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Finite Element Computational Homogenization of Nonlinear Multiscale Materials in Magnetostatics Niyonzima, Innocent ; V Sabariego, Ruth ; Dular, Patrick et al in IEEE Transactions on Magnetics (2012), 48(2), 587-590 The increasing use of composite materials in the technological industry (automotive, aerospace, ...) requires the development of effective models that account for the complexity of the microstructure of ... [more ▼] The increasing use of composite materials in the technological industry (automotive, aerospace, ...) requires the development of effective models that account for the complexity of the microstructure of these materials and the nonlinear behaviour they can exhibit. In this paper we develop a multiscale computational homogenization method for modelling nonlinear multiscale materials in magnetostatics based on the finite element method. The method solves the macroscale problem by getting data from certain microscale problems around some points of interest. The missing nonlinear constitutive law at the macroscale level is derived through an upscaling from the microscale solutions. The downscaling step consists in imposing a source term and determining proper boundary conditions for microscale problems from the macroscale solution. For a two-dimensional geometry, results are validated by comparison with those obtained with a classical brute force finite element approach and a classical homogenization technique. The method provides a good overall macroscale response and more accurate local data around points of interest. [less ▲] Detailed reference viewed: 135 (31 ULg)Influence of contact resistance on shielding efficiency of shielding gutters for high-voltage cables ; ; V Sabariego, Ruth et al in IET Electric Power Applications (2011), 5(9), 715-720 The shielding of buried three-phase high-voltage power lines can be done by placing them in conducting ferromagnetic U-shaped gutters covered with plates. In case of a perfect electrical contact between ... [more ▼] The shielding of buried three-phase high-voltage power lines can be done by placing them in conducting ferromagnetic U-shaped gutters covered with plates. In case of a perfect electrical contact between adjacent gutters and between adjacent cover plates, induced currents in the shield efficiently reduce the magnetic field generated by the cables. As however a perfect contact cannot be guaranteed, in practice, it is useful to quantify the effect of a defective electrical contact on the field reduction. From two-dimensional/three-dimensional finite element computations and experiments, the influence of the contact resistance on the shielding efficiency is investigated, as a function of the ratio of axial length to height of the shield elements. Furthermore, the effect of other parameters on the shielding efficiency is studied: the ratio of axial length to height, a parasitic air gap between the gutter and the cover plate and the type of the shield material. It was found that a low contact resistance deteriorates much more the shielding in case of an aluminium shield than in case of a steel shield. As expected, the effect is larger for shield elements with relatively short axial length with regard to the other dimensions. Nevertheless, the effect remains quite significant for aluminium shields with practically convenient dimensions. [less ▲] Detailed reference viewed: 71 (8 ULg)Subproblem method with dual finite element formulations for accurate thin shell models Dang, Quoc Vuong ; Dular, Patrick ; V Sabariego, Ruth et al in Proceedings of the XV International Symposium on Electromagnetic Fields in Mechatronics, Electrical and Electronic Engineering (ISEF2011) (2011, September) A subproblem method with dual finite element magnetostatic and magnetodynamic formulations is developed to correct the inaccuracies near edges and corners coming from thin shell models, that replace thin ... [more ▼] A subproblem method with dual finite element magnetostatic and magnetodynamic formulations is developed to correct 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 subproblem is independently solved on its own domain and mesh, which facilitates meshing and solving while controlling the importance and usefulness of each correction. Parameterized analyses of thin regions are efficiently performed. [less ▲] Detailed reference viewed: 136 (35 ULg)Subproblem Approach for Thin Shell Dual Finite Element Formulations Dang, Quoc Vuong ; Dular, Patrick ; V Sabariego, Ruth et al in Proceedings of the 18th Conference on the Computation of Electromagnetic Fields (COMPUMAG2011) (2011, July) A subproblem technique is applied on dual formu- lations to the solution of thin shell finite element models. Both the magnetic vector potential and magnetic field formulations are considered. The ... [more ▼] A subproblem technique is applied on dual formu- lations to the solution of thin shell finite element models. Both the magnetic vector potential and magnetic field formulations are considered. The subproblem approach developed herein couples three problems: a simplified model with inductors alone, 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 is solved on its own independently defined geometry and finite element mesh. [less ▲] Detailed