This dissertation focuses on interpreting the spatial variations of seismic amplitude data as a function of rock properties for the Haynesville Shale. To achieve this goal, I investigate the relationships between the rock properties and elastic properties, and calibrate rock-physics models by constraining both P- and S-wave velocities from well log data. I build a workflow to estimate the rock properties along with uncertainties from the P- and S-wave information. I correlate the estimated rock properties with the seismic amplitude data quantitatively. The rock properties, such as porosity, pore shape and composition, provide very useful information in determining locations with relatively high porosities and large fractions of brittle components favorable for hydraulic fracturing. Here the brittle components will have the fractures remain opened for longer time than the other components. Porosity helps to determine gas capacity and the estimated ultimate recovery (EUR); composition contributes to understand the brittle/ductile strength of shales, and pore shape provides additional information to determine the brittle/ductile strength of the shale. I use effective medium models to constrain P- and S-wave information. The rock-physics model includes an isotropic and an anisotropic effective medium model. The isotropic effective medium model provides a porous rock matrix with multiple mineral phases and pores with different aspect ratios. The anisotropic effective medium model provides frequency- and pore-pressure-dependent anisotropy. I estimate the rock properties with uncertainties using grid searching, conditioned by the calibrated rock-physics models. At well locations, I use the sonic log as input in the rock-physics models. At areas away from the well locations, I use the prestack seismic inverted P- and S-impedances as input in the rock-physics models. The estimated rock properties are correlated with the seismic amplitude data and help to interpret the spatial variations observed from seismic data. I check the accuracy of the estimated rock properties by comparing the elastic properties from seismic inversion and the ones derived from estimated rock properties. Furthermore, I link the estimated rock properties to the microstructure images and interpret the modeling results using observations from microstructure images. The characterization contributes to understand what causes the seismic amplitude variations for the Haynesville Shale. The same seismic reservoir characterization procedure could be applied to other unconventional gas shales. / text

Scanning Laser Epitaxy (SLE) is a new laser-based layer-by-layer generative manufacturing technology being developed in the Direct Digital Manufacturing Laboratory at Georgia Tech. SLE allows creation of geometrically complex three-dimensional components with as-desired microstructure through controlled melting and solidification of stationary metal-alloy powder placed on top of like-chemistry substrates. The proposed research seeks to garner knowledge about the fundamental physics of SLE through simulation-based studies and apply this knowledge for hot section turbine component repair and ultimately extend the process capability to enable one-step manufacture of complex gas turbine components. Prior methods of repair specifically for hot-section Ni-base superalloys have shown limited success, failed to consistently maintain epitaxy in the repaired part and suffered from several mechanical and metallurgical defects. The use of a fine focused laser beam, close thermal control and overlapping raster scan pattern allows SLE to perform significantly better on a range of so-called “non-weldable” Ni-base superalloys. The process capability is expanded further through closed-loop feedback control of melt pool temperature using an infra-red thermal camera. The process produces dense, crack-free and epitaxial deposit for single-crystal (SX) (CMSX4), equiaxed (René-80, IN 100) and directionally solidified (DS) (René-142) Ni-based superalloys. However, to enable consistent and repeatable production of defect-free parts and future commercial implementation of the technology several concerns related to process capabilities and fundamental physics need to be addressed. To explore the process capability, the fabricated components are characterized in terms of several geometrical, mechanical and metallurgical parameters. An active-contour based image analysis technique has been developed to obtain several microstructural responses from the optical metallography of sample cross-sections and the process goes through continuous improvement through optimization of the process parameters through subsequent design of experiments. The simulation-based study is aimed at developing a multiphysics model that captures the fundamental physics of the fabrication process and allows the generation of constitutive equations for microstructural transitions and properties. For this purpose, a computational fluid dynamics (CFD) finite-volume solver is used to model the melting and solidification process. The development work also focuses on studying process response to different superalloy materials and implementing a multivariate statistical process control that allows efficient management and optimization of the design parameter space. In contrast to the prior work on single-bead laser scan, the model incorporates the raster scan pattern in SLE and the temperature dependent local property variations. The model is validated through thermal imaging data. The flow-thermal model is further tied to an empirical microstructural model through the active-contour based optical image analysis technique, which enables the identification of several microstructural transitions for laser beam describing a raster scan pattern. The CFD model can effectively be coupled with finite element solver to assess the stress and deformation and can be coupled with meso-scale models (Cellular Automata) to predict different microstructural evolutions. The research thus allows extending the SLE process to different superalloy materials, performs statistical monitoring of the process, and studies the fundamental physics of the process to enable formulation of constitutive relations for use in closed-loop feedback control; thus imparting ground breaking capability to SLE to fabricate superalloy components with as-desired microstructures.

