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Thesis
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Metode integrale de rezolvare a problemelor de câmp electromagnetic
Maricaru, Mihai (UPB)
2007-01-01
Abstract: 1. Two procedures in the boundary element method (BEM) for multiply connected domains are firstly reported. The first procedure introduces cuts such that the multiply connected domain is transformed into a simply connected one, so that it allows the use of the scalar potential. Each cut introduces an additional term containing the “hall” current multiplied by the solid angle under which the cut is seen. The kernel singularities are easily solved by analytical evaluation of the matrix entries. The surface integral is transformed in line integral along the surface boundary when the magnetic flux has to be calculated. In order to obtain the inductivities, the computing of the fluxes of the cuts needs a special treatment because of the kernel singularity. The second procedure is based on a novel magnetic vector potential formulation. It uses edge elements and tree-cotree spanning. A zero normal component of this vector potential A and the condition for its line integral along any closed path on the boundary are imposed, such that the continuity of the normal component of the magnetic flux density be rigorously satisfied. The unknowns are the tangential components of A and the tree edge element values. 2. Then, a new, very efficient, iterative FEM-BEM procedure is proposed, taking into account nonlinear B-H characteristics. 3. An efficient iterative integral technique is proposed, where the material nonlinearity is treated by the polarization method, with the magnetic field determined at each iteration by superposing the contributions of the given electric currents and of the polarization. This computation technique has great advantages over the finite element based procedures used for electric machines, namely, the change in the rotor position does not require the construction of a new discretization mesh, very small airgaps can be taken into consideration without increasing the amount of computation, and the calculated magnetic field in the air is divergenceless and curlless, thus eliminating the introduction of spurious forces introduced by artificial boundary. 4. An efficient solution is presented for coupled nonlinear eddy currents – thermal diffusion problems. Applying the fixed point polarization method to the nonlinear eddy-current field problem, with the magnetization dependent on magnetic induction and on temperature, allows the field computation to be performed for each harmonic separately. Since the fictitious permeability can be chosen to be everywhere that of free space, the matrices of the linear systems to be solved at each iteration remain unchanged even when the nonlinear B-H characteristic changes with the temperature. A simple integral equation is used to compute the eddy currents, the inversion of the matrices corresponding to the harmonics being performed only once, before starting the iterative process. The heat conduction – diffusion equation is solved at each time step by the finite element method. Illustrative examples are also presented for all new developed methods.
Keyword(s): Element finit -- Teză de doctorat ; Câmp electromagnetic -- Modelare numerică -- Teze
Note: Hantila, Florea Ioan
OPAC: See record in BC-UPB Web OPAC
Full Text: see files
Notice créée le 2010-12-07, modifiée le 2011-11-11
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