A parallel two mesh method for speeding-up processes with localized deformations: application to cogging

International audienceIn order to reduce the very long computational time required for the simulation of incremental processes such as cogging or ring rolling, a Bimesh method is proposed. It consists in using different finite element meshes for the resolution of the different physical problems: a main fine mesh to store the results and to carry out the thermal computations, and an intermediate coarser mesh for the mechanical calculations. It makes it possible to take advantage of the localised deformations that characterize incremental processes to coarsen the mechanical mesh and consequently reduce the computational time. After presenting the main components of these Bimesh method, the building of the embedded meshes and the data transfer between the meshes, its extension for parallel calculations are discussed, before analysing the obtained speed-ups for several cogging applications, both in sequential and in parallel

Stabilized finite element solution to handle complex heat and turbulent flows in industrial furnaces

International audienceThe development of efficient methods to understand and simulate conjugate heat transfer for multicomponents systems is one of the most engineering challenges and still a need for industrials, especially in the case of the heat treatment of high-alloy steel by a continuously heating process inside industrial furnaces. The thermal history of the load and the temperature distribution in the furnace are critical for the final microstructure and the mechanical properties of the treated workpieces and can directly determined their final quality in terms of hardness, toughness and resistance. In this paper, a heat treatment furnace simulated using Computational Fluid Dynamics is presented. CFD simulation provides a useful tool to predict the temperature evolution in the furnace and within the walls and the support grid. The model consists of turbulent flow, thermal radiation and conjugate heat transfer. A 3D stabilized finite element methods is developed and used to solve the conjugate heat problem. An immersed volume method (IVM) is applied to heat and treat the fluid-solid interactions. Temperature measurements were carried in different location and are compared to the experimental results

Massively parallel computation on anisotropic meshes

International audienceIn this paper, we present developments done to obtain efficient parallel computations on supercomputers up to 8192 cores. While most massively parallel computation are shown using regular grid it is less common to see massively parallel computation using anisotropic adapted unstructured meshes. We will present here two mains components done to reach very large scale calculation up to 10 billions unknowns using a muligrid method over unstructured mesh running on 8192 cores. We firstly focus on the strategy used to generate computational meshes and in particular anisotropic ones adapted to capture a quite complicated test function. Then we will briefly describe a parallel multigrid method. Performance test over a large range of cores from 512 to 8192 cores is then presented using the French national supercomputers Jade and Curie. The last section will present a calculation done on smallest number of cores on our own cluster, but using more realistic data obtain directly from experimentation. The goal is to be able to realize such kind of simulation on really complex micro structure obtain by tomography at a larger scal

Multi-domain large deformations by monolithic approach for massive parallel computing

International audienceA monolithic approach is presented to solve multi-domain large deformations problems. It is based on an eulerian formulation using a fixed yet anisotropic adaptative mesh. Within this context, a level set method is used to capture the interface evolution of different domains. In terms of parallel computing, it is expected that the technique of single mesh and single mechanical solver developed under CimLib allows to obtain easily a very good scalability up to several hundred processors

Grandes déformations multi-domaines par une approche monolithique pour le calcul massivement parallèle

National audienceLe développement d'une approche performante au niveau du calcul massivement parallèle, capable de simuler des applications complexes ( multi domaine) est l'un des intérêts essentiels de l'industrie. Dans cet article, le sujet des grandes déformations est abordé tout en utilisant une approche eulérienne monolithique. Une méthode level set convective est utilisée afin de définir les différents domaines présents et leur évolution au cours du temps. Ainsi, un seul maillage est considéré sur lequel un ensemble d'équations est résolu dont les propriétés physiques sont gérées par des lois de mélange. Le maillage est adapté afin d'avoir une précision plus élevée au niveau du calcul. L'utilisation d'un maillage unique permet d'obtenir une très bonne performance parallèle de l'approche

Modélisation du procédé de chauffage de pièces dans un four industriel.

