The Experts below are selected from a list of 3867 Experts worldwide ranked by ideXlab platform

Gerard L. Vignoles - One of the best experts on this subject based on the ideXlab platform.

  • Isothermal Chemical Vapor Infiltration Modeling by Random Walks in CMT 3D Images at Two Scales
    2017
    Co-Authors: Gerard L. Vignoles, Ivan Szelengowicz, William Ros, Christianne Mulat, Christian Germain
    Abstract:

    The production cycle of high-quality Ceramic-Matrix Composites (CMCs) often involves interphase or matrix deposition by Chemical Vapor Infiltration (CVI). This costly step has motivated many modeling approaches, in order to provide guidelines for process control and optimization. In this context, numerical tools for direct modeling of isothermal, isobaric CVI in complex 3D images of the composite architecture, acquired e.g. by X-ray Computerized Microtomography (CMT) have been developed. To address inter- and intra-bundle length scales inherent to a composite with a woven textile reinforcement, a numerical strategy has been set up, based on two numerical tools. They solve diffusion-reaction equations and handle simultaneously the progressive evolution of the porous structure. They involve distinct random walk methods and image handling routines. The small-scale program uses Pearson random walks simulating rarefied gas transport; the fluid/solid interface is explicitly represented as a set of triangles through a Simplified Marching Cube approach. Direct simulation of CVI in intra-bundle pores is possible with such a tool. Effective laws for the evolution of porosity, surface and transport properties as infiltration proceeds are inferred from these simulations by averaging and are considered as inputs for the next modelling step. The large-scale solver uses Brownian motion simulation; the porous medium is considered as a continuum with locally heterogeneous and anisotropic diffusivities, and the deposition reaction is handled through a survival probability computation. Simulation of the infiltration of a whole composite material part is possible with this program. Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed.

  • A Brownian motion technique to simulate gasification and its application to C/C composite ablation
    Computational Materials Science, 2008
    Co-Authors: Jean Lachaud, Gerard L. Vignoles
    Abstract:

    Ablation of carbon-carbon composites (C/C) results in a heterogeneous surface recession mainly due to some gasification processes (oxidation, sublimation) possibly coupled to bulk mass transfer. In order to simulate and analyse the material/environment interactions during ablation, a Brownian motion simulation method featuring special Random Walk rules close to the wall has been implemented to efficiently simulate mass transfer in the low Péclet number regime. A sticking probability law adapted to this kind of Random Walk has been obtained for first-order heterogeneous reactions. In order to simulate the onset of surface roughness, the interface recession is simultaneously handled in 3D using a Simplified Marching Cube discretization. This tool is validated by comparison to analytical models. Then, its ability to provide reliable and accurate solutions of ablation phenomena in 3D is illustrated.

Wesley E. Bolch - One of the best experts on this subject based on the ideXlab platform.

  • a comparison of skeletal chord length distributions in the adult male
    Health Physics, 2005
    Co-Authors: Amish P Shah, Derek W Jokisch, Phillip W Patton, Didier A. Rajon, Wesley E. Bolch
    Abstract:

    : In radiation protection, skeletal dose estimates are required for the tissues of the hematopoietically active bone marrow and the osteogenic cells of the trabecular and cortical endosteum. Similarly, skeletal radiation dose estimates are required in therapy nuclear medicine in order to develop dose-response functions for myelotoxicity where active bone marrow is generally the dose-limiting organ in cancer radioimmunotherapy. At the present time, skeletal dose models in both radiation protection and medical dosimetry are fundamentally reliant on a single set of chord-length distribution measurements performed at the University of Leeds in the late 1970's for a 44-y-old male subject. These distributions describe the relative frequency at which linear pathlengths are seen across both the marrow cavities and bone trabeculae in seven individual bone sites: vertebrae (cervical and lumbar), proximal femur (head and neck), ribs, cranium (parietal bone), and pelvis (iliac crest). In the present study, we present an alternative set of chord-length distribution data acquired within a total of 14 skeletal sites of a 66-y-old male subject. The University of Florida (UF) distributions are assembled via 3D image processing of microCT scans of physical sections of trabecular spongiosa at each skeletal site. In addition, a tri-linear interpolation Marching Cube algorithm is employed to smooth the digital surfaces of the bone trabeculae while chord-length measurements are performed. A review of mean chord lengths indicate that larger marrow cavities are noted on average in the UF individual for the cervical vertebrae (1,038 vs. 910 microm), lumbar vertebrae (1,479 vs. 1,233 microm), ilium (1,508 vs. 904 microm), and parietal bone (812 vs. 389 microm), while smaller marrow cavities are noted in the UF individual for the femoral head (1,043 microm vs. 1,157 microm), the femoral neck (1,454 microm vs. 1,655 microm), and the ribs (1,630 microm vs. 1,703 microm). The mean chord-lengths for the bone trabeculae show close agreement for both individuals in the ilium (approximately 240 microm) and cervical vertebrae (approximately 280 microm). Thicker trabeculae were seen on average in the UF individual for the femoral head (ratio of 1.50), femoral neck (ratio of 1.10), lumbar vertebrae (ratio of 1.29), and ribs (ratio of 1.14), while thinner trabeculae were seen on average in the UF individual for the parietal bone of the cranium (ratio of 0.92). In two bone sites, prominent discrepancies in chord distribution shape were noted between the Leeds 44-y-old male and the UF 66-y-old male: (1) the bone trabeculae in the ribs, and (2) the marrow cavities and bone trabeculae within the cranium.

