Günther Lehner

A novel formulation for 3D eddy current problems with moving bodies using a Lagrangian description and BEM-FEM coupling

This paper summarizes the theoretical background of 3D eddy current problems with moving bodies. A novel 3D formulation combining a Lagrangian description and BEM-FEM coupling is subsequently developed. The conducting and permeable bodies are described by the FEM in their respective rest frame, whereas the surrounding space is treated by the BEM in the laboratory frame. The FEM and BEM descriptions are coupled together taking into account the transformation between the different frames. The proposed formulation contains no explicit velocity terms.

An improved algorithm for the BEM-FEM-coupling method using domain decomposition

The BEM-FEM-coupling method has the advantage of the correct representation of infinite space. But there are also disadvantages. The system matrix is non-symmetric and it has a large mean bandwidth. We apply domain decomposition so that the original problem is split into a separate BEM and FEM part. The typical advantages of both methods are preserved so that reduced computer resources are needed. The solution of the overall problem is obtained by iteration. This paper deals only with eddy current problems. >

Three-dimensional transient BEM-FEM coupled analysis of electrodynamic levitation problems

This paper deals with the numerical solution of three-dimensional electromagnetic levitation problems. The transient behaviour is described by the Maxwell equations, by the (possibly nonlinear) constitutive equations, and by the equations of motion. For the solution of the electromagnetic problem the BEM-FEM coupling method is used. An aluminium plate above two coils is presented as an example.

Inverse 2D obstacle scattering by adaptive iteration

The 2D inverse time harmonic electromagnetic scattering problem of reconstructing the starlike boundary /spl Lambda/ of an infinitely conducting obstacle from its far field scattering data is considered. An approach that employs weak a priori knowledge by choosing an auxiliary curve /spl Gamma/ inside the searched boundary /spl Lambda/ is used. Reconstructions are improved using an iteration scheme to adapt the internal curve /spl Gamma/ by exploiting information on the reconstruction /spl Lambda/ of the previous step. The adaptation algorithm yields significant improvements on /spl Lambda/, provided a reasonable first reconstruction may be obtained.

A novel iterative algorithm for the nonlinear BEM-FEM coupling method

A novel iterative algorithm for the application of BEM-FEM coupling to nonlinear magnetic problems is presented. It combines an algorithm for nonlinear solution with an algorithm for memory saving. The resulting iterative method contains a relaxation parameter which is determined adaptively. The proposed algorithm exhibits superior numerical performance compared,to earlier ones.

Comparison of analytical and numerical integration techniques for the boundary integrals in the BEM-FEM coupling considering TEAM workshop problem no. 13

When the BEM-FEM coupling is used for the solution of a boundary value problem the domain is decomposed into a multiple connected BEM subdomain and generally several FEM subdomains. Magnetic materials are treated in the FEM subdomains only. To keep the discretization process simple, the parts containing magnetic materials coincide with the FEM subdomains. The surrounding air space is described with the help of boundary elements. The coupling of both methods is carried out on the surface of the magnetic materials. The solution of problems discretized this way shows that the accuracy of the results strongly depends on the accuracy of the boundary element integral calculation. Therefore either a large number of Gauss points or an analytical integration scheme has to be used for the calculation of the BEM integrals.

Inverse electromagnetic medium scattering using a variable metric method

The 2D inverse electromagnetic scattering problem of reconstructing the material properties of inhomogeneous lossy dielectric cylindrical objects is considered. The material properties are reconstructed using scattering data from time-harmonic electromagnetic TM-polarized plane waves. The inverse scattering problem formulated as a nonlinear optimization problem is numerically solved using a variable metric method. This method is a quasi-Newton method and involves exact first-order gradients. Numerical examples are presented to show the efficiency of the algorithm.

Time Dependent Problems I (Quasi Stationary Approximation)

Maxwell,s equations were introduced in Chapter 1, but with a few exceptions, we have not discussed them in their complete form. So far, we have focused on time independent problems, specifically electrostatics in Chapter 2 and 3, stationary electric currents in Chapter 4 and magnetostatics in Chapter 5. Now, we turn to time dependent problems. We will do this in two steps.

Application of BEM-FEM coupling and the vector Preisach model for the calculation of 3D magnetic fields in media with hysteresis

This paper deals with the coupling of finite elements and boundary elements for the calculation of 3D magnetic fields in media with hysteresis. For the description of hysteresis effects the vector Preisach model is used. The numerical implementation of the 3D vector Preisach model is addressed. A boundary value problem (bvp) with ferromagnetic material for which an analytical solution exists is presented. This bvp can be used to validate the numerical approach. Numerical and analytical solution of the bvp show very good agreement.

A new approach to the 2D inverse electromagnetic medium scattering problem: reconstruction of anisotropic objects

A new method for reconstructing the material properties of inhomogeneous lossy dielectric biaxial cylindrical objects is presented. The material properties are reconstructed using scattering data from time-harmonic electromagnetic plane waves with the electric field vector perpendicular to the cylindrical object (TE-polarization). The inverse scattering problem formulated as a nonlinear optimization problem is numerically solved using a variable metric method. This method involves exact first-order gradients, Numerical examples illustrate the efficiency of the algorithm.