Robustness of a multigrid solver for time-harmonic electromagnetic problems
Tom Jonsthovel

Site of the project:
Hoekstede Building
Visseringlaan 26
2280AB Rijswijk

start of the project: September 2005

In December 2005 the Interim Thesis has been appeared and a presentation has been given.

The Master project has been finished in June 2006 by the completion of the Masters Thesis and a final presentation has been given. For working address etc. we refer to our alumnipage.

Summary of the master project:
The performance of a multigrid solver for time-harmonic electromagnetic problems occurring in geophysical exploration is investigated. The frequencies considered are sufficiently small for the light-speed waves to be negligible, so that a diffusive problem remains. The discretization of the governing equations is based on the Finite-Integration-Technique, which can be viewed as a finite volume staggered grid discretization.

The accuracy of the discretization and the performance of the iterative multigrid solution method for solving the discrete equations degrade when the grid is stretched. Whereas the multigrid solver provides excellent convergence rates with constant grid spacings, it performs far less satisfactory when substantial grid stretching is applied. The aim of this MSc project is to investigate whether known techniques to improve multigrid for a stretched grid discretization work well for the time-harmonic electromagnetic equations under consideration. We will compare line-wise smoothing methods in a standard grid coarsening sequence with a point-wise multigrid smoother in a semi-coarsened grid coarsening. The staggered grid discretization poses here some initial difficulties. The comparision between the two techniques will be done both from a practical, numerical point-of-view as from an analytical Fourier-analysis based view point.

Contact information: Kees Vuik

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