Publications abstracts


Intersecting and trimming parametric meshes on finite-element shells

Luiz Cristovão G. Coelho, Marcelo Gattass Luiz Henrique de Figueiredo
accepted for publication in International Journal for Numerical Methods in Engineering.

We present an algorithm for intersecting finite-element meshes defined on parametric surface patches. The intersection curves are modeled precisely and both meshes are adjusted to the newly formed borders, without unwanted reparametrizations. The algorithm is part of an interactive shell modeling program that has been used in the design of large offshore oil structures. To achieve good interactive response, we represent meshes with a topological data structure that stores its entities in spatial indexing trees instead of linear lists. These trees speed up the intersection computations required to determine points of the trimming curves; moreover, when combined with the topological information, they allow remeshing using only local queries. [Full ps version]

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Modeling shells with parametric intersections

Luiz Cristovão G. Coelho
thesis aproved by Informatics Department of PUC- Rio in 1998 August 11th.

We present a methodology for modeling finite-element meshes defined on parametric surface patches. The idea is to build curves and generate meshes over the parametric patches built with these curves, which also connect adjacent meshes. The final model is a representation of all meshes combined into a single data structure.

The basic tools to generate such meshes are the user interface to model space curves and the geometric algorithms to construct the elementary domain mappings. The main problem in composite modeling is how to handle mesh surfaces that intersect each other. We present an algorithm that models the intersection curves precisely and adjusts both meshes to the newly formed borders. The algorithm is part of an interactive shell modeling program, which has been used in the design of large offshore oil structures. We avoid unacceptable interaction delays by using a variant of the DCEL data structure that stores topological entities in spatial indexing trees instead of linked lists. These trees speed up the intersection computations required to determine points of the trimming curves, and also allows mesh reconstruction using only local queries. [Full ps version]

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Graphics Systems for Geometric Modeling of Semi-Submersible Oil Platforms

Luiz Cristovão G. Coelho
thesis aproved by Engineering Department of PUC- Rio in 1991 April 30th.

Interactive Computer Graphics can provide tools to create the necessary data to numerically simulate the behavior of semi-submersible oil platforms. The best geometric representation for these models, the possible techniques for conversion between these representations and the most adequate data structure are, however, areas where research is still needed.

This work investigates the geometric representation of two models for analysis of semi-submersible platforms: a model for static stability and a model for dynamic floating behavior. The former is referred here as the static model and the later as the dynamic model. Both analysis are used in the design of these systems.

The current available algorithms for hidden-line removal are not capable of handling the geometric representation of the static model. A new algorithm for hidden-line removal is proposed to solve problems related with peculiarities of this model. [Full ps version]

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An algorithm for intersecting and trimming parametric meshes

Luiz Cristovão Gomes Coelho, Marcelo Gattass, Luiz Henrique de Figueiredo
Proceedings of SIBGRAPI'98, 86-93.

We present an algorithm for intersecting finite-element meshes defined on parametric surface patches. The intersection curves are modeled precisely and both meshes are adjusted to the newly formed borders. The algorithm is part of an interactive shell modeling program, which has been used in the design of large offshore oil structures. We avoid unacceptable interaction delays by using a variant of the DCEL data structure that stores topological entities in spatial indexing trees instead of linked lists. These trees speed up the intersection computations required to determine points of the trimming curves, and also allows mesh reconstruction using only local queries. [Full ps version]

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Modeling Techniques to Generate 3D Meshes

Luiz Cristovão Gomes Coelho, and Luiz Fernando Martha
Proceedings of XVI CILAMCE 96, 169-172.

Among the various approaches to the modeling of surface patches for generating tridimensional finite element meshes for plate, shell, or solid analysis, two aspects are determinant: the user interface methodology and the internal representation used in the geometric algorithms. The paper presents the authors approach for the complete generation of 3D meshes. The interface is heavily based on direct manipulation techniques for three fundamental aspects: creation of forms, especifying 3D transformations, and changing viewing parameters. The data structure and geometric algorithms use the adaptative polygonalization idea for parametric curve and surface representation. The attributes are attached to the geometric model using an extensible database that can be addapted for a great variety of finite and boundary element analyses (stress, temperature, flow, and ship stability have been implemented). The techniques presented here, when combined, produce a powerfull, flexible and easy to use preprocessor for numerical analysis. [Full ps version]


Problem Comunication and Geometric Solutions in a 3D Interface

Luiz Cristovão Gomes Coelho and Clarisse Sieckenius de Souza
Proceedings of SIBGRAPI'95, 183-190.

Testing predictions on the use of graphical interfaces can result on redefinition of systems, and often changes the main assumptions of interface programmers. This work presents pilot-experiments done with a graphical geometric modeler. The system's interface is heavily based on direct manipulation of tridimensional entities; many tasks are guided by a moving plane, also controlled by direct manipulation. The events observed during the tests with users are classified. Based on the results and events observed, a methodology is proposed and used to redefine the system's interface. [Full ps version]

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Surface Mesh Generation with Direct Manipulation and Object Orientation

Luiz Cristovão Gomes Coelho, Luiz Fernando Martha, Clarisse Sieckenius de Souza and Marcelo Gattass
Proceedings of XVI CILAMCE 93, 169-172.

We present an user-interface proposal for the generation of shell finite element meshes with direct manipulation of the 3D primitives. We use an object oriented filosofy in the implementation with standard ANSI [C] language. The classes are exacly the graphic primitives that the users deal with. The meshes are constructed using transfinite or sweep (translational and rotational) mappings applied to a group of pre-selected curves. [Full ps version]

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Interface Generation for Data Aquisition over Drawings

Luiz Henrique de Figueiredo, Clarisse Siekenius de Souza, Marcelo Gattass, and Luiz Cristovão Gomes Coelho
Proceedings of SIBGRAPI'92, 169-175.

Input data for engineering programs that perform numerical simulation can be best prepared if the data entry process uses graphical interfaces based on engineering drawings. Two aspects of this process are considered here: the user interface language and the software tools required to implement it. [Full ps version]

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Last update: Mon Apr 5 16:51:37 EST 1999 by lula.