Dissertations / Theses on the topic 'Meshes'
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Valachová, Michaela. "Progressive Meshes." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2012. http://www.nusl.cz/ntk/nusl-236577.
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This thesis introduces a representation of graphical data, progressive meshes, and its fields of usage. The main part of this work is mathematical representation of progressive meshes and the simplification algorithm, which leads to this representation. Examples of changes in progressive mesh representation are also part of this thesis, along with few examples. The result is an application that implements the calculation of the Progressive Meshes model representation
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Feuillet, Rémi. "Embedded and high-order meshes : two alternatives to linear body-fitted meshes." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLY010/document.
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La simulation numérique de phénomènes physiques complexes requiert généralement l’utilisation d’un maillage. En mécanique des fluides numérique, cela consisteà représenter un objet dans un gros volume de contrôle. Cet objet étant celui dont l’on souhaite simuler le comportement. Usuellement, l’objet et la boîte englobante sont représentés par des maillage de surface linéaires et la zone intermédiaire est remplie par un maillage volumique. L’objectif de cette thèse est de s’intéresser à deux manières différentes de représenter cet objet. La première approche dite immergée consiste à mailler intégralement le volume de contrôle et ensuite à simuler le comportement autour de l’objet sans avoir à mailler explicitement dans le volume ladite géometrie. L’objet étant implicitement pris en compte par le schéma numérique. Le couplage de cette méthode avec de l’adaptation de maillage linéaire est notamment étudié. La deuxième approche dite d’ordre élevé consiste quant à elle consiste à augmenter le degré polynomial du maillage de surface de l’objet. La première étape consiste donc à générer le maillage de surface de degré élevé et ensuite àpropager l’information de degré élevé dans les éléments volumiques environnants si nécessaire. Dans ce cadre-là, il s’agit de s’assurer de la validité de telles modifications et à considérer l’extension des méthodes classiques de modification de maillages linéairesThe numerical simulation of complex physical phenomenons usually requires a mesh. In Computational Fluid Dynamics, it consists in representing an object inside a huge control volume. This object is then the subject of some physical study. In general, this object and its bounding box are represented by linear surface meshes and the intermediary zone is filled by a volume mesh. The aim of this thesis is to have a look on two different approaches for representing the object. The first approach called embedded method consist in integrally meshing the bounding box volume without explicitly meshing the object in it. In this case, the presence of the object is implicitly simulated by the CFD solver. The coupling of this method with linear mesh adaptation is in particular discussed.The second approach called high-order method consist on the contrary by increasing the polynomial order of the surface mesh of the object. The first step is therefore to generate a suitable high-order mesh and then to propagate the high-order information in the neighboring volume if necessary. In this context, it is mandatory to make sure that such modifications are valid and then the extension of classic mesh modification techniques has to be considered
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Zhou, Zhang. "Simplification of triangulated meshes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ31384.pdf.
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Moraes, Rafaela do Nascimento de. "Meshes of the afternoon." reponame:Repositório Institucional da UFSC, 2004. http://repositorio.ufsc.br/handle/123456789/101546.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão, Programa de Pós-Graduação em Letras/Inglês e Literatura Correspondente, Florianópolis, 2004Made available in DSpace on 2013-07-15T22:32:47Z (GMT). No. of bitstreams: 1 317489.pdf: 3857075 bytes, checksum: ac7e68b73b9413870fc0153917b60761 (MD5)
Abstract : This thesis examines the work of the filmmaker Maya Deren in the light of the aesthetics proposed by her main writings -"An Anagram of Ideas on Art, Form and Film"(1946), "Cinema as an Independent Art Form" (1946), "Cinematography: The Creative Use of Reality"(1960) -, as well as its relations to her first short film Meshes of the Afternoon, placing it among the numerous aesthetic and film trends in which it figured. Her writings depict a solid theoretic background, as well as her attempt to construct what she called "poetic cinema," through the conjunction of various forms of artistic expression. Such an attempt is made no less evident in the analysis of Meshes of the Afternoon, whose dream-like narrative evolves from the peculiar combination of symbolic elements and is responsible for the poetic effect coveted by the filmmaker.
Esta dissertação tem como objetivo examinar o trabalho da cineasta Maya Deren, principalmente no que se refere à estética proposta por ela em seus principais escritos: "An Anagram of Ideas on Art, Film and Form" (1946), "Cinema as an Independent Art Form" (1946) "Cinematography: The Creative Use of Reality" (1960) - e à relação que estes estabelecem com seu primeiro curta-metragem Meshes of the Afternoon, situando-o em meio às inúmeras correntes estéticas e cinematográficas com as quais se relacionou. Seus escritos evidenciam uma formação teórica sólida, bem como sua tentativa de elaborar o que denominou de "poetic cinema,"através do encontro das diversas formas de expressão artística. Esta tentativa fica não menos evidente ao se analisar Meshes of the Afternoon, cuja narrativa de caráter onírico se desenvolve a partir de uma combinação peculiar de elementos simbólicos, responsável pelo efeito poético almejado pela cineasta.
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Apel, Thomas, and Nico Düvelmeyer. "Transformation of hexahedral finite element meshes into tetrahedral meshes according to quality criteria." Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200601295.
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The paper is concerned with algorithms for transforming hexahedral finite element meshes into tetrahedral meshes without introducing new nodes. Known algorithms use only the topological structure of the hexahedral mesh but no geometry information. The paper provides another algorithm which can be extented such that quality criteria for the splitting of faces are respected.
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Gonen, Ozgur. "Modeling planar 3-valence meshes." Texas A&M University, 2007. http://hdl.handle.net/1969.1/85883.
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In architectural and sculptural practice, the eventual goal is constructing the
shapes that have been designed. Due to fabrication considerations, shapes with planar
faces are in demand for these practices.
In this thesis, a novel computational modeling approach to design constructible
shapes is introduced. This method guarantees that the resulting shapes are planar
meshes with 3-valence vertices, which can always be physically constructed using
planar or developable materials such as glass, sheet metal or plywood. The method
introduced is inspired by the traditional sculpture and is based on the idea of carving
a mesh by using slicing planes. The process of determining the slicing planes can
either be interactive or automated.
A framework is developed which allows user to sculpt shapes by using the in-
teractive and automated processes. The framework allows user to cut a source mesh
based on its edges, faces or vertices. The user can sculpt various kinds of developable
surfaces by cutting the parallel edges of the mesh. The user can also introduce in-
teresting conical patterns by cutting dierent vertex, edge, face combinations of the
mesh.
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Ågren, Rasmus. "Optimerad rendering av fluid meshes." Thesis, Högskolan i Gävle, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-15433.
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Simuleringen av vätskor är idag en viktig del inom både film-, spel- och reklamindustrin. Detta kräver dock mycket av hårdvaran vilket saktar ner processen att rendera markant. I detta projekt forskades det inom optimering av renderingstekniker för att göra det lättare att rendera fram kvalitativa resultat när man använder sig av fluids i program för 3D-grafik. Arbetet innehåller en undersökning där testpersoner bedömt ett antal renderingar samt de optimerade inställningar som används till rendering
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Pagnutti, Douglas. "Anisotropic adaptation: metrics and meshes." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/415.
