Archive ouverte de Centrale Lyon
Not a member yet
32420 research outputs found
Sort by
Dimensionnement au séisme des ouvrages en pierre sèche : cas des soutènements de talus
No full textDry stone construction is a millennia-old building technique found throughout the world. It is based on the use of roughly dressed stone blocks. The structure is erected by a skillful arrangement of these blocks, without the use of mortar. Retaining walls are the most common dry-stone structures within this heritage. Today, thousands of kilometers of such walls have been identified in France, many of which are still in service.In addition to their cultural value, these walls have always played an economic role, by enabling the development of agriculture and transportation in mountainous regions. Nowadays, although their economic role is less significant, their appeal continues to grow as they address the challenges posed by Sustainable Development.The absence of comprehensive theoretical knowledge and design standards remains a major challenge for the recognition of dry stone as a relevant engineering solution for the 21st century.In France, over the past three decades, experimental, analytical, and numerical studies have been carried out to improve the understanding of their mechanical behavior and to demonstrate their technical value. More recently, some studies have focused on their seismic behavior and have proposed preliminary recommendations for seismic design. Building on these advances, the present work aims to further investigate the seismic response of Dry-Stone Retaining Walls (DSRWs). This study is based on a numerical approach using a 3D mixed discrete--continuum (MDC) model. The 3D numerical model is validated against scaled experiments reported in the literature. Once validated, the model is used to study the mechanical behavior of DSRWs first within a simplified dynamic framework, and then within a fully dynamic framework. The dynamic response is first examined using artificial harmonic signals to identify initial trends and to assess their damaging potential. Then, the response of DSRWs is investigated under real seismic records (approximately M = 6) in order to better capture their actual seismic behavior. From these studies, we were able to highlight that a behavior factor equal to 2, as proposed by Eurocode 8 for reinforced concrete retaining walls, generally remains valid for DSRWs. Based on this result, the recommendations for the seismic design of DSRWs in metropolitan France have been revisited and extended to the cases of both frictional and cohesive backfills.La pierre sèche est une technique constructive pluri-millénaire présente dans le monde entier. Elle se fonde sur l'utilisation de moellons de pierre peu retaillés. L'ouvrage est érigé par un arrangement savant de ces moellons, et ce sans l'aide de mortier. Les murs de soutènement sont les ouvrages les plus représentés dans le patrimoine en pierre sèche. Actuellement, des milliers de kilomètres sont identifiés en France dont de nombreux toujours en service.En plus de leur valeur culturelle, ces murs ont toujours joué un rôle économique, en permettant le développement de l'agriculture et le transport dans les régions montagneuses. De nos jours, même si leur rôle économique est moindre, l'intérêt qu'ils suscitent va grandissant car ils répondent aux enjeux posés par le Développement Durable.L'absence de connaissances théoriques complètes et de normes de conception demeure ainsi un défi majeur pour l'affirmation de la pierre sèche comme solution d'ingénierie pertinente pour le XXIème siècle.En France, au cours des trois dernières décennies, des études expérimentales, analytiques et numériques ont été menées afin d'améliorer la compréhension de leur comportement mécanique et prouver leur valeur technique. Plus récemment, certaines études se sont concentrées sur leur comportement au séisme et ont proposé des recommandations préliminaires pour la conception sismique. Sur la base de ces avancées, le présent travail vise à approfondir l'étude de la réponse sismique des Murs de Soutènement en Pierre Sèche (MSPS). Cette étude s'appuie sur une approche numérique utilisant une modélisation 3D mixte discrète-continue (MDC). Le modèle numérique 3D est validé à partir d'expériences à échelle réduite issues de la littérature. Une fois validé, le modèle est utilisé pour étudier le comportement mécanique des MSPS dans le cadre d'une approche simplifiée du comportement dynamique puis dans le cadre d'une approche dynamique vraie. La réponse dynamique est d'abord examinée en utilisant des signaux harmoniques artificiels pour identifier des tendances premières et comprendre leur pouvoir endommageant. Ensuite, la réponse des MSPS est étudiée sous l'action d'enregistrements sismiques réels (approximativement M = 6) afin de mieux cerner le comportement réel des MSPS sous séisme. De ces études, nous avons pu mettre en évidence qu'un coefficient de comportement égal à 2, proposé par l'Eurocode 8 pour les murs de soutènement en béton armé, reste généralement valide pour les MSPS. Fort de ce résultat, les recommandations pour le dimensionnement sismique des MSPS sur le territoire français métropolitain ont été révisitées et élargies aux cas de remblais frottants et cohésifs
