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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.
261

Efficient Numerical Solution of Large Scale Algebraic Matrix Equations in PDE Control and Model Order Reduction

Saak, Jens 25 September 2009 (has links)
Matrix Lyapunov and Riccati equations are an important tool in mathematical systems theory. They are the key ingredients in balancing based model order reduction techniques and linear quadratic regulator problems. For small and moderately sized problems these equations are solved by techniques with at least cubic complexity which prohibits their usage in large scale applications. Around the year 2000 solvers for large scale problems have been introduced. The basic idea there is to compute a low rank decomposition of the quadratic and dense solution matrix and in turn reduce the memory and computational complexity of the algorithms. In this thesis efficiency enhancing techniques for the low rank alternating directions implicit iteration based solution of large scale matrix equations are introduced and discussed. Also the applicability in the context of real world systems is demonstrated. The thesis is structured in seven central chapters. After the introduction chapter 2 introduces the basic concepts and notations needed as fundamental tools for the remainder of the thesis. The next chapter then introduces a collection of test examples spanning from easily scalable academic test systems to badly conditioned technical applications which are used to demonstrate the features of the solvers. Chapter four and five describe the basic solvers and the modifications taken to make them applicable to an even larger class of problems. The following two chapters treat the application of the solvers in the context of model order reduction and linear quadratic optimal control of PDEs. The final chapter then presents the extensive numerical testing undertaken with the solvers proposed in the prior chapters. Some conclusions and an appendix complete the thesis.
262

Parameter identification problems for elastic large deformations - Part I: model and solution of the inverse problem

Meyer, Marcus 20 November 2009 (has links)
In this paper we discuss the identification of parameter functions in material models for elastic large deformations. A model of the the forward problem is given, where the displacement of a deformed material is found as the solution of a n onlinear PDE. Here, the crucial point is the definition of the 2nd Piola-Kirchhoff stress tensor by using several material laws including a number of material parameters. In the main part of the paper we consider the identification of such parameters from measured displacements, where the inverse problem is given as an optimal control problem. We introduce a solution of the identification problem with Lagrange and SQP methods. The presented algorithm is applied to linear elastic material with large deformations.
263

Virtual Partial Reconfiguration Framework for the Digilent Nexys 3 Board

Lertlaokul, Kawin 12 September 2019 (has links)
The modern embedded system is getting more complicated due to the functional requirements of the system are rapidly increasing. The modern system must have more reliable, as it deals with a lot of data. The distributed systems are used in variety technologies field due to it has more reliable than single control unit. It can transfer task to other processing unit when the one part of system failed while the single control unit failed cause the system to stop operate. The FPGA are being used increasingly in the distributed system due to the benefit of FPGA over microcontroller and ASIC. FPGA is flexible than ASIC due to the ability to reconfiguration its function. FPGA processes the data in parallel, therefore, it computes the data faster than the microcontroller that computes the data in concurrence. The flexibility of FPGA supports the development of reliable distributed system. When one of FPGA failed, the other FPGA can reconfiguration itself to operate on the task of the failed FPGA. The method to reconfigure the FPGA structure is a process of loading new bitstream file into FPGA. For generating variety configurations of distributed system. The developer must develop number of bitstream file according to number of reconfiguration designs. Although the FPGA is flexible and can reconfiguration anytime, the development process of configuration file is a redundancy workload. One FPGA design structure equals one configuration file. This project focus on reduce the redundancy workload, therefore, it can reduce the development time and make the development project launching faster. This virtual partial reconfiguration framework is developed to assist the developer in generating many configuration files without coding. The framework will determine all possible combination of modules and generates all combination design files. One set of the design contain the VHDL file and UCF file. The developer can use these files to synthesise in FPGA vendor development tool and generate bitstream. This virtual partial reconfiguration framework also provides the partial reconfiguration benefits except runtime reconfiguration.
264

Analytical solution of a linear, elliptic, inhomogeneous partial differential equation with inhomogeneous mixed Dirichlet- and Neumann-type boundary conditions for a special rotationally symmetric problem of linear elasticity

Eschke, Andy January 2014 (has links)
The analytical solution of a given inhomogeneous boundary value problem of a linear, elliptic, inhomogeneous partial differential equation and a set of inhomogeneous mixed Dirichlet- and Neumann-type boundary conditions is derived in the present paper. In the context of elasticity theory, the problem arises for a non-conservative symmetric ansatz and an extended constitutive law shown earlier. For convenient user application, the scalar function expressed in cylindrical coordinates is primarily obtained for the general case before being expatiated on a special case of linear boundary conditions.
265

