Dissertations / Theses on the topic 'Deep water flow'

Dans le jargon de l’océanographie physique, un «overflow » est une masse d’eau dense, formée sur un plateau continental ou dans une mer marginale, qui rejoint l’océan ouvert en s’écoulant par-delà de fortes contraintes topographiques telles que d’étroits détroits, des seuils ou des talus continentaux particulièrement pentus. Ces processus d'overflow jouent un rôle important en distribuant les flux de chaleur et de sel dans l'océan, car ils alimentent les courants profonds et la plus grande partie des eaux profondes de l'océan global. Une représentation irréaliste de ces processus dans les modèles peut avoir un impact sur leur aptitude à simuler d'autres aspects majeurs de la circulation océanique globale.Représenter de manière réaliste les overflows est encore un défi en modélisation numérique de l’océan. Cette thèse étudie ce problème en utilisant le modèle de la circulation générale océanique NEMO avec une configuration régionale de l’overflow du détroit du Danemark (Denmark Strait Overflow, DSO) avec des résolutions dites eddy-permitting/resolving (permettant la génération de turbulence de mésoéchelle). Dans ce travail je propose d’abord une définition du DSO pour pouvoir caractériser les masses d'eaux qui lui sont associées et pour mettre en évidence et quantifier les principaux défauts de représentation du DSO rencontrés dans une simulation de référence réalisée avec les paramètres standards couramment utilisés dans les configurations globales de NEMO (configurations Drakkar).Grâce à cette définition, j’ai pu quantifier l'impact d'un grand nombre de paramètres du modèle sur la représentation du DSO avec des résolutions allant de l'eddy-permitting (1/12°) à l'eddy-resolving (1/60°). Cette étude, qui a nécessité un grand nombre de simulations de sensibilité, a été faite avec le système de coordonnée verticale classique utilisé dans NEMO, qui est la coordonnée géopotentielle z.Les améliorations les plus importants ont été trouvées en augmentant la résolution verticale et horizontale de façon cohérente. Mes résultats ont cependant montrés que la plupart des paramètres du modèle ont un impact très faible sur la représentation finale du DSO. En particulier, nous avons trouvé qu'augmenter la résolution verticale sans utiliser une résolution horizontale cohérente détériore la solution. La principale raison est que la paramétrisation EVD, représentant la convection libre forcée par une instabilité statique de la colonne d’eau, propage la veine de fluide en direction de la pente de la grille, et non de la pente de la topographie, ce qui induit une trop forte dilution des propriétés de l’overflow. Une très haute résolution horizontale et verticale (1/60° et 300 niveaux) permet de résoudre la couche d'Ekman de fond et de maintenir l'EVD localisé au fond, limitant ainsi la dilution de la veine d’eau dense.J’ai ensuite étudié la représentation du DSO dans un système de coordonnée hybride combinant une coordonnée suivant-le-terrain (s) avec la coordonnée géopotentielle (z). Les améliorations obtenues dans la représentation du DSO sont remarquables et pour une faible augmentation du coût de calcul. Finalement, nous proposons un système de coordonnée verticale mixte s-z qui consiste en une implémentation locale de la coordonnée s à l’intérieur de la grille du modèle en coordonnée z, limité à la région où le DSO se produit. Cette implémentation locale minimise les effets des erreurs du gradient de pression liés à ce type de coordonnée, fait une connexion lisse avec la coordonnée z, et n'introduit pas de coûts de calcul démesurés. L'amélioration de la représentation du DSO est encore très importante.Ce travail souligne l'importance d’adapter le système de coordonnée verticale aux processus physiques les plus pertinents. Un défi de la modélisation serait d'avoir un système de coordonnée verticale qui est localement adapté aux processus océaniques dominants<br>Overflows play an important role distributing the heat and salt fluxes in the ocean, feeding deep boundary currents and most of the world ocean deep waters. Therefore, an unrealistic representation of overflows in global models may have impacts over many aspects of the simulated state of the ocean.To achieve a realistic representation of overflows is still a challenge for ocean modelling. This work addresses this problem using the community ocean general circulation model NEMO with a regional configuration of the Denmark Strait Overflow (DSO) at eddying resolutions. This work first proposes a definition of the DSO in order to characterize its associated water masses and to find the main caveats in a control simulation that uses the most standard parameters of the commonly used global configurations of NEMO (e.g. Drakkar configurations).Thanks to this definition we then study the impacts on the DSO of a large number of model parameters through a range of eddy-permitting to eddy-resolving resolutions (e.g. 1/12° and 1/60°) in the classic z-coordinate system used in NEMO. Main findings were found increasing the horizontal and vertical resolution, but most model parameters have no significant impacts. In particular it was found that increasing vertical resolution without using a coherent horizontal resolution degrades the solution. The main reason is the EVD parameterisation that propagates the dense vein of fluid along a grid-slope, instead the topographic slope. Coherent and very high resolution both in the horizontal and in the vertical is needed in order to resolve Ekman bottom boundary layer dynamics and keep the EVD localized to the very bottom.We also study the representation of the DSO with a hybrid terrain-following (s) and geopotential (z) coordinate system and obtained considerable improvements for a relatively small increase in computational cost. Finally, we propose a mixed s-z vertical coordinate that relies on a local implementation of s-coordinates within the z-coordinate model, limited to the area where DSO waters are produced. This local implementation is such that it minimizes the effects of pressure gradient errors linked to this type of coordinate, smoothly connects to the global z-coordinate, and does not add any significant computational cost. The improvement of the DSO is found to be drastic.This work emphasizes the utility of adapting the vertical coordinate system to the main physical problem. A modeling challenge would be to have a vertical coordinate system that is locally adapted to the most critical ocean process

