Η παρούσα διατριβή ασχολείται με την καμπτική ενίσχυση δοκών οπλισμένου σκυροδέματος με στρώσεις σκυροδέματος στο εφελκυόμενο ή στο θλιβόμενο πέλμα τους. Ιδιαίτερα ασχολείται με τον προσδιορισμό της ολίσθησης στη διεπιφάνεια τους. Συγκεκριμένα στο 1ο Κεφάλαιο γίνεται βιβλιογραφική ανασκόπηση για τις διεπιφάνειες σκυροδέματος. Παρουσιάζονται όλα τα προσομοιώματα που προτείνονται είτε σε Κανονισμούς, είτε από διάφορους ερευνητές, για τον προσδιορισμό της διατμητικής αντοχής της διεπιφάνειας, καθώς και για τον προσδιορισμό της σχέσης διατμητικής τάσης – ολίσθησης στη διεπιφάνεια σκυροδέματος. Στο 2ο Κεφάλαιο, παρουσιάζεται βιβλιογραφική ανασκόπηση για τις διεπιφάνειες σκυροδέματος με χάλυβα ή σύνθετα υλικά, σε σύμμικτες κατασκευές και σε μέλη ενισχυμένα με ελάσματα χάλυβα ή από ινοπλισμένα πολυμερή (ΙΟΠ), καθώς και πειραματικά αποτελέσματα κατανομής ολίσθησης σε διεπιφάνεια δοκών οπλισμένου σκυροδέματος ενισχυμένες με στρώση σκυροδέματος. Στο 3ο Κεφάλαιο παρουσιάζεται η πειραματική διερεύνηση δοκών οπλισμένου σκυροδέματος (Ο.Σ.) ενισχυμένων με στρώσεις σκυροδέματος. Εξετάστηκαν δύο ομάδες δοκιμίων. Στην πρώτη ομάδα εξετάστηκαν τέσσερα πρισματικά δοκίμια σκυροδέματος που ενισχύθηκαν με στρώση σκυροδέματος και στη συνέχεια δοκιμάστηκαν με φόρτιση τριών σημείων. Η δεύτερη ομάδα αναφέρεται σε πέντε δοκούς Ο.Σ. ενισχυμένες επίσης με στρώση σκυροδέματος, καθώς και σε αντίστοιχες μονολιθικές δοκούς που όλες δοκιμάστηκαν με φόρτιση τεσσάρων σημείων. Σε όλα τα δοκίμια και των δύο ομάδων μετρήθηκε η αντοχή τους καθώς και η ολίσθηση στη διεπιφάνεια τους. Στο 4ο Κεφάλαιο προτείνεται αναλυτική διαδικασία για τον υπολογισμό της ολίσθησης στη διεπιφάνεια σκυροδέματος και η εφαρμογή της στα πειραματικά δοκίμια που παρουσιάστηκαν στο Κεφάλαιο 3 καθώς και σε κάποια άλλα δοκίμια της βιβλιογραφίας που παρουσιάστηκαν στο 1ο Κεφάλαιο. Το 5ο Κεφάλαιο της παρούσας διατριβής, εξετάζει την επιρροή της συστολής ξήρανσης στο μέγεθος της ολίσθησης. Στο κεφάλαιο αυτό, παρουσιάζονται πειραματικές μετρήσεις της παραμόρφωσης και ολίσθησης λόγω συστολής ξήρανσης στα δοκίμια και των δύο ομάδων πειραματικών δοκιμίων που παρουσιάζονται στο Κεφάλαιο 3 και προτείνεται αναλυτικός τρόπος υπολογισμού της ολίσθησης και της διατμητικής τάσης στη διεπιφάνεια, συνυπολογίζοντας την επιρροή της συστολής ξήρανσης. Τέλος, παρουσιάζονται τα συνολικά συμπεράσματα που προέκυψαν στα πλαίσια της παρούσας διατριβής, καθώς και προτάσεις για μελλοντική έρευνα. / The present thesis concerns the flexural strengthening of reinforced concrete (RC) beams by placing a new concrete layer on their compressive or tensile side. The main objective of the thesis is to evaluate interface slip. The first chapter is a literature review on concrete interfaces. Theoretical models, suggested by design codes or other researchers, for the calculation of the shear resistance and the relationship between the shear stress and the slip at the interface are presented. Moreover, experimental results for the shear stress against slip relationship at the concrete interface are given. The second chapter presents a literature review on the shear stress and slip distribution at concrete to steel or concrete to fibre reinforced polymer (FRP) interfaces. Theoretical and experimental results for the value of shear stress at the interface of concrete beams strengthened with steel or FRP plates and shear stress and slip distribution at the interface of composite steel and concrete beams are presented. The third chapter concerns an experimental investigation of RC beams strengthened with concrete layers. Two types of specimens are examined. The first group are prismatic RC specimens