Approved for public release; distribution in unlimited. / As mesoscale models increase in resolution there is a greater need to understand predictability on smaller scales. The predictability of a model is related to forecast skill. It is possible that the uncertainty of one scale of motion can affect the other scales due to the nonlinearity of the atmosphere. Some suggest that topography is one factor that can lead to an increase of forecast skill and therefore predictability. This study examines the uncertainty of a mesoscale model and attempts to characterize the predictability of the wind field. The data collected is from the summer, when the synoptic forcing is relatively benign. Mesoscale Model 5 (MM5) lagged forecasts are used to create a three-member ensemble over a 12-hour forecast cycle. The differences in these forecasts are used to determine the spread of the wind field. Results show that some mesoscale features have high uncertainty and others have low uncertainty, shedding light on the potential predictability of these features with a mesoscale model. Results indicate that topography is a large source of uncertainty. This is seen in all data sets, contrary to other studies. The ability of the model to properly forecast the diurnal cycle also impacted substantially on the character and evolution of forecast spread. The persistent mesoscale features were represented reasonably well, however the detailed structure of these features had a fair amount of uncertainty. / Lieutenant Junior Grade, United States Navy

Approved for public release, distribution is unlimited / Performance of high resolution mesoscale models has been in a continuous state of refinement since their inception. Mesoscale models have become quite skillful in forecasting synoptic scale events such as mid-latitude cyclones. However, atmospheric forcing becomes a much more complicated process when faced with the challenge of forecasting near topography along the coastline. Phenomena such as gap flows, blocked flow winds and low level stratification become important to predictability at these scales. The problem is further complicated by the dynamics of a frontal passage event. The skill of mesoscale models in predicting these winds is not as well developed. This study examines several forecasts by the Coupled Ocean Atmospheric Mesoscale Prediction System (COAMPS) during frontal passage events for the Winter of 2003-2004. An attempt is made to characterize the predictability of the wind speed and direction both before and after frontal passage along the California coast. Synoptic forcing during this time is strong due to the effects of the mid-latitude cyclones propagate across the Pacific. The study's results indicate that the wind field predictability is subject to several consistent errors associated with the passage of fronts over topography. These errors arise due to difficulty in the model capturing weak thermal advection events and topographic wind funneling. The deficiencies in model representation of topography contributes to these errors. / Lieutenant, United States Navy

Models of tephra fallout are used to assess volcanic hazards in advance of eruptions and in near-real-time. Current models often approximate the wind field using simplistic assumptions of the atmosphere that cannot account for typical variations in wind velocity that occur in time and three-dimensional space. Here, a widely used mesoscale atmospheric model is used to improve forecasts of the location of the major axis of dispersion for erupting plumes. The Pennsylvania State University-National Center for Atmospheric Research fifth-generation Mesoscale Model (MM5) specializes in atmospheric prediction for regions on the order of ten to hundreds of kilometers on a side. MM5 generates realistic wind fields based on the laws of conservation of mass, energy, and momentum, along with land surface data and atmospheric forecasts and observations.

