The primary purpose of this study was to examine if the coupling effect could be overcome in a bimanual isometric tracking task, using methods similar to those of the Kovacs et al. team in previous bimanual kinematic research. Thirty right-handed participants, with a mean age 22.5 (SD 3.5) years, free from any neurological disorder or physical ailment, were randomly assigned to one of three groups that differed in percent of feedback provided during the practice trials (100%, 50% or 0%). The participants then performed a bimanual isometric manipulation tracking task that was a 2:1 rhythm (backwards C shape) scaled to 30% maximum voluntary contraction (MVC). Participants performed five blocks of five trials with the feedback schedule assigned to their group, rested for 30 minutes, then performed a retention task. Significant differences (p<.05) in Root Mean Square Error (RMSE) occurred between the 100% group and both the 50% and 0% groups during the practice blocks. Significant differences (p<.05) also occurred between the 50% group and the 100% and 0% group for the first four practice blocks. Though differences occurred between the groups during the practice trials, no differences occurred between the groups during the retention block. These findings support the position that the coupling effect in bimanual isometric manipulation tasks is very strong and cannot be as easily overcome as it is in kinematic bimanual task. This may be due to the feedback systems used in isometric conditions versus kinematic tasks (i.e. force and pressure sensation vs. position and motion proprioception). / text

Abstract Adding a dc circuit to an existing transmission line is one method of significantly increasing the power transfer capability of a transmission corridor. The resulting hybrid system has significant coupling between the ac and dc circuits, not only because of the proximity of the circuits, but also from the fact that they may share the same sending end or receiving end ac systems. The resultant interaction produces overvoltages on the dc system which can be somewhat higher than for a conventional dc scheme. This thesis investigates the overvoltages on a hybrid ac-dc transmission system and suggests some design considerations which could be taken into account to reduce stresses on certain critical components which result from such an arrangement. Blocking filters consisting of a parallel L-C combination in series with the dc converter were included to limit the flow of fundamental frequency current in the dc line. This thesis also investigates the proper blocking filter configuration to be used as an incorrectly chosen blocking filter can cause resonance overvoltages on the dc line at fundamental frequency. A method of eliminating dc components of the currents in the transformer windings of a dc converter is presented. The method uses the technique of firing angle modulation. It is shown that merely eliminating the fundamental frequency component on the dc side may not remove this dc component. The impact of such control action at one converter on the other converters in the dc transmission system is also presented. It is also shown that the undesirable side effects of such a scheme include increased generation of non-characteristic harmonies on both the ac and dc sides. The study is performed using an electromagnetic transients simulation program and theoretical calculations.

Abstract Adding a dc circuit to an existing transmission line is one method of significantly increasing the power transfer capability of a transmission corridor. The resulting hybrid system has significant coupling between the ac and dc circuits, not only because of the proximity of the circuits, but also from the fact that they may share the same sending end or receiving end ac systems. The resultant interaction produces overvoltages on the dc system which can be somewhat higher than for a conventional dc scheme. This thesis investigates the overvoltages on a hybrid ac-dc transmission system and suggests some design considerations which could be taken into account to reduce stresses on certain critical components which result from such an arrangement. Blocking filters consisting of a parallel L-C combination in series with the dc converter were included to limit the flow of fundamental frequency current in the dc line. This thesis also investigates the proper blocking filter configuration to be used as an incorrectly chosen blocking filter can cause resonance overvoltages on the dc line at fundamental frequency. A method of eliminating dc components of the currents in the transformer windings of a dc converter is presented. The method uses the technique of firing angle modulation. It is shown that merely eliminating the fundamental frequency component on the dc side may not remove this dc component. The impact of such control action at one converter on the other converters in the dc transmission system is also presented. It is also shown that the undesirable side effects of such a scheme include increased generation of non-characteristic harmonies on both the ac and dc sides. The study is performed using an electromagnetic transients simulation program and theoretical calculations.

