Méthode de visualisation adaptée aux simulations d'ordre élevé. Application à la compression-reconstruction de champs rayonnés pour des ondes harmoniques

Bien que les méthodes d'ordre élevé permettent de réaliser des simulations très précises et peu coûteuses, il y a un manque d'outils pour analyser et exploiter les résultats obtenus par ces nouveaux schémas. L'objectif de cette thèse est de mettre en place un cadre et des algorithmes efficaces pour visualiser des solutions calculées par des méthodes d'ordre élevé. Notre approche est basée sur la construction d'une approximation affine optimisée de la solution numérique qui peut être post-traitée dans un logiciel de visualisation standard. Un maillage de représentation est créé via un indicateur d'erreurs a posteriori qui contrôle l'erreur de visualisation entre la solution numérique et sa représentation ponctuellement. Une stratégie est établie afin d'assurer que les (dis)continuités soient bien rendues. Un travail particulier est développé pour traiter les éléments d'ordre élevé (éléments courbes) et utilise notamment des indicateurs d'erreurs a posteriori spécifiques. Des exemples numériques montrent le potentiel de la méthode de visualisation. Dans une seconde partie, nous nous intéressons au calcul et à la reconstruction de champs rayonnés pour des problèmes d'ondes en régime harmonique. Nous proposons une méthodologie pour générer une reconstruction précise de champs rayonnés tout en limitant le nombre d'informations nécessaires (i.e. en compressant les données). Pour ce faire, nous nous appuyons sur des fonctions de base composées de polynômes d'ordre élevé et d'ondes planes, ainsi que sur un développement du noyau de la formule intégrale servant au rayonnement. La méthode de visualisation permet alors de représenter fidèlement (décompression) les cartographies obtenues.While high order methods allow to perform very accurate simulations with low costs, there is a lack of tools to analyze and exploit results obtained by these new schemes. The objective of this thesis is to design a framework and efficient algorithms to visualize solutions computed by high order methods. Our approach is based on the construction of an optimized affine approximation of the numerical solution which can be handled by any standard visualization software. A representation mesh is created via an a posteriori estimate which control visualization error between the numerical solution and its representation, and is performed pointwise. A strategy is established to ensure that (dis)continuities are well-rendered. A special work is done to treat high order elements (curved elements) and in particular use specific a posteriori estimates. Several numerical examples demonstrate the potential of the visualization method. In a second part, we examine the computation and reconstruction of radiated fields for wave problems in harmonic regime. We propose a methodology to generate an accurate reconstruction of radiated fields while limiting the information needed (i.e. compressing the data). For this purpose, we rely on basis functions composed of high order polynomials and plane waves, as well as a development of the kernel used for the integral representation. The visualization method allows to faithfully represent (decompression process) the cartographies obtained

On pixel-exact rendering for high-order mesh and solution

International audienceWith the increasing use of high-order methods and high-order meshes, scientific visualization software need to adapt themselves to reliably render the associated meshes and numerical solutions. In this paper, a novel approach, based on OpenGL 4 framework, enables a GPU-based rendering of high-order meshes as well as an almost pixel-exact rendering of high-order solutions. Several aspects of the OpenGL Shading Language and in particular the use of dedicated shaders (GPU programs) allows to answer this visualization challenge. Fragment shaders are used to compute the exact solution for each pixel, made possible by the transfer of degrees of freedom and shape functions to the GPU with textures. Tessellation shaders, combined with geometric error estimates, allow us to render high-order curved meshes by providing an adaptive subdivision of elements on the GPU directly. A convenient way to compute bounds for high-order solutions is described. The interest of using Bézier basis instead of Lagrange functions lies in the existence of fast and robust evaluation of polynomial functions with de Casteljau algorithm. A technique to plot highly nonlinear isolines and wire frames with a desired thickness is derived. It is based on a finite difference scheme performed on GPU. In comparison with standard techniques, we remove the use of any linear interpolation step and the need to generate a priori a fixed subdivided mesh. This reduces the memory footprint, improves the accuracy and the speed of the rendering. Finally, the method is illustrated with various 3D examples

Using ViZiR 4 to analyze the 4th AIAA CFD High Lift Prediction Workshop Simulations

International audienceViZiR 4 is an interactive visualization software that uses OpenGL 4 graphic pipeline. It can be used to analyze large meshes with possibly solutions and in this paper the focus is made with results from the 4th AIAA CFD High Lift Prediction Workshop. To perform such simulations, it is necessary to have fast, precise and interactive tools to analyze, check and validate the numerical results obtained. Fast I/O and rendering is important to inspect results and comparisons with ParaView show that ParaView is much slower (ratio between 5 and 50). Many post-processing tools, such as picking, hiding surfaces by reference, isolines rendering and clip planes generation, allow to quickly investigate meshes and solutions. Pixel exact rendering permits to have a precise preview of solutions and tessellations on GPU are used to render high-order and curved elements. Some scripting tools allow to generate quickly images and go over sequences of several meshes that is useful when mesh adaptation is involved. All along the paper, results from the workshop are shown to illustrate the capabilities of ViZiR 4

