Vizir: High-order mesh and solution visualization using OpenGL 4.0 graphic pipeline

International audienceOpenGL 4 with GLSL shading language have become a standard on many common archi-tectures (Mac, Linux, Windows, , ...) from a couple of years. In the mean time, high-order methods (for flow solution and for meshing algorithm) are emerging. Many of them have proven their abilities to provide accurate results on complex (3D) geometries. However, the assessment of a particular meshing algorithm or of a high-order numerical scheme strongly relies on the capacity to validate and inspect visually the current mesh/solution at hand. However, having at the same time, an accurate and interactive visualization process for high-order mesh/solution is still a challenge as complex process are usually involved in the graphic pipeline: non linear root finding, ray tracing, GPU programming,. .. . In this paper, we discuss the current status and issues of using the (raw) OpenGL 4 pipeline to render curved high-order entities, and almost pixel-exact solutions. We illustrate this process on meshes and solutions issued from high-order curved from CAD and with high-order interpolated solutions

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

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

Optimization of P2 meshes and applications

International audienceMesh optimization techniques are a way to locally modify the mesh in order to improve it with respect to a given quality criterion. To this end, this work presents the generalization of two mesh quality-based optimization operators to P2 meshes. The generalized operators consist in mesh smoothing and generalized swapping. With the use of these operators, P2 mesh generation starting from a P1 mesh is more robust and P2 connectivity-change moving mesh methods for large displacements are now possible

A closed advancing-layer method for generating curved boundary layer mesh

International audienceA closed advancing-layer method for generating high-order (P2) high-aspect-ratio elements in the boundary layer (BL) region is presented. This approach efficiently and naturally produces a smooth anisotropic blending between colliding BL fronts. It is also able to guarantee mesh generation validity and quality prior to mesh modifications. In additions, it provides a robust strategy to couple unstructured anisotropic mesh adaptation and high-aspect-ratio element pseudo-structured BL meshes. Contrary to classical high-order approaches that deform an existing linear BL mesh into a curved BL mesh, the proposed check validity and quality of the high-order elements prior to including them in the BL mesh. In the same manner the mesh deformation approach for including the BL mesh in the overall mesh allows checking of validity and quality of the outer region high-order elements. This approach utilizes a recently developed connectivity-change based P2 moving mesh strategy for deforming the curved volume mesh as the BL is inflated. In regards to the high-order BL mesh generation, it features state-of-art capabilities, including ; optimal normal evaluation, normal smoothing, blended BL termination, mixed-elements BL, varying growth rate, and BL imprinting on curved surfaces. First results obtained on simple geometries are presented to assess the proposed strategy

Anisotropic Error Estimate for High-order Parametric Surface Mesh Generation

International audienceParametric surface mesh generation is one of the crucial step of the computational pipeline. Standard techniques, that are now mature, control the deviation to the tangent plane by using intrinsic quantities as the minimum and maximum curvatures. However, for high-order meshes, deriving intrinsic quantities that have the ability to control the mesh generation process is much more challenging. Indeed, those provided by the first and second fundamental forms of a surface are not sufficient when high order curved meshes are employed. In this paper, we introduce a new set of error estimates for high-order surface mesh generation. It is based on performing a Taylor expansion of the underlying surface in the tangent plane. The independence to the parametric space is obtained by using an inversion formula. High-order terms of this expansion are then used to derive an optimal metric by using the log-simplex approach. Examples are shown to prove the efficiency of the method

Measurement of pore size distribution of building materials by thermal method

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Numerical benchmarks for the comparison of inverse modeling techniques to identify building wall thermal resistance

ADMOS 2019 - International Conference on Adaptive Modeling and Simulation, Alicante, ESPAGNE, 27-/05/2019 - 29/05/2019European countries set a significant goal to reduce the energy consumption by 30% and CO2 emissions before 2030. As the building sector represents in Europe about one third of energy consumption, it is a sector of particular interest. To reduce the energy consumption in existing buildings, three complementary actions can be planned: the building thermal refurbishment, the smart management of building equipments and the awareness of users. In the presentation, we address the first point. The objective, fixed in the French national research project "ResBati", is to identify bad insulated building envelope and to quantify its thermal resistance by inverse modeling techniques coupling sensor outputs and physical models. To accelerate the identification process, a part of the envelope is excited by an imposed flux on the inside face using lights. During the active excitation, temperature are recorded on both faces of the wall and integrated in inverse modeling techniques. Three different inverse modeling strategies, developed by IFSTTAR, CSTB and UPEC, are compared on numerical benchmarks. Two kinds of envelopes are considered: interior insulated walls and single-walls. Both IFSTTAR and UPEC strategies use 1D thermal PDE to represent the thermal behavior of the wall while CSTB considers 0D resistance-capacitance model. Concerning the inverse techniques, a maximum likelihood estimation method is applied by CSTB[1], UPEC implements a trust region algorithm and a Bayesian inference technique. Lastly, IFSTTAR performed a data misfit minimization using the adjoint state with Tikhonov regularization. In IFSTTAR strategy, the regularization parameter is chosen using Morozov principle considering both measurement and model errors. Herein, the model error comes from the simplification of 3D thermal problem to a 1D thermal problem. All the considered inverse approaches propose an estimation of the uncertainty on the identified wall building thermal resistance. First results show that thermal resistance of interior insulated walls is better identified by CSTB approach at a low computational cost whereas IFSTTAR inverse technique is more relevant for single-walls

Numerical benchmarks for the comparison of inverse modeling techniques to identify building wall thermal resistance

ADMOS 2019 - International Conference on Adaptive Modeling and Simulation, Alicante, ESPAGNE, 27-/05/2019 - 29/05/2019European countries set a significant goal to reduce the energy consumption by 30% and CO2 emissions before 2030. As the building sector represents in Europe about one third of energy consumption, it is a sector of particular interest. To reduce the energy consumption in existing buildings, three complementary actions can be planned: the building thermal refurbishment, the smart management of building equipments and the awareness of users. In the presentation, we address the first point. The objective, fixed in the French national research project "ResBati", is to identify bad insulated building envelope and to quantify its thermal resistance by inverse modeling techniques coupling sensor outputs and physical models. To accelerate the identification process, a part of the envelope is excited by an imposed flux on the inside face using lights. During the active excitation, temperature are recorded on both faces of the wall and integrated in inverse modeling techniques. Three different inverse modeling strategies, developed by IFSTTAR, CSTB and UPEC, are compared on numerical benchmarks. Two kinds of envelopes are considered: interior insulated walls and single-walls. Both IFSTTAR and UPEC strategies use 1D thermal PDE to represent the thermal behavior of the wall while CSTB considers 0D resistance-capacitance model. Concerning the inverse techniques, a maximum likelihood estimation method is applied by CSTB[1], UPEC implements a trust region algorithm and a Bayesian inference technique. Lastly, IFSTTAR performed a data misfit minimization using the adjoint state with Tikhonov regularization. In IFSTTAR strategy, the regularization parameter is chosen using Morozov principle considering both measurement and model errors. Herein, the model error comes from the simplification of 3D thermal problem to a 1D thermal problem. All the considered inverse approaches propose an estimation of the uncertainty on the identified wall building thermal resistance. First results show that thermal resistance of interior insulated walls is better identified by CSTB approach at a low computational cost whereas IFSTTAR inverse technique is more relevant for single-walls