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Méthode de quasi-Trefftz pour l'aéroacoustique : Partie I - Problème modèle et application à l'équation d'Helmholtz
No full textThis work presents a quasi-Trefftz Discontinuous Galerkin method designed for the numerical resolution of problems governed by the Helmholtz equation. The method relies on local approximate solutions of the equation as test and trial functions. The formulation is based on a first-order system expressed within the Friedrichs framework. Three families of basis functions are considered: plane waves modulated in phase or amplitude, and polynomials. These are extended to the vector-valued setting, marking a key novelty in this work, and used within a variational formulation compatible with the Friedrichs structure. Numerical experiments confirm the expected convergence rate and demonstrate that the method achieves comparable accuracy with significantly fewer degrees of freedom compared to classical Discontinuous Galerkin approaches. This work lays the foundation for further developments, including the extension to the convected Helmholtz equation for the design of efficient numerical tools for aeroacoustic simulations.Ce travail présente une méthode de Galerkin discontinue de type quasi-Trefftz conçue pour la résolution numérique de problèmes modélisés par l’équation de Helmholtz. Cette méthode utilise comme fonctions test des solutions approchées locales de l’équation. La formulation repose sur un système de premier ordre exprimé dans le cadre des systèmes de Friedrichs. Trois familles de fonctions de base sont considérées : des ondes planes généralisées, dont la phase ou l’amplitude est perturbée, ainsi que des polynômes. Ces fonctions sont étendues au cas vectoriel, ce qui constitue une nouveauté majeure dans ce travail, puis utilisées dans une formulation variationnelle adaptée à la structure des systèmes de Friedrichs. Les simulations numériques confirment l’ordre de convergence attendu et montrent que cette approche atteint une précision comparable à celle des méthodes classiques de Galerkin discontinue, tout en nécessitant moins de degrés de liberté. Ce travail constitue une base pour de futurs développements, notamment l’adaptation à l’équation de Helmholtz convectée, et contribue à la conception d’outils numériques efficaces pour la simulation aéroacoustique
Time-averaged algorithm for solving the topology optimization problem for unsteady laminar, turbulent and anisothermal flows
No full textInternational audienceThis paper proposes a new algorithm to solve topology optimization problems for laminar unsteady or turbulent flows. Instead of computing the gradient of the cost function after solving the direct and adjoint (both unsteady) PDE on the full time interval, our algorithm uses averaged physical quantities on a smaller unspecified time interval to define a (steady) Reynolds-Averaged Method (RAM) model which is then used as constraint in an optimization problem to update the design variable. Another feature of the proposed method is that the RAM model can be defined whatever the initial model and CFD turbulence models initially chosen to compute the instantaneous physical quantities. The RAM model involves turbulent quantities such as turbulent kinetic viscosity and turbulent thermal diffusivity are estimated instead of using the concept of "frozen turbulence". In contrast with the classical methods built to solve unsteady topology optimization problems, the main advantage of the proposed algorithm is that it updates the design variable by solving an auxiliary steady topology optimization problem. Three configuration cases are studied to illustrate the ability of our algorithm to optimize pressure losses and heat transfer by adding material to smooth the laminar unsteady or turbulent flows. We also calculate the number of required design parameter updates to obtain an optimized design. Thus, our algorithm overcomes three major scientific challenges in solving optimization problems in turbulence, namely leveraging efficient temporal turbulence models or a Direct Numerical Simulation (DNS) model, computational cost and data storage requirements
Collection "Le fil de l'Histoire raconté par Ariane et Nino" de Fabrice Erre et Sylvain Savoia (Dupuis)
No full textChronique pour La Vie des Classique
Biomimetic UV photo-protection of skin surface by structured epicuticular wax films
No full textInternational audienceThe realms of biomimicry encourage us to explore and replicate the remarkable functionalities found in the big variety of living organisms such as plants, birds, animals etc. Inspired by the ultraviolet (UV) reflective characteristics of self-assembled epicuticular wax of plant leaves, in this article, we present a biomimetic plant-inspired approach to pattern the surface of skin with wax coatings and enhance its UV resistance. Through a physico-chemical approach, we coat chemically homogenous (as well as heterogenous) chemical composition of waxes from its solution on quartz substrate. By controlling the self-assembly conditions, diverse surface morphologies are obtained with Euphorbia cerifera (commonly known as Candelilla, chemically heterogenous wax) and Myristyl Palmitate (present in Phytolacca Acinosa, chemically homogenous alkyl esters wax). Optical measurements show increased reflectance in visible spectra for Candelilla wax coatings exhibiting globules, plate-like crystalline structures at the surface which contributes to higher roughness parameters. With homogenous wax, maximum reflectance is obtained for dual scale morphology which includes self-assembled 3D plate-like structures at an optimum length-scale. Our experiments reveal that the combined