Cette thèse s’inscrit dans le cadre du projet européen 3D-LightTrans ayant pour objectifs la fabrication à grande à échelle et à bas coût de pièces composites. Pour parvenir à ces objectifs, des semi-produits sous forme de tissus 3D de mèches comélées ont été réalisés. Le but de ces travaux est de caractériser le comportement mécanique de ces tissus en vue d’analyser leur formabilité et d’être en mesure de prédire leur comportement pendant les processus de mise en forme utilisés lors de la fabrication des pièces composites. Le premier objectif de ces travaux était de caractériser expérimentalement le comportement mécanique des tissus 3D. Après avoir effectué un état de l’art ayant permis de définir les types et paramètres d’essais à utiliser pour la caractérisation du comportement des tissus, l’analyse des résultats de ces différents essais a permis de mettre en évidence les spécificités du comportement des tissus 3D. Le deuxième objectif des travaux était de modéliser le comportement des tissus par une approche numérique. Le choix s’étant porté sur une approche à l’échelle mésoscopique, le comportement mécanique des mèches comélées a été caractérisé expérimentalement. Les limitations du logiciel GeoFab quant à son utilisation pour la génération de modèles CAO de mailles élémentaires de tissus 3D ont été identifiées. Des améliorations permettant de répondre à ces limitations ont été proposées et leur faisabilité démontrée. Un modèle CAO d’une sous partie de la maille élémentaire d’un des tissus a alors été généré. Après avoir modélisé le comportement des mèches comélées en se basant sur les résultats de leur caractérisation expérimentale, des premières simulations éléments finis ayant permis d’obtenir des résultats encourageants ont été réalisés. / This thesis is part of the European project 3D-LightTrans whose objectives are the large scale and low-cost manufacturing of composite parts. To achieve these goals, semi-finished products in the form of 3D fabrics of commingled yarns were produced. The purpose of this work is to characterize the mechanical behavior of these fabrics in order to investigate their formability and be able to predict their behavior during the forming processes used for the manufacturing of composite parts. The first objective of the work was to characterize experimentally the 3D fabrics mechanical behavior. A state of the art was realized in order to define the types and test parameters to use. The analysis of these test results allowed to highlight the specific 3D fabrics mechanical behaviour. The second objective of the work was to model the fabrics behavior using a numerical method. A mesoscopic scale approach having been selected, experimental characterization of the commingled yarns mechanical behavior was necessary. Then, GeoFab software limitations on its use for the generation of CAD models of 3D fabrics unit cells were identified. Improvements to address these limitations have been proposed and their feasibility was demonstrated. A CAD model of a sub part of one of the fabrics unit cell was then generated. After having modeled the commingled yarns behaviour using experimental results, finite element simulations were performed on fabric CAD model and first encouraging results were obtained.

Antarctic Wind Engineering deals with the effects of wind on the built environment. The assessment of wind induced forces, wind resource and wind driven snowdrifts are the main tasks for a wind engineer when participating on the design of an Antarctic building. While conventional Wind Engineering techniques are generally applicable to the Antarctic environment, there are some aspects that require further analysis due to the special characteristics of the Antarctic wind climate and its boundary layer meteorology. The first issue in remote places like Antarctica is the lack of site wind measurements and meteorological information in general. In order to complement this shortage of information various meteorological databases have been surveyed. Global Reanalyses, produced by the European Met Office ECMWF, and RACMO/ANT mesoscale model simulations, produced by the Institute for Marine and Atmospheric Research of Utrecht University (IMAU), have been validated versus independent observations from a network of 115 automatic weather stations. The resolution of these models, of some tens of kilometers, is sufficient to characterize the wind climate in areas of smooth topography like the interior plateaus or the coastal ice shelves. In contrast, in escarpment and coastal areas, where the terrain gets rugged and katabatic winds are further intensified in confluence zones, the models lack resolution and underestimate the wind velocity. The Antarctic atmospheric boundary layer (ABL) is characterized by the presence of strong katabatic winds that are generated by the presence of surface temperature inversions in sloping terrain. This inversion is persistent in Antarctica due to an almost continuous cooling by longwave radiation, especially during the winter night. As a result, the ABL is stably stratified most of the time and, only when the wind speed is high it becomes near neutrally stratified. This thesis also aims at making a critical review of the hypothesis underlying wind engineering models when extreme boundary layer situations are faced. It will be shown that the classical approach of assuming a neutral log-law in the surface layer can hold for studies of wind loading under strong winds but can be of limited use when detailed assessments are pursued. The Antarctic landscape, mostly composed of very long fetches of ice covered terrain, makes it an optimum natural laboratory for the development of homogeneous boundary layers, which are a basic need for the formulation of ABL theories. Flux-profile measurements, made at Halley Research Station in the Brunt Ice Shelf by the British Antarctic Survery (BAS), have been used to analyze boundary layer similarity in view of formulating a one-dimensional ABL model. A 1D model of the neutral and stable boundary layer with a transport model for blowing snow has been implemented and verified versus test cases of the literature. A validation of quasi-stationary homogeneous profiles at different levels of stability confirms that such 1D models can be used to classify wind profiles to be used as boundary conditions for detailed 3D computational wind engineering studies. A summary of the wind engineering activities carried out during the design of the Antarctic Research Station is provided as contextual reference and point of departure of this thesis. An elevated building on top of sloping terrain and connected to an under-snow garage constitutes a challenging environment for building design. Building aerodynamics and snowdrift management were tested in the von Karman Institute L1B wind tunnel for different building geometries and ridge integrations. Not only for safety and cost reduction but also for the integration of renewable energies, important benefits in the design of a building can be achieved if wind engineering is considered since the conceptual phase of the integrated building design process.

