[pt] Este trabalho consiste no desenvolvimento e implementação de um sistema computacional integrado para Modelagem Geo- étrica, Geração de Malhas, Análise Numérica, Auto- Adaptação do tipo h e Otimização de Forma e Espessura em Cascas. O Modelo Geométrico adotado consiste em representar a superfície por meio de B-Splines Racionais Recortadas, admitindo variação de espessura segundo as mesmas funções que descrevem a superfície. Para a utilização nos módulos de Auto-Adaptação e Otimização, Geradores de Malhas Não-Estruturadas sobre superfícies paramétricas foram empregados. Com base em um gerador de malhas triangulares que utiliza a técnica de avanço de Fronteira, dois geradores de malhas quadrilaterais foram desenvolvidos. Os elementos finitos empregados são baseados nas hipóteses de Reissner-Mindlin e no conceito de degeneração de sólidos. São considerados os elementos tradicionais, baseados puramente em deslocamentos, bem como elementos de formulação mais robusta, com base em campos assumidos de deformação. Um procedimento para Auto-Adaptação de Malhas do tipo foi desenvolvido para o Modelo Geométrico e para os elementos considerados. As malhas obtidas a partir de níveis de erro prescritos permitem aos modelos a obtenção de suas taxas de convergência mesmo em problemas com singularidades e efeitos de fronteira. A Análise de Sensibilidade, ferramenta essencial nos procedimentos de Otimização, é feita com a utilização do Método Semi-Analítico, considerando as características especiais dos elementos de casca. Foi desenvolvida para elementos degenerados de casca uma versão do Método Semi- Analítico que elimina sua imprecisão eventual, através da diferenciação exata das componentes de deslocamento de corpo rígido. Para os elementos baseados puramente em deslocamentos, o Método Analítico também foi desenvolvido. Os módulos de Otimização de Forma e Espessura trabalham sobre diversas possibilidades de definição das variáveis de projeto e com diferentes algoritmos de Programação Matemá tica. Permitem também a Otimização de Forma com consideração de Auto-Adaptatividade para obter as malhas durante o processo de mudança de forma. Devido à interconexão entre os diversos módulos e com o objetivo de facilitar a comunicação e a implementação dos mesmos, o sistema computacional foi completamente desenvolvido utilizando técnicas de Programação Orientada para Objetos. / [en] The purpose of this thesis is the development of an integrated computational system for Geometric Modelling, Unstructured Mesh Generation, Numerical Analysis, Adaptivity and Shape Optimization of Shells.The Geometric Model is composed of Non-Uniform Rational B-Spline Surfaces (NURBS), further modified by trimming loops described in the parametric plane. Smooth thickness variations may be modelled by means of the same functions that describe the surface geometry.For Unstructured Mesh Generation, two algorithms were implemented for quadrilateral elements and one for triangles. The triangular Mesh Generator is based on the Advancing Front Technique applied to parametric surfaces. The quadrilateral Mesh Generators employ the indirect approach for converting the triangular meshes to pure quadrilateral ones. The Finite Element formulation is based on the degenerated isoparametric approach. Pure displacement based elements, as well as assumed strain robust shell elements, are employed in the Analysis, Adaptivity and Optimization modules. A procedure for h-Adaptive Mesh Refinement was developed for the shell models. For this purpose an Error Estimator scheme, based upon a Zienkiewicz-Zhu Patch Recovery Technique, adapted to handle curved shell surfaces, was employed. The adaptive procedure allows the convergence rates of the Finite Element Model to be maintained even in the presence of singularities and boundary layers.For the Sensitivity Evaluation, the well- known Semi-Analytical Method is employed and adapted for the degenerated solid shell element approach. In order to solve the inaccuracy problems inherent to the application of the method for certain types of structures, the recent Refined Semi- Analytical Method, is extended for degenerated shell elements. For the pure displacement-based elements, the Analytical Method is also developed. The Shape and Thickness Optimization modules work with a wide variety of design variable descriptions, different mathematical Programming algorithms, Sensitivity schemes and Finite Element Models. The possibility of h-Adaptive Mesh refinement in conjunction with Shape Optimization is also considered in this stage. In order to ease up code expansion, communication and data exchange between the modules,the computational system was fully developed employing Object-Oriented Programming techniques.