Array processing involves manipulation of signals induced on various antenna elements. In an adaptive array system, the radiation pattern is formed according to the signal environment by using signal processing techniques. Adaptive arrays improve the capacity of mobile communication systems by placing nulls in the direction of interfering sources and by directing independent beams toward various users. Adaptive beamforming algorithms process signals induced on each array element that are assumed not to be affected by mutual coupling between the elements. The aim of this thesis is to investigate the effects of mutual coupling on the performance of various adaptive beamforming algorithms. The performance parameters such as signal to interference plus noise ratio and speed of convergence of the adaptive algorithms are studied and compared by both neglecting and considering the mutual coupling for the least mean squares, recursive least squares, conjugate gradient and constant modulus algorithms. Finally, it is concluded that the effect of mutual coupling is major in the performance of blind algorithms rather than non-blind algorithms. The results are obtained by simulations carried out on MATLAB.

No description available.

No description available.

La décroissance de la consommation électrique des dispositifs électroniques leur a permis une croissance sans précédent. Néanmoins, les éléments de stockage d’énergie (piles et batteries), bien qu’ayant initialement promus ce développement, sont devenus un frein à la prolifération des microsystèmes électroniques, de part leur durée de vie limitée ainsi que des considérations environnementales (recyclage). Pour palier à ce problème, la possibilité d’exploiter l’énergie de l’environnement immédiat du dispositif a été proposée et a fait l’objet de nombreuses recherches au cours des dernières années. En particulier, la récupération d’énergie mécanique exploitant l’effet piézoélectrique est l’une des pistes les plus étudiées actuellement pour la conception de microgénérateurs autonomes capables d’alimenter les dispositifs électroniques. Par ailleurs, dans ce domaine, il a été démontré qu’un traitement non-linéaire de la tension de sortie de l’élément actif permet d’améliorer les capacités de récupération de l’énergie vibratoire. L’une de ces approches, nommée «Synchronized Switch Harvesting on Inductor» (récupération par commutation synchronisée sur inductance) et consistant en une inversion de la tension de manière synchrone avec le déplacement, s’est montrée particulièrement efficace, pouvant augmenter la quantité d’énergie récupérée par un facteur supérieur à 10. Cette dernière conduit à un processus cumulatif qui augmente artificiellement la tension de sortie de l’élément piézoélectrique ainsi qu’à une réduction du déphasage entre tension et vitesse de déplacement ; ces deux effets conduisant à l’augmentation importante des capacités de conversion. Néanmoins, l’étude des microgénérateurs d’énergie s’est quasiment toujours faite en considérant une excitation sinusoïdale, ce qui correspond rarement à la réalité. Peu de travaux expérimentaux, et encore moins théoriques, ont été menés en considérant une excitation large bande ; ceci étant d’autant plus vrai pour les dispositifs incluant un élément non-linéaire. Ainsi l’objectif de cette thèse est d’étudier le comportement des récupérateurs d’énergie piézoélectriques interfacés de manière non-linéaire. Pour ce faire, différentes approches seront envisagées, en considérant le processus de commutation comme un « auto-échantillonnage » du signal, ou en appliquant des théories d’analyse stochastique pour quantifier les performances du dispositif. Ainsi, plusieurs formes d’excitation appliquée au système pourront être analysées, permettant d’étudier la réponse du système sous des conditions plus réalistes. Toujours dans l’optique d’une implémentation réaliste, un autre objectif de cette thèse consistera à évaluer l’impact de la récupération d’énergie par couplage sismique sur la structure hôte, démontrant la nécessité d’envisager le système dans sa globalité afin de disposer de systèmes performants capables de convertir efficacement l’énergie vibratoire sous forme électrique pour un usage ultérieur. / A nonlinear interface consisting in a switching device has been proved to improve the piezoelectric harvester performance. Although existing works are usually done under single frequency excitation. practical cases are more likely broadband and random. In addition, the coupling effect due to the harvesting process is also an interesting issue to discuss. In terms of energy conversion process in seismic piezoelectric harvesters, mechanical interactions between host structure and harvester is an essential issue as well. The purpose of this work is to analysis seismic type piezoelectric harvesters from a practical perspective and to provide an optimal design of the latter. The broadband modeling based on the concepts of self-sampling and self-aliasing is described under broadband excitations for the nonlinear interface called "Periodic Switching Harvesting on Inductor" (PSHI). For this technique, the switching device is considered to be turned on at a fixed switching frequency. Then stochastic modeling is applied to have mathematical expressions that can describe broadband performance of the harvester with power spectral density (PSD) function of signals. As the switch is turned on at a given frequency, the modeling can be derived using cyclostationary theory. The effectiveness of stochastic modeling is validated with experimental measurements and time-domain iterative calculations, and the harvester performance under a band-limited noise excitation is discussed under bell-curved spectra excitations. An optimal switching frequency slightly less than twice the harvester resonant frequency is proved to have the optimal power output under the optimal resistive load. This switching frequency is however dependent on the electromechanical coupling factor of the harvester. Another part of this work discusses the interaction between the host structure and the harvester. The analysis is conducted with a Two-Degree-of-Freedom (TDOF) model. An energy conversion loop is therefore formed between the host structure and the harvester, within the harvester and the resistive load. The TDOF model is verified with Finite Element model and experimental work. An optimal mass ratio is proved to provide the maximal power output. The modeling is further applied to a practical self-powered Structural Health Monitoring system providing the best design of the harvester. A practical consideration of the broadband excitation is also introduced showing the effect of frequency detuning between the host structure and the harvester. Compared to constant force factor case, the harvester performance with a constant electromechanical coupling factor is surprisingly with very little decreases due to the mismatching of harvester and host structure resonant.

