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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Thermo-hydro-mechanical analysis of soft rock. Application to a large scale heating test and large scale ventilation test

Muñoz, Juan Jorge 30 March 2007 (has links)
Esta Tesis está dirigida al análisis teórico y experimental de problemas acoplados Termo-Hidro Mecánico (THM) que se desarrollan en formaciones geológicas profundas destinadas al almacenamiento de residuos radiactivos de alta actividad. En las últimas décadas, han sido estudiadas las formaciones arcillosas para ser utilizadas como barreras geológicas debido a su reducida conductividad hidráulica. La degradación de las rocas arcillosas producida por efectos de temperatura y por efectos de variación en el grado de saturación, es un factor de fundamental importancia, que es actualmente investigado en ensayos in situ a gran escala, como así también en ensayos de laboratorio. En ésta tesis, la roca Opalinus Clay ha sido ampliamente caracterizada mediante ensayos de laboratorios. Desde un punto de vista macro-estructural se ha obtenido la curva de retención de agua, conductividad hidráulica, resistencia y deformación. El análisis micro-estructural está enfocado a la caracterización mineralógica obtenida por difracción de rayos X, la distribución del tamaño de los poros determinada por porosimetría de mercurio (MIP) y microscopía electrónica (SEM). La tesis describe también un ensayo in situ de calentamiento diseñado para analizar la interacción entre la barrera de ingeniería (bloques de bentonita compactada) y la barrera geológica (Opalinus clay). Esta interacción ha sido analizada a través de simulaciones numéricas realizadas con el código de elementos finitos CODE_BRIGHT. Una célula termo-hidráulica fue especialmente diseñada para observar el comportamiento THM de la roca en condición drenada y no drenada, a través de pulsos de calor. Parámetros térmicos e hidráulicos de la roca fueron determinados por retro análisis a través de simulaciones numéricas realizadas con CODE_BRIGHT. Desde el punto de vista mecánico, un modelo constitutivo ha sido formulado en 3D e implementado en CODE_BRIGHT con el objetivo de reproducir el comportamiento mecánico anisótropo y rotura frágil de las rocas arcillosas. El modelo es formulado en un marco viscoplástico y considera la resistencia y deformabilidad de la matriz y de las juntas. El criterio de falla de la matriz y de las juntas es definido por superficies de fluencias hiperbólicas en el espacio de tensiones p-J y τ−σ, respectivamente. El comportamiento frágil de las rocas arcillosas es simulado por un reblandecimiento isótropo y cinemático definido en términos de trabajo de deformación plástico. El modelo constitutivo ha sido calibrado mediante ensayos triaxiales de laboratorio realizados en especimenes con diferentes ángulos de buzamiento. El modeloconstitutivo anisótropo ha sido aplicado a la simulación numérica en 3D de un ensayo de calentamiento in-situ. Una simulación numérica en 3D de un ensayo de ventilación in-situ realizado en un micro-túnel sin recubrimiento ha sido realizada para reproducir el brusco cambio de permeabilidad por efectos de secado de la roca. En este caso, un modelo hidráulico que considera la apertura de las juntas por efectos de secado ha sido implementado para reproducir los cambios de permeabilidad en excavaciones subterráneas. / This thesis deals with the theoretical and experimental analysis of the coupled Thermo- Hydro-Mechanical (THM) processes developed in geological formations suitable for the repository of radioactive waste of high activity. In the last decades, the argillaceous formations have been studied to be used as geological barriers, due to its reduced hydraulic conductivity. The degradation of clay shales induced by temperature and saturation effects is an important factor which is currently being investigated in large scale in situ tests as well as in laboratory studies. In this thesis, the Opalinus clay rock has been widely characterized by means of laboratory tests. From a macro-structural point of view, the water retention curve, hydraulic conductivity, strength and deformability parameters have been determined. The micro-structural analysis is focused to the mineralogical characterization obtained by means of X ray diffraction, pore size distribution (PSD) determined by means of mercury intrusion porosimetry (MIP) and scanning electronic microscopy (SEM). The thesis describes also a large scale heating in situ test designed to analyze the interaction between the engineer barrier (compacted bentonite blocks) and by the geological barrier, (Opalinus clay). This interaction has been analyzed by means of numerical simulations performed with the finite element code CODE_BRIGHT. A thermo hydraulic cell was specially designed to observe the coupled THM behaviour of the clay shale rock under drained and undrained conditions by means of heat pulses. Thermal and hydraulic parameters of rock were determined by means of back-analysis performed with the help of CODE_BRIGHT. In order to reproduce the anisotropic and brittle behaviour of the clay shale, a 3D mechanical constitutive model has been formulated and implemented in CODE_BRIGHT. The constitutive model is formulated in a viscoplastic framework and it considers the strength and deformability of both matrix and discontinuities (joints). The failure criterion of the matrix and the joints is defined by means of hyperbolic yield surfaces in the p-J and τ-σ stress space, respectively. The brittle behaviour of clay shale is simulated by means of isotropic and kinematic softening defined in terms of a workhardening criterion. The anisotropic constitutive model has been calibrated against triaxial laboratory tests performed on specimens with a main family of discontinuities having different dip angles. The constitutive model has been applied to a 3D numerical simulation of an "in-situ" heating test. A 3D numerical simulation of a ventilation test performed in an unlined micro tunnel was also performed in order to reproduce the changes of the rock permeability by drying effects. In this case, a hydraulic model able to consider the changes in joint thickness by drying effects has been developed to reproduce the changes of permeability in underground excavations.
2

Open Innovation in EVs: A Case Study of Tesla Motors

Karamitsios, Achilleas January 2013 (has links)
This study examines the topic of open innovation in EVs. Initially a brief description of the concept of innovation and open innovation is carried out. Moreover, the three processes of open innovation are deployed while the coupled process is described in more detail. Furthermore, a short description is also given for corporate entrepreneurship, alliances, and the U.S. government policy. Also, this report considers Tesla Motors’ partnerships as a case study and it aims to give an insight of how the coupled process of open innovation is. Concluding, Tesla Motors follows the coupled innovation process by establishing strategic partnerships.

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