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L'ablation laser dans l'air à la pression atmosphérique est souvent appliquée dans l'industrie, l'analyse chimique, la chirurgie, ... Pour un développement plus approfondi des technologies laser basées sur l'effet d'ablation, il est nécessaire de mieux comprendre les phénomènes à l'origine de l'interaction laser-matière. Lors d'un impact du faisceau laser sur la surface d'un matériau, une plume plasma se forme au dessus de la cible. Ce plasma contient des électrons, des atomes et des ions du matériau évaporé, ainsi que du gaz ambiant, s'il est présent. Lors de l'impulsion laser, cette plume absorbe une grande partie d'énergie du faisceau laser, réduisant ainsi la quantité du rayonnement laser qui arrive à la surface de la cible. Les dimensions, ainsi que les paramètres de cette plume plasma évoluent très rapidement avec le temps. L'étude de la dynamique et des paramètres de cette plume est très importante, parce qu'ils influent sur tous les processus physiques ayant lieu à la surface du matériau traité. Nous avons étudié l'expansion de la plume plasma formée lors de l'ablation des échantillons métalliques (Al, Ti, Fe) par faisceau laser Nd :YAG nanoseconde (durée d'impulsion : 5.1 ns, longueur d'onde : 1064 nm, irradiance de l'ordre de grandeur de GW/cm2) dans l'air à la pression atmosphérique en utilisant la technique d'imagerie rapide. Cette technique nous a permis d'observer l'évolution spatio-temporelle de la plume au début de son expansion. Les résultats obtenus indiquent que la plume d'ablation laser a une structure : deux régions ont été distinguées - le cœur et la périphérie de la plume. La dynamique de ces deux régions de la plume a été étudiée et les vitesses de leur expansion ont été déterminées. En plus, nous avons examiné l'influence de l'irradiance laser, ainsi que l'influence de la composition de la cible sur la dynamique de la plume. D'autre part, nous avons développé des modèles numériques sous COMSOL Multiphysics pour simuler le processus d'ablation laser. Un modèle thermique a été utilisé pour simuler l'interaction laser - cible. Les résultats de ce modèle ont été employés comme conditions à la limite du modèle hydrodynamique, utilisé pour simuler l'expansion de la plume du plasma dans l'air ambiant. Deux approches ont été proposées : approche microscopique et macroscopique. Les résultats de simulation basée sur l'approche macroscopique donnent l'évolution temporelle et distribution spatiale (1D) des paramètres de la plume : masse volumique, vitesse, pression.

<p>Nuclear reactors release small amounts of radioactivity during their normal operations. The most common method of calculating the dose to the public that results from such releases uses Gaussian Plume models. We are investigating these methods using CAP88-PC, a computer code developed for the Environmental Protection Agency (EPA) in the USA that calculates the concentration of radionuclides released from a stack using Pasquill stability classification. A buoyant or momentum driven part is also included. The uptake of the released radionuclide by plants, animals and humans, directly and indirectly, is then calculated to obtain the doses to the public. This method is well established but is known to suffer from many approximations and does not give answers that are accurate to be better than 50% in many cases. More accurate, though much more computer-intensive methods have been developed to calculate the movement of gases&nbsp / using fluid dynamic models. Such a model, using the code FLUENT can model complex terrains and will also be investigated in this work. This work is a preliminary study to compare the results of the traditional Gaussian plume model and a fluid dynamic model for a simplified case. The results indicate that Computational Fluid Dynamics calculations give qualitatively similar results with the possibility of including much more effects than the simple Gaussian plume model.</p>

Over 7.8 km of seismic reflection data and 2 km of electrical resistivity data were acquired, processed, and interpreted during this multi-method geophysical study. Objectives included the definition of geologic conditions underlying a contaminant plume in McCracken County, western Kentucky, and the determination of the potential for structural control on the rate and direction of plume migration. Both geophysical methods indicate the presence of multiple high-angle normal faults outlining a series of asymmetric grabens ranging in width from 160 m to almost 300 m and striking between N40°E and N45°E. There was agreement between the two methods on fault location and degree of near-surface offset, with offsets of 1 to 2 m observed at 10 to 20 m below ground surface and 3 to 8 m observed at 20 to 30 m depth. Bedrock displacement was generally 2 to 3 times larger, with offsets of 10 to 26 m observed. The faults appear to have originated in the Paleozoic with predominantly normal reactivation occurring as recently as the Pleistocene. The fault strikes generally approximate the orientation of the northwestern contaminant plume. Observed offset of the Regional Gravel Aquifer may form a preferential flow path for contaminant migration.