[Truncated abstract] Rocks, as the host to natural chains of coupled thermal, hydraulic and mechanical processes, are heterogeneous at a variety of length scales, and in their mechanical properties, as well as in the hydraulic and thermal transport properties. Rock heterogeneity affects the ultimate hydro-carbon recovery or geothermal energy production. This heterogeneity has been considered one important and difficult problem that needs to be taken into account for its effect on the coupled processes. The aim of this thesis is to investigate the effect of rock heterogeneity on multi-physical processes. A fully coupled finite element model, hereinafter referred to as a porosity-based model (PBM) was developed to characterise the thermal-hydraulic-mechanical (THM) coupling processes. The development of the PBM consists of a two-staged workflow. First, based on poromechanics, porosity, one of the inherent rock properties, was derived as a variant function of the thermal, hydraulic and mechanical effects. Then, empirical relations or experimental results, correlating porosity with the mechanical, hydraulic and thermal properties, were incorporated as the coupling effects. In the PBM, the bulk volume of the model is assumed to be changeable. The rate of the volumetric strain was derived as the difference of two parts: the first part is the change in volume per unit of volume and per unit of time (this part was traditionally considered the rate of volumetric strain); and the second is the product of the first part and the volumetric strain. The second part makes the PBM a significant advancement of the models reported in the literature. ... impact of the rock heterogeneity on the hydro-mechanical responses because of the requirement of large memory and long central processing unit (CPU) time for the 3D applications. In the 2D PBM applications, as the thermal boundary condition applied to the rock samples containing some fractures, the pore pressure is generated by the thermal gradient. Some pore pressure islands can be generated as the statistical model and the digital image model are applied to characterise the initial porosity distribution. However, by using the homogeneous model, this phenomenon cannot be produced. In the 3D PBM applications, the existing fractures become the preferential paths for the fluid flowing inside the numerical model. The numerical results show that the PBM is sufficiently reliable to account for the rock mineral distribution in the hydro-mechanical coupling processes. The applications of the statistical method and the digital image processing technique make it possible to visualise the rock heterogeneity effect on the pore pressure distribution and the heat dissipation inside the rock model. Monitoring the fluid flux demonstrates the impact of the rock heterogeneity on the fluid product, which concerns petroleum engineering. The overall fluid flux (OFF) is mostly overestimated when the rock and fluid properties are assumed to be homogeneous. The 3D PBM application is an example. As the rock is heterogeneous, the OFF by the digital core is almost the same as that by the homogeneous model (this is due to that some fractures running through the digital core become the preferential path for the fluid flow), and around 1.5 times of that by the statistical model.