strengthened with a concrete layer and tested by three point bending. The second group contains 10 RC beams. Five are strengthened with a concrete layer on their compressive or tensile side, four are respective monolithic specimens and the final one is a control beam without any strengthening. These beams are tested under four point bending. In all tests, for both groups of specimens, load against deflection curves are determined and the slip along the interface is measured. An analytical evaluation of the slip at the interface of RC beams strengthened with concrete layers and the verification of the method comparing the analytical results with respective experimental results presented in Chapters one and three is presented in Chapter four. The shrinkage effect on interface slip and shear stress is examined in Chapter five. Experimental measurements of shrinkage strains and slip on specimens of both experimental groups presented in Chapter three are presented. An analytical evaluation of the extra slip and shear stress at the interface caused by shrinkage effect is also suggested. Finally, all results of the thesis and suggestions for future work are given.

Je me focalise sur trois grands systèmes de failles transformantes obliques au Tibet et en Californie du Sud, et ce, afin de mieux comprendre et quantifier les relations entre les différentes structures qui les définissent. L'interférométrie radar à Synthèse d'Ouverture (InSAR) dispose du potentiel pour cartographier et localiser précisément la déformation sur des zones étendues et ainsi contraindre la géométrie des structures profondes. Cependant son utilisation en milieu naturel se trouve fortement entravée par la décorrelation due à la végétation, au relief, et aux cycles de gel et dégel, mais aussi par les délais troposphériques et les rampes orbitales résiduelles. J'ai développé des méthodes pour palier ces limitations. Au Tibet, j'ai ainsi traité les archives du satellite Envisat au niveau de deux zones de lacune sismique, à la bordure Nord du plateau, se présentant comme des zones intéressantes pour étudier le partitionnement de la convergence: le système de faille de Haiyuan au north-est Tibet et la faille sénestre de l'Altyn Tagh, au nord-ouest du plateau. Une attention spécifique sur les déformations liées au pergélisol m'a permis de (1) retrouver la continuité du signal sur de grandes zones, (2) de quantifier le comportement temporel des cycles de gel et dégel des sédiments recouvrant le pergélisol, (3) d'isoler les zones stables des sédiments se déformant. Je montre que les déformations saisonnières sont fortement dépendantes des unités géomorphologiques et que la fonte du pergélisol est plus important à faible qu'à haute altitude. J'analyse aussi le signal saisonnier au travers la marche topographique et je définie un proxy pour les incertitudes de la correction atmosphérique. J'observe un gradient de déformation au travers la faille de l'Altyn Tagh de l'ordre de 11-15 mm/an et un alignement claire de la déformation dans le Tarim, parallèle à la faille de l'Altyn Tagh, ainsi que des soulèvements de l'ordre de 1 mm/an associés à des chevauchements. Ce travail montre aussi un gradient de déformation associé à la terminaison ouest de la faille du Kunlun, re-définissant ainsi la géométrie des blocs tectoniques dans cette région. Parallèlement à cette acquisition de données, je développe des outils d'inversion basés sur des algorithmes de Monte Carlo afin d'explorer l'ensemble des géométries en accord avec les observations et d'estimer la compatibilité de la déformation actuelle avec des modèles tectoniques long-termes. Je