L’apport de l’imagerie numérique à l’étude d’un décor architectural complexe : le mur de scène du théâtre antique d’Orange

Le théâtre augustéen d’Orange est le seul dans l’Occident romain à avoir conservé l’intégralité de son bâtiment de scène ; il est cependant aujourd’hui entièrement dépouillé du riche décor de marbre qui le parait à l’origine. Alors que des milliers de fragments de cette parure nous sont parvenus, il est paradoxalement difficile d’en proposer une restitution complète, du fait des conditions de conservation, de la présence de restaurations anciennes et de l’état de fragmentation extrême des vestiges. Dans la continuité de la nouvelle étude du théâtre entreprise en 2000, le recours à l’imagerie numérique pour l’étude du décor figuré a permis de dépasser une partie de ces obstacles : la numérisation et la réunion des fragments de certaines frises dans un même espace virtuel grâce à la mise au point d’un outil logiciel dédié a facilité considérablement observations, comparaisons, rapprochements et propositions de restitution. Dans un second temps, l’intégration de ces frises aux ordres du mur de scène a pu être envisagée. Qu’elle se soit fondée sur des critères techniques (relevé des traces d’outil, des mortaises de fixation, etc.), iconographiques ou stylistiques (détermination de rythmes et d’alternances caractéristiques, comparaisons volumétriques, restaurations de séquences figuratives, etc.), l’application de ces technologies aura non seulement fourni un outil de visualisation sans équivalent jusqu’à présent, mais aussi permis la multiplication des hypothèses de restitution et leur validation sans avoir à manipuler ou à déplacer les fragments.The Augustan Theatre of the Roman city of Arausio (Orange, France) is the only one in the Roman West to have preserved its entire stage building; however, it is now completely stripped of the rich marble decoration that originally adorned it. While thousands of fragments of this decoration have survived, it is paradoxically difficult to propose a global restitution, due to the conservation conditions, the presence of ancient restorations and the extreme fragmentation of the remains. As a step of the new researches on the theatre undertaken in 2000, the use of digital imaging to study the figurative set has made it possible to overcome some of these obstacles: the digitisation and gathering of fragments of certain friezes in the same virtual space thanks to the development of a dedicated software tool has considerably facilitated observations, comparisons and restitution proposals. In a second step, the integration of these friezes into the orders of the scaenae fronscould be considered. Whether based on technical criteria (tool traces, fixing mortices, etc.), iconographic or stylistic criteria (determination of characteristic rhythms, volumetric comparisons, restoration of figurative sequences, etc.), the application of these technologies has not only provided an unparalleled visualization tool to date, but also allowed the multiplication of restitution hypotheses and their validation

BioDeg: A finite element software for the simulation ofthe corrosion and biodegradation process in metallicbiomaterials

peer reviewe

Predicting atrial fibrillation recurrence by combining population data and virtual cohorts of patient-specific left atrial models

Background: Current ablation therapy for atrial fibrillation is suboptimal, and long-term response is challenging to predict. Clinical trials identify bedside properties that provide only modest prediction of long-term response in populations, while patient-specific models in small cohorts primarily explain acute response to ablation. We aimed to predict long-term atrial fibrillation recurrence after ablation in large cohorts, by using machine learning to complement biophysical simulations by encoding more interindividual variability. Methods: Patient-specific models were constructed for 100 atrial fibrillation patients (43 paroxysmal, 41 persistent, and 16 long-standing persistent), undergoing first ablation. Patients were followed for 1 year using ambulatory ECG monitoring. Each patient-specific biophysical model combined differing fibrosis patterns, fiber orientation maps, electrical properties, and ablation patterns to capture uncertainty in atrial properties and to test the ability of the tissue to sustain fibrillation. These simulation stress tests of different model variants were postprocessed to calculate atrial fibrillation simulation metrics. Machine learning classifiers were trained to predict atrial fibrillation recurrence using features from the patient history, imaging, and atrial fibrillation simulation metrics. Results: We performed 1100 atrial fibrillation ablation simulations across 100 patient-specific models. Models based on simulation stress tests alone showed a maximum accuracy of 0.63 for predicting long-term fibrillation recurrence. Classifiers trained to history, imaging, and simulation stress tests (average 10-fold cross-validation area under the curve, 0.85±0.09; recall, 0.80±0.13; precision, 0.74±0.13) outperformed those trained to history and imaging (area under the curve, 0.66±0.17) or history alone (area under the curve, 0.61±0.14). Conclusion: A novel computational pipeline accurately predicted long-term atrial fibrillation recurrence in individual patients by combining outcome data with patient-specific acute simulation response. This technique could help to personalize selection for atrial fibrillation ablation

Numerical Simulation of Nonclassical Aileron Buzz over 3D Unstructured Adaptive Meshes

Aileron buzz refers to the self–sustained oscillations of an aileron flapping behind an aircraft wing. Nonclassical buzz occurs in transonic flow regimes, and it is characterized by the oscillation of the shock wave location on and off the aileron surface. In order to simulate this phenomenon, we couple the rigid aileron dynamics with the finite volume ALE compressible flow solver Flowmesh. Dynamic grid adaptation is performed through the MMG remeshing library; a local conservative procedure tracks each mesh modification in time, thus avoiding any explicit solution interpolation step, while complying with the moving boundaries and performing solution–driven adaptation. We simulate a simplified test case, consisting of a straight wing between two walls, with a finite–span aileron. Simulations of different aileron spans highlight the 3D flow effects on the frequency of the aileron oscillations. Simulations over an alternative 2D setup, in which the aileron is still connected to the main wing by means of two flexible elements, show the influence of the air gap between aileron and wing on the shock wave movement and on the development of self–sustained aileron oscillations

