is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. a b s t r a c tA new approach to the merging of Finite Element (FE) triangle meshes is proposed. Not only it takes into account the geometric aspects, but it also considers the way the semantic information possibly associated to the groups of entities (nodes, faces) can be maintained. Such high level modification capabilities are of major importance in all the engineering activities requiring fast modifications of meshes without going back to the CAD model. This is especially true in the context of industrial maintenance where the engineers often have to solve critical problems in very short time. Indeed, in this case, the product is already designed, the CAD models are not necessarily available and the FE models might be tuned. Thus, the product behaviour has to be studied and improved during its exploitation while prototyping directly several alternate solutions. Such a framework also finds interest in the preliminary design phases where alternative solutions have to be simulated. The algorithm first removes the intersecting faces in an n-ring neighbourhood so that the filling of the created holes produces triangles whose sizes smoothly evolve according to the possibly heterogeneous sizes of the surrounding triangles. The holefilling algorithm is driven by an aspect ratio factor which ensures that the produced triangulation fits well the FE requirements. It is also constrained by the boundaries of the groups of entities gathering together the simulation semantic. The filled areas are then deformed to blend smoothly with the surroundings meshes.

Nowadays, most of the numerical simulations are carried out by successively performing the following steps: CAD model definition or modification, conversion to a mesh model and enrichment with semantic data relative to the simulation (e.g. material behaviour laws, boundary conditions), Finite Element simulation and analysis of the results. Classically, the semantic data are attached to the mesh through the use of groups of geometric entities sharing the same characteristics. Thus, any modification of the CAD model always implies an update of the mesh as well as an update of the attached semantic data. This is time-consuming and not adapted to the context of industrial maintenance. Moreover, the CAD models do not always exist and should therefore be reconstructed starting from scratch or from the physical object. In this paper, we set up a framework towards the definition of CAD-less Finite Element analyses wherein enriched meshes are manipulated directly. The geometric manipulations are constrained with information extracted from the group definition. Actually, the boundaries of those groups are exploited to constrain the modifications. The concept of Virtual Group Boundaries is introduced to focus on the extension of the attached semantic information instead of the actual tessellation while generalising the approach to groups of any dimension going from 0D (vertex) to 3D (e.g. tetrahedron). The notion of Elementary Group is also introduced as a mean to ease the forthcoming transfer of the semantics from the initial to the modified models. Such a framework also finds interest in the preliminary design phases where alternative solutions have to be evaluated.

Communicated by (xxxxxxxxxx) firstly created FE mesh, enriched with physical/geometric semantics, to perform the product modifications required to achieve its optimised version. In order to accomplish the proposed CAD-less FE analysis framework, modification operators acting on both the mesh geometry and the associated semantics need to be devised. In this paper we discuss the underlying concepts and present possible components for the development of such operators. A high-level operator specification is proposed according to a modular structure that allows an easy realisation of different mesh modification operators. Here, two instances of this high-level operator are described: the planar cracking and the drilling. The realised prototypes validated on industrial FE models show clearly the feasibility of this approach.

The aspects of adequate simulation of the flexible parts for path planning during the Assembly/Disassembly (A/D) operation simulation are discussed in this paper. An interactive system forming two complementary levels and incorporating mechanical models of flexible part is described. The approach proposed will be used as a basis to the simulation of flexible parts into a Virtual Reality (VR) environment for the A/D evaluation. First of all, the study of current assembly path planning systems is performed. Secondly, as an issue of the problems discussed, a new system integrating real-time and interactive mechanical simulation approaches is proposed. Finally, an example of the interactive mechanical behavior model applicable to flexible rods used into an A/D path planning context is presented. Numerical modeling focuses on typical boundary conditions. The present approach is considered as a proposal for a methodology used with VR environments during the product design process.

Companies exploiting industrial installations are currently submitted to various constraints in the context of maintenance and lifecycle problem analysis: time and cost of production stops, efficiency of maintenance solutions, production safety criteria, etc. Hence, the reduction of the time of projects may lead to important research perspectives in terms of fast numerical prototyping and solution assessment methods. In this paper, we present a typical industrial problem of fast assessment of mechanical state of a production installation. We focused on the study of a cracked component of a reheater as well as we proposed a new design for this component to improve its mechanical behavior under an exceptional overload. In order to reduce the operational study time, the Extended Finite Element Method (X-FEM) has been used to model non-linear crack phenomenon without any human modification of a complex 3D model on the level of geometric model and mesh. An alternative design of a damageable element has been proposed to avoid all risk of possible cracking. This design task requires a mechanical analysis of locally modified structure under a cyclic loading. We also present a new prototyping method based on direct modification of meshes and allowing reducing the time of numerical study.