Efficient modelling techniques for complicated boundary conditions applied to structured grids

Certain sophisticated boundary conditions offer powerful modelling features for many electrotechnical models. Their application, however, wipes out the particular structure of the system matrices which occurs when structured grids are applied. In this paper, this effect is prevented by considering the unconstrained system together with additional constraint equations or by projecting the algebraic system using an oblique or orthogonal projector. The numerical tests indicate that the efficiency of sparse iterative solvers can be preserved even in the presence of complicated boundary relations. The described projections are also advantageous for formulations derived for unstructured grids.