Static/Dynamic Filtering for Mesh Geometry

The joint bilateral filter, which enables feature-preserving signal smoothing according to the structural information from a guidance, has been applied for various tasks in geometry processing. Existing methods either rely on a static guidance that may be inconsistent with the input and lead to unsatisfactory results, or a dynamic guidance that is automatically updated but sensitive to noises and outliers. Inspired by recent advances in image filtering, we propose a new geometry filtering technique called static/dynamic filter, which utilizes both static and dynamic guidances to achieve state-of-the-art results. The proposed filter is based on a nonlinear optimization that enforces smoothness of the signal while preserving variations that correspond to features of certain scales. We develop an efficient iterative solver for the problem, which unifies existing filters that are based on static or dynamic guidances. The filter can be applied to mesh face normals followed by vertex position update, to achieve scale-aware and feature-preserving filtering of mesh geometry. It also works well for other types of signals defined on mesh surfaces, such as texture colors. Extensive experimental results demonstrate the effectiveness of the proposed filter for various geometry processing applications such as mesh denoising, geometry feature enhancement, and texture color filtering

Zeffiro user interface for electromagnetic brain imaging: a GPU accelerated FEM tool for forward and inverse computations in Matlab

This article introduces the Zeffiro interface (ZI) version 2.2 for brain imaging. ZI aims to provide a simple, accessible and multimodal open source platform for finite element method (FEM) based and graphics processing unit (GPU) accelerated forward and inverse computations in the Matlab environment. It allows one to (1) generate a given multi-compartment head model, (2) to evaluate a lead field matrix as well as (3) to invert and analyze a given set of measurements. GPU acceleration is applied in each of the processing stages (1)-(3). In its current configuration, ZI includes forward solvers for electro-/magnetoencephalography (EEG) and linearized electrical impedance tomography (EIT) as well as a set of inverse solvers based on the hierarchical Bayesian model (HBM). We report the results of EEG and EIT inversion tests performed with real and synthetic data, respectively, and demonstrate numerically how the inversion parameters affect the EEG inversion outcome in HBM. The GPU acceleration was found to be essential in the generation of the FE mesh and the LF matrix in order to achieve a reasonable computing time. The code package can be extended in the future based on the directions given in this article

On structural shape optimization using an embedding domain discretization technique

This contribution presents a novel approach to structural shape optimization that relies on an embedding domain discretization technique. The evolving shape design is embedded within a uniform finite element background mesh which is then used for the solution of the physical state problem throughout the course of the optimization. We consider a boundary tracking procedure based on adaptive mesh refinement to separate between interior elements, exterior elements, and elements intersected by the physical domain boundary. A selective domain integration procedure is employed to account for the geometric mismatch between the uniform embedding domain discretization and the evolving structural component. Thereby, we avoid the need to provide a finite element mesh that conforms to the structural component for every design iteration, as it is the case for a standard Lagrangian approach to structural shape optimization. Still, we adopt an explicit shape parametrization that allows for a direct manipulation of boundary vertices for the design evolution process. In order to avoid irregular and impracticable design updates, we consider a geometric regularization technique to render feasible descent directions for the course of the optimization

Reconstruction of the road surface

Táto práca pojednáva o rozličných prístupoch k problematike rekonštrukcie povrchu trate na základe rôznych na to určených algoritmoch. Taktiež okrem metód rekonštrukcie trate predstavuje aj návrhy na doplnenie polygonálnej siete do nezosnímaných oblastí okolo trate.This thesis presents various approaches for race track surface reconstruction based on different algorithms designated for these purposes. In addition to surface reconstruction it also offers proposals for polygon mesh filling in the unscanned areas around the track.

Template based mesh fitting through a set of curves.

