Meshless interface tracking for the simulation of dendrite envelope growth

The growth of dendritic grains during solidification is often modelled using the Grain Envelope Model (GEM), in which the envelope of the dendrite is an interface tracked by the Phase Field Interface Capturing (PFIC) method. In the PFIC method, an phase-field equation is solved on a fixed mesh to track the position of the envelope. While being versatile and robust, PFIC introduces certain numerical artefacts. In this work, we present an alternative approach for the solution of the GEM that employs a Meshless (sharp) Interface Tracking (MIT) formulation, which uses direct, artefact-free interface tracking. In the MIT, the envelope (interface) is defined as a moving domain boundary and the interface-tracking nodes are boundary nodes for the diffusion problem solved in the domain. To increase the accuracy of the method for the diffusion-controlled moving-boundary problem, an \h-adaptive spatial discretization is used, thus, the node spacing is refined in the vicinity of the envelope. MIT combines a parametric surface reconstruction, a mesh-free discretization of the parametric surfaces and the space enclosed by them, and a high-order approximation of the partial differential operators and of the solute concentration field using radial basis functions augmented with monomials. The proposed method is demonstrated on a two-dimensional \h-adaptive solution of the diffusive growth of dendrite and evaluated by comparing the results to the PFIC approach. It is shown that MIT can reproduce the results calculated with PFIC, that it is convergent and that it can capture more details in the envelope shape than PFIC with a similar spatial discretization.Comment: Preprint submitted to Journal of Computational Physic

Mesoscopic modeling of spacing and grain selection in columnar dendritic solidification: Envelope versus phase-field model

We investigate and assess the capability of the mesoscopic envelope model of dendritic solidification to represent the growth of columnar dendritic structures. This is done by quantitative comparisons to phase-field simulations in two dimensions. While the phase-field model resolves the detailed growth morphology at the microscale, the mesoscopic envelope model describes a dendritic grain by its envelope. The envelope growth velocities are calculated by an analytical dendrite-tip model and matched to the numerical solution of the solute concentration field in the vicinity of the envelope. The simplified representation of the dendrites drastically reduces the calculation time compared to phase field. Larger ensembles of grains can therefore be simulated. We show that the mesoscopic envelope model accurately reproduces the evolution of the primary branch structure, the undercooling of the dendrite tips, and the solidification path in the columnar mushy zone. We further show that it can also correctly describe the transient adjustments of primary spacing, both by spacing increase due to elimination of primary branches and by spacing reduction due to tertiary rebranching. Elimination and tertiary rebranching are also critical phenomena for the evolution of grain boundaries between columnar grains that have a different crystallographic orientation with respect to the temperature gradient. We show that the mesoscopic model can reproduce the macroscopic evolution of such grain boundaries for small and moderate misorientation angles, i.e., up to 30°. It is therefore suitable for predicting the texture of polycrystalline columnar structures. We also provide guidelines for the calibration of the main parameters of the mesoscopic model, required to obtain reliable predictions.ANR-11-LABX-0008/11-LABX-0008 - DAMAS - Design des Alliages Métalliques pour Allègement des Structures (2011) - German Space Agency DLR under Contract FKZ 50WM144

Automated flow unit with smart phone control

V diplomski nalogi opisujemo nadzorno enoto, ki bo vinarjem prihranila čas pri pretakanju mošta ali vina. Nadzorna enota je na eni strani sestavljena iz elektro omarice in dveh stikal –pretočnega stikala za merjejnje količine tekočine in nivojskega stikala za nadziranje vklopa in izklopa črpalke. Oboje komunicira preko kabla s platformo Arduino. Na drugi strani preko bluetooth HC-06 modula pošiljamo odčitane podatke s senzorjev na aplikacijo na telefonu, kjer lahko spremljamo količino tekočine v cisternah. Nadzorna enota je splošen model in ne velja samo za črpalko, ki smo jo uporabili pri projektu. Važno je le, da je črpalka enofazna.The graduation thesis describes a control unit that will save time for wine producers when pumping must (a wine making term which means unfermented grapes, in nonprofessional’s terms), or wine. On the one hand, the control unit is composed of an electrical box and two switches. First, a liquid flow switch for measuring the liquid level and the second, a level switch for controlling the turning on and off of the pump. Both switches communicate via cable with the Arduino platform. On the other hand, bluetooth HC-06 module sends data readings from switches into the app on the phone, where the amount of liquid in the tank is monitored. The control unit is a generic model and does not apply only to the pump, which was used in the project. It is also, of utmost importance that the pump is single-phased