Méthode de visualisation adaptée aux simulations d’ordre élevé. Application à la compression-reconstruction de champs rayonnés pour des ondes harmoniques

While high order methods allow to perform very accurate simulations with low costs, there is a lack of tools to analyze and exploit results obtained by these new schemes. The objective of this thesis is to design a framework and eÿcient algorithms to visualize solutions computed by high order methods.Our approach is based on the construction of an optimized aÿne approximation of the nu-merical solution which can be handled by any standard visualization software. A representation mesh is created via an a posteriori estimate which control visualization error between the nu-merical solution and its representation, and is performed pointwise. A strategy is established to ensure that (dis)continuities are well-rendered. A special work is done to treat high order ele-ments (curved elements) and in particular use specific a posteriori estimates. Several numerical examples demonstrate the potential of the visualization method.In a second part, we examine the computation and reconstruction of radiated fields for wave problems in harmonic regime. We propose a methodology to generate an accurate reconstruction of radiated fields while limiting the information needed (i.e. compressing the data). For this purpose, we rely on basis functions composed of high order polynomials and plane waves, as well as a development of the kernel used for the integral representation. The visualization method allows to faithfully represent (decompression process) the cartographies obtained.Bien que les méthodes d’ordre élevé permettent de réaliser des simulations très précises et peu coûteuses, il y a un manque d’outils pour analyser et exploiter les résultats obtenus par ces nouveaux schémas.L’objectif de cette thèse est de mettre en place un cadre et des algorithmes efficaces pour visualiser des solutions calculées par des méthodes d’ordre élevé. Notre approche est basée sur la construction d’une approximation affine optimisée de la solution numérique qui peut être post-traitée dans un logiciel de visualisation standard. Un maillage de représentation est créé via un indicateur d’erreurs a posteriori qui contrôle l’erreur de visualisation entre la solution numérique et sa représentation ponctuellement. Une stratégie est établie afin d’assurer que les (dis)continuités soient bien rendues. Un travail particulier est développé pour traiter les éléments d’ordre élevé (éléments courbes) et utilise notamment des indicateurs d’erreurs a posteriori spécifiques. Des exemples numériques montrent le potentiel de la méthode de visualisation.Dans une seconde partie, nous nous intéressons au calcul et à la reconstruction de champs rayonnés pour des problèmes d’ondes en régime harmonique. Nous proposons une méthodologie pour générer une reconstruction précise de champs rayonnés tout en limitant le nombre d’informations nécessaires (i.e. en compressant les données). Pour ce faire, nous nous appuyons sur des fonctions de base composées de polynômes d’ordre élevé et d’ondes planes, ainsi que sur un développement du noyau de la formule intégrale servant au rayonnement. La méthode de visualisation permet alors de représenter fidèlement (décompression) les cartographies obtenues

Visualization, post-processing, high order numerical solutions, radiated fields, high order reconstruction

Bien que les méthodes d'ordre élevé permettent de réaliser des simulations très précises et peu coûteuses, il y a un manque d'outils pour analyser et exploiter les résultats obtenus par ces nouveaux schémas. L'objectif de cette thèse est de mettre en place un cadre et des algorithmes efficaces pour visualiser des solutions calculées par des méthodes d'ordre élevé. Notre approche est basée sur la construction d'une approximation affine optimisée de la solution numérique qui peut être post-traitée dans un logiciel de visualisation standard. Un maillage de représentation est créé via un indicateur d'erreurs a posteriori qui contrôle l'erreur de visualisation entre la solution numérique et sa représentation ponctuellement. Une stratégie est établie afin d'assurer que les (dis)continuités soient bien rendues. Un travail particulier est développé pour traiter les éléments d'ordre élevé (éléments courbes) et utilise notamment des indicateurs d'erreurs a posteriori spécifiques. Des exemples numériques montrent le potentiel de la méthode de visualisation. Dans une seconde partie, nous nous intéressons au calcul et à la reconstruction de champs rayonnés pour des problèmes d'ondes en régime harmonique. Nous proposons une méthodologie pour générer une reconstruction précise de champs rayonnés tout en limitant le nombre d'informations nécessaires (i.e. en compressant les données). Pour ce faire, nous nous appuyons sur des fonctions de base composées de polynômes d'ordre élevé et d'ondes planes, ainsi que sur un développement du noyau de la formule intégrale servant au rayonnement. La méthode de visualisation permet alors de représenter fidèlement (décompression) les cartographies obtenues.While high order methods allow to perform very accurate simulations with low costs, there is a lack of tools to analyze and exploit results obtained by these new schemes. The objective of this thesis is to design a framework and efficient algorithms to visualize solutions computed by high order methods. Our approach is based on the construction of an optimized affine approximation of the numerical solution which can be handled by any standard visualization software. A representation mesh is created via an a posteriori estimate which control visualization error between the numerical solution and its representation, and is performed pointwise. A strategy is established to ensure that (dis)continuities are well-rendered. A special work is done to treat high order elements (curved elements) and in particular use specific a posteriori estimates. Several numerical examples demonstrate the potential of the visualization method. In a second part, we examine the computation and reconstruction of radiated fields for wave problems in harmonic regime. We propose a methodology to generate an accurate reconstruction of radiated fields while limiting the information needed (i.e. compressing the data). For this purpose, we rely on basis functions composed of high order polynomials and plane waves, as well as a development of the kernel used for the integral representation. The visualization method allows to faithfully represent (decompression process) the cartographies obtained

