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The vulnerability of a ship to the impact of underwater explosions (UNDEX) and how to incorporate this factor into early-stage ship design is an important aspect in the ship survivability study. In this dissertation, attention is focused on the cost-efficient simulation of the ship response to a far-field UNDEX which involves fluid shock waves, cavitation, and fluid-structural interaction. Traditional fluid numerical simulation approaches using the Finite Element Method to track wave propagation and cavitation requires a high-level of mesh refinement to prevent numerical dispersion from discontinuities. Computation also becomes quite expensive for full ship-related problems due to the large fluid domain necessary to envelop the ship. The burden is aggravated by the need to generate a fluid mesh around the irregular ship hull geometry, which typically requires significant manual intervention. To accelerate the design process and enable the consideration of far-field UNDEX vulnerability, several contributions are made in this dissertation to make the simulation more efficient. First, a Cavitating Acoustic Spectral Element approach which has shown computational advantages in UNDEX problems, but not systematically assessed in total ship application, is used to model the fluid. The use of spectral elements shows greater structural response accuracy and lower computational cost than the traditional FEM. Second, a novel fully automatic all-hexahedral mesh generation scheme is applied to generate the fluid mesh. Along with the spectral element, the all-hex mesh shows greater accuracy than the all-tetrahedral finite element mesh which is typically used. This new meshing approach significantly saves time for mesh generation and allows the spectral element, which is confined to the hexahedral element, to be applied in practical ship problems. A further contribution of this dissertation is the development of a surrogate non-numerical approach to predict structural peak responses based on the shock factor concept. The regression analysis reveals a reasonably strong linear relationship between the structural peak response and the shock factor. The shock factor can be conveniently employed in the design aspects where the peak response is sufficient, using much less computational resources than numerical solvers. / Doctor of Philosophy / The vulnerability of a ship to the impact of underwater explosions (UNDEX) and how to incorporate this factor into early-stage ship design is an important aspect in the ship survivability study. In this dissertation, attention is focused on the cost-efficient simulation of the ship response to a far-field UNDEX which involves fluid shock waves, cavitation, and fluid-structural interaction. Traditional fluid numerical simulation approaches using the Finite Element Method to track wave propagation and cavitation requires a highly refined mesh to deal with large numerical errors. Computation also becomes quite expensive for full ship-related problems due to the large fluid domain necessary to envelop the ship. The burden is aggravated by the need to generate a fluid mesh around the irregular ship hull geometry, which typically requires significant manual intervention. To accelerate the design process and enable the consideration of far-field UNDEX vulnerability, several contributions are made in this dissertation to make the simulation more efficient. First, a Cavitating Acoustic Spectral Element approach, which has shown computational advantages in UNDEX problems but not systematically assessed in total ship application, is used to model the fluid. The use of spectral elements shows greater structural response accuracy and lower computational cost than the traditional FEM. Second, a novel fully automatic all-hexahedral mesh generation scheme is applied to generate the fluid mesh. Along with the spectral element, the all-hex mesh shows greater accuracy than the all-tetrahedral finite element mesh which is typically used. A further contribution of this dissertation is the development of a non-numerical approach which can approximate peak structural responses comparable to the numerical solution with far less computational effort.