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We present a method for anisotropic mesh refinement to high-order numerical solutions. We accomplish this by assigning metrics to vertices that approximate the error in that region. To choose values for each metric, we first reconstruct an error equation from the leading order terms of the Taylor expansion. Then, we use a Fourier approximation to choose the metric associated with that vertex. After assigning a metric to each vertex, we refine the mesh anisotropically using three mesh operations. The three mesh operations we use are swapping to maximize quality, inserting at approximate circumcenters to decrease cell size, and vertex removal to eliminate small edges. Because there are no guarantees on the results of these modification tools, we use them iteratively to produce a quasi-optimal mesh. We present examples demonstrating that our anisotropic refinement algorithm improves solution accuracy for both second and third order solutions compared with uniform refinement and isotropic refinement. We also analyze the effect of using second derivatives for refining third order solutions.
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Zheng, Yun. "Computational aerodynamics on unstructed meshes." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2830/.
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New 2D and 3D unstructured-grid based flow solvers have been developed for simulating steady compressible flows for aerodynamic applications. The codes employ the full compressible Euler/Navier-Stokes equations. The Spalart-Al Imaras one equation turbulence model is used to model turbulence effects of flows. The spatial discretisation has been obtained using a cell-centred finite volume scheme on unstructured-grids, consisting of triangles in 2D and of tetrahedral and prismatic elements in 3D. The temporal discretisation has been obtained with an explicit multistage Runge-Kutta scheme. An "inflation" mesh generation technique is introduced to effectively reduce the difficulty in generating highly stretched 2D/3D viscous grids in regions near solid surfaces. The explicit flow method is accelerated by the use of a multigrid method with consideration of the high grid aspect ratio in viscous flow simulations. A solution mesh adaptation technique is incorporated to improve the overall accuracy of the 2D inviscid and viscous flow solutions. The 3D flow solvers are parallelised in a MIMD fashion aimed at a PC cluster system to reduce the computing time for aerodynamic applications. The numerical methods are first applied to several 2D inviscid flow cases, including subsonic flow in a bump channel, transonic flow around a NACA0012 airfoil and transonic flow around the RAE 2822 airfoil to validate the numerical algorithms. The rest of the 2D case studies concentrate on viscous flow simulations including laminar/turbulent flow over a flat plate, transonic turbulent flow over the RAE 2822 airfoil, and low speed turbulent flows in a turbine cascade with massive separations. The results are compared to experimental data to assess the accuracy of the method. The over resolved problem with mesh adaptation on viscous flow simulations is addressed with a two phase mesh reconstruction procedure. The solution convergence rate with the aspect ratio adaptive multigrid method and the direct connectivity based multigrid is assessed in several viscous turbulent flow simulations. Several 3D test cases are presented to validate the numerical algorithms for solving Euler/Navier-Stokes equations. Inviscid flow around the M6 wing airfoil is simulated on the tetrahedron based 3D flow solver with an upwind scheme and spatial second order finite volume method. The efficiency of the multigrid for inviscid flow simulations is examined. The efficiency of the parallelised 3D flow solver and the PC cluster system is assessed with simulations of the same case with different partitioning schemes. The present parallelised 3D flow solvers on the PC cluster system show satisfactory parallel computing performance. Turbulent flows over a flat plate are simulated with the tetrahedron based and prismatic based flow solver to validate the viscous term treatment. Next, simulation of turbulent flow over the M6 wing is carried out with the parallelised 3D flow solvers to demonstrate the overall accuracy of the algorithms and the efficiency of the multigrid method. The results show very good agreement with experimental data. A highly stretched and well-formed computational grid near the solid wall and wake regions is generated with the "inflation" method. The aspect ratio adaptive multigrid displayed a good acceleration rate. Finally, low speed flow around the NREL Phase 11 Wind turbine is simulated and the results are compared to the experimental data.
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THEDIN, REGIS SANTOS. "TOPOLOGY OPTIMIZATION USING POLYHEDRAL MESHES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=37112@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A otimização topológica tem se desenvolvido bastante e possui potencial para revolucionar diversas áreas da engenharia. Este método pode ser implementado a partir de diferentes abordagens, tendo como base o Método dos Elementos Finitos. Ao se utilizar uma abordagem baseada no elemento, potencialmente, cada elemento finito pode se tornar um vazio ou um sólido, e a cada elemento do domínio é atribuído uma variável de projeto, constante, denominada densidade. Do ponto de vista Euleriano, a topologia obtida é um subconjunto dos elementos iniciais. No entanto, tal abordagem está sujeita a instabilidades numéricas, tais como conexões de um nó e rápidas oscilações de materiais do tipo sólido-vazio (conhecidas como instabilidade de tabuleiro). Projetos indesejáveis podem ser obtidos quando elementos de baixa ordem são utilizados e métodos de regularização e/ou restrição não são aplicados. Malhas poliédricas não estruturadas naturalmente resolvem esses problemas e oferecem maior flexibilidade na discretização de domínios não Cartesianos. Neste trabalho investigamos a otimização topológica em malhas poliédricas por meio de um acoplamento entre malhas. Primeiramente, as malhas poliédricas são geradas com base no conceito de diagramas centroidais de Voronoi e posteriormente otimizadas para uso em análises de elementos finitos. Demonstramos que o número de condicionamento do sistema de equações associado pode ser melhorado ao se minimizar uma função de energia relacionada com a geometria dos elementos. Dada a qualidade da malha e o tamanho do problema, diferentes tipos de resolvedores de sistemas de equações lineares apresentam diferentes desempenhos e, portanto, ambos os resolvedores diretos e iterativos são abordados. Em seguida, os poliedros são decompostos em tetraedros por um algoritmo específico de acoplamento entre as malhas. A discretização em poliedros é responsável pelas variáveis de projeto enquanto a malha tetraédrica, obtida pela subdiscretização da poliédrica, é utilizada nas análises via método dos elementos finitos. A estrutura modular, que separa as rotinas e as variáveis usadas nas análises de deslocamentos das usadas no processo de otimização, tem se mostrado promissora tanto na melhoria da eficiência computacional como na qualidade das soluções que foram obtidas neste trabalho. Os campos de deslocamentos e as variáveis de projeto são relacionados por meio de um mapeamento. A arquitetura computacional proposta oferece uma abordagem genérica para a solução de problemas tridimensionais de otimização topológica usando poliedros, com potencial para ser explorada em outras aplicações que vão além do escopo deste trabalho. Finalmente, são apresentados diversos exemplos que demonstram os recursos e o potencial da abordagem proposta.
Topology optimization has had an impact in various fields and has the potential to revolutionize several areas of engineering. This method can be implemented based on the finite element method, and there are several approaches of choice. When using an element-based approach, every finite element is a potential void or actual material, whereas every element in the domain is assigned to a constant design variable, namely, density. In an Eulerian setting, the obtained topology consists of a subset of initial elements. This approach, however, is subject to numerical instabilities such as one-node connections and rapid oscillations of solid and void material (the so-called checkerboard pattern). Undesirable designs might be obtained when standard low-order elements are used and no further regularization and/or restrictions methods are employed. Unstructured polyhedral meshes naturally address these issues and offer fl exibility in discretizing non-Cartesians domains. In this work we investigate topology optimization on polyhedra meshes through a mesh staggering approach. First, polyhedra meshes are generated based on the concept of centroidal Voronoi diagrams and further optimized for finite element computations. We show that the condition number of the associated system of equations can be improved by minimizing an energy function related to the element s geometry. Given the mesh quality and problem size, different types of solvers provide different performances and thus both direct and iterative solvers are addressed. Second, polyhedrons are decomposed into tetrahedrons by a tailored embedding algorithm. The polyhedra discretization carries the design variable and a tetrahedra subdiscretization is nested within the polyhedra for finite element analysis. The modular framework decouples analysis and optimization routines and variables, which is promising for software enhancement and for achieving high fidelity solutions. Fields such as displacement and design variables are linked through a mapping. The proposed mapping-based framework provides a general approach to solve three-dimensional topology optimization problems using polyhedrons, which has the potential to be explored in applications beyond the scope of the present work. Finally, the capabilities of the framework are evaluated through several examples, which demonstrate the features and potential of the proposed approach.