Remaillage parallèle rapide pour les simulations de grands écoulements (LES) sur des maillages de très grande taille

Numerical simulations on very large meshes, such as large-addy simulations (LES), cannot be performed without resorting to distributed-memory parallelism. For these methods, a sufficient precision can only be achieved by remeshing dynamically the areas that need it. Such a remeshing must therefore be performed in parallel.This paper presents the coarse-grain parallel remeshing method which has been devised and implemented in the PaMPA library for handling distributed meshes in parallel. This method is validated in the context of an industrial LES simulation on a helicopter turbine combustion chamber, on a mesh of more than one billion elements.Les simulations numériques portant sur des maillages de très grande taille, telles que les méthodes LES ("large-eddy simulations"), ne peuvent être réalisées qu'en ayant recours au parallélisme à mémoire distribuée. Pour ces méthodes, une précision suffisante ne peut être atteinte qu'en remaillant dynamiquement les zones qui le nécessitent. Ce remaillage doit donc être effectué en parallèle.Cet article présente la méthode de remaillage parallèle à gros grain conçue et mise en œuvre au sein de la bibliothèque PaMPA de gestion parallèle de maillages distribués. Cette méthode est validée dans le cadre d'une simulation LES industrielle de chambre de combustion de turbine d'hélicoptère, portant sur un maillage à plus d'un milliard d'éléments

Combination of an adaptive remeshing technique with a coupled FEM–DEM approach for analysis of crack propagation problems

The final publication is available at Springer via http://dx.doi.org/10.1007/s40571-019-00306-4This paper presents an enhanced coupled approach between the finite element method (FEM) and the discrete element method (DEM) in which an adaptive remeshing technique has been implemented. The remeshing technique is based on the computation of the Hessian of a selected nodal variable, i.e. the mesh is refined where the curvature of the variable field is greater. Once the Hessian is known, a metric tensor is defined node-wise that serves as input data for the remesher (MmgTools) that creates a new mesh. After remeshing, the mapping of the internal variables and the nodal values is performed and a regeneration of the discrete elements on the crack faces of the new mesh is carried out. Several examples of fracturing problems using the enhanced FEM–DEM formulation are presented. Accurate results in comparison with analytical and experimental solutions are obtained.This work has been supported by the Spanish Government program FPU: FPU16/02697. The authors gratefully acknowledge the received support.Peer ReviewedPostprint (author's final draft

Shape optimization under constraints on the probability of a quadratic functional to exceed a given treshold

This article is dedicated to shape optimization of elastic materials under random loadings where the particular focus is on the minimization of failure probabilities. Our approach relies on the fact that the area of integration is an ellipsoid in the high-dimensional parameter space when the shape functional of interest is quadratic. We derive the respective expressions for the shape functional and the related shape gradient. As showcase for the numerical implementation, we assume that the random loading is a Gaussian random field. By exploiting the specialties of this setting, we derive an efficient shape optimization algorithm. Numerical results in three spatial dimensions validate the feasibility of our approach

Calibrating cardiac electrophysiology models using latent Gaussian processes on atrial manifolds

Models of electrical excitation and recovery in the heart have become increasingly detailed, but have yet to be used routinely in the clinical setting to guide personalized intervention in patients. One of the main challenges is calibrating models from the limited measurements that can be made in a patient during a standard clinical procedure. In this work, we propose a novel framework for the probabilistic calibration of electrophysiology parameters on the left atrium of the heart using local measurements of cardiac excitability. Parameter fields are represented as Gaussian processes on manifolds and are linked to measurements via surrogate functions that map from local parameter values to measurements. The posterior distribution of parameter fields is then obtained. We show that our method can recover parameter fields used to generate localised synthetic measurements of effective refractory period. Our methodology is applicable to other measurement types collected with clinical protocols, and more generally for calibration where model parameters vary over a manifold

Reconstructing Haemodynamics Quantities of Interest from Doppler Ultrasound Imaging

The present contribution deals with the estimation of haemodynamics Quantities of Interest by exploiting Ultrasound Doppler measurements. A fast method is proposed, based on the PBDW method. Several methodological contributions are described: a sub-manifold partitioning is introduced to improve the reduced-order approximation, two different ways to estimate the pressure drop are compared, and an error estimation is derived. A test-case on a realistic common carotid geometry is presented, showing that the proposed approach is promising in view of realistic applications.Comment: arXiv admin note: text overlap with arXiv:1904.1336

Shape optimization with a level set based mesh evolution method

International audienceIn this article, we discuss an approach for geometry and topology optimization of structures which benefits from an accurate description of shapes at each stage of the iterative process - by means of a mesh amenable for mechanical analyses - while retaining the whole versatility of the level set method when it comes to accounting for their evolution. The key ingredients of this method are two operators for switching from a meshed representation of a domain to an implicit one, and conversely; this notably brings into play an algorithm for generating the signed distance function to an arbitrary discrete domain, and a mesh generation algorithm for implicitly-defined geometries