Gilles Foucault

Functional restructuring of CAD models for FEA purposes

Purpose – Preparing digital mock-ups (DMUs) for finite element analyses (FEAs) is currently a long and tedious task requiring many interactive CAD model transformations. Functional information about components appears to be very useful to speed this preparation process. The purpose of this paper is to shows how DMU components can be automatically enriched with some functional information. Design/methodology/approach – DMUs are widespread and stand as reference model for product description. However, DMUs produced by industrial CAD systems essentially contain geometric models, which lead to tedious preparation of finite element Models (FEMs). Analysis and reasoning approaches are developed to automatically enrich DMUs with functional and kinematic properties. Indeed, geometric interfaces between components form a key starting point to analyze their behaviors under reference states. This is a first stage in a reasoning process to progressively identify mechanical, kinematic as well as functional properties ...

Qualitative behavioral reasoning from components' interfaces to components' functions for DMU adaption to FE analyses

A digital mock-up (DMU), with its B-Rep model of product components, is a standard industrial representation that lacks geometric information about interfaces between components. Component shapes reflect common engineering practices that influence component interfaces with interferences and not only contacts. The proposed approach builds upon relationships between function, behavior, and shape to derive functional information from the geometry of component interfaces. Among these concepts, the concept of behavior is more difficult to set up and connect to the geometry of interfaces and functions. Indeed, states and design rules are introduced to express the behavior of components through a qualitative reasoning process. This reasoning process, in turn, takes advantage of domain knowledge rules and facts, checking the validity of certain hypotheses that must hold true all along a specific state of the products lifecycle, such as operational, stand-by or relaxed states. Eliminating configurations that contradict one or more of those hypotheses in their corresponding reference state reduces ambiguity, subsequently producing functional information in a bottom-up manner. This bottom-up process starts with the generation of a conventional interfaces graph (CIG) with components as nodes, and conventional interfaces (CIs) as arcs. A CI is initially defined by a geometric interaction that can be a contact or an interference between two components. CIs are then populated with functional interpretations (FIs) according to their geometric properties, producing potentially many combinations. A first step of the reasoning process, the validation against reference states, reduces the number of FIs per CI. Domain knowledge rules are then applied again to group semantics of component interfaces into one functional designation per component to connect together geometric entities of its boundary with its function.

Generalizing the advancing front method to composite surfaces in the context of meshing constraints topology

Being able to automatically mesh composite geometry is an important issue in the context of CAD-FEA integration. In some specific contexts of this integration, such as using virtual topology or meshing constraints topology (MCT), it is even a key requirement. In this paper, we present a new approach to automatic mesh generation over composite geometry. The proposed mesh generation approach is based on a generalization of the advancing front method (AFM) over curved surfaces. The adaptation of the AFM to composite faces (composed of multiple boundary representation (B-Rep) faces) involves the computation of complex paths along these B-Rep faces, on which progression of the advancing front is based. Each mesh segment or mesh triangle generated through this progression on composite geometry is likely to lie on multiple B-Rep faces and consequently, it is likely to be associated with a composite definition across multiple parametric spaces. Collision tests between new front segments and existing mesh elements also require specific and significant adaptations of the AFM, since a given front segment is also likely to lie on multiple B-Rep faces. This new mesh generation approach is presented in the context of MCT, which requires being able to handle composite geometry along with non-manifold boundary configurations, such as edges and vertices lying in the interior domain of B-Rep faces.

An Extension of the Advancing Front Method to Composite Geometry

This paper introduces a new approach to automatic mesh generation over composite geometry. This approach is based on an adaptation of advancing front mesh generation techniques over curved surfaces, and its main features are: elements are generated directly over multiple parametric surfaces: advancing front propagation is adapted through the extension to composite geometry of propagation direction, propagation length, and target point concepts, each mesh entity is associated with sets of images in each reference entity of the composite geometry, the intersection tests between segments are performed in the parametric domain of their images.

Template-based Geometric Transformations of a Functionally Enriched DMU into FE Assembly Models

Pre-processing of CAD models derived from Digital Mock-Ups (DMUs) into finite element (FE) models is usually completed after many tedious tasks of model preparation and shape transformations. It is highly valuable for simulation engineers to automate time-consuming sequences of assembly preparation processes. Here, it is proposed to use an enriched DMU with geometric interfaces between components (contacts and interferences) and functional properties. Then, the key concept of template-based transformation can connect to assembly functions to locate consistent sets of components in the DMU. Subsequently, sets of shape transformations feed the template content to adapt components to FE requirements. To precisely monitor the friction areas and the mesh around bolts, the template creates sub-domains into their tightened components and preserves the consistency of geometric interfaces for the mesh generation purposes. From a user-selected assembly function, the method is able to robustly identify, locate and transform groups of components while preserving the consistency of the assembly needed for FE models. To enlarge the scope of the template in the assembly function taxonomy, it is shown how the concept of dependent function enforces the geometric and functional consistency of the transformed assembly. To demonstrate the proposed approach, a business oriented prototype processes bolted junctions of aeronautical structures.

