Title: Shell-like structures in the ISM: Observation versus simulations Author: Vojtěch Sidorin (vojtech.sidorin@gmail.com)1 Department: Astronomical Institute of Charles University2 Supervisor: Prof. RNDr. Jan Palouš, DrSc. (palous@asu.cas.cz), Astronomical Institute of the Czech Academy of Sciences3 Abstract: Shell-like structures are objects found in large numbers in the inter- stellar medium (ISM). They usually appear as bubbles or segments of bubbles and are believed to result from the deposition of mass and energy into the ISM by stars, gamma-ray bursts, or high-velocity clouds. Interstellar turbulence may play a role in their creation too. These structures influence the dynamics of the ISM and are also linked to star formation. In this thesis, I review our current knowledge of the ISM, interstellar turbulence, and shell-like structures in the ISM. Then I present the research into the GLIMPSE bubble N107 conducted in collaboration with my colleagues. N107 is a dusty shell-like structure found in our Galaxy. We explored its atomic, molecular, and radio-continuum components; derived its distance (3.6 kpc), size (radius of 12 pc), and expansion velocity (8 km s−1 ); and identified 49 associated molecular clumps. Using numerical simulations, we estimated the conditions under which N107 formed and concluded...

To improve the control of a steel casting process ABB has developed an Electro Magnetic Brake (EMBR). This product is designed to improve steel quality, i.e. reduce non-metallic inclusions and blisters as well as risk of surface cracks. There is a demand of increasing the steel quality and in order to optimize the steel casting, simulations and experiments play an important role in achieving this. An advanced CFD simulation model has been created to carry out this task. The validation of the simulation model is performed on a water model that has been built for this purpose. This water model also makes experiments possible. One step to the simulation model is to measure the velocity and motion pattern of the seeding particles and the air bubbles in the water model to see if it corresponds to the simulation results. Since the water is transparent, seeding particles have been added to the liquid in order to observe the motion of the water. They have the same density as water. Hence the particles will follow the flow accurately. The motions of the air bubbles that are added into the water model need also to be observed since they influence the flow pattern. An algorithm - ”Transparent motions” - is thoroughly inspected and implemented. ”Transparent motions” was originally designed to post process x-ray images. However in this thesis, it is investigated whether the algorithm might be applicable to the water model and the image sequences containing seeding particles and air bubbles that are going to be used for motion estimation. The result show satisfying results for image sequences of particles only, however with a camera with a faster sampling interval, these results would improve. For image sequences with both bubbles and particles no results have been achieved.

