Gravity waves in the atmosphere are the waves with gravity and buoyancy force as the restoring forces. Gravity waves will significantly impact the Mesosphere Lower / Thermosphere (MLT), and the breaking of gravity waves is the key factor to cause the cool summer and warm winter in the Mesopause region. Therefore, it is important for us to investigate gravity waves. In this dissertation, we mainly use USU Na lidar data to explore gravity waves in the MLT. The exploration is made up of two projects. One is the investigation of gravity wave breaking and the associated dynamic instability by USU Na Lidar and Advanced Mesosphere Temperature Mapper (AMTM). Another is the calculation of gravity wave temperature perturbations and potential energy density by least-squares fitting based on the data from the full-diurnal cycle observation of Na lidar. The sporadic sodium layer is the sharp increase of Na density in a small vertical range (several kilometers) above the Na main layer in the MLT. The formation of the sporadic sodium layer above 100 km remains unknown until now. Here we will investigate the mechanism of the generation of sporadic sodium layer using numeric modeling, including the effect of tide and gravity wave on the variation of Na density.

Many different numeric models have been created to address a variety of hydraulic and hydrologic engineering applications. Each utilizes formulations and numeric methods to represent processes such as contaminant transport, coastal circulation, and watershed runoff. Although one process may be adequately represented by a model, this does not guarantee that another process will be represented even if that process is similar. For example, a model that computes subcritical flow does not necessarily compute supercritical flow. Selecting an appropriate numeric model for a situation is a prerequisite to obtaining accurate results. Current policies and resources do not provide adequate guidance in the model selection process. Available resources range from approved lists to guidelines for performing calculations to technical documentation of candidate numeric models. Many of these resources are available only from the developers of the numeric models. They focus on strengths with little or no mention of weaknesses or limitations. For this reason, engineers must make a selection based on publicity and/or familiarity rather than capability, often resulting in inappropriate application, frustration, and/or incorrect results. A comprehensive selection tool to aid engineers needs to test model capabilities by comparing model output with analytical solutions, laboratory tests, and physical case studies. The first step in building such a tool involves gathering and categorizing robust data the can be used for such model comparisons. A repository has been designed for this purpose, created, and made available to the engineering community. This repository can be found at http://verification.aquaveo.com. This allows engineers and regulators to store studies with assigned characteristics, as well as search and access studies based on a desired set of characteristics. Studies with characteristics similar to a desired project can help identify appropriate numeric models.

The aim of diploma thesis is to design one variant of technical flood protection in the urban area of the town of Litovel. The subject of the work is the elaboration of the so called "zero variant", consisting in the transfer of part of the flood flows through the Morava riverbed in km 259,852 - 262,070 and the Power Plant drive in km 0.000 - 1.791. Hydraulic calculations were carried out using a 1D numerical model. The outputs have been processed in the form of project documentation of flood protection.