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NUVOLI, STEFANO. "Composing quadrilateral meshes for animation." Doctoral thesis, Università degli Studi di Cagliari, 2021. http://hdl.handle.net/11584/312917.
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The modeling-by-composition paradigm can be a powerful tool in modern animation pipelines. We propose two novel interactive techniques to compose 3D assets that enable the artists to freely remove, detach and combine components of organic models. The idea behind our methods is to preserve most of the original information in the input characters and blend accordingly where necessary.
The first method, QuadMixer, provides a robust tool to compose the quad layouts of watertight pure quadrilateral meshes, exploiting the boolean operations defined on triangles. Quad Layout is a crucial property for many applications since it conveys important information that would otherwise be destroyed by techniques that aim only at preserving the shape. Our technique keeps untouched all the quads in the patches which are not involved in the blending. The resulting meshes preserve the originally designed edge flows that, by construction, are captured and incorporated into the new quads.
SkinMixer extends this approach to compose skinned models, taking into account not only the surface but also the data structures for animating the character. We propose a new operation-based technique that preserves and smoothly merges meshes, skeletons, and skinning weights. The retopology approach of QuadMixer is extended to work on quad-dominant and arbitrary complex surfaces. Instead of relying on boolean operations on triangle meshes, we manipulate signed distance fields to generate an implicit surface. The results preserve most of the information in the input assets, blending accordingly in the intersection regions. The resulting characters are ready to be used in animation pipelines.
Given the high quality of the results generated, we believe that our methods could have a huge impact on the entertainment industry. Integrated into current software for 3D modeling, they would certainly provide a powerful tool for the artists. Allowing them to automatically reuse parts of their well-designed characters could lead to a new approach for creating models, which would significantly reduce the cost of the process.
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Krause, Jens. "On boundary conforming anisotropic delaunay meshes /." Zürich, 2001. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=14219.
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Gillette, Russell. "Augmentation of coarse meshes with wrinkles." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54687.
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Folds and wrinkles are an important visual cue in the recognition of realistically dressed characters in virtual environments. Wrinkles must, however, move dynamically within the context of an animation to retain much of this realism. Adding wrinkles to real-time cloth visualization proves challenging, as the animations used in games, pre-render visualization, and other such applications, often have no reference shape, an extremely low triangle count, and poor temporal and spatial coherence. I contribute approaches towards the persistence of wrinkles over time, and the creation and rendering of wrinkle geometry in a real-time context, towards a novel real-time method for adding believable, dynamic wrinkles to coarse cloth animations. With this method we trace spatially and temporally coherent wrinkle paths and overcomes the inaccuracies and noise in low-end cloth animation. We employ a two stage stretch tensor estimation process, first detecting regions of consistent surface behaviour, and then using these regions to construct a per-triangle, temporally adaptive reference shape and a stretch tensor based on it. We use this tensor to dynamically generate new wrinkle geometry on coarse cloth meshes through use of the GPU tessellation unit. Our algorithm produces plausible fine wrinkles on real-world data sets at real-time frame rates, and is suitable for the current generation of consoles and PC graphics cards.Science, Faculty of
Computer Science, Department of
Graduate
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Harbrecht, Helmut, Ulf Kähler, and Reinhold Schneider. "Wavelet Galerkin BEM on unstructured meshes." Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200601459.
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The present paper is devoted to the fast solution of boundary integral equations on unstructured meshes by the Galerkin scheme. On the given mesh we construct a wavelet basis providing vanishing moments with respect to the traces of polynomials in the space. With this basis at hand, the system matrix in wavelet coordinates can be compressed to $\mathcal{O}(N\log N)$ relevant matrix coefficients, where $N$ denotes the number of unknowns. The compressed system matrix can be computed within suboptimal complexity by using techniques from the fast multipole method or panel clustering. Numerical results prove that we succeeded in developing a fast wavelet Galerkin scheme for solving the considered class of problems.
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Brochu, Tyson. "Dynamic explicit surface meshes and applications." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/42829.
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Explicit surface tracking encompasses the discretization of moving surfaces in 3D with triangle meshes. This thesis presents key contributions towards making explicit surface tracking tractable. I first deal with the topology change problem (the merging and splitting of mesh surfaces), introducing a framework for guaranteeing intersection-free surfaces while handling these topological changes. I then introduce new methods for continuous collision detection which are “exact” in the sense of returning the same results as they would if computed with symbolic or exact arithmetic, but which are implemented using faster, floating-point arithmetic.
The thesis also showcases several application domains in which explicit surface tracking can offer improvements over traditional methods: geometric flows, adaptive cloth simulation, and passive visualization of smoke simulation. It also presents two simulation techniques which take advantage of the explicit surface mesh representation and would not be possible with traditional methods: vortex sheet smoke and adaptive liquid simulation with high-resolution surface tension.
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Gurung, Topraj. "Compact connectivity representation for triangle meshes." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47709.
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Many digital models used in entertainment, medical visualization, material science, architecture, Geographic Information Systems (GIS), and mechanical Computer Aided Design (CAD) are defined in terms of their boundaries. These boundaries are often approximated using triangle meshes. The complexity of models, which can be measured by triangle count, increases rapidly with the precision of scanning technologies and with the need for higher resolution. An increase in mesh complexity results in an increase of storage requirement, which in turn increases the frequency of disk access or cache misses during mesh processing, and hence decreases performance. For example, in a test application involving a mesh with 55 million triangles in a machine with 4GB of memory versus a machine with 1GB of memory, performance decreases by a factor of about 6000 because of memory thrashing. To help reduce memory thrashing, we focus on decreasing the average storage requirement per triangle measured in 32-bit integer references per triangle (rpt).
This thesis covers compact connectivity representation for triangle meshes and discusses four data structures:
1. Sorted Opposite Table (SOT), which uses 3 rpt and has been extended to support tetrahedral meshes.
2. Sorted Quad (SQuad), which uses about 2 rpt and has been extended to support streaming.
3. Laced Ring (LR), which uses about 1 rpt and offers an excellent compromise between storage compactness and performance of mesh traversal operators.
4. Zipper, an extension of LR, which uses about 6 bits per triangle (equivalently 0.19 rpt), therefore is the most compact representation.
The triangle mesh data structures proposed in this thesis support the standard set of mesh connectivity operators introduced by the previously proposed Corner Table at an amortized constant time complexity. They can be constructed in linear time and space from the Corner Table or any equivalent representation. If geometry is stored as 16-bit coordinates, using Zipper instead of the Corner Table increases the size of the mesh that can be stored in core memory by a factor of about 8.
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Kongevold, Dimitry. "Merging Meshes from Different 3D Scanners." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for datateknikk og informasjonsvitenskap, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-23013.
