<p>The overall aim of this thesis was to discuss kinematics and muscle function changes due to foot and ankle injury or deformity. The first study aims to characterize gait patterns of subjects with a common lower limb injury, ankle fractures. Using three-dimensional movement analysis with a modified multi-segment foot model, the inter-segment foot kinematics was determined during gait in 18 subjects one year after surgically treated ankle fractures. Gait data were compared to an age- and gender-matched control group and the correlations between functional ankle score and gait parameters were determined. It was observed that even with fairly good clinical results, restricted range of motion at and around the injured area, and less adducted forefoot were found in the injured limb. The second study aims to quantify the effect of subtalar inversion/eversion on the dynamic function of the main ankle dorsi/plantarflexors: gastrocnemius, soleus and tibialis anterior. Induced acceleration analysis was used to compute muscle-induced joint angular and body center of mass accelerations. A three-dimensional subject specific linkage model was configured by gait data and driven by 1 Newton of individual muscle force. The excessive subtalar inversion or eversion was modified by offsetting up to ±20˚ from the normal subtalar angle while other configurations remain unaltered. We confirmed that in the normal gait, muscles generally acted as their anatomical definitions and muscles can create motion in joints, even not spanned by the muscles. The plantarflexors play important roles in body support and forward progression. Excessive subtalar eversion had negative effect on ankle plantarflexion, which may induce a less plantarflexed ankle, less extended knee and more flexed hip after initial contact. This thesis focused on gait kinematics and muscle functions in the foot and ankle area employing both experimental gait and computational simulations. The findings can be regarded as references for evaluating of future patients and for dynamic muscle functions during gait.</p>

<p>Converging cylindrical shock waves have been studied experimentally. Numericalcalculations based on the Euler equations and analytical comparisons basedon the approximate theory of geometrical shock dynamics have been made tocomplement the study.Shock waves with circular or polygonal shock front shapes have been createdand focused in a shock tube. With initial Mach numbers ranging from 2 to4, the shock fronts accelerate as they converge. The shocked gas at the centreof convergence attains temperatures high enough to emit radiation which isvisible to the human eye. The strength and duration of the light pulse due toshock implosion depends on the medium. In this study, shock waves convergingin air and argon have been studied. In the latter case, the implosion lightpulse has a duration of roughly 10 μs. This enables non-intrusive spectrometricmeasurements on the gas conditions.Circular shock waves are very sensitive to disturbances which deform theshock front, decreasing repeatability. Shocks consisting of plane sides makingup a symmetrical polygon have a more stable behaviour during focusing,which provides less run-to-run variance in light strength. The radiation fromthe gas at the implosion centre has been studied photometrically and spectrometrically.Polygonal shocks were used to provide better repeatability. Thefull visible spectrum of the light pulse created by a shock wave in argon hasbeen recorded, showing the gas behaving as a blackbody radiator with apparenttemperatures up to 6000 K. This value is interpreted as a modest estimation ofthe temperatures actually achieved at the centre as the light has been collectedfrom an area larger than the bright gas core.As apparent from experimental data real gas effects must be taken intoconsideration for calculations at the implosion focal point. Ideal gas numericaland analytical solutions show temperatures and pressures approaching infinity,which is clearly not physical. Real gas effects due to ionisation of theargon atoms have been considered in the numerical work and its effect on thetemperature has been calculated.The propagation of circular and polygonal have also been experimentallystudied and compared to the self-similar theory and geometrical shock dynamics,showing good agreement.</p>

L'objectif de ce travail réside dans la compréhension de la force sur un objet pénétrant un milieu granulaire. À partir de mesures de forces sur un cylindre en pénétration à vitesse constante, nous avons caractérisé cette force qui est indépendante de la vitesse imposée, proportionnelle au diamètre du cylindre et varie non-linéairement avec la taille des grains. En complément, nous avons mesuré le champ de vitesse des grains : celui-ci est stationnaire et l'écoulement est incompressible. On observe une localisation du cisaillement dans une zone proche du cylindre avec une dépendance spatiale exponentielle gouvernée par le diamètre du cylindre. Un modèle hydrodynamique s'appuyant sur la théorie cinétique étendue aux régimes d'écoulements denses reproduit correctement cette localisation et fournit des lois d'échelles pour la force similaires aux résultats expérimentaux. En dé finissant un nombre de Reynolds granulaire, nous avons montré que ce régime est l'équivalent d'un régime visqueux de Stokes à petit nombre de Reynolds. Il existe une transition vers un autre régime à grand Reynolds où les pro fils de vitesses perdent leur symétrie amont-aval et la force change sans doute d'expression. Enfin, le cas de l'impact d'un projectile où ces deux régimes existent successivement a aussi été étudié expérimentalement et numériquement. L'existence d'un terme supplémentaire de force proportionnelle au carré de la vitesse est sans doute issue du régime à grand Reynolds. Les deux termes donnent lieu à deux temps caractéristiques dont le temps d'arrêt est fonction et à l'origine d'un temps d'arrêt plus court pour une vitesse d'impact plus grande.

Le parachèvement des pièces de fonderie de haute technicité est une tâche indispensable, réalisée en grande partie manuellement, et vouée à disparaître de par sa pénibilité. Le travail présenté concerne la mise en oeuvre industrielle d'une cellule robotisée de parachèvement. Une première partie présente les contraintes liées au procédé de fonderie sable et leurs impacts sur le parachèvement. Le processus robotisé comporte une phase d'usinage et de ponçage associées à un recalage par vision. Un état de l'art en regard de nos contraintes d'intégration a conduit au choix d'un robot à structure parallèle (Tricept) associé à deux axes supplémentaires introduisant des redondances cinématiques. Sa mise en oeuvre vis-à-vis du processus a suivi une démarche en trois étapes : la modélisation analytique de la cellule obtenue par équivalent sériel, la formalisation des contraintes du processus et une résolution par optimisation multicritères. Elle a nécessité la définition de critères d'optimisation spécifiques (précision, cinématique, rigidité) et permet d'améliorer le comportement de la cellule par la gestion des redondances cinématiques. La dernière partie présente la mise en production industrielle sur une pièce de validation et l'outil d'optimisation développé.

The thesis is concerned with the flow of polymeric fluids and their response to deformations. The current state of research into the rheology of polymers is reviewed and an introduction to non-Newtonian fluid mechanics is given. A novel numerical algorithm for simulating the flow of non-Newtonian fluids is presented, in which the fluid is represented by a set of Lagrangian particles embedded in it. Each particle carries a velocity and a stress with it as it moves through the flow geometry. The velocity gradient tensor and the divergence of the stress tensor are calculated for each particle by averaging over the neighbouring particles. The velocity is changed according to a discretised form of the equation of conservation of momentum and the stress is updated according to the constitutive equation for the fluid. Extra algorithms are presented to deal with the boundary conditions. The simulation is used to study the two-dimensional flow of a co-rotational Maxwell fluid past an array of cylinders between two walls. In the second part of the thesis, a computer simulation is developed which will allow the constitutive equation for a polymer melt to be replaced by a numerical version. Previous computer simulations of polymers are reviewed and a new, real space, reptation model is presented. This model is shown to have the correct behaviour for a reptating chain and is used to study the stress response to a step shear deformation. The long-term behaviour agrees with reptation theory, but the short-time behaviour is also found.

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