montre ainsi une convergence uniforme de 8.5-11.5 mm/an et d'orientation N81-98E à travers le système de faille d'Haiyuan et quantifie son partitionnement le long des différentes structures. Par ailleurs, j'applique mon approche en Californie du Sud, au niveau du « Big Bend » de la faille de San Andreas où, en analogie avec des modèles structuraux géologiques, j'utilise des lois de conservations du mouvement pour contraindre la géométrie des chevauchements aveugles. Je montre la compatibilité du champs de déformation actuel avec un décollement grande échelle et quantifie une accumulation de contrainte de 2.5 mm/an le long de la structure majeure sous Los Angeles. / I focus on three major oblique transform faults in Tibet and in Southern California, in order to better measure and quantify the present-day strain accumulation on these structures. Interferometric synthetic Aperture Radar (InSAR) has the potential to map and localize precisely the deformation over wide areas and thus constrain the deep geometry of these structures. However, its application in natural environments in hindered by strong decorrelation of the radar phase due to vegetation, relief, and freeze and thaw cycles, but also due to variable tropospheric phase delays across topographic feature and long-wavelength residual orbital ramps. Here, I develop methodologies to circumvent these limitations and separate tectonic from other parasite signals. In Tibet, I process data from the Envisat satellite archives, at the boundary of the Tibetan plateau, in two seismic gaps, which appear interesting to study the partitioning of the convergence: the Haiyuan Fault system in northeastern Tibet and the left-lateral Altyn Tagh Fault, in northwestern Tibet. A specific focus on the permafrost related deformation signal allows us to: (1) correctly unwrap interferograms from north to south, (2) quantify the temporal behavior of the freeze/thaw cycles, and (3) isolate bedrock pixels that are not affected by the permafrost signal for further tectonic analysis. I show that the seasonal subsidence depends greatly on the geological land unit and that lower elevations are thawing faster than higher elevations. I analyze the atmospheric signal across the high plateau margin and estimate proxy for the uncertainty on atmospheric corrections. I observe a strike-slip deformation of around 11-15 mm/yr across the Altyn Tagh fault, a clear line of concentrated strike-slip deformation of around 3 mm/yr within the Tarim basin, trending parallel to the Altyn Tagh Fault trace, as well as thrust signal uplifting terraces at a rate of 1 mm/yr. This work also shows a strain accumulation around the west extension of the south trace of the Kunlun Fault, redefining the block boundaries in northwestern Tibet. In parallel this data acquisition, I develop Monte Carlo inversion tools in order to explore the various geometries in agreement with observations and estimate the compatibility of actual surface displacements with long-term slip partitioning models. I thus show a uniform convergence rate of 8.5-11.5 mm/yr with a N81-98E across the Haiyuan fault system and quantify the partitioning along the various structures. I also apply my approach in Southern California, across the « Big Bend » of the San Andreas Fault, where, in analogy with structural geological models, I use conservation of motion to help constraining the geometry and the kinematics of blind thrust faults. I show the compatibility of surface displacements with a large-scale décollement and quantify a loading rate of 2.5 mm/yr along the major thrust structure developing under Los Angeles.