  • Marching Cube algorithm review and trilinear interpolation adaptation for image based dosimetric models
    Computerized Medical Imaging and Graphics, 2003
    Co-Authors: Didier A. Rajon, Wesley E. Bolch
    Abstract:

    Current internal organ dose assessment methodologies utilize three-dimensional (3D) medical images of the body to model organ shapes and tissue interfaces. These models are coupled to computer programs that measure radionuclide energy deposition or chord-length distributions directly within these images. Previous studies have shown that the rectangular shape of image voxels generates voxel effects that alter the outcome of these calculations. To minimize voxel effects, the present study proposes to use the Marching Cube (MC) algorithm to generate isosurfaces delineating tissue interfaces from the gray-level images. First, a review of the different techniques surrounding the MC algorithm is presented. Next, an adaptation of the algorithm is proposed in which a trilinear interpolation of the gray levels is used to generate a hyperboloid surface within the MCs. This new technique is shown to solve the classic ambiguity problem of the MC algorithm and also to reduce the data size inherent to the triangulated surface. It also provides a simple algorithm to accurately measure distances within the image. The technique is then tested with a mathematical model of trabecular bone. The trilinear interpolation method is shown to remove voxel effects and to produce reliable chord-length distributions across image regions. The technique is thus recommended for use with digital medical images needed for internal radiation transport simulations. The current study is performed for a single isosurface that separates two media within the same image, but it is proposed that the technique can be extended to multiple isosurfaces that delineate several organs or organ regions within 3D tomographic voxels of human anatomy.

Germain Christian - One of the best experts on this subject based on the ideXlab platform.

  • Isothermal Chemical Vapor Infiltration Modeling by Random Walks in CMT 3D Images at Two Scales
    'Wiley', 2010
    Co-Authors: Vignoles, Gerard L., Mulat Christianne, Szelengowicz Ivan, Ros William, Germain Christian
    Abstract:

    International audienceThe production cycle of high-quality Ceramic-Matrix Composites (CMCs) often involves interphase or matrix deposition by Chemical Vapor Infiltration (CVI). This costly step has motivated many modeling approaches, in order to provide guidelines for process control and optimization. In this context, numerical tools for direct modeling of isothermal, isobaric CVI in complex 3D images of the composite architecture, acquired e.g. by X-ray Computerized Microtomography (CMT) have been developed. To address inter- and intra-bundle length scales inherent to a composite with a woven textile reinforcement, a numerical strategy has been set up, based on two numerical tools. They solve diffusion-reaction equations and handle simultaneously the progressive evolution of the porous structure. They involve distinct random walk methods and image handling routines. The small-scale program uses Pearson random walks simulating rarefied gas transport; the fluid/solid interface is explicitly represented as a set of triangles through a Simplified Marching Cube approach. Direct simulation of CVI in intra-bundle pores is possible with such a tool. Effective laws for the evolution of porosity, surface and transport properties as infiltration proceeds are inferred from these simulations by averaging and are considered as inputs for the next modelling step. The large-scale solver uses Brownian motion simulation; the porous medium is considered as a continuum with locally heterogeneous and anisotropic diffusivities, and the deposition reaction is handled through a survival probability computation. Simulation of the infiltration of a whole composite material part is possible with this program. Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed

  • Détection, caractérisation d'objets 3D et simulation d'évolution morphologique appliquée à l'infiltrabilité de préformes fibreuses
    2008
    Co-Authors: Mulat Christianne, Vignoles Gérard, Germain Christian
    Abstract:

    Cette thèse associe analyse d image et modélisation physico-chimique afin de caractériser l infiltrabilité d un milieu poreux. Infiltrabilité signifie : propension d un milieu poreux à se laisser pénétrer par un fluide apportant un dépôt solide . Une application est la fabrication de composites à matrice céramique par dépôt chimique en phase gazeuse (CVI). Des études ont montré que l agencement des fibres d un matériau composite a un impact sur sa densité finale. Nous proposons d étudier l évolution du milieu poreux au cours de l infiltration pour des architectures complexes. La première étape consiste en la segmentation et la caractérisation de composites déjà densifiés obtenus par micro-tomographie. Les objets à segmenter sont des fibres quasi-cylindriques. Deux outils ont été développés : un estimateur optimal de l orientation vers l axe de cylindres, et un algorithme de détection et de caractérisation d objets quasi-cylindriques. Appliquée aux composites fibreux, cette étape fournit un bloc contenant les fibres. Il constitue le milieu poreux complexe dont on cherche à caractériser l infiltrabilité. La seconde étape est la modélisation à l échelle des fibres du procédé CVI. Elle utilise des marcheurs aléatoires, avec une gestion de l interface du solide par Marching Cube simplifié . L algorithme proposé est novateur car il prend en compte simultanément les réactions chimiques, le transport de gaz en régime raréfié ou continu et l évolution temporelle de la morphologie d un milieu poreux. Le couplage des deux étapes permet de comparer le dépôt issu de la segmentation à celui résultant de la simulation dans divers régimes physiques. Il est alors possible d effectuer une analyse inverse des conditions d élaboration à partir de la morphologie du dépôt. Les outils proposés permettent aussi de comparer l infiltrabilité de différentes architectures fibreuses.This thesis connects image processing and physicochemical modeling to characterize the infiltrability of porous media. Infiltrability means ability of a porous medium to receive a solid deposit brought by penetration of a carrier fluid . A practical case is the preparation of ceramic-matrix composites by Chemical Vapor Infiltration (CVI). Various studies have proved that the fiber arrangement in preforms of composite materials affects the density of the material at the final stage. In this work, the morphological evolution of complex 3D porous media during the gas-phase infiltration is studied. The first step consists in the segmentation and characterization X-ray Micro Tomography of the infiltrated composite. The objects to be segmented are quasi cylindrical fibers. Two tools have been developed: an optimal estimator of the orientation toward the axis; and an algorithm to detect and characterize quasi cylindrical objects. Applied on images of fiber-reinforced composites, this approach makes it possible to obtain the block containing the fibers. This block is the complex porous medium used for infiltrability characterization. The second step addresses the fiber-scale modeling of CVI. It is based on random walkers and fluid / solid interface management by a simplified Marching Cube. Our algorithm is innovative since it handles simultaneously chemical reactions, gas transport in rarefied and continuum regimes, and the morphological evolution of porous structure. By combining these two steps, we can compare the deposit obtained by segmentation to simulated deposits obtained in various physicochemical regimes. This allows performing an inverse analysis of the actual deposition conditions from the morphology of the deposit. The provided computational approach also allows the comparison of different porous textures with respect to their infiltrability.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Jurgen Brickmann - One of the best experts on this subject based on the ideXlab platform.

  • Fast generation of molecular surfaces from 3D data fields with an enhanced “Marching Cube” algorithm
    Journal of Computational Chemistry, 1993
    Co-Authors: W. Heiden, Thomas Goetze, Jurgen Brickmann
    Abstract:

    An improved version of the ''Marching Cubes'' algorithm W. Lorensen and H. Cline, Comp. Graph. 21, (1987) for the generation of isosurfaces from 3D data fields is presented and applied to molecular surfaces. The new algorithm avoids inconsistent pattern definitions of the original one, which lead to artificial gaps. The advantage of a logarithmic interpolation procedure, in particular for data fields typically occurring in molecular science, is demonstrated. An example is the generation of molecular surfaces based upon electron density data.

  • Marching Cube algorithmen zur schnellen generierung von isoflachen auf der basis dreidimensionaler datenfelder
    1991
    Co-Authors: Wolfgang Heiden, T Goetze, Jurgen Brickmann
    Abstract:

    Die Visualisierung und Quantifizierung von Datenfeldern im dreidimensionalen Raum gewinnt in vielen Bereichen von Wissenschaft und Technik mehr und mehr an Bedeutung. Anschauliche Visualisierung der Daten stellt eine Voraussetzung fur effektive Kommunikation zwischen Mensch und Maschine dar. Dies last sich mit Hilfe der Computergraphik durch die Darstellung von Isoflachen, die einen bestimmten Datenwert reprasentieren, erreichen. Fur die Visualisierung zeitabhangiger Resultate (z.B. dynamische Simulationen) sowie zur hochgradig interaktiven Bearbeitung der Daten sind extrem schnelle Computerprogramme zur Generierung dieser Isooberflachen erforderlich. Ein Beispiel fur einen derartigen Algorithmus ist die hier vorgestellte Triangulation dreidimensionaler Gitter auf der Basis einzelner Wurfel als Gitterelemente.

