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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.
11

Static and dynamic job-shop scheduling using rolling-horizon approaches and the Shifting Bottleneck Procedure

Ghoniem, Ahmed 10 July 2003 (has links)
Over the last decade, the semiconductor industry has witnessed a steady increase in its complexity based on improvements in manufacturing processes and equipment. Progress in the technology used is no longer the key to success, however. In fact, the semiconductor technology has reached such a high level of complexity that improvements appear at a slow pace. Moreover, the diffusion of technology among competitors shows that traditional approaches based on technological advances and innovations are not sufficient to remain competitive. A recent crisis in the semiconductor field in the summer 2001 made it even clearer that optimizing the operational control of semiconductor wafer fabrication facilities is a vital key to success. Operating research-oriented studies have been carried out to this end for the last 5 years. None of them, however, suggest a comprehensive model and solution to the operational control problem of a semiconductor manufacturing facility. Two main approaches, namely mathematical programming and dispatching rules, have been explored in the literature so far, either partially or entirely dealing with this problem. Adapting the Shifting Bottleneck (SB) procedure is a third approach that has motivated many studies. Most research focuses on optimizing a certain objective function under idealized conditions and thus does not take into consideration system disruptions such as machine breakdown. While many papers address the adaptations of the SB procedure, the problem of re-scheduling jobs dynamically to take disruptions and local disturbances (machines breakdown, maintenance...) into consideration shows interesting perspectives for research. Dealing with local disturbances in a production environment and analyzing their impact on scheduling policies is a complex issue. It becomes even more complex in the semiconductor industry because of the numerous inherent constraints to take into account. The problem that is addressed in this thesis consists of studying dynamic scheduling in a job-shop environment where local disturbances occur. This research focuses on scheduling a large job shop and developing re-scheduling policies when local disturbances occur. The re-scheduling can be applied to the whole production horizon considered in the instance, or applied to a restricted period T that becomes a decision variable of the problem. The length of the restricted horizon T of re-scheduling can influence significantly the overall results. Its impact on the general performance is studied. Future extensions can be made to include constraints that arise in the semiconductors industry, such as the presence of parallel and batching machines, reentrant flows and the lot dedication problem. The theoretical results developed through this research will be applied to data sets to study their efficiency. We hope this methodology will bring useful insights to dealing effectively with local disturbances in production environments. / Master of Science
12

ε-SUPERPOSITION AND TRUNCATION DIMENSIONS IN AVERAGE AND PROBABILISTIC SETTINGS FOR ∞-VARIATE LINEAR PROBLEMS

Dingess, Jonathan M. 01 January 2019 (has links)
This thesis is a representation of my contribution to the paper of the same name I co-author with Dr. Wasilkowski. It deals with linear problems defined on γ-weighted normed spaces of functions with infinitely many variables. In particular, I describe methods and discuss results for ε-truncation and ε-superposition methods. I show through these results that the ε-truncation and ε-superposition dimensions are small under modest error demand ε. These positive results are derived for product weights and the so-called anchored decomposition.
13

Efektivní systém odměňování ve veřejné správě / An Effective System of Remuneration In the Public Sector