Orientadores: Antonio Carlos Bannwart, Ricardo Dias M. de Carvalho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica, Instituto de Geociências / Made available in DSpace on 2018-08-16T20:19:45Z (GMT). No. of bitstreams: 1 GrangeiroFilho_FernandoAntonio_M.pdf: 4784973 bytes, checksum: 5e420546996f33fd8f25a4488a55967a (MD5) Previous issue date: 2010 / Resumo: O transporte de misturas complexas, como o escoamento gás-líquido, depende de vários parâmetros, incluindo o padrão de escoamento. O escoamento bifásico é bastante comum na indústria petrolífera. Em operações off-shore, líquido e gás escoam por longos trechos verticais, horizontais e inclinados através de linhas de escoamento e risers antes de serem separados na superfície. No presente trabalho, um aparato experimental, com uma tubulação de 54 mm de diâmetro, foi montado para simular o escoamento horizontal intermitente, água-ar. As características do escoamento foram investigadas usando duas estações de sensores ultrassônicos, separados por uma distância conhecida ao longo da tubulação, e filmagens realizadas com uma câmera ultrarrápida (1000 quadros por segundo). Cada estação ultrassônica consistia de um transdutor pulso-eco (posicionado a 0o) e três sensores receptores posicionados em diferentes ângulos ao longo da circunferência da tubulação (45o, 135o, 180o). Os parâmetros obtidos foram: velocidade da bolha alongada, comprimentos da bolha alongada, do pistão de líquido e da célula unitária, e frequência de passagem da célula unitária. Um algoritmo foi elaborado a fim de identificar qual estrutura (bolha alongada ou pistão de líquido) escoava na frente do sensor. Através desse programa foi possível calcular a espessura do filme de líquido assim como as vazões volumétricas das fases. A técnica de ultrassom se mostrou eficiente e apresentou um custo relativamente baixo para investigar as características do escoamento pistonado. A presença de muitas bolhas na cauda da bolha alongada pode causar erros nas medições que pôde ser observado através da filmagem, porém, dados provenientes de outros sensores em conjunto com os dados do sensor posicionado na parte inferior da tubulação podem auxiliar a detectar a transição da cauda da bolha para o começo do pistão de líquido / Abstract: Transport processes in complex mixtures such as gas-liquid flows depend on various parameters, including the flow pattern. Two-phase flow is very common in petroleum industry. During off-shore production, liquid and gas phases travel long distances through flow-lines and risers before being separated. In the present work, experimental data are presented on the axial flow topology of horizontal, air-water slug flows in a 54-mm inner diameter acrylic pipe. The flow structure was investigated using two stations of an ultrasonic apparatus positioned at a known distance from each other along the flow direction and high-speed motion pictures (1000 fps) of the flow. Each ultrasonic station consisted of one emitter transducer (positioned at 0o) and three receivers at different angles (45º, 135º and 180º) along the pipe circumference. The parameters obtained were: elongated bubble velocity; elongated bubble, liquid slug and unit cell lengths, and unit cell frequency and flow rates of liquid and gas phases. An algorithm was made to identify which structure (elongated bubble or liquid slug) was passing in front of the transducer. This program made it possible to calculate the volumetric flow rates. Results shown by both techniques agreed against each other, however, more tests at other flow rates should be held to which for correlations could be made / Mestrado / Explotação / Mestre em Ciências e Engenharia de Petróleo