Depuis quelques décennies, les flavonoïdes sont de plus en plus utilisés dans différents domaines d’applications alimentaires et non alimentaires. Cet engouement est dû principalement à leurs activités antioxydantes. Cependant, la solubilisation, la dispersion et la stabilisation de ces molécules sont variables et constituent un frein à leur utilisation. L’objectif de ce travail est de pallier cet inconvénient en visant à comprendre les interactions entre ces composés et leur milieu en absence et en présence de polymères, par une double approche expérimentale et par modélisation et mésomodélisation moléculaire. Dans un premier temps les interactions entre 3 flavonoïdes la quercétine et ses deux formes glycosilées la rutine et l’isoquercétine dans différents solvants organiques ont été étudiées. Les résultats obtenus (paramètre de Flory Huggins et fonction de la distribution radiale) ont montré que la partie B2 commune aux trois flavonoïdes avec des valeurs de paramètres de Flory Huggins proche de 0.5 dans le M2B2 et plus importantes dans l’acétonitrile est la responsable du comportement des flavonoïdes dans le solvant. Les simulations par DDFT ont montré une agrégation de la quercétine dans le M2B2 contre une dispersion dans l’acétonitrile. Toutes ces observations ont été validées expérimentalement (étude de la solubilité et observations microscopiques). Dans un deuxième temps on a étudié la quercétine en présence d’un bioploymère le PLGA dans l’eau. Des nanoparticules ont été formées en variant la concentration des différents composés et le ratio acide lactique / acide glycolique du PLGA. Les méthodes de la modélisation moléculaire et de la mésomodélisation (calcul du paramètre de solubilité par dynamique moléculaire et observation de la dispersion ou de la séparation de phase par DDFT) ainsi que l’approche expérimentale (DSC, MET …) nous ont menées à la même constatation. En effet la taille des particules augmente avec la concentration du PLGA et le taux d’acide lactique dans le polymère. Aussi la concentration de l’émulsifiant dans le milieu joue un rôle important dans la formation d’agrégats PLGA-Q. Plus sa concentration est importante, plus la formation des particules est difficile comme il joue un rôle sur la viscosité du milieu et par conséquence la diffusivité des molécules dans l’eau. Tous les résultats obtenus par modélisation moléculaire et par mésomodélisation ont été validés expérimentalement. On peut donc conclure que la méthodologie adoptée en simulation peut constituer un outil d’aide à la prédiction du comportement des flavonoïdes / Over the past few decades, flavonoids have become increasingly used in different food and non-food applications due to their important antioxidant activities. However, the solubilization, dispersion and stabilization of these molecules are variable and constitute a brake on their use in different formulations. The objective of this work is to overcome those limitations by understanding the interactions between these compounds and their environment without and with the add of polymers, by a multi-scale approach approach (molecular modeling and mesoscale modeling and experimental study). Initially, interactions between 3 flavonoids (quercetin, rutin and isoquercetin) in various organic solvents, were studied. The obtained results (mainly Flory Huggins parameter and radial distribution function RDF) showed that the B2 part common to the three flavonoids (For example Flory Huggins parameter values were close to 0.5 in the M2B2 and much more important in acetonitrile) is responsible for the miscibility behavior of the flavonoids in the solvent. DDFT simulations showed aggregation of quercetin in M2B2 against dispersion in acetonitrile. All these observations were confirmed experimentally (study of solubility and microscopic observations). Then, quercetin was studied in the presence of a biopolymer, PLGA in water. Nanoparticles were formed by varying the concentration of the various compounds and the lactic acid / glycolic acid ratio in the PLGA. The tools of molecular modeling and mesoscale modeling (calculation of the solubility parameter by molecular dynamics and observation of the dispersion or the phase separation by DDFT) as well as the experimental approach (DSC, MET ...) led us to the same conclusions. Indeed, the particle size increases with the concentration of PLGA and the rate of lactic acid in the polymer. Also the concentration of the emulsifier in the medium has an important role in the formation of PLGA-Q aggregates. The higher its concentration, the more difficult the formation of the particles as it affects the viscosity of the medium and consequently the diffusivity of the molecules in the water. All the results obtained by molecular modeling and by mesoscale modeling have been confirmed experimentally. We can therefore conclude that the methodology adopted in the simulations can be considered as a tool to help on predicting the behavior of flavonoids in different medium