Eulerian chemical transport models are extensively used to steer environmental policy, forecast air quality and study atmospheric processes. However, the ability of these models to simulate concentrated atmospheric plumes, including fire-related smoke, may be limited. Wildland fires are important sources of air pollutants and can significantly affect air quality. Emissions released in wildfires and prescribed burns have been known to substantially increase the air pollution burden at urban locations across large regions. Air quality forecasts generated with numerical models can provide valuable information to environmental regulators and land managers about the potential impacts of fires. Eulerian models present an attractive framework to simulate the transport and transformation of fire emissions. Still, the limitations inherent to chemical transport models when applied to replicate smoke plumes must be identified and well understood to adequately interpret results and further improve the models' predictive skills. Here, a modeling framework centered on the Community Multiscale Air Quality modeling system (CMAQ) is used to simulate several fire episodes that occurred in the Southeastern U.S. and investigate the sensitivity of fine particulate matter concentration predictions to various model inputs and parameters. Significant sources of uncertainty in the model are identified and discussed, including the spatiotemporal allocation of fire emissions and meteorological drivers. In addition, special attention is given to model grid resolution. Adaptive grid modeling is explored as a strategy to simulate fire-related plumes. An adaptive version of CMAQ, capable of dynamically restructuring the grid on which solution fields are estimated and providing refinement at the regions where accuracy is most dependent on resolution, is presented. The fully adaptive three-dimensional modeling technique can be applied to reach unprecedented levels of grid resolution and provide insight into plume dynamics unattainable with static grid models. Through this work the capability of current chemical transport models to replicate fire-related air quality impacts is evaluated, key research needs to achieve effective simulations are identified, and numerical tools designed to improve model performance are developed.

An electrochemical sensor array can provide information about the spatial and temporal distribution of chemicals in liquid turbulent plumes. Planar laser induced fluorescence (PLIF) and amperometric sensor arrays were used to record signals from modulated chemical plumes released into a recirculating aquatic flume. Coherence analysis was applied to extract the frequency components contained in the sensor response. Effects due to release distance, modulation frequency, and array orientation were investigated. This study has demonstrated that frequency encoded information can be extracted from a turbulent chemical plume using an array of amperometric sensors with optimized three-dimensional geometry and tuning.

Orientador: Chang Hung Kiang / Banca: Everton de Oliveira / Banca: Holger Weiss / Banca: Luis Tadeu Furlan / Banca: Miguel Alfaro Soto / Resumo: Vazamentos acidentais de derivados de petróleo podem ocorrer em refinarias, dutos, postos de serviços e no transporte rodoviário ou ferroviário, ocasionando diversos impactos ambientais. Este trabalho teve por objetivo avaliar o comportamento de uma pluma de fase livre de querosene, presente em uma área industrial no município de Paulínia (SP), e estudar a recuperação de querosene em resposta à variação sazonal das chuvas. A área de estudo apresentou seis litotipos de origem fluvial, destacando-se a presença de paleocanais preenchidos por areias grossas. Verificou-se que as grandes variações nos níveis d'água proporcionam o fenômeno de trapeamento/destrapeamento do querosene, afetando diretamente o processo de remediação. A área apresenta altas taxas de recarga, variando de 370 mm a 550 mm em um ano. Após 40 meses de remediação, em que se procedeu ao bombeamento de oito poços, foram recuperados 176.000 litros de querosene. O período de maior recuperação foi de outubro a janeiro. Cálculos efetuados a partir dos índices físicos do solo, das propriedades físicas do querosene e da espessura observada de fase livre, em dezembro de 2008, permitiram estimar um volume remanescente recuperável de 192.000 litros de querosene no subsolo / Abstract: Accidental spills of petroleum products may occur in refineries, pipelines, and service stations, as well as during roadway and railway transportation, causing environmental damages. The main objective of this thesis is to evaluate the behavior of a kerosene free phase plume in an industrial area of the municipality of Paulinia, and evaluate the role of water table fluctuation on hydrocarbon recovery. Six lithofacies deposited in fluvial environment were identified, in particular paleochannels filled by coarse grain sands. An important finding was large water table fluctuation induce entrapment/release of kerosene, greatly affecting aquifer remediation. The studied aquifer underwent high recharge rates of 370 mm to 550 mm per year. Throughout 40 months of remediation, in which eight submersible pumps were employed, 176.000 liters of kerosene were recovered. The largest period of kerosene recovery was in the interval comprising October to January. Calculations using soil physical indexes, physical properties of kerosene and the observed thickness of free phase, as measured in December of 2008, allowed to estimate a volume of 192.000 liters of recoverable remnant kerosene yet in the ground / Doutor

