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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.
101

Hybridization of FETI Methods / Hybridation de méthodes FETI

Molina-Sepulveda, Roberto 19 December 2017 (has links)
Dans le présent travail, des nouvelles méthodes de décomposition de domaine et des nouvelles implémentations pour des méthodes existantes sont développées. Une nouvelle méthode basée sur les méthodes antérieures de décomposition du domaine est formulée. Les méthodes classiques FETI plus FETI-2LM sont utilisées pour construire le nouveau Hybrid-FETI. L'idée de base est de développer un nouvel algorithme qui peut utiliser les deux méthodes en même temps en choisissant dans chaque interface l'état le plus adapté en fonction des caractéristiques du problème. En faisant cela, nous recherchons un code plus rapide et plus robuste qui peut fonctionner avec des configurations selon lesquelles les méthodes de base ne le géreront pas de manière optimale par lui-même. La performance est testée sur un problème de contact. La partie suivante implique le développement d'une nouvelle implémentation pour la méthode S-FETI, l'idée est de réduire l'utilisation de la mémoire de cette méthode, afin de pouvoir fonctionner dans des problèmes de taille plus important. Différentes variantes pour cette méthode sont également proposées, tout en cherchant la réduction des directions stockées chaque itération de la méthode itérative. Finalement, une extension de la méthode FETI-2LM à sa version en bloc comme dans S-FETI, est développée. Les résultats numériques pour les différents algorithmes sont présentés. / In this work new domain decomposition methods and new implementations for existing methods are developed. A new method based on previous domain decomposition methods is formulated. The classic FETI plus FETI-2LM methods are used to build the new Hybrid-FETI. The basic idea is to develop a new algorithm that can use both methods at the same time by choosing in each interface the most suited condition depending on the characteristics of the problem. By doing this we search to have a faster and more robust code that can work with configurations that the base methods will not handle it optimally by himself. The performance is tested on a contact problem. The following part involves the development of a new implementation for the S-FETI method, the idea is to reduce the memory usage of this method, to make it able to work in larger problem. Different variation for this method are also proposed, all searching the reduction of directions stored each iteration of the iterative method. Finally, an extension of the FETI-2LM method to his block version as in S-FETI, is developed. Numerical results for the different algorithms are presented.
102

Multiphysics and Large-Scale Modeling and Simulation Methods for Advanced Integrated Circuit Design

Shuzhan Sun (11564611) 22 November 2021 (has links)
<div>The design of advanced integrated circuits (ICs) and systems calls for multiphysics and large-scale modeling and simulation methods. On the one hand, novel devices and materials are emerging in next-generation IC technology, which requires multiphysics modeling and simulation. On the other hand, the ever-increasing complexity of ICs requires more efficient numerical solvers.</div><div><br></div><div>In this work, we propose a multiphysics modeling and simulation algorithm to co-simulate Maxwell's equations, dispersion relation of materials, and Boltzmann equation to characterize emerging new devices in IC technology such as Cu-Graphene (Cu-G) hybrid nano-interconnects. We also develop an unconditionally stable time marching scheme to remove the dependence of time step on space step for an efficient simulation of the multiscaled and multiphysics system. Extensive numerical experiments and comparisons with measurements have validated the accuracy and efficiency of the proposed algorithm. Compared to simplified steady-state-models based analysis, a significant difference is observed when the frequency is high or/and the dimension of the Cu-G structure is small, which necessitates our proposed multiphysics modeling and simulation for the design of advanced Cu-G interconnects. </div><div><br></div><div>To address the large-scale simulation challenge, we develop a new split-field domain-decomposition algorithm amenable for parallelization for solving Maxwell’s equations, which minimizes the communication between subdomains, while having a fast convergence of the global solution. Meanwhile, the algorithm is unconditionally stable in time domain. In this algorithm, unlike prevailing domain decomposition methods that treat the interface unknown as a whole and let it be shared across subdomains, we partition the interface unknown into multiple components, and solve each of them from one subdomain. In this way, we transform the original coupled system to fully decoupled subsystems to solve. Only one addition (communication) of the interface unknown needs to be performed after the computation in each subdomain is finished at each time step. More importantly, the algorithm has a fast convergence and permits the use of a large time step irrespective of space step. Numerical experiments on large-scale on-chip and package layout analysis have demonstrated the capability of the new domain decomposition algorithm. </div><div><br></div><div>To tackle the challenge of efficient simulation of irregular structures, in the last part of the thesis, we develop a method for the stability analysis of unsymmetrical numerical systems in time domain. An unsymmetrical system is traditionally avoided in numerical formulation since a traditional explicit simulation is absolutely unstable, and how to control the stability is unknown. However, an unsymmetrical system is frequently encountered in modeling and simulating of unstructured meshes and nonreciprocal electromagnetic and circuit devices. In our method, we reduce stability analysis of a large system into the analysis of dissembled single element, therefore provides a feasible way to control the stability of large-scale systems regardless of whether the system is symmetrical or unsymmetrical. We then apply the proposed method to prove and control the stability of an unsymmetrical matrix-free method that solves Maxwell’s equations in general unstructured meshes while not requiring a matrix solution.<br></div><div><br></div>
103

Quelques approches non linéaires en réduction de complexité / A few non linear approaches in model order reduction