Choi, Yuet Kei.Thesis (M.Phil.)--Chinese University of Hong Kong, 2007.Includes bibliographical references (leaves 68-72).Abstracts in English and Chinese.Acknowledgement --- p.iAbstract --- p.iiContents --- p.viList of Figures --- p.viiiChapter 1. --- Introduction --- p.1Chapter 1.1 --- Previous Works --- p.3Chapter 1.1.1 --- Template deformation --- p.3Chapter 1.1.2 --- Mesh partitioning --- p.3Chapter 1.1.3 --- Mesh Smoothing --- p.4Chapter 1.2 --- Overview of the approach --- p.5Chapter 1.3 --- Thesis outline --- p.7Chapter 2. --- Global Deformation --- p.8Chapter 2.1 --- The closet point method --- p.10Chapter 2.1.1 --- Computational complexity --- p.11Chapter 2.2 --- Deformation Techniques --- p.12Chapter 2.2.1 --- Existing deformation method --- p.12Chapter 2.2.2 --- Radial Basis Functions (RBFs) --- p.14Chapter 2.2.2.1 --- Computational complexity --- p.18Chapter 2.2.3 --- Result --- p.18Chapter 2.3 --- Face flip prevention --- p.20Chapter 2.3.1 --- Detection of the flipped face --- p.22Chapter 2.3.1.1 --- Common approach: --- p.22Chapter 2.3.1.2 --- Our Approach --- p.23Chapter 2.3.1.3 --- Comparisons of the face flip detection method: --- p.26Chapter 2.3.2 --- Local Subdivision --- p.27Chapter 3. --- Partitioning of the mesh --- p.29Chapter 3.1 --- Existing method --- p.29Chapter 3.2 --- Our approach --- p.31Chapter 3.3 --- Computational complexity --- p.34Chapter 4. --- Mesh smoothing algorithm --- p.35Chapter 4.1 --- The Laplacian flow method --- p.36Chapter 4.2 --- The mean-curvature method --- p.40Chapter 4.3 --- Our Approach --- p.43Chapter 4.3.1 --- The modified mean-curvature method --- p.43Chapter 4.3.2 --- The modified Laplacian flow method --- p.45Chapter 4.3.3 --- Feature constraints --- p.47Chapter 4.3.4 --- Computational complexity --- p.47Chapter 4.4 --- Comparison of the mesh smoothing approach --- p.48Chapter 5. --- Implementation and Results --- p.51Chapter 5.1 --- Construction of the template mesh and boundary curves --- p.51Chapter 5.2 --- Selection of the corresponding vertex pairs --- p.52Chapter 5.3 --- Results --- p.54Chapter 6. --- Conclusions --- p.63Chapter 6.1 --- Future development --- p.65Appendix A --- p.66Determination of the projected path on a mesh: --- p.66Reference --- p.6

Metodologias para projeto mecânico ótimo de estruturas espaciais obtidas por fabrico aditivo

