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Modélisation haute fidélité de réservoirs hydrogène fabriqués par enroulement filamentaire
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Early Measurements of Silicon Axisymmetric MEMS Gyro
No full textInternational audienceThis paper presents preliminary results of a new silicon MEMS gyro. This MEMS Coriolis Vibratory Gyroscope (CVG) is based on link elements with counterweight that balance the proof mass momentum assuring its insulation from the environment. We demonstrated high quality factor up to 100 000 for a resonant frequency of 8 kHz. A high linearity (R2 > 0.9999) of the scale factor has been demonstrated over a +/-1000 °/s angular rate range. An Allan variance has been measured and it demonstrated an ARW in open loop of 17 °/√h, which suggest promising performance in closed-loop operation
HOPPS: A performance portable spectral difference solver for high-fidelity computational fluid dynamics
No full textInternational audienceHigh-fidelity computational fluid dynamics (CFD) enables the study of complex and subtle fluid dynamics phenomena, but remains to this day very computationally expensive. Therefore, being able to take advantage of all the raw compute power provided by high-performance computing (HPC) hardware evolutions such as the rise of GPU computing is key to making high-fidelity CFD more affordable. However, considering the diverse and fast-evolving HPC hardware landscape, long-term sustainability and software maintainability can rapidly be compromised. The use of adequate numerical methods is also key to reduce the computational cost, and discontinuous high-order methods which combine geometric flexibility and efficient hardware use in an increasingly bandwidth-bound HPC landscape, are very promising in this regard. This work reports the implementation of such a high-order CFD solver using the open source library Kokkos to address the performance portability and sustainability issues. Performance is investigated over a broad range of CPU and GPU architectures, demonstrating the relevance of the approach. This work also highlights the fitness of the chosen numerical method to achieve high orders of accuracy without compromising performance nor scalability
Mechanical Behavior of Metallic Nanoparticles and Alloys: Influence of Shape, Size, and Composition on Elastic and Plastic Properties
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Comparison of high-order numerical solvers for scalere solved simulations of the supersonic Taylor-Green vortex flow
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Formalizing Concentration Inequalities in Rocq: Infrastructure and Automation
No full textInternational audienceConcentration inequalities are standard lemmas providing upper bounds on deviations of random variables. To formalize concentration inequalities, we have been developing a general library of lemmas for probability theory in the Rocq prover. This effort led us to revisit already established technical aspects of the Mathematical Components libraries. In this paper, we report on improvements of general interest resulting from our formalization. We devise types for numeric values and a lightweight semi-decision procedure, based on interval arithmetic. We also extend the hierarchy of available mathematical structures to formalize Lebesgue spaces. We illustrate our new formalization of probability theory with the complete proof of a concentration inequality for Bernoulli sampling
Détection de signaux radar LPI par YOLO en présence d'interférences et de signaux inconnus
No full textInternational audienceDans un contexte de guerre électronique, la détection de signaux radar à faible probabilité d'interception (LPI) représente un défi majeur, en particulier en présence d'interférences ou face à des formes d'ondes inédites. Cela souligne la nécessité de développer des modèles d'apprentissage profond robustes et adaptatifs. Ce travail explore les capacités du modèle YOLOv8 dans deux situations critiques : la détection sous interférences et la généralisation à de nouvelles modulations LPI. Les résultats expérimentaux montrent que YOLOv8 conserve une bonne probabilité de détection et un taux de fausses alarmes faible, même en conditions dégradées, soulignant ainsi son potentiel pour des applications en environnement opérationnel
When Buildings Blur the Lines: Revealing the Hidden Performance Equivalences in MANET Routing Protocols *
No full textInternational audienceThe study finds that in urban environments, the performance of non-cross-layer routing protocols (AODV, OLSR, DSDV) becomes nearly identical, contradicting earlier research that ranked their effectiveness. Using a new building-aware loss model in ns-3, we show that realistic urban conditions, unlike traditional open-field models, cause end-to-end delay to increase up to tenfold, with high variability due to unstable links. We also investigate whether adjusting parameters in open-field models could mimic urban connectivity. While this tuning matched some network connectivity metrics, it failed to replicate more complex concepts linked with propagation dynamics of cities, proving that open-field models cannot accurately simulate urban networks without fundamental changes
