A widely used approach for the computation of time-harmonic electromagnetic
fields is based on the well-known double-curl equation for either E or H,
where edge elements are an appealing choice for finite element discretizati
ons. Yet, the nullspace of the curl-operator comprises a considerable part
of all spectral modes on the finite element grid. Thus standard multilevel
solvers are rendered inefficient, as they essentially hinge on smoothing pr
ocedures like Gauss-Seidel relaxation, which cannot provide a satisfactory
error reduction for modes with small or even negative eigenvalues.
We propose to remedy this situation by an extended multilevel algorithm whi
ch relies on corrections in the space of discrete scalar potentials. After
every standard V-cycle with respect to the canonical basis of edge elements
, error components in the nullspace are removed by an additional projection
step. Furthermore, a simple criterion for the coarsest mesh is derived to
guarantee both stability and efficiency of the iterative multilevel solver.
For the whole scheme we observe convergence rates independent of the refin
ement level of the mesh.
The sequence of nested meshes required for our multilevel techniques is con
structed by adaptive refinement. To this end we have devised an a posterior
i error indicator based on stress recovery. Copyright (C) 1999 John Wiley &
Sons, Ltd.