Additive Layer Manufacturing (ALM) is growing rapidly due to the unprecedented design freedom. Thus, the structures' complexity can be drastically increased without significant raises in costs. However, the economic viability of ALM is strongly dependent on the full exploration of the referred design freedom. In fact, the ALM is only cost-effective in highly customized parts. Moreover, the mechanical behavior of materials processed via ALM is an ongoing challenge due to defects, uncertainties in material characterization, and verification methods. Thus, the goal of the present work is the development of a robust methodology for the mechanical optimum design of metallic space structures obtained from additive manufacturing. Thus, two main tasks were established. The first task is related to the mechanical characterization of a Ti6Al4V alloy, processed via Selective Laser Melting (SLM). Therefore, an experimental testing campaign of Ti6Al4V samples is presented using homogeneous macroscopic testing (tensile, compression, density, hardness, and fatigue) and microscopic testing (defects detection via microcomputed tomography). These samples show better static properties than the other counterparts, obtained by traditional manufacturing processes. However, the repeatability of the SLM samples is still a challenge (particularly in its fatigue behavior) and more testing is needed. Furthermore, these campaigns are expensive and, consequently, more information per test is required. With the development of full-field measurement methods, material model calibration strategies call upon the use of heterogeneous testing specimens. In the scope of this work, an indirect TO methodology is presented, being capable of designing a wide range of different heterogeneous specimens. Then, a stress states performance indicator is also presented to help the selection of the most promising geometry. The second task is related to the definition of the engineering cycle for ALM structures in its mains phases: (i) design for ALM, (ii) bridging between Topology Optimization (TO) and ALM, (iii) process simulation and structural verification, and (iv) manufacturing. Concerning the first phase, ALM provides great geometric freedom however, there are some design limitations. Therefore, a systematic design methodology is presented, being based on a topology optimization algorithm capable of incorporating the main ALM design limitations (minimum member size and overhang angle). Furthermore, the non-trivial task of bridging between TO and the final smooth geometry is also studied (second phase). The referred task uses a Laplacian smoothing algorithm, which is based on the new concept of mutable diffusion. This new concept shows better properties than the classic algorithms, giving promising results. Furthermore, a new volume constraint is presented, which exhibits a less detrimental impact on the chosen structural indicators. Regarding the remaining phases, these were analyzed via industrial case studies. For instance, process simulation can provide crucial insight into the optimum manufacturing direction and might dictate the difference between success and failure upon manufacturing. The impact of this Ph.D. is related with some improvements in (i) the characterization of ALM-produced materials as well as the geometry of the specimens used for their characterization; and in (ii) the engineering cycle of ALM structures, allowing higher efficiency in the structural solutions for the space industry with lower costs.O uso do fabrico aditivo por camadas está a crescer a um elevado ritmo devido À elevada liberdade de projeto de estruturas. Assim, a complexidade das estruturas pode ser aumentada significativamente sem incrementos significativos nos custos. Todavia, a viabilidade económica do fabrico aditivo por camadas é fortemente dependente de uma exploração inteligente da liberdade de projeto estrutural. Na verdade, o fabrico aditivo por camadas só é rentável em peças de elevada complexidade e valor acrescentado. Adicionalmente, o comportamento mecânico de materiais processados através do fabrico aditivo por camadas é ainda um desafio por resolver devido à existência de defeitos, incertezas na caracterização de materiais e nos seus métodos de velicação. Deste modo, o objetivo deste trabalho é o desenvolvimento de uma metodologia robusta que permita o projeto mecânico ótimo de estruturas obtidas por fabrico aditivo para a indústria espacial. Para isso, foram estabelecidas duas tarefas principais. A primeira tarefa está relacionada com a caracterização mecânica da liga Ti6Al4V, processada através da fusão seletiva a laser. Portanto, foi realizado uma campanha de testes experimentais com provetes da liga Ti6Al4V composta por testes macroscópicos homogéneos (tração, compressão, densidade, dureza e fadiga) e testes microscópicos (deteção de defeitos usando uma análise com recurso à tomografia microcomputorizada). Foi verificado que estas amostras exibem melhor propriedades estáticas que amostras idênticas produzidas através de processos tradicionais. Contudo, a sua repetibilidade ainda é um desafio (particularmente o comportamento à fadiga), sendo necessário mais testes. Adicionalmente, estas campanhas experimentais são onerosas e, consequentemente, é crítico obter mais informação por cada teste realizado. Dado o desenvolvimento dos métodos de medição full-field, as estratégias de calibração de modelos de material propiciam o uso de provetes heterogéneos em testes mecânicos. No ^âmbito deste trabalho apresenta-se uma metodologia de otimização topológica indireta capaz de projetar uma grande variedade de provetes heterógenos. Posteriormente apresenta-se um indicador de desempenho baseado na quantidade de estados de tensão para selecionar o provete mais promissor. A segunda tarefa está relacionada com a definição do ciclo de engenharia para o fabrico aditivo por camadas de estruturas metálicas nas suas fases principais: (i) projeto para fabrico aditivo por camadas, (ii) transição entre a otimização topológica e o fabrico aditivo por camadas, (iii) simulação do seu processo de fabrico e sua verificação estrutural e (iv) fabrico. Relativamente à primeira fase, o fabrico aditivo por camadas proporciona uma grande liberdade geométrica, contudo existe limitações ao design. Portanto é apresentada uma metodologia de projeto sistemática, baseada num algoritmo de otimização topológica capaz de incorporar as principais limitações de projeto do fabrico aditivo por camadas tais como a espessura mínima e ângulo do material sem suporte. Adicionalmente, a tarefa complexa de efetuar a transição entre os resultados da otimização topológica e uma geometria final suave também é objeto de estudo. A tarefa anteriormente referida baseia-se na suavização Laplaciana que por sua vez se baseia no novo conceito de difusão mutável. Este novo conceito apresenta melhores e mais promissores resultados que os algoritmos clássicos. Adicionalmente, é apresentado uma nova restrição de volume que proporciona um menor impacto nos indicadores estruturais escolhidos. Relativamente às restantes fases, estas são analisadas através de casos de estudo industriais. A título exemplar, a simulação do processo de fabrico pode fornecer informações crucias para a escolha da direção de fabrico que, por sua vez, pode ditar a diferença entre o sucesso ou o insucesso durante o fabrico. O impacto deste trabalho está relacionado com melhorias na (i) caracterização de materiais produzidos através de fabrico aditivo por camadas assim como nas geometrias de provetes usados durante a sua caracterização e no (ii) ciclo de projeto em engenharia de estruturas obtidas através do fabrico aditivo por camadas, permitindo soluções estruturais com maior eficiência e menor custo para indústria espacial.Programa Doutoral em Engenharia Mecânic

