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Dynamic damage modelling through phase-field approaches: Assessment, critical analysis and comparison
No full textInternational audienceThis work assesses the ability of various phase field approaches to model dynamic damage evolution up to fracture. The damage evolution can be formulated using several types of Partial Differential Equations (PDEs), such as elliptic, parabolic and hyperbolic damage PDEs. The latter enable the use of explicit time integration, which is a crucial feature if an implementation in solvers dedicated to transient analysis is targeted. The challenge of the damage irreversibility constraint through different strategies is also investigated. It is shown that the classical history variable does not strictly assure the damage irreversibility and can induce some numerical instabilities. However, combining this history variable with the damage viscosity term of the PDE might help to restore the irreversibility, even though explicit time stepping offers the opportunity to force this condition algorithmically. Finally, we propose a quantitative comparison of the solutions of each phase field dynamic approach through physically-based metrics. Eventually, the classical Kalthoff experiment is simulated and the predictions of different PDEs with different set of damage parameters are compared.Ces travaux évaluent l'aptitude de différents modèles à champs de phase pour modéliser l'évolution dynamique de l'endommagement jusqu'à rupture. L'évolution de l'endommagement peut être décrite par une équation à dérivée partielle (EDP) de type elliptique, parabolique ou hyperbolique. Ces dernières permettent l'utilisation de schémas d'intégration explicites, stratégie majoritairement employée dans les cas d'étude de dynamique transitoire. La condition d'irréversibilité de l'endommagement a également été imposée de différente manières. Il est montré que l'utilisation d'une variable d'histoire de la densité d'énergie élastique positive ne permet pas de garantir. strictement l'irréversibilité et peut induire des instabilités. Néanmoins, si cette stratégie est combinée à l'utilisation d'un terme de viscosité d'endommagement dans l'EPD gouvernant son évolution, il est possible d'assurer l'irréversibilité. Autrement, le cadre explicite de la stratégie de résolution offre la possibilité d'imposer l'irréversibilité de façon algorithmique. Ensuite, au travers des cas test d’une barre en traction et de l’expérience d’impact de Kalthoff et al., des études paramétriques ont été effectuées pour évaluer la sensibilité aux paramètres des EPDs. Pour finir, une étude comparative des solutions obtenues par les modèles de champs de phase en dynamique a été réalisée via l’utilisation de métrique basée sur des quantités physiques
Caractérisation azimutale et radiale du champ acoustique en conduit par antennerie externe
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Space traffic management: Improvements to spacecraft collision avoidance (COLA)
No full textInternational audienceCollision avoidance, the process of planning and possibly executing a manoeuvre to mitigate the risk of a collision in orbit, is becoming increasingly important as the amount of space traffic increases. This paper discusses different types of conjunction events, the technical processes involved in identifying higher risk conjunctions and possible mitigation techniques, and gaps and limitations in the processes. Possible solutions to these gaps are addressed including improved communication and coordination, more accurate and precise data, and improved education of operators. Several recommendations are made to improve the collision avoidance process and effectiveness
Méthodes formelles pour la programmation et l'analyse de comportements robustes des systèmes autonomes
No full textThe development of autonomous robotic systems uses intelligent functions, system control, data treatment or trajectory planning. These functions are implemented through programmation environments such as ROS, which results in complex software architectures, where dozens of processus run together.The design of autonomous missions demands high-level behavior specifications, which lie on functions given by the robotic system. These behaviors require to be robust if problems arise (for instance, sensor failure), or external events due to the mission and its environment. Furthermore, in critical contexts, high risk missions or when the intervention of a human operator is impossible, it is necessary to bring proofs on the robust and correct behavior of the system. To that end, classical test methods or simulations can prove insufficient for the system.This thesis subject aims to tackle the problematic of specification and analysis of behaviors, through formal methods. Formal methods and Petri networks in particular will be studied for its convenience when specifying concurrent behaviors, possibility to run models, as well as existing