The present thesis is composed of two parts. The first part presents the chemo-mechanical effect on the volumetric and shearing behaviour of saturated soil as a continuum. The second part presents the chemo-mechanical effect on the shearing behaviour of a discontinuity. Following Gajo and Loret, 2003, saturated soil is considered as a two-phase deformable porous medium, namely solid and fluid phase consisting of different species. There are clay particles, adsorbed water and ion in the solid phase. The fluid phase includes pore water and salt which may diffuse through the porous medium. In addition, water may be exchanged between solid and fluid phases while the mass of clay particles and ions in the solid phase remains constant. Thus, the balance equations are momentum balance, the mass balance of pore water and salt in the fluid phase, the mass balance of absorbed water. A two-dimensional element is proposed to approximate the solution of the balance equations which has been implemented in a user-defined subroutine (UEL) of the commercial code ABAQUS. This element has taken into account the 2D displacement of the soil skeleton, multidimensional flow of water, osmotic effect, advection and diffusion of salt. A new hyperelastic law is presented by extending the chemo-mechanical model proposed by Loret et al., 2002. The innovative aspects of the proposed model are the following: 1) both the tangent shear stiffness and bulk stiffness depend on the applied stress state and pore water solution, 2) the anisotropy of fabric tensor is introduced in the elasticity law. Moreover, the yield function has been modified to obtain smaller peak strength for highly overconsolidated samples to have better agreement with experimental results. The proposed 2D model is validated with experimental results on natural bentonite (a very active clay) and the soil extracted from low activity clay of Costa della Gaveta slope in Southern Italy. The swelling and swelling pressure of these two types of soil have been computed and compared with the experimental data to show the accuracy and reliability of the proposed model. Furthermore, the effects of elastic anisotropy are investigated on the soil behaviour such as swelling, swelling pressure, stress paths and horizontal stress. Furthermore, a simplified analysis has been performed to show the effect of swelling pressure on slope stability. In the second part, a contact element is proposed to account for the flow of water and diffusion of salt in addition to displacement in the simulation of interface behaviour. This element has been implemented in a user-defined subroutine (UEL) of ABAQUS. Moreover, a nonlinear elasticity law is proposed in which traction in the contact region has been taken into account. The Mohr-Columb yield criterion is used for the plastic regime in which it is assumed that the friction angle is a function of salt concentration and displacement rate based on the experimental data. Some preliminary results are shown for the flux of salt and water through the element. In addition, the effects of salt concentration and displacement rate are presented on the shearing behaviour of the contact element.

Hydraulic fracturing is an important and abundant process in both industrial applications and natural environments. The current work is the first systematic quantitative study of the effect of interaction in and between complex hydraulic fractures at different spatial scales. A mathematical model, based on the boundary collocation method, has been developed. The model has been employed for a typical field case, a highly segmented vein. This vein is well-mapped, and therefore, represents a well constrained example. The computed apertures are compared to the measured apertures. By using the simplest constitutive model, based on an ideal elastic material, and including the effect of interaction between the segments, it was possible to obtain an excellent match at all considered scales. It was also shown that the concept of effective fracture, as currently accepted in the literature, is not always applicable and may lead to unbounded inaccuracy. Unfortunately, in most cases, very little (if any) directly measured data on fracture and material properties is available. An important example of such a weakly constrained case, involving hydraulic fracturing, is diking beneath the seafloor at mid-oceanic ridges. In this study, it is shown that the commonly accepted scenario of a dike propagating from the center of the pressurized magma chamber to the ocean floor is not consistent with conventional fracture mechanics due to the fact that the chamber has the shape of a thin lens. Even at such a large scale (i.e., a kilometer or more), the mechanical principles of elastic interaction appear to be applicable. Since diking is likely to generate a region of high permeability near its margin, in addition to heat, the ongoing hydrothermal activity becomes localized. Our modeling suggests the probable positions of the propagating dikes. Consequently, comparing the observed locations of hydrothermal sites with respect to that of the magma chamber could be useful for constraining the mechanisms of magma lens evolution.

Modern 'more-electric' aircraft demand increased levels of electrical power as non-propulsive power systems are replaced with electrical equivalents. This electrical power is provided by electrical generators, driven via a mechanical transmission system, from a rotating spool in the gas turbine core. A wide range of electrical loads exist throughout the aircraft, which may be pulsating and high powered, and this electrical power demand is transferred though the generators to produce a torque load on the drivetrain. The mechanical components of the drivetrain are designed for minimum mass and so are susceptible to fatigue, therefore the electrical loading existing on modern airframes may induce fatigue in key mechanical components and excite system resonances in both mechanical and electrical domains. This electro-mechanical interaction could lead to a reduced lifespan for mechanical components and electrical network instability.This project investigates electro-mechanical interaction in the electrical power offtake from large diameter aero gas turbines. High fidelity modelling of the drivetrain, and generator, allow the prediction of system resonances for a generic gas turbine-generator system. A Doubly-Fed Induction Generator (DFIG) is considered and modelled. DFIGs offer opportunities due to their fast dynamics and their ability to decouple electrical and mechanical frequencies (e.g. enabling a constant frequency electrical system with a variable speed mechanical drive). A test platform is produced which is representative of a large diameter gas turbine and reproduces the electro-mechanical system behaviour. The test platform is scaled with respect to speed and power but maintains realistic sizing between component dimensions which include: a gas turbine mechanical spool emulation, transmission driveshafts and gearbox, and accessory loads such as a generator. This test platform is used to validate theoretical understanding and suggest alternative mechanical configurations, and generator control schemes, for the mitigation of electro-mechanical interaction.The novel use of a DFIG and an understanding of electro-mechanical interaction allow future aircraft designs to benefit from the increased electrification of systems by ensuring that sufficient electrical power can be provided by a robust gas turbine-generator system.