Mulat Christianne - One of the best experts on this subject based on the ideXlab platform.

  • Isothermal Chemical Vapor Infiltration Modeling by Random Walks in CMT 3D Images at Two Scales
    'Wiley', 2010
    Co-Authors: Vignoles, Gerard L., Mulat Christianne, Szelengowicz Ivan, Ros William, Germain Christian
    Abstract:

    International audienceThe production cycle of high-quality Ceramic-Matrix Composites (CMCs) often involves interphase or matrix deposition by Chemical Vapor Infiltration (CVI). This costly step has motivated many modeling approaches, in order to provide guidelines for process control and optimization. In this context, numerical tools for direct modeling of isothermal, isobaric CVI in complex 3D images of the composite architecture, acquired e.g. by X-ray Computerized Microtomography (CMT) have been developed. To address inter- and intra-bundle length scales inherent to a composite with a woven textile reinforcement, a numerical strategy has been set up, based on two numerical tools. They solve diffusion-reaction equations and handle simultaneously the progressive evolution of the porous structure. They involve distinct random walk methods and image handling routines. The small-scale program uses Pearson random walks simulating rarefied gas transport; the fluid/solid interface is explicitly represented as a set of triangles through a Simplified Marching Cube approach. Direct simulation of CVI in intra-bundle pores is possible with such a tool. Effective laws for the evolution of porosity, surface and transport properties as infiltration proceeds are inferred from these simulations by averaging and are considered as inputs for the next modelling step. The large-scale solver uses Brownian motion simulation; the porous medium is considered as a continuum with locally heterogeneous and anisotropic diffusivities, and the deposition reaction is handled through a survival probability computation. Simulation of the infiltration of a whole composite material part is possible with this program. Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed

  • Détection, caractérisation d'objets 3D et simulation d'évolution morphologique appliquée à l'infiltrabilité de préformes fibreuses
    2008
    Co-Authors: Mulat Christianne
    Abstract:

    Cette thèse associe analyse d’image et modélisation physico-chimique afin de caractériser l’infiltrabilité d’un milieu poreux. Infiltrabilité signifie : « propension d’un milieu poreux à se laisser pénétrer par un fluide apportant un dépôt solide ». Une application est la fabrication de composites à matrice céramique par dépôt chimique en phase gazeuse (CVI). Des études ont montré que l’agencement des fibres d’un matériau composite a un impact sur sa densité finale. Nous proposons d’étudier l’évolution du milieu poreux au cours de l’infiltration pour des architectures complexes. La première étape consiste en la segmentation et la caractérisation de composites déjà densifiés obtenus par micro-tomographie. Les objets à segmenter sont des fibres quasi-cylindriques. Deux outils ont été développés : un estimateur optimal de l’orientation vers l’axe de cylindres, et un algorithme de détection et de caractérisation d’objets quasi-cylindriques. Appliquée aux composites fibreux, cette étape fournit un bloc contenant les fibres. Il constitue le milieu poreux complexe dont on cherche à caractériser l’infiltrabilité. La seconde étape est la modélisation à l’échelle des fibres du procédé CVI. Elle utilise des marcheurs aléatoires, avec une gestion de l’interface du solide par « Marching Cube simplifié». L’algorithme proposé est novateur car il prend en compte simultanément les réactions chimiques, le transport de gaz en régime raréfié ou continu et l’évolution temporelle de la morphologie d’un milieu poreux. Le couplage des deux étapes permet de comparer le dépôt issu de la segmentation à celui résultant de la simulation dans divers régimes physiques. Il est alors possible d’effectuer une analyse inverse des conditions d’élaboration à partir de la morphologie du dépôt. Les outils proposés permettent aussi de comparer l’infiltrabilité de différentes architectures fibreuses.This thesis connects image processing and physicochemical modeling to characterize the infiltrability of porous media. Infiltrability means “ability of a porous medium to receive a solid deposit brought by penetration of a carrier fluid”. A practical case is the preparation of ceramic-matrix composites by Chemical Vapor Infiltration (CVI). Various studies have proved that the fiber arrangement in preforms of composite materials affects the density of the material at the final stage. In this work, the morphological evolution of complex 3D porous media during the gas-phase infiltration is studied. The first step consists in the segmentation and characterization X-ray Micro Tomography of the infiltrated composite. The objects to be segmented are quasi cylindrical fibers. Two tools have been developed: an optimal estimator of the orientation toward the axis; and an algorithm to detect and characterize quasi cylindrical objects. Applied on images of fiber-reinforced composites, this approach makes it possible to obtain the block containing the fibers. This block is the complex porous medium used for infiltrability characterization. The second step addresses the fiber-scale modeling of CVI. It is based on random walkers and fluid / solid interface management by a simplified Marching Cube. Our algorithm is innovative since it handles simultaneously chemical reactions, gas transport in rarefied and continuum regimes, and the morphological evolution of porous structure. By combining these two steps, we can compare the deposit obtained by segmentation to simulated deposits obtained in various physicochemical regimes. This allows performing an inverse analysis of the actual deposition conditions from the morphology of the deposit. The provided computational approach also allows the comparison of different porous textures with respect to their infiltrability

