Teaching co-simulation basics through practice

International audienceCyber-physical system representation is one of the current challenges in Modeling and Simulation. In fact, multi-domain modeling requires new approaches to rigorously deal with it. Co-simulation, one of the approaches, lets modelers use several M&S tools in collaboration. The challenge is to find a way to enable co-simulation use for non-IT experts while being aware of assumptions and limitations involved. This paper deals with co-simulation basic principles teaching through practice. we propose an iterative and modular co-simulation process supported by a DSL-based environment for the MECSYCO co-simulation platform. Through a thermal use case, we are able to introduce co-simulation in a 4 hours tutorial destined to our students. Efficient energy management is one of this century challenges. The current trend to deal with it is to build cyber-physical system (CPS) [Kleissl and Agarwal, 2010]. CPS are physical systems monitored and supervised by one or several computers through a communication networks [Ra-jkumar et al., 2010]. Smart-grids are examples of CPS where the energy network is coupled with a communication network to enable remote monitoring and control. The Modeling and Simulation (M&S) of such systems is one of the current challenges in M&S due to the inter-disciplinary issues they raise. It requests the development of new methods which deal with multi-domain by integrating each expert point of view in the same rigorous and efficient M&S activity. Co-simulation [Gomes et al., 2018] is a way to achieve it

Teaching co-simulation basics through practice

International audienceCyber-physical system representation is one of the current challenges in Modeling and Simulation. In fact, multi-domain modeling requires new approaches to rigorously deal with it. Co-simulation, one of the approaches, lets modelers use several M&S tools in collaboration. The challenge is to find a way to enable co-simulation use for non-IT experts while being aware of assumptions and limitations involved. This paper deals with co-simulation basic principles teaching through practice. we propose an iterative and modular co-simulation process supported by a DSL-based environment for the MECSYCO co-simulation platform. Through a thermal use case, we are able to introduce co-simulation in a 4 hours tutorial destined to our students. Efficient energy management is one of this century challenges. The current trend to deal with it is to build cyber-physical system (CPS) [Kleissl and Agarwal, 2010]. CPS are physical systems monitored and supervised by one or several computers through a communication networks [Ra-jkumar et al., 2010]. Smart-grids are examples of CPS where the energy network is coupled with a communication network to enable remote monitoring and control. The Modeling and Simulation (M&S) of such systems is one of the current challenges in M&S due to the inter-disciplinary issues they raise. It requests the development of new methods which deal with multi-domain by integrating each expert point of view in the same rigorous and efficient M&S activity. Co-simulation [Gomes et al., 2018] is a way to achieve it

The effect of corporate governance on stock repurchases: evidence from Sweden

Research Question/Issue: The paper examines whether corporate governance differences affect firms' stock repurchasing behaviour. Previous hypotheses on stock repurchases, well-supported by US data, are based on assumptions of managerial autonomy that might not be descriptive in corporate governance systems characterised by influential controlling shareholders such as the Swedish. Firm-level corporate governance arrangements may also affect firms' incentives to repurchase stock. Research Findings/Insights: Stock-repurchasing patterns among Swedish firms differ from those previously observed among US firms. The findings indicate that Swedish firms do not repurchase stock to distribute excess cash, signal undervaluation or fend off takeovers. Stock repurchases are made in addition to dividends and thus do not substitute for them. Firm-level corporate governance arrangements directly affect stock repurchasing behaviour. Firms without a dominant controlling owner seem to use stock repurchases to increase leverage. The existence of a dominant controlling shareholder diminishes the propensity for stock repurchases, while cross listing on a US or UK stock market increases that propensity. Theoretical/Academic Implications: The findings suggest that corporate governance differences affect stock repurchasing behaviour. The agency-theoretical view of the firm, on which the leading hypotheses on stock repurchases are based, accurately predicts stock repurchases only in certain institutional and governance settings. Practitioner/Policy Implications: The study suggests that differences in national and firm-level corporate governance must be taken into account in order to accurately assess outcomes of regulatory reforms and/or harmonisation attempts

Études des actions des forces magnétiques volumiques créées par un champ magnétique intense sur des fluides à seuil - possibilités de transition solide-gel

