Méthode locale de type mortar pour le contact dans le cas de maillages incompatibles de degré élevé

In this thesis, we develop a local "mortar" kind method to deal with the problem of contact with non-matching meshes in an optimal way into a finite element code of industrial level. In the first part of the thesis, we introduce the mathematical framework of the Local Average Contact method (LAC). This approach consists in satisfying the non-interpenetration condition in average on each element of a macro-mesh defined in a suitable way. We start by developing a new technique for proving the optimality of variational inequality approaches discretized by finite elements modeling Signorini problem without other hypothesis than the Sobolev regularity of the solution of the continuous problem. Then we define the LAC method and prove, using the new technical tools, the optimality of this local approach modeling the unilateral contact in the general case of non-matching meshes. Finally, we introduce the equivalent mixed formulation and prove its optimality and stability. In the second part of the thesis, we are interested in the numerical study of the LAC method. We confirm its ability to optimally treat the contact problem when considering non-matching meshes like standard "mortar" methods, while remaining easily implementable in an industrial finite element code. We show, for example, that the method successfully passes the Taylor patch test. Finally, we show its contribution in terms of robustness and at the quality of the contact pressures on an industrial study.Dans cette thèse, nous développons une méthode locale de type "mortar" pour traiter le problème de contact avec maillages incompatibles de manière optimale dans un code de calcul par éléments finis de niveau industriel. Dans la première partie de la thèse, nous introduisons le cadre mathématique de la méthode intitulée "Local Average Contact" (LAC). Cette approche consiste à imposer la condition de non-interpénétration en moyenne sur chaque élément d'un macro-maillage défini de manière idoine. Nous commençons par développer une nouvelle technique de preuve pour démontrer l'optimalité des approches de type inéquation variationnelle discrétisée par éléments finis standards pour le problème de Signorini, sans hypothèse autre que la régularité Sobolev de la solution du problème continu. Puis nous définissons la méthode LAC et démontrons, à l'aide des nouveaux outils techniques, l'optimalité de cette approche locale modélisant le contact unilatéral dans le cas général des maillages incompatibles. Pour finir, nous introduisons la formulation mixte équivalente et démontrons son optimalité et sa stabilité. Dans la seconde partie de la thèse, nous nous intéressons à l'étude numérique de la méthode LAC. Nous confirmons sa capacité à gérer numériquement le contact unilatéral avec maillages incompatibles de manière optimale à l'instar des méthodes "mortar" classiques, tout en restant facilement implémentable dans un code de calcul industriel. On montre ainsi, entre autres, que la méthode passe avec succès le patch test de Taylor. Finalement, nous montrons son apport en terme de robustesse et au niveau de la qualité des pressions de contact sur une étude de type industrielle

A reduced basis method for frictional contact problems formulated with Nitsche's method

We develop an efficient reduced basis method for the frictional contact problem formulated using Nitsche's method. We focus on the regime of small deformations and on Tresca friction. The key idea ensuring the computational efficiency of the method is to treat the nonlinearity resulting from the contact and friction conditions by means of the Empirical Interpolation Method. The proposed algorithm is applied to the Hertz contact problem between two half-disks with parameter-dependent radius. We also highlight the benefits of the present approach with respect to the mixed (primal-dual) formulation

Détection automatique de réseaux enterrés par imagerie géoradar

National audienceAfin d’améliorer la connaissance de l’existant et d’éviter l’endommagement d’ouvrages tiers au cours de travaux de voirie, la localisation des canalisations de gaz de manière non destructive est devenue un important domaine de recherche ces dernières années. Pour répondre à cette problématique, nous utilisons un géoradar. La forme de l’ensemble des réflexions ainsi que leurs intensités donnent une indication sur la nature de l’objet. Une forme hyperbolique indique la présence d’un objet "ponctuel" situé au niveau de son aplomb. Ainsi la détection d’hyperbolesdans le radargramme permet de localiser des canalisations. Dans ces travaux, nous proposons une méthode pour détecter automatiquement les hyperboles des données géoradar à partir d'un dictionnaire de formes théoriques et de deux modèles obtenus par apprentissage supervisé.Cette méthode montre des résultats quantitatifs intéressants et a été testée sur des données réelles

Application of the curvelet transform for pipe detection in GPR images

International audienceThis paper is dedicated to the detection of buried pipeswith a ground penetrating radar (GPR). The imagesfrom GPR acquisitions also called B-scan are corruptedby clutter and noise. In order to remove these undesirableitems we propose to use the properties of the curvelettransform. Were using this method as a first step of theautomatic detection of hyperbola in a B-scan

Enhanced two-photon absorption cross-sections of zinc(II) tetraphenylporphyrins peripherally substituted with d(6)-metal alkynyl complexes

International audienceThe syntheses of new Zn(II) tetraphenylporphyrin (ZnTPP) derivatives functionalized with electron-rich d6-transition metal alkynyl complexes at their periphery are reported. Z-scan measurements reveal remarkably large effective two-photon absorption (TPA) cross-sections in the visible range for these compounds

Small-scale study of Debris-Flows Interactions with a Lateral Debris Basin and Crossings: The Manival Torrent case study

Small-scale models are useful tools to study the interactions between debris flows and structures and channels. Small-scale modelling of debris flows remains however complicated because of the complex rheology and scaling challenges of these geophysical processes. An on-going study of a debris basin and the downstream channel where two fords and a bridge are located is presented in this extended abstract. The studied torrent is the Manival catchment, located near Grenoble in France. We present the catchment features, the scientific questions studied, some preliminary calibration results describing the mixtures used to model debris flows as well as results from three debris-flood and two debris-flow runs. In essence, the model highlighted that the structure enable a large share of the bedload transport to pass downstream. Debris flows can be more or equally trapped depending on their rheology which controls the surges dynamics and the deposition slope in the debris basin

Comparative analysis of CAR T-cell therapy access for DLBCL patients: associated challenges and solutions in the four largest EU countries

IntroductionCAR T-cell therapy has emerged as a promising new immuno-oncology treatment that engages the patient’s immune system to fight certain hematological malignancies, including diffuse large B-cell lymphoma (DLBCL). In the European Union (EU), CAR T-cell therapies have been approved for relapsed/refractory (R/R) DLBCL patients since 2018, but patient access is often still limited or delayed. This paper is aimed at discussing challenges to access and possible solutions in the largest four EU countries.MethodsThe analysis relied on literature review, market data collection, since homogeneous data coming from registries were not available, and discussion with experts coming from all four countries.ResultsWe calculated that in 2020, between 58% and 83% of R/R DLBCL patients (EMA approved label population) or between 29% and 71% of the estimated medically eligible R/R DLBCL patients, were not treated with a licensed CAR T-cell therapy. Common challenges along the patient journey that may result in limited access or delays to CAR T-cell therapy were identified. These include timely identification and referral of eligible patients, pre-treatment funding approval by authorities and payers, and resource needs at CAR T-cell centers.DiscussionThese challenges, existing best practices and recommended focus areas for health systems are discussed here, with the aim to inform necessary actions for overcoming patient access challenges for current CAR T-cell therapies as well as for future cell and gene therapies