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Creating digital representation of physical objects is becoming more and more popular as scanning technology becomes more available on the consumer marked. High precision close range scanners, based on structured light, can produce high precision meshes in short amount of time, while automated photogrammetric software can process images taken with ordinary cameras to re-create a three dimensional scenes. Unfortunately the quality of digitalization is bound to the volume of the captured scene, creating a trade of between quality and speed of acquisition. In this master thesis we present software that can merge the output of two different scanners to create a combined mesh with regions of different resolution. We propose two methods to identify corresponding regions in meshes and a variation of greedy triangulation algorithm. At the end we perform tests on combined meshes to assess the quality of merging and present the results.
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Coyle, Steven. "Chameleon metals : sub-wavelength metallic meshes." Thesis, University of Southampton, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403823.
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ROCHA, ALLAN CARLOS AVELINO. "ILLUSTRATIVE VOLUME VISUALIZATION FOR UNSTRUCTURED MESHES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=18748@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORTécnicas de visualização científica criam imagens na tentativa de revelar estruturas e fenômenos complexos. Técnicas ilustrativas têm sido incorporadas aos sistemas de visualizacão científica para melhorar a expressividade de tais imagens. A visualização de linhas caracteríticas é uma técnica importante para transmitir uma melhor informacão sobre a forma das superfícies. Neste trabalho, propomos combinar visualização volumétrica de malhas não estruturadas com isosuperfícies ilustradas. Isto é feito estendendo um algoritmo de traçado de raio em GPU para incorporar ilustração com linhas de variação extrema da iluminação(photic extremum lines), um tipo de linha característica que captura mudanças bruscas de luminância, revelando formas de um jeito perceptualmente correto.
Scientic visualization techniques create images attempting to reveal complex structures and phenomena. Illustrative techniques have been incorporated to scientic visualization systems in order to improve the expressiveness of such images. The rendering of feature lines is an important technique for better depicting surface shapes and features. In this thesis, we propose to combine volume visualization of unstructured meshes with illustrative isosurfaces. This is accomplished by extending a GPU-based ray-casting algorithm to incorporate illustration with photic extremum lines, a type of feature lines able to capture sudden changes of luminance, conveying shapes in a perceptually correct way.
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MIRANDA, FABIO MARKUS NUNES. "VOLUME RENDERING OF UNSTRUCTURED HEXAHEDRAL MESHES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2011. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=28921@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
Importantes aplicações de engenharia usam malhas não estruturadas de hexaedros para simulações numéricas. Células hexaédricas, comparadas com tetraedros, tendem a ser mais numericamente estáveis e requerem um menor refinamento da malha. Entretando, visualização volumétrica de malhas não estruturadas é um desafio devido a variação trilinear do campo escalar dentro da célula. A solução convencional consiste em subdividir cada hexaedro em cinco ou seis tetraedros, aproximando uma variação trilinear por uma inadequada série de funções lineares. Isso resulta em imagens inadequadas e aumenta o consumo de memória. Nesta tese, apresentamos um algoritmo preciso de visualização volumétrica utilizando ray-casting para malhas não estruturadas de hexaedros. Para capturar a variação trilinear ao longo do raio, nós propomos usar uma integração de quadratura. Nós também propomos uma alternativa rápida que melhor aproxima a variação trilinear, considerando os pontos de mínimo e máximo da função escalar ao longo do raio. Uma série de experimentos computacionais demonstram que nossa proposta produz resultados exatos, com um menor gasto de memória. Todo algoritmo é implementado em placas gráficas, garantindo uma performance competitiva.
Important engineering applications use unstructured hexahedral meshes for numerical simulations. Hexahedral cells, when compared to tetrahedral ones, tend to be more numerically stable and to require less mesh refinement. However, volume visualization of unstructured hexahedral meshes is challenging due to the trilinear variation of scalar fields inside the cells. The conventional solution consists in subdividing each hexahedral cell into five or six tetrahedra, approximating a trilinear variation by an inadequate piecewise linear function. This results in inaccurate images and increases the memory consumption. In this thesis, we present an accurate ray-casting volume rendering algorithm for unstructured hexahedral meshes. In order to capture the trilinear variation along the ray, we propose the use of quadrature integration. We also propose a fast approach that better approximates the trilinear variation to a series of linear ones, considering the points of minimum and maximum of the scalar function along the ray. A set of computational experiments demonstrates that our proposal produces accurate results, with reduced memory footprint. The entire algorithm is implemented on graphics cards, ensuring competitive performance.
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Kelly, Alan. "The optimisation of finite element meshes." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5730/.
Full textAbstract:
Among the several numerical methods which are available for solving complex problems in many areas of engineering and science such as structural analysis, fluid flow and bio-mechanics, the Finite Element Method (FEM) is the most prominent. In the context of these methods, high quality meshes can be crucial to obtaining accurate results. Finite Element meshes are composed of elements and the quality of an element can be described as a numerical measure which estimates the effect that the size/shape of an element will have on the accuracy of an analysis. In this thesis, the strong link between mesh geometry and the accuracy and efficiency of a simulation is explored and it is shown that poor quality elements cause both interpolation errors and poor conditioning of the global stiffness matrix. Numerical optimisation is the process of maximising or minimising an objective func- tion, subject to constraints on the solution. When this is applied to a finite element mesh it is referred to as mesh optimisation, where the quality of the mesh is the objec- tive function and the constraints include, for example, the domain geometry, maximum element size, etc. A mesh optimisation strategy is developed with a particular focus on optimising the quality of the worst elements in a mesh. Using both two and three dimensional examples, the most efficient and effective combination of element quality measure and objective function is found. Many of the problems under consideration are characterised by very complex geometries. The nodes lying on the surfaces of such meshes are typically treated as unmovable by most mesh optimisation software. Techniques exist for moving such nodes as part of the mesh optimisation process, however, the resulting mesh geometry and area/volume is often not conserved. This means that the optimised mesh is no longer an accurate discretisation of the original domain. Therefore, a method is developed and demonstrated which optimises the positions of surface nodes while respecting the geometry and area/volume of a domain. At the heart of many of the problems being considered is the Arbitrary Lagrangian Eulerian (ALE) formulation where the need to ensure mesh quality in an evolving mesh is very important. In such a formulation, a method of determining the updated nodal positions is required. Such a method is developed using mesh optimisation techniques as part of the FE solution process and this is demonstrated using a two-dimensional, axisymmetric simulation of a micro-fluid droplet subject to external excitation. While better quality meshes were observed using this method, the time step collapsed resulting in simulations requiring significantly more time to complete. The extension of this method to incorporate adaptive re-meshing is also discussed.
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Katz, Maximilian Peter. "White Dwarf Mergers on Adaptive Meshes." Thesis, State University of New York at Stony Brook, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10183090.
Full textAbstract:
The mergers of binary white dwarf systems are potential progenitors of astrophysical explosions such as Type Ia supernovae. These white dwarfs can merge either by orbital decay through the emission of gravitational waves or by direct collisions as a result of orbital perturbations. The coalescence of the stars may ignite nuclear fusion, resulting in the destruction of both stars through a thermonuclear runaway and ensuing detonation. The goal of this dissertation is to simulate binary white dwarf systems using the techniques of computational fluid dynamics and therefore to understand what numerical techniques are necessary to obtain accurate dynamical evolution of the system, as well as to learn what conditions are necessary to enable a realistic detonation. For this purpose I have used software that solves the relevant fluid equations, the Poisson equation for self-gravity, and the systems governing nuclear reactions between atomic species. These equations are modeled on a computational domain that uses the technique of adaptive mesh refinement to have the highest spatial resolution in the areas of the domain that are most sensitive to the need for accurate numerical evolution. I have identified that the most important obstacles to accurate evolution are the numerical violation of conservation of energy and angular momentum in the system, and the development of numerically seeded thermonuclear detonations that do not bear resemblance to physically correct detonations. I then developed methods for ameliorating these problems, and determined what metrics can be used for judging whether a given white dwarf merger simulation is trustworthy. This involved the development of a number of algorithmic improvements to the simulation software, which I describe. Finally, I performed high-resolution simulations of typical cases of white dwarf mergers and head-on collisions to demonstrate the impacts of these choices. The results of these simulations and the corresponding implications for white dwarf mergers as astrophysical explosion progenitors are discussed.