Orientadores: Milton Mori, Marcos Akira d'Avila / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-17T21:18:36Z (GMT). No. of bitstreams: 1 Silva_MarcelaKotsukada_D.pdf: 43160482 bytes, checksum: b46a2b0225fdad527404b8c745e2f23b (MD5) Previous issue date: 2011 / Resumo: Os principais problemas da simulação da fluidodinâmica em sistemas gás-líquido por CFD são as simplificações do comportamento dinâmico das bolhas. Na maioria dos processos industriais com escoamento gás-líquido em colunas de bolhas, as bolhas estão em velocidades altas e a coluna opera em regime heterogêneo. Existe ainda a influência da geometria do sistema e das propriedades físicas dos fluídos envolvidos no processo. Para que a técnica CFD seja aplicada adequadamente, visando aplicações industriais, é necessário considerar os fenômenos de quebra e coalescência. No entanto, existe uma carência de dados experimentais em tal regime de operação para testar a aplicabilidade dos modelos matemáticos empregados nas simulações. Neste trabalho é apresentado um estudo numérico e experimental de duas colunas de bolhas operando em regime heterogêneo. No primeiro caso, foram realizadas análises quanto a influência de diferentes modelos de arraste, além do emprego das forças interfaciais de sustentação e de dispersão turbulenta. Diferentes modelos de turbulência foram também verificados, tomando a fração volumétrica de gás em diferentes posições axiais e velocidade do gás provenientes da literatura. No segundo caso, realizou-se medidas por meio da técnica PIV de velocidades axiais médias da fase líquida e suas flutuações. Análises de intensidade turbulenta, tensores de Reynolds e energia sindética turbulenta foram realizadas, a fim de obter informações acerca da turbulência em três diferentes velocidades superficiais de gás. Para as análises numéricas foi aplicado um modelo matemático tridimensional, turbulento e transiente para a representação do escoamento nas duas colunas utilizadas. Este modelo trata ambas as fases, gás e líquido, a partir de uma abordagem Euleriana. Diferentes distribuições de tamanhos de bolhas foram empregados por meio do balanço populacional considerando os fenômenos de quebra e coalescência. Perfis radiais de fração volumétrica e velocidade de gás, além de perfis de velocidade média de líquido foram confrontados com dados experimentais publicados e medidos respectivamente. O modelo matemático previu um escoamento semelhante aos que foram encontrados nas colunas propostas / Abstract: The main problems encountered in the simulation of gas-liquid systems with the use of CFD are related to the simplifications of the bubble dynamic behavior. In most industrial procedures with gas-liquid flown in bubble columns, bubbles are at high speed and the column operates in the heterogeneous regime. There still is the influence of the system's geometry and fluids physical properties involved in the process. For correctly applying the CFD technique, aiming industrial applications, it is necessary to consider the breakup and coalescence phenomena. Nevertheless, there is a lack of experimental data available in this operational regimen to test the feasible application of the mathematical models used in simulations. In this work it is presented a numeric and experimental study of two bubble columns operating in the heterogeneous regime. In the first case, analyses of different drag models, besides the employ of the interfacial forces of lift and turbulent dispersion were performed. Different turbulence models were also verified, taking the gas holdup in different axial positions and gas velocity from literature. In the second case, measurements of mean axial liquid velocities and their fluctuations were performed with the PIV technique. Turbulence intensity, Reynolds stress tensors and turbulent kinetics energy analyses were performed in order to obtain information about the turbulence for three different gas superficial velocities. For the numerical analyses a tridimensional, turbulent and transient mathematical model to represent the flow in the two columns was applied. This model treats both phases, gas and liquid, with an Eulerian approach. Different bubbles size distributions were used by population balance considering the breakup and coalescence phenomena. Gas holdup, gas velocity and mean axial liquid velocity radial profiles were confronted to the published and acquired experimental data respectively. The mathematical model predicted a developed flow similar to those found in the proposed columns / Doutorado / Desenvolvimento de Processos Químicos / Doutor em Engenharia Química

Playing and enjoying games might seem like a simple task to most people even though many games rely heavily on sensory, cognitive and motoric ability. To create games that are accessible and inclusive to a wide range of audiences, it is important that design choices are considered carefully. This thesis aims to provide an investigation into closed captioning and enhanced speech bubbles. The goal is to clarify and to compare what effects these features have on the perception of situational and affective information and how they affect the immersion of non-disabled players. Two experiments were performed with a total of 38 participants at the University of Skövde. Each experiment investigated a separate accessibility feature and evaluated their influence on the gameplay experience. By performing two experiments, it was possible to identify the strengths and weaknesses of both features in comparison to each other. The results show that closed captions can have a negative effect on the immersion of the player and that enhanced speech bubbles increase immersion and provide additional affective information to the player.

Les mousses sont des assemblées de bulles de gaz dans une matrice liquide et sont utilisées dans plusieurs applications telles que par exemple l'isolation thermique et phonique, le forage pétrolier. Cependant, elles sont instables et tendent donc à disparaître. Les mécanismes qui gouvernent la stabilité d'une mousse et son effondrement restent encore incompris au niveau fondamental. Ce travail de thèse vise à étudier le couplage physico-chimique et rhéologique au sein d'une mousse par des simulations numériques, au niveau d'un amas de bulles cisaillées, afin de mieux comprendre l'origine de cette instabilité / Foams are gaz bubbles assemblies in a liquid matrix and are used in several applications such as for example the thermal and phonic insulating, ore drilling. However, they are instables and trend to disappear. the mechanisms that gouverns the foam stability and its collapse are still not well understood from a fundamental point of vue. The goal of this thesis work is to study the physico-chemical and rheological coupling in a foam, by numerical simulations of a cluster of sheared bubbles, in order to better understand the origin of this foam instability