reference viewed: 93 (25 ULg)A Finite Element Subproblem Method for Position Change Conductor Systems Dular, Patrick ; ; V Sabariego, Ruth et al (2011, July) Analyses of magnetic circuits with position changes of both massive and stranded conductors are performed via a finite element subproblem method. A complete problem is split into subproblems associated ... [more ▼] Analyses of magnetic circuits with position changes of both massive and stranded conductors are performed via a finite element subproblem 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 benefit from the developed approach. [less ▲] Detailed reference viewed: 24 (4 ULg)Finite Element Computational Homogenization of Nonlinear Multiscale Materials in Magnetostatics Niyonzima, Innocent ; V Sabariego, Ruth ; Dular, Patrick et al in 18th Conference on the Computation of Electromagnetic Fields (COMPUMAG2011) (2011) This paper deals with the modelling of nonlinear multiscale materials in magnetostatics by means of a finite element computational homogenization method. The method couples a macroscale problem with many ... [more ▼] This paper deals with the modelling of nonlinear multiscale materials in magnetostatics by means of a finite element computational homogenization method. The method couples a macroscale problem with many microscale problems. During the upscaling step, the homogenized magnetic permeability and its derivative with respect to the magnetic field are calculated from the microscale solution and transferred to the macroscale. The downscaling step consists in imposing proper boundary conditions for the microscale problems from the macroscale solution. Results are validated by comparison with those obtained with classical finite element brute force approach. [less ▲] Detailed reference viewed: 90 (18 ULg)Refinement of Non-Linear Magnetic Models via a Finite Element Subproblem Method Dular, Patrick ; ; V Sabariego, Ruth et al (2011) Model refinements of non-linear magnetic circuits are performed via a finite element subproblem method. A com- plete problem is split into subproblems to allow a progression from 1-D to 3-D including ... [more ▼] Model refinements of non-linear magnetic circuits are performed via a finite element subproblem method. A com- plete problem is split into subproblems to allow a progression from 1-D to 3-D including linear to non-linear model corrections. Its solution is then expressed as the sum of the subproblem solu- tions supported by different meshes. A convenient and robust correction procedure is proposed allowing independent overlapping meshes for both source and reaction fields. It simplifies both meshing and solving processes, and quantifies the gain given by each refinement on both local fields and global quantities. [less ▲] Detailed reference viewed: 18 (3 ULg)Integration of a new hysteresis model in the Finite Elements method ; V Sabariego, Ruth ; et al (2011) In this work we present an original magnetic hysteresis model with parameters fitted from measured reversal curves. This model is used together with the Finite Element method for studying a structure ... [more ▼] In this work we present an original magnetic hysteresis model with parameters fitted from measured reversal curves. This model is used together with the Finite Element method for studying a structure composed of a magnetic core with air-gap excited by a coil. [less ▲] Detailed reference viewed: 19 (0 ULg)Computation of induced fields into the human body by using dual formulations ; V Sabariego, Ruth ; et al (2011) In this work we present the use of two dual formulations to compute Extremely Low frequency (ELF) induced fields into the human body. This allows to estimate the numerical error, as well as rigorously ... [more ▼] In this work we present the use of two dual formulations to compute Extremely Low frequency (ELF) induced fields into the human body. This allows to estimate the numerical error, as well as rigorously bound the (global) co-energy. This method is here applied to the classical case of the exposure to a homogeneous magnetic field. [less ▲] Detailed reference viewed: 23 (2 ULg)Numerical dosimetry of elf fields by using dual formulations ; V Sabariego, Ruth ; Geuzaine, Christophe et al in Proceedings of 10th International Conference of the European Bioelectromagnetics Association (EBEA2011) (2011) Detailed reference viewed: 48 (7 ULg)Stochastic Uncertainty Quantification of Eddy Currents in the Human Body by Polynomial Chaos Decomposition Gaignaire, Roman ; ; V Sabariego, Ruth et al (2011) The finite element method can be used to compute the electromagnetic fields induced into the human body by envi- ronmental extremely low frequency fields. However, the electric properties of tissues are ... [more ▼] The finite element method can be used to compute the electromagnetic fields induced into the human body by envi- ronmental extremely low frequency fields. However, the electric properties of tissues are not precisely known and may vary depending on the individual, his/her age and other physiological parameters. We propose to account for some uncertainties on the conductivities of the brain tissues and to spread them out to the induced fields by means of a non-intrusive approach based on the chaos Hermite polynomial with the finite element method as