Ce travail est consacré à l'élaboration et à la caractérisation des trois éléments d'une cellule SOFC fonctionnant à température intermédiaire (650-750°C). <br />Une conductivité purement ionique de 9x10-3 S.cm-1 a été mesurée à 700°C sur l'électrolyte retenu de composition La9Sr1Si6O26,5. Cette céramique de structure apatite est stable chimiquement au contact du matériau de cathode conducteur mixte Nd1,95NiO4+Δ. L'étude de la réduction de l'oxygène a montré que l'étape limitante est le transfert des ions oxyde à l'interface cathode/électrolyte. Le cermet anodique Ni-apatite a été élaboré par imprégnation de la matrice poreuse d'apatite par un sel de nickel. Cette méthode permet une meilleure stabilisation du nickel dans la structure hôte. Ces travaux mettent en évidence l'intérêt d'une nouvelle cellule SOFC fonctionnant à température intermédiaire composée d'électrolyte de structure apatite.

Cette thèse est une contribution à l'étude de la dynamique des écoulements tournants de grand nombre de Reynolds. Elle vise à expliquer la déstabilisation, à nombre de swirl élevé, d'un écoulement en rotation solide se développant dans une conduite cylindrique de section constante puis contractante, et débouchant en un jet. On caractérise d'abord la turbulence qui en résulte dans le plan de sortie du jet. Des mesures par anémométrie fil chaud, effectuées en faisant varier le taux de contraction final, confirment que l'origine de cette turbulence doit être principalement recherchée dans l'écoulement de conduite et non dans le jet. On montre ensuite par une étude bibliographique que l'écoulement à l'amont de la contraction peut être fortement affecté par celle-ci lorsqu'il est s! ous-critique vis-à-vis des ondes inertielles (ou ondes de Kelvin) axisymétriques. A l'aide d'un modèle de fluide parfait axisymétrique, on étudie alors l'influence du taux de contraction et des conditions aux limites amont au régime transcritique. On montre l'apparition d'une recirculation de paroi dans la contraction. On explore ensuite l'écoulement de conduite par PIV stéréoscopique, et on compare ces mesures avec une simulation numérique axisymétrique à nombre de Reynolds modéré. En présence d'une contraction finale, on constate une dynamique nouvelle puisque la transition critique est franchie sans éclatement tourbillonnaire. On observe à la place des ondes inertielles axisymétriques stationnaires de grande amplitude. On montre finalement que des instabilités centrifuges de petite échelle ainsi qu'une instabilité global! e axisymétrique peuvent participer à la créatio! n de tur bulence.

No description available.

This thesis is an investigation on water reuse in the fresh-cut fruits and vegetable industry. Fresh water is used intensively in washing, cutting/peeling processes and disinfecting fruits and vegetables, as a result washwater with heavy solids is generated. Effective removal of solids is needed to allow for water reuse. Thus dissolved air flotation (DAF) and centrifuge with coagulation and flocculation process were explored for solid removal capabilities; some settling analysis was also conducted. Bench scale studies show DAF and centrifuge produce waters of similar quality (Turbidity). DAF is able to produce waters with higher UV transmittance and can work better with membrane filtration and UV disinfection. While centrifuge showed higher reduction in pathogen levels, it can be cost effective and compact in design. Membrane filtration feasibility showed that high quality waters (low turbidity) can be produced, but were unable to remove pathogens. Collimated beam results show UV disinfection can further be used to completely eliminate pathogens and allow for water reuse. This allows the processors to reduce their water foot-print, increase sustainability of their operations, and meet the increasing demand for fresh-cut fruits and vegetables.