abstract: The role of environmental factors that influence atmospheric propagation of sound originating from freeway noise sources is studied with a combination of field experiments and numerical simulations. Acoustic propagation models are developed and adapted for refractive index depending upon meteorological conditions. A high-resolution multi-nested environmental forecasting model forced by coarse global analysis is applied to predict real meteorological profiles at fine scales. These profiles are then used as input for the acoustic models. Numerical methods for producing higher resolution acoustic refractive index fields are proposed. These include spatial and temporal nested meteorological simulations with vertical grid refinement. It is shown that vertical nesting can improve the prediction of finer structures in near-ground temperature and velocity profiles, such as morning temperature inversions and low level jet-like features. Accurate representation of these features is shown to be important for modeling sound refraction phenomena and for enabling accurate noise assessment. Comparisons are made using the acoustic model for predictions with profiles derived from meteorological simulations and from field experiment observations in Phoenix, Arizona. The challenges faced in simulating accurate meteorological profiles at high resolution for sound propagation applications are highlighted and areas for possible improvement are discussed. A detailed evaluation of the environmental forecast is conducted by investigating the Surface Energy Balance (SEB) obtained from observations made with an eddy-covariance flux tower compared with SEB from simulations using several physical parameterizations of urban effects and planetary boundary layer schemes. Diurnal variation in SEB constituent fluxes are examined in relation to surface layer stability and modeled diagnostic variables. Improvement is found when adapting parameterizations for Phoenix with reduced errors in the SEB components. Finer model resolution (to 333 m) is seen to have insignificant ($<1\sigma$) influence on mean absolute percent difference of 30-minute diurnal mean SEB terms. A new method of representing inhomogeneous urban development density derived from observations of impervious surfaces with sub-grid scale resolution is then proposed for mesoscale applications. This method was implemented and evaluated within the environmental modeling framework. Finally, a new semi-implicit scheme based on Leapfrog and a fourth-order implicit time-filter is developed. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2014

<p>The MIUU mesoscale model was further developed, in order to include information on large-scale atmospheric fields from global or regional atmospheric climate- and weather-prediction models. For this purpose, a new lateral boundary condition was developed and implemented into the model. The new lateral boundary condition is a combination of two existing conditions, namely the flow relaxation scheme and the tendency modification scheme.</p><p>Tests indicated that an optimum lateral boundary configuration would be obtained with moderate to strong flow relaxation at higher levels, small flow relaxation at lower levels (within the atmospheric boundary layer), upstream advection at the outermost 4 grid points, and 6% horizontal grid stretching starting at a substantial distance from the lateral boundaries. The flow relaxation coefficients should be specified carefully, in order to minimize the reflection of all kinds of waves at the lateral boundaries.