Les fluides à seuil ont des propriétés mécaniques étonnantes : en dessous d'une certaine contrainte, appelée contrainte seuil, le fluide se comporte comme un solide. Au-delà de la contrainte seuil, ils s'écoulent comme un gel. Ce mémoire porte sur l'étude des actions des forces magnétiques volumiques sur ces fluides. Nous étudions la possibilité de réaliser la transition solide-gel à partir des forces magnétiques volumiques créées par différents dispositifs magnétiques. Ces fluides n'ont pas de propriétés magnétiques particulières. Il est donc nécessaire de créer des champs magnétiques intenses pour agir sans contact sur ces fluides. Nous étudions différentes configurations magnétiques capables de dépasser la contrainte seuil au sein du fluide. L'influence des différents paramètres des configurations magnétiques est explorée, notamment à l'aide d'études paramétriques. Notre travail mêle des équations de magnétostatique et de mécanique des fluides non-newtoniens. Les calculs de magnétostatique sont menés de façon analytique alors que la partie mécanique et le couplage magnéto-mécanique sont traités par un logiciel de simulation numérique par la méthode des éléments finis. Les conditions magnétiques et mécaniques nécessaires à la transition solide-gel et à la modification d'écoulements de fluides à seuil sont discutées, notamment à l'aide de simulations numériques et de nombres adimensionnelsYield stress fluids have amazing mechanical properties: below a particular shear stress, called yield stress, the fluid behaves like a solid. Once the yield stress is exceeded, they flow like a viscous fluid or a gel. This thesis deals with the effects of magnetic volume forces on these fluids. We study the opportunity of the solid-gel transition from magnetic volume forces created by various magnetic devices. These fluids have no special magnetic properties. It is therefore necessary to create intense magnetic fields to act without contact on these fluids. We study different magnetic configurations that are able to exceed the yield stress in the fluid. The influences of different parameters of the magnetic configurations is explored, including using parametric studies. Our work combine equations of magnetostatic and non-newtonian fluid mechanics. Magnetostatic calculations are carried out analytically, while the mechanical and magneto-mechanical coupling are processed by a finite element analysis software. Magnetic and mechanical conditions required to the solid-gel transition and to the modification of yield stress fluids flows are discussed, using numerical simulations and dimensionless numbersMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Dimensionnement d'un moteur supraconducteur HTc

L'apparition des supraconducteurs à hautes températures (HTc) a permis un développement continu des moteurs supraconducteurs. Ces dispositifs supraconducteurs permettent d'obtenir des puissances et des couples massiques et volumiques très élevés, et sont des alternatives intéressantes aux machines conventionnelles. Le dimensionnement des ces moteurs nécessite une bonne connaissance des caractéristiques électromagnétiques, thermiques et mécaniques des supraconducteurs HTc. Ainsi, le travail présenté ici traite du dimensionnement de machines HTc avec la prise en compte des contraintes liées aux fils supraconducteurs. Le manuscrit débute par une étude bibliographique approfondie dans laquelle trois points sont abordés : les fils supraconducteurs, description des réalisations remarquables de machines HTc de fortes puissances et une analyse statistique sur ces réalisations. Ensuite, la caractérisation DC des fils supraconducteurs HTc et la détermination de leurs pertes AC sous champ variable sont abordées. Des méthodes numériques sont utilisées pour la modélisation et les résultats obtenus sont comparés à ceux de l'expérience. La dernière partie aborde le dimensionnement électromagnétique de moteurs supraconducteurs HTc par des méthodes analytiques et numériques, avec la prise en compte des contraintes liées aux courants critiques dans les bobinages. Les premiers résultats concernant le dimensionnement électromagnétique et thermique d'une structure de machine synchrone supraconductrice à pôles saillants sont donnés. Les solutions techniques envisagées sont largement commentéesThe appearance of high-temperature superconductors (HTS) has led to a continuous development of superconducting motors. These superconducting devices allow high power and torque densities, so they constitute and novel alternative to conventional motors. The design of such motors requires a deep knowledge of the electromagnetic, thermal and mechanical characteristics of the HTS materials. Hence, the work presented here is related to the design of HTS motors which includes the constraints due to the HTS conductors. The manuscript begins with an extensive literature review where three main points are discussed, viz. HTS conductors, already constructed HTS motors and statistical analysis on these achievements. The dc characterization of HTS superconductors as well as their ac losses under time varying magnetic fields are theoretically and experimentally studied. In so doing, numerical techniques are used and the obtained results are compared the measurements. The last part deals with the design of HTS motors by analytical and finite element methods. A particular attention is given to the constraints introduced by the use of HTS materials. The first results of the electromagnetic and thermal design of a salient pole HTS synchronous machine are provided with the emphasis of the adopted technical solutionsMETZ-SCD (574632105) / SudocNANCY1-Bib. numérique (543959902) / SudocNANCY2-Bibliotheque electronique (543959901) / SudocNANCY-INPL-Bib. électronique (545479901) / SudocSudocFranceF