Étude de l'utilisation d'éléments finis quadratiques dans le cadre de l'application de la méthode du mouvement normal

L'objectif de cette recherche est d'intégrer une méthode d'optimisation de structures au processus de Conception Assistée par Ordinateur (CAO) avec un maillage quadratique. La méthode utilisée est la méthode du mouvement normal (MMN) qui vise à uniformiser la valeur des contraintes sur la frontière d'une structure en déplaçant de manière itérative les points de design dans la direction normale. La méthode a été implémentée précédemment dans le Modèle de Topologie Unifié (MTU) de l'Équipe de Recherche en Intégration CAO-Calcul (ERlCCA) de l'Université du Québec à Trois-Rivières avec un maillage linéaire. Néanmoins, pour les structures courbes, les éléments linéaires ne permettent pas d'avoir une bonne approximation de la géométrie contrairement à des éléments curvilignes. La MMN est implémentée avec un maillage quadratique et appliquée sur un tube en porte-à-faux définis avec des zones de design et de non design. La méthode conduit à l'amélioration de la répartition des contraintes et une diminution de la contrainte moyenne dans le tube, mais conduit aussi à l'apparition d'un déplacement trop important à la jonction entre la zone de design et la zone de non design près de l'encastrement. Pour cela, plusieurs méthodes sont utilisées pour contrôler le déplacement des nœuds. Une méthode de lissage (lissage Taubin), filtres (filtrage des déplacements) et la MMN modifiée. Les différents contrôles utilisés permettent d'avoir une forme valide géométriquement. Finalement, la MMN avec et sans contrôle est appliquée à plusieurs structures tubulaires et une reconstruction géométrique des résultats d'optimisation d'un tube en porte-à-faux (sans zone de non-design) est effectuée afm de valider les résultats de la méthode. L'objectif de cette recherche est d'intégrer une méthode d'optimisation de structuresau processus de Conception Assistée par Ordinateur (CAO) avec un maillagequadratique. La méthode utilisée est la méthode du mouvement normal (MMN) quivise à uniformiser la valeur des contraintes sur la frontière d'une structure en déplaçantde manière itérative les points de design dans la direction normale. La méthode a étéimplémentée précédemment dans le Modèle de Topologie Unifié (MTU) de l'Équipede Recherche en Intégration CAO-Calcul (ERlCCA) de l'Université du Québec àTrois-Rivières avec un maillage linéaire. Néanmoins, pour les structures courbes, leséléments linéaires ne permettent pas d'avoir une bonne approximation de la géométriecontrairement à des éléments curvilignes. La MMN est implémentée avec un maillagequadratique et appliquée sur un tube en porte-à-faux définis avec des zones de designet de non design. La méthode conduit à l'amélioration de la répartition des contrainteset une diminution de la contrainte moyenne dans le tube, mais conduit aussi àl'apparition d'un déplacement trop important à la jonction entre la zone de design etla zone de non design près de l'encastrement. Pour cela, plusieurs méthodes sontutilisées pour contrôler le déplacement des nœuds. Une méthode de lissage (lissageTaubin), filtres (filtrage des déplacements) et la MMN modifiée. Les différentscontrôles utilisés permettent d'avoir une forme valide géométriquement. Finalement,la MMN avec et sans contrôle est appliquée à plusieurs structures tubulaires et unereconstruction géométrique des résultats d'optimisation d'un tube en porte-à-faux(sans zone de non-design) est effectuée afm de valider les résultats de la méthode

