτήριο όμως έχει τοπική ισχύ και περιορίζεται σε περιοδικές διαταραχές μικρού πλάτους. Η παρούσα εργασία αναπτύσσει μια μέθοδο προσδιορισμού διορθώσεων υψηλότερης τάξης στο πι-κριτήριο, προερχόμενη από βασικά αποτελέσματα της θεωρίας κεντρικής πολλαπλότητας (Center Manifold theory). Η προτεινόμενη μέθοδος βασίζεται στην επίλυση της μερικής διαφορικής εξίσωσης της κεντρικής πολλαπλότητας με χρήση δυναμοσειρών. Το τελικό αποτέλεσμα της προτεινόμενης προσέγγισης είναι ο κατά προσέγγιση υπολογισμός του δείκτη απόδοσης υπό μορφή σειράς, η οποία παρέχει ακριβή αποτελέσματα σε μεγαλύτερα εύρη. Η προτεινόμενη μέθοδος εφαρμόζεται σε έναν συνεχή αντιδραστήρα πλήρους ανάδευσης (CSTR), όπου στόχος είναι η μεγιστοποίηση της παραγωγής του επιθυμητού προϊόντος.
Κατασκευάστηκε αλγόριθμος που προβλέπει την μόνιμη κατάσταση στην οποία καταλήγει ένα σύστημα απομάκρυνσης αζώτου που αποτελείται από αντιδραστήρα εμβολικής ροής και δεξαμενή δευτεροβάθμιας καθίζησης με ανακύκλωση. Με χρήση υπολογιστικού μοντέλου βασιζόμενο στο ASM3 υπολογίστηκαν οι μόνιμες καταστάσεις αυτού του συστήματος για ένα εύρος καταστάσεων λειτουργίας. Βρέθηκαν οι βέλτιστες τιμές των βαθμών ελευθερίας για την ελαχιστοποίηση του συνολικού αερισμού και για την ελαχιστοποίηση του συνολικού αζώτου στην απορροή. Και στις δύο περιπτώσεις στις βέλτιστες μόνιμες καταστάσεις παρατηρήθηκε έκπλυση των Nitrobacter δηλαδή παράκαμψη της παραγωγής των νιτρικών.The frequency-dependent Pi criterion of Bittanti et al. (1973) has been used extensively in applications to predict potential performance improvement under periodic forcing in a nonlinear system. The criterion, however, is local in nature and is limited to periodic forcing functions of small magnitude. The present work develops a method to determine higher-order corrections to the pi criterion, derived from basic results of Center Manifold theory. The proposed method is based on solving the Center Manifold partial differential equation via power series. The end result of the proposed approach is the approximate calculation of the performance index in the form of a series expansion, which provides accurate results under larger amplitudes. The proposed method is applied to a continuous stirred tank reactor, where the yield of the desired product must be maximized. An algorithm was constructed, that predicts the steady state of a nitrogen removal system consisting of a plug flow reactor and a secondary clarifier with recycle. Using a numerical model based on ASM3 and a grid of degrees of freedom, the steady states of this system were calculated. The optimal values for minimizing the total aeration were found, as well as those for minimizing the total nitrogen exit flow. In both cases the Nitrobacter bacteria were washed out thus indicating the bypassing of nitrate production.