Noël Burais

Variational tetrahedral mesh generation from discrete volume data

In this paper, we propose a novel tetrahedral mesh generation algorithm, which takes volumic data (voxels) as an input. Our algorithm performs a clustering of the original voxels within a variational framework. A vertex replaces each cluster and the set of created vertices is triangulated in order to obtain a tetrahedral mesh, taking into account both the accuracy of the representation and the elements quality. The resulting meshes exhibit good elements quality with respect to minimal dihedral angle and tetrahedra form factor. Experimental results show that the generated meshes are well suited for Finite Element Simulations.

Temperature Dependent Extension of the Jiles-Atherton Model: Study of the Variation of Microstructural Hysteresis Parameters

Environmental requirements currently placed on magnetic materials that are used in both domestic and professional electromagnetic devices are becoming more stringent. The growing demand for components to operate under extreme environmental conditions prompted this study of the effect of temperature variation on magnetic materials. Thus, the knowledge of their behavior, especially under high temperatures, is of prime importance. In this paper, two methods for determining the evolution of Jiles-Atherton model parameters with temperature are presented. The parameters evolution of the model as a function of temperature is discussed. Both methods are compared.

Numerical Dosimetry of Induced Phenomena in the Human Body by a Three-Phase Power Line

We computed by finite element the fields induced in an heterogeneous model of the human body by both the electric and magnetic field generated by a three-phase power line. Results were partially validated and analyzed by comparison with existing data with uniform magnetic field. Induced currents due to both E and B were developed inside the body in an asymmetrical manner.

Computation of Induced Fields Into the Human Body by Dual Finite Element Formulations

In this work we present two dual finite element 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 herein applied to the classical case of the exposure to a homogeneous magnetic field, and to the field generated by an infinite wire.

Characterization and Modeling of a Current Transformer Working Under Thermal Stress

This paper focuses on the thermal stress on magnetic materials under Curie temperature. The influence of the temperature on static and dynamic major B(H) loops is studied. Then, the Jiles-Atherton (JA) model and “flux tube” model are used, in order to reproduce the static and dynamic hysteresis loops for a NiFe (80/20) alloy. For each temperature, the six model parameters are optimized from measurements. Finally, these parameters are used in order to reproduce the behavior of a current transformer. The simulation results are compared with measurements and discussed.

Simulation of Low-Nickel-Content Alloys for Industrial Ground Fault Circuit-Breaker Relays

The aim of this paper is to simulate the performances of a ground fault circuit-breaker (GFCB) relay with new low-nickel-content alloys. Indeed, in the construction industry, the materials become more expensive as their nickel content increases. Moreover, the demand for nickel is particularly sensitive to the economic conjuncture. Therefore, an original electromagnetic relay model has been developed and validated in different working conditions (current amplitude, frequency, and temperature). A dedicated magnetic characterization of materials is needed, using basically a usual and industrial GFCB relay for reference and design data in modeling. First, the magnetic model of the relay is built and checked against experimental data. The simulation may predict the tripping current threshold of the relay. On the other hand, new low-nickel-content alloys for relay parts are studied in this framework, thanks to the developed model. The effects of temperature on the magnetic properties of the candidate materials and the electrical performances of the virtual relays are presented. The results, analysis, and conclusions are given. Finally, a first attempt to predict the economic gain obtained with a change of material is made.

Numerical dosimetry of currents induced in the human body by ELF magnetic fields

The classical φ − a formulation for numerical dosimetry of currents induced by ELF magnetic fields requires that the source field is provided through a vector potential. We present here a new formulation t − b which directly takes the flux density as source term. This formulation is implemented through Finite Element and validated by comparison with analytical solutions. The results obtained by both formulations are compared in the case of an anatomical computational phantom exposed to a vertical uniform field. As example, the t − b formulation is used for computing the induced fields in the body exposed to the stray field of a 2.5 MW HTA/BT three-phase power transformer.

Electromagnetic characterization of biological cells

This paper presents the most commonly used method to characterize individual biological cells on a dielectric point of view. It is a force based technique which lays on dielectrophoresis and/or electrorotation. First the principle of these phenomena are described and analyzed with an extension to magnetic forces at the micrometric scale level. Secondly we present an experimental setup which permits to acquire the dielectrophoretic spectrum which is a dielectric signature of a cell. The main dielectric parameters can be deduced by fitting the theoretical response of the cell issued from a dielectric model and the experimental data. At the end we present an improved fitting method which takes advantage of a sensitivity analysis based on a probabilistic approach.

Domain decomposition for computing extremely low frequency induced current in the human body

Computation of electromagnetic fields in high resolution computational phantoms requires solving large linear systems. We present an application of Schwarz preconditioners with Krylov subspace methods for computing extremely low frequency induced fields in a phantom issued from the Visible Human.