Polymeco : uma ferramenta de análise e comparação de malhas poligonais

Mestrado em Engenharia Electrónica e TelecomunicaçõesOs modelos definidos usando malhas poligonais são usados em diversas áreas de aplicação para representar diferentes objectos e estruturas. Dependendo da aplicação, pode ser necessário processar esses modelos, por exemplo, para diminuir a sua complexidade (simplificação). Este processamento introduz diferenças, em relação ao modelo original, cuja avaliação é um passo fundamental para permitir escolher a sequência de operações e os métodos de processamento que permitam a obtenção de melhores resultados. Apesar de algumas ferramentas de análise e comparação das características de malhas poligonais serem descritas na literatura, pouca atenção tem sido prestada à forma como os dados provenientes dessa análise e comparação podem ser visualizados. Para além disso, devem ser disponibilizadas várias funcionalidades de forma a permitir uma utilização sistemática destas ferramentas, assim como uma adequada análise e exploração dos dados fornecidos. O PolyMeCo — uma ferramenta de análise e comparação das características de malhas poligonais — foi projectado e desenvolvido tendo em conta os objectivos acima referidos. Através de um ambiente integrado onde diferentes opções de visualização estão disponíveis e podem ser usadas de forma coordenada, o PolyMeCo permite aos utilizadores uma melhor compreensão dos dados resultantes da aplicação dos números de mérito disponibilizados. Esta nova ferramenta foi usada com sucesso em dois trabalhos de investigação: (1) para comparar as características das malhas resultantes de dois algoritmos de simplificação de malhas poligonais, e (2) para testar a aplicabilidade dos números de mérito que disponibiliza como estimadores da qualidade de modelos poligonais, tal como percebida pelos utilizadores. ABSTRACT: Polygonal meshes are used in several application areas to model different objects and structures. Depending on the application, such models sometimes have to be processed to, for instance, reduce their complexity (mesh simplification). Such processing introduces error, whose evaluation is of paramount importance when choosing the sequence of operations that is to be applied for a particular purpose. Although some mesh analysis and comparison tools are described in the literature, little attention has been given to the way mesh features (analysis) and mesh comparison results can be visualized. Moreover, particular functionalities have to be made available by such tools, to enable systematic use and proper data analysis and exploration. PolyMeCo — a tool for polygonal mesh analysis and comparison — was designed and developed taking the above objectives into account. It enhances the way users perform mesh analysis and comparison, by providing an integrated environment where various mesh quality measures and several visualization options are available and can be used in a coordinated way, thus leading to greater insight into the visualized data. This new tool has been successfully applied in two research works: (1) to compare between mesh simplification algorithms, and (2) to study the applicability of the provided computational measures as estimators of user perceived quality as obtained through an observer study