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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Homogenization of Rapidly Oscillating Riemannian Manifolds

Hoppe, Helmer 12 April 2021 (has links)
In this thesis we study the asymptotic behavior of bi-Lipschitz diffeomorphic weighted Riemannian manifolds with techniques from the theory of homogenization. To do so we re-interpret the problem as different induced metrics on one reference manifold. Our analysis is twofold. On the one hand we consider second-order uniformly elliptic operators on weighted Riemannian manifolds. They naturally emerge when studying spectral properties of the Laplace-Beltrami operator on families of manifolds with rapidly oscillating metrics. We appeal to the notion of H-convergence introduced by Murat and Tartar. In our first main result we establish an H-compactness result that applies to elliptic operators with measurable, uniformly elliptic coefficients on weighted Riemannian manifolds. We further discuss the special case of locally periodic coefficients and study the asymptotic spectral behavior of Euclidean submanifolds with rapidly oscillating geometry. On the other hand we study integral functionals featuring non-convex integrands with non-standard growth on the Euclidean space in a stochastic framework. Our second main result is a Γ-convergence statement under certain assumptions on the statistics of their integrands. Such functionals provide a tool to study the Dirichlet energy on non-uniformly bi-Lipschitz diffeomorphic manifolds. We show Mosco-convergence of the Dirichlet energy and deduce conditions for the spectral behavior of weighted Riemannian manifolds with locally oscillating random structure, especially in the case of Euclidean submanifolds.:Introduction Outline Notation I. Preliminaries 1. Convergence of Riemannian Manifolds 1.1. Hausdorff-Convergence 1.2. Gromov-Hausdorff-Convergence 1.3. Spectral Convergence 1.4. Mosco-Convergence 2. Homogenization 2.1. Periodic Homogenization 2.2. Stochastic Homogenization II. Uniformly bi-Lipschitz Diffeomorphic Manifolds 3. Uniformly Elliptic Operators on a Riemannian Manifold 3.1. Setting 3.2. Main Results 3.3. Strategy of the Proof and Auxiliary Results 3.4. Identi cation of the Limit via Local Coordinate Charts 3.5. Examples 3.6. Proofs 4. Application to Uniformly bi-Lipschitz Diffeomorphic Manifolds 4.1. Setting and Results 4.2. Examples 4.3. Proofs III. Rapidly Oscillating Random Manifolds 5. Integral Functionals with Non-Uniformal Growth 5.1. Setting 5.2. Main Results 5.3. Strategy of the Proof and Auxiliary Results 5.4. Proofs 6. Application to Rapidly Oscillating Riemannian Manifolds 6.1. Setting and Results 6.2. Examples 6.3. Proofs Summary and Discussion Bibliography List of Figures
2

Existence Theorems, Stationarity Conditions and Adaptive Numerical Methods for Generalized Nash Equilibrium Problems Constrained by Partial Differential Equations

Stengl, Steven-Marian 18 November 2024 (has links)
Die vorliegende Arbeit befasst sich mit verallg. Nash-Gleichgewichtsproblemen im Zusammenhang mit Optimalsteuerungsproblemen mit (nichtlinearen) partiellen Differentialgleichungen. Ausgehend von der Existenzfrage von Nash-Gleichgewichten werden Bedingungen an Optimalsteuerungsprobleme mit nichtlinearen Lösungsoperatoren hergeleitet, welche die Konvexität des reduzierten Problems garantieren. Dazu nutzen wir die verallg. Konvexität von vektorwertigen Operatoren. Da keine expl. Darstellung des Lösungsoperators bekannt ist, werden hinreichende Bedingungen an die Operatorgleichung formuliert. Zusammen mit Anforderungen an das Zielfunktional wird so die Konvexität des reduzierten Problems garantiert. Das erlaubt auch Stationaritätssysteme im nichtglatten Fall herzuleiten. Eine zusätzliche Bedingung an die Lösung der Operatorgleichung koppelt die Strategien der Spieler. Das markiert den Übergang zu verallgemeinerten Nash-Spielen. Um diese Probleme anzugehen, wenden wir eine Penalty-Technik an. Damit wird die beschriebene Abhängigkeit vermieden und zum Zielfunktional transportiert. Damit wird eine Folge von Ersatzproblemen formuliert, deren Grenze das ursprüngliche Problem ist. Für die mathematische Beschreibung entwickeln wir eine erweiterte Γ-Konvergenz für Gleichgewichtsprobleme. Das Verhalten der Lagrange-Multiplikatoren im Stationaritätssystem wird unter Verwendung einer Pfadverfolgungstechnik analysiert und eine numerisch nutzbare Updatestrategie wird hergeleitet. Für ein praktisch anwendbares Lösungsverfahren ist eine Diskretisierung notwendig. Dazu verwenden wir eine Finite-Elemente-Methode. Die Herleitung der A-priori-Konvergenz basierend auf der zuvor verallgemeinerten Γ-Konvergenz wird für Gleichgewichtsprobleme mit gleichzeitiger Regularisierung etabliert. Im Blick auf durch Hindernisbedingungen erzeugte Kontaktmengen wenden wir uns auch adaptiven Finite-Elemente-Methoden zu. Unsere theoretischen Ergebnisse werden durch mehrere akademische Anwendungen illustriert. / The present work deals with generalized Nash equilibrium problems related to optimal control problems on (nonlinear) partial differential equations. Starting from the question of the existence of Nash equilibria, conditions for optimal control problems with nonlinear solution operators are derived that guarantee the convexity of the reduced problem. To do so, we discuss generalized convexity of vector-valued operators. As no explicit representation of the solution operator is known, conditions on the operator equation that imply this property are formulated. In combination with requirements for the objective functional, the convexity of the reduced problem can be guaranteed. This approach also allows us to derive stationarity systems even in the nonsmooth case. The presence of a condition on the solution of the operator equation couples the players' strategies. This marks the transition to generalized Nash games. To address these problems, we apply a penalty technique. Hence, the described dependency is avoided and transported to the objective. As the penalty functional is scaled with a parameter, a sequence of surrogate problems, whose limit is the original problem, is formulated. For its mathematical description, we introduce an extended Γ-convergence for equilibrium problems. The behavior of the Lagrangian multipliers in the stationarity system is analyzed using a path-following technique, and a numerically usable update strategy is derived. A discretization is necessary for a practically applicable solution method. For this, we use a finite element method. The derivation of the a priori convergence based on the previously generalized Γ-convergence is established for equilibrium problems with simultaneous regularization. With regard to the presence of contact sets induced by obstacle conditions, we also turn to adaptive finite element methods. Our theoretical results are illustrated by several academic applications.

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