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Influence of the mesh on the crack path in phase-field fracture simulations
No full textMeeting of the 10th GAMM workshop on phase-field modeling and the workshop Materials/Microstructure modelling: Analytics & Benchmarks organized and hosted by KIT with support by the DGM.International audienceOver the past 25 years, phase-field fracture models [1, 2] have become increasingly popular for modeling crack propagation. In particular, their (Γ-)convergence towards the Linear Elastic Fracture Mechanics (LEFM) provides strong theoretical foundations. Despite this popularity, limitedresearch has been conducted on how spatial discretization (e.g., mesh size, structure, and element geometry) affects the predicted crack path. This study addresses this gap from the perspective of the mechanical engineering community. We employ a benchmark problem inspired by the PureShear test [3] (also called strip specimen), involving an infinite strip with an initial horizontal edge crack located above the specimen center and subjected to tensile loading. The crack path is expected to deviate towards the center of the specimen exponentially. This result has been recovered using an incremental crack propagation solver based on LEFM, which serves as our reference. Phase-field fracture simulations, performed using the Finite Element Method, are then carried out. Different meshes (varying mesh size, structured/unstructured, and element geometry) are used in the simulations to assess their influence on the crack path. The bias induced by the mesh is evaluated by comparing the phase field simulation results with the reference. The final goal of this study is to provide recommendations to avoid, or at least mitigate, any bias induced by spatial discretization
A Coupled Criterion-based approach to develop an adherence test for adhesively bonded joints
No full textInternational audienc
Rénag infiltre le réseau collaboratif Centipède-RTK pour augmenter la couverture GNSS du territoire
No full textNational audienceNé en 2019, le réseau Centipède-RTK est un réseau collaboratif de stations GNSS fixes, en majorité à bas coût (quelques centaines d'euros) servant de base pour du positionnement centimétrique temps réel (RTK). Il bénéficie de l'implication de ses contributeurs, mettant à disposition de tous, gratuitement et librement, les corrections générées par ces bases. Initialement limité à la France métropolitaine, le réseau s'est récemment développé en Outre-Mer et à l'étranger, avec près d'un millier de bases actives aujourd'hui. Depuis 2022, le Réseau national GNSS permanent d'Epos-France rediffuse les corrections temps-réel issues de la moitié des stations permanentes de son réseau via Centipède, ce qui a conduit à un bond d’utilisation des données issues des stations académiques. Parallèlement, le centre de données Rénag utilise le flux issu de l’ensemble des stations Centipède-RTK.Bien moins onéreux que les réseaux conventionnels en termes d’équipement et d’abonnement, le réseau Centipede-RTK permet d’envisager une nouvelle approche pour l’observation de notre environnement et de la Terre solide. Un déploiement participatif de ces bases permettrait une meilleure couverture des territoires et aiderait à la démocratisation du positionnement GNSS temps réel
Structural interactions in global trade
No full textInternational audienceWe provide a methodological framework for investigating global trade networks thatdistinguish between categories of goods. We introduce a multi-layer network version of the Lantner diffusion model, in which each layer represents a specific good and each node corresponds to a country. By establishing several mathematical results involving structural alterations of the network, and by leveraging interaction indices, we show how to quantify structural interactions between categories of goods and offer recommendations for decision-makers designing embargoes against target countries
Sensibilité à la forme des pales d'un rotor isolé pour l'optimisation aéroacoustique à l'aide de la méthode adjointe discrète
No full textInternational audienceA discrete adjoint framework is developed to optimize rotor self-noise from steady fluid simulations in the rotating frame. To this end, a simplified expression of the off-body frequency-domain Ffowcs-Williams and Hawkings (FW-H) equation is derived for far-field observers, following the model of Hanson and Parzych (1993) originally written for on-body surfaces. The latter is implemented and compared against the results given by an established time-domain FW-H solver. Far-field acoustic pressure sensitivities are derived analytically and validated by comparison with second-order accurate finite differences. The sensitivities of any objective function expressed in terms of the acoustic pressure can therefore be reconstructed. Then the discrete adjoint of a Reynolds-averaged Navier-Stokes solver provides the objective function gradients with respect to the blade shape parameters. The complete workflow is validated against finite difference evaluations on an isolated open rotor in cruise conditions.Un cadre adjoint discret est développé pour optimiser le bruit propre du rotor à partir de simulations de fluides stationnaires dans le domaine tournant. À cette fin, une expression simplifiée de l'équation de Ffowcs-Williams et Hawkings (FW-H) dans le domaine fréquentiel perméable est dérivée pour les observateurs en champ lointain, suivant le modèle de Hanson et Parzych (1993) écrit à l'origine pour les surfaces solides. Ce dernier est mis en œuvre et comparé aux résultats donnés par un solveur FW-H établi dans le domaine temporel. Les sensibilités à la pression acoustique en champ lointain sont dérivées analytiquement et validées par comparaison avec des différences finies précises du second ordre. Les sensibilités de toute fonction objective exprimée en termes de pression acoustique peuvent donc être reconstruites. Ensuite, l'adjoint discret d'un solveur de Navier-Stokes à moyenne de Reynolds fournit les gradients de la fonction objectif par rapport aux paramètres de forme de la pale. L'ensemble de chaîne complète est validé par des évaluations par différences finies sur un rotor ouvert isolé dans des conditions de croisière
Characterisation of small-scale laser breakdown-induced blast waves with a PVDF gauge
No full textInternational audienc
Design and validation of an experimental set-up to study shock wave propagation in liquid foams
No full textInternational audienc
Chemical servoing with hexapod robot for gas source localization and YOLO-based visual defect detection
No full textInternational audienceRobotic systems have the ability to perform industrial inspection tasks through the integration of visual and chemical servoing functions. A commonly used system is the image-based servoing system. This study presents an innovative approach that merges chemical servoing with visual defect detection in industrial settings using a hexapod robot. The main goal is to develop a hexapod robot capable of detecting and approaching a gas source through chemical servoing, and subsequently analyzing the source using a pretrained YOLOv5m model, a one-stage CNN detector architecture. The effectiveness of the proposed methodology is showcased through simulations that compare different chemical servoing algorithms and image defect detection techniques for gas source identification. In addition, a prototype of the hexapod robot is presented
Bathtub vortex effect on Torricelli's law
No full textInternational audienceWe investigate experimentally the unsteady draining flow from a rotating tank. The fluid in the tank is first set in solid rotation, before the draining hole is opened. We show that the draining may be drastically reduced by the rotation, as the vortex circulation increases together with the surface deformation. We demonstrate that the usual Torricelli's draining law has to be modified with the surface deformation and that the draining time is mainly governed by a nondimensional parameter corresponding to the ratio of the size of the outlet to the thickness of the Ekman boundary layer
Emergent kin selection of altruistic feeding via non-episodic neuroevolution
No full text13 pages, 5 figuresInternational audienceKin selection theory has proven to be a popular and widely accepted account of how altruistic behaviour can evolve under natural selection. Hamilton's rule, first published in 1964, has since been experimentally validated across a range of different species and social behaviours. In contrast to this large body of work in natural populations, however, there has been relatively little study of kin selection \emph{in silico}. In the current work, we offer what is to our knowledge the first demonstration of kin selection emerging naturally within a population of agents undergoing continuous neuroevolution. Specifically, we find that zero-sum transfer of resources from parents to their infant offspring evolves through kin selection in environments where it is hard for offspring to survive alone. In an additional experiment, we show that kin selection in our simulations relies on a combination of kin recognition and population viscosity. We believe that our work may contribute to the understanding of kin selection in minimal evolutionary systems, without explicit notions of genes and fitness maximisation