a black box [3], [4]. [less ▲] Detailed reference viewed: 28 (4 ULg)Time-Domain Surface Impedance Boundary Conditions Enhanced by Coarse Volume Finite-Element Discretisation V Sabariego, Ruth ; Geuzaine, Christophe ; Dular, Patrick et al (2011) The time-domain surface impedance boundary conditions allow to accurately account for the high-frequency flux components while removing the massive conducting regions from the computation domain. In this ... [more ▼] The time-domain surface impedance boundary conditions allow to accurately account for the high-frequency flux components while removing the massive conducting regions from the computation domain. In this paper, a coarse volume finite-element discretization of the conductors together with a fictitious frequency-dependent conductivity are added to capture the slow varying flux components. This hybrid approach extends thus the frequency range of these impedance conditions. A 2-D test case illustrates the method. [less ▲] Detailed reference viewed: 26 (1 ULg)Considering Laminated Cores and Eddy Currents in 2D and 3D Finite Element Simulation of Electrical Machines ; Geuzaine, Christophe ; V Sabariego, Ruth (2011) This paper deals with a time-domain homogeniza- tion method for laminated cores and its application to the 2D finite element simulation of rotating electrical machines. The number of additional degrees of ... [more ▼] This paper deals with a time-domain homogeniza- tion method for laminated cores and its application to the 2D finite element simulation of rotating electrical machines. The number of additional degrees of freedom of the model, for considering the variation of the flux density along the lamination thickness, can be tuned so as to reach a good compromise between accuracy and computation time. The results obtained for a switched reluctance motor agree very well with those produced by a precise full 3D model in which eddy currents are explicitly modeled. [less ▲] Detailed reference viewed: 156 (3 ULg)An Amplitude Finite Element Formulation for Multiple-Scattering by a Collection of Convex Obstacles Geuzaine, Christophe ; Vion, Alexandre ; Gaignaire, Roman et al in IEEE Transactions on Magnetics (2010), 46(8), 2963-2966 We present a multiple-scattering solver for nonconvex geometries obtained as the union of a finite number of convex obstacles. The algorithm is a finite element reformulation of a high-frequency integral ... [more ▼] We present a multiple-scattering solver for nonconvex geometries obtained as the union of a finite number of convex obstacles. The algorithm is a finite element reformulation of a high-frequency integral equation technique proposed previously. It is based on an iterative solution of the scattering problem, where each iteration leads to the resolution of a single scattering problem in terms of a slowly oscillatory amplitude. [less ▲] Detailed reference viewed: 82 (21 ULg)Homogenization of form- wound windings in finite element modelling of electrical machines ; Dular, Patrick ; et al in IEEE Transactions on Magnetics (2010), 46(8), 2852-2855 In this paper, the authors deal with the finite-element (FE) modeling of eddy-current effects in form-wound windings of electrical machines using a previously proposed general frequency- and time-domain ... [more ▼] In this paper, the authors deal with the finite-element (FE) modeling of eddy-current effects in form-wound windings of electrical machines using a previously proposed general frequency- and time-domain homogenization method. By way of demonstration and validation, a real-life 1250-kW induction machine with double-layer stator winding is considered. The skin and proximity effects in one stator conductor (copper bar) are first quantified by means of a simple low-cost FE model, leading to complex and frequency-dependent coefficients for the homogenized winding (reluctivity for proximity effect and conductivity or resistance for skin effect). These complex coefficients are subsequently translated into real-valued and constant coefficients that allow for time-domain homogenization when introducing a limited number of additional degrees of freedom in the FE model. All results obtained with the homogenized model (considering one conductor or a complete slot) agree well with those produced by a brute-force approach (modeling and finely discretizing each conductor). [less ▲] Detailed reference viewed: 32 (1 ULg)Electrokinetic Model Refinement Via a Perturbation Finite-Element Method—From 2-D to 3-D ; Dular, Patrick ; V Sabariego, Ruth et al in IEEE Transactions on Magnetics (2010), 46(8), 2839-2842 A method for increasing the contact area of a grounding system with the earth is the installation of counterpoise wires. Counterpoise wires improve the reliability of overhead power transmission lines ... [more ▼] A method for increasing the contact area of a grounding system with the earth is the installation of counterpoise wires. Counterpoise wires improve the reliability of overhead power transmission lines. They are conductors buried in the ground parallel to or at an angle to the line conductors. This paper presents an electrokinetic model refinement via a perturbation finite-element method to calculate the grounding resistance of counterpoise wires. The perturbation method is herein developed for refining the electric field distribution in soil starting from simplified models, based on electric field distributions from 2-D models, that evolve towards a 3-D accurate model. The analysis of the distribution of the electric field and of the electric potential around the tower footing allows accurately determining the tower footing resistance. The comparisons between the grounding resistance simulated and calculated analytically of a counterpoise wire are presented. [less ▲] Detailed reference viewed: 119 (1 ULg)Finite Element Magnetic Models via a Coupling of Subproblems of Lower Dimensions Dular, Patrick ; V Sabariego, Ruth ; Geuzaine, Christophe et al in IEEE Transactions on Magnetics (2010), 46(8), 2827-2830 Model refinements of magnetic circuits are performed via a subdomain finite element method based on a perturbation technique. A complete problem is split into subproblems, some of lower dimensions, to ... [more ▼] Model refinements of magnetic circuits are performed via a subdomain finite element method based on a perturbation technique. A complete problem is split into subproblems, some of lower dimensions, to allow a progression from 1-D to 3-D models. Its solution is then expressed as the sum of the subproblem solutions supported by different meshes. A convenient and robust correction procedure is proposed allowing independent overlapping meshes for both source and reaction fields, the latter being free of cancellation error in magnetic materials. The procedure simplifies both meshing and solving processes, and quantifies the gain given by each model refinement on both local fields and global quantities. [less ▲] Detailed reference viewed: 44 (6 ULg)Stochastic Uncertainty Quantification of the Conductivity in EEG Source Analysis by Using Polynomial Chaos Decomposition Gaignaire, Roman ; ; et al in IEEE Transactions on Magnetics (2010), 46(8), 3457-3460 The electroencephalogram (EEG) is one of the techniques used for the non-invasive diagnosis of patients suffering from epilepsy. EEG source localization identifies the neural activity, starting from ... [more ▼] The electroencephalogram (EEG) is one of the techniques used for the non-invasive diagnosis of patients suffering from epilepsy. EEG source localization identifies the neural activity, starting from measured EEG. This numerical localization procedure has a resolution, which is difficult to determine due to uncertainties in the EEG forward models. More specifically, the conductivities of the brain and the skull in the head models are not precisely known. In this paper, we propose the use of a non-intrusive stochastic method based on a polynomial chaos decomposition for quantifying the possible errors introduced by the uncertain conductivities of the head tissues. The accuracy and computational advantages of this non-intrusive method for EEG source analysis is illustrated. Further, the method is validated by means of Monte Carlo simulations. [less ▲] Detailed reference viewed: 65 (12 ULg)Surface-Impedance Boundary Conditions in Dual Time-Domain Finite-Element Formulations V Sabariego, Ruth ; Dular, Patrick ; Geuzaine, Christophe et al in IEEE Transactions on Magnetics (2010), 46(8), 3524-3531 This paper deals with time-domain surface-impedance boundary conditions in computational magnetodynamics considering two dual finite-element formulations and a nonlinear magnetic constitutive law. Based ... [more ▼] This paper deals with time-domain surface-impedance boundary conditions in computational magnetodynamics considering two dual finite-element formulations and a nonlinear magnetic constitutive law. Based on the resolution of the 1-D eddy-current problem in a semi-infinite slab, the massive conducting region is accounted for by choosing a number of exponentially decreasing trigonometric basis functions covering the relevant frequency range of the application in hand. Herein the method is elaborated for the magnetic-vector- potential formulation and the magnetic-field formulation. Results for both formulations are compared and validated on 2-D linear and nonlinear test cases. [less ▲] Detailed reference viewed: 96 (14 ULg)Non-linear magnetic model refinement via a finite element subproblem method Dular, Patrick ; V Sabariego, Ruth ; et al in Proceedings of the XXI Symposium on Electromagnetic Phenomena in Nonlinear Circuits (EPNC 2010) (2010, June) Model refinements of non-linear magnetic circuits are performed via a finite element subproblem method. A complete problem is split into subproblems to allow a progression from 1- D to 3-D including ... [more ▼] Model refinements of non-linear magnetic circuits are performed via a finite element subproblem method. A complete problem is split into subproblems to allow a progression from 1- D to 3-D including linear to non-linear model corrections. Its solution is then expressed as the sum of the subproblem solutions supported by different meshes. A convenient and robust correction procedure is proposed allowing independent overlapping meshes for both source and reaction fields. The procedure simplifies both meshing and solving processes, and quantifies the gain given by each model refinement on both local fields and global quantities. [less ▲] Detailed reference viewed: 17 (1 ULg) |
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