Alain Nicolas

Electromagnetic fields and human body: a new challenge for the electromagnetic field computation

The electromagnetic fields have a great influence on the behaviour of all the living systems. The as low as reasonably achievable (ALARA) principle imposes, in case of long exposures to low (i.e. power systems) or high frequency (i.e. microwave systems or cell phones) fields, some limitations to the radiated fields by the industrial equipment. On the other hand, some benefits can be taken from the effects of the electromagnetic fields on the living being: the hyperthermal technique is well known for the treatment of the cancer. Either we want to be protected from the fields, or we want to take benefit of the positive effects of these fields, all the effects thermal as well as genetic have to be well known. Like in any industrial application, the electromagnetic field computation allows a better knowledge of the phenomena, and an optimised design. Hence, there is a very important challenge for the techniques of computation of electromagnetic fields. The major difficulties that appear are: (1) related to th...

A boundary integral equation method for the calculation of the effective permittivity of periodic composites

We present a numerical method based upon the resolution of boundary integral equations for the calculation of the effective permittivity of a lossless composite structure consisting of a two component mixture, each with its own dielectric and shape characteristics. The topological arrangements considered are periodic lattices of inhomogeneities. Our numerical simulations are compared to the effective medium approach and with results of previous works.

Genetic algorithm coupled with a deterministic method for optimization in electromagnetics

In this paper, a hybrid technique for global optimization based on the genetic algorithm and a deterministic method is presented. A potential advantage of the hybrid method compared to the genetic algorithm is that global optimization can be performed more efficiently. An intrinsic problem of the hybrid techniques is related to the moment of stopping the stochastic routine to launch the deterministic one. This is investigated using some natural criteria for the commutation between the two methods. The results show that it is possible to gain in efficiency and in accuracy but the criterion is usually problem dependent. Finally, to show the solution of a real problem, the hybrid algorithm is coupled to a 2D code based on the boundary element method to optimize a connector of 145 kV GIS.

Niching genetic algorithms for optimization in electromagnetics. I. Fundamentals

Niching methods extend genetic algorithms and permit the investigation of multiple optimal solutions in the search space. In this paper, we review and discuss various strategies of niching for optimization in electromagnetics. Traditional mathematical problems and an electromagnetic benchmark are solved using niching genetic algorithms to show their interest in real world optimization. Index terms-Genetic algorithms, niching methods, sharing, crowding, clearing, shape optimization, magnetizer.

Computation of electric fields and potential on polluted insulators using a boundary element method

The authors present a calculation method for electric fields and potential applicable in the case of a polluted insulator. This method, based on boundary integral equations, is suitable for 3-D geometries and polluted layers. Results obtained by this method are compared with analytical solutions (potential, currents) and with measured values (potential, leakage current). >

Numerical solution of eddy currents problems including moving conducting parts

In the study of transient or steady-state eddy current effects, a general diffusion equation derived from Maxwells equations is solved by a classical finite element method for the spatial problem with time discretization. The moving part of the system is taken into account by a mesh distortion where the mesh points associated with this part have to follow the displacement. This technique can be used when the movement is time harmonic and displacement limited in order to obtain a few distorted mesh. It is applied to an axisymmetric apparatus and eddy current losses calculations are compared with experimental results.

Flaws characterization with pulsed eddy currents NDT

In this paper, we present a method for characterizing flaws in metallic structures with pulsed eddy current nondestructive testing (NDT). In a first step, we explain why we have chosen a deconvolution method based on conjugate gradient algorithm (CG). After a description of this method and the way it is used for characterization, a validation is performed by coupling it with a 2D FEM (2 dimensional finite elements method) package. The obtained results are compared with experimental measurements. In the last step, a parametric study on parameters obtained with the impulse response gives an estimation of the dimensions of the flaw.

On line diagnosis of defaults on squirrel cage motors using FEM

In industry, predictive maintenance has become a strategic concept. Economic interest of online diagnosis of faults in electric machines gave rise to various researches in that field. This paper proposes a local approach to tackle the problem of breaking bars and end-rings of squirrel cage in induction machines based mainly on the signature of the local variables, such as the normal flux density. This allows a finer analysis, by use of a finite element based simulation.

Computation of 3D induction hardening problems by combined finite and boundary element methods

A method for the solution of high frequency three dimensional coupled magneto-thermal problems such as those of the induction hardening of steel is proposed. The magnetic problem Is treated first using the Boundary Element Method (BEM) to calculate magnetic parameters. From eddy-currents and Joule effects, source values are obtained to solve the thermal problem by the Finite Element Method (FEM). The two problems are then indirectly coupled to obtain a solution for the entire problem. >

Efficient genetic algorithms for solving hard constrained optimization problems

This paper studies many Genetic Algorithm strategies to solve hard-constrained optimization problems. It investigates the role of various genetic operators to avoid premature convergence. In particular, an analysis of niching methods is carried out on a simple function to show advantages and drawbacks of each of them. Comparisons are also performed on an original benchmark based on an electrode shape optimization technique coupled with a charge simulation method.