Cette thèse s'intéresse à l'écoulement convectif induit par une paroi chauffante isotherme. La couche limite turbulente qui s'établit le long de celle-ci s'apparente à un panache, bien que les conditions de paroi en modifient significativement certaines caractéristiques typiques. Dans l'étude présentée, l'environnement est un milieu clos. Puisque le fluide de moindre densité s'accumule dans la partie haute de l'enceinte, une stratification en température s'établit. Afin de mieux comprendre les mécanismes qui entrent en jeu dans ce type de panache et son interaction avec le fluide ambiant, nous déployons une approche à la fois expérimentale et théorique. Sur le plan expérimental, une technique combinant Velocimétrie par Images de Particules (PIV) et Fluorescence Induite par Laser (LIF) est mise au point, et permet d'acquérir simultanément la vitesse et la température du fluide dans un plan de mesure qui couvre l'ensemble de l'écoulement. Sur le plan théorique, un modèle numérique mono-dimensionnel est développé. Il est basé sur la théorie d'entraînement de Morton et al (1956) pour la partie turbulente du panache, et tient compte de son caractère laminaire initial grâce à des solutions de similarité. Les comparaisons détaillées entre ce modèle et les résultats expérimentaux montrent les limites des modèles classiques et la pertinence des améliorations introduites. Nous évaluons notamment la contribution de la portion laminaire, et mettons en évidence le fait que le coefficient d'entraînement varie en fonction de la stratification ambiante. / This thesis focuses on the convective flow induced by a heated isotherm wall. A turbulent boundary layer develops along this wall, and resembles to a plume unlike its typical characterics are significantly modified by the boundary condition at the wall. In this study the environment is a closed box in which the lighter fluid continuously accumulates in the upper part, thus producing a temperature stratification in the interior. In order to better understand the dynamics of such a plume as well as its interaction with the ambient fluid, we deploy an approach that is both experimental and theoretical. Concerning the experiments, we developed a technique which combines Particle Image Velocimetry (PIV) with Laser Induced Fluorescence (LIF). This technique allows to simultaneously acquire the velocity and the temperature of the fluid in a plane which covers the entire flow. As concerning the theory, a one-dimensional numerical model is developed. It is based on the entrainment theory by Morton et al (1956) as for the turbulent part of the plume, and it takes into account the initial laminar character of the plume thanks to similarity solutions. The detailed comparisons between this model and the experimental results show the limits of the classical models and the relevance of the introduced improvements. In particular we evaluate the contribution of the laminar part and we highlight that the entrainment coefficient varies as a function of the ambient stratification.