Picka, Jakub January 2008 (has links)
Expenditures on the salaries of public sector employees constitute a very important component of public expenditures, currently around CZK 200 billion annually in the Czech Republic. Adjusting the remuneration of employees in public administration (sector) is therefore an important option for increasing the efficiency of use of public funds. The assessment of the current system of public sector employee remuneration and a proposal for some specific changes to be made to it is the focus of this dissertation. The primary aim of my dissertation is to analyze the system of remuneration of employees of public and private sectors, both qualitatively and quantitatively. Within the primary target there is also a decomposition analysis, which indicates whether the employees are discriminated against in any of the sectors. The secondary objective is to make recommendations for the system of remunerating public sector employees of the in order to increase its efficiency in terms of public spending while maintaining its incentive function. The work is divided into five chapters. The first chapter, entitled "Theoretical Foundations," provides an overview of the relevant literature, the fundamental basis in economic theory, and issues of the Mincer wage equation, which is then later used as the basis for regression and decomposition analyses, and mainly describes in detail the decomposition method that is used to explain the difference in the salary level in the private and the public sector. These decomposition methods represent, together with quantile regression, the main tool used to meet the objectives of this work. The second chapter, entitled "The Remuneration of Public Sector Employees," describes the structure of the remuneration of employees of the public sector. The data shows that the current system produces results in the form of salaries that do not correspond to the market. The third chapter, called "Regression Model," builds on the analysis performed on data from QSAE, which was discussed in the second part of the previous chapter, and its purpose is to prepare the documents for verification and deepen their conclusions. The fourth chapter, called "Regression and Decomposition Analysis," is based on the regression model assembled in the previous chapter, and describes the results of the regression decomposition analysis performed on the described sample data. This chapter verifies the hypotheses set out in the introduction and answers research questions. The fifth and final chapter, entitled "Interpretation of the Results and Recommendations," focuses on the interpretation of the results, the proposed regulation of remuneration, and recommendations for further research. The main finding of this work is that the system of remuneration of public sector workers is set so that, while the overall average brings quite comparable results in terms of the salary as the entire labor market, it is not throughout the distribution. The performed regression analysis showed that both the public and private sectors evaluate the same things differently (different values of the regression coefficients of variables), and both at the average and along the entire distribution. We can say that the mechanism of the remuneration of employees of the public sector is different from that of the market. This fact is confirmed by the significantly higher coefficient of determination of the regression model of the public sector. Regarding possible discrimination in wages, the analysis showed that employees in the public sector may in contrary to the preposition of positive discrimination be positively discriminated against only up to approximately fifteenth percentile. From fifteenth percentile they are discriminated against negatively. This was confirmed by the decomposition analysis performed on the average salaries, which indicates that public sector employees are, at this level, negatively discriminated against (if the public sector employees have the same regression coefficients as private sector employees, their earnings increase). Finally, this conclusion is confirmed by the dummy variable, which represents belonging to the private sector when the value of its corresponding regression coefficients, in quantile regression analysis along the distribution, evolves from negative to positive and is significantly increasing. The thesis also shows how the system of remunerating public sector employees can be adjusted to reward employees in a way that is comparable with the market.
14

Multielementární chemická analýza popílků ze zpracování druhotných surovin olova / Multielement analysis of flue gas residues from secondary lead smelting

Šebek, Ondřej January 2014 (has links)
Multielement analysis of flue gas residues from secondary lead smelting was tested using seven decomposition methods on four different flue gas residues and certified reference materials (CRM) CPB-2 (Pb concentrate, CCRMP). The studied samples contained both silicates and also high contents of phases with Pb, primarily Pb chlorides and sulphates. Solutions prepared by various decomposition methods were analysed using ICP OES (Al, As, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sb, Se, Si, Sn, Sr, Ti, Tl, V, Zn). Greater yields were found for most of the elements by combined decomposition (with fusion) and decomposition by sintering. Nonetheless, both methods exhibited major losses of volatile elements (As, Bi, Sb, Tl). Thus, one of these methods must always be combined with a method of decomposition in a closed system. The work also demonstrates that, for investigation of untraditional waste geological materials (e.g. flue residues from high- temperature industrial processes), it will be necessary in the future to produce new certified reference materials with anomalous chemical and mineralogical compositions, which are not currently available on the market. Laboratory extraction tests were performed on two different types of flue residues - kinetic (30 days) with ratio L/S...
15

Détecteurs spectrométriques pour la mammographie et traitement associés / Signal processing methods for energy sensitive mammography exams