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Dong, Zhaonan. "Discontinuous Galerkin methods on polytopic meshes." Thesis, University of Leicester, 2017. http://hdl.handle.net/2381/39140.
Full textAbstract:
This thesis is concerned with the analysis and implementation of the hp-version interior penalty discontinuous Galerkin finite element method (DGFEM) on computational meshes consisting of general polygonal/polyhedral (polytopic) elements. Two model problems are considered: general advection-diffusion-reaction boundary value problems and time dependent parabolic problems. New hp-version a priori error bounds are derived based on a specific choice of the interior penalty parameter which allows for edge/face-degeneration as well as an arbitrary number of faces and hanging nodes per element. The proposed method employs elemental polynomial bases of total degree p (Pp- bases) defined in the physical coordinate system, without requiring mapping from a given reference or canonical frame. A series of numerical experiments highlighting the performance of the proposed DGFEM are presented. In particular, we study the competitiveness of the p-version DGFEM employing a Pp-basis on both polytopic and tensor-product elements with a (standard) DGFEM and FEM employing a (mapped) Qp-basis. Moreover, a careful theoretical analysis of optimal convergence rate in p for Pp-basis is derived for several commonly used projectors, which leads to sharp bounds of exponential convergence with respect to degrees of freedom (dof) for the Pp-basis.
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Silva, Luis Fernando Maia Santos. "Merging meshes using dynamic regular triangulation." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/25512.
Full textAbstract:
Malhas simpliciais são utilizadas em várias áreas da Computação Gráfica e Engenharia, como por exemplo, em vizualização, simulação, prototipação, além de outras aplicações. Este tipo de malha é, geralmente, utilizada como aproximações discretas de espaços contínuos, onde eles oferecem representações flexíveis e eficientes. Muito esforço é gasto visando gerar malhas de boa qualidade, porém, em alguns casos as malhas acabam sendo modificadas. Entretanto, este tipo de operação é geralmente custosa e inflexível, o que pode resultar na geraão de malhas bem diferentes das originais. A habilidade de manipular cenas dinâmicas revela-se um dos problemas mais desafiadores da computação gráfica. Este trabalho propõe um método alternativo para atualizar malhas simpliciais que vai além de mudanças geométricas e topológicas. Tal método explora uma das propriedade das Tringulações de Delaunay com Pesos, que permite a usá-las para definir implicitamente as relações de conectividade de uma malha. Ao contrário de manter as informações de conectividade explicitamente, a atual abordagem simplesmente armazena uma coleção de pesos associados a cada vértice. Além disso, criamos um algoritmo para calcular uma Tringulação de Delaunay com Pesos a partir de uma dada triangulação. O algoritmo consiste em uma busca em largura que atribui pesos aos vértices, e uma estratégia de de subdivisão para assegurar que a triangulação reconstruída será correspondente à original. Este método apresenta diversas aplicações e, em particular, permite a criação de um sistema simples de realizar combinação entre triangulações, que será ilustrada com exemplos em 2D e 3D.Simplicial meshes are used in many fields of Computer Graphics and Engineering, for instance, in visualization, simulation, prototyping, among other applications. This kind of mesh is often used as discrete approximations of continuous spaces, where they offer flexible and efficient representations. Considerable effort is spent in generating good quality meshes, but in some applications the meshes can be modified over time. However, this kind of operation is often very expensive and inflexible, sometimes leading to results very different from the original meshes. The ability to handle dynamic scenes reveals itself as one of the most challenging problems in computer graphics. This work proposes an alternative technique for updating simplicial meshes that undergo geometric and topological changes. It explores the property that a Weighted Delaunay Triangulation (WDT) can be used to implicitly define the connectivity of a mesh. Instead of explicitly maintaining connectivity information, this approach simply keeps a collection of weights associated to each vertex. It consists of an algorithm to compute a WDT from any given triangulation, which relies on a breadth-first traversal to assign weights to vertices, and a subdivision strategy to ensure that the reconstructed triangulation conforms with the original one. This technique has many applications and, in particular, it allows for a very simple method of merging triangulations, which is illustrated with both 2D and 3d examples.
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Bingöl, Özgür Neslitürk Ali İhsan. "Uniformly Convergent Approximation On Special Meshes /." [S.l. : s.n.], 2007. http://library.iyte.edu.tr/tezler/master/matematik/T000649.pdf.
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Friedel, Ilja Heinrich Schröder Peter. "Approximation of surfaces by normal meshes /." Diss., Pasadena, Calif. : California Institute of Technology, 2005. http://resolver.caltech.edu/CaltechETD:etd-05242005-164959.
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Gregorski, Benjamin F. "Multiresolution tetrahedral meshes for scientific visualization /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.
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CABIDDU, DANIELA. "Distributed processing of large triangle meshes." Doctoral thesis, Università degli Studi di Cagliari, 2016. http://hdl.handle.net/11584/266876.
Full textAbstract:
Thanks to modern high-resolution acquisition techniques, 3D digital representations
of real objects are easily made of millions, or even billions, of
elements. Processing and analysing such large datasets is often a non trivial
task, due to specific software and hardware requirements.
Our system allows to process large triangle meshes by exploiting nothing
more than a standard Web browser. A graphical interface allows to select
among available algorithms and to stack them into complex pipelines, while
a central engine manages the overall execution by exploiting both hardware
and software provided by a distributed network of servers.
As an additional feature, our system allows to store work
ows and to make
them publicly available. A semantic-driven search mechanism is provided
to allow the retrieval of specific work
ows.
Besides the technological contribution, an innovative mesh transfer protocol
avoids possible bottlenecks during the transmission of data across scattered
servers. Also, distributed parallel processing is enabled thanks to an innovative
divide and conquer approach. A simplification algorithm based on this
paradigm proves that the overhead due to data transmission is negligible.
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Kraus, Martin. "Direct volume visualization of geometrically unpleasant meshes." [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=968311210.
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Frank, Tobias. "Advanced visualization and modeling of tetrahedral meshes." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2009. http://nbn-resolving.de/urn:nbn:de:swb:105-0716552.
Full textAbstract:
Tetrahedral meshes are becoming more and more important for geo-modeling applications. The presented work introduces new algorithms for efficient visualization and modeling of tetrahedral meshes. Visualization consists of a generic framework that includes the extraction of geological information like stratigraphic columns, fault block boundaries, simultaneous co-rendering of different attributes and boolean operations of Constructive Solid Geometry with constant complexity. Modeling can be classified into geometric and implicit modeling. Geometric modeling addresses local mesh refinement to increase the numerical resolution of a given mesh. Implicit modeling covers the definition and manipulation of implicitly defined models. A new surface reconstruction method was developed to reconstruct complex, multi-valued surfaces from noisy and sparse data sets as they occur in geological applications. The surface can be bounded and may have discontinuities. Further, this work proposes a new and innovative algorithm for rapid editing of implicitly defined shapes like horizons based on the GeoChron parametrization. The editing is performed interactively on the 3d-volumetric model and geological constraints are respected automatically.
