Vincent François

3D automatic remeshing applied to model modification

The design process usually involves modifications of an initial design solution. At this point in time, design tools do not allow us to perform these modifications efficiently enough. Particularly, when using FE methods, a new FE model has to be rebuilt in order to take into account any modification of the geometric model. We propose an original approach that allows the automatic remeshing of 3D parts, which provides a better integration of FE methods into the entire CAD/CAM process.

Integration of CAD, FEA and Topology Optimization through a Unified Topological Model

We have been involved in research work in the field of finite element analysis (FEA) integration with computer aided design (CAD) for several years and have developed several concepts and tools that have aroused interest and shown efficiency. In the meantime, both the evolution of our research developments (on topics like geometry comparison, geometry reconstruction and simplification, mixed-dimensional analysis and topology optimization) and the evolution of CAD systems and CAD kernels made us reconsider our database organization. This led to the design of an original development environment and database organization referred to as the Unified Topological Model (UTM). The main interests of this new CAD/FEA database organization is its ability to tackle multi-platform CAD/FEA integration (handling geometries coming from different CAD kernels), mixed-dimensional modeling and analysis (3D solid geometry mixed and integrated with surface geometry and curvilinear geometry) and topology optimization (TO) proce...

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.

Automatic mesh generation and transformation for topology optimization methods

This paper presents automatic tools aimed at the generation and adaptation of unstructured tetrahedral meshes in the context of composite or heterogeneous geometry. These tools are primarily intended for applications in the domain of topology optimization methods but the approach introduced presents great potential in a wider context. Indeed, various fields of application can be foreseen for which meshing heterogeneous geometry is required, such as finite element simulations (in the case of heterogeneous materials and assemblies, for example), animation and visualization (medical imaging, for example). Using B-Rep concepts as well as specific adaptations of advancing front mesh generation algorithms, the mesh generation approach presented guarantees, in a simple and natural way, mesh continuity and conformity across interior boundaries when trying to mesh a composite domain. When applied in the context of topology optimization methods, this approach guarantees that design and non-design sub-domains are meshed so that finite elements are tagged as design and non-design elements and so that continuity and conformity are guaranteed at the interface between design and non-design sub-domains. The paper also presents how mesh transformation and mesh smoothing tools can be successfully used when trying to derive a functional shape from raw topology optimization results.

Towards adaptive topology optimization

A new approach to adaptive topology optimization.A higher resolution in the description of the optimal shape.The approach proposed requires revisiting density and sensitivity filtering.Applied to the optimization of 3D parts and structures. This paper presents a new fully-automated adaptation strategy for structural topology optimization (TO) methods. In this work, TO is based on the SIMP method on unstructured tetrahedral meshes. The SIMP density gradient is used to locate solid-void interface and h-adaptation is applied for a better definition of this interface and, at the same time, de-refinement is performed to coarsen the mesh in fully solid and void regions. Since the mesh is no longer uniform after such an adaptation, classical filtering techniques have to be revisited to ensure mesh-independency and checkerboard-free designs. Using this adaptive scheme improves the objective function minimization and leads to a higher resolution in the description of the optimal shape boundary (solid-void interface) at a lower computational cost. This paper combines a 3D implementation of the SIMP method for unstructured tetrahedral meshes with an original mesh adaptation strategy. The approach is validated on several examples to illustrate its effectiveness.

Towards the Integration of Topology Optimization into the CAD Process

This paper presents a contribution to the automation and integration of topology optimization methods (TOM) with CAD, in the context of the design of statically loaded mechanical structures and parts. Starting from an initial CAD model with relevant engineering data, the goal is automatically generating an optimized CAD model with respect to engineering objectives and constrains. Though many optimization methods are now available, their complete and efficient integration into the design process faces several problems. After introducing the basic steps involved in the whole process and identifying the challenges inherent to this integration, this paper presents our contribution in addressing these challenges. The paper is focused on the specification of design and non-design sub-domains, on automatic mesh generation problems induced and on the adaptation of TO concepts in the context of 3D unstructured meshes. TO itself is adapted from a SIMP scheme, which is an arbitrary choice as any other optimization m...

Automatic 3D Mesh Generation of Multiple Domains for Topology Optimization Methods

This paper presents an automatic approach to generate unstructured tetrahedral meshes in the context of composite or heterogeneous geometry. Using B-Rep concepts and specific adaptations of advancing front mesh generation algorithms, this approach guarantees, in a simple and natural way, mesh continuity and conformity across the interior boundaries of a composite domain. This method presents a great potential in various fields of application such as finite element simulations (in the case of heterogeneous materials and assemblies for example), animation and visualization (medical imaging for example). After a description of the approach and its context, the paper presents a potential application in the specific domain of topology optimization.

Automatic CAD Models Comparison and Re-meshing in the Context of Mechanical Design Optimization

A lot of research work has been focused on integrating FEA (finite elements analysis) with CAD (Computer Aided Design) over the last decade. In spite of improvements brought by this integration, research work remains to be done in order to better integrate all the operations led during the whole design process. The design process involves several modifications of an initial design solution and until now, in this context, the communication between CAD modules (dedicated to different tasks involved in the product design process) remains static. Consequently, there is a need for more flexible communication processes between CAD modules through the design cycle, if not through the product life cycle. Some approaches have been developed aiming at the reduction of the design process length when using FEA, and aiming at the automation of part’s data transfer from one step of the process to the next one. Automatic re-meshing is one of these approaches. It consists in automatically updating the part’s mesh around modifications zones, in the case of a minor change in the part’s design, without the need to re-mesh the entire part. The purpose of this paper is to present a new tool, aiming at the improvement of automatic re-meshing procedures. This tool basically consists in automatically identifying and locating modifications between two versions of a CAD model (typically an initial design and a modified design) through the design process. The knowledge of these modifications is then used to fit portions of the initial design’s mesh to the modified design (a process referred to as automatic re-meshing). A major benefit of the approach presented here is that it is completely independent of the description frame of both models, which is made possible with the use of vector-based geometric representations.

A Mesh-Geometry Based Approach for Mixed-Dimensional Analysis

When conducting a finite element analysis, the total number of degrees of freedom can be dramatically decreased using finite elements such as beams and shells. Because of geometric complexities, entire models (or portions of models) must be meshed using volume elements in order to obtain accurate simulation results. If however some parts of these models fit the description of shells or beams, then a mixed-dimensional model containing shell, beam and volume elements side by side can be used. This approach can significantly reduce the time needed to mesh and solve the system. Unfortunately, problems arise when trying to connect elements of different dimensions in part due to the incompatible degrees of freedom and the independently created meshes. This paper presents a solution to these problems based on the generation of a compatible mesh composed solely of basic elements and without the requirement of constraint equations.