http://hdl.handle.net/2042/16654International audienceDans cet article, on considère un maillage unique de l'enceinte d'un four industriel et on utilise d'abord une technique d'immersion de domaines pour prendre en compte les différentes positions et géométries des pièces à chauffer. Par la suite, la thermique est calculée par des méthodes Eléments Finis de type P1 stabilisées, pour à la fois contrôler la convection forcée (au niveau des brûleurs) et les chocs thermiques dûs à la diffusion transitoire (au niveau des lingots). Ces méthodes de stabilisation de type SUPG et SCPG pour la convection dominante et de type GGLS pour la diffusion pure sont présentées et analysées. La vitesse de convection est calculée en résolvant les équations de Navier Stokes couplées faiblement avec la thermique = We present in this paper the thermal modelling for an industrial oven. We begin by considering a single grid of this oven and then, in order to take into consideration different positions and forms of the heated parts inside, an immersion technique for multi-domain problem is used. Different stabilised finite element methods will be presented, such as SUPG and SCPG for reducing spurious oscillations in convectiondominated diffusion problem (at the burner's level) and GGLS for thermal shock's treatment in transient conduction heat transfer (at ingot's level). The velocity field is computed by solving the Navier-Stokes equations coupled to heat equations

Une méthode MultiMaillages MultiPhysiques parallèle pour accélérer les calculs des procédés multiphysiques incrémentaux

National audienceL'objectif de ces travaux est de réduire le temps de calcul pour des procédés multiphysiques incrémentaux. Le principe de la méthode est d'utiliser un maillage adéquat pour chaque physique du problème. Un autre point important de l'approche est l'utilisation d'un maillage de stockage, lequel permet de conserver la précision malgré les remaillages. La stratégie proposée permet d'obtenir des accélérations importantes en temps de calcul. Enfin, on propose une extension de cette approche dans le cadre d'une description Arbitrairement Lagrangienne ou Eulérienne.See http://hal.archives-ouvertes.fr/docs/00/59/27/13/ANNEX/r_08GV6R71.pd

3D CAFE simulation of a macrosegregation benchmark experiment

International audienceA macrosegregation benchmark experiment is simulated using a three dimensional (3D) Cellular Automaton (CA) - Finite Element (FE) model. It consists of a Sn - 3 wt% Pb alloy solidified in a rectangular cavity. Thanks to tabulated thermodynamic properties and solidification paths with temperature and composition, the effect of natural convection and macrosegregation on cooling curves is correctly predicted. Nucleation parameters are adjusted so that the simulated grain structure correlates with the real grain structure. Although macrosegregation is well predicted, this is not the case for freckles yet observed in the solidified sample

Adaptation de maillage anisotrope : théorie et applications

National audienceL'adaptation de maillage anisotrope est une technique de mieux en mieux maîtrisée. Elle est basée sur l'estimation a posteriori, la construction de métrique et des opérations de modifications locales des maillages. La combinaison Level Set et adaptation anisotrope permet des simulations jusque alors considérées infaisables. Quelques exemples sont présentés

Capture d'interface et application au procédé d'injection assistée eau

http://hdl.handle.net/2042/16392International audienceNous proposons une amélioration des techniques de capture d'interfaces, pour la simulation d'écoulements multiphasiques, en utilisant une méthode de h-adaptation de maillage. Une technique d'adaptation de maillage anisotrope basée sur les variations de gradients de la fonction level-set permet de capturer les discontinuités des paramètres physiques qui caractérisent les écoulements fortement hétérogènes. Cette méthode permet l'observation précise de l'évolution des différentes phases (eau/ polymère liquide eau/ polymère solide) ainsi que leurs interactions. Une application directe de cette amélioration est la simulation des problèmes multiphasiques complexes intervenant dans le procédé de fabrication de pièces creuses tel que l'injection assistée eau = We propose an improvement of interface capturing techniques by using an h-adaptation technique to improve computation of the multiphase flows. An anisotropic mesh adaptation technique based on variations of the level-set function allows a better capture of the discontinuities of the physical parameters that characterize the strongly heterogeneous flows. This method allows an accurate observation of the evolution of the various phases (water/liquid polymer, water solid polymer) as well as their interactions. A direct application of this improvement is the simulation of complex multiphase problems involved in the manufacturing processes of hollow parts such as the water assisted injection process