Les actionneurs piézoélectriques font partie des outils les plus utilisés dans les applications à l'échelle micro/nano-métrique (micromanipulation, microassemblage, micropositionnement, etc…). Du point de vue fonctionnel, on distingue les actionneurs mono-axe (permettant d'obtenir la déflection suivant une direction) et les actionneurs multi-axes (pouvant fléchir suivant plusieurs directions). La notoriété des actionneurs piézoélectriques est due à un certain nombre de performances telles qu'une large bande passante (plus du kHz possible), une très bonne résolution (de l'ordre du nanomètre), une faible consommation en énergie électrique, une grande densité de force, une facilité d'alimentation et d'intégration, etc. Cependant, ces actionneurs sont caractérisés par des non-linéarités fortes (hystérésis et la dérive lente), des oscillations mal-amorties, et sont sensibles à la variation des conditions ambiantes (en particulier à la variation de la température). Pour les actionneurs multi-axes, il s'ajoute un problème des couplages entre les différents axes de l'actionneur. Cette thèse propose des stratégies innovantes de commande des actionneurs piézoélectriques multi-axes pour contrer les problèmes sus-mentionnés. Ces stratégies sont groupées en deux catégories. La première catégorie concerne les techniques de commande en boucle fermée. Ces techniques sont les plus adaptées pour garantir la robustesse et un niveau de précision élevé pour les actionneurs piézoélectriques. Cependant, à l'échelle micro/nano-métrique, ces techniques sont limitées par un manque d'espace suffisant pour installer des capteurs de position. La deuxième catégorie concerne la commande en boucle ouverte dont l'intérêt majeur est lié au fait qu'il n'y a pas besoin de capteurs pour la commande, ce qui constitue un avantage en terme de coût et facilité d'intégration. Dans cette thèse, nous proposons d'abord les techniques de modélisation et de commande en boucle ouverte multivariables. Ensuite, nous faisons une analyse des effets de la température sur les actionneurs piézoélectriques et nous proposons des techniques de commande en boucle ouverte et en boucle fermée de ces effets. Enfin, une stratégie de commande en boucle fermée par découplage, visant à obtenir des correcteurs d'ordre réduit pour les actionneurs multi-axes est proposée. Toutes ces techniques sont vérifiées et appliquées expérimentalement à un actionneur piézoélectrique de type tube. / Piezoelectric actuators are among the most used tools in many applications at micro/nano-scale (micromanipulation,microassembly, micropositioning, etc). From a functional perspective, there exist mono-axis actuators(which are made to bend in one direction) and multi-axis actuators (which provide deflections in different directions).The popularity of piezoelectric actuators is especially due to their high resolution (nanometric resolution),the large bandwidth (greater than 1kHz possible), the low electrical power consumption, the high force density,the ease of integration in positioning systems, etc. However, piezoelectric actuators are characterized by hysteresisand creep nonlinearities, badly damped vibrations and they are sensitive to the variation of ambient conditions(especially to the temperature variation). In addition, multi-axis actuators exhibit cross-couplings betweentheir axis. This thesis proposes novel strategies for modeling and control of multi-axis piezoelectric actuators,with the aim to counteract the aforementionned problems. These strategies are grouped into two categories.The first category concerns feedback control techniques. These techniques are the most suitable to ensurethe robustness and a high level of precision for piezoelectric actuators. However, at the micro/nanoscale, thesetechniques are limited by the lack of enough physical space to install feedback sensors. The second categoryconcerns the feedforward control techniques. The main advantage of these techniques is related to the factthat, in feedforward control schemes, feedback sensors are not needed for tracking. This allows to achieve ahigh degree of packageability and the cost reduction. In this thesis, we first propose multivariable modelingand feedforward control techniques. Then, we analyse the effects of temperature variation on piezoelectricactuators and we propose feedforward and feedback control techniques for these effects. Finally, a feedbackstrategy based on decoupling techniques with an aim to reduce the order of feedback controllers for multi-axispiezoelectric actuators, is proposed. All these modeling and control strategies are experimentally applied on apiezoelectric tube actuator.