[pt] Este trabalho apresenta uma metodologia para geração de malhas adaptativas de elementos finitos 2D e 3D usando modeladores geométricos com multi-regiões e superfícies paramétricas. A estratégia adaptativa adotada é fundamentada no refinamento independente das curvas, superfícies e sólidos. Inicialmente as curvas são refinadas, no seu espaço paramétrico, usando uma técnica de partição binária da curva (binary-tree). A discretização das curvas é usada como dado de entrada para o refinamento das superfícies. A discretização destas é realizada no seu espaço paramétrico e utiliza uma técnica de avanço de fronteira combinada com uma estrutura de dados do tipo quadtree para gerar uma malha não estruturada de superfície. Essas malhas de superfícies são usadas como dado de entrada para o refinamento dos domínios volumétricos. A discretização volumétrica combina uma estrutura de dados do tipo octree juntamente com a técnica de avanço de fronteira para gerar uma malha sólida não estruturada de elementos tetraédricos. As estruturas de dados auxiliares dos tipos binary-tree, quadtree e octree são utilizadas para armazenar os tamanhos característicos dos elementos gerados no refinamento das curvas, superfícies e regiões volumétricas. Estes tamanhos característicos são definidos pela estimativa de erro numérico associado à malha global do passo anterior do processo adaptativo. A estratégia adaptativa é implementada em dois modeladores: o MTOOL (2D) e o MG (3D), que são responsáveis pela criação de um modelo geométrico, podendo ter, multi-regiões, onde no caso 3D as curvas e superfícies são representadas por NURBS. / [en] This work presents a methodology for adaptive generation of 2D and 3D finite-element meshes using geometric modeling with multi- regions and parametric surfaces. The adaptive strategy adopted in this methodology is based on independent refinements of curves, surfaces and solids. Initially, the model´s curves are refined using a binary-partition algorithm in parametric space. The discratizetion of these curves is used as input for the refinement of adjacent surfaces. Surface discretization is also performed in parametric space and employs a quadtree-based refinement coupled to an advancing-front technique for the generation of an unstructured triangulation. These surface meshes are used as input for the refinement adjacent volumetric domains. Volume discretization combines an octree refinement with an advancing-front technique to generate an unstructural mesh of tetrahedral elements. In all stages of the adaptive strategy, the refinement of curves, surface meshes and solid meshes is based on estimated numerical errors associated to the mesh of the previous step in the adaptive process. In addition, curve and surface refinement takes into account metric distortions between parametric and Cartesian spaces and high curvatures of the model´s geometric entities. The adaptive strategies are implemented in two different modelers: MTOOL (2D) and MG (3D), which are responsible for the creation of a geometric model with multi-regions, where for case 3D the curves and surfaces are represented by NURBS, and for the interactive and automatic finite-element mesh generation associated to surfaces and solid regions. Numerical examples of the simulation of engineering problems are presented in order to validate the methodology proposed in this work.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / This work describes a technique for generating three-dimensional tetrahedral meshes using parallel computing, with shared, distributed, or hybrid memory processors. The input for the algorithm is a triangular mesh that models the surface of one of several objects, that might have holes in its interior or internal or boundary cracks. A binary tree structure for spatial partitioning is proposed in this work to recursively decompose the domain in as many subdomains as processes or threads in the parallel system, in which every subdomain has the geometry of a rectangular parallelepiped. This decomposition attempts to balance the amount of work in all the subdomains. The amount of work, known as load, of any mesh generator is usually given as a function of its output size, i.e., the size of the generated mesh. Therefore, a technique to estimate the size of this mesh, the total load of the domain, is needed beforehand. This work uses a refined octree, generated from the surface mesh, to estimate this load, and the decomposition is performed on top of this octree. Once the domain is decomposed, each process/thread generates the mesh in its subdomain by means of an advancing front technique, in such a way that it does not overpass the limits defined by its subdomain, and applies an improvement on it. Some of the processes/threads are responsible for generating the meshes connecting the subdomains, i.e., the interface meshes, in order to generate the whole mesh. This technique presented good speed-up results, keeping the quality of the mesh comparable to the quality of the serially generated mesh. / Este trabalho descreve uma tÃcnica para gerar malhas tridimensionais tetraÃdricas utilizando computaÃÃo paralela, com processadores de memÃria compartilhada, memÃria distribuÃda ou memÃria hÃbrida. A entrada para o algoritmo à uma malha triangular que modela a superfÃcie de um ou vÃrios objetos, que podem conter buracos no interior ou fraturas internas ou na borda. Uma estrutura em forma de Ãrvore binÃria de partiÃÃo espacial à proposta neste trabalho para, recursivamente, decompor o domÃnio em tantos subdomÃnios quantos forem os processos ou threads no sistema paralelo, em que cada subdomÃnio tem a geometria de um paralelepÃpedo retangular. Esta decomposiÃÃo tenta equilibrar a quantidade de trabalho em todos os subdomÃnios. A quantidade de trabalho, conhecida como carga, de qualquer gerador de malha à geralmente dada em funÃÃo do tamanho da saÃda do algoritmo, ou seja, do tamanho da malha gerada. Assim, faz-se necessÃria uma tÃcnica para estimar previamente o tamanho dessa malha, que à carga total do domÃnio. Este trabalho faz uso de uma octree refinada, gerada a partir da malha de superfÃcie dada como entrada, para estimar esta carga, e a decomposiÃÃo à feita a partir dessa octree. Uma vez decomposto o domÃnio, cada processo/thread gera a malha em seu subdomÃnio por uma tÃcnica de avanÃo de fronteira, de forma que ela nÃo ultrapasse os limites definidos pelo seu subdomÃnio, e aplica um melhoramento nela. Alguns dos processos/threads ficam responsÃveis por gerar as malhas conectando os subdomÃnios, ou seja, as malhas de interface, atà que toda a malha tenha sido gerada. Esta tÃcnica apresentou bons resultados de speed-up, mantendo a qualidade da malha comparÃvel à qualidade da malha gerada sequencialmente.

