[pt] As atividades realizadas em estruturas Onshore e Offshore, relacionadas a exploração e produção de petróleo estão associadas ao risco iminente de vazamento de gás ou óleo, que encontrando qualquer tipo de ignição, pode causar incêndios e explosões com o potencial de causar perdas financeiras substanciais e mortes. No presente trabalho, a metodologia em CFD foi utilizada para analisar o vazamento de gás natural em um ponto localizado no módulo de compressão de gás em uma plataforma offshore. A turbulência do escoamento foi modelada com a metodologia RANS, empregando o modelo de duas equações K-epsilon. Considerando a situação crítica, o vazamento foi analisado em regime permanente, e modelado como uma fonte pontual. Foram consideradas duas intensidades de vento: 0,5 m/s representando a condição de calmaria e 6,5 m/s representando a velocidade mais frequente, e uma única direção no sentido PROA-POPA. Para cada condição de vento, foram estudadas quatro direções de vazamentos distintos (direção de liberação do gás), ou seja, a partir da junção entre o bocal do compressor e o flange da tubulação de alimentação do sistema (localizados imediatamente acima do compressor) tem-se vazamentos nas direções norte, sul, leste e oeste. A partir dos resultados de sobrepressão (DeltaP) (diferença entre a pressão ambiente (P0) e a pressão máxima de onda de choque (Pmáxima) obtida, pontos críticos foram identificados. O volume da nuvem foi determinado para cada cenário e, posteriormente, um cálculo de TNT equivalente (comparação do potencial da mistura explosiva com a massa de TNT necessária para produzir efeitos semelhantes) foi realizado para identificação dos potenciais riscos a estrutura offshore em caso de ignição do material gasoso disperso. Os resultados obtidos coincidiram com medidas experimentais de sobre pressão em situações semelhantes. Identificou-se como o pior cenário, vazamento no flange do compressor na direção sul, correspondente a direção contraria ao vento, com alta concentração de gás natural numa grande região da plataforma. / [en] Oil exploration and production activities in Onshore and Offshore structures are associated with the imminent risk of gas or oil leakage, which encountering any type of ignition, can cause fires and explosions with the potential to cause substantial financial losses and deaths. In the present work, the CFD methodology was used to analyze the leakage of natural gas at a point located in the gas compression module on an offshore platform. The flow turbulence was modeled with the RANS methodology, using the two-equation K-epsilon model. Consider the critical situation, the leak was analyzed in steady state, and modeled as a point source. Two wind intensities were considered: 0.5 m / s represents the calm condition and 6.5 m / s represents the most frequent speed, and a single direction in the PROA-POPA direction. For each wind condition, four distinct leakage results (direction of gas release) were studied, i.g., from the junction between the compressor nozzle and the system supply piping flange (driven above the compressor) there are leaks in the north, south, east and west directions. From the results of overpressure (deltaP) (the difference between the ambient pressure (P0) and the maximum shock wave pressure (P maximum) obtained, points obtained were separated. The cloud volume was determined for each scenario and, subsequently, a calculation of equivalent TNT (comparison of the potential of the explosive mixture with the mass of TNT necessary to produce similar effects) was performed to identify potential risks to the offshore structure in case of ignition make dispersed gaseous material. The results obtained coincided with experimental pressure measurements under similar conditions. It was identified as the worst scenario, a leak in the compressor flange in the south direction, corresponding to the direction against the wind, with a high concentration of natural gas in a large region of the platform.

With the increased frequency of accidental and deliberate explosions, the response of civil infrastructure systems to blast loading has become a research topic of great interest. However, with the high cost and complex safety and logistical issues associated with live explosives testing, North American blast resistant construction standards (e.g. ASCE 59-11 & CSA S850-12) recommend the use of shock tubes to simulate blast loads and evaluate relevant structural response. This study aims first at developing a 2D axisymmetric shock tube model, implemented in ANSYS Fluent, a computational fluid dynamics (CFD) software, and then validating the model using the classical Sod’s shock tube problem solution, as well as available shock tube experimental test results. Subsequently, the developed model is compared to a more complex 3D model in terms of the pressure, velocity and gas density. The analysis results show that there is negligible difference between the two models for axisymmetric shock tube performance simulation. However, the 3D model is necessary to simulate non-axisymmetric shock tubes. The design of a shock tube depends on the intended application. As such, extensive analyses are performed in this study, using the developed 2D axisymmetric model, to evaluate the relationships between the blast wave characteristics and the shock tube design parameters. More specifically, the blast wave characteristics (e.g. peak reflected pressure, positive phase duration and the reflected impulse), were compared to the shock tube design parameters (e.g. the driver section pressure and length, the driven v section length, and perforation diameter and their locations). The results show that the peak reflected pressure increases as the driver pressure increases, while a decrease of the driven length increases the peak reflected pressure. In addition, the positive phase duration increases as both the driver length and driven length are increased. Finally, although shock tubes generally generate long positive phase durations, perforations located along the expansion section showed promising results in this study to generate short positive durations. Finally, the developed 2D axisymmetric model is used to optimize the dimensions of a proposed large-scale conical shock tube system developed for civil infrastructure blast response evaluation applications. The capabilities of this proposed shock tube system are further investigated by correlating its design parameters to a range of explosion threats identified by different hemispherical TNT charge weight and distance scenarios. / Thesis / Master of Applied Science (MASc)

Les travaux présentés dans ce mémoire de thèse s’inscrivent dans le cadre des études liées aux dégâts sur les structures et les blessures subies par les personnes à la suite d’explosions de charges explosives en milieu confiné et semi-confiné. Afin de mener cette étude, des expériences sont réalisées à petite échelle en laboratoire et sont complétées par des simulations numériques. Les ondes de choc sont obtenues grâce à la détonation d’une charge explosive gazeuse composée de propane-oxygène en proportion stoechiométrique. L’étude consiste donc à réaliser des expériences à petite échelle en laboratoire afin d’apprécier les champs de pression obtenus à la suite de la détonation d’une charge explosive au sein de deux configurations différentes. La première représente un atelier pyrotechnique et la seconde met en jeu un entrepôt de stockage de bouteilles de gaz. Les résultats expérimentaux sont ensuite confrontés à des résultats obtenus par simulations numériques réalisées grâce au logiciel AUTODYN. En complément de ces deux configuration principales, une étude est menée sur l’identification des pics de surpressions réfléchis grâce à une approche expérimentale appelée paroi par paroi. Une étude est également menée sur la détermination d’une équivalence massique entre le TNT et le mélange gazeux utilisé pour les expériences. / The goal of this study is to investigate shock waves propagation, in a geometrically complex confined and semi-confined environment, consecutive to the detonation of a spherical explosive charge. In this objective, small scale experiments are conducted in laboratory and are completed with numerical analysis. Shock waves are generated thanks to spherical detonation of a gas mixture composed of propane-oxygen in stoechiometric proportion. Two main configurations are studied: the first represents a pyrotechnic workshop and the second is a warehouse containing gas cylinder. Experimental and numerical results are then compared. Complementary studies are realised to describe blast wave propagation inside a semi-confined volume thanks to a new experimental approach named wall by wall. Finally, in order to simulate TNT charges detonation by computational means, an important study is conducted to determine a mass equivalent between TNT and gas mixture.