7 research outputs found

    Comprendre les auto-oscillations dans le caloduc pulsé mono-branche

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    Abstract : In this thesis, scientific contributions on the understanding of the self-oscillations in the Single-Branch Pulsating Heat Pipe (SBPHP) and on the Self-Oscillating Heat Engine (SOFHE) are presented. The SBPHP is a tube of small diameter closed at one end in which a vapor bubble is followed by a liquid plug. Surprisingly, heating the closed end over a threshold leads to oscillations of the liquid plug which can be maintained indefinitely. Those self-oscillations can be used for cooling, pumping or energy harvesting when coupled to an electromechanical transducer (SOFHE). However the lack of understanding of the dynamics makes it difficult to control the self-oscillations and to understand how to design good devices. In this thesis, some fundamental questions on the dynamics are answered by a theoretical approach and experimental validation, in order to better understand the phenomenon and to provide guidelines for the design of effective devices. We first look at where the oscillations come from and why the amplitude grows during the startup. We show that the compression and expansion of the vapor coupled with the liquid plug inertia leads to a spring-mass system. We then uncover the existence of an instability mechanism due to the interplay of phase-change which acts as a positive feedback and viscous friction, which dissipates energy. The startup occurs when the phase-change coefficient is greater than the friction coefficient. Both the spring-mass system and the instability mechanism are validated experimentally. We then ask: why does the amplitude saturate during the startup? We show, using nonlinear dynamical techniques, that this is explained by a limiting mechanism produced by the nonlinearities . The system reaches a limit cycle, created through a PoincarĂ©-Andronov-Hopf bifurcation. By controlling the phase-change and the friction, one can promote the instability mechanism and reduce the limiting mechanism such that the oscillations amplitude increases. We also study the dynamics further, from small to large oscillations amplitude. To do so, we use numerical continuation first, and then obtain accurate analytical solutions. We then consider the behavior of a SOFHE. We show how the dynamics, the power output and the efficiency are impacted by the electromechanical transducer. We find that self-oscillating harvesters (as SOFHE) differs qualitatively from forced-oscillating harvesters. Finally, we review our results from a general energy perspective. We show that the instability mechanism and the limiting mechanism can be explained by the phase-change and the friction work rate. One can increase the oscillations amplitude or the power output and the efficiency significantly by increasing the phase-change work rate or reducing the friction work rate. We conclude by suggesting that controlling the magnitude and the timing of the phase-change by engineered tubes seems a promising approach to increase the performance of devices.Dans cette thĂšse, des contributions scientifiques sur la comprĂ©hension des auto-oscillations dans le caloduc auto-oscillant mono-branche (SBPHP) et le moteur fluidique auto-oscillant (SOFHE) sont prĂ©sentĂ©es. Le SBPHP est un tube de faible diamĂštre fermĂ© Ă  l’une des extrĂ©mitĂ©s, dans lequel une bulle de vapeur est suivie d’une colonne de liquide. Étonnamment, chauffer l’extrĂ©mitĂ© fermĂ©e au-delĂ  d’un certain seuil mĂšne Ă  des oscillations de la colonne de liquide qui peuvent ĂȘtre maintenues indĂ©finiment. Ces auto-oscillations peuvent ĂȘtre utilisĂ©es pour refroidir, pomper ou pour rĂ©cupĂ©rer de l’énergie lorsque couplĂ©es Ă  un transducteur Ă©lectromĂ©canique (SOFHE). Toutefois, parce que la dynamique est mal comprise, il est difficile de contrĂŽler les auto-oscillations et de comprendre comment concevoir des dispositifs performants. Dans cette thĂšse, des rĂ©ponses Ă  des questions fondamentales sur la dynamique sont obtenues, par une approche thĂ©orique et des validations expĂ©rimentales, pour mieux comprendre le phĂ©nomĂšne et guider la conception. Nous nous demandons d’abord d’oĂč proviennent les oscillations et pourquoi leur amplitude augmente durant le dĂ©marrage. Nous montrons que l’inertie de la colonne de liquide couplĂ©e Ă  la compression/ dilatation de la vapeur produit un systĂšme masse-ressort. Nous rĂ©vĂ©lons ensuite l’existence d’un mĂ©canisme d’instabilitĂ©, dĂ» Ă  l’interaction du changement de phase qui agit comme force de rĂ©troaction positive et Ă  la friction visqueuse, qui dissipe de l’énergie. Le dĂ©marrage se produit lorsque le coefficient du changement de phase est supĂ©rieur au coefficient de friction. Le systĂšme masse-ressort et le mĂ©canisme d’instabilitĂ© sont validĂ©s expĂ©rimentalement. Nous nous demandons ensuite : pourquoi l’amplitude sature durant le dĂ©marrage ? Nous montrons, Ă  l’aide de techniques de dynamique non linĂ©aire, que cela s’explique par l’existence d’un mĂ©canisme limitant produit par les non-linĂ©aritĂ©s. Le systĂšme atteint un cycle limite, produit par une bifurcation de PoincarĂ©-Andronov-Hopf. En contrĂŽlant le changement de phase et la friction, il est possible d’augmenter l’instabilitĂ© et de rĂ©duire la limitation et ainsi, d’augmenter l’amplitude des oscillations. Nous poussons l’étude de la dynamique plus loin, de faibles Ă  grandes amplitudes. Pour ce faire, nous utilisons la continuation numĂ©rique d’abord, puis obtenons des solutions analytiques prĂ©cises. Nous nous intĂ©ressons ensuite au comportement du SOFHE. Nous montrons comment la dynamique, la puissance et l’efficacitĂ© sont influencĂ©es par le transducteur Ă©lectromĂ©canique. Des rĂ©cupĂ©rateurs auto-oscillants (comme SOFHE) diffĂšrent qualitativement de rĂ©cupĂ©rateurs forcĂ©s. Finalement, nous revisitons nos rĂ©sultats selon une approche Ă©nergĂ©tique gĂ©nĂ©rale. Nous montrons que le mĂ©canisme d’instabilitĂ© et le mĂ©canisme limitant peuvent ĂȘtre expliquĂ©s en fonction du travail produit par le changement de phase et par la friction. Il est possible d’augmenter significativement l’amplitude, la puissance ou l’efficacitĂ© en augmentant le travail fait par le changement de phase ou en rĂ©duisant celui fait par la friction. Nous concluons en suggĂ©rant que contrĂŽler l’amplitude et le synchronisme du changement de phase par des tubes modifiĂ©s semble ĂȘtre une avenue trĂšs prometteuse pour amĂ©liorer la performance des dispositifs