The ENE-trending Himalayan fold-thrust belt in Pakistan exhibits contrasting deformation styles both along and across the strike. The centrifuge modelling technique has been used to investigate these variations in structural style. For the purpose of modelling, the Salt Range and Potwar Plateau (SR/PP) stratigraphy has been grouped into four mechanical units. From bottom to top these are the Salt Range Formation, carapace unit (Cambrian-Eocene platform sequences), Rawalpindi Group, and Siwalik Group. These stratigraphic units of alternating competence, composed of thin layers of plasticine modelling clay and silicone putty, rest on a rigid base plate that represents the crystalline basement of the Indian plate. The models are built at a linear scale ratio of ~10-6 (1mm=1km) and deformed in a centrifuge at 4000g. The models are subjected to horizontal shortening by collapse and lateral spreading of a “hinterland wedge” which simulates overriding by the Himalayan orogen (above the Main Boundary Thrust). The models of the central SR/PP show that the accretionary wedge develops a prominent culmination structure with fault-bend fold geometry over the frontal ramp, while the eastern SR/PP is more internally deformed by detachment folds, fault-propagation folds and pop-up and pop-down structures. Model results show that the transition from fault-bend fold to detachment-fold and fault-propagation-fold geometry in the prototype may take place in a transfer zone marked by an S-bend structure (Chambal Ridge and Jogi Tilla) at the surface and the lateral ramp in the subsurface. Moreover, the models suggest that an oblique ramp below the Kalabagh strike-slip connecting the two frontal ramps below the Surghar Range and the central Salt Range developed similar structure that can be observed in the prototype. The model results also show that the Northern Potwar Deformed Zone may have been developed over ductile substrata due to the close similarity between the models and the prototype structures. The deformation style in the models illustrates the importance of mechanical stratigraphic and basement ramp systems in the evolution and the structural styles of the SR/PP. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-07-29 19:42:25.027

When a jack-up foundation is installed on seabeds consisting of a sand layer overlying soft clay, potential for 'punch-through' failure exists. This happens due to an abrupt reduction in bearing resistance when the foundation punches a block of sand into the underlying soft clay in an uncontrolled manner. This can lead to a sudden large penetration that can cause temporary decommissioning and even toppling of the unit. This research has addressed this problem with the aim of developing a practical design method for the jack-up industry to assess potential punch-through hazards. This objective has been achieved with the successful development of a new conceptual model for predicting the peak penetration resistance and a consistent method for constructing a complete resistance profile of spudcan foundations penetrating through sand into the underlying clay. The analytical basis of the new conceptual model follows the approach for silo analysis, and takes into account the stress level and dilatant response of sand. It is therefore a significant improvement over the punching shear and load spread models recommended in the current industry guidelines SNAME (2002), which do not consider the strength properties of the sand. To provide relevant experimental data for the new model, an extensive series of 30 continuous penetration tests were performed using the UWA drum centrifuge. These experimental results were retrospectively simulated using finite element (FE) analysis, in order to back-calculate the stress-level dependent friction and dilation angles in the sand during peak penetration resistance. The back-analysis showed that larger values of peak resistance gave lower friction and dilation angles, which is consistent with gradual suppression of dilatancy under high confining stress. When compared to published results from visualisation experiments, the FE analysis showed a similar failure mechanism during peak resistance, where a frustum of sand was forced into the underlying clay, with the outer angle reflecting the dilation in the sand. This has formed the basis of the new conceptual model. The performance of the new model in predicting the experimental peak resistance was compared with other existing analytical methods. Additional experimental results, including those already in the literature, were incorporated in the comparative study. It was found that the new conceptual model generally gave a good prediction of the experimental values, while the prediction from SNAME (2002) was conservative, with the predicted values being about half the experimental results on average. It was also shown that the new model could be modified to predict the post-peak penetration resistance in the sand layer. Finally, an analytical method for predicting the resistance profiles in the underlying clay was devised based on new bearing capacity factors developed through FE analysis. By joining the values of peak resistance, post-peak resistance and the resistance profile in the underlying clay, a complete simplified penetration resistance profile for spudcan foundations in sand overlying clay can be generated. The predicted profiles were shown to match the experimental results well.

