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.

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.

In this paper the notion of free form feature for aesthetic design is presented. The design of industrial products constituted by free form surfaces is done by using CAD systems representing curves and surfaces by means of NURBS functions, which are usually defined by low level entities that are not intuitive and require some knowledge of the mathematical language. Similarly to the feature‐based approach adopted by CAD systems for classical mechanical design, a set of high level modelling entities which provides commonly performed shape modifications has been identified. Particularly, the paper suggests a classification of the so‐called detail features for an aesthetic and/or functional characterization of predefined free form surfaces. Feature types are formally described by means of an analytical definition of the surface modification through deformation and elimination laws. A topological classification is then given according to the application domain of such laws. A further sub‐classification of morphological types is then suggested according to geometric properties of weak convexity and concavity for the resulting modified shape, leading to a taxonomy of simple free form features meaningful for aesthetic design.

As entities for describing products, features are commonly conceived as being of a semantically higher level than the purely geometric elements traditionally used in CAD systems. Thus, they constitute an effective means for the designer and process planner to consider objects in terms of entities that are meaningful for their activities. The greatest difficulty in using feature technology is the dependence of features on the specific context, i.e. features in one context may be meaningless in another. In this paper, a method for recognizing and deriving volumetric features from boundary representations is presented. The main advantage of this method is the possibility it provides for deriving different feature-based descriptions of the same part by considering the environment used and the degree of multiple interpretation required by the user.

A double description is proposed for the representation of a feature-based model which supports the distinction between form and functionality. This description consists of a primary representation in terms of geometric features ( geometric feature graph) and a set of feature-based representations which are created by transformations that are viewpoint specific and apply to the geometric feature graph.

The system described works in two steps. The first step starts from a boundary model of an object and identifies the generic shape features by considering only geometric and topological aspects. These features are divided into two general classes, protrusions and depressions, extracted as solid volumes, and arranged in a multilevel structure. This representation, called shape-feature object graph (SFOG), is capable of representing the recursive decomposition of an object in its main shape and the set of its form features (possibly compound). The SFOG is a hierarchical and relational boundary model represented by a graph in which the root component nodes correspond to the boundary representation of the main shape, while the other nodes correspond to the boundary representations of features; arcs between nodes define parent-child relations between components. In the second step, the identified features are classified according to the functional meaning in the application context. Thus, the hierarchical representation is reorganized by gluing and/or grouping sets of shape features which are functionally related in the context considered.>

A method is presented for the automatic identification and extraction of feature information from the solid model of an object. The procedure consists of recognizing shape features, extracting those features as solid volumes and arranging them in a hierarchical structure. In this hierarchical model the main shape of the object is represented at the highest levels of abstraction, while form features are described at lower levels of specification. The system is divided into three modules: feature recognition, feature extraction and feature organization. The recognition step works on a face-based representation of solid objects, called Face Adjacency Hypergraph [1] and it takes advantage of the Kyprianou's method [12]. In the extraction phase every recognized form feature is completed with dummy entities to form a feasible object and in the organization step the completed features are arranged in a hierarchical graph, called Structured Face Adjacency Hypergraph, which is a modification of a model defined in a previous work [1].