effect of vertically and horizontally placed stacks of crystal plates at micron and sub-micron scales induces maximum scattering effect. This geometrical organisation effectively decreases transmission of incident radiations to the underlying surface leading to enhanced photo-protection. Further, to showcase the feasibility of such approach for potential cosmetic applications, we replicate best performing structures on a commonly used model skin surface for UV absorption evaluation (polymethyl methacrylate plates) and on real ex-vivo Stratum Corneum, the outermost layer of skin. For realistic substrates, scattering effect is additionally dependent on nature of intrinsic substrate patterns and roughness in which case the feature height (hF) of 3D structures should be greater than substrate patterns to achieve maximum reflectance. This study highlights the formation of physical structuration with biomaterials and presents insights on scattering induced by such plant-based structures with potential for dermatological or cosmetic applications
Early Detection of the Marathon Wall to Improve Pacing Strategies in Recreational Marathoners
No full textEthics: The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of “CPP Sud-Est V, Grenoble, France; reference: 2018-A01496-49” for studies involving humans.International audienceThe individual marathon optimal pacing sparring the runner to hit the “wall” after 2 h of running remain unclear. In the current study we examined to what extent Deep neural Network contributes to identify the individual optimal pacing training a Variational Auto Encoder (VAE) with a small dataset of nine runners. This last one has been constructed from an original one that contains the values of multiple physiological variables for 10 different runners during a marathon. We plot the Lyapunov exponent/Time graph on these variables for each runner showing that the marathon wall could be anticipated. The pacing strategy that this innovative technique sheds light on is to predict and delay the moment when the runner empties his reserves and ’hits the wall’ while considering the individual physical capabilities of each athlete. Our data suggest that given that a further increase of marathon runner using a cardio-GPS could benefit of their pacing run for optimizing their performance if AI would be used for learning how to self-pace his marathon race for avoiding hitting the wall
Une chaleur souterraine. Trajectoire sociotechnique de la géothermie profonde française
No full textInternational audienc
Energy restriction cancels the effect of temperature on the growth of common soles (Solea solea) in the Gironde estuary
No full textInternational audienceEstuarine and coastal ecosystems are key nursery habitats for the development and growth of many juveniles of marine fish species. Human-induced environmental changes, to which coastal and estuarine areas are particularly sensitive, will largely impact juveniles’ life history traits and consequently, the whole population at sea. Increase of water temperature is the best described and predicted environmental change related to climate change, and will certainly affect the nursery function of estuarine areas. Yet, our capacity to estimate consequences are limited and lack mechanistic models applied at the population level. As a major estuary of Western Europe, the Gironde estuary is a relevant case study to evaluate the effects of rising temperature on fish populations.To study the specific impact of temperature on life history traits of juvenile common soles (Solea solea) in the Gironde estuary, we used a bioenergetic model based on DEB theory. Since the estuary is supposed to have reached its maximum carrying capacity, effects were also estimated in a context of limited energy availability, with forecast scenario based on IPCC previsions.As soles in the Gironde estuary are below their thermal optimum, growth and development are expected to accelerate with increased temperature when food is not a limiting factor. Consequently, soles reach maturity sooner and grow larger. However, when we consider a restriction in available energy, linked to limited carrying capacity of the estuary, the effect of temperature is cancelled and changes in life history traits are negligible. However, a reduced energy in the reserve is estimated, which might alter the response to other environmental changes
Insensitivity for Matching Systems
No full textInternational audienceAbstract We study matching queues motivated by applications in ride-sharing platforms, where items (e.g., drivers and riders) arrive over time and are matched based on a compatibility graph. Our model generalizes classical compatibility queueing models and queue-based ride-sharing models by allowing exogenous driver arrivals, queues for both drivers and riders, and arbitrary bipartite compatibility structures. We provide sufficient conditions under which the stationary distribution exhibits insensitivity to 1) service-time (drive-time) distributions and 2) the matching policies of drivers and riders, respectively. Using tools from Kelly networks and order-independent queues, we provide simple and unified proofs of insensitivity to service-time distributions and to matching policies for a broad class of models. Our policy insensitivity result requires a finite buffer; we demonstrate through counterexamples that such insensitivity may fail when the buffer is infinite. Our results also shed light on insensitivity in related redundancy systems, offering new insights into their stationary behavior
Japan's Demographic Decline and its Geoeconomic Implications in the Long Run
No full textPart 3. Policy implications. Chapitre 12International audienc