L'objectif de cette thèse est l'étude de la population de bulles générée entre deux morceaux de verre mis en contact et portés à 1100 °C sans matières premières. Comprendre la transition gaz dissous/gaz est un sujet scientifique majeur, par ailleurs les bulles sont le principal défaut dans les verres industriels et la quantité de verre recyclé introduite dans les fours est destinée à augmenter. Nous étudions la vie d'une bulle de sa nucléation à sa remontée dans le verre fondu en passant par sa croissance. Nous montrons que la nucléation homogène n'existe pas dans un verre car les réactions chimiques ne génèrent pas les sursaturations suffisantes. L'écoulement du verre après la transition vitreuse enferme des poches de gaz qui sont les précurseurs naturels des bulles. Nous modélisons la sursaturation à l'interface entre deux verres et montrons son influence sur le nombre de nuclei stables qui forment des bulles. Nous modélisons la dynamique de croissance des bulles en utilisant la même caractérisation de l'état d'oxydation que pour la nucléation. Nous constatons que la croissance des bulles à l'interface entre un verre réduit et un verre oxydé est plus rapide que celle des bulles situées dans un verre oxydé seul. Nous attribuons cette accélération à l'interaction entre les verres qui décale l'équilibre du soufre vers la formation de SO2 gazeux. Pour finir, nous présentons un montage expérimental qui permet de mesurer des champs de vitesse dans du verre grâce à l'utilisation de rayons X et à un algorithme de flot optique. Cette mesure permet d'évaluer la capacité d'une population de bulles à favoriser le mélange du verre au début de la fusion. / This thesis focuses on the bubbles population that appears between two glass pieces when heated at 1100 °C without any reactive raw materials. Understanding the mechanisms involved in the transition from dissolved gas to gas is still a fundamental issue of materials science. Industrially, bubbles are the major sources of defects in the final glass product and the amount of recycled glass introduced in glass furnaces will likely increase.We have studied the life of a bubble at different times, from its creation to its growth behavior, and to its rise in the molten glass. We show that homogeneous nucleation cannot exist in molten glass because chemical reactions are not able to generate the needed supersaturations by themselves. Thus, right after glass transition, glass flow is responsible for the entrapment of gas pockets, which then become natural precursors of bubbles.We model the supersaturation at the interface between two glasses, and we show its influence over the number of stable nuclei that can form bubbles.We also model the growth dynamic by using the same characterization of glasses' oxidation states than for nucleation. We experimentally show that bubbles located at the interface between a reduced glass and an oxidized glass grow faster than bubbles located in an oxidized glass only. The main effect of the interaction between the two glasses is to move the sulfur equilibrium towards the formation of gaseous SO2.Finally, using X-rays and an optical flow algorithm, we present a new experimental setup which measure velocity fields in an opaque medium to assess bubbles ability to promote glass mixing.

The “Great Recession” of 2007 created havoc in the homebuilding industry, more than any other previous economic down cycle. Countless seasoned local homebuilders across the country did not survive. The impact of their failure on the economy, community, employment, lenders, suppliers, and subcontractors was devastating. While previous studies have sought to identify the symptoms and causes of business failure, very little research has been done on home builder business failure due to acts, omissions, characteristics, or other events which are non-financial. Specifically, those that are attributable to the failed entities' top management and leadership during the housing crisis and the Great Recession. Therefore, the purpose of this qualitative inquiry is to uncover those nonfinancial factors and help to fill the gap in the literature Additionally, we seek to find specific strategies that could be incorporated into the business models of local homebuilders which allow them to anticipate and navigate turbulent economic times. The ultimate goal of such strategies, however, is to shield the organizations of those builders from the negative effects of recessions and allow them to thrive in the aftermath.