Of all the strategies to reduce carbon emissions, carbon dioxide (CO₂) geological sequestration is an immediately available option for removing large amounts of the gas from the atmosphere. However, our understanding of the transition behavior between Forchheimer and Darcy flow through porous media during CO₂ injection is currently very limited. In addition, the kinetic mass transfer of SO₂ and CO₂ from CO₂ stream to the saline and the fully coupling between the changes of porosity and permeability and multiphase flow are two significant dimensions to investigate the brine acidification and the induced porosity and permeability changes due to SO₂ co-injection with CO₂. Therefore, this dissertation develops a multiphase flow, contaminant transport and geochemical model which includes the kinetic mass transfer of SO₂ into deep saline aquifers and obtains the critical Forchheimer number for both water and CO₂ by using the experimental data in the literature. The critical Forchheimer numbers and the multiphase flow model are first applied to analyze the application problem involving the injection of CO₂ into deep saline aquifers. The results show that the Forchheimer effect would result in higher displacement efficiency with a magnitude of more than 50% in the Forchheimer regime than that for Darcy flow, which could increase the storage capacity for the same injection rate and volume of a site. Another merit for the incorporation of Forchheimer effect is that more CO₂ would be accumulated in the lower half of the domain and lower pressure would be imposed on the lower boundary of the cap-rock. However, as a price for the advantages mentioned above, the injection pressure required in Forchheimer flow would be higher than that for Darcy flow. The fluid flow and contaminant transport and geochemical model is then applied to analyze the brine acidification and induced porosity and permeability changes due to SO₂ co-injection. The results show that the co-injection of SO₂ with CO₂ would lead to a substantially acid zone near the injecting well and it is important to include the kinetic dissolution of SO₂ from the CO₂ stream to the water phase into the simulation models, otherwise considerable errors would be introduced for the equilibrium assumption. This study provides a useful tool for future analysis and comprehension of multiphase Darcy-Forchheimer flow and brine acidification of CO₂ injection into deep saline aquifers. Results from this dissertation have practical use for scientists and engineers concerned with the description of flow behavior, and transport and fate of SO₂ during SO₂ co-injection with CO₂ in deep saline aquifers.