</p><p>The summer thermal low in the mean-sea-level pressure field over North America is traditionally analyzed over the northern end of the Gulf of California. The position of this low is influenced by the application of the so-called plateau correction in obtaining mean-sea-level pressure values from highly elevated stations in North America. A model study indicated that the low should be located approximately 450 km to the north and somewhat to the east of the above location. </p><p>A statistical comparison of model results from two mesoscale models against upper-air and surface measurements from several sites was carried out. Statistical methods, however, give only an insufficient picture of overall model performance. A comparison between predicted and measured tracer concentrations could be used to better evaluate the overall performance of different models.</p><p>Sound propagation in the atmosphere was predicted in a mountain valley using a mesoscale atmospheric model together with a sound propagation model. This suggests that forecasts of sound propagation should be possible in future.</p>

The MIUU mesoscale model was further developed, in order to include information on large-scale atmospheric fields from global or regional atmospheric climate- and weather-prediction models. For this purpose, a new lateral boundary condition was developed and implemented into the model. The new lateral boundary condition is a combination of two existing conditions, namely the flow relaxation scheme and the tendency modification scheme. Tests indicated that an optimum lateral boundary configuration would be obtained with moderate to strong flow relaxation at higher levels, small flow relaxation at lower levels (within the atmospheric boundary layer), upstream advection at the outermost 4 grid points, and 6% horizontal grid stretching starting at a substantial distance from the lateral boundaries. The flow relaxation coefficients should be specified carefully, in order to minimize the reflection of all kinds of waves at the lateral boundaries. The summer thermal low in the mean-sea-level pressure field over North America is traditionally analyzed over the northern end of the Gulf of California. The position of this low is influenced by the application of the so-called plateau correction in obtaining mean-sea-level pressure values from highly elevated stations in North America. A model study indicated that the low should be located approximately 450 km to the north and somewhat to the east of the above location. A statistical comparison of model results from two mesoscale models against upper-air and surface measurements from several sites was carried out. Statistical methods, however, give only an insufficient picture of overall model performance. A comparison between predicted and measured tracer concentrations could be used to better evaluate the overall performance of different models. Sound propagation in the atmosphere was predicted in a mountain valley using a mesoscale atmospheric model together with a sound propagation model. This suggests that forecasts of sound propagation should be possible in future.

Le béton est un matériau très utilisé dans l'industrie de construction. Une limite essentielle à un usage de ce matériau est sa dégradation par écaillage lorsqu’il est exposé au feu. Le phénomène d'écaillage consiste en une éjection du béton sous forme d'écailles à la surface du béton exposée à l'incendie. La section de béton s'en trouve progressivement réduite. De plus, ce phénomène expose les armatures et peut conduire à une rupture prématurée de structures telles que les tunnels, les gratte-ciels, les centrales nucléaires etc. De nombreuses recherches ont été consacrées à la mise au point de méthodes de prévention de l'écaillage et à la détermination des paramètres qui ont une influence sur ce phénomène. Cependant, la physique qui contrôle l'écaillage n'est pas encore entièrement comprise. L'objectif principal de la thèse est de fournir une meilleure compréhension des mécanismes impliqués dans l’écaillage du béton en utilisant une approche numérique-expérimentale, i.e., la tomographie neutronique couplée à la modélisation numérique avancée à une échelle adéquate.Dans ce travail, les premières mesures 3D de la teneur en eau du béton (grandeur locale indispensable au suivi du processus de déshydratation potentiellement responsable de l’écaillage) soumis à un chargement thermique sévère ont été réalisées à l'aide de tomographies neutroniques rapides. Le suivi de la déshydratation rapide du béton a été possible en réalisant un scan 3D toutes les minutes grâce à la source neutrons de l'Institut Laue Langevin (leader mondial), à Grenoble, France. Cette vitesse d'acquisition est dix fois plus rapide que toute autre étude tomographique rapportée dans la littérature. Un dispositif, adapté à l'imagerie neutronique