Time-lapse seismic allows oil/gas reservoir monitoring during production, highlighting compaction and water movement. Time-lapse modeling, using a stress-dependent rock physics model, helps determine the need and frequency of expensive repeat seismic acquisition. We simulate a Gulf of Mexico gas reservoir time-lapse response for depletion and water flooding using uncertainty ranges in water saturation, porosity, stress-induced velocity changes, and pore compressibility. An analysis is conducted to see if a water-swept region could have been predicted. Findings show the swept and un-swept monitor cases amplitude differences range from 6% to 15%, which is higher than the actual monitor seismic noise level. Thus, it is unlikely these cases could be differentiated. However, the modeled amplitude changes from base to monitor cases do not match measured amplitude changes. This suggests the rock property model requires pressure-variance improvement and/or the changes in seismic amplitudes are associated with pressure/porosity, thickness, or saturation cases not modeled.

An important part of the fusion research program is to understand and control the large number of plasma instabilities that a fusion plasma can exhibit. One such instability is known as the “sawtooth” instability, which is a perturbation in the plasma electric and magnetic fields that manifests itself as periodic relaxations of the temperature and density in the plasma center. The aim of this project was to investigate how the fuel ions in a fusion plasma react to the sawtooth instability. We were able to implement a model of the plasma electromagnetic field during a sawtooth relaxation into an existing code that computes the orbits of the fuel ions in the tokamak magnetic field. To this end, it was necessary to modify the orbit code to allow for non-zero electric fields, and for time-varying fields. In order to validate the new additions to the code, we compared simulated results to analytical ones. The model of the sawtooth electromagnetic fields required for our simulations was set up within a different student project. However, due to unforeseen complications, only the magnetic (not the electric) field contribution was available to us during our project, but once the electric field is available it is straightforward to include in our code. Our simulations did not exhibit any noticeable perturbation to the particle orbit during a sawtooth crash. However, before the electric field contribution is included it is not possible to draw any physics conclusions from these results. Our code could also be used as a foundation for future projects since it is possible (with further implementations to the existing code) to simulate how the spatial profile of the neutron emission is expected to vary during the sawtooth. These simulations can be compared against experimental measurements of the neutron emission profile in order to investigate the accuracy of the sawtooth model under consideration.

This dissertation presents an experimentally supported multi-physics model of a dielectric barrier discharge boundary layer flow control actuator. The model is independent of empirical data about the specific behavior of the system. This model contributes to the understanding of the specific mechanisms that enable the actuator to induce flow control. The multi-physics numerical model couples a fluid model, a chemistry model, and an electrostatics model. The chemistry model has been experimentally validated against known spectroscopic techniques, and the fluid model has been experimentally validated against the time-resolved shadowgraphy. The model demonstrates the capability to replicate emergent flow structures near a wall. These structures contribute to momentum transport that enhance the boundary layer’s wall attachment and provide for better flow control. An experiment was designed to validate the model predictions. The spectroscopic results confirmed the model predictions of an electron temperature of 0.282eV and an electron number density of 65.5 × 10⁻¹²kmol/m³ matching to within a relative error of 12.4% and 14.8%, respectively. The shadowgraphic results also confirmed the model predicted velocities of flow structures of 3.75m/s with a relative error of 10.9%. The distribution of results from both experimental and model velocity calculations strongly overlap each other. This validated model provides new and useful information on the effect of Dielectric Barrier Discharge actuators on flow control and performance. This work was supported in part by NSF grant CNS-0960081 and the HokieSpeed supercomputer at Virginia Tech. / Ph. D.

No description available.