Pavia, Yoann 23 May 2017 (has links)
Nous avons étudié l’utilisation de détecteurs spectrométriques, qui émergent dans le domaine de l’imagerie médicale, pour leur application à la mammographie. Ces détecteurs permettent de discriminer l’énergie des photons reçus, ce qui apporte une information supplémentaire à l’imagerie d’atténuation traditionnelle. Ainsi, il est possible d’utiliser des techniques de décomposition en base de deux matériaux, notamment pour déterminer la densité glandulaire dans le sein, qui correspond au pourcentage de tissus glandulaires, et qui est un facteur de risque pour le développement d’un cancer, à partir d’une seule irradiation. Jusqu’alors, il était possible d’utiliser cette méthode à partir de deux expositions à deux énergies distinctes. Dans certains cas, une nouvelle tendance consiste à pratiquer des mammographies avec injection d’un produit de constratse iodé, mais cela nécessite également au moins deux irradiations. Nous avons donc proposé d’estimer la densité du sein et la concentration d’iode simultanément, à partir d’une seule irradiation, à une dose 0,93 mGy, en appliquant des méthodes de décomposition en base de trois matériaux. Premièrement, des méthodes polynomiales ont été adaptées pour être comptibles avec l’information spectrale provenant de 3 canaux d’énergies. Ensuite, nous avons montré qu’une deuxième approche, capable de prendre en compte une information spectrale plus fine, basée sur la maximisation de la vraisemblance entre un spectre mesuré et des spectres de références, était capable d’atteindre de meilleurs résultats. Enfin, nous avons développé une méthode capable de prendre en compte la compression du sein en mammographie pour améliorer les résultats obtenus par la méthode de maximum de vraisemblance. / Energy sensitive X-ray detectors are emerging in the field of medical imaging. We have investigated the use of this new type of X-ray detectos for their application to mammography exams. These detectors are able to discriminate the energy of received photons, which provides additional information to a standard mammography image only composed of the total attenuation signal. Thus, these detectors allow the use of basis material decomposition techniques, from a single x-ray exposure, and permit to determine the breast density, which corresponds to the percentage of glandular tissues in the breast. Breast density is known for being a risk factor for the development of breast cancers. Without energy sensitive X-ray detectors, this method requires two X-ray exposures at different energies. Contrast enhanced mammography is also developing but it requires the use an iodinated contrast media and at least two irradiations. Hence, we proposed to take benefit of energy-sensitive detectors to simultaneously estimate the breast density and the iodine concentration, using a single X-ray exposure at a mean glandular dose of 0.93 mGy. This approach is based on three basis material decomposition methods. First, different polynomial methods have been adapted to comply with spectral information from 3 energy channels. Then, we showed that a second approach, based on the maximisation of the likelihood between a measured spectrum and reference spectra, was able take into consideration finer spectral information and achieved better results. Finally, we have developed a method that can take into consideration the thickness of the compressed breast during a mammography exam to improve the results obtained by the maximum likelihood method.
16

Parallélisation sur un moteur exécutif à base de tâches des méthodes itératives pour la résolution de systèmes linéaires creux sur architecture multi et many coeurs : application aux méthodes de types décomposition de domaines multi-niveaux / Parallelization of iterative methods to solve sparse linear systems using task based runtime systems on multi and many-core architectures : application to Multi-Level Domain Decomposition methods

Roussel, Adrien 06 February 2018 (has links)
Les méthodes en simulation numérique dans le domaine de l’ingénierie pétrolière nécessitent la résolution de systèmes linéaires creux de grande taille et non structurés. La performance des méthodes itératives utilisées pour résoudre ces systèmes représente un enjeu majeur afin de permettre de tester de nombreux scénario.Dans ces travaux, nous présentons une manière d'implémenter des méthodes itératives parallèles au dessus d’un support exécutif à base de tâches. Afin de simplifier le développement des méthodes tout en gardant un contrôle fin sur la gestion du parallélisme, nous avons proposé une API permettant d’exprimer implicitement les dépendances entre tâches : la sémantique de l'API reste séquentielle et le parallélisme est implicite.Nous avons étendu le support exécutif HARTS pour enregistrer une trace d'exécution afin de mieux exploiter les architectures NUMA, tout comme de prendre en compte un placement des tâches et des données calculé au niveau de l’API. Nous avons porté et évalué l'API sur les processeurs many-coeurs KNL en considérant les différents types de mémoires de l’architecture. Cela nous a amené à optimiser le calcul du SpMV qui limite la performance de nos applications.L'ensemble de ce travail a été évalué sur des méthodes itératives et en particulier l’une de type décomposition de domaine. Nous montrons alors la pertinence de notre API, qui nous permet d’atteindre de très bon niveaux de performances aussi bien sur architecture multi-coeurs que many-coeurs. / Numerical methods in reservoir engineering simulations lead to the resolution of unstructured, large and sparse linear systems. The performances of iterative methods employed in simulator to solve these systems are crucial in order to consider many more scenarios.In this work, we present a way to implement efficient parallel iterative methods on top of a task-based runtime system. It enables to simplify the development of methods while keeping control on parallelism management. We propose a linear algebra API which aims to implicitly express task dependencies: the semantic is sequential while the parallelism is implicit.We have extended the HARTS runtime system to monitor executions to better exploit NUMA architectures. Moreover, we implement a scheduling policy which exploits data locality for task placement. We have extended the API for KNL many-core systems while considering the various memory banks available. This work has led to the optimization of the SpMV kernel, one of the most time consuming operation in iterative methods.This work has been evaluated on iterative methods, and particularly on one method coming from domain decomposition. Hence, we demonstrate that the API enables to reach good performances on both multi-core and many-core architectures.
17

