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Resistivity-induced coupling between voltage distribution and vibrations in dielectric elastomers
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Dynamique de sédimentation de particules
No full textThe dynamics of heavy inertial particles evolving in a fluid are of interest in many fields.They are found both in nature (water droplets in clouds, sediments in rivers and in the oceans, planetary accretion disks) and in human activities and technological applications (fuel drops in combustion chambers, chemical reactors).These systems are complex, their modelling using often strong simplifying hypotheses, and experimental data is still required in their study.A large range of behaviours can be found in such dispersed two-phase flows.This work focuses on two of these.The first is clustering, or the observation that particles accumulate in specific regions and leave others void.The second is settling velocity alteration, as particles have been observed to fall either faster or slower than in a quiescent fluid.These two phenomena are intertwined, and depend on parameters like the size and density of the particles, what the carrier phase is (water or air usually) and whether it is in a quiescent or turbulent state.An experimental device was built in which small (diameters of at most 200 µm) solid particles settle in water.Particles of various densities have been separated by size by sieving.This allows access to a large variety of particle properties.An easy to implement double-measurement technique allowing simultaneous measurements of particle and fluid velocities was developed, providing insight into particle-fluid interactions that was seldomly achieved in previous works.Increases of the settling velocity of particles falling in a quiescent fluid have been observed and could be attributed to the development of a flow that pushes the particles down.Voronoï analysis were also performed, but could not confirm with certainty whether particles formed clusters or not.This work gives interesting data, relevant in the study of particles settling in quiescent fluids in closed spaces.It also provides a reference point for future works where turbulence will be added to the system.La dynamique de particules inertielles lourdes évoluant dans un fluide présente un intérêt dans de nombreux domaines.On les trouve aussi bien dans la nature (gouttes d'eau dans les nuages, sédiments dans les rivières et les océans, disques d'accrétion planétaire) que dans des activités humaines et applications technologiques (gouttes de carburant en chambres de combustion, réacteurs chimiques).Ces systèmes sont complexes, leur modélisation requérant des hypothèses simplificatrices souvent fortes, et leur étude nécessite encore des données expérimentales.De nombreux comportements sont observés dans ces écoulements diphasiques dispersés.Cette thèse s'intéresse à deux d'entre eux.D'abord le clustering, phénomène où les particules s'accumulent dans des régions spécifiques et en laissent d'autres vides.Le second est l'altération de la vitesse de sédimentation, des particules tombant plus vite ou plus lentement que dans un fluide au repos.Ces phénomènes sont liés, et dépendent de paramètres comme la taille et la densité des particules, de la phase porteuse (eau ou air généralement) et de si celle-ci est au repos ou dans un état turbulent.Un dispositif expérimental a été construit dans lequel de petites particules solides (diamètre maximal de 200 µm) sédimentent dans de l'eau.Des particules de différentes densités ont été séparées par taille par tamisage.Ceci a permis d'accéder à une large gamme de paramètres pour les particules.Une technique de double mesure simple à mettre en œuvre permettant de mesurer simultanément la vitesse des particules et du fluide a été développée, fournissant un aperçu des interactions particules-fluides rarement réussi jusqu'à présent.Des augmentations de la vitesse de sédimentation des particules tombant dans un fluide au repos ont été observées et ont été attribuées au développement d'un écoulement descendant, poussant les particules.Des analyses de Voronoï ont également été effectuées, mais n'ont pas pu déterminer avec certitude si les particules formaient des amas ou non.Ce travail fournit des données intéressantes, pertinentes pour l'étude des particules qui sédimentent dans des fluides au repos en espace clos.Il fournit également un point de référence pour de futurs travaux où la turbulence sera ajoutée au système
Experimental evidence of energy transfer and vibration mitigation in a vibro-impact acoustic black hole