Cagniart, Nicolas 05 November 2018 (has links)
Les méthodes de réduction de modèles offrent un cadre général permettant une réduction de coûts de calculs substantielle pour les simulations numériques. Dans cette thèse, nous proposons d’étendre le domaine d’application de ces méthodes. Le point commun des sujets discutés est la tentative de dépasser le cadre standard «bases réduites» linéaires, qui ne traite que les cas où les variétés solutions ont une petite épaisseur de Kolmogorov. Nous verrons comment tronquer, translater, tourner, étirer, comprimer etc. puis recombiner les solutions, peut parfois permettre de contourner le problème qui se pose lorsque cette épaisseur de Kolmogorov n’est pas petite. Nous évoquerons aussi le besoin de méthodes de stabilisation sur-mesure pour le cadre réduit. / Model reduction methods provide a general framework for substantially reducing computational costs of numerical simulations. In this thesis, we propose to extend the scope of these methods. The common point of the topics discussed here is the attempt to go beyond the standard linear "reduced basis" framework, which only deals with cases where the solution manifold have a small Kolmogorov width. We shall see how truncate, translate, rotate, stretch, compress etc. and then recombine the solutions, can sometimes help to overcome the problem when this Kolmogorov width is not small. We will also discuss the need for tailor-made stabilisation methods for the reduced frame.
104

How to improve the numerical reproducibility of hydrodynamics simulations : analysis and solutions for one open-source HPC software

Nheili, Rafife 07 December 2016 (has links)
La non-reproductibilité numérique apparait dans divers domaines d'application de la simulation HPC. En effet, les différentes distributions d'un calcul parallèle peuvent mener à des résultats numériques différents, à cause des particularités de l'arithmétique flottante. Le besoin de reproductibilité numérique est motivé pour le débogage, le test et la validation des codes de calcul scientifique. Nous nous intéressons aux simulations par éléments finis en hydrodynamique implémentées dans le logiciel openTelemac qui est largement utilisé pour des applications industrielles et scientifiques. Nous identifions et analysons les sources de cette non-reproductibilité. Nous définissons et implementons comment récupérer la reproductibilité numérique de deux modules d'openTelemac. Nous mesurons que le sur-coût en terme de temps de calcul de la version reproductible est tout à fait raisonnable en pratique. / HPC simulations in various scientific domains suffer from failures of numerical reproducibility because of floating-point arithmetic peculiarities. Different distributions of a parallel computation may yield different numerical results. Numerical reproducibility is a requested feature to facilitate the debug, the validation and the test of industrial or large software. In this thesis, we focus on the openTelemac software that implements finite element simulation for industrial and scientific hydrodynamics. We identify and analyze the sources of this reproducibility failure. We define and implement how to recover numerical reproducibility in two openTelemac modules. We also measure that the running time extra-cost of the reproducible version is reasonable enough in practice.
105

FEM auf irregulären hierarchischen Dreiecksnetzen

Groh, U. 30 October 1998 (has links)
From the viewpoint of the adaptive solution of partial differential equations a finit e element method on hierarchical triangular meshes is developed permitting hanging nodes arising from nonuniform hierarchical refinement. Construction, extension and restriction of the nonuniform hierarchical basis and the accompanying mesh are described by graphs. The corresponding FE basis is generated by hierarchical transformation. The characteristic feature of the generalizable concept is the combination of the conforming hierarchical basis for easily defining and changing the FE space with an accompanying nonconforming FE basis for the easy assembly of a FE equations system. For an elliptic model the conforming FEM problem is solved by an iterative method applied to this nonconforming FEM equations system and modified by projection into the subspace of conforming basis functions. The iterative method used is the Yserentant- or BPX-preconditioned conjugate gradient algorithm. On a MIMD computer system the parallelization by domain decomposition is easy and efficient to organize both for the generation and solution of the equations system and for the change of basis and mesh.
106

Operational Modal Analysis of the Stockholm Waterfront Congress Centre

Grundström, Ulrika January 2010 (has links)
No description available.
107

Advanced Algorithms for Virtual Reconstruction and Finite Element Modeling of Materials with Complex Microstructures

Yang, Ming January 2021 (has links)
No description available.
108

Globalization of Nonlinear FETI–DP Methods

Köhler, Stephan 20 February 2024 (has links)
Nichtlineare Finite-Element-Probleme sind unentbehrlich für die Modellierung und Simulation im Bereich der Mechanik. Für die Lösung solcher Probleme sind schnelle und robuste Algorithmen unverzichtbar. Nichtlineare FETI--DP-Verfahren haben ihre Robustheit und Skalierbarkeit für Probleme der nichtlinearen Strukturmechanik nachgewiesen. Typischerweise werden diese nichtlinearen FETI--DP-Verfahren in Kombination mit dem Newton-Verfahren oder Varianten des Newton-Verfahrens verwendet. Diese Verfahren sind nicht global konvergent. In der vorliegenden Arbeit wird gezeigt, wie nichtlineares FETI--DP unter Verwendung einer exakten differenzierbaren Penalty-Funktion oder mittels eines SQP-Verfahren globalisiert werden kann. Es werden Standardkonvergenzaussagen, unter direkter Verwendung von nichtlinearer Elimination, welche ein zentraler Baustein für nichtlineares FETI--DP ist, bewiesen. Numerische Ergebnisse zeigen, dass die Robustheit und Skalierbarkeit durch die Globalisierung erhalten bleiben.
109

A Non-Conformal Domain Decomposition Method for Solving Large Electromagnetic Wave Problems

Vouvakis, Marinos N. 13 September 2005 (has links)
No description available.
110

Finite Element Domain Decomposition with Second Order Transmission Conditions for Time-Harmonic Electromagnetic Problems

Rawat, Vineet 26 August 2009 (has links)
No description available.

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