Les spectres de bruit mesurés en cabine d’hélicoptère montrent que la boîte de transmission principale (BTP) est un des principaux contributeurs au bruit perçu par les usagers. Elle génère en effet plusieurs raies émergeant fortement du bruit large bande et dont les fréquences se situent dans la plage de sensibilité maximale de l’oreille humaine. Dans un contexte d’amélioration permanente du confort acoustique des usagers, un modèle numérique est développé pour prédire le comportement dynamique des BTP. Les équations du mouvement sont écrites sur la base de fonctions du temps représentatives des excitations générées par l’engrènement (raideur d’engrènement et erreurs de transmission). Plusieurs éléments de validation sont présentés pour confirmer la pertinence de la formulation proposée. Différents résultats numériques et expérimentaux de la littérature sont utilisés à des fins de comparaison, montrant que le modèle s’applique aux systèmes à simple étage de réduction, par engrenage cylindrique ou spiro-conique. La validation est ensuite étendue aux systèmes à deux étages de réduction et les résultats confirment que la formulation basée sur les erreurs de transmission permet de tenir compte des corrections de profil. Finalement, le modèle est utilisé pour diverses applications. Premièrement, l’influence des erreurs de pas sur le comportement dynamique de transmissions par engrenages est discutée, ainsi que l’influence combinée du niveau de chargement appliqué. Dans un second temps, la relation entre l’erreur de transmission dynamique et différents coefficients dynamiques est étudiée. Le contenu spectral de la réponse au niveau des roulements est ensuite analysé pour des systèmes à deux engrènements cylindriques et l’influence de différents paramètres est discutée. Enfin, une application est réalisée sur un système comprenant un engrenage cylindrique et un engrenage spiro-conique. Les phénomènes de couplage entre les étages successifs sont mis en évidence ainsi que la contribution des deux engrènements au contenu spectral de la réponse aux roulements. / Noise measurements have shown that helicopters main gearboxes highly contribute to the overall cabin noise. Gear mesh vibrations propagate through the shafts to the rolling element bearings and the casing which becomes a source of radiated noise. The latter is characterized by high-amplitude tones emerging from broadband noise whose frequencies lie in the range of maximum human ear sensitivity. In the context of continuous improvement in the acoustic comfort of helicopter passengers, it is therefore necessary to analyse and optimize gearbox vibrations in order to reduce casing noise radiations. The research work presented in this memoir is focused on the development of a numerical model dedicated to the prediction of gear system dynamic behaviour, comprising several gear stages and different types of gears. This model relies on classic beam and lumped parameter elements along with specific two-node gear elements for both cylindrical (spur, helical) and spiral-bevel gears. The equations of motion are developed based on time-varying functions representative of mesh excitations which comprise: (a) mesh stiffness functions, (b) quasi-static transmission error under load, and (c) kinematic (or no-load) transmission error. A number of comparisons with benchmark numerical and experimental results from the literature are presented which demonstrate that the proposed approach is sound as far as single-stage systems with spur, helical or spiral-bevel gears are considered. Validations are then extended to double-stage gears and, here again, it is confirmed that the proposed transmission error based formulation is accurate and can account for tooth shape modifications. In the second part of the memoir, several examples of application are presented and commented upon. First, the combined influence of tooth pitch errors and load on the dynamic behaviour of gear transmissions is tackled. An extended three-dimensional model and a reduced torsional version are then confronted in order to investigate the dependency between dynamic transmission errors and mesh force / root stress dynamic factors. Further investigations on bearing dynamic response in two-stage spur gear systems are conducted and the particular contributions of profile modifications are analysed. Finally, a system combining a cylindrical gear and a spiral-bevel gear is considered and particular attention is paid to the dynamic couplings between the various meshes and their influence on bearing dynamic responses.

The thesis deals with the issue of protection of Prague's main train station as a soft target and it's regular operation, mainly by using evacuation model with emphasis on barrier-free issues. Mapping of the building was conducted by using Decree No. 398/2009 Coll. general technical requirements ensuring the barrier-free usage of buildings and their parts. Adapting the environment to people with reduced mobility is not always axiomatic, especially in terms of evacuation. For the movement of these persons it is necessary to take into account their needs and possibilities in normal traffic and during evacuation. The sociological and psychological aspects of crowd and individuals have also significant impact on evacuation. For identifying critical points of the main train station, it has been used knowledge of local research, knowledge of barrier-free buildings, sociology and psychology, and special simulation tools for modeling the movement of people. It has been found that space can be optimized by detailed analysis of simulation outputs to meet all expected requirements without negative impact on barrier-free domain. Thanks to this, it was possible to achieve a new design, which accomplishes higher safety of people with movement and orientation disabilities, especially during emergency situations in building of main train station Prague.