Cette thèse s'intéresse aux mécanismes initiateurs de l'endommagement laser du KDP et du DKDP en régime nanoseconde. C'est un matériau non linéaire utilisé notamment dans les cristaux de conversion de fréquence du Laser MégaJoule, en cours de construction sur le centre du CEA-Cesta, en France. La tenue au flux de ces cristaux est une des clés de la réussite de cette installation et demeure actuellement une problématique à résoudre. C'est pourquoi, cette thèse propose différentes études permettant de répondre en partie à deux volets essentiels de l'endommagement laser du KDP en régime nanoseconde : les défauts précurseurs et les mécanismes initiateurs de l'endommagement. Tout d'abord, nous proposons une étude en longueur d'onde des dommages créés suite à un tir laser. Cette étude est basée à la fois sur l'observation de clichés de dommages obtenus en microscopie DIC ainsi que sur la comparaison à un code de calcul couplant dépôt d'énergie et hydrodynamique. Par la suite, nous étudions l'influence de la géométrie des défauts précurseurs par le biais d'une étude de l'effet de la polarisation du faisceau laser sur la tenue au flux d'un cristal de KDP. A l'aide d'un code interne au CEA, cette étude permet notamment d'introduire une nouvelle géométrie des défauts, de type ellipsoïdale et respectant les propriétés de la structure cristalline d'un tel cristal. Enfin, nous abordons plus largement les mécanismes d'initiation de l'endommagement à partir d'expériences pompe--pompe. Ces tests mettent en jeu le mélange de deux longueurs d'onde différentes -- impactant l'échantillon de manière concomitante ou désynchronisée l'une par rapport à l'autre -- et son influence sur la tenue au flux du KDP. Il est notamment montré qu'il peut y avoir un couplage entre les longueurs d'onde, donc par extension entre les mécanismes, en fonction de la combinaison des fluences qui sont employées. Au final, l'intérêt de ces études est d'acquérir de nouvelles données permettant d'améliorer la compréhension des mécanismes de l'endommagement du KDP en régime nanoseconde. A terme, elles permettront également de développer des modèles de prédiction de l'endommagement des cristaux de KDP et de DKDP montés sur les chaînes laser. / This thesis interests in the laser-induced damage mechanisms of KDP and DKDP crystals in the nanosecond regime. KDP is a non-linear material particularly used in the frequency converters of the Laser MegaJoule, which is under construction at the CEA-Cesta in France. For this facility, the KDP laser damage resistance is one of the keystones and is still under investigations to fix this problem. This is why this manuscript presents different studies which highlight the two main aspects of the nanosecond laser-induced damage of KDP frequency converters : the precursor defects and the mechanims to initiate damage. First, we propose a study based on the analysis of several photos obtained by DIC microscopy of damage initiated by different wavelengths. A comparison with a code coupling the energy deposition and hydrodynamic is also done. Then, we interest in the influence of the defects geometry through a study based on the laser polarization effet on the laser damage resistance. By the comparison with a CEA home-made code, this study particularly underlines the possibility to define a new geometry for the precursor defects. This geometry proposed has the shape of an ellipsoid and is supposed to keep the crystal structure properties. Finally, we enlarge on the physical mechanisms initiating laser damage with pump--pump experiments. These tests consist in combinating two radiations of different wavelengths which imping the crystal simultaneously or are delayed one by the other. We then observe the influence of this wavelengths mixing on the KDP laser damage resistance. In particular, a coupling effet between the wavelengths of the mixture may occur as a function of the fluences combination. Finally, the goal of these specific studies is to accumulate new data in order to improve the undertanding in the intiation of the laser damage in KDP and DKDP crystals in the nanosecond regime. In the end, these data will allow us to develop predictive models to simulate the laser damage of KDP and DKDP crystals on the LMJ laser chains.