Multiscale modeling of solidification: from microstructures to castings

La solidification est une étape clé pour la fabrication de la plupart des produits métalliques. Pendant la couléeou la fabrication additive, la microstructure de base pour toutes les étapes de traitement suivantes et pour lespropriétés finales du produit est formée. Les défauts et la hétérogénéité de la structure et de la compositionchimique peuvent être introduits à différentes échelles, de l'échelle des interfaces entre phases jusqu’à l'échelledu produit. La description de la genèse des microstructures, macrostructures et des défauts de solidification estrendue difficile par à la large gamme d'échelles (du micron au mètre) et par les nombreux aspects de la physiquequ’impliquent les phénomènes élémentaires. Des modèles multi-échelles sont développés pour couplerles échelles. Ce mémoire présente d’abord les travaux de recherche sur la solidification dans des procédés industrielsde coulée, en se focalisant sur les couplages entre le transport à l'échelle du procédé et la germinationet la croissance des microstructures. À travers les résultats, les limitations des modèles macroscopiques multiéchellesdans la description des phénomènes à petite échelle sont également présentées. La modélisation mésoscopiqueest développée ensuite avec l’objectif principal de l'utiliser dans une approche de changementd’échelle (upscaling) vers des modèles macroscopiques afin d'améliorer la description de la cinétique de croissancedes microstructures à l'échelle du procédé. Les premières résultats de changement d’échelle sont présentés.Finalement les projets de recherche qui se développeront dans les années à venir sont exposés

Predictive Capabilities of Multiphysics and Multiscale Models in Modeling Solidification of Steel Ingots and DC Casting of Aluminum

International audiencePrediction of solidification defects, such as macrosegregation and inhomogeneous microstructures constitutes a key issue for the industry. The development of models of casting processes needs to account for several imbricated length scales and different physical phenomena. For example, the kinetics of the growth of microstructures needs to be coupled with the multiphase flow at the process scale. We introduce such a state-of-the-art model and outline its principles. We present the most recent applications of the model to casting of a heavy steel ingot and to direct chill casting of a large Al alloy sheet ingot. Their ability to help in the understanding of complex phenomena, such as the competition between nucleation and growth of grains in the presence of convection of the liquid and of grain motion is shown, and its predictive capabilities are discussed. Key issues for future developments and research are addressed

DEM simulation of dendritic grain random packing: application to metal alloy solidification

The random packing of equiaxed dendritic grains in metal-alloy solidification is numerically simulated and validated via an experimental model. This phenomenon is characterized by a driving force which is induced by the solid-liquid density difference. Thereby, the solid dendritic grains, nucleated in the melt, sediment and pack with a relatively low inertia-to-dissipation ratio, which is the so-called Stokes number. The characteristics of the particle packed porous structure such as solid packing fraction affect the final solidified product. A multi-sphere clumping Discrete Element Method (DEM) approach is employed to predict the solid packing fraction as function of the grain geometry under the solidification conditions. Five different monodisperse noncohesive frictionless particle collections are numerically packed by means of a vertical acceleration: a) three dendritic morphologies; b) spheres and c) one ellipsoidal geometry. In order to validate our numerical results with solidification conditions, the sedimentation and packing of two monodisperse collections (spherical and dendritic) is experimentally carried out in a viscous quiescent medium. The hydrodynamic similarity is respected between the actual phenomenon and the experimental model, that is a low Stokes number, o(10−3). In this way, the experimental average solid packing fraction is employed to validate the numerical model. Eventually, the average packing fraction is found to highly depend on the equiaxed dendritic grain sphericity, with looser packings for lower sphericity

DEM simulation of dendritic grain random packing: application to metal alloy solidification

The random packing of equiaxed dendritic grains in metal-alloy solidification is numerically simulated and validated via an experimental model. This phenomenon is characterized by a driving force which is induced by the solid-liquid density difference. Thereby, the solid dendritic grains, nucleated in the melt, sediment and pack with a relatively low inertia-to-dissipation ratio, which is the so-called Stokes number. The characteristics of the particle packed porous structure such as solid packing fraction affect the final solidified product. A multi-sphere clumping Discrete Element Method (DEM) approach is employed to predict the solid packing fraction as function of the grain geometry under the solidification conditions. Five different monodisperse noncohesive frictionless particle collections are numerically packed by means of a vertical acceleration: a) three dendritic morphologies; b) spheres and c) one ellipsoidal geometry. In order to validate our numerical results with solidification conditions, the sedimentation and packing of two monodisperse collections (spherical and dendritic) is experimentally carried out in a viscous quiescent medium. The hydrodynamic similarity is respected between the actual phenomenon and the experimental model, that is a low Stokes number, o(10−3). In this way, the experimental average solid packing fraction is employed to validate the numerical model. Eventually, the average packing fraction is found to highly depend on the equiaxed dendritic grain sphericity, with looser packings for lower sphericity