published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Applied Geosciences / Master / Master of Science

published_or_final_version / Applied Geosciences / Master / Master of Science

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No description available.

Orientador: Victor Orlando Gamarra Rosado / Banca: Fernando de Azevedo Silva / Banca: Maurício Guimarães da Silva / Resumo: Controlar a pressão de poços petrolíferos durante a perfuração pode ser um dos processos mais complexos e perigosos da etapa de exploração. O sistema de perfuração varia constantemente e aleatoriamente, isto principalmente, devido à mudança da profundidade de perfuração, a qual faz variar outros parâmetros do processo. Assim, a aplicação de um controle variante no tempo torna-se necessário. Este estudo propõe o projeto de um controlador Gain Scheduling (GS) no controle da pressão no fundo de poços durante a perfuração. Este controlador GS consiste na sintonia dos ganhos relacionados aos diferentes pontos operacionais, para este caso, a profundidade do poço. Primeiro, apresentam-se as teorias a serem utilizadas durante o desenvolvimento do trabalho. Segundo, obtém-se o modelo matemático do processo o qual se fundamenta na mecânica dos fluidos. Da linearização do modelo, a função de transferência resultante apresenta um elemento integrador o que faz que a dinâmica do processo seja difícil de manipular. Também se adiciona um tempo de atraso, o que torna mais complexo o controle do processo. Na terceira parte, utilizaram-se três tipos de metodologias IMC (Internal Model Control) para sintonizar os ganhos do controlador PID (Proporcional, Integral e Derivativo) para diferentes profundidades de perfuração procurando o melhor desempenho, estabilidade e robustez do sistema. Finalmente, escolhe-se a estratégia de melhor desempenho (IMC de dois graus de liberdade) para especificar e mo... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Controlling the pressure of oil wells during drilling can be one of the most complex and dangerous processes of exploration stage. The drilling system is constantly end randomly changing due, among other things, the drilling depth, which varies other process parameters, accordingly to apply a time variant control becomes necessary. This study proposes the design of a Gain Scheduling controller to control the pressure at the bottom of wells during drilling. The GS controller is based on the corresponding tuning gains at different operating points in this case, the depth. First, presents the theories that will be used during development work. In the second part, was obtained a mathematical model of the process which is based on fluid mechanics. In the linearization of the, the final transfer function presents an integrating element which makes the process dynamics more difficult to handle. It becomes even more complex in the presence of time delay. In the third part, three IMC controllers' types were used to tuning the PID (Proportional, Integral and Derivative) controller gains for different depths of drilling looking for the best performance, stability and robustness. Finally, was chose the best performing strategy (IMC of two degrees of freedom) to specify and assemble the GS controller table, which is evaluated by simulations of problems that usually occur during drilling, considered as disturbances, which check its viability. Also, the results of the controlled GS system a... (Complete abstract click electronic access below) / Mestre

Thesis. 1977. Mech.E.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by K. Subramanian. / Mech.E.

Este trabalho visou a averiguação do status taxonômico das esponjas bioerosivas do complexo Cliona celata da América do Sul por meio de técnicas moleculares, utilizando como marcadores a subunidade I da Citocromo c oxidase (cox1) e os Espaçadores Internos Transcritos do RNAr nuclear (ITS1 e ITS2), além de testar outros marcadores. Igualmente, avaliou o grau de variabilidade morfológica encontrado nessas espécies, principalmente por meio da morfometria dos tilóstilos, a fim de estabelecer uma diagnose para elas. Ainda, tentou determinar as relações filogenéticas dessas espécies com as demais esponjas bioerosivas utilizando o gene 28S do RNAr nuclear. Foi possível determinar a existência de cinco clados de esponjas bioerosivas do complexo Cliona celata para a América do Sul, e dois outros clados não-sulamericanos, por meio dos marcadores moleculares utilizados. Embora seja discutida a validade desses clados como espécies distintas, continua impossível, por meio de caracteres morfológicos, distingui-los, e dessa forma, a proposição formal de novas espécies é evitada. Através da reconstrução filogenética do grupo, é possível verificar que as esponjas bioerosivas analisadas se apresentaram como um grupo monofilético, e se separa em três principais clados: Pione, Spirastrellidae, e Clionaidae. Por meio desta, é sugerida a alocação das espécies do complexo C. viridis e C. schimidti dentro de Spirastrella, além de ser necessária a criação de um novo gênero para alocar as espécies do novo complexo identificado aqui, o complexo C. delitrix. / This work intended the validation of the taxonomic status of boring sponges from the Cliona celata complex of South America by molecular techniques, using Cytochrome coxidase, subunit I (cox1), and Internal Transcribed Spacers (ITS) of rRNA nuclear genes as molecular markers. Additionally, the degree of morphological variation necessary to establisha correct diagnosis for the studied species was evaluated, and additional markers were tested. Finally, a phylogenetic analysis comparing this species with other boring sponges, using the 28S rRNA nuclear gene was carried out. It was possible to point out the existence of five clades of boring sponges from the C. celata complex in South America, and two more from Mexico and Australia. Although these clades can comprise new valide species, no morphological evidence was found to separate them, and thus, no formal species descriptions were presented. Through out phylogenetic analyses it was possible to conclude that boring sponges form a monophyletic group, which can be separated in three clades: Pione, Spirastrellidae, and Clionaidae. This work suggests to allocate C. viridis and C. schimidti species complexes inside Spirastrella, and to create a new genus for the new C. delitrix species complex.

Tese de mestrado integrado. Mestrado Integrado em Engenharia Civil. Especialização em Hidráulica. Faculdade de Engenharia. Universidade do Porto. 2012

With advances in material technology, allowing, for instance, engines to withstand higher combustion pressure and consequently improving performance, comes challenges to productivity. These materials are, in fact, more difficult to machine with regards to tool wear and especially machine tool stability. Machining vibrations have historically been one of the major limitations to productivity and product quality and the cost of machining vibration for cylinder head manufacturing has been estimated at 0.35 euro per part. The literature review shows that most of the research on cutting stability has been concentrating on the use of the stability limits diagram (SLD), addressing the limitations of this approach. On the other hand, research dedicated to development of machine tool components designed for chatter avoidance has been concentrating solely on one component at the time. This thesis proposes therefore to extend the stability limits of the machining system by enhancing the structure’s damping capability via a unified concept based on the distribution of damping within the machining system exploiting the joints composing the machine tool structure. The design solution proposed is based on the enhancement of damping of joint through the exploitation of viscoelastic polymers’ damping properties consciously designed as High Damping Interfaces (HDI). The tool-turret joint and the turret-lathe joint have been analysed. The computational models for dimensioning the HDI’s within these joints are presented in the thesis and validated by the experiments. The models offer the possibility of consciously design damping in the machining system structure and balance it with regards to the needed stiffness. These models and the experimental results demonstrate that the approach of enhancing joint damping is viable and effective. The unified concept of the full chain of redesigned components enables the generation of the lowest surface roughness over the whole range of tested cutting parameters. The improved machining system is not affected by instability at any of the tested cutting parameters and offers an outstanding surface quality. The major scientific contribution of this thesis is therefore represented by the proposed unified concept for designing damping in a machining system alongside the models for computation and optimisation of the HDIs. From the industrial application point of view, the presented approach allows the end user to select the most suitable parameters in terms of productivity as the enhanced machine tool system becomes less sensitive to stability issues provoked by difficult-to-machine materials or fluctuations of the work material properties that may occur in ordinary production processes. / <p>QC 20120413</p> / DampComat / Production 4 micro / FFI Robust Machining