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Jain, Ankita. "Efficient Parallel Algorithm for Overlaying Surface Meshes." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16315.
Full textAbstract:
Many computational applications involve multiple physical components, each having its own computational domain discretized by a mesh. An
integrated simulation of these physical systems require transferring data across these boundaries, which are typically represented by surface meshes composed of triangles or quadrilaterals and are non-matching with differing connectivities and geometry. It is necessary to constructa common refinement (or common tessellation) of the surface meshes to transfer data between different domains accurately and conservatively. For large-scale problems that involve moving boundary, the common
tessellation must be updated frequently within the integrated simulations running on parallel computers.
Previously, Jiao and Heath developed an algorithm for constructing a common tessellation by overlaying the surface meshes. The original
algorithm is efficient and robust, but unfortunately, it is complex and difficult to parallelize. In this thesis, we develop a modified
algorithm for overlaying surface meshes. Our algorithm employs a high-level primitive, face-intersection, which combines the low-level point-projection and edge-intersection primitives of the original algorithm. A main advantage of our modified algorithm is its ease of implementation
and parallelization. Our implementation utilizes flexible data structures for efficient computation and query of the common tessellation and avoids potential redundancy in computations to achieve high efficiency. To achieve robustness, we pay special attention to avoid potential topological inconsistencies due to numerical errors, and introduce a preprocessing step to project a far-apart surface mesh onto other before computing the common tessellation. We present numerical examples to demonstrate the robustness and efficiency of our method on parallel computers.
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Wojtan, Chris. "Animating physical phenomena with embedded surface meshes." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37256.
Full textAbstract:
Accurate computational representations of highly deformable surfaces are indispensable in the fields of computer animation, medical simulation, computer vision, digital modeling, and computational physics. The focus of this dissertation is on the animation of physics-based phenomena with highly detailed deformable surfaces represented by triangle meshes.
We first present results from an algorithm that generates continuum mechanics animations with intricate surface features. This method combines a finite element method with a tetrahedral mesh generator and a high resolution surface mesh, and it is orders of magnitude more efficient than previous approaches. Next, we present an efficient solution for the challenging problem of computing topological changes in detailed dynamic surface meshes. We then introduce a new physics-inspired surface tracking algorithm that is capable of preserving arbitrarily thin features and reproducing realistic fine-scale topological changes like Rayleigh-Plateau instabilities. This physics-inspired surface tracking technique also opens the door for a unique coupling between surficial finite element methods and volumetric finite difference methods, in order to simulate liquid surface tension phenomena more efficiently than any previous method. Due to its dramatic increase in computational resolution and efficiency, this method yielded the first computer simulations of a fully developed crown splash with droplet pinch off.
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Jonsson, Kristoffer. "Matching of geometrically and topologically changing meshes." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-262249.
Full textAbstract:
The aim for this thesis is to develop a foundation for a compression system for animated mesh sequences, specifically under dynamic change of mesh geometry and topology. Compression of mesh sequences is of special interest in the game industry and this particular thesis is a part of an ongoing series of projects at EA DICE. One of the primary challenges when creating a mesh compression system is creating a matching bijective subset of the mesh surfaces between two subsequent frames in the animation to guide remeshing of the sequence. This thesis describes a method for producing a bijective set of matching mesh patches between two meshes along with an error metric that captures the quality of the matching in terms of shape similarity and distortion. Theory of mathematical topology and tensor algebra used in methods for high performance scientific digital 3D-image recognition are here adopted to extract similar local features between meshes. Techniques for creating parametrizations of mesh patches are combined with techniques for matching point clouds and deforming mesh geometry under energy minimization in order to produce a matching set of patches. The presented algorithm successfully creates bijective sets of matched patches for subsequent meshes in a sequence as well as measures the error for the matchings. Results show an average matching set size of approximately 25% of the mesh areas over a sequence of meshes. This suggests that the data size of such a sequence could potentially be reduced by 25%.
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Sharbatdar, Mahkame. "Anisotropic mesh adaptation : recovering quasi-structured meshes." Thesis, University of British Columbia, 2012. http://hdl.handle.net/2429/43568.
Full textAbstract:
An adaptive method for producing anisotropic quasi-structured meshes is presented in this thesis. Current anisotropic adaptation schemes produce meshes without any regular structure which can hurt accuracy and efficiency of the solution. By modifying the anisotropic adaptation schemes, producing aligned, quasi-structured meshes is possible which means that the accuracy and efficiency of the flow solution are improved. By using quasi-structured meshes, we can get the advantages of flexibility of unstructured meshes for complex geometries and accuracy of the high directional qualities of the structured meshes at the same time. The construction of the quasi-structured meshes from initial isotropic unstructured meshes is accomplished by assigning metrics to vertices based on the error estimation methods. The metrics are used to communicate the desired anisotropy to the meshing program. After assigning a metric to each vertex, the mesh is refined anisotropically using four mesh quality improvements operations to produce high quality anisotropic quasi-structured meshes: swapping to choose the diagonal of the quadrilateral formed by two neighboring triangles which results the maximum quality, inserting vertices for large triangles, vertex removal to eliminate small edges and vertex movements to optimize the location of the vertices so that quasi-structured meshes are created. The idea in the optimization process is to smooth a vertex location by seeking so that the final mesh contains target elements dictated by the metrics assigned in the three vertices of that triangle. The final, high quality mesh is produced by using these operations iteratively based on the metrics assigned to each vertex in an adaptive, solution-based process.
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Leksell, Mats. "Parameterization of triangular meshes for texture mapping." Thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-95298.
Full textAbstract:
A parameterization of a three-dimensional triangular mesh M to a two dimensional parameter domain is a invertibel PM : S - R, where is the set of all points on the surface. one of the use for such a mapping is for mapping an image from the parameter space D-R onto S. thesis evalutes several apporaches for creating such a mapping. for this purpos , the optimal mapping is an isomtry, i.e. a mapping that preserves the length of all the edges. Such a mapping is however often impossible or somputationally unpratical, so various tradeoffs have to made. each method evaluated here has its own set of strengths and weaknesses tha needa to be taken into account when selecting a method to use.
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Ling, Ruotian, and 凌若天. "Methods for generating meshes with sharp features." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B49799368.
Full textAbstract:
Computer graphics applications call for various mesh generation techniques to visualize objects, store shape data, perform numerical analyses, etc. Mesh generation is also a fundamental research topic in many other engineering areas related to physical models described by partial differential equations. The reason that meshed surfaces are preferred over spline surfaces in many engineering applications is its flexibility in handling complex objects, while sharp features and boundaries can be represented without trimming, which is highly desired in numerical simulations.
In this thesis, we study two methods for generating meshes with sharp features. Sharp features, such as creases and corners, are very common in mechanical objects. Hence effectively handling sharp features is of great importance to this kind of objects.
The first method is to generate triangular subdivision surfaces with sharp features. Although there have been various methods to fit subdivision surfaces to different types of shape data, e.g., dense meshes and point clouds, none of these methods can handle sharp features effectively. We present a new exact evaluation scheme for all types of sharp features in Loop subdivision, and integrate the new evaluation scheme into the optimization framework to fit Loop subdivision surfaces to dense meshes.