La préservation de la chaîne du froid est un paramètre particulièrement important dans le cadre de la distribution urbaine, où les fréquentes ouvertures de portes induisent une charge thermique d’infiltration. Afin de réduire les transferts de masse et de chaleur et de protéger l’ouverture, des rideaux d’air ont récemment été installés au niveau de l’ouverture des camions frigorifiques. L’objet de la présente étude est d’étudier ce type confinement. Deux modèles CFD ont été développés pour simuler les champs de températures et de vitesses dans un camion réfrigéré clos. Ils ont permis de montrer que la variation de la vitesse de soufflage ne modifie pas de manière significative la structure des écoulements. Différents conduits d’air sont modélisés. Les résultats numériques montrent que la configuration avec un conduit ouvert améliore fortement le renouvellement d’air. Puis, une étude numérique est réalisée dans le but d’étudier les infiltrations de chaleur et de masse au cours de l’ouverture des portes. Ces écoulements sont bien prédits par le modèle CFD, excepté à la transition entre les deux régimes d’infiltration. Une caisse expérimentale a été équipée d’un dispositif de rideau d’air composé d’un jet ambiant, d’un jet froid ou d’un jet double. En parallèle, un modèle numérique CFD a été développé pour étudier l’influence de différents paramètres. Une bonne concordance entre les résultats numériques et expérimentaux a été observée. L’efficacité du rideau d’air ambiant est maximale lorsque le point d’impact du rideau se situe dans le plan de l’ouverture. Le rideau double maintient efficacement l’homogénéité de la température pour de courtes ouvertures. Le rideau d’air froid est la meilleur configuration, il limite fortement l’augmentation de température de l’enceinte et permet des gains énergétiques importants. / Cold chain safety is a key parameter for urban distribution where the frequent door-opening induces a heat infiltration. In order to reduce heat and mass transfer, air curtain have recently been installed to protect the doorway of refrigerated truck. The aim of this work is to study this type of door insulation. Two CFD numerical models were developed to simulate the temperature and velocity fields in a closed refrigerated truck. These models showed that modifying the blowing velocity does not modify the air flow structure inside the cavity. Different air chutes were modelled. Numerical results demonstrate that the configuration with a convergent and an open duct strongly improves the air renewal. A numerical investigation was performed in order to study heat and mass infiltration rates during the opening. The infiltration flow rate is well predicted by the CFD model, except at the transition between both flow regimes. An experimental truck was equipped with an air curtain setup, composed by an ambient air jet, a cold air jet or a double jet. In parallel, a numerical CFD model was developed to study the influence of various parameters. Experimental and numerical results were found to be in good agreement. The maximum efficiency of the ambient air curtain is reached when the impact point of the jet occurs in the door plane at the ground level. This configuration is only relevant for short opening times. The double air curtain efficiently maintains the temperature homogeneity for short openings. The cold air curtain is the best configuration which strongly limits the temperature increase during the opening and allows important energy savings.

Les engrenages roues et vis sans fin sont une solution avantageuse pour transmettre le couple entre des axes perpendiculaires non concourants. Ces engrenages offrent une solution simple et efficace en terme de coût dans les applications de transmission de puissance, où un grand rapport de réduction est nécessaire, en comparaison avec les engrenages classiques à axes parallèles qui nécessitent normalement deux ou trois étapes pour obtenir les mêmes réductions avec une augmentation conséquente de complexité et du nombre de pièces. L’usure de surface est un des modes de défaillance observés dans la vie des engrenages roues et vis sans fin qui influe sur la portée de contact, les caractéristiques de transmission et le bruit résultant. La première étape de ces travaux est la mise au point d’un modèle numérique pour étudier le comportement quasi statique des engrenages roues et vis sans fin avec une roue en bronze et une vis en acier. Le modèle est basé sur la résolution des équations de compatibilité des déplacements ainsi que sur la méthode des coefficients d’influence. Les effets globaux de flexion et les effets locaux de contact ont été séparés. Les effets de contact ont été obtenus par la théorie de Boussinesq. Les coefficients de flexion sont estimés par la combinaison d’un calcul Éléments Finis et des fonctions d’interpolation, permettant d’une part de prendre en compte l’environnement de l'engrenage (la géométrie des arbres, des jantes et des voiles, l’emplacement des roulements,...) et d’autre part de réduire significativement les temps de calculs. Dans une seconde étape, une méthodologie est proposée pour modéliser l’usure de la surface de dent de la roue. Le modèle de contact quasi-statique de la répartition des charges est combiné avec un modèle d’usure d’Archard. Ce modèle suppose que la profondeur d’usure est directement proportionnelle à la pression de contact et à la distance de glissement et inversement proportionnelle à la dureté du matériau. Cette loi d’usure est modifiée pour prendre en compte l’influence des conditions de lubrification en utilisant un coefficient d’usure local, dépendant de l’épaisseur du film lubrifiant, rapportée à l’amplitude des rugosités des surfaces. L’enlèvement de matière par l’usure du flanc de la roue influe sur la répartition des pressions et donc les modifications de la géométrie des dents doivent être incluses dans la prédiction de l’usure. Le calcul des pressions de contact est ainsi mis à jour pour tenir compte des changements de géométrie. Enfin, pour valider le modèle développé des comparaisons du modèle avec des résultats expérimentaux issus de la bibliographie ont été effectuées. / Worm gears are one of the technical devices for transmitting torque between spatial crossed axes. They provide a simple and cost effective solution in power transmission applications, where a high reduction ratio is required. Comparable conventional parallel axis gearing would normally require two or three stages to achieve the same reduction, with a consequent increase in complexity and number of parts. Surface wear is one of the failure modes observed in life worm gear sets which affects the contact patterns, the other transmission characteristics and the resultant noise. The first step of this work is the development of a numerical model to study provide the quasi-static behavior of worm gears with bronze wheel and steel worm. The model is based on solving of the equation of displacement compatibility and the influence coefficient method. The global effects of bending and local effects of contact are separated. The contact effects are obtained with the theory of Boussinesq. Bending effects are estimated by the combination of one standard FEM computation and interpolation functions. These methods allow, on the one hand, to take into account the environment of the gear (shaft shape, rim, web, bearing location ...) and on the other to reduce significantly the computation time. In a second step, a methodology is proposed for predicting the wear of the wheel tooth surface. In this process, a quasi-static contact model of the load distribution is combined with Archard's wear model. This model assumes that the wear depth is directly proportional to the contact pressure and sliding distance and inversely proportional to the hardness of the material. The wear law is modified to take into account the influence of the lubrication conditions using a local wear coefficient, depending on the lubricant film thickness, relative to the amplitude of surface roughness. Removal of material by wear on the wheel flank affects the pressure distribution, therefore the changes in teeth must be included in the prediction of wear. The calculation of contact pressures must also be updated to take into account the modification of the gear flank geometry. The last step concerns the validation of the numerical. Comparisons have been carried out between the model results and experimental ones issued from the bibliography.