La formation des noyaux planétaires métalliques est un évènement majeur pour l’évolution des propriétés physico-chimiques des planètes telluriques telles que nous les connaissons aujourd’hui. En effet, l’abondance des éléments sidérophiles (i.e. qui ont des affinités chimiques avec les phases métalliques) dans les manteaux planétaires s’explique par les conditions dans lesquelles se sont séparées les phases métalliques et silicatées. Au premier rang de ces conditions se trouvent la pression, la température et la fugacité d’oxygène. La distribution des éléments dans le noyau et le manteau ne peut en effet s’expliquer que pour un équilibre obtenu dans un océan magmatique profond, donc à haute pression et haute température ; et dans des conditions d’oxydo-réduction variables, dont l’évolution la plus probable est de passer d’un état réduit à un état oxydé. Un autre paramètre important est la présence ou non d’eau dans l’océan magmatique primitif. En effet, nous disposons de plus en plus d’arguments permettant d’expliquer l’arrivée des éléments volatils, notamment l’eau, pendant l’accrétion, à partir de briques élémentaires qui contiennent ces éléments. Si l’eau est présente tout au long de l’accrétion, et donc pendant la ségrégation du noyau, elle peut donc avoir un effet sur ce dernier phénomène. Dans cette hypothèse, nous avons mené des expériences de haute pression et haute température permettant de modéliser expérimentalement la formation du noyau en condition hydratée. Ces expériences nous ont permis de montrer que la présence d’eau a un effet sur l’évolution de l’état d’oxydation des manteaux planétaires. Cette évolution oxydo-réductive nous a permis de contraindre des modèles d’accrétion basés sur un mélange de chondrites EH et CI, qui confirment des modèles construits à partir de données isotopiques. Ces modèles nous ont permis de contraindre les concentrations primitives maximum en eau probables sur Terre (1,2-1,8 % pds.) et sur Mars (2,5-3,5 % pds.). D’autre part, nos avons mis en évidence le caractère lithophile (i.e. qui a des affinités chimiques avec les phases silicatées) de l’hydrogène à haute pression, a contrario de plusieurs études précédentes. De ce fait, la différence entre les concentrations initiales élevées en eau que nous obtenons dans nos modèles d’accrétion et les concentrations en eau estimées sur Terre et sur Mars actuellement (2000 ppm et 200 ppm, respectivement) ne peut pas être expliquée par un réservoir d’hydrogène dans le noyau. Enfin, pour améliorer les modèles de formation du noyau, nous avons mis en évidence, par des modèles numériques, l’effet important de la viscosité de l’océan magmatique sur le taux d’équilibre entre noyaux et manteaux des planètes telluriques. Cela nous mène à ré-évaluer les modèles de formation des planètes telluriques basés sur des résultats expérimentaux à l’équilibre, notamment l’extension maximale de l’océan magmatique. L’évolution de la viscosité de l’océan magmatique a donc un impact important sur la composition finale des noyaux planétaires (par exemple les teneurs en soufre, oxygène ou silicium des noyaux terrestres et martiens)<br>The formation of the metallic planetary cores is a major event regarding to the evolution of physical and chemical properties of the telluric planets as we know it today. Indeed, the siderophile elements (i.e. which has affinities with metallic phases) abundances in planetary mantles is explained by the conditions of core-mantle segregation. Among these conditions, pressure, temperature and oxygen fugacity are the main ones controlling distribution of the elements between mantle and core. This distribution can only be explained by an equilibrium between metal and silicate obtained in a deep magma ocean, which implies high pressure and high temperature of equilibrium. Moreover, the oxygen fugacity must have varied during core-mantle segregation, in a reduced-to-oxidized path most probably. Another important parameter is whether or not water is present in the primordial magma ocean. Indeed, we now have more and more lines of evidences showing that the volatile elements, especially water, arrived during accretion and therefore during the core-mantle segregation, which means that water can have an effect on the latter phenomenon. Considering this hypothesis, we performed several high pressure-high temperature experiments which allowed us to model the formation of the core under hydrous conditions. These experiments demonstrated that water has a significant effect on the redox state evolution of planetary mantles. We use this redox evolution to constrain models of planetary accretions, based on a mix of EH and CI chondrites, showing a good agreement with models based on isotopic data. The output of these models is the maximum initial concentration in water on the Earth (1.2 -1.8 %wt) and on Mars (2.5-3.5 %wt). Furthermore, these experiments showed a lithophile behavior (i.e. which has affinities with silicated phases) of hydrogen at high pressures, contrary to previous studies. Therefore, the difference between high initial concentrations in water yielded by our accretion models and the estimated actual concentrations on the Earth and Mars (2000 ppm and 200 ppm, respectively) cannot be explained by a hydrogen reservoir in the core. Finally, to improve the models of core-mantle segregation, we showed by numerical simulations the important effect of the magma ocean viscosity on the equilibrium between planetary mantles and cores. it lead us to reevaluate the models of accretion based on experimental data, especially the maximum extent of magma oceans. The evolution of the magma ocean viscosity has therefore significant implications on the final composition of planetary cores (for instance on the sulfur, oxygen and silicon content of the Earth’s and Mars’ core)

碩士<br>國立臺灣大學<br>工程科學及海洋工程學研究所<br>97<br>Deep water breaking impact on a vertical wall were investigated in this research. The breaking waves were generated by linearly-varying-frequency wave trains. A P.I.V. measurement system was used to record the particle motion in fluids, such that the instantaneous wave flow field can be calculated. Based on the measured results, qualitative descriptions of the variations of flow field around the vertical wall during breaking wave impact process were made in this research. It showed that due to a plunging breaker causes much more violated flow filed than a spilling breaker does an air bag entrapped during the plunging breaking process. At wave crest, a vortex generation was produced during breaking processes. After wave impacting on a vertical wall, water recedes and the mores with water, then leaves the region of the vortex measured flow filed. Using the measured velocity information near the vertical wall and the method of linear momentum conservation in a control volume, the pressure distribution on the vertical wall were calculated and distributed as a log law curve for spilling and plunging breaker cases. The obtained result was similar to the results obtained by Kirkgoz (1995) using pressure gauges measurements.

A new measurement technique called fiber optic reflectometer (FOR) was developed to investigate multiphase flows. The principle and setup of the FOR technique were introduced and applied to various experiments. Based on the coherently mixed signal between the Fresnel reflection off the fiber-liquid interface and the scattered signal off the object, such as a gas bubble, and a solid particle, this single probe technique is capable of simultaneously measuring the velocity of the object with a high accuracy and the phase of the fluid. In addition, bubble diameter, velocity, and void fraction were measured directly. By means of a simple modification of the FOR technique, solute concentration and refractive index change were measured with a greatly improved accuracy. This modified technique was used for measuring of a NaCl concentration in deionized water to validate a new normalization technique. In the second part of this thesis, a plunging breaking wave in deep water has been studied. Using the wave focusing method, a strong plunging breaker was generated with accuracy in the deep water condition in a two-dimensional wave tank. It was possible to describe the breaking process in detail using a high speed camera with a frame rate of 500 or 1000 fps. Four kinds of experimental techniques were employed or developed to investigate the plunging breaker. Bubble image velocimetry (BIV) and particle image velocimetry (PIV) were used to measure the velocity fields. The velocity fields of the highly aerated region were obtained from the BIV measurements. In addition, the modified PIV technique is capable of measuring the velocities in the entire flow field including the aerated region. Mean and turbulent properties were obtained by the ensemble average. The mean velocity, mean vorticity, and mean kinetic energy were examined over the entire flow field. In addition, the Reynolds stresses and turbulent kinetic energy were calculated with high temporal and spatial resolutions. Free surface elevation was obtained from wave gauge measurements. BIV and PIV images were also used to obtain the free surface elevation and the boundary of the aerated region for more accurate results. The FOR technique was used to obtain the void ratio at each splash-up region. Compressibility of the plunging breaker was considered. Mass flux, momentum flux, kinetic energy, and Reynolds stresses at each FOR station were recalculated using the void ratio obtained from the FOR measurements. All terms at the first splash-up region were highly overestimated more than 100 percent unless the void ratio was applied to the calculation of fluxes and energies. Compared with the fully developed first splash-up region, the overestimation at the second and third splash-up was less significant. However, most terms were overestimated by 20~30 percent when the void ratio was not considered.

Well testing has long been used to determine the dynamic characteristics of a reservoir. However due to the increase in interest in exploring deep offshore reservoirs and the expense associated with performing well tests of sufficient duration, alternative methods for retrieving reservoir specific information from tests of limited duration are necessary. This thesis presents analysis of derivative plots from well tests in different locations along a heterogeneous channelized environment and the information that can be derived the shape of these plots. The viability of calibrating a multiple point proxy that captures the reservoir flow connectivity information contained in well test data is explored. Such a proxy can provide useful insight into the nature of reservoir heterogeneity in the vicinity of the well. The behavior of the log-log derivative plot gives invaluable information about the nature of the reservoir surrounding the penetrating wells. Based on the change in slope of the derivative plot one can tell if a flow conduit or a low permeability zone is close to the well. Proximity to these features is also indicated in the curvature of the derivative plot with the test plot showing increasing symmetry as flow boundaries are approached. This was found to be true in both systematic simulations as well as in real build up test data. The calibration of the multiple point permeability proxy also provides information about the connectivity of the reservoir. Single point statistics provide the best estimate for wells either inside a channel or very close to the channel boundary. This is because of the relative homogeneity of permeability values within the spatial template used for averaging. The further the well gets from the channel fewer high permeability blocks will be picked up by the template and thus multiple point models provide the best estimate for effective permeability, Keff. Three point models were found to be the most accurate when the template exhibited complex permeability transition from the mudstone to the channel facies.<br>text

Oil well blow outs are investigated to determine methods to quickly and accurately respond to an emergency situation. Flow rate is needed to guide containment and dispersal operations. The Stratified Integral Multiphase Plume, SIMP, model was used to investigate the range of initial conditions available to integral modeling. Sensitivity to initial conditions is modest, but without experimental data at the appropriate scale the most accurate condition is unable to be determined. Flow rates are difficult to directly measure in blow out situations, so another method must be determined; therefore, sensitivity of several parameters to flow rate was also evaluated. Methane concentration in the first intrusion can be used in conjunction with velocity and trap height measurements to determine flow rate using an integral model. Plume width and temperature were determined to have little sensitivity. Separately, a containment dome was tested in the laboratory to determine if a full scale dome can be used to contain an oil leak in the field. The dome was found to have satisfactory entrapment in the designed position.

Hydrothermal fluid circulation is an important process in the formation and evolution of ocean crust. A tectonic window located at Pit Deep (NE corner Easter Microplate) provides an ideal location to examine a 3-dimensional view of ocean crust formed at the fast-spreading East Pacific Rise. This study focuses on the base metal (Cu, Ni, Mn, Co, Zn, and Pb) content of the bulk rock and mineral components in the sheeted dike complex. There is no observable trend of metal mobility with depth, geographic location, or dominant alteration phase. Secondary mineral analyses (using LA-ICP-MS) show that metals are redistributed throughout the sheeted dikes, entering into secondary sulphides, chlorite, and amphibole. Temperature and mineral stability is a primary control of metal mobility in these rocks. Due to highly variable metal concentrations and observed temperatures of alterations, the hydrothermal cell is suggested to be a continuously evolving system, and can cause the large variability observed in the metal distribution in the sheeted dikes.<br>Graduate<br>0996<br>0411<br>0372

A wave cavity resonator (WCR) is investigated to determine the suitability of the device as an energy harvester in rivers or tidal flows. The WCR consists of coupling between self-excited oscillations of turbulent flow of water in an open channel along the opening of a rectangular cavity and the standing gravity wave in the cavity. The device was investigated experimentally for a range of inflow velocities, cavity opening lengths, and characteristic depths of the water. Determining appropriate models and empirical relations for the system over a range of depths allows for accuracy when designing prototypes and tools for determining the suitability of a particular river or tidal flow as a potential WCR site. The performance of the system when coupled with a wave absorber/generator is also evaluated for a range piston strokes in reference to cavity wave height. Video recording of the oscillating free-surface inside the resonator cavity in conjunction with free-surface elevation measurements using a capacitive wave gauge provides representation of the resonant wave modes of the cavity as well as the degree of the flow-wave coupling in terms of the amplitude and the quality factor of the associated spectral peak. Moreover, application of digital particle image velocimetry (PIV) provides insight into the evolution of the vortical structures that form across the cavity opening. Coherent oscillations were attainable for a wide range of water depths. Variation of the water depth affected the degree of coupling between the shear layer oscillations and the gravity wave as well as the three-dimensionality of the flow structure. In terms of the power investigation, conducted with the addition of a load cell and linear table-driven piston, the device is likely limited to running low power instrumentation unless it can be up-scaled. Up-scaling of the system, while requiring additional design considerations, is not unreasonable; large-scale systems of resonant water waves and the generation of large scale vortical structures due to tidal or river flows are even observed naturally.<br>Graduate<br>0547<br>0548<br>reaumejd@uvic.ca