abstract: Effective tactile sensing in prosthetic and robotic hands is crucial for improving the functionality of such hands and enhancing the user's experience. Thus, improving the range of tactile sensing capabilities is essential for developing versatile artificial hands. Multimodal tactile sensors called BioTacs, which include a hydrophone and a force electrode array, were used to understand how grip force, contact angle, object texture, and slip direction may be encoded in the sensor data. Findings show that slip induced under conditions of high contact angles and grip forces resulted in significant changes in both AC and DC pressure magnitude and rate of change in pressure. Slip induced under conditions of low contact angles and grip forces resulted in significant changes in the rate of change in electrode impedance. Slip in the distal direction of a precision grip caused significant changes in pressure magnitude and rate of change in pressure, while slip in the radial direction of the wrist caused significant changes in the rate of change in electrode impedance. A strong relationship was established between slip direction and the rate of change in ratios of electrode impedance for radial and ulnar slip relative to the wrist. Consequently, establishing multiple thresholds or establishing a multivariate model may be a useful method for detecting and characterizing slip. Detecting slip for low contact angles could be done by monitoring electrode data, while detecting slip for high contact angles could be done by monitoring pressure data. Predicting slip in the distal direction could be done by monitoring pressure data, while predicting slip in the radial and ulnar directions could be done by monitoring electrode data. / Dissertation/Thesis / M.S. Bioengineering 2012

X / A combined experimental and computational investigation of the deformation behavior of pure magnesium single crystal at the micron length scale has been carried out. Employing the recently exploited method of microcompression testing, uniaxial microcompression experiments have been performed on magnesium single crystals with [0001], [2-1-12], [10-11], [11-20] and [10-10] compression axes. The advantage of the microcompression method over conventional mechanical testing techniques is the ability to localize a single crystalline volume which is characterizable after deformation. The stress-strain relations resulting from microcompression experiments are presented and discussed in terms of orientation dependent slip activity, twinning mechanisms and an anisotropic size effect. Such a mechanistic picture of the deformation behavior is revealed through SEM, EBSD and TEM characterization of the deformation structures, and further supported by 3D discrete dislocation dynamics simulations. The [0001], [2-1-12], and [10-11] compression axes results show dislocation plasticity. Specifically, the deformation due to [0001] compression is governed by pyramidal slip and displays significant hardening and massive unstable shear at stresses above 500MPa. In the case of the two orientations with compression along an axis 45 degrees to the basal plane, unsurpringly it is found that basal slip dominates the deformation. In contrast, compression along the [11-20] and [10-10] directions show deformation twinning in addition to dislocation plasticity. In the case of compression along [11-20], the twinning leads to easy basal slip, while the twin resultant during compression along [10-10] does not lead to easy basal slip. In all cases, a size effect in the stress-strain behavior is observed; the flow stress increases with decreasing column diameter. Furthermore, the extent of the size effect is shown to depend strongly on the number of active slip systems; compression along the [0001] axis is associated with 12 slips systems and displays a saturation of the size effect at a diameter of 10μm, while the other orientations still show a significant size effect at this diameter. The experimental evidence of an orientation-dependent deformation behavior in flow stress has been investigated by 3D discrete dislocation dynamics simulations. Here, the code TRIDIS was modified for hcp structure and c/a ratio of Mg. By matching the simulation results to experimental results, some proper constitutive material parameters such as initial dislocation density, dislocation source length, the critical resolved shear stress were suggested. For the case of [0001] and [2-1-12] orientation, dislocation feature in the pillar during the deformation was exhibited and strain burst was discussed.

During space missions, real time tele-operation of a rover is not practical because of significant signal latencies associated with inter planetary distances, making some degree of autonomy in rover control desirable. One of the challenges to achieving autonomy is the determination of terrain traversability. As part of this field, the determination of motion state of a rover on rough terrain via the estimation of wheel-terrain contact angles is proposed. This thesis investigates the feasibility of estimating the contact angles from the kinematics of the rover system and measurements from the onboard inertial measurement unit (IMU), joint angle sensors and wheel encoders. This approach does not rely on any knowledge of the terrain geometry or terrain mechanical properties. An existing framework of rover velocity and wheel slip estimation for flat terrain has been extended to additionally estimate the wheel-terrain contact angle along with a side slip angle for each individual wheel, for rough terrain drive. A random walk and a damped model are used to describe the evolution of the contact angle and side slip angle over an unknown terrain. A standard strapdown algorithm for the estimation of attitude and velocity from IMU measurements, is modified to incorporate the 3D kinematics of the rover in the implementation of a nonlinear Kalman filter to estimate the motion states. The estimation results from the filter are verified using tests performed on the ExoMars BB2. The obtained contact angle estimates are found to be consistent with the reference values.