Engineers frequently use computerized numeric models to calculate and predict water levels and current patterns for rivers, bays, and other bodies of water. This computation often involves an iterative process known as incremental loading that can cause frustration and consume a lot of time. Although the steering module in the Surface-water Modeling System (SMS) automates incremental loading to minimize user interaction, it can still be very time consuming. This thesis examines the steering module and the incremental loading process to improve its efficiency. Specifically, the RMA2 and FESWMS models are utilized. Two methods of improving efficiency are examined. The first includes creating predicted solution files for each step of the incremental loading process. These predictions allow the steering module to take larger steps and decrease the computation time. The second method changes the algorithm used to determine the size of each step. Finally, the interface to the process was examined and simplified to require minimal input and to make the input more intuitive.

Many numeric models simulate the transport of sediment within rivers and streams. Engineers use such models to monitor the overall condition of a river or stream and to analyze the impact that the aggradation and degradation of sediment has on the stability of bridge piers and other features within a stretch of a river or stream. A model developed by the Federal Highway Administration, FST2DH, was recently modified to include the simulation of sediment movement within a channel. The tools for modeling sediment movement with FST2DH remain unproven. This thesis examines the sediment capabilities of FST2DH. It evaluates the sediment results for reasonableness and compares the results to those obtained from a sediment transport model developed by the Army Corps of Engineers, SED2D WES. Resulting concentrations from another program created by the Army Corps of Engineers, SAMwin, provide additional data comparison for FST2DH sediment solutions. Several test cases for laboratory flumes give additional insight into the model's functionality. Finally, this thesis suggests further enhancements for the sediment capabilities of the FST2DH model and provides direction for future research of the sediment transport capabilities of FST2DH. Results show that FST2DH appropriately models sediment movement in channels with clear-water and equilibrium transport rate inflow conditions. Transport formulas found to be functional include the Engelund—Hansen, Yang sand and gravel, and Meyer-Peter—Mueller equations. FST2DH has difficulty modeling channels with user-specified inflow concentrations or transport rates, models with very small particles, models containing hydraulic jumps, and models with small elements. The test cases that successfully run to completion provide appropriate patterns of scour and deposition. Other trends in the results further verify the functionality of many of the sediment transport options in FST2DH.