Enriching Assembly CAD Models With Functional and Mechanical Informations to Ease CAE

Assembly models can be regarded as a kernel for product development processes where they can efficiently contribute to many product simulation behaviors. Assembly models are often containing 3D B-Rep CAD models, possibly with geometric constraints between the components and bill of materials. However, these models are often difficult to process for simulations because algorithms often face a very large diversity of configurations. One origin of such difficulties can be found in companies’ practice where components may be represented differently from one company to another and their interfaces as well. In any case, interfaces between components are not explicit, which leads to tedious model processing tasks. This paper illustrates preparation of assembly models to ease CAE through an analysis of company practices, showing that a concept of conventional representations is an important starting point to efficient treatments of assemblies. In addition, it is described how interfaces and conventional representations can be combined to derive functional and mechanical information from geometric models of components. Illustrations of the proposed approach is given throughout the paper using various standard components.Copyright

Fast global and partial reflective symmetry analyses using boundary surfaces of mechanical components

Axisymmetry and planar reflective symmetry properties of mechanical components can be used throughout a product development process to restructure the modeling process of a component, simplify the computation of tool path trajectories, assembly trajectories, etc. To this end, the restructured geometric model of such components must be at least as accurate as the manufacturing processes used to produce them, likewise their symmetry properties must be extracted with the same level of accuracy to preserve the accuracy of their geometric model. The proposed symmetry analysis is performed on a B-Rep CAD model through a divide-and-conquer approach over the boundary of a component with faces as atomic entities. As a result, it is possible to identify rapidly all global symmetry planes and axisymmetry as well as local symmetries. Also, the corresponding algorithm is fast enough to be inserted in CAD/CAM operators as part of interactive modeling processes, it performs at the same level of tolerance than geometric modelers and it is independent of the face and edge parameterizations.

Automated contextual annotation of B-Rep CAD mechanical components deriving technology and symmetry information to support partial retrieval

Mechanical components are often related to technological meaning: it is a screw, a ball bearing, . . . Technological meaning relates to the notion of function which, in turn, refers to the environment of a component. Here, it is shown how a digital mock-up contextualizing a set of components is used to annotate its components with technological information. This information is derived from the interfaces between components. Interfaces together with the concept of state of a digital mock-up initiate annotations of components with functional information. Symmetries of components is a complementary information that can contribute to a query. Local rotational symmetry is analyzed and adapted to the context of mechanical components. Then, combining these two categories of information enables the generation of high level queries addressing a subset of a component boundary. Technological as well as symmetry informations are component annotations automatically derived from the digital mock-up analysis and from components analyzed separately.

Symmetry Plane Detection for 3D CAD Volumes

Symmetry properties of components have many applications during a product development process, including shape transformations for modification purposes, Finite Element Analysis (FEA), model retrieval, etc. This paper presents an algorithm to generate 3D model symmetry planes using the B-Rep model of CAD volumes. In the framework of CAD software, 3D models are described as B-Rep volume models. Design processes of volume models strongly rely on extrusion and revolution primitives from sketches containing essentially straight line segments and circular arcs. Hence, the boundary surfaces considered are planes, cylinders, cones, tori and spheres. The object boundary is effectively processed as an infinite set of points. Global symmetry properties of faces are derived to initiate the global symmetry planes of the object. To this end, the intersection curves between two adjacent faces are used to characterize possible global symmetry planes of the object. Then, the algorithm starts analyzing the symmetry properties of couple of faces. Subsequently, the candidate symmetry planes set up contains all the possible global symmetry planes. Finally, the symmetry properties of neighboring faces help determining robustly the global symmetry planes, whether there is a finite number or an infinite number.Copyright

A topological model for the representation of meshing constraints in the context of finite element analysis

The preparation of Finite Element analysis models (FE models) from Computer Aided Design (CAD) models is still a difficult task since its Boundary Representation (B-Rep) is often composed of a large number of thin faces, small edges, which are much smaller than the desired element size, and are not relevant for the meshing process. Such inconsistencies often cause poor-shaped FE elements, overdensities of elements, not only slowing down the computation of the FE solution, but also producing poor simulation results. In this paper, we present a “Mesh Constraint Topology” (MCT) model with adaptation operators aiming at transforming the CAD model in a FE model which only contains meshing-relevant edges and vertices, i.e. the explicit model of data intrinsic to the meshing process. Because the topology of faces adapted for meshing could contain interior edges, the MCT is represented with adjacency graphs instead of the B-Rep data-structure. We demonstrate how graphs provide efficient schemes to qualify interior and boundary entities, and facilitate the design of adaptation operators using high-level graph operators. Application and results are presented through adaptation issues of CAD models solved using MCT adaptation operators.Copyright