Résumé de la thèse en français : Le clouage des sols est une technique de soutènement d’excavations développée en France dans les années 1970. En pratique aujourd’hui, les parements de tels ouvrages sont souvent dimensionnés pour reprendre les efforts de traction admissibles dans les renforcements. De manière générale, dans la profession il est notoire qu’au parement les efforts de service dans les renforcements sont en fait plus faibles que calculés, et ce d’autant plus à proximité du pied de parement en raison du phasage de construction de ces ouvrages, du haut vers le bas. En 2015 la Commission de Normalisation Française Justification des Ouvrages Géotechnique (CNJOG) a engagé une révision de la norme NF P 94 270, notamment pour clarifier la justification du parement. Dans ce contexte, cette thèse vise à améliorer les connaissances sur le fonctionnement des massifs de sol cloué en place et en particulier sur la mobilisation du parement. Les travaux réalisés ont comporté une étude paramétrique expérimentale sur modèle physique réduit en centrifugeuse géotechnique (trois longueurs de clous), complétée par une analyse par modélisation numérique en déformations. Sur le modèle réduit, la mobilisation des efforts dans les clous était observée à plusieurs niveaux à l’aide de fibres optiques munies de réseaux de Bragg, situées à l’axe neutre des clous. Les réseaux de Bragg étaient distants de 5 mm, soit 25 cm dans l’ouvrage réel modélisé. Les déplacements au sein du massif ont été suivis à l’aide d’une technique d’imagerie de type Particle Image Velocimetry (PIV), par suivi de motifs de grains de sables au travers d’une paroi latérale transparente du modèle physique à échelle réduite. Les essais ont montré une nette influence de l’élancement des ouvrages sur l’amplitude des déplacements et le profil des efforts mobilisés. Parallèlement, un modèle numérique tridimensionnel de calcul par éléments finis et respectant le phasage de construction a été développé sous CESAR-LCPC. Les clous ont été modélisés par des éléments linéiques partageant leurs nœuds avec les éléments volumiques par l’intermédiaire d’un degré de liberté supplémentaire, correspondant au déplacement relatif sol-clou. Le comportement en déformations du sol a été représenté par le modèle Hardening Soil Model (HSM). La comparaison des résultats expérimentaux et des simulations numériques a permis de mettre en avant l’influence de l’élancement sur le comportement du mur mais a souligné les limites de l’utilisation des éléments finis, et en particulier la forte sensibilité aux raideurs du sol et de l’interface sol-clou. Cette comparaison a également permis de proposer une amélioration du dimensionnement des sols cloués. Le logiciel PROSPER réalise ce dimensionnement en choisissant une courbe de rupture le long de laquelle le déplacement du sol mobilise la réaction des clous. Ce déplacement est généralement considéré homogène mais les résultats de ce travail permettent d’en proposer une allure. Des abaques ont été établis donnant cette distribution en fonction du rapport d’élancement. Cette approche du calcul des efforts au parement dans les renforcements a été mise en œuvre dans le cas d’un ouvrage expérimental. / Soil nailing is technique developped in France during the 70s for the retaining of excavations. Today, the facing of such structures is often designed to support the maximal tensions admissible in the reinforcements. The professionals generally admit that the service loads in the reinforcements are smaller than the calculated ones. Especially at the facing foot because of the construction phasage, from top to bottom. In 2015, The French Standardization for Geotechnical Structures Verification launched a revision of the standard concerning soil-nailing, especially about the facing design. In this context, this thesis aims at a better knowledge of soil-nailed walls behaviour and especially about the mobilization of the facing. The works consisted of a parametrical study on a centrifuge model (three nail lengths) and of a numerical modelling. On the centrifuge model, the nail tensions were observed, at each level, using Bragg grated optic fibers, placed at the core of the nails. The Bragg networks were placed 5 mm from each other (25 cm on the real wall). The displacements inside the soil were followed by a Particle Image Velocimetry like technique. The grains patterns were observed through a lateral translucid face. The experiments have shown a strong influence of the structure slenderness on displacements amplitude and on tensions allures. A 3D numerical model was also developped with CESAR-LCPC. It was realized with Finite Elements Method and the building phasage was respected. Nails were modelized by lineic elements whose nodes where shared with volumic elements. In order to simulate the friction law, an additional degree of freedom was introduced : the relative displacement between soil and nail. The deformation behaviour of the soil was simulated using Hardening Soil Model. The comparison of experimental and numerical results highlighted the influence of slenderness on wall behaviour as well as the limits of Finite Elements Method. In particular, the results are strongly dependant on the stiffness of soil and of the interface between soil and nail. This comparison also allowed to propose an improvement of the soil-nailing design. The PROSPER software choses a failure surface along which the displacement of soil mobilizes the reaction of the nails. This displacement is generally considered as homogenous but the results of the present work allow to propose an allure. Abacus have proposed for the distribution of this displacement and this design approach has been tested on an experimental wall.

