A diffusion-split method to deal with thermal shocks using standard linear tetrahedral finite elements

International audienceThe thermal analysis using linear standard tetrahedral finite elements may be affected by spurious local extrema in the regions affected by thermal shocks, in such a severe way to directly discourage the use of these elements. The present work proposes a slight modification to the discrete heat equation in order to obtain a system matrix in M-matrix form, which assures an oscillation-free solution. The performance of this method is evaluated by means of test case with analytical solution, as well as an industrial application, for which a well-behaved numerical solution is available

A two-phase two-dimensional finite element thermomechanics and macrosegregation model of mushy zone. Application to continuous casting

International audienceThe main lines of a coupled thermomechanical - solute transport model are first summarized. Macroscopic conservation equations for mass, momentum, energy and solute are obtained by a spatial averaging method. The mechanical model is a "sponge-like" one: assuming a semi-solid saturated mushy zone, the solid phase is macroscopically modeled as a compressible viscoplastic continuum, while the liquid phase flow obeys Darcy's law. Regarding solute transport, the study is limited to a binary alloy for which the solidification path is not given a priori but results from a microsegregation model (here the lever rule). A validation check of the correct implementation of this coupled model is achieved by comparing with an analytical solution in the case of a free compression of a saturated semi-solid medium. Application to the study of the solidification during secondary cooling in steel continuous casting is considered

Linear tetrahedral finite elements for thermal shock problems

International audiencePurpose - The paper seeks to present an original method for the numerical treatment of thermal shocks in non-linear heat transfer finite element analysis. Design/methodology/approach - The 3D finite element thermal analysis using linear standard tetrahedral elements may be affected by spurious local extrema in the regions affected by thermal shocks, in such a severe ways to directly discourage the use of these elements. This is especially true in the case of solidification problems, in which melted alloys at very high temperature contact low diffusive mould materials. The present work proposes a slight modification to the discrete heat equation in order to obtain a system matrix in M-matrix form, which ensures an oscillation-free solution. Findings - The proposed "diffusion-split" method consists basically of using a modified conductivity matrix. It allows for solutions based on linear tetrahedral elements. The performance of the method is evaluated by means of a test case with analytical solution, as well as an industrial application, for which a well-behaved numerical solution is available. Originality/value - The proposed method should be helpful for computational engineers and software developers in the field of heat transfer analysis. It can be implemented in most existing finite element codes with minimal effort

A 3D-fem model solving thermomechanics and macrosegregation in binary alloys solidification

International audienceThis paper introduces a three-dimensional numerical model for the coupled solution of momentum, energy and solute conservation equations, for binary alloys solidification. The spatial discretisation is carried out using linear tetrahedral finite elements, particularly those of P1+/P1 type for the velocity-pressure resolution of momentum equation. The liquid flow in the mushy zone is assumed to be governed by the Darcy's law. Thermal and buoyancy forces are taken into account by means of the Boussinesq's model. Microsegregation obeys the lever rule. The resulting solute transport equation is solved by the SUPG method. Coupling strategy between momentum, energy and solute equations is discussed and two applications are studied

Application of the arbitrary Eulerian Lagrangian finite element formulation to the thermomechanical simulation of casting processes, with focus on pipe shrinkage prediction

International audienceThe Arbitrary Lagrangian-Eulerian formulation (ALE) has become an indispensable component of finite element thermomechanical computations of casting processes. As it is an intermediate formulation between the Lagrangian formulation (material convected mesh) and the Eulerian one (fixed mesh), it allows the simultaneous computation of important phenomena: Deformation and stresses affecting solidified regions, yielding the computation of air gap evolution at part/mold interfaces. In such regions, the formulation is essentially Lagrangian. Thermosolutal convection flow in the non solidified regions; here the ALE formulation tends to a pure Eulerian one (stationary mesh). Free surface evolution at top of risers, leading to the prediction of pipe defects (macroshrinkage). In this case the ALE formulation allows the follow up of the free surface. After a brief reminder of the constitutive equations to be used in thermomechanical modeling of solidification, the mechanical equations are presented and their resolution in the context of FEM-ALE. We insist on the transport analysis, a key-point of ALE, and present a validation of the original scheme that is used here. Finally, we focus on the prediction of pipe shrinkage formation and show two industrial examples

Problema térmico inverso de conducción de calor aplicado al tratamiento térmico de austemperado usando optimización basada en simulaciones

La etapa de enfriamiento desde la temperatura de austenización hasta la temperatura ambiente es la etapa más crítica del tratamiento térmico de austemperado de una pieza de fundición nodular. La estimación tanto espacial como temporal del flujo de calor a través la superficie externa de la pieza durante dicha etapa, a fin de que la evolución de la temperatura en puntos interiores de la pieza siga unacurva temperatura-tiempo de austemperado prestablecida, constituye un problema térmico inverso de conducción de calor (IHCP, por sus siglas en inglés). En el presente trabajo, se propone la resolución de dicho problema inverso mediante el algoritmo de punto interior conocido como IPOPT. La función objetivo, que es el error en la consecución de la temperatura deseada a lo largo del tratamiento en una seriede puntos, requiere la solución de la ecuación de calor en estado transitorio durante todo el tratamiento, obtenida mediante el Método de Elementos Finitos (MEF). Las variables de diseño del problema definen la evolución de las condiciones de borde enfriamiento superficial a lo largo del tratamiento. En particular, se adoptó como variables de diseño la magnitud del flujo de calor impuesto en distintas porciones de la frontera, a distintos instantes de tiempo. De la aplicación del modelo a un caso de estudio representativo del austemperado de una pieza de fundición nodular, se demuestra que se puede puede determinar con precisión las condiciones de enfriamiento óptimas en ciertas porciones de la pieza, pero el resto de la pieza puede sufrir historias de temperaturas que perjudiquen sus propiedades mecánicas. A partir de esas observaciones, se determinan finalmente las limitaciones del tratamiento de austemperado de fundición nodular por enfriamiento superficial.Publicado en: Mecánica Computacional vol. XXXV no.30Facultad de Ingenierí