Well-suited and adaptive post-processing for the visualization of hp simulation results

International audienceWhile high order methods became very popular as they allow to perform very accurate solutions with low computational time and memory cost, there is a lack of tools to visualize and post-treat the solutions given by these methods. Originally, visualization softwares were developed to post-process results from methods such that finite differences or usual finite elements and therefore process linear primitives. In this paper, we present a methodology to visualize results of high order methods. Our approach is based on the construction of an optimized affine approximation of the high order solution which can therefore be handled by any visualization software. A representation mesh is constructed and the process is guided by an a posteriori estimate which control the error between the numerical solution and its representation pointwise. This point by point control is crucial as under their picture form, data correspond to values mapped on elements where anyone can pick up a pointwise information. A strategy is established to ensure that discontinuities are well represented. These discontinuities come either from the physical problem (material change) or the numerical method (discontinuous Galerkin method) and are pictured accurately. Several numerical examples are presented to demonstrate the potential of the method

Cost-effectiveness analysis of bundled innovative devices versus standard approach in the prevention of unscheduled peripheral venous catheters removal due to complications in France

International audienceThe objective of the study was to perform a cost-effectiveness analysis of bundled devices (BDs) versus standard devices (SDs) for the prevention of unscheduled peripheral venous catheter (PVC) removal due to complication from a French investigator-initiated, open-label, single center, randomized-controlled, two-by-two factorial trial (CLEAN-3 study). A 14-day time non homogeneous semi-markovian model was performed to be fitted to longitudinal individual patient data from CLEAN-3 database. This model includes five health states and eight transitional events; a base case scenario, two scenario analyses and bootstrap sensitivity analyses were performed. The cost-effectiveness criterion was the cost per patient with unscheduled PVC removal avoided. 989 adult (age≥18 years) patients were analyzed to compare the BDs group (494 patients), and the SDs group (495 patients). The assessed intervention was a combination of closed integrated catheters, positive displacement needleless-connectors, disinfecting caps, and single-use prefilled flush syringes compared with the use of open catheters and three-way stopcocks for treatment administration. For the base case scenario, an unscheduled 1 st PVC removal before discharge was significantly more frequent in the SDs group (235 patients (47.5%) in the SDs group and 172 patients (34.8%) in the BDs group, p = 0.00006). After adjustment for 1 st catheter time, the number of patients with unscheduled PVC removal per day was of 16 (95%CI: 15; 18) patients (out of 100) in the BDs group and of 26 (95%CI: 24; 28) patients (out of 100) in the SDs group. The mean cost per patient (adjusted on catheter-time) was of €144 (95%CI: €135-€154) for patients in the SDs group versus €102 (95%CI: €95-€109) for patients in the BDs group; the mean saving per patient was of €42 (95%CI: €32-€54). As a consequence, the assessed BDs strategy was less costly and more effective than the SDs strategy. Trail registration: CLEAN-3 study is registered with ClinicalTrials.gov, NCT03757143

4\textsuperscriptth AIAA CFD High Lift Prediction Workshop results using metric-based anisotropic mesh adaptation

International audienceThis article presents CFD results obtained with the metric-based mesh adaptation platform for the 4th AIAA CFD High-Lift Prediction Workshop on the new CRM-HL geometry. We emphasize the need for a strong solver to achieve iterative convergence for this complex case and we propose an alpha-continuation mesh adaptation algorithm to improve the prediction. Two test cases of the workshop have been carried out: the mesh convergence study at an angle of attack of 7.05 degrees and the C_L,max study