The master thesis deals with possibilities of utilization of conventional power plant fly ash after introduction of SNCR (Selective non-catalytic reduction) as a method of flue gas denitrification. Behaviour of fly ash containing products of denitrification, ash with water and stabilizate prepared from contaminated ash was studied. Experiments were focused on the study of various factors affecting the release of ammonia from prepared mixtures. Samples were exposed to the weather conditions to simulate deposition in addition to the laboratory experiment. Influence of the fly ash containing denitrification to mechanical properties and volume stability of pastes and mortars were also studied. The interaction of denitrification products with superplasticizers was studied on pastes. Achieved results were verified on concretes.

A falta de controle e planejamento dos espaços públicos, entre eles, as calçadas, gera problemas como a falta de segurança e de acesso aos equipamentos urbanos e até impede a livre circulação das pessoas. As calçadas são uma pequena, mas importante parte da complexa infraestrutura urbana. O provimento de calçadas adequadas é um meio de incentivo ao deslocamento a pé e ao uso de transporte coletivo. A calçada não deveria oferecer nenhum risco aos pedestres, porém, grande parte das calçadas existentes no Brasil é imprópria para a circulação, seja pela existência de obstáculos, seja pela precariedade ou inadequação dos materiais utilizados em sua construção. Essa falta de qualidade das calçadas é a causa de muitos acidentes. Os pedestres em geral e, além dos idosos, principalmente as crianças e as pessoas portadoras de necessidades especiais, podem ser considerados usuários vulneráveis. No presente trabalho, as exigências dos usuários, no que se refere à segurança em uso, de acordo com a abordagem de desempenho, foram identificadas como sendo segurança ao risco de quedas, segurança ao risco de atropelamentos, segurança ao risco de lesões por choque e acessibilidade. As exigências dos usuários foram traduzidas em requisitos de desempenho a serem cumpridos em calçadas seguras e, após, foram identificados os respectivos critérios, níveis de atendimento e métodos de avaliação, com base na legislação e bibliografia. Com isso, foi elaborado um instrumento de avaliação de segurança em calçadas. Um estudo de caso em um trecho da Av. Independência, em Porto Alegre, foi realizado para testar o instrumento elaborado, com aplicação experimental em 17 calçadas. O instrumento mostrou-se eficiente na aquisição, processamento e registro de dados. Para a validação definitiva do instrumento, é necessário que se amplie os testes. Além disso, foi realizada pesquisa exploratória com aplicação do ensaio com o Pêndulo Britânico, para avaliação da resistência ao escorregamento. Todas as calçadas foram aprovadas quanto a este critério. O método de avaliação se mostrou adequado, porém limitado a calçadas com pequena inclinação. Adicionalmente, as diversas falhas relativas à segurança encontradas nas calçadas avaliadas foram analisadas. Nenhuma calçada do estudo de caso foi aprovada e considerada segura. A calçada com pior desempenho atendeu a apenas 38,88% dos critérios. Já o melhor resultado foi de uma calçada com taxa de atendimento aos critérios de 68,42%. Os critérios menos atendidos foram o desnível em relação à via, o rebaixo para acesso de veículos adequado, rampa nos pontos de travessia e a sinalização tátil no piso. Diante da grande quantidade de falhas encontradas no estudo de caso, aponta-se a ausência de um técnico no processo de construção de uma calçada, como uma das principais causas das não conformidades, junto à falta de um documento, preferencialmente uma Norma Técnica, que reúna as informações necessárias para o projeto de calçadas. Desta forma, este trabalho visa contribuir para o tema desempenho de calçadas, com foco nos requisitos relativos à segurança dos usuários. / The absence of control and planning of public spaces, including sidewalks, creates problems such as lack of security and access to urban equipment and even prevents the free movement of people. The sidewalks are a small but important part of the complex urban infrastructure. Providing adequate sidewalks is a means of encouraging walking and the use of public transport. The sidewalk should not pose any risk to pedestrians, but most of the existing sidewalks in Brazil are unfit for circulation, either by the existence of obstacles, or by the precariousness or inadequacy of the materials used in their construction. This lack of quality in sidewalks is