Control of heat flux using computationally designed metamaterials

To gain control over the diffusive heat flux in a given domain, one has to design metamaterials with a specifc distribution of the generally anisotropic thermal conductivity throughout the domain. Until now, the appropriate conductivity distribution was usually determined using transformation thermodynamics. By this way, only a few particular cases of heat flux control in simple domains having simple boundary conditions were studied. As a more general approach, we propose to define the heat control problem as an optimization problem where we minimize the error in guiding the heat flux in a given way, taking as design variables the parameters that define the variable microstructure of the metamaterial. Anisotropic conductivity is introduced by using a metamaterial made of layers of two materials with highly dfferent conductivities, the thickness of the layers and their orientation throughout the domain are the current design variables. As an application example we design a device that thermally shields the region it encloses, while it keeps unchanged the flux outside it.Preprin

Optimization-based design of a heat flux concentrator

To gain control over the diffusive heat flux in a given domain, one needs to engineer a thermal metamaterial with a specific distribution of the generally anisotropic thermal conductivity throughout the domain. Until now, the appropriate conductivity distribution was usually determined using transformation thermodynamics. By this way, only a few particular cases of heat flux control in simple domains having simple boundary conditions were studied. Thermal metamaterials based on optimization algorithm provides superior properties compared to those using the previous methods. As a more general approach, we propose to define the heat control problem as an optimization problem where we minimize the error in guiding the heat flux in a given way, taking as design variables the parameters that define the variable microstructure of the metamaterial. In the present study we numerically demonstrate the ability to manipulate heat flux by designing a device to concentrate the thermal energy to its center without disturbing the temperature profile outside it.Peer ReviewedPostprint (published version

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 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

Les bibliothèques scientifiques et les données de la recherche: défis et enjeux

Les données produites lors des activités de recherche sont partie intégrante de l’information scientifique. Traditionnellement, les bibliothèques académiques ont pris en main les activités de gestion des données de recherche (GDR) et les formations auprès des chercheurs. La Suisse, avec un temps de retard sur d’autres pays, lance désormais un projet national, le DLCM, pour créer des solutions adaptées à la gestion des données de recherche tout au long de leur cycle de vie. Elle espère ainsi notamment faire face aux exigences du programme européen Horizon 2020. Dans ce contexte, certains professionnels de l’information, et notamment les bibliothécaires académiques, seront appelés à dispenser des formations à la gestion des données de recherche. Le propos de cette recherche est de fournir des éléments d’analyse pour aider à la prise de décision en vue de prochaines formations de formateurs. A travers une veille sur l’offre internationale de formations à la GDR, nous dressons un panorama analytique de 57 programmes différents ainsi qu’un tableau comparatif synoptique. Un questionnaire destiné aux professionnels de l’information en Suisse a été diffusé, visant à estimer parmi cette population les niveaux d’activités liées à la GDR et les connaissances et compétences déjà acquises ou à développer. Les résultats montrent que les connaissances actuelles sont très hétéroclites, avec des différences parfois extrêmes entre les participants. Néanmoins, la grande majorité d’entre eux a des compétences balbutiantes. Il apparaît que les besoins en formation se dessinent sur un large spectre de thématiques liées à la GDR, plutôt que sur des aspects très précis. 88% des participants estiment qu’ils seront confrontés à la GDR d’ici 5 ans. Des entretiens auprès des collaborateurs responsables du dossier GDR de trois universités romandes (EPFL, UNIGE, UNIL) nous ont permis de déterminer le positionnement de ces dernières en termes de développement de services. La combinaison de ces informations avec celles obtenues à travers l’enquête permet de voir se profiler deux grandes tendances concernant la mise en place de services dans les institutions suisses : il s’agit du développement d’infrastructures et outils et du conseil/formation. Notre recherche aboutit à une esquisse de formation modulaire destinée aux professionnels qui seront en charge de sensibiliser et former les chercheurs et le staff de leurs institutions respectives. Ce canevas de formation comprend trois niveaux, de basique à avancé ; les modules peuvent servir de base pour des workshops, ou, s’ils sont suivis en intégralité, constituer un Certificate of advanced studies en GDR

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

Simulación Interactiva de Dinámica de Fluidos con Transferencia de Calor mediante Métodos de Partículas

Este trabajo esta dedicado a mostrar los primeros resultados obtenidos en simulación de problemas acoplados de dinámica de fluidos y de transferencia de calor usando el método de partículas llamado Smoothed Particle Hydrodynamics (SPH). La técnica empleada consiste en la solución simultánea de las ecuaciones de dinámica de fluidos y de transferencia de calor en formulación Lagrangiana usando una discretización tipo SPH desarrollada en el CIMEC. Aquí se presentan las primeras validaciones del modelo y los primeros ejemplos de su aplicación. En el trabajo se podrá apreciar como influyen los fenómenos de advección en la transferencia de calor. Los ejemplos y el código han sido corridos en una plataforma de simulación también desarrollada en el CIMEC. La plataforma permite cambiar interactivamente propiedades físicas del fluido, condiciones de contorno como el movimiento de paredes, o su temperatura, todo ello interactivamente mientras transcurre la simulación. El desarrollo permitirá la solución y simulación interactiva de variados e interesantes problemas de convección natural y transferencia de calor.Fil: Limache, Alejandro Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico Para la Industria Química (i); ArgentinaFil: Rojas Fredini, Pablo Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico Para la Industria Química (i); ArgentinaFil: Fachinotti, Victor Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico Para la Industria Química (i); Argentin

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

A computational multi-objective optimization method to improve energy efficiency and thermal comfort in dwellings

In the last years, multi-objective optimization techniques became into one of the main challenges of the building energy efficiency area. The objective of this paper is to develop and validate a computational code for multi-objective building performance optimization by linking an evolutionary algorithm and a building simulation software in a powerful cluster. A sophisticated version of the multi-objective Non-dominated Sorting Genetic Algorithm-II (NSGA-II) was implemented in Python code to determine the optimal building design, which allows working with categorical and discrete variables, and the objectives were evaluated using the building energy simulation software EnergyPlus. NSGA-II was implemented to run in a high-performance cluster for the parallel computing of the fitness of each population (set of possible designs). In this work, the strengths of the proposed method were demonstrated by its application to the optimal design of a typical single-family house, located in the Argentine Littoral region. This house has some rooms conditioned only by natural ventilation, and other rooms with natural ventilation supplemented by mechanical air-conditioning (hybrid ventilation). The most influential design variables like roof types, external and internal wall types, solar orientation, solar absorptance, size, type, and windows shading of this house among others were studied in two complex cases of 108 and 1016 possibilities to obtain the best trade-off (Pareto front) between heating and cooling performance. Finally, a decision-making method was applied to select one configuration of the Pareto front. Optimal simulation results for the study cases indicated that is possible to improve up to 95% the thermal comfort in naturally ventilated rooms and up to 82% energy performance in air-conditioned rooms of the building with respect to the original configuration by using a design that takes simultaneous advantage of passive strategies like thermal inertia and natural ventilation. The methodology was proved to give a robust and powerful tool to design efficient dwellings reducing the optimization time from almost 12 days to 4.4 h.Fil: 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; Argentina. Universidad Tecnológica Nacional. Facultad Regional Concepción del Uruguay; ArgentinaFil: 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; Argentin