Dynamique des VTOL dans les Conférences Décennales d'Aéromécanique de la AHS/VFS, 1074-2014
No full textInternational audienceThe AHS/VFS Decennial Specialists' Conferences on Aeromechanics have provided the rotorcraft community with periodic benchmarks of the state of aeromechanics research. At its launch in 1974, there was an acknowledgment that the government and industry required an improved collaboration of rotorcraft dynamics experts to overcome current and future challenges. The focus gradually shifted from simply dynamics to aeromechanics, a more all-encompassing term that includes structural dynamics, aerodynamics, modeling and simulation, vibration, test and evaluation, controls, and many other technical areas. This paper offers a retrospective look at some of pivotal works from the first five decennial conferences that have shaped the industry, some trends observed in each discipline, and some reflections on the future of aeromechanics research.La série de conférences décennales spécialistes de l'AHS/VFS en aéromécanique a offert à la communauté des voilures rotatives des repères périodiques de l’état de la recherche en aéromécanique. Lors de son lancement en 1974, il était reconnu que le gouvernement et l’industrie avaient besoin d’une meilleure collaboration entre les experts en dynamique des rotors afin de relever les défis actuels et futurs. L’accent s’est progressivement déplacé d’une simple dynamique vers l’aéromécanique, un terme plus englobant qui inclut la dynamique structurelle, l’aérodynamique, la modélisation et la simulation, les vibrations, les essais et évaluations, les commandes, ainsi que de nombreux autres domaines techniques. Cet article propose un retour sur certains travaux majeurs des cinq premières conférences décennales qui ont façonné l’industrie, les tendances observées dans chaque discipline, ainsi que quelques réflexions sur l’avenir de la recherche en aéromécanique
Comment repenser les retours vibrotactiles dans les interfaces humain-machine : Utilisation des principes de la Gestalt pour concevoir des messages intelligibles pour des situations critiques
No full textInternational audienceIn safety-critical systems, vibrotactile interfaces may offer a suitable substitute or a complement to visual and auditory channels to convey information to operators. However, the conception of vibrotactile stimuli for such applications often relies on a low-level signal design, focusing on sensation with limited consideration for the overall perceptual organization of the stimulus. This PhD research aims to rethink vibrotactile feedback design through the lens of Gestalt theory, in order to create structured tactile messages that follow Gestalt organizational laws of perception. The central hypothesis supports that Gestalt principles can lead to the design of patterns that are more robust and efficiently processed. To this end, this research seeks to provide Gestalt-grounded design guidelines for vibrotactile stimuli applied to high-demand contexts. These guidelines will support the implementation of vibrotactile interfaces that improve operational performance by redistributing cognitive load across sensory modalities, integrating the tactile channel alongside vision and audition, while maintaining intelligibility of the transmitted message.Dans des environnements critiques, les interfaces vibrotactiles pourraient représenter un substitut ou un complément approprié aux canaux visuels et auditifs pour transmettre des informations aux opérateurs. Cependant, la conception de stimuli vibrotactiles pour de telles applications repose souvent sur un design du signal de bas niveau, se concentrant notamment sur la sensation avecune considération limitée pour l’organisation perceptive globale du stimulus. Cette thèse vise à repenser la conception des retours vibrotactiles à travers le prisme de la Gestalt, afin de créer des messages tactiles structurés qui suivent les lois organisationnelles perceptives de la Gestalt.L’hypothèse centrale soutient que les principes de la Gestalt peuvent conduire à l’élaboration de patterns qui sont traités de manière plus robuste et efficace. Ainsi, cette recherche a pour but de fournir des directives de conception basées sur la Gestalt pour les stimuli vibrotactiles appliqués aux contextes critiques. Ces principes de conception viseront à soutenir l’implémentation d’interfaces vibrotactiles qui améliorent la performance opérationnelle en redistribuant la charge cognitive entre les modalités sensorielles, intégrant la modalité tactile aux côtés de la vision et de l’audition, touten maintenant l’intelligibilité du message transmis