the cause of many accidents. Pedestrians in general and, in addition to the elderly, especially children and people with special needs, can be considered vulnerable users. In this work, users' requirements regarding safety in use, according to the performance approach, have been identified as safety for the risk of falls, safety for the risk of pedestrian crashes, safety for the risk of shock injuries and accessibility. The users’ requirements were translated into performance requirements to be met on safe sidewalks and, afterwards, the respective criteria, suitable levels and evaluation methods were identified, based on legislation and bibliography. And therewith, a safety assessment instrument for sidewalks was developed. A case study on an excerpt from Av. Independência, in Porto Alegre, was carried out to test the instrument, with experimental application on 17 sidewalks. The instrument was efficient in data acquisition, processing and recording. For definitive validation of the instrument, it is necessary to expand the tests. In addition, an exploratory study was carried out with the application of the British Pendulum test to evaluate the slip resistance. All sidewalks were approved for this criterion. The method of evaluation was adequate, but limited to sidewalks with a small slope. In addition, the various safety flaws found on the evaluated sidewalks were analyzed. No sidewalk from the case study was approved and considered safe. The sidewalk with the poorest performance met only 38.88% of the criteria. The best result was a sidewalk with a rate of meeting the criteria of 68.42%. The least attended criteria were the height in relation to the roadway, adequate vehicle access ramp, ramp at crossing points and tactile signage on the ground. Considering the large number of flaws found in the case study, it is pointed out that the absence of a technician in the process of building a sidewalk is one of the main causes of nonconformities, due to the lack of a document, preferably a Technical Standard, that gathers the necessary information for sidewalk projects. Thus, this work aims to contribute to the theme of performance of sidewalks, focusing on requirements regarding user safety.

L'objectif initial de cette thèse consistait à fournir un analogue de terrain de réservoirs pétroliers avec un modèle 3D des structures et de l'architecture des sédiments développés sur la bordure d'un basin étroit et confiné. La zone d'étude, située entre Bakio et Plenzia (Pays Basque, Espagne), appartient au fossé Basque, souvent interprété comme un basin en pull-apart. Nous avons focalisé ce travail sur le diapir de Bakio, sur les modalités de la montée du sel, sa chronologie et sur l'impact de la tectonique salifère sur sédimentation et la déformation des sédiments environnants. Un éventail sédimentaire composé de dépôts albiens, avec un amincissement vers le diapir montre la monté synsédimentaire du sel. Nous démontré l'existence d'une première phase de montée du sel réactive puis une seconde phase passive. La phase réactive est expliquée par l'extension régionale. Durand le stade passive, des séquences halokinetiques, qui résultent de variations entre la monté du sel et le taux de sédimentation, ont été formées. Nos données montre qu'une grande partie de la déformation est due à la rotation des flancs du diapir et non à un cisaillement significatif induit par la montée su sel. Nous avons aussi concentré ce travail sur les structures albiennes de notre zone d'étude. La comparaison avec l'ensemble du Bassin Basco Cantabrien montre deux stades d'activation des failles. De l'Aptien à l'Albien moyen, les nombreuses failles orientées NE-SO, largement distribuées,contrôlaient les plates formes urgoniennes et les fossés marneux associés. Quelques failles majeures héritées, orientées NO-SE contrôlaient aussi les dépocentres surtout dans la partie centrale du Basin Basco-Cantabrien. Ce premier stage est interprété comme le résultat d'un extension NO-SE. De l'Albien moyen à supérieur, la déformation était localisée essentiellement le long de la faille Guernika-Elgoibar, orientée NO-SE, qui contrôle un bassin asymétriques, étroit et allongé remplis par les Flyschs Noirs. Durant le second stage, les dépocentres du Flysch Noir sont interprétés comme des bassins en transtension et non en pull-apart, car une seule faille majeure contrôlait ces basins asymétriques. / The initial purpose of this thesis was to provide a field analogue for petroleum reservoirs with a 3D model of the main structures and of the architecture of deposits developed on the border