La dernière décennie a vu l'émergence d'Internet et l'apparition des applications multimédia qui requièrent de plus en plus de bande passante, ainsi que des utilisateurs qui exigent une meilleure qualité de service. Dans cette perspective, beaucoup de travaux ont été effectués pour améliorer l'utilisation du spectre sans fil.Le sujet de ma thèse de doctorat porte sur l'application de la théorie des jeux, la théorie des files d'attente et l'apprentissage dans les réseaux sans fil,en particulier dans des environnements partiellement observables. Nous considérons différentes couches du modèle OSI. En effet, nous étudions l'accès opportuniste au spectre sans fil à la couche MAC en utilisant la technologie des radios cognitifs (CR). Par la suite, nous nous concentrons sur le contrôle de congestion à la couche transport, et nous développons des mécanismes de contrôle de congestion pour le protocole TCP. / Since delay-sensitive and bandwidth-intense multimedia applications have emerged in the Internet, the demand for network resources has seen a steady increase during the last decade. Specifically, wireless networks have become pervasive and highly populated.These motivations are behind the problems considered in this dissertation.The topic of my PhD is about the application of game theory, queueing theory and learning techniques in wireless networks under some QoS constraints, especially in partially observable environments.We consider different layers of the protocol stack. In fact, we study the Opportunistic Spectrum Access (OSA) at the Medium Access Control (MAC) layer through Cognitive Radio (CR) approaches.Thereafter, we focus on the congestion control at the transport layer, and we develop some congestion control mechanisms under the TCP protocol.The roadmap of the research is as follows. Firstly, we focus on the MAC layer, and we seek for optimal OSA strategies in CR networks. We consider that Secondary Users (SUs) take advantage of opportunities in licensed channels while ensuring a minimum level of QoS. In fact, SUs have the possibility to sense and access licensed channels, or to transmit their packets using a dedicated access (like 3G). Therefore, a SU has two conflicting goals: seeking for opportunities in licensed channels, but spending energy for sensing those channels, or transmitting over the dedicated channel without sensing, but with higher transmission delay. We model the slotted and the non-slotted systems using a queueing framework. Thereafter, we analyze the non-cooperative behavior of SUs, and we prove the existence of a Nash equilibrium (NE) strategy. Moreover, we measure the gap of performance between the centralized and the decentralized systems using the Price of Anarchy (PoA).Even if the OSA at the MAC layer was deeply investigated in the last decade, the performance of SUs, such as energy consumption or Quality of Service (QoS) guarantee, was somehow ignored. Therefore, we study the OSA taking into account energy consumption and delay. We consider, first, one SU that access opportunistically licensed channels, or transmit its packets through a dedicated channel. Due to the partial spectrum sensing, the state of the spectrum is partially observable. Therefore, we use the Partially Observable Markov Decision Process (POMDP) framework to design an optimal OSA policy for SUs. Specifically, we derive some structural properties of the value function, and we prove that the optimal OSA policy has a threshold structure.Thereafter, we extend the model to the context of multiple SUs. We study the non-cooperative behavior of SUs and we prove the existence of a NE. Moreover, we highlight a paradox in this situation: more opportunities in the licensed spectrum may lead to worst performances for SUs. Thereafter, we focus on the study of spectrum management issues. In fact, we introduce a spectrum manager to the model, and we analyze the hierarchical game between the network manager and SUs.Finally, we focus on the transport layer and we study the congestion control for wireless networks under some QoS and Quality of Experience (QoE) constraints. Firstly, we propose a congestion control algorithm that takes into account applications' parameters and multimedia quality. In fact, we consider that network users maximize their expected multimedia quality by choosing the congestion control strategy. Since users ignore the congestion status at bottleneck links, we use a POMDP framework to determine the optimal congestion control strategy.Thereafter, we consider a subjective measure of the multimedia quality, and we propose a QoE-based congestion control algorithm. This algorithm bases on QoE feedbacks from receivers in order to adapt the congestion window size. Note that the proposed algorithms are designed based on some learning methods in order to face the complexity of solving POMDP problems.

This thesis presents the design and analysis of Spasiba, a context-aware mobile advisor. We argue that current context-aware mobile applications exhibit significant flaws with respect to (1) limited use of context information, (2) incomplete or irrelevant content generation, and (3) low usability. The proposed model attempts to tackle these limitations by advancing the usage and manipulation of context information, automating the back-end systems in terms of self-management and seamless extensibility, and shifting the logic away from the client side. A distinguishing characteristic of Spasiba is the proactive approach to notifying the user of information of interest. In this proactive approach, the user subscribes to the service and receives content updates as the context changes. This proposed model is realised in a proof-of-concept prototype that uses a Nokia Web Runtime widget as the client application. The widget, which sports an elegant, touch-optimised interface, collects multiple context parameters to deliver high-quality results. The server-side architecture employs the publish/subscribe paradigm for managing the active users and Comet—for proactively notifying the clients of updated information of interest. IRS-III, a Semantic Web Services broker, handles the process of content generation. The prototype employs nine data sources, seven of which are open API web services and two of which are regular web pages, to deliver diverse and complete results. A simple autonomic element, implemented with the help of aspect-oriented programming, ensures partial self-management of the back-end systems. Spasiba is evaluated by means of a case study that involves a tourist couple visiting Victoria. The application assists the tourist couple with finding attractions, relevant stores, and places serving food.

