Sparse Volumetric Deformation

Volume rendering is becoming increasingly popular as applications require realistic solid shape representations with seamless texture mapping and accurate filtering. However rendering sparse volumetric data is difficult because of the limited memory and processing capabilities of current hardware. To address these limitations, the volumetric information can be stored at progressive resolutions in the hierarchical branches of a tree structure, and sampled according to the region of interest. This means that only a partial region of the full dataset is processed, and therefore massive volumetric scenes can be rendered efficiently. The problem with this approach is that it currently only supports static scenes. This is because it is difficult to accurately deform massive amounts of volume elements and reconstruct the scene hierarchy in real-time. Another problem is that deformation operations distort the shape where more than one volume element tries to occupy the same location, and similarly gaps occur where deformation stretches the elements further than one discrete location. It is also challenging to efficiently support sophisticated deformations at hierarchical resolutions, such as character skinning or physically based animation. These types of deformation are expensive and require a control structure (for example a cage or skeleton) that maps to a set of features to accelerate the deformation process. The problems with this technique are that the varying volume hierarchy reflects different feature sizes, and manipulating the features at the original resolution is too expensive; therefore the control structure must also hierarchically capture features according to the varying volumetric resolution. This thesis investigates the area of deforming and rendering massive amounts of dynamic volumetric content. The proposed approach efficiently deforms hierarchical volume elements without introducing artifacts and supports both ray casting and rasterization renderers. This enables light transport to be modeled both accurately and efficiently with applications in the fields of real-time rendering and computer animation. Sophisticated volumetric deformation, including character animation, is also supported in real-time. This is achieved by automatically generating a control skeleton which is mapped to the varying feature resolution of the volume hierarchy. The output deformations are demonstrated in massive dynamic volumetric scenes

Visualization Algorithms for Maps and Diagrams

One of the most common visualization tools used by mankind are maps or diagrams. In this thesis we explore new algorithms for visualizing maps (road and argument maps). A map without any textual information or pictograms is often without use so we research also further into the field of labeling maps. In particular we consider the new challenges posed by interactive maps offered by mobile devices. We discuss new algorithmic approaches and experimentally evaluate them

Pore-scale Modeling and Multi-scale Characterization of Liquid Transport in Shales

Distinct from conventional reservoirs, shale formations have limited pore connectivity and unique pore spatial-distribution. Consequently, theoretical pore-network models developed for conventional formations are not representative of the porous media in unconventional rocks. This work presents a novel theoretical pore-network model, the dendroidal model, based on the analysis of pore-scale model reconstruction extracted from Scanning Electron Microscope images. The dendroidal model is a “semi-acyclic” model, which characterizes the limited connectivity of void space without sacrificing the interaction among main flow paths. The dendroidal model infers pore-body distribution based on the hysteresis effect of isothermal adsorption/desorption measurements and characterizes pore-throat distribution using mercury drainage capillary pressure experiments. The use of dual-compressibility model in the pore-network model construction eliminates the compressibility effect of void space, including connected pores and dead-end pores, in mercury drainage experiments. The total organic carbon (TOC) content and minerology are measured by experiments to determine the composition of pore bodies and pore throats in the dendroidal model. The difference in mercury intrusion and extraction caused by the trapping hysteresis and contact-angle hysteresis affects the stochastically distributed parameters, including pore-throat length, pore-throat cross-sectional geometry, coordination number and pore-body spatial distribution. I validate the dendroidal model by predicting the absolute permeability of the core samples from Marcellus and Wolfcamp shales. This newly developed pore-network model integrates the aforementioned seven distinct types of experiments to capture the realistic pore structures of shales. Extracted pore-network modeling is an efficient and reliable way to provide a platform for mathematical simulation of fluid flow in porous media and for predicting the transport properties. However, the existing algorithms for pore-network extraction have deficiencies in characterizing the porous media of shale core samples in as much as they cannot capture the unique features of unconventional reservoirs. In nano-scale pores, the accurate characterization of the porous geometry is important, since the relative error will be significant without considering trivial information. The newly developed approach, based on the maximal-ball method, proposes a novel and enhanced algorithm for the classification of pore throats and pore bodies. It also has a better performance in characterizing the corresponding properties that include pore-throat length, pore size and geometric factors. The Marcellus shale core samples are scanned using scanning electron microscope imaging with the resolution of 4 nm. The pore-network models based on the tomographic images are constructed, and the aforementioned parameters are compared and analyzed. The quantification of liquid transport in liquid-rich shales is crucial for an economical exploitation of hydrocarbon. The laboratory measurement of permeability is challenging as it is time-consuming and includes large uncertainties. Direct pore-scale modeling and extracted pore-network modeling are alternatives for the prediction of transport properties. But due to its prohibitively high computational cost, its applications are limited to micro-scale. The emphasis of this work is to understand the mechanisms of nano-confined liquid transportation (nano-scale) and to quantify the liquid transport capacity in the scales of core samples (centi-scale). A modified Navier-Stokes equation is developed to integrate the variation of fluid properties with respect to the strength of liquid-wall interaction. To predict the apparent permeability in large scale, the dendroidal theoretical pore-network model is constructed by integrating mercury drainage/imbibition and isothermal adsorption/desorption experiments. The dendroidal model also integrates the data of Fourier Transform infra-red spectroscopy experiments to characterize the mineralogy distribution and total organic carbon to distinguish organic pores and inorganic pores. Results from molecular dynamics simulation indicate that the flow capacity of nano-confined liquid can be 1-3 orders different from that calculated by Navier-Stokes equation without considering the boundary-slippage effect. The geometry and composition also have considerable effect on the surface friction factor and viscosity in the near-wall fluid film, which in turn significantly influence the flow capacity in nano-pores. This work investigates the mechanisms of liquid flow in nano-confined pores with various composition and geometries. Accurate characterizations of liquid transport in shales will provide significant advantage in the field development planning of unconventional resources

