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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.
1

On numerical investigations of flow-induced vibration and heat transfer for flow around cylinders

Elbanhawy, Amr Yehia Hussein January 2011 (has links)
Vortex shedding is an important mechanism, by which the flow around bluff bodies create forces that excite vibratory motion. Vortex-induced vibration (VIV) is studied for a single circular cylinder by means of Computational Fluid Dynamics (CFD) simulations. An arbitrary Lagrangian Eulerian (ALE) formulation is used to achieve the grid deformation needed for VIV. In this thesis, a multifaceted approach is undertaken by which response dynamics and wake interaction are addressed. Four major aspects are considered in the study: the Reynolds number (Re); the mass and damping; the degree-of-freedom for VIV; and the mutual effect between VIV and heat transfer.As attention is paid towards high pre-critical Re flow, the turbulent flow around the cylinder is treated by two turbulence modelling approaches: unsteady Reynolds Averaged Navier Stokes (uRANS), and Large Eddy Simulation (LES). The wake-VIV interaction is analyzed by looking at mean velocities and Reynolds stresses, where decomposition of flow scales is undertaken to explore the evolution of coherent eddy structures, downstream of the cylinder. Conversely, the VIV response is analyzed by considering oscillation amplitude and frequency, in addition to the excitation and inertial dynamics.High turbulence in the separated shear layers disorders the cylinder's VIV response and induces higher amplitudes. The sensitivity for Re is found more pronounced in cylinders with low mass and damping. Meanwhile, VIV is found to enhance wake mixing, and to significantly change the near wake Reynolds stresses. It is suggested that the increase in Re brings a change to the wake patterns, which are known in VIV at lower Re. The kinetic energy production, of near wake eddy structures, is qualitatively altered with the presence of VIV. Furthermore, the surface heat flux is found to cause a noticeable increase in VIV amplitude, as long as it does not disorder the wake correlation. The cylinder's oscillation increases the average value of the Nusselt number (Nu), while the local variance of Nu rises markedly post-separation.
2

[pt] CARACTERIZAÇÃO DAS FORÇAS E DO AMORTECIMENTO VISCOSO AGINDO SOBRE AS LINHAS DE CONTROLE DE COMPLETAÇÃO INTELIGENTE / [en] CHARACTERIZATION OF FORCES AND VISCOUS DAMPING ACTION ON INTELLIGENT COMPLETION CONTROL LINES

THIAGO HANDERSON TORRES EDUARDO 28 October 2022 (has links)
[pt] Diante dos cenários de produção cada vez mais desafiadores, a indústria de petróleo tem sido forçada a expandir os limites operacionais para vazões, temperaturas e pressões mais elevadas. Como consequência, cenários mais rigorosos são encontrados, levando à redução da vida útil dos equipamentos atuais, como por exemplo, a falha prematura por fadiga de linhas de controle de poços com completação inteligente. Estas linhas encontram-se expostas ao escoamento turbulento na região anular da coluna de produção, causando vibrações e tensões suficientemente altas, podendo levar a uma falha prematura das linhas por fadiga. Para prevenir estes problemas e desenvolver projetos mais eficientes, é necessário investigar os fenômenos associados a interação da vibração da linha com os desprendimentos de vórtices do escoamento. Estes foram modelados utilizando-se a metodologia DDES (Delayed Detached Eddy Simulation), o que requer alto custo computacional, devido à necessidade de utilização de pequenos passos de tempo e de espaçamento de malha. Buscando reduzir o custo computacional para a modelagem do problema, propõe-se, neste trabalho, tratar de forma desacoplada a análise estrutural e de fluidodinâmica. As forças atuantes nas linhas de controle no espaço anular do poço de completação são obtidas desprezando-se a flexibilidade das linhas. Paralelamente, o fator de amortecimento crítico, necessário para a análise estrutural da vibração da linha, é obtido através de uma simulação Fluido- Estrutura de um escoamento cruzado a um cilindro elástico. Os resultados obtidos mostram que a presente metodologia é promissora, pois permite uma representação dos fenômenos envolvidos melhor do que a encontrada nos procedimentos atualmente disponíveis na literatura. / [en] In face of increasingly challenging production scenarios, the oil industry has been forced to expand operational limits to higher flow rates, temperatures, and pressures. Therefore, challenging production scenarios are found, from integrity standpoint, leading to reduction in current equipment life expectancy. Premature failure of control lines due to fatigue in wells with intelligent completion is one of the problems that arises from those extreme conditions. These lines are exposed to turbulent flow in the annular region of the production string, causing sufficiently high vibrations and stresses. These dynamic stresses can lead to premature failure of the lines due to fatigue. To prevent these problems, and to develop more efficient designs, it is necessary to investigate the phenomena associated with the interaction of the line vibration with the vortex shedding of the flow. We modeled the phenomena using the DES (Delayed Detached Eddy Simulation) methodology, which has high computational cost due to the need of using small time steps and high mesh refinement. In order to reduce these computational costs, this work proposes to deal with structural and fluid dynamics analysis in a decoupled way. The forces acting on the control lines in the annular space of the completion well are obtained neglecting the flexibility of the lines. In parallel, the critical damping factor, necessary for the structural vibration analysis of control lines, is obtained through a Fluid-Structure Interaction (FSI) simulation of an elastic cylinder subjected to cross flow. The results obtained show that the present methodology is promising, allowing a better representation of the involved phenomena, compared to procedures currently available in the literature.

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