<p>Digitizing objects and environments from real world has become an important part of creating realistic computer graphics. Through the use of structured lighting and laser time-of-flight measurements the capturing of geometric models is now a common process. The result are visualizations where viewers gain new possibilities for both visual and intellectual experiences. </p><p>This thesis presents the reconstruction of the Parthenon temple and its environment in Athens, Greece by using a 3D laser-scanning technique. </p><p>In order to reconstruct a realistic model using 3D scanning techniques there are various phases in which the acquired datasets have to be processed. The data has to be organized, registered and integrated in addition to pre and post processing. This thesis describes the development of a suitable and efficient data processing pipeline for the given data. </p><p>The approach differs from previous scanning projects considering digitizing this large scale object at very high resolution. In particular the issue managing and processing huge datasets is described. </p><p>Finally, the processing of the datasets in the different phases and the resulting 3D model of the Parthenon is presented and evaluated.</p>

In the thesis work, a code to solve the two dimensional compressible Euler equations for external flows around arbitrary geometries have been developed. A Cartesianmesh generator is incorporated to the solver. Hence the pre-processing can be performed together with the solution within a single code. The code is written in the C++ programming language and its object oriented capabilities have been exploited to save memory in the data structure developed. The Cartesian mesh is formed by dividing squares successively into its four quadrants. The main advantage of using this type of a mesh is the ability to generate meshes around geometries of arbitrary complexity quickly and to adapt the mesh easily based on the solution. The main disadvantage of this method is that the treatment of the cells that are cut by the geometry. For the solution procedure Roe&rsquo / s method as well as flux vector splitting methods are used for the flux evaluation. The flux vector splitting schemes used are van Leer, AUSM, AUSMD and AUSMV methods. Time discretization is performed using a multi-stage method. To increase the accuracy least squares reconstruction is employed. The code is validated by performing calculations around a NACA0012 airfoil profile. The effect of reconstruction is demonstrated by plotting the pressure coefficient on the airfoil. The distribution obtained using reconstruction is very close to the experimental one while there is a considerable deviation for the case without reconstruction. Also the shock capturing capabilities of different methods have been investigated. In addition the performance of each method is analyzed for flow around an NLR 7301 airfoil with a flap.

Electro-Magnetic Source Imaging (EMSI) is the estimation of the position, orientation and strength of active electrical sources within the brain from electrical and magnetic measurements. For an accurate source localization, the head model must correctly represent the electrical and geometrical properties of the head. To solve the forward problem using realistic head models numerical techniques must be used. This work uses the Boundary Element Method (BEM) for solving the forward problem. The accuracy of the existing BEM formulation is improved by using second order elements, recursive integration and the isolated problem approach (IPA). Two new formulations are developed to improve the solution speed by computing transfer matrices for EEG and MEG solutions. The IPA formulation is generalized and integrated into the accelerated BEM algorithm. Once the transfer matrices are computed, the forward solutions take about 300 ms for a 256 sensor EEG and MEG system. The head model used in the BEM solutions is constructed by segmenting three dimensional multimodal magnetic resonance images. For segmentation, a semi-automatic hybrid algorithm is developed that makes use of snakes, morphological operations, thresholding and region growing. The mesh generation algorithm allows intersecting tissue compartments. For the inverse problem solution genetic algorithm (GA) is used to search for a given number of dipoles. Source localization with simulated data show that the localization error is within 1.1 mm for EEG and 1.2 mm for MEG when SNR is 10 on a realistic model with 7 compartments. When a single-dipole source in a realistic model is explored using a best-fit spherical model, the localization errors increase up to 8.5 mm for EEG and 7 mm for MEG. Similar tests are also performed with multiple dipoles. It was observed that realistic models provide definitely more accurate results compared to spherical models. The EMSI approach is also tested using experimental EEG data to localize the sources of auditory evoked potentials. The reconstructed source locations are correctly found in the Heschl&#039 / s gyrus. In conclusion, this thesis presents a complete source localization framework for future brain research using the EMSI.