Solution strategies for stochastic finite element discretizations

Ullmann, Elisabeth 23 June 2008 (has links)
The discretization of the stationary diffusion equation with random parameters by the Stochastic Finite Element Method requires the solution of a highly structured but very large linear system of equations. Depending on the stochastic properties of the diffusion coefficient together with the stochastic discretization we consider three solver cases. If the diffusion coefficient is given by a stochastically linear expansion, e.g. a truncated Karhunen-Loeve expansion, and tensor product polynomial stochastic shape functions are employed, the Galerkin matrix can be transformed to a block-diagonal matrix. For the solution of the resulting sequence of linear systems we study Krylov subspace recycling methods whose success depends on the ordering and grouping of the linear systems as well as the preconditioner. If we use complete polynomials for the stochastic discretization instead, we show that decoupling of the Galerkin matrix with respect to the stochastic degrees of freedom is impossible. For a stochastically nonlinear diffusion coefficient, e.g. a lognormal random field, together with complete polynomials serving as stochastic shape functions, we introduce and test the performance of a new Kronecker product preconditioner, which is not exclusively based on the mean value of the diffusion coefficient.
266

Well-posedness and causality for a class of evolutionary inclusions

Trostorff, Sascha 25 October 2011 (has links)
We study a class of differential inclusions involving maximal monotone relations, which cover a huge class of problems in mathematical physics. For this purpose we introduce the time derivative as a continuously invertible operator in a suitable Hilbert space. It turns out that this realization is a strictly monotone operator and thus, the question on existence and uniqueness can be answered by well-known results in the theory of maximal monotone relations. Furthermore, we show that the resulting solution operator is Lipschitz-continuous and causal, which is a natural property of evolutionary processes. Finally, the results are applied to a system of partial differential equations and inclusions, which describes the diffusion of a compressible fluid through a saturated, porous, plastically deforming media, where certain hysteresis phenomena are modeled by maximal montone relations.
267

Quantum signatures of partial barriers in phase space

Michler, Matthias 30 September 2011 (has links)
Generic Hamiltonian systems have a mixed phase space, in which regular and chaotic motion coexist. In the chaotic sea the classical transport is limited by partial barriers, which allow for a flux \Phi given by the corresponding turnstile area. Quantum mechanically the transport is suppressed if Planck's constant is large compared to the classical flux, h >> \Phi, while for h << \Phi classical transport is recovered. For the transition between these limiting cases there are many open questions, in particular concerning the correct scaling parameter and the width of the transition. To investigate this transition in a controlled way, we design a kicked system with a particularly simple phase-space structure, consisting of two chaotic regions separated by one dominant partial barrier. We find a universal scaling with the single parameter \Phi/h and a transition width of almost two orders of magnitude in \Phi/h. In order to describe this transition, we consider several matrix models. While the numerical data is not well described by the random matrix model proposed by Bohigas, Tomsovic, and Ullmo, a deterministic 2x2-model, a channel coupling model, and a unitary model are presented, which describe the transitional behavior of the designed kicked system. This is also confirmed for the generic standard map, suggesting a universal scaling behavior for the quantum transition of a partial barrier. / Generische Hamilton'sche Systeme besitzen einen gemischten Phasenraum, in dem sowohl reguläre als auch chaotische Dynamik vorkommen. Der klassische Transport in der chaotischen See wird durch partielle Barrieren begrenzt, die nur einen Fluss \Phi hindurch lassen. Der quantenmechanische Transport ist stark unterdrückt, wenn die Planck'sche Konstante groß gegen den klassischen Fluss ist, h >> \Phi. Ist hingegen h << \Phi folgt die Quantenmechanik der klassischen Dynamik. Für den Übergangsbereich zwischen diesen Grenzfällen gibt es noch viele offene Fragen, insbesondere bezüglich des richtigen Skalierungsparameters und der Breite des Übergangs. Um gezielt diesen Übergang zu untersuchen, haben wir ein System mit einem besonders einfachen Phasenraum entworfen. Er besteht aus zwei chaotischen Gebieten, die durch eine dominante partielle Barriere getrennt sind. Es zeigt sich, dass das universelle Verhalten durch den Parameter \Phi/h beschrieben wird und der Übergang sich über zwei Größenordnungen erstreckt. Wir betrachten verschiedene Matrixmodelle um diesen Übergang zu verstehen. Die numerischen Daten werden nicht durch das Zufallsmatrixmodell von Bohigas, Tomsovic und Ullmo beschrieben. Ein deterministisches 2x2-Modell, eine Kanalkopplung und ein unitäres Matrixmodell beschreiben hingegen den Übergang des entworfenen gekickten Systems. Die Tatsache, dass auch die generische Standardabbildung diesem Verhalten folgt, spricht für ein universelles Verhalten des Quantenübergangs einer partiellen Barriere.
268