  • Détection, caractérisation d'objets 3D et simulation d'évolution morphologique appliquée à l'infiltrabilité de préformes fibreuses
    2008
    Co-Authors: Mulat Christianne, Vignoles Gérard, Germain Christian
    Abstract:

    Cette thèse associe analyse d image et modélisation physico-chimique afin de caractériser l infiltrabilité d un milieu poreux. Infiltrabilité signifie : propension d un milieu poreux à se laisser pénétrer par un fluide apportant un dépôt solide . Une application est la fabrication de composites à matrice céramique par dépôt chimique en phase gazeuse (CVI). Des études ont montré que l agencement des fibres d un matériau composite a un impact sur sa densité finale. Nous proposons d étudier l évolution du milieu poreux au cours de l infiltration pour des architectures complexes. La première étape consiste en la segmentation et la caractérisation de composites déjà densifiés obtenus par micro-tomographie. Les objets à segmenter sont des fibres quasi-cylindriques. Deux outils ont été développés : un estimateur optimal de l orientation vers l axe de cylindres, et un algorithme de détection et de caractérisation d objets quasi-cylindriques. Appliquée aux composites fibreux, cette étape fournit un bloc contenant les fibres. Il constitue le milieu poreux complexe dont on cherche à caractériser l infiltrabilité. La seconde étape est la modélisation à l échelle des fibres du procédé CVI. Elle utilise des marcheurs aléatoires, avec une gestion de l interface du solide par Marching Cube simplifié . L algorithme proposé est novateur car il prend en compte simultanément les réactions chimiques, le transport de gaz en régime raréfié ou continu et l évolution temporelle de la morphologie d un milieu poreux. Le couplage des deux étapes permet de comparer le dépôt issu de la segmentation à celui résultant de la simulation dans divers régimes physiques. Il est alors possible d effectuer une analyse inverse des conditions d élaboration à partir de la morphologie du dépôt. Les outils proposés permettent aussi de comparer l infiltrabilité de différentes architectures fibreuses.This thesis connects image processing and physicochemical modeling to characterize the infiltrability of porous media. Infiltrability means ability of a porous medium to receive a solid deposit brought by penetration of a carrier fluid . A practical case is the preparation of ceramic-matrix composites by Chemical Vapor Infiltration (CVI). Various studies have proved that the fiber arrangement in preforms of composite materials affects the density of the material at the final stage. In this work, the morphological evolution of complex 3D porous media during the gas-phase infiltration is studied. The first step consists in the segmentation and characterization X-ray Micro Tomography of the infiltrated composite. The objects to be segmented are quasi cylindrical fibers. Two tools have been developed: an optimal estimator of the orientation toward the axis; and an algorithm to detect and characterize quasi cylindrical objects. Applied on images of fiber-reinforced composites, this approach makes it possible to obtain the block containing the fibers. This block is the complex porous medium used for infiltrability characterization. The second step addresses the fiber-scale modeling of CVI. It is based on random walkers and fluid / solid interface management by a simplified Marching Cube. Our algorithm is innovative since it handles simultaneously chemical reactions, gas transport in rarefied and continuum regimes, and the morphological evolution of porous structure. By combining these two steps, we can compare the deposit obtained by segmentation to simulated deposits obtained in various physicochemical regimes. This allows performing an inverse analysis of the actual deposition conditions from the morphology of the deposit. The provided computational approach also allows the comparison of different porous textures with respect to their infiltrability.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF