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See detailSubproblem Approach for Modeling Multiply Connected Thin Regions with an h-Conformal Magnetodynamic Finite Element Formulation
Dang, Quoc Vuong ULg; Dular, Patrick ULg; Vazquez Sabariego, Ruth ULg et al

in European Physical Journal : Applied physics (2013), in press

A subproblem h-conformal eddy current nite element method is proposed for correcting the inaccuracies inherent to thin shell models. Such models replace volume thin regions by surfaces but neglect border ... [more ▼]

A subproblem h-conformal eddy current nite element method is proposed for correcting the inaccuracies inherent to thin shell models. Such models replace volume thin regions by surfaces but neglect border e ects in the vicinity of their edges and corners. The developed surface-to-volume correction problem is de ned as a step of the multiple subproblems that can split a complete problem, consisting of inductors and magnetic or conducting regions, some of these being thin regions. The general case of multiply connected thin regions is considered [less ▲]

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See detailSubproblem h-Conform Formulation for Accurate Thin Shell Models Between Conducting and Nonconducting Regions
Dang, Quoc Vuong ULg; Dular, Patrick ULg; Vazquez Sabariego, Ruth ULg et al

in Proceeding of the 9th International Symposium on Electric and Magnetic Fields, EMF 2013 (2013, April 23)

A subproblem method (SPM) with h-formulation is developed for correcting the inaccuracies near edges and corners that arise from using thin shell (TS) models to replace thin volume regions by surfaces ... [more ▼]

A subproblem method (SPM) with h-formulation is developed for correcting the inaccuracies near edges and corners that arise from using thin shell (TS) models to replace thin volume regions by surfaces. The developed surface-to-volume correction problem is defined as a step of multiple SPs, with inductors and magnetic or conducting regions, some of them being thin. The TS model assumes that the fields in the thin regions are approximated by a priori 1-D analytical distributions along the shell thickness (C. Geuzaine et al., “Dual formulations for the modeling of thin electromagnetic shells using edge elements,” IEEE Trans. Magn., vol. 36, no. 4, pp. 799–802, 2000). Their interior is not meshed and ratherextracted from the studied domain, which is reduced to a zero-thickness double layer with interface conditions (ICs) linked to 1-D analytical distributions that however neglect end and curvature effects. This leads to inaccuracies near edges and corners that increase with the thickness. To cope with these difficulties, the authors have recently proposed a SPM based on the h-formulation for a thin region located between non-conducting regions (Vuong Q. Dang et al., “Subproblem Approach for Thin Shell Dual Finite Element Formulations”, IEEE Trans. Magn., vol. 48, no. 2, pp. 407–410, 2012). The magnetic field h is herein defined in nonconducting regions by means of a magnetic scalar potential , i.e. h = -grad{\phi} , with discontinuities of through the TS. In this paper, the SPM is extended to account for thin regions located between conducting regions or between conducting and nonconducting regions, in the general case of multiply connected regions. In these regions, the potential is not defined anymore on both sides of the TS and the problem has to be expressed in terms of the discontinuities of h, possibly involving on one side only, to be strongly defined via an IC through the TS. In the proposed SP strategy, a reduced problem with only inductors is first solved on a simplified mesh without thin and volume regions. Its solution gives surface sources (SSs) as ICs for added TS regions, and volume sources (VSs) for possible added volume regions. The TS solution is further improved by a volume correction via SSs and VSs that overcome the TS assumptions, respectively suppressing the TS model and adding the volume model. Each SP has its own separate mesh, which increases the computational efficiency. Details on the proposed method will be given in the extended paper, with practical applications. [less ▲]

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See detailA Computational Homogenization Method for the Evaluation of Eddy Current in Nonlinear Soft Magnetic Composites
Niyonzima, Innocent ULg; Vazquez Sabariego, Ruth ULg; Dular, Patrick ULg et al

in Proceeding of the 9th International Symposium on Electric and Magnetic Fields, EMF 2013 (2013, April 23)

The use of the soft magnetic composite (SMC) in electric devices has increased in recent years. These materials made from a metallic powder compacted with a dielectric binder are a good alternative to ... [more ▼]

The use of the soft magnetic composite (SMC) in electric devices has increased in recent years. These materials made from a metallic powder compacted with a dielectric binder are a good alternative to laminated ferromagnetic structures as their granular mesoscale structure allows to significantly reduce the eddy current losses. Furthermore unlike the laminated ferromagnetic structures, SMC exhibit isotropic magnetic properties what makes them good candidates for manufacturing machines with 3D flux paths. The isotropy of the thermal conductivity also allows for a more efficient heat dissipation. The use of classical numerical methods such as the finite element method to study the behavior of SMC is computational very expensive. Indeed a very fine mesh would be required in order to capture fine scale variations i.e. variations at level of metallic grains whence the use of multiscale methods for modelling SMC. The application of multiscale method to study the behaviour of SMC is relatively recent. In (A. Bordianu et al “A Multiscale Approach to Predict Classical Losses in Soft Magnetic Composites”, IEEE Trans. Mag., vol. 48, no. 4, 2012.), the authors used a homogenization technique to compute electrical and magnetic constitutive laws on a representative volume element (RVE). These laws were then used in finite element computations. Herein, the RVE has been chosen to account for the grain- grain contact that can occur in a actual SMC structure due to the compaction process and that can lead to the appearance of macroscale eddy currents. In this paper, we will extend the computational homogenization method success- fully used for modelling the behaviour of laminated ferromagnetic cores in mag- netodynamics (I. Niyonzima et al “Computational Homogenization for Laminated Ferromagnetic Cores in Magnetodynamics”, in Proc. of the 15th Biennal Confer- ence on Electromagnetic Field Computation, 2012) to the case of SMC. The method is based on the heterogeneous multiscale method (HMM) and couples two types of problems: a macroscale problem that captures the slow variations of the overall so- lution and many microscale problems that allow to determine the constitutive laws at the macroscale. The choice of RVE will also be discussed. [less ▲]

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See detailDual Formulations for Accurate Thin Shell Models in a Finite Element Subproblem Method
Dang, Quoc Vuong ULg; Dular, Patrick ULg; Vazquez Sabariego, Ruth ULg et al

in Proceeding of the 19th COMPUMAG Conference on the Computation of Electromagnetic Fields, 2013 (2013, April 01)

A subproblem finite with dual finite element magnetostatic and magnetodynamic formulations is developed for correcting the inaccuracies near edges and corners coming from thin shell models, that replace ... [more ▼]

A subproblem finite with dual finite element magnetostatic and magnetodynamic formulations is developed for correcting the inaccuracies near edges and corners coming from thin shell models, that replace thin volume regions by surfaces. The surface-to-volume correction problem is defined as one of the multiple subproblems applied to a complete problem, considering successive additions of inductors and magnetic or conducting regions, some of these being thin regions. Each SP requires a proper adapted mesh of its regions, which facilitates meshing and increases computational e ciency. [less ▲]

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See detailAccurate h-Conform Finite Element Model of Multiply Connected Thin Regions via a Subproblem Method
Dang, Quoc Vuong ULg; Dular, Patrick ULg; Vazquez Sabariego, Ruth ULg et al

in Proceedings of the 15th Biennial IEEE Conference on Electromagnetic Field Computation (CEFC2012) (2012, November)

A subproblem method for solving eddy current finite element is developed to correct the inaccuracies near edges and corners arising from thin shell models. Such models replace thin volume regions by ... [more ▼]

A subproblem method for solving eddy current finite element is developed to correct the inaccuracies near edges and corners arising from thin shell models. Such models replace thin volume regions by surfaces but neglect border effects in the vicinity of their edges and corners. A thin shell solution, performed by a simplified mesh near the thin structures, serves as a source of a correction problem consisting of the actual volume thin regions alone and concentrating the meshing effort on the thin regions. The general case of multiply connected thin regions is considered. [less ▲]

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See detailComputational Homogenization for Laminated Ferromagnetic Cores in Magnetodynamics
Niyonzima, Innocent ULg; Vazquez Sabariego, Ruth ULg; Henrotte, François et al

in Proceedings of the 15th Biennial IEEE Conference on Electromagnetic Field Computation (CEFC2012) (2012, November)

In this paper, we investigate the modeling of fer- romagnetic multiscale materials. We propose a computational homogenization method based on the heterogeneous multiscale method (HMM) that includes eddy ... [more ▼]

In this paper, we investigate the modeling of fer- romagnetic multiscale materials. We propose a computational homogenization method based on the heterogeneous multiscale method (HMM) that includes eddy currents and hysteretic losses at the mesoscale. The HMM comprises: 1) a macroscale problem that captures the slow variations of the overall solution; 2) many microscale problems that allow to determine the constitutive law at the macroscale. As application example, a laminated iron core is considered. [less ▲]

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See detailHomogenisation of Windings and Laminations in Time-Domain Finite-Element Modeling of Electrical Machines
Gyselinck, Johan; Geuzaine, Christophe ULg; Vazquez Sabariego, Ruth ULg

in Proceedings of the 15th Biennial IEEE Conference on Electromagnetic Field Computation (CEFC2012) (2012, November)

This paper deals with time-domain homogenisation of multi-turn windings and laminated cores in 2D and 3D finite- element (FE) modelling of rotating electrical machines. Herein the number of additional ... [more ▼]

This paper deals with time-domain homogenisation of multi-turn windings and laminated cores in 2D and 3D finite- element (FE) modelling of rotating electrical machines. Herein the number of additional degrees of freedom (auxiliary field variables) in the homogenised regions can be fixed depending on the extent of the eddy current effects and on the desired accuracy. The homogenisation technique is illustrated and validated by means of a 2D model of a switched reluctance motor. Global quantities, such as the phase impedance, converge very well to those produced by a precise but very expensive 3D model. [less ▲]

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See detailTime-domain finite-element modelling of laminated iron cores – Large skin effect homogenization considering the Jiles-Atherton hysteresis model
Vazquez Sabariego, Ruth ULg; Niyonzima, Innocent ULg; Geuzaine, Christophe ULg et al

in Proceedings of the 15th Biennial IEEE Conference on Electromagnetic Field Computation (CEFC2012) (2012, November)

This paper deals with the incorporation of the Jiles- Atherton (J-A) hysteresis model in a time-domain finite-element homogenization technique for laminated iron cores. The separate discretization of each ... [more ▼]

This paper deals with the incorporation of the Jiles- Atherton (J-A) hysteresis model in a time-domain finite-element homogenization technique for laminated iron cores. The separate discretization of each lamination is avoided by using dedicated skin-effect basis functions, which also serve to interpolate the J- A hysteretic material law. As validation test case, a stacked ring core surrounded by a toroidal coil is considered. [less ▲]

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See detailSubproblem h-Conform Magnetodynamic Finite Element Formulation for Accurate Model of Multiply Connected Thin Regions
Dang, Quoc Vuong ULg; Dular, Patrick ULg; Vazquez Sabariego, Ruth ULg et al

in Proceedings of the 7th European Conference on Numerical Methods in Electromagnetism (NUMELEC 2012) (2012, July 03)

A subproblem $\vh$-conform eddy current finite element method is proposed for correcting the inaccuracies inherent to thin shell models. Such models replace volume thin regions by surfaces but neglect ... [more ▼]

A subproblem $\vh$-conform eddy current finite element method is proposed for correcting the inaccuracies inherent to thin shell models. Such models replace volume thin regions by surfaces but neglect border effects in the vicinity of their edges and corners. The developed surface-to-volume correction problem is defined as a step of the multiple subproblems applied to a complete problem, consisting of inductors and magnetic or conducting regions, some of these being thin regions. The general case of multiply connected thin regions is considered. [less ▲]

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See detailMultiscale Quasistatic Homogenization for Laminated Ferromagnetic Cores
Niyonzima, Innocent ULg; Vazquez Sabariego, Ruth ULg; Dular, Patrick ULg et al

in Proceedings of the 7th European Conference on Numerical Methods in Electromagnetism (NUMELEC 2012) (2012, July 03)

In this paper, we investigate the modeling of ferromagnetic multiscale materials. We propose a computational homogenization method based on the heterogeneous multiscale method (HMM) with inclusion of a ... [more ▼]

In this paper, we investigate the modeling of ferromagnetic multiscale materials. We propose a computational homogenization method based on the heterogeneous multiscale method (HMM) with inclusion of a hysteresis model. The HMM involves: 1) a macroscale problem that captures the slow variations of the overall solution; 2) many microscale problems that allow to determine the constitutive law at the macroscale. At the microscale, a novel energy consistent hystere- sis model is incorporated. As application example, a laminated iron core is considered. [less ▲]

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See detailONELAB: Open Numerical Engineering LABoratory
Geuzaine, Christophe ULg; Henrotte, F.; Marchandise, E. et al

in Proceedings of the 7th European Conference on Numerical Methods in Electromagnetism (NUMELEC2012) (2012, July)

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See detailA dynamical model with hysteresis for the homogenization of ferromagnetic laminated cores
Henrotte, F.; Niyonzima, Innocent ULg; Steentjes, S. et al

in Proceedings of the 7th European Conference on Numerical Methods in Electromagnetism (NUMELEC2012) (2012, July)

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See detailSubproblem Approach for Thin Shell Dual Finite Element Formulations
Dang, Quoc Vuong ULg; Dular, Patrick ULg; Vazquez Sabariego, Ruth ULg et al

in IEEE Transactions on Magnetics (2012), 48(2), 407-410

A subproblem technique is applied to dual thin shell finite element formulations. Both the magnetic vector potential and magnetic field formulations are considered. The subproblem approach developed ... [more ▼]

A subproblem technique is applied to dual thin shell finite element formulations. Both the magnetic vector potential and magnetic field formulations are considered. The subproblem approach developed herein couples three problems: a simplified model with only inductors, a thin region problem using approximate interface conditions and a correction problem to improve the accuracy of the thin shell approximation, in particular near their edges and corners. Each problem has its own geometry and is solved on its associated finite element mesh. [less ▲]

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See detailA Finite Element Subproblem Method for Position Change Conductor Systems
Dular, Patrick ULg; Krähenbühl, Laurent; Vazquez Sabariego, Ruth ULg et al

in IEEE Transactions on Magnetics (2012), 48(2), 403-406

Analyses of magnetic systems with position changes of both massive and stranded conductors are performed via a finite element sub- problem method. A complete problem is split into subproblems associated ... [more ▼]

Analyses of magnetic systems with position changes of both massive and stranded conductors are performed via a finite element sub- problem method. A complete problem is split into subproblems associated with each conductor and the magnetic regions. Each complete solution is then expressed as the sum of subproblem solutions supported by different meshes. The subproblem procedure simplifies both meshing and solving processes, with no need of remeshing, and accurately quantifies the effect of the position changes of conductors on both local fields, e.g., skin and proximity effects, and global quantities, e.g., inductances and forces. Applications covering parameterized analyses on conductor positions to moving conductor systems can benefit from the developed approach. [less ▲]

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See detailTime-domain surface impedance boundary conditions enhanced by coarse volume finite-element discretisation
Vazquez Sabariego, Ruth ULg; Geuzaine, Christophe ULg; Dular, Patrick ULg et al

in IEEE Transactions on Magnetics (2012), 48(2), 631-634

In computational magnetodynamics, surface impedance boundary conditions allow to accurately account for high-frequency flux components while removing the massive conducting regions from the computation ... [more ▼]

In computational magnetodynamics, surface impedance boundary conditions allow to accurately account for high-frequency flux components while removing the massive conducting regions from the computation domain. The time-domain approach previously proposed by the authors relies on the spatial discretisation of a 1-D eddy-current problem by means of dedicated basis functions derived from the analytical frequency-domain solution. In this paper, these time-domain impedance conditions are combined with a coarse volume finite-element discretisation of the massive conductors to capture slowly varying flux components. The accuracy of the hybrid approach can further be improved by introducing a fictitious frequency-dependent conductivity. The method is illustrated and validated by means of 1-D and 2-D test cases in the frequency and time domain. [less ▲]

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See detailComputation of induced fields into the human body by dual Finite Element formulations
Scorretti, R.; Vazquez Sabariego, Ruth ULg; Morel, L. et al

in IEEE Transactions on Magnetics (2012), 48(2), 783-786

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See detailStochastic uncertainty quantification of eddy currents in the human body by polynomial chaos decomposition
Gaignaire, R.; Scorretti, R.; Vazquez Sabariego, Ruth ULg et al

in IEEE Transactions on Magnetics (2012), 48(2), 451-454

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See detailFinite Element Computational Homogenization for Heterogeneous Materials in Magnetodynamics
Niyonzima, Innocent ULg; Vazquez Sabariego, Ruth ULg; Dular, Patrick ULg et al

in Proceedings of the Fifth International Conference on Advanced COmputational Methods in ENgineering (ACOMEN 2011) (2011, November)

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See detailA Pluto-like radius and a high albedo for the dwarf planet Eris from an occultation
Sicardy, B.; Ortiz, J. L.; Assafin, M. et al

in Nature (2011), 478

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 ... [more ▼]

The dwarf planet Eris is a trans-Neptunian object with an orbital eccentricity of 0.44, an inclination of 44 degrees and a surface composition very similar to that of Pluto. It resides at present at 95.7 astronomical units (1AU is the Earth-Sun distance) from Earth, near its aphelion and more than three times farther than Pluto. Owing to this great distance, measuring its size or detecting a putative atmosphere is difficult. Here we report the observation of a multi-chord stellar occultation by Eris on 6 November 2010 UT. The event is consistent with a spherical shape for Eris, with radius 1,163+/-6kilometres, density 2.52+/-0.05 grams per cm[SUP]3[/SUP] and a high visible geometric albedo, . No nitrogen, argon or methane atmospheres are detected with surface pressure larger than ~1nanobar, about 10,000 times more tenuous than Pluto's present atmosphere. As Pluto's radius is estimated to be between 1,150 and 1,200 kilometres, Eris appears as a Pluto twin, with a bright surface possibly caused by a collapsed atmosphere, owing to its cold environment. We anticipate that this atmosphere may periodically sublimate as Eris approaches its perihelion, at 37.8 astronomical units from the Sun. [less ▲]

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See detailSubproblem finite element method for magnetic model refinements
Dular, Patrick ULg; Ferreira da Luz, Mauricio V.; Kuo-Peng, Patrick et al

in Proceedings of the XV International Symposium on Electromagnetic Fields in Mechatronics, Electrical and Electronic Engineering (ISEF2011) (2011, September)

Model refinements of magnetic circuits are performed via a subproblem finite element method. A complete problem is split into subproblems with overlapping meshes, to allow a progression from source to ... [more ▼]

Model refinements of magnetic circuits are performed via a subproblem finite element method. A complete problem is split into subproblems with overlapping meshes, to allow a progression from source to reaction fields, ideal to real flux tubes, 1-D to 2-D to 3-D models, perfect to real materials, with any coupling of these changes. Its solution is the sum of the subproblem solutions. The procedure simplifies both meshing and solving processes, and quantifies the gain given by each refinement on both local fields and global quantities. [less ▲]

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