No full textInternational audienceAn experimental demonstration of the broadband passive damping capacity of a vibro-impact acoustic black hole (VI-ABH) is reported. A VI-ABH is an adaptation of the classical ABH design consisting of a beam with a tapered edge of decreasing thickness creating an acoustic black hole (ABH), complemented by contact points on which the beam impacts during its vibration. The contact nonlinearity creates a rapid and efficient transfer of vibrational energy from the low-frequency range, where the ABH is known to be ineffective, to the high-frequency range, thus improving the global passive vibration mitigation characteristics. The optimal design of a VI-ABH follows the rule of locating the contact points at local maxima of the low-frequency modes. Experiments clearly demonstrate the gain in performance, both in forced and free vibrations
PAMELA: an annotation-based Java Modeling Framework
No full textInternational audienceThis article presents PAMELA, an annotation-based Java modeling framework. PAMELA provides a smooth integration between model and code and enables Java developers to handle software development both at conceptual level and at source-code level, without code transformation and/or generation, avoiding round-trip-related issues
Energy absorption characteristics in hybrid composite materials for marine applications under impact loading: Case of tidal current turbine
No full textInternational audienceThe tidal current turbine is the most efficient way to extract energy from the sea. This system can be prone to critical loads such as impact accidental in the installation and maintenance phase. Indeed, several complex modes of damage susceptible to harming the stability of the structure are studied to conceive hybrid composite nozzles with better resistance to damage. For this reason, two scenarios of low-velocity impact of a hybrid composite nozzle (glass/carbon) were investigated. In both cases, the impact was realized in the region of the trailing edge of the nozzle, and the results obtained were compared between three different laminated. On the other hand, damage modeling was formulated using the finite element method based on the Hashin criteria. Energy conservation of the nozzle was verified to validate the numerical model. Also, the effects of the impact velocity and the panel's flexibility on the initiation and propagation of damage have been studied. Depending on the results, the stacking sequence significantly influences the formation of damage. However, the results show that the hybrid nozzle with CGG (carbon/glass/glass) stacking has a higher impact resistance compared to other laminates
Traitement statistique de l'information et du signal pour l'internet des objets sous-marins
No full textThere has been recently a large development of human activities associated to the ocean world, where no standard has emerged for the Internet of Things (IoT) linked to marine autonomous objects. Though it has a limited bandwidth, the acoustic wave is the only way to communicate over average to large distances and it is thus used by many underwater systems to communicate, navigate, or infer information about the environment. This led to a high demand for wireless networks that require both spectral efficiency and energy efficiency with the associated low-complexity algorithms. Therefore, in this Ph.D. thesis, we proposed several original solutions to face this challenge.Indeed, due to the inherent Signal Space Diversity (SSD), rotated constellations allow better theoretical performance than conventional constellations with no spectral spoilage. We review the structural properties of uniformly projected rotated M-QAM constellations, so as to propose a low complexity soft demapping technique for fading channels. Then, we present an original blind technique for the reduction of the PAPR for OFDM systems using the rotated constellations with SSD. In order to reduce the complexity of blind decoding for this technique, we again rely on the properties of uniformly projected M-QAM rotated constellations to design a low-complexity estimator. Moreover, to face the selectivity of the acoustic channel, we suggest a sparse adaptive turbo detector with only a few taps to be updated in order to lower down the complexity burden. Finally, we have proposed an original self-optimized algorithm for which the step-sizes of both the equalizer and the phase estimator are updated adaptively and assisted by soft-information in an iterative manner, so as to meet the requirement of fast convergence and low MSE over time-varying channels.On assiste au développement des activités humaines liées au monde océanique, mais aucune norme n'a encore émergé pour l'Internet des objets appliqué aux objets autonomes marins. Bien qu'elle possède une bande passante limitée, l'onde acoustique est le seul moyen de communiquer sur des distances importantes et elle est donc utilisée par de nombreux systèmes sous-marins pour communiquer, naviguer ou déduire des informations sur l'environnement. Cela a conduit à une forte demande de réseaux sans fil qui nécessitent à la fois une bonne efficacité