    Artificial general intelligence: Proceedings of the Second Conference on Artificial General Intelligence, AGI 2009, Arlington, Virginia, USA, March 6-9, 2009

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    Artificial General Intelligence (AGI) research focuses on the original and ultimate goal of AI – to create broad human-like and transhuman intelligence, by exploring all available paths, including theoretical and experimental computer science, cognitive science, neuroscience, and innovative interdisciplinary methodologies. Due to the difficulty of this task, for the last few decades the majority of AI researchers have focused on what has been called narrow AI – the production of AI systems displaying intelligence regarding specific, highly constrained tasks. In recent years, however, more and more researchers have recognized the necessity – and feasibility – of returning to the original goals of the field. Increasingly, there is a call for a transition back to confronting the more difficult issues of human level intelligence and more broadly artificial general intelligence

    Détection d'un objet immergé dans un fluide

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    Cette thÚse s inscrit dans le domaine des mathématiques appelé optimisation de formes. Plus précisément, nous étudions ici un problÚme inverse de détection à l aide du calcul de forme et de l analyse asymptotique. L objectif est de localiser un objet immergé dans un fluide visqueux, incompressible et stationnaire. Les questions principales qui ont motivé ce travail sont les suivantes : peut-on détecter un objet immergé dans un fluide à partir d une mesure effectuée à la surface ? peut-on reconstruire numériquement cet objet, i.e. approcher sa position et sa forme, à partir de cette mesure ? peut-on connaßtre le nombre d objets présents dans le fluide en utilisant cette mesure ?Les résultats obtenus sont décrits dans les cinq chapitres de cette thÚse : le premier met en place un cadre mathématique pour démontrer l existence des dérivées de forme d ordre un et deux pour les problÚmes de détection d inclusions ; le deuxiÚme analyse le problÚme de détection à l aide de l optimisation géométrique de forme : un résultat d identifiabilité est montré, le gradient de forme de plusieurs types de fonctionnelles de forme est caractérisé et l instabilité de ce problÚme inverse est enfin démontrée ; le chapitre 3 utilise nos résultats théoriques pour reconstruire numériquement des objets immergés dans un fluide à l aide d un algorithme de gradient de forme ; le chapitre 4 analyse la localisation de petites inclusions dans un fluide à l aide de l optimisation topologique de forme : le gradient topologique d une fonctionnelle de forme de Kohn-Vogelius est caractérisé ; le dernier chapitre utilise cette derniÚre expression théorique pour déterminer numériquement le nombre et la localisation de petits obstacles immergés dans un fluide à l aide d un algorithme de gradient topologique.This dissertation takes place in the mathematic field called shape optimization. More precisely, we focus on a detecting inverse problem using shape calculus and asymptotic analysis. The aim is to localize an object immersed in a viscous, incompressible and stationary fluid. This work was motivated by the following main questions: can we localize an obstacle immersed in a fluid from a boundary measurement? can we reconstruct numerically this object, i.e. be close to its localization and its shape, from this measure? can we know how many objects are included in the fluid using this measure?The results are described in the five chapters of the thesis: the first one gives a mathematical framework in order to prove the existence of the shape derivatives oforder one and two in the frame of the detection of inclusions; the second one analyzes the detection problem using geometric shape optimization: an identifiabilityresult is proved, the shape gradient of several shape functionals is characterized and the instability of thisinverse problem is proved; the chapter 3 uses our theoretical results in order to reconstruct numerically some objets immersed in a fluid using a shape gradient algorithm; the fourth chapter analyzes the detection of small inclusions in a fluid using the topological shape optimization : the topological gradient of a Kohn-Vogelius shape functional is characterized; the last chapter uses this theoretical expression in order to determine numerically the number and the location of some small obstacles immersed in a fluid using a topological gradient algorithm.PAU-BU Sciences (644452103) / SudocSudocFranceF

    Has Metaphysics Done Its Time?

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    Edoardo Benvenuto Prize. Collection of papers

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    The promotion of studies and research on the science and art of building in their historical development constitutes the objective that the Edoardo Benvenuto Association has set itself, since its establishment, in order to honor the memory of Edoardo Benvenuto (1940-1998). The Association in recent years has achieved interesting results by developing various activities such as: organization of national and international meetings, conferences, study days; collaborations with national and foreign research institutions; promotion of the editorial series “Between Mechanics and Architecture"; activation of the portal Bibliotheca Mechanica Architectonica, first “open source” digitized library dedicated to historical research on mechanical and architectural texts. But perhaps the most qualifying initiative was the institution of the Edoardo Benvenuto Prize, arrived in 2019 in its twelfth edition, reserved for young researchers in the field of historical studies on science and the art of building. The awarding of the Prize takes place after an in-depth examination of the texts received by the Association by an international commission of experts. The purpose of this book is to collect and present the most recent studies and publications produced by the winners of the various editions of the Edoardo Benvenuto Prize

    Proceedings of the 19th Sound and Music Computing Conference

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    Proceedings of the 19th Sound and Music Computing Conference - June 5-12, 2022 - Saint-Étienne (France). https://smc22.grame.f
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