Cette étude a pour objectif d’étudier différentes approches de modélisation de la turbulence sur un compresseur centrifuge industriel à fort taux de pression afin d’essayer d’élargir notre compréhension des différents phénomènes physiques mis en jeu et leur interaction avec la turbulence. D’abord, la sensibilité au maillage et au modèle turbulence est évalué sur des calculs RANS. Une analyse de simulations LES est ensuite effectuée. En particulier, une étude de l’effet de la turbulence sur l’écoulement et une comparaison aux résultats RANS et expérimentaux est réalisée. Enfin, deux approches hybrides DES sont étudiées afin d’exposer les problèmes rencontrés par ces modèles sur cette configuration. Il en résulte une évaluation des différentes méthodes et de leur applicabilité future dans un contexte industriel. / This study aims to assess the abilities of existing numerical simulation methods to predict the complex physical phenomena occurring in an industrial centrifugal compressor and especialy the effect of turbulence on the different flow features. RANS simulations are first performed using various turbulence model, then LES simulations and finally, two simulations using RANS/LES hybrid models of DES type are carried out. The whole compressor operating range is simulated using RANS, but because of LES and DES high computational costs, attention is focussed on the nominal operating point. Particular care is devoted to determine the impact of grid refinement on the simulation results. To this end, simulations are performed on three grids, respectively composed of over 8, 26 and 165 million cells. Even though the grids used do not fulfill the mesh refinement criteria recommended in the litterature for an accurate wall-resolved LES simulation, the simulation performed on the denser grid provides interesting conclusions on the turbulence generation and its interaction with the mean flow.The hybrid DES approches used involve a shield function to prevent the boundary layers to be computed in LES. However, this function is found to be unsuited to this centrifugal compressor flow. Indeed, the RANS and LES regions are not correctly located and most of the tip leakage flow is resolved using a RANS approach, preventing the development of turbulence.This work allowed us to evalute the various approches and highlight some of the problems and advantages of each for the simulation of this centrifugal compressor.

A moagem e mistura rápidas e efetivas de materiais em pequenos volumes é uma necessidade nos laboratórios e na indústria moderna. Diversos tipos de métodos e equipamentos prestam este serviço, dentre eles o moinho e misturador planetário. Estes equipamentos são máquinas centrífugas que combinam movimentos rotacionais com translacionais e que utilizam os efeitos otimizados das forças, direções e movimentos dos materiais em processo. Para o moinho é otimizado e ampliado o poder dos mecanismos de moagem, sendo então considerado um processo de alta energia. No caso dos misturadores há a combinação do movimento planetário com um ângulo de inclinação entre o eixo de rotação do jarro com o eixo de translação que promovem vórtices helicoidais efetivos para promover a mistura. O presente trabalho objetiva o desenvolvimento de moinho e misturador planetário visando determinar condições otimizadas de moagem e mistura, o estabelecimento de limites de operação para ambas aplicações e a seleção de um sistema de transmissão simplificada. Inicialmente foram fabricados bancos híbridos de moagem e mistura para pequenas amostras (25 g para moagem e 100 g para mistura). O desempenho de moagem foi analisado pela determinação do tamanho de partículas antes e após o processo de moagem em pós de alumina de granulação grosseira com diâmetro médio de partícula em torno de 4,2 &#956;m, variando-se as combinações de relação de transmissão, velocidade de translação e tamanho do meio de moagem. Para o misturador foi aplicado ângulo de inclinação de 30º e realizado ensaios nas misturas de massa plástica em diferentes rotações. Na configuração moinho, o melhor desempenho experimental resultou em pó de alumina submicrométrico de Øee ~ 0,9 mm em uma hora de moagem na rotação de translação de 450 rpm e relação de transmissão eixo principal/jarro de 1:-2. Na configuração misturador a condição otimizada foi com rotação de 2000 rpm e relação transmissão eixo principal/jarro de -2:1 que proporcionou mistura relativamente homogênea em 30 s. Para carregamentos de até 25 g de pós cerâmicos, em que o conjunto excêntrico (jarro, fixação, matéria prima e meios de moagem) são inferiores à 1 kg, utilizou-se a transmissão baseada em rodas de atrito que permitiu um projeto econômico e compacto, sendo o aço (AISI 4340 temperado e revenido) o material da roda de atrito que apresentou a melhor durabilidade e confiabilidade. Entretanto, apresentou limitação na moagem de amostras maiores (jarro acima de 1 kg) e nas misturas com rotações acima de 2000 rpm. A maior potência de transmissão exigida causou aquecimento excessivo na transmissão, ocasionando dilatação das rodas de atrito e consequentemente travamento do sistema. Para aumentar a capacidade de moagem para até 100 g de matéria prima, que reflete a conjuntos com massas superiores a 2 kg, um protótipo utilizando engrenagens foi projetado, construído e testado. Neste trabalho concluiu-se que, através de uma rápida reconfiguração, um único equipamento híbrido atende às ambas demandas. Entretanto observou-se que como as condições otimizadas de moagem e mistura ocorreram em condições opostas, ficou evidenciado que a condição ótima para um sistema, quando aplicado no outro sistema, oferece alto risco de acidentes, o que exige o desenvolvimento de um sistema de segurança inteligente sofisticado e oneroso que, em virtude do agregado financeiro dos componentes permanentes, para aplicações nos processos industriais, aconselha-se equipamentos individuais. / Fast and effective milling and mixing of materials in small volumes is a need for laboratories and modern industry. Several methods and equipment provide these services such as planetary mill and Dual Asymmetric Centrifuge (DAC). These pieces of equipment are centrifuge machines that combine rotation and revolution and use the optimized effects of forces, directions and movements of materials in process. In the mill, the power of the milling mechanisms is optimized, being considered a high-energy process. For the mixers there is a combination of planetary motion and a tilt angle between the axis of rotation of the jar and the revolution axis, which promote effective helical vortices for mixing. The present work aims at the development of planetary mill and mixer aiming to determine optimum grinding and mixing conditions, establishment of operating limits for both applications and transmission selection. Initially hybrid grinding and mixing benches for small samples (25 g for milling and 100 g for mixing) were manufactured. The planetary mill performance was analyzed by determining particle size before and after milling of coarse calcined alumina (initial median particle size of 4.2 mm) by varying combinations of transmission ratio, translation speed and media size. For the mixer, a tilting angle of 30º was applied and tests were performed on the modeling clay mixtures applied at different rotations. For the mill configuration, the optimized design with the best experimental setup resulted in sub micrometric alumina powder (Øee ~ 0.9 mm) in only one hour of milling (revolution of 450 rpm and speed ratio main axis/jar transmission ratio of 1:-2). For the mixer configuration, the optimized condition (revolution of 2000 rpm and speed ratio of -2:1) provided relatively homogeneous mixing in 30 s. For loadings up to 25 g of ceramic powders, where the eccentric assembly (jar, fixing, raw material and grinding media) is lighter than 1kg, the transmission based on friction wheels was used, which allowed an economical and compact design, being the steel (tempered AISI 4340) the material of the friction wheel that presented the best durability and reliability. However, there was a limitation in the grinding of larger samples (jar over 1 kg) and mixtures with rotations above 2000 rpm. The higher transmission power required caused excessive heat in the transmission, causing the friction wheels to dilate and consequently system malfunction. To perform loads greater than 100g of raw material, which reflects sets with masses over 2 kg, a prototype using gears was designed, built and tested. This work concluded that a quick reconfiguration allows a single device meets both demands. However, considering that optimized parameters of grinding and mixing occur at very different conditions, it is emphasizedthat the optimal operation for a system if applied in the optimal conditions of the other system offers high risk of accidents, which requires the development of a costly security system. Therefore, individual pieces of equipment for grinding and mixing are advised for industry application due to the financial aggregate of the permanent components.