Nos travaux s’inscrivent dans le contexte global de la transition énergétique et de l’émergence des micro-réseaux, et de leur capacité, à terme, d’intégrer la production distribuée d’énergie tout en assurant la stabilité et la qualité du service. Parmi les technologies émergentes, les procédés Power-To-Gaz et en particulier le Power-to-Methane que nous étudions ici (production de CH4 à partir de l’électricité, en passant par H2 et CO2) ont l’avantage : d’absorber le surplus de production électrique, de récupérer et valoriser les émissions de CO2, et d’offrir des capacités de stockage importantes et de longue durée.Notre problématique porte sur la modélisation et la simulation d’un système PtM avec comme objectif d’assurer la continuité d’alimentation en CH4, ainsi que la sécurité du système en fonctionnement.Dans un premier temps nous effectuons le choix de technologies adaptées afin de déterminer la structure d’un système PtM avant de dimensionner ce système. Nous nous appuyons sur la modélisation REM (Représentation Energétique Macroscopique) pour intégrer les comportements physiques des équipements du système en régime stationnaire, mais également en régime transitoire, en prenant en compte des phases comme : le démarrage, le préchauffage…, et ainsi simuler le fonctionnement de ce système.Dans un second temps, nous développons une stratégie de gestion d’énergie multiniveaux afin de garantir le bon fonctionnement des équipements et du système dans sa globalité. Nous choisissons de la mettre en œuvre à travers la proposition d’un système multi-agents (SMA) et nous modélisons chacun des agents. Nous implémentons partiellement ce SMA et nous le simulons en connexion avec le modèle REM du système PtM pour montrer la faisabilité de notre approche. / Our work is concerned with energy transition and the emergence of micro-grids and their ability to integrate distributed power generation while at the same time ensure stability and service quality. Among the emerging technologies, the Power to Gas process and in particular the Power to Methane process which we are addressing here (production of CH4 from electricity, via H2 and CO2), have the advantage of absorbing surplus of electricity production, recovering CO2 emissions, as well as offering significant and long-term storage capacity.Our concern was in relation to the modeling and simulation of a PtM system with the objective of ensuring the continuity of CH4 supply and ensuring the safety of the system in operation.First, we chose the appropriate technologies to determine the structure of a PtM system before sizing this system. We utilised the REM modeling (Energetic Macroscopic Representation) to integrate the physical behaviors of the equipment of the system in a steady state, and in a transient state, taking into account phases like starting, preheating…, and ultimately the simulation of the operation system.In the second phase, we developed a multilevel energy management strategy to ensure the proper working order of each piece of equipment and of the global system. We chose to implement it through a multi-agent system (MAS) and we modeled each one of the agents. We partially implemented the MAS and simulated it with the REM model of the PtM system to show the feasibility of our approach.

L’analyse de sûreté des réacteurs nucléaires nécessite la modélisation fine des phénomènes y survenant et plus spécifiquement ceux permettant d’assurer l’intégrité des barrières de confinement. Les outils de modélisation et codes actuels favorisent une analyse fine du système réacteur par discipline dédiée, et couplée avec des modèles simplifiés. Néanmoins, le développement depuis plusieurs années d’une approche dite « Best Estimate », basée sur des calculs multiphysiques et multi-échelle, est en cours de réalisation. Cette approche permettra d’accéder au suivi et à l’analyse détaillée de problèmes complexes tels que l’étude des Réacteurs nucléaires en situation standard et accidentelle. Dans cette approche, les phénomènes physiques sont simulés aussi précisément que possible (selon la connaissance actuelle) par les modèles couplés. Par exemple, des codes disciplinaires existent et permettent la modélisation précise de la neutronique, de la thermohydraulique du cœur du réacteur ou de la thermohydraulique sur l'ensemble du système, de la thermomécanique du combustible ou des structures. Une approche « Best Estimate » consiste à coupler ces modèles afin de réaliser une modélisation globale et précise du système de réacteur nucléaire. Cette approche nécessite de bien définir les modèles qui sont utilisés afin de préciser exactement leurs limites, et donc préciser les incertitudes des résultats des modèles couplés afin de les assumer et de les optimiser.C’est dans ce contexte de travail que s’inscrit cette thèse. Elle consiste dans le développement d'un couplage multiphysique et multi-échelle « Best Estimate » afin d'obtenir une analyse précise des Réacteurs à Eau Légère en situations normale et accidentelle. Elle a consisté principalement en l’analyse des modèles et de leurs interactions et à la mise en œuvre d'un algorithme de couplage multiphysique entre une neutronique et une thermohydraulique exprimées à l'échelle du réacteur, ainsi qu’avec une thermomécanique fine à l'échelle élémentaire du crayon combustible. En outre, un travail spécifique a été effectué afin de préparer ou d'améliorer l’accés à l'information physique locale nécessaire à la mise en œuvre de modélisations couplées multi-échelles, à l'échelle du combustible. / The safety analysis of nuclear power plants requires a deep understanding of underlying key physical phenomena that determine the integrity of the physical containment barriers. At the present time, cutting edge models focus on a single aspect (discipline) of the physical system coupled with rough models of the other aspects needed to simulate the global system. But, safety analyses can be carried out based on Multiphysics and Multiscales modelling. This Best Effort approach would give a full and accurate (High Fidelity) comprehension of the reactor core under standard and accidental situations. In this approach, the physical phenomena are simulated as accurately as possible (according to present knowledge) by coupled models in the most efficient way. For example, codes exists that are accurate modellings of Neutronics, or modellings of thermal fluid mechanics inside the core, or modellings of thermal fluid mechanics over the whole system, or modellings of thermal mechanics of the fuel pin or over the whole device structure. A Best Estimate approach would couple these models in order to realize a global and accurate modelling of the Nuclear reactor. This approach requires to define well the models that are used in order to exactly specify their limits, and hence, specify uncertainties of the coupled model results in order to assume and optimize them.It is in this context that this PhD thesis work is being under taken. It consists in the development of a Multi-physics and multi-scale Best Estimate modelling in order to obtain an accurate analysis of Pressurized Water Reactor under standard and accidental operating situations. It mainly involves the understanding of each model and their interactions, followed by the implementation of multiphysics algorithms coupling Neutronics and Thermohydraulics at reactor scale to an accurate Thermomechanics at the elementary scale of the fuel pin. In addition, a work project has been carried out in order to prepare or improve the access to the local physical informations that are needed for the implementation of multiscale coupling scheme, at the elementary scale of the fuel pin.