Our society is increasingly demanding situation-aware smarter software (SASS) systems, whose goals change over time and depend on context situations. A system with such properties must sense their dynamic environment and respond to changes quickly, accurately, and reliably, that is, to be context-aware and self-adaptive. The problem addressed in this dissertation is the dynamic management of context information, with the goal of improving the relevance of SASS systems' context-aware capabilities with respect to changes in their requirements and execution environment. Therefore, this dissertation focuses on the investigation of dynamic context management and self-adaptivity to: (i) improve context-awareness and exploit context information to enhance quality of user experience in SASS systems, and (ii) improve the dynamic capabilities of self-adaptivity in SASS systems. Context-awareness and self-adaptivity pose signi cant challenges for the engineering of SASS systems. Regarding context-awareness, the rst challenge addressed in this dissertation is the impossibility of fully specifying environmental entities and the corresponding monitoring requirements at design-time. The second challenge arises from the continuous evolution of monitoring requirements due to changes in the system caused by self-adaptation. As a result, context monitoring strategies must be modeled and managed in such a way that they support the addition and deletion of context types and monitoring conditions at runtime. For this, the user must be integrated into the dynamic context management process. Concerning self-adaptivity, the third challenge is to control the dynamicity of adaptation goals, adaptation mechanisms, and monitoring infrastructures, and the way they a ect each other in the adaptation process. This is to preserve the eff ectiveness of context monitoring requirements and thus self-adaptation. The fourth challenge, related also to self-adaptivity,concerns the assessment of adaptation mechanisms at runtime to prevent undesirable system states as a result of self-adaptation. Given these challenges, to improve context-awareness we made three contributions. First, we proposed the personal context sphere concept to empower users to control the life cycle of personal context information in user-centric SASS systems. Second, we proposed the SmarterContext ontology to model context information and its monitoring requirements supporting changes in these models at runtime. Third, we proposed an effi cient context processing engine to discover implicit contextual facts from context information speci fied in changing context models. To improve self-adaptivity we made three contributions. First, we proposed a framework for the identi cation of adaptation properties and goals, which is useful to evaluate self-adaptivity and to derive monitoring requirements mapped to adaptation goals. Second, we proposed a reference model for designing highly dynamic self-adaptive systems, for which the continuous pertinence between monitoring mechanisms and both changing system goals and context situations is a major concern. Third, we proposed a model with explicit validation and veri cation (V&V) tasks for self-adaptive software, where dynamic context monitoring plays a major role. The seventh contribution of this dissertation, the implementation of Smarter-Context infrastructure, addresses both context-awareness and self-adaptivity. To evaluate our contributions, qualitatively and quantitatively, we conducted several comprehensive literature reviews, a case study on user-centric situation-aware online shopping, and a case study on dynamic governance of service-oriented applications. / Graduate

[pt] Sistemas Multiagentes Orientados a Serviços (SOMS) têm surgido visando incorporar os benefícios de duas disciplinas da Engenharia de Software: Arquitetura Orientada a Serviços e Engenharia de Software Orientada a Agentes. A primeira visa fornecer serviços fracamente acoplados que podem ser utilizados em diferentes domínios. A segunda se baseia em um novo paradigma que visa o desenvolvimento de Sistemas Multiagentes, que são compostos por entidades, chamadas agentes, com raciocínio, autonomia e pró-atividade. Um dos principais objetivos de SOMS é ajudar no desenvolvimento de sistemas orientados a serviços capazes de adaptar-se em ambientes computacionais dinâmicos, onde é necessário reagir às mudanças em seus requisitos em tempo de execução, assim como, adaptar-se eficientemente diante de erros de execução e baixa qualidade de serviço. Neste contexto, este trabalho propõe um framework (Java self-Adaptive Agent Framework - JAAF) para implementar agentes autoadaptativos capazes de autonomamente e pró-ativamente descobrir serviços, selecionar o mais apropriado e adaptar-se caso algum problema ocorra durante a execução do serviço. A aplicabilidade do framework proposto é demonstrada através de dois estudos de caso. O primeiro é um sistema responsável por gerar mapas de susceptibilidades, ou seja, mapas que mostram locais com risco de deslizamento em determinada área. O segundo é um sistema onde o principal objetivo é satisfazer necessidades, relacionadas à viagens, de usuários. / [en] Service Oriented Multi-agent Systems (SOMS) have emerged in order to incorporate the benefits of two software engineering disciplines: Serviceoriented Architecture and Agent-oriented Software Engineering. The first provides loosely coupled services that can be used within different domains. The second is based on a new software engineering paradigm that addresses the development of Multi-agent Systems, which are composed of autonomous, pro-active and reasoning entities, named software agents. One of the main goal of SOMS is to help the development of service-oriented systems able to adapt themselves on dynamic computing environments. Those systems must be able to react at runtime to changes in their requirements, as well as to efficiently accommodate for deviations from their expected functionality or quality of services. In this context, this work proposes a framework (Java self- Adaptive Agent Framework - JAAF) to implement self-adaptive agents able to autonomously and pro-actively discover services, decide about the most appropriate one and adapt themselves if they face a problem while executing the service. The applicability of the proposed framework is demonstrated through two case studies. The first is a system responsible for generating susceptibility maps, i.e., maps that show locations with landslides risks in a given area. The second is a system where the main goal is to satisfy the users’ needs related to travel.