This thesis addresses aspects of the transport of bubbles and capsules (a thin elastic membrane enclosing a viscous fluid) by means of a viscous flow in complex vessel geometries. It focusses on two related themes: (i) the trapping of air bubbles in a sudden streamwise tube expansion and (ii) the extreme deformation of bubbles and capsules in a localised tube constriction. Air bubbles of different volumes were trapped in a tube with a square cross-section, which contains a sudden streamwise expansion in tube width. The liquid filling the tube was driven by constant volume-flux flow, and experiments were performed in both millimetric and micrometric tubes to identify the range of flow rates for which bubbles could get trapped. The gradients in surface energy generated by the broadening of the bubble into the expansion depend strongly on bubble volume and the expansion length. It is shown that in order for a trapped bubble to release from the expansion, the work of the pressure forces due to flow past the bubble must exceed the change in surface energy required to squeeze into the narrower channel. This criterion for trapping was verified by direct pressure measurements and a capillary static model, which uses three-dimensional Surface Evolver calculations. The extreme deformation of bubbles and capsules was investigated using a localised constriction of the tube width. Both bubbles and capsules were shown to adopt highly contorted configurations and exhibit broadly similar features over a wide range of flow rates, suggesting that the deformation was primarily imposed by the geometry through viscous shear forces. However, bubbles and capsules also display distinguishing features. Bubbles can breakup and exhibit thinning of the rear of the bubble at a critical flow rate, which is associated with a divergence of the rear tip speed and curvature. In contrast, the capsule membrane can wrinkle and fold, and the membrane thickness imposes the value of the maximum curvature locally available to the capsule.

Nitrogen-alloyed austenitic stainless steels are becoming increasingly popular, mainly due to their excellent combination of strength and toughness. Nitrogen desorption to the atmosphere during the autogenous welding of these steels is often a major problem, resulting in porosity and nitrogen losses from the weld. In order to counteract this problem, the addition of nitrogen to the shielding gas has been proposed. This study deals with the absorption and desorption of nitrogen during the autogenous arc welding of a number of experimental stainless steels. These steels are similar in composition to type 310 stainless steel, but with varying levels of nitrogen and sulphur. The project investigated the influence of the base metal nitrogen content, the nitrogen partial pressure in the shielding gas and the weld surface active element concentration on the nitrogen content of autogenous welds. The results confirm that Sievert's law is not obeyed during welding. The weld nitrogen content increases with an increase in the shielding gas nitrogen content at low nitrogen partial pressures, but at higher partial pressures a dynamic equilibrium is created where the amount of nitrogen absorbed by the weld metal is balanced by the amount of nitrogen evolved from the weld pool. In alloys with low sulphur contents, this steady-state nitrogen content is not influenced to any significant extent by the base metal nitrogen content, but in high sulphur alloys, an increase in the initial nitrogen concentration results in higher weld nitrogen contents over the entire range of nitrogen partial pressures evaluated. A kinetic model can be used to describe nitrogen absorption and desorption during welding. The nitrogen desorption rate constant decreases with an increase in the sulphur concentration. This is consistent with a site blockage model, where surface active elements occupy a fraction of the available surface sites. The absorption rate constant is, however, not a strong function of the surface active element concentration. Alloys with higher base metal nitrogen contents require increased levels of supersaturation prior to the onset of nitrogen evolution as bubbles. These increased levels of supersaturation for the higher-nitrogen alloys is probably related to the higher rate of nitrogen removal as N2 the onset of bubble formation. Given that nitrogen bubble formation and detachment require nucleation and growth, it is assumed that a higher nitrogen removal rate would require a higher degree of supersaturation. Nitrogen losses from nitrogen-alloyed stainless steels can be expected during welding in pure argon shielding gas. Small amounts of nitrogen can be added to the shielding gas to counteract this effect, but this should be done with care to avoid bubble formation. Supersaturation before bubble formation does, however, extend the range of shielding gas compositions which can be used. Due to the lower desorption rates associated with higher surface active element concentrations, these elements have a beneficial influence during the welding of high nitrogen stainless steels. Although higher sulphur contents may not be viable in practice, small amounts of oxygen added to the shielding gas during welding will have a similar effect. / Dissertation (PHD)--University of Pretoria, 2004. / Materials Science and Metallurgical Engineering / unrestricted