Chaotic transport and partial barriers in 4D symplectic maps

Firmbach, Markus 02 March 2021 (has links)
Hamiltonian systems typically exhibit a mixed phase space in which regions of regular and chaotic dynamics coexist. The chaotic transport is restricted due to partial barriers, since they only allow for a small flux between different regions of phase space. In systems with a two-dimensional (2D) phase space these partial barriers are well understood. However, in systems with a four-dimensional (4D) phase space their dynamical origin is an open question. Thus, we study these partial barriers and the related chaotic transport in 4D maps. For the chaotic transport, we observe a slow power-law decay of the Poincaré recurrence statistics. This is caused by long-trapped orbits exploring stochastic layers of resonance channels. Moreover, we analyze them and find clear signatures of partial transport barriers. We identify normally hyperbolic invariant manifolds (NHIMs) as the relevant objects determining the flux across these barriers. In addition, NHIMs also form the backbone for the explicit construction of partial barriers. This allows us to determine the flux by measuring the turnstile volume. Moreover, we conjecture the existence of a relevant partial barrier with minimal flux by generalizing a cantorus barrier present in 2D maps. Local properties of the flux are studied and explained in terms of the NHIM. / Hamiltonische Systeme zeigen üblicherweise einen gemischten Phasenraum, in dem Bereiche regulärer und chaotischer Dynamik vorherrschen. Der chaotische Transport wird durch partielle Barrieren behindert, da diese nur einen kleinen Fluss zwischen getrennten Bereichen des Phasenraums zulassen. Für Systeme mit einem zweidimensionalen (2D) Phasenraum sind diese bereits gut verstanden. Hingegen ist deren dynamischer Ursprung in Systemen mit einem vierdimensionalen (4D) Phasenraum noch ungeklärt. In dieser Arbeit betrachten wir deshalb in 4D Abbildungen sowohl chaotischen Transport, als auch partielle Barrieren. Für den chaotischen Transport lässt sich die Verteilung der Poincaré-Rückkehrzeiten durch ein Potenzgesetz beschreiben. Lange Rückkehrzeiten sind dabei auf Trajektorien zurückzuführen, die in den chaotischen Bereichen von Resonanzkanälen verweilen. Für diese stellen wir eindeutige Signaturen von partiellen Barrieren fest. Es zeigt sich, dass normal hyperbolische invariante Mannigfaltigkeiten (NHIM) die maßgeblichen Objekte sind, die den Fluss über partielle Barrieren beschreiben. Anhand dieser lassen sich auch partiellen Barrieren explizit konstruieren, was uns wiederum ermöglicht den Fluss mittels einer Volumenmessung zu bestimmen. Durch die Verallgemeinerung einer Cantorusbarriere, die bereits in 2D Abbildungen auftreten, finden wir eine relevante partielle Barriere mit kleinstem Fluss. Weiterhin betrachten wir die lokale Abhängigkeit des Flusses, welche sich mittels der NHIM beschreiben lässt.
269

Le maintien de la cohérence dans les systèmes de stockage partiellement repliqués / Ensuring consistency in partially replicated data stores

