Simulation of free surface and molten metal behavior during induction melting of an aluminium alloy

International audienceElectromagnetic forces are widely used for processing metal alloys in particular in the aluminium casting industry. Induction is used in melting technologies (both crucible and channel induction furnaces). Magnetic stirrers are also used in melting or casting furnaces. However these technologies applied to opaque melts require modelling to be done to understand the resultant impact on the fluid and improve the process control. This is especially the case of crucible induction furnaces. A 2D axially symmetric numerical model describing the coupled magnetohydrodynamic and free surface phenomena taking place in an induction metal bath has been developed. The model uses the Ansys Fluent software, supplemented with additional User Defined Functions for the calculation of the Lorentz forces acting on the metal. The calculation of the shape of the free surface is based on the Volume Of Fluid method and a RANS k-ω Shear Stress Transport (SST) approach is used to describe the turbulent stirring of the metal. An original feature of our model is the consideration of an oxide skin covering the metal free surface. It was considered that the oxide film behaves similarly to a deforming wall and that friction effects between the oxide film and the metal result in the development of a shear stress at the top surface of the melt. Two examples of application of model are reported, for lab scale and industrial scale induction furnaces. The lab scale results are compared with measurements of the free surface shape obtained using a fringe projection technique

Non-linear numerical simulations of magneto-acoustic wave propagation in small-scale flux tubes

We present results of non-linear, 2D, numerical simulations of magneto-acoustic wave propagation in the photosphere and chromosphere of small-scale flux tubes with internal structure. Waves with realistic periods of three to five minutes are studied, after applying horizontal and vertical oscillatory perturbations to the equilibrium model. Spurious reflections of shock waves from the upper boundary are minimized thanks to a special boundary condition. This has allowed us to increase the duration of the simulations and to make it long enough to perform a statistical analysis of oscillations. The simulations show that deep horizontal motions of the flux tube generate a slow (magnetic) mode and a surface mode. These modes are efficiently transformed into a slow (acoustic) mode in the vA < cS atmosphere. The slow (acoustic) mode propagates vertically along the field lines, forms shocks and remains always within the flux tube. It might deposit effectively the energy of the driver into the chromosphere. When the driver oscillates with a high frequency, above the cut-off, non-linear wave propagation occurs with the same dominant driver period at all heights. At low frequencies, below the cut-off, the dominant period of oscillations changes with height from that of the driver in the photosphere to its first harmonic (half period) in the chromosphere. Depending on the period and on the type of the driver, different shock patterns are observed.Comment: 22 pages 6 color figures, submitted to Solar Physics, proceeding of SOHO 19/ GONG 2007 meeting, Melbourne, Australi

Modeling the Subsurface Structure of Sunspots

While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this paper, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out an helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by \citeauthor{gizonetal2009}~(\citeyear{gizonetal2009,gizonetal2009a}). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.Comment: 73 pages, 19 figures, accepted by Solar Physic

The European Solar Telescope

The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems

Cinétique de volatilisation en métallurgie d'élaboration sous vide

International audienceUne étude théorique, s’appuyant sur la simulation numérique, a été mise en place pour évaluer la cinétique de volatilisation des éléments métalliques lors d’opérations d’élaboration sous vide. Des résultats sont donnés pour un procédé de fusion d’alliages de titane par faisceaux d’électrons, procédé pour lequel le contrôle de la composition chimique demeure une des difficultés principales

Mathematical modelling of the plasma arc behaviour in the vacuum arc remelting process

International audienceAs part of a complete theoretical description of the behaviour of the electric arc in the vacuum arc remelting process, a model has been developed for the column of plasma generated by a single cluster of cathode microspots. The model aims in particular to calculate the distribution of thermal energy transferred by the plasma to the surface of the anodic melt pool. The theoretical approach combines a kinetic model, taking into account the formation of the plasma in the cathodic region, and a hydrodynamic model, describing the expansion of the plasma in the vacuum between the electrodes

Mycorrhization and application of urban composit in order to improve survival and growth of seeds of Pinus halepensis under semi-arid conditions

Título del Cahier: La mycorhization des plantes forestières en milieu aride et semi-aride et la lutte contre la désertification dans le bassin méditerranéen = Mycorrhization of forest plants under arid and semi-arid conditions and desertification control in the MediterraneaWe have assessed the effect of controlled mycorrhizal infection in the nursery and the application of urban compost on the survival and on the aboveground and belowground biomass of Pinus halepensiss seedlings. They were planted on limestone and marls, under semiarid meso-Mediterranean climate. After two years, mortality was higher in those seedlings planted on limestone, and no treatment effect on seedlings survival was evident. Compost had a positive effect on seedling growth. Treatments showed no effect on the proportion of mycorrhizal short-roots. Controlled mycorrhizal infection had a relatively small effect on seedling growth.Generalitat Valenciana (Programa de Investigación de las Zonas Afectadas por Incendios Forestales en la Comunidad Valenciana, proyecto "Ensayos de Especies Autóctonas y Técnicas de Restauración Forestal") y la C.E.C. DG XII (EV5V-CT94-0475; "Reclamation of Mediterranean Ecosystems Affected by Wildfires"

Mycorrhization and application of urban compost to improve survival and growth of seeds of Quercus ilex spp. ballota in dry environments

Título del Cahier: La mycorhization des plantes forestières en milieu aride et semi-aride et la lutte contre la désertification dans le bassin méditerranéen = Mycorrhization of forest plants under arid and semi-arid conditions and desertification control in the MediterraneaWe have assessed the effect of controlled mycorrhizal infection in the nursery and the application of urban compost on the survival and on the aboveground and belowground biomass of Quercus ilex ssp. ballota seedlings planted in the field. They were planted on limestone and marls, under dry thermo Mediterranean climate. After two years Quercus ilex ssp. ballota seedlings mortality was relatively high (42-70%) and was not affected by bedrock. Compost had a negative effect on the survival and growth of seedlings, probably due to the interspecific competition. Controlled mycorrhizal infection showed no effect on the aboveground biomass of the seedlings. Mortality of the seedlings treated with mycorhizal fungi was lower, although the difference was not statistically significant.Generalitat Valenciana (Programa de Investigación de las Zonas Afectadas por Incendios Forestales en la Comunidad Valenciana, proyecto "Ensayos de Especies Autóctonas y Técnicas de Restauración Forestal") y la C.E.C. DG XII (EV5V-CT94-0475; "Reclamation of Mediterranean Ecosystems Affected by Wildfires"