The recent thinning, acceleration and retreat of tidewater glaciers around Greenland suggests that these systems are highly sensitive to a change in climate. Tidewater glacier dynamics have already had a significant impact on global sea level, and, given projected future climate warming, will likely continue to do so over the coming century. Understanding of the processes connecting climatic change to tidewater glacier response is, however, at an early stage. Current leading thinking links tidewater glacier change to ocean warming by submarine melting of glacier calving fronts, yet the process of submarine melting remains poorly understood. This thesis combines modelling and field data to investigate submarine melting at tidewater glaciers, ultimately seeking to constrain the sensitivity of the Greenland Ice Sheet to climate change. Submarine melting is thought to be enhanced where subglacial runoff enters the ocean and drives energetic ice-marginal plumes. In this thesis, two contrasting models are used to examine the dynamics of these plumes; the Massachusetts Institute of Technology general circulation model (MITgcm) and the simpler buoyant plume theory (BPT). The first result of this thesis, obtained with the MITgcm, is that the spatial distribution of subglacial runoff at the grounding line of a tidewater glacier is a key control on the rate and spatial distribution of submarine melting. Focussed subglacial runoff induces rapid but localised melting, while diffuse runoff induces slower but spatially homogeneous melting. Furthermore, for the same subglacial runoff, total ablation by submarine melting from diffuse runoff exceeds that from focussed runoff by at least a factor of five. BPT is then used to examine the relationship between plume-induced submarine melting and key physical parameters, such as plume geometry, fjord stratification, and the magnitude of subglacial runoff. It is shown that submarine melt rate is proportional to the magnitude of subglacial runoff raised to the exponent of 1/3, regardless of plume geometry, provided runoff lies below a critical threshold and the fjord is weakly stratified. Above the runoff threshold and for strongly stratified fjords, the exponent respectively decreases and increases. The obtained relationships are combined into a single parameterisation thereby providing a useful first-order estimate of submarine melt rate with potential for incorporation into predictive ice flow models. Having investigated many of the factors affecting submarine melt rate, this thesis turns to the effect of melting on tidewater glacier dynamics and calving processes. Specifically, feedbacks between submarine melting and calving front shape are evaluated by coupling BPT to a dynamic ice-ocean boundary which evolves according to modelled submarine melt rates. In agreement with observations, the model shows calving fronts becoming undercut by submarine melting, but hints at a critical role for subglacial channels in this process. The total ablation by submarine melting increases with the degree of undercutting due to increased ice-ocean surface area. It is suggested that the relative pace of undercutting versus ice velocity may define the dominant calving style at a tidewater glacier. Finally, comparison of plumes modelled in both MITgcm and BPT with those observed at Kangiata Nunata Sermia (KNS), a large tidewater glacier in south-west Greenland, suggests that subglacial runoff at KNS is often diffuse in nature. In addition to the above implications for submarine melting, diffuse drainage may enhance basal sliding during warmer summers, thereby providing a potential link between increasing atmospheric temperature and tidewater glacier acceleration which does not invoke the role of the ocean. This thesis provides a comprehensive investigation and quantification of the factors affecting submarine melting at tidewater glaciers, a complex process that is believed to be one of the key influences on the current and future stability of the Greenland Ice Sheet. Based on the magnitude of modelled melt rates, and their effect on calving front shape, the process of submarine melting is a likely driver of retreat at slower-flowing tidewater glaciers in Greenland. For melting to influence the largest and fastest-flowing glaciers requires invoking a sensitive coupling between melting and calving which is as yet obscure. It should however be noted that modelled melt rates depend critically on parameters which are poorly constrained. The results and parameterisations developed in this thesis should now be taken forward through testing against field observations - which are currently rare - and, from a modelling perspective, coupling with ice flow models to provide a more complete picture of the interaction of the Greenland Ice Sheet with the ocean.

xv, 151 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / To explain the origin of several distinct aspects of the Galápagos volcanic hotspot, such as the broad geographical extent of recent volcanism and the unusual pattern of geochemical anomalies, we conducted seismic tomography studies of the upper mantle and crust beneath the Galápagos Archipelago. The studies combine measurements of group and phase velocities of surface waves and delay times of body waves. We find that upper mantle seismic velocities are lower than those beneath other regions of comparable age in the Pacific and consistent with an excess temperature of 30 to 150°C and ∼0.5% melt. We attribute the excess temperature and presence of melt to an upwelling thermal mantle plume. Crustal seismic velocity is up to 25% lower than that of very young crust at the East Pacific Rise (EPR) and is comparable to that of Hawaii, which we attribute to heating by increased intrusive activity above the Galápagos plume and the construction of a highly porous volcanic platform. In addition, we find that the Galápagos hotspot is underlain by a high-velocity region whose thickness varies from 40 to 100 km. The tomographic images reveal that the upwelling mantle plume tilts northward (towards the nearby Galápagos Spreading Center) as it rises and then spreads laterally when it reaches the bottom the lid. The lid, which we attribute to residuum from melting, is thickest where it is farthest from the spreading center, suggesting that ridge processes may affect the generation and amount of thinning of the residuum layer. In addition, the thickness of the lid correlates well with the geographical pattern of geochemical anomalies of erupted lavas, suggesting that the lid may control the final depth of decompression melting. We conclude that many of the distinct characteristics of the Galápagos can be attributed to the interaction of the upwelling plume with the lid and the nearby ridge. We further suggest that the ridge affects the geometry of plume upwelling in the upper mantle and also the pattern of lateral spreading of the plume due to its effect on the thickness of the residuum layer. This dissertation includes previously published co-authored material. / Committee in charge: Dr. Douglas R. Toomey, Chairperson; Dr. Eugene Humphreys, Member; Dr. Emilie Hooft Toomey, Member; Dr. Paul Wallace, Member; Dr. John Conery, Outside Member