Saeida Ardekani, Masoud 16 September 2014 (has links)
Dans une première partie, nous étudions la cohérence dans les systèmes transactionnels, en nous concentrant sur le problème de réconcilier la scalabilité avec des garanties transactionnelles fortes. Nous identifions quatre propriétés critiques pour la scalabilité. Nous montrons qu’aucun des critères de cohérence forte existants n’assurent l’ensemble de ces propriétés. Nous définissons un nouveau critère, appelé Non-Monotonic Snapshot Isolation ou NMSI, qui est le premier à être compatible avec les quatre propriétés à la fois. Nous présentons aussi une mise en œuvre de NMSI, appelée Jessy, que nous comparons expérimentalement à plusieurs critères connus. Une autre contribution est un canevas permettant de comparer de façon non biaisée différents protocoles. Elle se base sur la constatation qu’une large classe de protocoles transactionnels distribués est basée sur une même structure, Deferred Update Replication(DUR). Les protocoles de cette classe ne diffèrent que par les comportements spécifiques d’un petit nombre de fonctions génériques. Nous présentons donc un canevas générique pour les protocoles DUR.La seconde partie de la thèse a pour sujet la cohérence dans les systèmes de stockage non transactionnels. C’est ainsi que nous décrivons Tuba, un stockage clef-valeur qui choisit dynamiquement ses répliques selon un objectif de niveau de cohérence fixé par l’application. Ce système reconfigure automatiquement son ensemble de répliques, tout en respectant les objectifs de cohérence fixés par l’application, afin de s’adapter aux changements dans la localisation des clients ou dans le débit des requête. / In the first part, we study consistency in a transactional systems, and focus on reconciling scalability with strong transactional guarantees. We identify four scalability properties, and show that none of the strong consistency criteria ensure all four. We define a new scalable consistency criterion called Non-Monotonic Snapshot Isolation (NMSI), while is the first that is compatible with all four properties. We also present a practical implementation of NMSI, called Jessy, which we compare experimentally against a number of well-known criteria. We also introduce a framework for performing fair comparison among different transactional protocols. Our insight is that a large family of distributed transactional protocols have a common structure, called Deferred Update Replication (DUR). Protocols of the DUR family differ only in behaviors of few generic functions. We present a generic DUR framework, called G-DUR. We implement and compare several transactional protocols using the G-DUR framework.In the second part, we focus on ensuring consistency in non-transactional data stores. We introduce Tuba, a replicated key-value store that dynamically selects replicas in order to maximize the utility delivered to read operations according to a desired consistency defined by the application. In addition, unlike current systems, it automatically reconfigures its set of replicas while respecting application-defined constraints so that it adapts to changes in clients’ locations or request rates. Compared with a system that is statically configured, our evaluation shows that Tuba increases the reads that return strongly consistent data by 63%.
270

Classical and quantum transport in 4D symplectic maps

Stöber, Jonas 21 March 2023 (has links)
Partial transport barriers in the chaotic sea of Hamiltonian systems restrict classical chaotic transport, as they only allow for a small flux between phase-space regions. In two-dimensional (2D) symplectic maps, the most restrictive partial barriers are based on a cantorus, the remnants of a broken one-dimensional (1D) torus forming a Cantor set. Quantum mechanically for 2D symplectic maps one has a universal transition from impeded to unimpeded transport. The scaling parameter is the ratio of flux to the Planck cell of size h, so quantum transport is suppressed if h is much bigger than the flux while mimicking classical transport if it is much smaller. Whether a transition exists in higher-dimensional systems and how it scales is still an open question and will be answered in this talk. In a four-dimensional (4D) symplectic map, the cantorus is generalized to a normally hyperbolic invariant manifold (NHIM) with the structure of a cantorus. Using the general flux formula, we consider higher-order periodic NHIMs to approximate the global flux across a partial barrier. One naively expects that the scaling parameter of the universal transition is the same, but now with a Planck cell h squared. We show that due to classical diffusive transport along resonance channels, the quantized system exhibits dynamical localization and the localization length modifies the scaling parameter. / Partielle Transportbarrieren in der chaotischen See von Hamiltonischen Systemen schränken den klassischen chaotischen Transport ein, indem sie nur einen kleinen Fluss zwischen Phasenraumregionen zulassen. In zweidimensionalen (2D) symplektischen Abbildungen basieren die restriktivsten partiellen Barrieren auf einem Cantorus, die Cantor-Menge der Überreste eines zerstörten ein-dimensionalen (1D) Torus. In quantisierten 2D symplektischen Abbildungen findet man einen universellen Übergang von eingeschränktem zu uneingeschränktem Transport. Der Skalierungsparameter ist das Verhältnis vom Fluss zur Planck-Zelle der Größe h, so dass der quantenmechanische Transport unterdrückt ist, wenn h sehr viel größer ist als der Fluss, während klassischer Transport nachgeahmt wird, wenn er sehr viel kleiner ist. Ob jedoch auch ein universeller Übergang in höherdimensionalen Systemen existiert und wie er skaliert, ist bislang ungeklärt und wird in dieser Arbeit untersucht. In einer vierdimensionalen (4D) symplektischen Abbildung ist die Verallgemeinerung des Cantorus eine normal hyperbolische invariante Mannigfaltigkeit (NHIM) mit der Struktur eines Cantorus. Wir betrachten periodische NHIMs höherer Ordnung um den globalen Fluss durch eine partielle Barriere mit der allgemeinen Flussformel zu approximieren. Naiverweise erwartet man, dass der Skalierungsparameter des universellen Übergangs gleich ist, jedoch mit der neuen Größe der Planck-Zelle h quadriert. Wir zeigen, dass aufgrund von klassischen, diffusiven Transport entlang von Resonanzkanälen das quantisierte System dynamische Lokalisierung aufweist und die Lokalisierungslänge Einfluss auf den Skalierungsparameter hat.

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