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Séminaire de modélisation et calcul scientifique

Séminaire de modélisation et calcul scientifique

© INRIA Sophie Auvin - M comme Multimédia

  • Date : 5/05/2015
  • Place : Inria Paris-Rocquencourt - Amphi Alan Turing - Bâtiment 1 - 10h00
  • Guest(s) : Franck Ledoux, CEA - Olivier Allain, Lemma (company)

Hexahedral meshing – Towards an automatic and reliable solution?

Franck Ledoux, CEA

For some numerical simulation codes, hexahedral meshes are preferred to tetrahedral meshes. Depending on the interlocutor with whom you will discuss this, usual given reasons are that you need less hexahedral elements than tetrahedral elements to discretize a geometrical domain (with the same accuracy), hexahedral elements are less rigid than tetrahedral ones, the layered structure of hexahedral meshes can fit some specific physical alignments (shock waves, flows), legacy codes, etc. All of these reasons can be discussed, especially because you can find very good reasons to prefer tetrahedral elements (for instance reliable meshing algorithm and mesh adaptation technics). But it remains that industry strongly asks for having robust and efficient hexahedral meshing algorithms. And, until now, there is no automatic solution that allows engineers getting the expected hexahedral mesh.

The main aim of the presented talk will be to explain why hexahedral meshes are so difficult to generate and which research directions are promising to get results. In this context, I will first give the usual geometric features that hexahedral meshes have to fulfil, and describe their topological structure. Then, I will give an overview of the main existing approaches to generate hexahedral meshes in an automatic manner. I will give benefits and limitations of each approach, and eventually, I will sketch the main trends, that I think promising to follow in the future.

Application of the mesh adaptation to industrial problem.

Olivier Allain, Lemma (company)

Engineering  problems require a continuous progress in the simulation of systems coupling  structures and fluids with interfaces.The main difficulties of these problems come from the multi-scale aspect (for rheological phenomena, or sloshing problem), or from the important deformation of the mesh (fluid-structure interaction, rotating movement,...).

The improvement in capturing small scale details thanks to local refinement can be determinant for the final overall accuracy. Indeed, local numerical errors can be of paramount impact on the accuracy of the predictions in multi-fluid and free surface flows. A typical example of a physical phenomenon where improving the accuracy is significant is the slamming of an obstacle on a liquid surface. The contact of a body with the liquid is a complex event with high pressure variations. These remarks motivate the use of a mesh adaptation.

On an other hand, a metric-based mesh adaptation is presented. Two approaches are proposed for the mesh size prescription. The first one uses simple geometric criteria. The mesh is refined close to the body and around the initial interface area. The second method employs advanced error estimates and mesh adaptation algorithm dedicated to time dependent problems. The mesh is adapted to compute accurately the dynamic of the flow and to accurately capture the interface position. The mesh adaptation algorithm enables us to predict the phenomenon evolution and to automatically refine all the regions of interest.

The presentation will be illustrated with different industrial cases (offshore, space, ...).

Keywords: Modélisation Séminaire Calcul CEA Lemma Scientifique