Axial-Field Eddy-Current Couplings: a 3D Test Problem for Numerical Experiments

International audienceThis paper deals with a device which is particularly relevant to test 3D quasi-static magnetic numerical computations: axial eddy-current couplings. It consists in two rotors, a driving and a driven one. The driving rotor is made with a ring of magnets, alternating north and south poles, glued on an iron yoke. The driven one is constituted by only a copper ring and another yoke. The rotating permanent magnets induces eddy currents in copper, producing an electromagnetic torque and the rotation of the copper side. The phenomena are analogous to those existing in an induction machine. This application is a really interesting test case because of the following advantages: 1. Its geometry is purely 3D but simple. It can be meshed with structured or unstructured grid and includes anti-periodic symmetries. 2. The eddy currents due to movement can be treated without remeshing. 3. There are two kinds of field sources: magnets and eddy-currents. 4. The simplicity of the device permits to easily build prototypes and to obtain experimental measurements needed to validate computational results. The authors had performed several numerical FEM computations on this particular device. The eddy currents problem is solved thanks to two classical formulations based on magnetic vector and scalar potentials, i.e. (a, v) and (h e , φ). The general GPL solver GetDP had been chosen because it really suits to our weak formulations. A comparison between these two formulations has been performed. Problems can be solved both considering a linear b(h) relationship, or a more realistic curve. A special focus is put on the electromagnetic torque evaluation thanks to three post-processing computations: Laplace forces (L-F), average Maxwell stress tensor in the airgap (M-T), and global Joule losses (J-L). Results are compared with experimental measurements made on a magnetic transmission already designed and built by ourselves

Schéma de co-simulation pour l'équilibrage des échanges d'énergie dans un micro-réseau

International audienceThe design and management of physical systems, and particularly of microgrids, require models and simulators related to the telecommunication, energy or decision domains; it is a privileged context for co-simulation. However, the structure of the interactions between physical models is conditioned by the decision system and leads to modifications in the implemented multi-model.We show that an ad-hoc treatment limits iterative and modular approaches. We propose a (multi-)modeling of the problem that allows to easily implement co-simulations of microgrids testing different network and decision system configurations.After highlighting the problem from examples, we present our contribution and illustrate its interest by taking the examples in the middleware framework Mecsyco.Le dimensionnement et la gestion de systèmes physiques, et particulièrement de microgrilles, nécessitent l'utilisation de modèles et de simulateurs relatifs aux domaines de télécommunication, énergétique ou décisionnel ; c'est un contexte privilégié pour la cosimulation. Cependant l'essence même des interactions entre modèles physiques, conditionnée par un système décisionnel, peut entrainer des modifications dans le multi-modèle implémenté. Nous montrons ici qu'un traitement ad-hoc limite l'approche itérative et modulaire.Nous proposons une (multi-)modélisation du problème qui permet de manière aisée de réaliser des co-simulations de microgrid testant différentes configurations de réseaux et de système de décision. Après avoir mis en évidence le problème à partir d'exemples représentatifs, nous présentons notre contribution puis illustrons son intérêt en reprenant les exemples dans le cadre de l'intergiciel MECSYCO

Three dimensional pole shape optimization of claw pole machines based on a hybrid model

International audienceThis paper deals with the shape optimization of the claws of a claw-pole synchronous machine. A hybrid model combining 3D FEM and Permeance Network is developed for this purpose. The optimization of the average torque with fixed stator geometry is performed using Mesh Adaptative Direct Search methods. The developed methodology has led to improve the performances of claw-pole synchronous machines used in mild-hybrid vehicles