Dynamic analysis of periodic structures via wave-based numerical approaches and substructuring techniques = Análise dinâmica de estruturas periódicas utilizando uma abordagem de propagação de ondas e técnicas de sub-estruturação / Análise dinâmica de estruturas periódicas utilizando uma abordagem de propagação de ondas e técnicas de sub-estruturação

Silva, Priscilla Brandão, 1986- 28 August 2018 (has links)
Orientadores: José Roberto de França Arruda, Jean-Mathieu Mencik / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-28T14:24:53Z (GMT). No. of bitstreams: 1 Silva_PriscillaBrandao_D.pdf: 13049086 bytes, checksum: 2f821e196dd604384d15489bda2360cb (MD5) Previous issue date: 2015 / Resumo: Nesta tese de doutorado, o método dos elementos finitos ondulatórios é utilizado para cálculo da resposta harmônica de sistemas mecânicos envolvendo estruturas com periodicidade unidimensional, i.e., estruturas compostas por subestruturas idênticas arranjadas ao longo de uma direção. Tais sistemas mecânicos podem ser complexos e são comumente encontrados em aplicações de engenharia como, por exemplo, nas fuselagens de aviões. A primeira parte da tese é dedicada ao cálculo das ondas que se propagam ao longo dessas estruturas. Uma breve revisão da literatura sobre as formulações disponíveis para o problema de autovalor associado ao método dos elementos finitos ondulatórios é apresentada, assim como um estudo dos erros numéricos induzidos por estes problemas de autovalor no caso de um guia de ondas sólido. Na segunda parte desta tese, modelagens de superelementos para estruturas periódicas são propostas. Neste contexto, matrizes de rigidez dinâmica e de receptância ou flexibilidade de estruturas periódicas são expressas a partir dos modos de onda. Comparadas às matrizes de rigidez dinâmica e receptância obtidas pelo método dos elementos finitos convencional, as matrizes baseadas no método dos elementos finitos ondulatórios são calculadas de forma bastante rápida e sem perda de acuracidade. Ademais, uma estratégia eficiente de redução de ordem de modelo é apresentada. Comparada às formulações que utilizam a base completa de ondas, esta estratégia proporciona redução do tempo computacional requerido para cálculo da resposta forçada de estruturas periódicas. De fato, é mostrado que elementos espectrais numéricos de alta ordem podem ser construídos a partir do método dos elementos finitos ondulatórios. Isto constitui uma alternativa ao método dos elementos espectrais convencional, cuja utilização está limitada a estruturas simples para as quais soluções analíticas por ondas existam. A motivação por trás das formulações de matrizes de superelementos a partir do método dos elementos finitos ondulatórios está na utilização do conceito de ondas numéricas para calcular a resposta harmônica de sistemas mecânicos acoplados que envolvam estruturas com periodicidade unidimensional e junções elásticas a partir de procedimentos de montagem clássicos de elementos finitos ou técnicas de decomposição de domínio. Este assunto é tratado na terceira parte desta tese. Nesse caso, o método de Craig-Bampton é usado para expressar as matrizes de superelementos de junções por meio de modos estáticos e de interface fixa. Um critério baseado no método dos elementos finitos ondulatórios é considerado para a seleção dos modos da junção que mais contribuem para a resposta forçada do sistema. Isto também contribui para o aumento da eficiência da simulação numérica de sistemas acoplados. Finalmente, na quarta parte desta tese, o método dos elementos finitos ondulatórios é utilizado para mostrar que é possível projetar estruturas periódicas com potencial para funcionar como filtros de vibração em bandas de frequência específicas. Com o intuito de destacar a relevância dos desenvolvimentos propostos nessa tese, ensaios numéricos envolvendo guias de onda sólidos, pórticos planos e estruturas tridimensionais do tipo fuselagem aeronáutica são realizados / Abstract: In this thesis, the wave finite element (WFE) method is used for assessing the harmonic forced response of mechanical systems that involve structures with one-dimensional periodicity, i.e., structures which are made up of several identical substructures along one direction. Such mechanical systems can be quite complex and are commonly encountered in engineering applications, e.g., aircraft fuselages. The first part of the thesis is concerned with the computation of wave modes traveling along these structures. A brief literature review is presented regarding the available formulations for the WFE eigenproblem, which need to be solved for expressing the wave modes, as well as a study of the numerical errors induced by these eigenproblems in the case of a solid waveguide. In the second part of the thesis, the WFE-based superelement modeling of periodic structures is proposed. In this context, the dynamic stiffness matrices and receptance matrices of periodic structures are expressed in terms of wave modes. Compared to the conventional FE-based dynamic stiffness and receptance matrices, the WFE-based matrices can be computed in a very fast way without loss of accuracy. In addition, an accurate strategy for WFE-based model order reduction is presented. It provides significant computational time savings for the forced response analysis of periodic structures compared to WFE-based superelement modeling, which makes use of the full wave basis. Indeed, it is shown that higher-order numerical spectral elements can be built by means of the WFE method. This is an alternative to the conventional spectral element method, which is limited to simple structures for which closed-form wave solutions exist. The motivation behind the formulation of WFE-based superelement matrices is the use of the concept of numerical wave modes to assess the forced response of coupled mechanical systems that involve structures with one-dimensional periodicity and coupling elastic junctions through classic finite element assembly procedures or domain decomposition techniques. This issue is addressed in the third part of this thesis. In this case, the Craig-Bampton method is used to express superelement matrices of coupling junctions by means of static and fixed-interface modes. A WFE-based criterion is considered to select among junction modes those that contribute most to the system forced response. This also contributes to enhancing the efficiency of the numerical simulation of coupled systems. Finally, in the fourth part of this thesis, the WFE method is used to show the potential of designing periodic structures which work as vibration filters within specific frequency bands. In order to highlight the relevance of the developments proposed in this thesis, numerical experiments which involve solid waveguides, two-dimensional frame structures, and three-dimensional aircraft fuselage-like structures are carried out / Doutorado / Mecanica dos Sólidos e Projeto Mecanico / Doutora em Engenharia Mecânica / 2010/17317-9 / FAPESP
18

