Conception assistée par ordinateur

vignette La conception assistée par ordinateur ou CAO (en anglais, computer aided design ou CAD) comprend l'ensemble des logiciels et des techniques de modélisation géométrique permettant de concevoir, de tester virtuellement – à l'aide d'un ordinateur et des techniques de simulation numérique – et de réaliser des produits manufacturés et les outils pour les fabriquer. Le grand public confond souvent CAO et DAO (dessin assisté par ordinateur) : la CAO n'a pas pour fonction première l'édition du dessin. Il s'agit d'un outil informatique souvent lié à un métier, fonctionnant en langage dit objet, et permettant l'organisation virtuelle de fonctions techniques. Cela permet ensuite la simulation de comportement de l'objet conçu, l'édition éventuelle d'un plan ou d'un schéma étant automatique et accessoire. En DAO, un trait est un trait et le logiciel ne permet pas l'interprétation technique de l'ensemble. L'informatique et l'aide à la conception Tout système technique est l'

Parallel mesh adaptive techniques for complex flow simulation

Angelo Casagrande

Dynamic mesh adaptation on unstructured grids, by localised refinement and derefinement, is a very efficient tool for enhancing solution accuracy and optimise computational time. One of the major drawbacks however resides in the projection of the new nodes created, during the refinement process, onto the boundary surfaces. This can be addressed by the introduction of a library capable of handling geometric properties given by a CAD (Computer Aided Design) description. This is of particular interest also to enhance the adaptation module when the mesh is being smoothed, and hence moved, to then re-project it onto the surface of the exact geometry. However, the above procedure is not always possibly due to either faulty or too complex designs, which require a higher level of complexity in the CAD library. It is therefore paramount to have a built-in algorithm able to place the new nodes, belonging to the boundary, closer to the geometric definition of it. Such a procedure is proposed in this work, based on the idea of interpolating subdivision. In order to efficiently and effectively adapt a mesh to a solution field, the criteria used for the adaptation process needs to be as accurate as possible. Due to the nature of the solution, which is obtained by discretisation of a continuum model, numerical error is intrinsic in the calculation. A posteriori error estimation allows us to somewhat assess the accuracy by using the computed solution itself. In particular, an a posteriori error estimator based on the Zienkievicz Zhu model is introduced. This can be used in the adaptation procedure to refine the mesh in those areas where the local error exceeds a set tolerance, hence further increasing the accuracy of the solution in those regions during the next computational step. Variants of this error estimator have also been studied and implemented. One of the important aspects of this project is the fact that the algorithmic concepts are developed thinking parallel, i.e. the algorithms take into account the possibility of multiprocessor implementation. Indeed these concepts require complex programming if one tries to parallelise them, once they have been devised serially. Another important and innovative aspect of this work is the consistency of the algorithms with parallel processor execution.

EPFL2008

Medial axis transformation as a solid modeling representation method for computer aided design software

Florian Barras, Guillaume Goualard, Mihai-Bogdan Lazar, Ian Anthony Stroud, Paul Xirouchakis

A method for achieving a representation of an object within a data structure for a Computer Aided Design system employing a Medial Axis Transformation (MAT), the representation of the object comprising a set of adjacent bounded surface elements called MAT faces, the MAT faces being bound by sets of MAT edges, which are portions of curves lying on a surface of the MAT faces on either side of the edge, and points where several MAT faces meet are called MAT vertices. The method comprises at least defining each of the MAT vertices as points in a space domain; assigning a radius function to each of the MAT vertices, based on only a single value; defining each of the MAT edges as a curve in space; defining limits of each of the MAT edges as two MAT vertexes which lie on the curve; assigning a radius function to each of the MAT edges; defining each of MAT faces as a surface in space; defining the limits of each of the MAT faces as a MAT loop, comprising at least three MAT edges, sharing each a MAT node, whereby a direction, clockwise or counter-clockwise, of the MAT loop defines on which side of the MAT loop the MAT face will be formed; defining the MAT links as the edges which are shared by at least two MAT faces; assigning a radius function to each of the MAT faces; and defining a MAT object as a connected set of MAT faces, edges and vertices.

2016

Parallel mesh adaptive techniques for complex flow simulation

Angelo Casagrande

EPFL2008

Conception assistée par ordinateur

Computer-aided creative mechanism design

Parallel mesh adaptive techniques for complex flow simulation

Medial axis transformation as a solid modeling representation method for computer aided design software

Computer-aided creative mechanism design

Medial axis transformation as a solid modeling representation method for computer aided design software

Parallel mesh adaptive techniques for complex flow simulation