The second method is to generate quadrilateral meshes with varying element sizes which observe the user requirement. This method is inspired by the idea of spectral quadrangulation, but existing spectral quadrangulation methods are limited to closed surfaces due to its lack of proper boundary treatment. We present a new set of boundary conditions, and introduce the Quasi-Eigenfunction to assist the mesh generation process. The proposed boundary treatment is further applied to sharp features to handle mechanical objects. The quasi-eigenfunction based quadrangulation framework is also extended to 3D volumetric domain to generate hexahedral meshes.
Experimental results and comparisons with existing methods are presented in each chapter to demonstrate the effectiveness of the proposed methods.published_or_final_version
Computer Science
Doctoral
Doctor of Philosophy
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Linß, Torsten. "Layer-adapted meshes for convection-diffusion problems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1203582105872-58676.
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This is a book on numerical methods for singular perturbation problems - in particular stationary convection-dominated convection-diffusion problems. More precisely it is devoted to the construction and analysis of layer-adapted meshes underlying these numerical methods. An early important contribution towards the optimization of numerical methods by means of special meshes was made by N.S. Bakhvalov in 1969. His paper spawned a lively discussion in the literature with a number of further meshes being proposed and applied to various singular perturbation problems. However, in the mid 1980s this development stalled, but was enlivend again by G.I. Shishkin's proposal of piecewise- equidistant meshes in the early 1990s. Because of their very simple structure they are often much easier to analyse than other meshes, although they give numerical approximations that are inferior to solutions on competing meshes. Shishkin meshes for numerous problems and numerical methods have been studied since and they are still very much in vogue. With this contribution we try to counter this development and lay the emphasis on more general meshes that - apart from performing better than piecewise-uniform meshes - provide a much deeper insight in the course of their analysis. In this monograph a classification and a survey are given of layer-adapted meshes for convection-diffusion problems. It tries to give a comprehensive review of state-of-the art techniques used in the convergence analysis for various numerical methods: finite differences, finite elements and finite volumes. While for finite difference schemes applied to one-dimensional problems a rather complete convergence theory for arbitrary meshes is developed, the theory is more fragmentary for other methods and problems and still requires the restriction to certain classes of meshes.
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Linß, Torsten. "Layer-adapted meshes for convection-diffusion problems." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A24058.
Full textAbstract:
This is a book on numerical methods for singular perturbation problems - in particular stationary convection-dominated convection-diffusion problems. More precisely it is devoted to the construction and analysis of layer-adapted meshes underlying these numerical methods. An early important contribution towards the optimization of numerical methods by means of special meshes was made by N.S. Bakhvalov in 1969. His paper spawned a lively discussion in the literature with a number of further meshes being proposed and applied to various singular perturbation problems. However, in the mid 1980s this development stalled, but was enlivend again by G.I. Shishkin's proposal of piecewise- equidistant meshes in the early 1990s. Because of their very simple structure they are often much easier to analyse than other meshes, although they give numerical approximations that are inferior to solutions on competing meshes. Shishkin meshes for numerous problems and numerical methods have been studied since and they are still very much in vogue. With this contribution we try to counter this development and lay the emphasis on more general meshes that - apart from performing better than piecewise-uniform meshes - provide a much deeper insight in the course of their analysis. In this monograph a classification and a survey are given of layer-adapted meshes for convection-diffusion problems. It tries to give a comprehensive review of state-of-the art techniques used in the convergence analysis for various numerical methods: finite differences, finite elements and finite volumes. While for finite difference schemes applied to one-dimensional problems a rather complete convergence theory for arbitrary meshes is developed, the theory is more fragmentary for other methods and problems and still requires the restriction to certain classes of meshes.
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Frank, Tobias. "Advanced visualization and modeling of tetrahedral meshes." Doctoral thesis, Vandoeuvre-les-Nancy, INPL, 2006. https://tubaf.qucosa.de/id/qucosa%3A22536.
Full textAbstract:
Tetrahedral meshes are becoming more and more important for geo-modeling applications. The presented work introduces new algorithms for efficient visualization and modeling of tetrahedral meshes. Visualization consists of a generic framework that includes the extraction of geological information like stratigraphic columns, fault block boundaries, simultaneous co-rendering of different attributes and boolean operations of Constructive Solid Geometry with constant complexity. Modeling can be classified into geometric and implicit modeling. Geometric modeling addresses local mesh refinement to increase the numerical resolution of a given mesh. Implicit modeling covers the definition and manipulation of implicitly defined models. A new surface reconstruction method was developed to reconstruct complex, multi-valued surfaces from noisy and sparse data sets as they occur in geological applications. The surface can be bounded and may have discontinuities. Further, this work proposes a new and innovative algorithm for rapid editing of implicitly defined shapes like horizons based on the GeoChron parametrization. The editing is performed interactively on the 3d-volumetric model and geological constraints are respected automatically.
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Sheng, Ming-Jye. "Computations on reconfigurable meshes: strategies and algorithms /." The Ohio State University, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487858106116822.
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Woodbury, Adam C. "Localized Coarsening of Conforming All-Hexahedral Meshes." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2578.pdf.
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Frank, Tobias Mallet Jean-Laurent. "Advanced visualization and modeling of tetrahedral meshes." Vandoeuvre-les-Nancy : INPL, 2006. http://www.scd.inpl-nancy.fr/theses/2006_FRANK_T.pdf.
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Au, Kin Chung. "Sampling-sensitive multiresolution hierarchy for irregular meshes /." View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?COMP%202003%20AU.
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Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 57-59). Also available in electronic version. Access restricted to campus users.
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Casella, Tyler. "ARTIST-DRIVEN FRACTURING OF POLYHEDRAL SURFACE MESHES." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1302.
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This paper presents a robust and artist driven method for fracturing a surface polyhedral mesh via fracture maps. A fracture map is an undirected simple graph with nodes representing positions in UV-space and fracture lines along the surface of a mesh. Fracture maps allow artists to concisely and rapidly define, edit, and apply fracture patterns onto the surface of their mesh.
The method projects a fracture map onto a polyhedral surface and splits its triangles accordingly. The polyhedral mesh is then segmented based on fracture lines to produce a set of independent surfaces called fracture components, containing the visible surface of each fractured mesh fragment. Subsequently, we utilize a Voronoi-based approximation of the input polyhedral mesh’s medial axis to derive a hidden surface for each fragment. The result is a new watertight polyhedral mesh representing the full fracture component.
Results are aquired after a delay sufficiently brief for interactive design. As the size of the input mesh increases, the computation time has shown to grow linearly. A large mesh of 41,000 triangles requires approximately 3.4 seconds to perform a complete fracture of a complex pattern. For a wide variety of practices, the resulting fractures allows users to provide realistic feedback upon the application of extraneous forces.
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Isenberg, Tobias. "Capturing the essence of shape of polygonal meshes." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=971682089.
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Hong, Sung Min. "Shape Modeling of Plant Leaves with Unstructured Meshes." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1182.
Full textAbstract:
The plant leaf is one of the most challenging natural objects to be realistically depicted by computer graphics due to its complex morphological and optical characteristics. Although many studies have been done on plant modeling, previous research on leaf modeling required for close-up realistic plant images is very rare. In this thesis, a novel method for modeling of the leaf shape based on the leaf venation is presented. As the first step of the method, the leaf domain is defined by the enclosure of the leaf boundary. Second, the leaf venation is interactively modeled as a hierarchical skeleton based on the actual leaf image. Third, the leaf domain is triangulated with the skeleton as constraints. The skeleton is articulated with nodes on the skeleton. Fourth, the skeleton is interactively transformed to a specific shape. A user can manipulate the skeleton using two methods which are complementary to each other: one controls individual joints on the skeleton while the other controls the skeleton through an intermediate spline curve. Finally, the leaf blade shape is deformed to conform to the skeleton by interpolation. An interactive modeler was developed to help a user to model a leaf shape interactively and several leaves were modeled by the interactive modeler. The ray-traced rendering images demonstrate that the proposed method is effective in the leaf shape modeling.