of a narrow and confined basin. The study area, located between Bakio and Plenzia (Basque Country, Spain), belongs to the Basque Trough, commonly interpreted as a pull-apart basin. We focused on the Bakio diapir, which allows a discussion of the modalities of salt rising, its chronology and of the impacts of salt on the overburden deformation and on sedimentation. A well exposed wedge-shaped structure composed of Albian deposits, with thinning toward the diapir documents synsedimentary salt rising. We showed that the diapir rose firstly as a reactive diapir in response to regional extension and then as a passive diapir. During the passive stage, halokinetic sequences developed, induced by variations of the ratio between net salt rising and net sedimentation rate. All our data from the Bakio diapir show that an important part of deformation is related to diapir flank rotation and not to significant shear associated with salt rising. We also focused on the Albian structural geology in our study area. The comparison of the local Albian fault system with faults from the whole Basque-Cantabrian Basin emphasizes two stages of faults activity. From Aptian to Early-Middle Albian, widely distributed NE-SW striking faults controlled the development of the Urgonian platforms and associated marly troughs. Some major inherited NW-SE striking faults also controlled the localization of depocenters, especially in the central part of the Basque-Cantabrian Basin. The first stage is assumed to result of a NW-SE extension. From Middle to Late Albian, the deformation localized mainly along the Gernika-Elgoibar fault, striking NW-SE, and controlled the formation of a narrow and elongated asymmetric basin developed, filled by Black Flysch units. During this second stage, Black Flysch depocenter are interpreted to form in transtensional setting and cannot be interpreted as pull-apart basins, as only one major fault controlled asymmetric basins.

Ces dernières années ont vu le développement d'une nouvelle méthode d'imagerie des structures géologiques basée sur l'utilisation du bruit sismique continu. Dans ce travail nous avons utilisé cette approche dans deux problématiques différentes. La première consiste à réaliser le suivi temporel des vitesses des ondes sismiques dans la croûte lors de séismes lents qui ont eu lieu dans la région de Guerrero au Mexique. Les séismes lents sont des glissements asismiques et transitoires qui ont été découverts récemment dans la lacune sismique de Guerrero. Ils sont considérés comme une part importante de la relaxation des déformations dans le cycle sismique. Les séismes lents affectent le processus de chargement et déchargement de l'interface, il est donc important de comprendre le comportement mécanique de la subduction dans cette région pour mieux évaluer le risque sismique. Dans notre étude, nous avons mesuré les perturbations de vitesse des ondes associées à deux séismes lents en 2006 et 2009-2010 à partir des enregistrements continus du bruit sismique. Pour chacun des deux séismes lents on observe une chute de vitesse : elle s'élève à 0.2% pour celui de 2006 et à 0.8 % pour celui de 2009-2010. Au cours de ces séismes lents, les ondes de longues périodes (>10 s) sont perturbées. A courtes périodes, aucune variation de vitesse n'est observée ce qui suggère qu'un endommagement des couches superficielles de la croûte ne peut pas être à l'origine du changement de vitesse. Par ailleurs, la perturbation de vitesse est reliée au taux de dé- formation plutôt qu'à la déformation elle-même. Cette observation suggère que pendant de forts séismes lents, la croûte chevauchante présente un comportement mécanique non linéaire. Nous pouvons donc utiliser les variations de vitesse comme des marqueurs du taux de déformation du milieu. Enfin, une corrélation entre les trémors non volcaniques et les variations de vitesse suggère qu'une part importante de la déformation résultant des séismes lents est accommodée par la croute chevauchante. La deuxième problématique abordée dans cette thèse est l'imagerie de structures à fort contraste de vitesse et dans lesquelles la propagation des ondes de surface est complexe. Imager et comprendre la propagation des ondes dans la vallée de Mexico est crucial pour l'estimation du risque sismique à la capitale. Nous mesurons la dispersion des ondes de Rayleigh reconstruites à partir d'intercorrélations de bruit de fond sismique. Pour identifier les modes nous utilisons une mesure du rapport spectral des composantes horizontales sur la composante vertical (H/V) sur la coda des séismes que l'on compare