Sustainability is one of the most critical issues in today's packaging and supply chain industries. With the increase of environmental concerns, there has been a tremendous effort to improve packaging sustainability. However, most of these works have focused on individual packaging components rather than an integrated unit load. In global supply chains, three levels of packaging components (primary, secondary, and tertiary) are commonly assembled in the unit load form to facilitate efficient and economical storage and transport of goods to customers. Unit loads is important to improved, packaging sustainability. This study developed the fundamental information that facilitates understanding and enhanced sustainability of unit loads from two different perspectives: physical interactions and end-of-life options of unit load components. From the physical interaction perspective, the effects of various characteristics of secondary and tertiary packaging components on load-bridging within unit loads are investigated.. Packaging component characteristics investigated included the flute type and size of corrugated paperboard boxes, stretch wrap containment force, and pallet stiffness. From the end-of-life option perspective, process methods and environmental impacts of wood pallet repair in the United States are analyzed to provide fundamental information for accurate life cycle assessment of pallets. The experimental results of this study demonstrate that the size of corrugated paperboard boxes and stretch wrap containment force significantly affected the bridging of loads on pallets. The results regarding load-bridging, verified in this study, provides essential knowledge regarding factors influencing unit load deflection. Pallet design procedure should include the load-bridging effect. For simulated pallets which was comparable to a stringer class wood pallet spanning the width of a storage rack, average deflection in the unit load decreased by 70% when package size increased to 20 in. x 10 in. x 10 in. from 5 in. x 10 in. x 10 in. In addition, average deflection in the unit load consisting of 5 in. x 10 in. x 10 in. packages decreased by 50% when stretch wrap containment force increased to 30 lbs. from zero pounds. Updated design methods that consider the effect of packaging characteristics on unit load deflection can help to reduce the amount of raw materials required to build pallets using current pallet design methodologies. The life cycle inventory analysis results of this study determined that pallet repair is an environmentally beneficial end-of-life option for 48 by 40- inch stringer class wood pallets in terms of greenhouse gas generation. Most wood pallet repair firms in the United States utilized high levels of manual labor with non-automated machinery support. The life cycle inventory results from this study can be a useful resource for researchers as an input to the life cycle assessment. / Ph. D.

No description available.

Ce travail de thèse s’inscrit dans le cadre de l’étude de l’Interaction mécanique Pastille-Gaine (IPG) se produisant dans les crayons combustibles des réacteurs à eau pressurisée. Ce mémoire porte sur le développement de méthodes de raffinement de maillage permettant de simuler plus précisément le phénomène d’IPG tout en conservant des temps de calcul et un espace mémoire acceptables pour des études industrielles. Une stratégie de raffinement automatique basée sur la combinaison de la méthode multi-grilles Local Defect Correction (LDC) et l’estimateur d’erreur a posteriori de type Zienkiewicz et Zhu est proposée. Cette stratégie s’appuie sur l’erreur fournie par l’estimateur pour détecter les zones à raffiner constituant alors les sous-grilles locales de la méthode LDC. Plusieurs critères d’arrêt sont étudiés afin de permettre de stopper le raffinement quand la solution est suffisamment précise ou lorsque le raffinement n’apporte plus d’amélioration à la solution globale.Les résultats numériques obtenus sur des cas tests 2D élastiques avec discontinuité de chargement permettent d’apprécier l’efficacité de la stratégie proposée.Le raffinement automatique de maillage dans le cas de problèmes de contact unilatéral est ensuite abordé. La stratégie proposée dans ce travail s’étend aisément au raffinement multi-corps à condition d’appliquer l’estimateur d’erreur sur chacun des corps séparément. Un post-traitement est cependant souvent nécessaire pour garantir la conformité des zones de raffinement vis-à-vis des frontières de contact. Une variété de tests numériques de contact entre solides élastiques confirme l’efficacité et la généricité de la stratégie proposée. / This Ph.D. work takes place within the framework of studies on Pellet-Cladding mechanical Interaction (PCI) which occurs in the fuel rods of pressurized water reactor. This manuscript focuses on automatic mesh refinement to simulate more accurately this phenomena while maintaining acceptable computational time and memory space for industrial calculations. An automatic mesh refinement strategy based on the combination of the Local Defect Correction multigrid method (LDC) with the Zienkiewicz and Zhu a posteriori error estimator is proposed. The estimated error is used to detect the zones to be refined, where the local subgrids of the LDC method are generated. Several stopping criteria are studied to end the refinement process when the solution is accurate enough or when the refinement does not improve the global solution accuracy anymore.Numerical results for elastic 2D test cases with pressure discontinuity shows the efficiency of the proposed strategy.The automatic mesh refinement in case of unilateral contact problems is then considered. The strategy previously introduced can be easily adapted to the multibody refinement by estimating solution error on each body separately. Post-processing is often necessary to ensure the conformity of the refined areas regarding the contact boundaries. A variety of numerical experiments with elastic contact (with or without friction, with or without an initial gap) confirms the efficiency and adaptability of the proposed strategy.