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Sun, Feng, and 孙峰. "Shape-preserving meshes and generalized Morse-Smale complexes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B4786963X.
Full textAbstract:
Discrete representation of a surface, especially the triangle mesh, is ubiquitous in numerical
simulation and computer graphics. Compared with isotropic triangle meshes,
anisotropic triangle meshes provide more accurate results in numerical simulation by
capturing anisotropic features more faithfully. Furthermore, emerging applications in
computer graphics and geometric modeling require reliable differential geometry information
estimated on these anisotropic meshes. The first part of this thesis proposes
a special type of anisotropic meshes, called shape-preserving meshes, provides guaranteed
convergence of discrete differential operators on these meshes and devises an
algorithm for generating shape-preserving meshes on free-form surfaces based on the
mesh optimization framework with centroidal Voronoi tessellation (CVT). To improve
the numerical stability in simulation, we discuss how to reduce the number of obtuse
triangles in the mesh. The second part of the thesis discusses the non-uniqueness
of anisotropic meshes to represent the same anisotropy defined on a domain, shows
that of all anisotropic meshes, there exists one instance minimizing the number of
obtuse triangles, and proposes a variational approach to suppressing obtuse triangles
in anisotropic meshes by introducing a Minkowski metric in the CVT framework.
On a complex shape, its topological information is also highly useful to guide the
mesh generation. To extract topology properties, the Morse-Smale complex (MSC) is
a classical tool and widely used in computer graphics. However, on a manifold with
boundary, its MSC is not well defined. The final part of this thesis generalizes the MSC
to manifolds with boundaries. Based on this generalized MSC (GMSC), an operator to
merge n GMSCs of manifolds partitioning a large manifold is proposed. The merging
operator is used in a divide-and-conquer approach on a massive data set, providing
the potential to employ the computational power in a parallel manner.published_or_final_version
Computer Science
Doctoral
Doctor of Philosophy
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Kenai, Said. "Properties of cement composites reinforced with geotextile meshes." Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235667.
Full text
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DIAZ, RUBEN GOMEZ. "A SIMPLE COMPRESSION FOR IRREGULAR MESHES WITH HANDLES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=5553@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOMuitas são as aplicações onde se faz necessário transmitir modelos 3D via Internet. Entre eles merece destaque o compartilhamento de dados entre ambientes colaborativos situados em diferentes localidades. Este compartilhamento permite a sua análise e visualização, porém restrições de largura de banda da rede (Internet/Intranet) assim como o custo de armazenamento limitam a complexidade do modelo a ser transmitido/armazenado. As malhas geométricas são utilizadas em diferentes áreas da computação gráfica e visualização científica, como exemplos podem se citar elementos finitos os quais são utilizados em modelos CAD, jogos, modelagem de terrenos, geometria computacional entre outros. Devido à grande complexidade das malhas, estas são processadas por meios computacionais usando alguma estrutura de dados que represente da melhor forma o modelo em questão. A principal motivãção deste trabalho é verificar a viabilidade do uso de uma nova estrutura de dados para representar e comprimir malhas irregulares (triângulos e quadrângulos). Nesta nova abordagem será apresentada a estrutura de dados CHalfEdge. Ela usa os conceitos e idéias da representação HalfEdge e esta por sua vez possui um baixo custo de armazenamento e mantém um alto poder de expressão. Neste trabalho é desenvolvido tambem um algoritmo de compressão de malhas triangulares e/ou quadrangulares com suporte a alças. Este novo algoritmo proposto é uma extensão da compressão de malhas triangulares EdgeBreaker.
Many applications need to transmit 3D models over the Internet, among those data sharing between collaborative environments situated in different locations. Those data sharing aim to analyze and visualize them but bandwidth constraints and storage costs limit the complexity of models than can be transmitted/stored. Polygonal meshes are used in different areas of Computer Graphics and Scientific Visualization. For instance, finite elements and boundary representations are used in CAD models, games, terrain modelling, etc. Due the great complexity of those meshes, they must be represented by a specific data structure that suits them. The main motivation of this work is to verify the feasibility of the use of a new data structure to represent and to compress irregular meshes (triangles and quads). It is introduced the CHalfEdge data structure based on the ideas of the HalfEdge data structure, which are used to represent models by boundary representation. In this work it is also proposed a new algorithm to compress and decompress irregulars meshes with genus, this new algorithm is an extension of the EdgeBreaker compression for regular meshes.
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FRANCESCHIN, BERNARDO BIANCHI. "VISUALIZATION OF ARBITRARY CROSS SECTION OF UNSTRUCTURED MESHES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2013. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=23874@1.
Full textAbstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
PROGRAMA DE EXCELENCIA ACADEMICA
Na visualização de campos escalares de dados volumétricos, o uso de seções de corte é uma técnica eficaz para se inspecionar a variação do campo no interior do domínio. A técnica de visualização consiste em mapear sobre a superfície da seção de corte um mapa de cores, o qual representa a variação do campo escalar na interseção da superfície com o volume. Este trabalho propõe um método eficiente para o mapeamento de campos escalares de malhas não estruturadas em seções de corte arbitrárias. Trata-se de um método de renderização direta (a interseção da superfície com o modelo não é extraída) que usa a GPU para garantir bom desempenho. A idéia básica do método proposto é utilizar o rasterizador da placa gráfica para gerar os fragmentos da superfície de corte e calcular a interseção de cada fragmento com o modelo em GPU. Para isso, é necessário testar a localização de cada fragmento na malha não estruturada de maneira eficiente. Como estrutura de aceleração, foram testadas três variações de grades regulares para armazenar os elementos (células) da malha, e cada elemento é representado pela lista de planos de suas faces, facilitando o teste de pertinência fragmento-elemento. Uma vez determinado o elemento que contém o fragmento, são aplicados procedimentos para interpolar o campo escalar e para identificar se o fragmento está próximo à fronteira do elemento, a fim de representar o aramado (wireframe) da malha na superfície de corte. Resultados obtidos demonstram a eficácia e a eficiência do método proposto.
For the visualization of scalar fields in volume data, the use of cross sections is an effective technique to inspect the field variation inside the domain. The technique consists in mapping, on the cross section surfaces, a colormap that represents the scalar field on the surfasse-volume intersection. In this work, we propose an efficient method for mapping scalar fields of unstructured meshes on arbitrary cross sections. It is a direct-rendering method (the intersection of the surface and the model is not extracted) that uses GPU to ensure efficiency. The basic idea is to use the graphics rasterizer to generate the fragments of the cross-section surface and to compute the intersection of each fragment with the model. For this, it is necessary to test the location of each fragment with respect to the unstructured mesh in an efficient way. As acceleration data structure, we tested three variations of regular grids to store the elements (cells) of the mesh, and each elemento is represented by the list of face planes, easing the in-out test between fragments and elements. Once the element that contains the fragment is determined, it is applied procedures to interpolate the scalar field and to check if the fragment is close to the element boundary, to reveal the mesh wireframe on the surface. Achieved results demonstrate the effectiveness and the efficiency of the proposed method.