SOMBRA, Tiago Guimarães. Geração adaptativa de malhas de superfícies paramétricas em paralelo com controle de curvatura. 2016. 71 f. Dissertação (Mestrado em ciência da computação)- Universidade Federal do Ceará, Fortaleza-CE, 2016. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-07-12T19:12:42Z No. of bitstreams: 1 2016_dis_tgsombra.pdf: 7997002 bytes, checksum: 8e8712a9b19d272a16ac263f62596436 (MD5) / Approved for entry into archive by Rocilda Sales (rocilda@ufc.br) on 2016-07-22T16:43:38Z (GMT) No. of bitstreams: 1 2016_dis_tgsombra.pdf: 7997002 bytes, checksum: 8e8712a9b19d272a16ac263f62596436 (MD5) / Made available in DSpace on 2016-07-22T16:43:38Z (GMT). No. of bitstreams: 1 2016_dis_tgsombra.pdf: 7997002 bytes, checksum: 8e8712a9b19d272a16ac263f62596436 (MD5) Previous issue date: 2016 / This work describes a technique for generating parametric surfaces meshes using parallel computing, with distributed memory processors. The input for the algorithm is a set of parametric patches that model the surface of a given object. A structure for spatial partitioning is proposed to decompose the domain in as many subdomains as processes in the parallel system. Each subdomain consists of a set of patches and the division of its load is guided following an estimate. This decomposition attempts to balance the amount of work in all the subdomains. The amount of work, known as load, of any mesh generator is usually given as a function of its output size, i.e., the size of the generated mesh. Therefore, a technique to estimate the size of this mesh, the total load of the domain, is needed beforehand. This work makes use of an analytical average curvature calculated for each patch, which in turn is input data to estimate this load and the decomposition is made from this analytical mean curvature. Once the domain is decomposed, each process generates the mesh on that subdomain or set of patches by a quad tree technique for inner regions, advancing front technique for border regions and is finally applied an improvement to mesh generated. This technique presented good speed-up results, keeping the quality of the mesh comparable to the quality of the serially generated mesh. / Este trabalho descreve uma técnica para gerar malhas de superfícies paramétricas utilizando computação paralela, com processadores de memória compartilhada. A entrada para o algoritmo é um conjunto de patches paramétricos que modela a superfície de um determinado objeto. Uma estrutura de partição espacial é proposta para decompor o domínio em tantos subdomínios quantos forem os processos no sistema paralelo. Cada subdomínio é formado por um conjunto de patches e a divisão de sua carga é guiada seguindo uma estimativa de carga. Esta decomposição tenta equilibrar a quantidade de trabalho em todos os subdomínios. A quantidade de trabalho, conhecida como carga, de qualquer gerador de malha é geralmente dada em função do tamanho da saída do algoritmo, ou seja, do tamanho da malha gerada. Assim, faz-se necessária uma técnica para estimar previamente o tamanho dessa malha, que é a carga total do domínio. Este trabalho utiliza-se de um cálculo de curvatura analítica média para cada patch, que por sua vez, é dado de entrada para estimar esta carga e a decomposição é feita a partir dessa curvatura analítica média. Uma vez decomposto o domínio, cada processo gera a malha em seu subdomínio ou conjunto de patches pela técnica de quadtree para regiões internas, avanço de fronteira para regiões de fronteira e por fim é aplicado um melhoramento na malha gerada. Esta técnica apresentou bons resultados de speed-up, mantendo a qualidade da malha comparável à qualidade da malha gerada de forma sequencial.