A new hybrid data and model-centric predictive approach dedicated to industrial pipe maintenance
No full textInternational audiencePredictive Maintenance (PdM) for pipe clogging is a critical challenge in the industrial sector, particularly with the increasing adoption of Artificial Intelligence (AI) and the Internet of Things (IoT). Frequent clogging incidents, such as those faced by Orano/La Hague, lead to energy waste, operational inefficiencies, financial losses, and potential safety hazards, highlighting the critical need for effective maintenance solutions to protect both assets and personnel. This study proposes a novel hybrid approach that combines the strengths of data-centric and model-centric methodologies for Prognostic and Health Monitoring (PHM) of pipeline systems in constrained industrial environments. The approach utilizes passive acceleration measurements to predict clogging occurrences and quantify clogging severity under varying airflow rates. Experimental results indicate that the proposed method achieves up to 100% accuracy in clogging detection and robust performance across diverse operational conditions. This integrated methodology represents a significant step forward in predictive maintenance, offering scalable and adaptable solutions to enhance safety, operational efficiency, and cost-effectiveness in industrial settings
Une nouvelle topologie de convertisseur DC/DC fonctionnant en ZVS et ZCS sur une large gamme de charges aux fréquences HF / VHF
No full textInternational audienceUne nouvelle topologie de convertisseur DC/DC résonant adaptée aux opérations en hautes et très hautes fréquences de commutation est présentée dans cet article. Le convertisseur proposé est capable de maintenir à la fois une commutation à zéro de tension (ZVS) et à zéro de courant (ZCS) sur une large gamme de charges. Les équations de dimensionnement essentielles sont fournies, et une démonstration expérimentale d’un convertisseur fonctionnant à 15 MHz pour une puissance de 40 W est fournie
Super rewriting theory and nondegeneracy of odd categorified sl(2)
No full textInternational audienceWe develop the rewriting theory for monoidal supercategories and 2-supercategories. This extends the theory of higher-dimensional rewriting established for (linear) 2-categories to the super setting, providing a suite of tools for constructing bases and normal forms for 2-supercategories given by generators and relations. We then employ this newly developed theory to prove the non-degeneracy conjecture for the odd categorification of quantum sl(2) from arXiv:1307.7816 and arXiv:1701.04133. As a corollary, this gives a classification of dg-structures on the odd 2-category conjectured in arXiv:1808.04924
Regional Control Strategies for a Spatiotemporal SQEIAR Epidemic Model: Application to COVID-19
No full textInternational audienceIn this work, we develop a spatial SEIAR-type epidemic model considering a quarantined population (denoted as Q), which we call the SQEIAR model. The dynamics of the SQEIAR model are described by six Partial Differential Equations (PDEs) that represent the changes in the susceptible, quarantined, exposed, asymptomatic, infected, and recovered populations. Our goal is to reduce the number of susceptible, exposed, asymptomatic, and infected individuals while accounting for the environment, which plays a critical role in the spread of epidemics. We then propose a novel strategy for epidemic control, incorporating two key control measures: regional quarantine for the susceptible population and treatment for the infected. This ap-proach serves as an alternative to widespread quarantine, minimizing the economic, social, and other potential impacts. Additionally, we consider the possibility of re-infection among recovered individuals, a common occurrence in many diseases. To demonstrate the practical utility of our results, a numerical example centered on COVID-19 is presented
Hamiltonian representation of isomonodromic deformations of twisted rational connections: The Painlevé hierarchy
No full textInternational audienceIn this paper, we build the Hamiltonian system and the corresponding Lax pairs associated to a twisted connection in admitting an irregular and ramified pole at infinity of arbitrary degree, hence corresponding to the Painlevé hierarchy. We provide explicit formulas for these Lax pairs and Hamiltonians in terms of the irregular times and standard Darboux coordinates associated to the twisted connection. Furthermore, we obtain a map that reduces the space of irregular times to only non-trivial isomonodromic deformations. In addition, we perform a symplectic change of Darboux coordinates to obtain a set of symmetric Darboux coordinates in which Hamiltonians and Lax pairs are polynomial. Finally, we apply our general theory to the first cases of the hierarchy: the Airy case , the Painlevé case and the next two elements of the Painlevé hierarchy