Optimization of Multilayered Walls for Building Envelopes Including PCM-Based Composites

This work proposes a numerical procedure to simulate and optimize the thermal response of a multilayered wallboard system for building envelopes, where each layer can be possibly made of Phase Change Materials (PCM)-based composites to take advantage of their Thermal-Energy Storage (TES) capacity. The simulation step consists in solving the transient heat conduction equation across the whole wallboard using the enthalpy-based finite element method. The weather is described in detail by the Typical Meteorological Year (TMY) of the building location. Taking the TMY as well as the wall azimuth as inputs, EnergyPlusTM is used to define the convective boundary conditions at the external surface of the wall. For each layer, the material is chosen from a predefined vade mecum, including several PCM-based composites developed at the Institut für Werkstoffe im Bauwesen of TU Darmstadt together with standard insulating materials (i.e., EPS or Rockwool). Finally, the optimization step consists in using genetic algorithms to determine the stacking sequence of materials across the wallboard to minimize the undesired heat loads. The current simulation-based optimization procedure is applied to the design of envelopes for minimal undesired heat losses and gains in two locations with considerably different weather conditions, viz. Sauce Viejo in Argentina and Frankfurt in Germany. In general, for each location and all the considered orientations (north, east, south and west), optimal results consist of EPS walls containing a thin layer made of the PCM-based composite with highest TES capacity, placed near the middle of the wall and closer to the internal surface

Finite-element modelling of heat transfer in shaped metal deposition and experimental validation

Shaped metal deposition (SMD) is a novel technology for building near-net-shaped components by successive layer deposition using a welding machine. The SMD rig consists of a robot with a tungsten inert gas welding torch and manipulator, both of which are housed inside a sealed chamber. A series of walls were made from Ti-6Al-4V alloy by SMD and the heat transfer problem during layer deposition was analysed in all cases. The specimens were built using a wide range of process parameters (number of layers, layer height, wire feed rate, travel speed, heat input, etc.) and wall dimensions. During the fabrication process, the SMD built part is subjected repeatedly to high temperature gradients and high heating and cooling rates, resulting in a unique morphology and microstructures usually not observed in conventional fabrication techniques. A finite-element model for the thermal analysis of this deposition process was constructed. The aims of this study are, firstly, to correlate the predicted temperature field to experimental observations to validate the numerical model of this complex process; and secondly, to explain on the basis of the computed temperature and temperature rate the appearance of characteristic microstructures on the top of the walls, and in the substrate and intermediate region. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.status: publishe

Optimization of Multilayered Walls for Building Envelopes Including PCM-Based Composites

This work proposes a numerical procedure to simulate and optimize the thermal response of a multilayered wallboard system for building envelopes, where each layer can be possibly made of Phase Change Materials (PCM)-based composites to take advantage of their Thermal-Energy Storage (TES) capacity. The simulation step consists in solving the transient heat conduction equation across the whole wallboard using the enthalpy-based finite element method. The weather is described in detail by the Typical Meteorological Year (TMY) of the building location. Taking the TMY as well as the wall azimuth as inputs, EnergyPlusTM is used to define the convective boundary conditions at the external surface of the wall. For each layer, the material is chosen from a predefined vade mecum, including several PCM-based composites developed at the Institut für Werkstoffe im Bauwesen of TU Darmstadt together with standard insulating materials (i.e., EPS or Rockwool). Finally, the optimization step consists in using genetic algorithms to determine the stacking sequence of materials across the wallboard to minimize the undesired heat loads. The current simulation-based optimization procedure is applied to the design of envelopes for minimal undesired heat losses and gains in two locations with considerably different weather conditions, viz. Sauce Viejo in Argentina and Frankfurt in Germany. In general, for each location and all the considered orientations (north, east, south and west), optimal results consist of EPS walls containing a thin layer made of the PCM-based composite with highest TES capacity, placed near the middle of the wall and closer to the internal surface.Fil: Fachinotti, Victor Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; ArgentinaFil: Bre, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones en Métodos Computacionales. Universidad Nacional del Litoral. Centro de Investigaciones en Métodos Computacionales; ArgentinaFil: Mankel, Christoph. Universitat Technische Darmstadt; AlemaniaFil: Koenders, Eduardus A. B.. Universitat Technische Darmstadt; AlemaniaFil: Caggiano, Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; Argentin

Early-stage analysis of a novel insulation material based on MPCM-doped cementitious foam: Modelling of properties, identification of production process hotspots and exploration of performance trade-offs

This study presents an early-stage design exploration of NRG-Foam, an innovative insulation material composed of cementitious foam doped with microencapsulated phase change materials (MPCMs). The study comprises the static part that utilizes life cycle assessment and life cycle costing assessment for getting insight into the impacts of the NRG-Foam production process and the dynamic part that identifies the trade-offs between performance characteristics of NRG-Foam using multi-objective optimization. The production of MPCMs was found to be a major contributor to environmental impacts while the addition of small amounts of reduced graphene oxide amplifies the impacts even further. The hot spot analysis pinpointed high electricity consumption as the main driver of environmental impacts. A multi-objective optimization analysis revealed trade-offs between performance characteristics, emphasizing the necessity of compromises during material development. The selection of the MPCM type was shown to be determinative of the final properties of NRG-Foam.Materials and Environmen