avec le rapport H/V théorique. Grâce à cette identification des modes, nous pouvons retrouver le modèle de vitesse de la structure. / Recent years have seen the development of a new method for imaging geological structures based on continuous seismic noise. In this work we used this approach in two different problems. The first is to monitor seismic waves velocity in the crust during slow slip events that occurred in the region of Guerrero in Mexico. These slow slip events are aseismic transients that were observed recently in the seismic gap of Guerrero. They are considered an important part of the strain relaxation in the seismic cycle. Since slow slip events affect the process of loading and unloading of the interface, it is important to understand the mechanical behavior of the subduction in this region to better assess the seismic risk. In our study, we measured wave velocity perturbations associated with two slow slip events in 2006 and 2009-2010 from continuous recordings of seismic noise. For both events we observed a drop in wave speed : it reaches 0.2 % in 2006 and 0.8 % in 2009-2010. During these slow slip events waves of long periods (> 10 s) are disturbed. At short period, no velocity variation is observed suggesting that damage of the superficial layers of the crust cannot produce such velocity perturbation. Moreover, the wave speed change is related to the strain rate rather than the deformation itself. This observation suggests that during strong slow slip events the overriding crust presents a nonlinear mechanical behavior. We can therefore use the velocity variations as a proxy of the strain rate of the medium. Finally, a correlation between non-volcanic tremor and changes in waves speed suggests that part of the deformation resulting from the slow slip events is accommodated by the overriding crust. The second issue addressed in this thesis is imaging geological structures with high velocity contrast in which the propagation of surface waves is complex. Charac- terizing and understanding wave propagation in the Valley of Mexico is crucial for the estimation of seismic risk in Mexico City. We measure the dispersion of Rayleigh waves reconstructed from cross-correlations of seismic noise. To identify the modes of Rayleigh waves we use a measure of the spectral ratio of the horizontal components to the vertical component (H / V) in the coda of earthquakes which are compared with the theoretical H / V. With this identification method, we can find the velocity model of the structure.

Thesis submitted in fulfillment of the requirements for the degree Doctor of Technology: Mechanical Engineering Cape Peninsula University of Technology, 2013 / Fluid flow through a porous channel and cylindrical pipe walls are important area of research due to its wide applications in transpiration cooling, gaseous diffusion technology, cooling of rocket, mechanized irrigation and filtration processes. It is therefore necessary to examine the effect of Navier slip, combined effects of buoyancy forces and variable viscosity on the entire flow structure. Analyzing the magneto- hydrodynamics (MHD) of unsteady flow with buoyancy effect and also investigate numerically the entropy generation in an unsteady flow through porous pipe. We have also examined the thermal stability and entropy generation in the system. The problems were investigated theoretically using appropriate mathematical models for both transient and steady state scenario. Both analytical techniques and numerical methods are employed to tackle the model nonlinear equations derived from the law of conservation of mass, momentum and energy balance. Some definitions of terms to come across and introduction to fluid flow are given in chapter 1, together with literature reviews, statement of problem and objectives of the study. Chapter 2 lays the foundation for basic fundamental equations governing fluid flow. In chapter 3, the combined effect of suction/injection and asymmetric Navier slip on the entropy generation rate for steady flow of an incompressible viscous fluid through a porous channel subjected to different temperature at the walls are investigated. Chapter 4 analyze combined effects of buoyancy forces together with Navier slip on the entropy generation in a vertical porous channel wall with suction/injection wall. Analysis of MHD unsteady flow through a porous pipe with buoyancy effects are carried out in chapter 5, while chapter 6 investigates numerically entropy generation of unsteady flow through a porous pipe with suction and chapter 7 gives concluding remarks.