An Octree-based adaptive moving thermal-fluid framework for efficient multi-scale and multi-physics simulation of laser-based manufacturing processes
No full textInternational audienceMultiphysics and multi-scale thermal-fluid models are essential for understanding the coupling of physical phenomena, enabling the optimization of welding and additive manufacturing process parameters. However, the thermal-fluid simulations are extremely time-consuming due to the need for a fine mesh (approximately 100µm) and small time steps (around 10 -5 s), which restrict the modeling domain to very small dimension. This paper proposes a multiphysics, multi-scale thermal-fluid model based on the Moving Thermal-Fluid (MTF) framework combined with Octree-based Adaptative Mesh Refinement (AMR) that can solve heat and mass transfer problem in an optimal way. The MTF framework consists of solving the thermal-fluid problem only within a small, moving region containing the melt pool, while calculating a heat transfer problem in the rest of the domain. Therefore, much fewer degrees of freedom (DOF) should be solved for a gvien mesh.The Octree-based AMR will create a fine mesh in the moving region containing the melt pool and a coarser mesh in the rest of the region. Thanks to the presence of Octree structure, the remeshing and variables transfer for the nodes and Gauss point can be performed in an analytical way with negligible CPU time. To validate the proposed approach, simulations of a laser welding benchmark and a single-track direct energy deposition process were conducted using both the Octree-based MTF framework and the MTF</p
Engineering a low-loss aluminum nitride on insulator platform for integrated photonics
No full textInternational audienceAluminum nitride on insulator (AlNOI) is a promising platform for integrated photonics due to its broad transparency range and electro-optic properties. However, optical and electrical losses in sputtered AlN thin films pose significant challenges. In this work, we present a novel cyclic thermal annealing (CTA) method that substantially enhances waveguide performance. A five-cycle 900 °C-1350 °C annealing process improves crystalline quality, reducing waveguide losses by 63% to 0.54 dB/cm and enhancing electrical breakdown fields to 2.95 MV/cm. These results highlight CTA as a promising approach for developing high-performance AlN photonic devices.Aluminum nitride (AlN) offers a unique combination of properties, such as a wide bandgap, high transparency from UV to mid-infrared [1,2], and notable electro-optic coefficients, making it highly suitable for integrated photonics. However, sputtered AlNOI films often suffer from intrinsic defects [3], residual tensile stress [4], and high optical losses that degrade device performance. This work introduces a cyclic thermal annealing (CTA) protocol designed to address these limitations and significantly improve film quality and device performance. In this study, AlN films were deposited via pulsed-DC magnetron sputtering on 8-inch silicon wafers. The five-cycle annealing process, alternating between 900°C and 1350°C, significantly enhanced crystalline quality. X-ray diffraction (XRD), micro-Raman spectroscopy, and infrared reflectivity measurements confirmed these improvements. XRD analysis revealed a narrowing of the rocking curve to 0.85°, indicating improved crystallinity, while the c-axis tilt angle decreased to 0.7°. Residual tensile stress was reduced by 85%, and grain size increased significantly, improving structural uniformity and reducing surface roughness. Waveguide characterization demonstrated a 63% reduction in optical losses, from 1.44 dB/cm to 0.54 dB/cm, when CTA was applied prior to waveguide fabrication. Electrical analysis of metal-insulator-semiconductor (MIS) and metal-semiconductor-metal (MSM) devices revealed that resistivity increased exponentially (up to 2×10 14 Ω•cm), while leakage current decreased significantly. The breakdown field improved to 2.95 MV/cm, further highlighting the effectiveness of the CTA in enhancing electrical properties. These findings underscore the potential of cyclic thermal annealing for improving AlNOI films for integrated photonics. This method is scalable approach for reducing defects and losses in AlN -based devices, paving the way for high-performance optical and electro-optic components.</div
Sharp bounds on the half-space two-point function for high-dimensional Bernoulli percolation
No full text15p.We consider Bernoulli percolation on Z^d with d > 6. We prove an up-to-constant estimate for the critical two-point function restricted to a half-space. This completes previous results of Chatterjee and Hanson (Commun. Pure Appl. Math., 2021), and Chatterjee, Hanson, and Sosoe (Commun. Math. Phys., 2023), and solves a question asked by Hutchcroft, Michta, and Slade (Ann. Probab., 2023)
The First 18 Months of JGR: MLC
No full textInternational audienceAs editors of Journal of Geophysical Research: Machine Learning and Computation , we are delighted to celebrate the successes of our first 18 months