Ce mémoire présente une étude numérique du bruit aéroacoustique large bande d'une roue de ventilateur centrifuge. La recherche bibliographique démontre qu'il existe peu de méthod~s pour identifier les zones responsables de la propagation du bruit large bande des centrifuges due à la complexité de la géométrie du ventilateur. La connaissance de ces zones responsables de ce type de bruit orientera la conception d'un ventilateur silencieux. Afin d'accroître la gamme de méthode pour la localisation de ces zones, un code spécifique a été développé et présenté dans ce mémoire. L'approche utilisée vise à simuler d'une part, l'écoulement dans le ventilateur par la LES (Large Eddy Simulation) sous le logiciel Fluent. En effet, la LES permet d'avoir accès aux petites échelles responsables du bruit large bande. Ensuite, les fluctuations de pression pariétales émanant de cette simulation sont récupérées pour alimenter l'analogie acoustique. D'autre part, la puissance acoustique rayonnée est calculée par le biais du code spécifiquement développé. Ce code s'appuie sur la méthode de la décomposition modale (DOP). Finalement, on extrait les modes et les zones qui rayonnent le plus sur les pales de la roue (principale source de bruit large bande). Les résultats de validation numériques entre le code développé et le logiciel Fluent sont convaincants. En effet, les variations des champs acoustiques des deux codes sont comparables avec une différence en moyenne de 2.5dB. De plus, on obtient une atténuation du bruit par la distance qui correspond à la décroissance d'une onde plane en fonction de la distance. Les résultats d'identification des zones de la pale qui contribuent le plus au rayonnement acoustique sont également présentés dans ce mémoire. Cette technique permettra aux concepteurs d'aiguiller les modifications à faire pour rendre la roue de ventilation plus silencieuse.