et aux essais à haute température, a été développé pour réaliser de telles expériences. L'influence de la taille des agrégats sur la distribution de l'humidité au sein de l'échantillon est présentée. Les résultats quantitatifs sur l'accumulation d'humidité derrière le front de déshydratation, connue sous le nom de 'moisture-clog" et considérée comme un des facteurs principaux engendrant un excès de pression, sont également présentés et discutésEn parallèle, un modèle thermo-hydro-mécanique (THM) entièrement couplé a été mis en œuvre sur le logiciel élément fini Cast3M afin d'étudier et prédire le comportement du béton à haute température. Le code nouvellement implémenté est remarquablement plus rapide (20-30 fois) que le code existant sur lequel il est basé. Une approche mésoscopique a été adaptée au modèle pour prendre en compte l'hétérogénéité du béton. D'abord, le modèle est appliqué à des expériences de la littérature, qui étu-dient les paramètres standards tels que la température, la pression du gaz et la perte de masse. En-suite, des profils d'humidité 1D obtenus à partir d'expériences de radiographie neutronique sont utili-sés pour vérifier et améliorer le modèle en termes de lois de comportement critiques telles que les courbes de déshydratation et de rétention d'eau. Enfin, le modèle est utilisé pour prédire la distribution d'humidité 3D mesurée dans ce travail de doctorat par tomographie neutronique. Entre autres, des simulations THM mésoscopiques sont effectuées pour étudier l'influence d'un agrégat sur le front de séchage. / Concrete has been extensively used in the construction industry as a building material. A major drawback of this material is its instability at high temperature, expressed in the form of violent or non-violent detachment of layers or pieces of concrete from the surface of a structural element. This phenomenon, known as fire spalling, can lead to the failure of concrete structures such as tunnels, high rise buildings, nuclear power-plants, underground parkings etc. because the reinforcement steel is directly exposed to high temperature and the designed cross section of the concrete elements (e.g., columns, beams, slabs) is reduced. A lot of research has been dedicated on developing preventing methods for spalling and also on determining the parameters that have an influence on it. However, the physics behind this phenomenon is not yet fully understood.In this doctoral, the first 3D measurements of moisture content in heated concrete, which is believed to be one of the processes directly related to spalling, have been performed using in-situ neutron tomography. In order to follow the fast dehydration process of concrete, one 3D scan (containing 500 radiographs) per minute was captured thanks to the world leading flux at the Institute Laue Langevin (ILL) in Grenoble France. This acquisition speed, which is ten times faster than any other experiment reported in the literature, was sufficient to follow the dehydration process. A dedicated setup, adapted to neutron imaging and high temperature, has been developed for performing such kind of experiments. Concrete samples with different aggregate size have been tested. Quantitative analysis showing the effect of the aggregate size on the moisture distribution is presented. Results on the moisture accumulation behind the drying front, known as the moisture-clog, are also presented and discussed.In parallel, a numerically-efficient coupled thermo-hydro-mechanical (THM) model has been implemented in the finite element software Cast3M for understanding and predicting the complex behavior of concrete at high temperature in the context of spalling. The newly implemented code is remarkably faster (20-30 times) than an existing one, on which it is based. A mesoscopic approach has been adapted to the model for taking into account the heterogeneity of concrete. First the model is applied to experiments from literature monitoring standard parameters such as temperature, gas pressure and mass loss. Then, 1D moisture profiles obtained from neutron radiography experiments are used for verifying and improving the model in terms of some critical constitutive laws such as dehydration and water retention curves. Finally, the model is employed for predicting the 3D moisture distribution measured in this doctoral work via neutron tomography. Among others, mesoscopic THM simulations are performed for investigating the influence of an aggregate on the drying front.