Analyse mésoscopique par éléments finis de la déformation de renforts fibreux 2D et 3D à partir de microtomographies X

The simulation at meso-scale of textile composite reinforcement deformation provides important information. In particular, it gives the direction and density of the fibres that condition the permeability of the textile reinforcement and the mechanical properties of the final composite. These meso FE analyses are highly dependent on the quality of the initial geometry of the model. Some software have been developed to describe composite reinforcement geometries. The obtained geometries imply simplification that can disrupt the reinforcement deformation computation. The present work presents a direct method using computed microtomography to determine finite element models based on the real geometry of the textile reinforcement. The FE model is obtained for any specificity or variability of the textile reinforcement, more or less complex. The yarns interpenetration problems are avoided. These models are used with two constitutive laws : a hypoelastic law and a hyperelastic one. An analysis of their properties is presented and their implementation in the software ABAQUS is detailed. Finally, an identification method is presented and the results of forming simulations are compared to experimental tests, which shows a good fit between the both.La simulation à l'échelle mésoscopique de la déformation des renforts composites fournit des informations importantes. En particulier, elle donne la direction et la densité de fibres qui conditionne la perméabilité du renfort textile et les propriétés mécaniques du composite final. Ces analyses mésoscopiques par éléments finis dépendent fortement de la qualité de la géométrie initiale du modèle. Certains logiciels ont été développés pour décrire ces géométries de renforts composites. Mais, les géométries obtenues impliquent une simplification (notamment dans la section transversale de mèche) qui peut perturber le calcul de déformation du renfort. Le présent travail présente une méthode directe utilisant la microtomographie à rayon X pour générer des modèles éléments finis, basée sur la géométrie réelle de l'armure textile. Le modèle EF peut être obtenu pour tout type de renfort, plus ou moins complexe. Les problèmes d’interpénétrations de mèches sont évités. Ces modèles sont utilisés avec deux lois de comportement : une loi hypoélastique et une loi hyperélastique. Les propriétés de chacune d'entre elles, ainsi que les grandeurs caractéristiques nécessaires à leur implémentation dans le logiciel ABAQUS sont développées. Enfin, une identification des paramètres matériau à l'aide d'une méthode inverse est proposée. Les résultats obtenus pour les simulations de mise en forme sont comparés avec les résultats expérimentaux et montrent une bonne correspondance entre les deux

Large bichromatic point sets admit empty monochromatic 4-gons

We consider a variation of a problem stated by Erd˝os and Szekeres in 1935 about the existence of a number fES(k) such that any set S of at least fES(k) points in general position in the plane has a subset of k points that are the vertices of a convex k-gon. In our setting the points of S are colored, and we say that a (not necessarily convex) spanned polygon is monochromatic if all its vertices have the same color. Moreover, a polygon is called empty if it does not contain any points of S in its interior. We show that any bichromatic set of n ≥ 5044 points in R2 in general position determines at least one empty, monochromatic quadrilateral (and thus linearly many).Postprint (published version

The 1995 Science Information Management and Data Compression Workshop

This document is the proceedings from the 'Science Information Management and Data Compression Workshop,' which was held on October 26-27, 1995, at the NASA Goddard Space Flight Center, Greenbelt, Maryland. The Workshop explored promising computational approaches for handling the collection, ingestion, archival, and retrieval of large quantities of data in future Earth and space science missions. It consisted of fourteen presentations covering a range of information management and data compression approaches that are being or have been integrated into actual or prototypical Earth or space science data information systems, or that hold promise for such an application. The Workshop was organized by James C. Tilton and Robert F. Cromp of the NASA Goddard Space Flight Center

Application de la compression à la tractographie en imagerie par résonance magnétique de diffusion

Ce mémoire présente un nouvel algorithme de compression de fibres développé spécifiquement pour la tractographie. Validé et testé sur un large éventail d’algorithmes et de paramètres de tractographie, celui-ci présente trois grandes étapes : la linéarisation, la quantization ainsi que l’encodage. Les concepts clés de l’imagerie par résonance magnétique de diffusion (IRMd) et de la compression sont également introduits afin de faciliter la compréhension du lecteur