Electric vehicles contain hundreds of high-energy density lithium-ion batteries. The crashworthiness of these vehicles can be improved by better understanding the response of these batteries in an event of an accident or abusive loads. These loads can induce short-circuit and thermal runways in extreme cases. Therefore, an efficient finite element model of a battery that can precisely predict the coupled multi-physics behavior of a cell in a real-world application is desired. This investigation incorporates detailed and homogenized multi-physics modeling of various form factors of lithium-ion batteries. In the first two chapters of this thesis, a multi-physics homogenized model of a pouch cell was developed and validated in a wide range of multi-disciplines of the battery. In contrast to other similar models described in the literature, which are only applicable in certain scenarios, this model has a much broader range of applications due to the innovative techniques developed for material calibration and cell modeling. In addition, due to the homogenized nature and computational cost efficiency of this technique, the developed model has significance in the crashworthiness analysis of battery packs and electric vehicles where hundreds of these batteries exist. In the final chapter, a detailed layered model of an 18650 cylindrical cell was developed. Component and cell-level tests were performed on the cell to calibrate the material properties and extract the geometries of all the components of the cell. This model is the first of its kind that precisely predicts the load-displacement response and shape of deformation in various loading scenarios. This developed model has crucial importance in the safety assessment of the batteries by providing insight into the sequence of deformation of the internal layers and components and their interplay during mechanical abuse loadings. Overall, the two developed models in this thesis provide battery-related industries with a tool to improve the safety of future electrified industries. / Mechanical Engineering

Le LNCMI est un grand équipement du CNRS. Il met à la disposition de la communauté scientifique internationale des aimants produisant des champs magnétiques intenses (entre 24 et 36 Teslas pendant plusieurs heures), utilisés par les chercheurs comme un moyen d'exploration et de contrôle de la matière. Dans la thèse, nous nous intéressons à la simulation de ce type d'aimants, dans le but de les étudier, d'optimiser leur design, ou encore de faire des analyses d'incidents. Ces modèles 30 sont basés sur des équations aux dérivées partielles couplées non-linéaires. Au vu de leur complexité, nous avons développé des méthodes de réduction d'ordre, permettant de réduire considérablement les temps de calcul associés. En particulier, nous pensons avoir levé un verrou majeur de l'utilisation du cadre méthodologique de réduction d'ordre pour des problèmes multi-physiques non-linéaires. / The magnetic field constitutes a powerfull tool for researchers, especially to determine the properties of the matter. This kind of applications requires magnetic fields of high intensity. The "Laboratoire National des Champs Magnetiques Intenses" (LNCMI) develops resistive magnets providing such magnetic field to scientists. The design of these magnets represents a challenge interms of design. We have developed a range of non-linear coupled models taking into account the whole involved physics, implemented through the Feel++ library. Designed for many query context, the reduced basis method applied to the multi-physics model aims to circumvent the complexity of the problem. lts efficiency allows to move towards parametric studies and sensitivity analysis in various concrete applications. Especially, the method SER we introduce in this thesis is a significant breakthrough for non-linear and non-affine problems in an industrial context.