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.
19

Advanced Decomposition Methods in Stochastic Convex Optimization / Advanced Decomposition Methods in Stochastic Convex Optimization

Kůdela, Jakub Unknown Date (has links)
Při práci s úlohami stochastického programování se často setkáváme s optimalizačními problémy, které jsou příliš rozsáhlé na to, aby byly zpracovány pomocí rutinních metod matematického programování. Nicméně, v některých případech mají tyto problémy vhodnou strukturu, umožňující použití specializovaných dekompozičních metod, které lze použít při řešení rozsáhlých optimalizačních problémů. Tato práce se zabývá dvěma třídami úloh stochastického programování, které mají speciální strukturu, a to dvoustupňovými stochastickými úlohami a úlohami s pravděpodobnostním omezením, a pokročilými dekompozičními metodami, které lze použít k řešení problému v těchto dvou třídách. V práci popisujeme novou metodu pro tvorbu “warm-start” řezů pro metodu zvanou “Generalized Benders Decomposition”, která se používá při řešení dvoustupňových stochastických problémů. Pro třídu úloh s pravděpodobnostním omezením zde uvádíme originální dekompoziční metodu, kterou jsme nazvali “Pool & Discard algoritmus”. Užitečnost popsaných dekompozičních metod je ukázána na několika příkladech a inženýrských aplikacích.
20

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>

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