Advances in modeling of discrete models have allowed the development of approaches for direct mesh modeling and modification. These tools mainly focus on modeling the visual appearance of the shape which is a key criterion for animation or surgical simulation. Most of the time, the resulting mesh quality as well as the semantics preservation capabilities are not considered as key features. These are the limits we overcome in this paper to enable fast and efficient mesh modifications when carrying out numerical simulations of product behaviors using the Finite Element (FE) analysis. In our approach, the modifications involve the resolution of an optimization problem where the constraints come from the shapes of the operating tools and the FE groups (sets of mesh entities) used to support the semantic information (e.g. boundary conditions, materials) contained in the FE mesh model and required for FE simulation. The overall mesh quality, a key point for accurate FE analysis, is guaranteed while minimizing an objective function based on a mechanical model of bar networks which smoothes the repositioning of nodes. Principle of the devised mesh operators is exemplified through the description of a 2D/3D mesh drilling operator. The proposed mesh modification operators are useful in the context of fast maintenance studies and help engineers to assess alternative design solutions aimed at improving the physical behavior of industrial machinery.

Even if today's CAD systems can easily represent free-form shapes by means of NURBS surfaces, their definition and modification still require a deep knowledge and a great skill in the manipulation of the underlying mathematical models. This paper presents an attempt to bring the feature concepts, well-known in the classical mechanical domain, to the free-form domain. The paper extends our previous work on fully free-form features to include parameterised feature templates. The free-form shapes are obtained by deformation according to specific constraint lines taking part to the feature templates definition. The feature template is adapted to the user-specified parameter values by our deformation engine, which can applied either to surfaces and curves. The method is illustrated with examples obtained with our prototype software.

Visualisation, assembling/disassembling simulation, reverse engineering, or finite element analyses are so many applications where a polyhedral simplification can be mandatory. In most of the configurations, such an operation must preserve the significant shapes of the original model. This paper addresses the way these simplifications can be performed while preserving character lines, i.e. those lines which affect significantly the object visual appearance. The proposed simplification process is based on a vertex removal algorithm that uses a heterogeneous map of sizes computed with information extracted from 2D images of the object. The farther the vertices are from the character lines, the more the simplification is important. The geodesic distances are estimated while using a new algorithm based on the analysis of multiple filtering of the images. This method might reduce the computational time since there is no need to compute either the curvature or the saliency. Thus, a first attempt to enrich a polyhedral model with semantic information extracted from images is proposed.

Fully free form deformation features (/spl delta/-F/sup 4/) have been proposed to overcome the limits of low-level manipulations of free form surfaces. They correspond to shapes obtained by deformation of a surface part according to geometric constraints. In our approach, a /spl delta/-F/sup 4/ is a result of the indirect manipulation of external forces applied to the nodes of a bar network coupled to the control polyhedron of a B-spline surface. The solution of the equation system corresponding to the constraint specifications, often under-constrained, requires the definition of an optimisation problem where an additional objective function has to be minimised. In this paper, we propose a new formulation of this optimisation problem where the proposed objective functions can be defined as a multiple combination of various local quantities. They can be related either to the geometry of the bar network (e.g. the length of a bar or the displacement of a node), or to its mechanical magnitudes (e.g. the external force applied at a node or a bar deformation energy). Different types of combinations are also proposed and classified according to the induced level of multi-minimisations. In this way, the shape of a /spl delta/-F/sup 4/ can be controlled globally, with a unique minimisation, or locally with different minimisations applied to sub-domains of the surface.

This paper addresses the designers' work and in particular the way they express an object shape through character lines. Based on this concept, a deformation feature is presented. The proposed approach includes curvilinear constraints to match the designer's requirements and techniques for the quality and accuracy of the produced model. This method is applied to B-spline surfaces coupled with a mechanical model of a bar network; geometric constraints are automatically and adaptively added to monitor and control the deformation process. A few examples show the results obtained by this deformation feature with the help of curvature maps, used to analyze the influence of the constraints and the resulting quality.