tools for model-checking.Le développement de systèmes robotiques autonomes met en oeuvre des fonctionnalités intelligentes, de contrôle du système, de traitement de ses données, ou de planification de sa trajectoire. Ces fonctionnalités sont implantées au travers d’environnements de programmation tels que ROS, ce qui résulte en des architectures logicielles complexes, faisant intervenir plusieurs dizaines de processus.La réalisation de missions en autonomie nécessite de pouvoir spécifier des comportements haut-niveau, qui reposent sur les fonctionnalités fournies par le système robotique. Ces comportements nécessitent d’être robustes à la survenue de pannes sur le système robotique (par ex. pannes de capteurs), ou à des événements extérieurs liés à la mission et à son environnement. De plus, dans des contextes critiques, pour des missions risquées ou lorsque l’intervention d’un opérateur humain est quasiment impossible, il est nécessaire d’apporter des preuves a priori sur le comportement robuste et correct du système. Dans ce cadre, les techniques classiques de tests ou de simulation peuvent se révéler insuffisants à garantir une confiance suffisante dans le système.Ce sujet de thèse vise à aborder cette problématique de la spécification et de l’analyse de comportements, au moyen de méthodes formelles. Le formalisme des réseaux de Petri sera en particulier étudié de par son adéquation à la spécification de comportements concurrents, la possibilité d’exécuter les modèles, ainsi que les outils de model-checking existants
Numerical simulation of the oblique water impact of double curvature bodies involving suction and cavitation phenomena
No full textInternational audienceThe present study aims to assess the capability of a numerical method to model hydrodynamicimpacts representative of an aircraft ditching. The considered numerical method is based onthe Finite Element explicit solver Radioss and a Coupled Eulerian–Lagrangian approach. Thefluid–structure interaction is dealt with using an immersed contact interface and a penaltycoupling method. The oblique water impacts of three different fuselage sections have beenstudied based on the experimental campaigns carried out during the European project SARAHat the High-Speed Ditching Facility of CNR-INM in Rome, Italy. The results are presented interms of force coefficient, local relative pressure, and free surface elevation. The effect of thecoupling stiffness and size of the fluid elements on the numerical results is analysed to assessthe robustness of the numerical method. The numerical method shows a satisfying capabilityto reproduce most of the experimental results. Particular attention is given to the capabilityof the numerical method to describe the suction and cavitation phenomena. The effect of thespecimens’ transversal cross-section, the specimens’ longitudinal curvature and the developmentof cavitation phenomenon on the hydrodynamic loads are also investigate
Unsteady simulations of an aircraft in take-off conditions with installed engine and rotating fan
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Réflexions sur l'utilisation de la LST pour la cartographie de l'indice de vulnérabilité à la chaleur : cas d’étude sur la métropole de Toulouse, France
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Tomographie par spectroscopie d’absorption laser pour la cartographie de température et d’espèces chimiques en combustion
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aquaDenoising: AI-enhancement of in situ liquid phase STEM video for automated quantification of nanoparticles growth
No full textInternational audienceAutomatic processing and full analysis of in situ liquid phase scanning transmission electron microscopy (LP-STEM) acquisitions are yet to be achievable with available techniques. This is particularly true for the extraction of information related to the nucleation and growth of nanoparticles (NPs) in liquid as several parasitic processes degrade the signal of interest. These degradations hinder the use of classical or state-of-the-art techniques making the understanding of NPs formation difficult to access. In this context, we propose aquaDenoising, a novel simulation-based deep neural framework to address the challenges of denoising LP-STEM images and videos. Trained on synthetic pairs of clean and noisy images obtained from kinematic-model-based simulations, we show that our model is able to achieve a fifteenfold improvement in the signal-to-noise ratio of videos of gold NPs growing in water. The enhanced data unleash unprecedented possibilities for automatic segmentation and extraction of structures at different scales, from assemblies of objects down to the individual NPs with the same precision as manual segmentation performed by experts, but with higher throughput. The present denoising method can be easily adapted to other nanomaterials imaged in liquid media. All the codes developed in the present work are open and freely available