spectrale et énergétique avec la faible complexité des algorithmes associés. Par conséquent, au cours de ce doctorat, nous avons proposé plusieurs solutions originales pour relever le défi de développer des techniques numériques, capables de faire face au canal acoustique.En raison d’une diversité inhérente d'espace du signal (SSD), les constellations tournées permettent de meilleures performances théoriques que les constellations conventionnelles et ce, sans détérioration spectrale. Nous passons en revue les propriétés structurelles des constellations tournées M-QAM uniformément projetées, afin de proposer une technique de demapping souple à faible complexité pour les canaux à fading. Puis, nous proposons une technique originale de réduction du PAPR pour les systèmes OFDM utilisant les constellations tournées. Afin de réduire la complexité du décodage aveugle, nous nous appuyons sur les propriétés des constellations tournées M-QAM uniformément projetées, pour concevoir un estimateur de faible complexité. De plus, pour faire face à la sélectivité du canal acoustique, nous avons proposé un turbo-détecteur parcimonieux adaptatif avec seulement quelques coefficients à mettre à jour afin de réduire la complexité. Enfin, nous avons proposé un algorithme original auto-optimisé pour lequel les tailles de pas de l'égaliseur sont mises à jour de manière adaptative et assistées par des informations souples de manière itérative, afin de répondre à l'exigence de convergence rapide et de faible erreur quadratique sur des canaux variant rapidement dans le temps
Outer Space, Expansive Sustainable Development, and the Future of the Environmental Humanities
No full textAcademia LettersInternational audienceWhat does it mean to be live sustainably? Work within the environmental humanities assumes that sustainable development will happen on planet Earth. Sustainability is associated with respecting the limits of the planet, the transition away from fossil fuels, the escape from the growth mindset, and the protection of biodiversity. However, a new wave of space expansion advocates is using sustainable development in an alternative way. "Sustainable" is used to refer to self-perpetuating private economic activities off-world. "Sustainable" is also employed to refer to permanent space habitats that rely on the harvest of local (but unrenewable) space resources. Finally, "sustainable" is used to describe forms of extra-terrestrial extractivism-e.g., strip-mining asteroids-which would be carried out with the aim of offsetting Earth-side resource deficits. From the point of view of traditional understandings of sustainable development, these uses of the term "sustainable" are perverse. By expanding horizons of the world out beyond the Earth-by becoming post-planetary-expansive sustainability subsumes a whole range of current practicesconsumerism, extensive reliance on unrenewable resources, unending population growth, and even unbridled pollution-within the limits of what is judged "sustainable." Post-planetary or expansive sustainability seems to legitimate the sustainability of the unsustainable. Nevertheless, expansive sustainability seems to meet the Brundtland commission's definition of sustainable development: "development which meets the needs of current generations without compromising the ability of future generations to meet their own needs." This is in part because expansive sustainability, like Earth-bounded sustainability, takes into account the long-term future: "deep time." Yet expansive sustainability differs sharply from traditional sustainability with respect to the location of those future generations. Earth-bound advocates of sustainability have always imagined the future in terms of intensification
Influence on strain-rate history effects on the development of necking instabilities under dynamic loading conditions
No full textInternational audienceThe present paper is devoted to the analysis of strain-rate history effects on neck formation under dynamic loading. For materials presenting strain-rate history effects, two different strain-rate sensitivities should be distinguished: the instantaneous strain-rate sensitivity and the work-hardening strain-rate sensitivity. We have analysed the relative contributions of these two kinds of strain-rate sensitivities to neck retardation for two different configurations: a bar under impact tension and a dynamically expanding ring. For this purpose, we have developed finite element models and, for the second configuration, an analytical model based on the linear stability analysis. The obtained results show that strain-rate history effects have a significant influence on the onset and development of necking. The reason of this phenomenon is that, contrary to the instantaneous strain-rate sensitivity, the work-hardening strain-rate sensitivity does not contribute to delay the neck formation