  A novel approach to the simulation with the boundary element method using
trimmed NURBS patches is presented. The advantage of this approach is its
efficiency and easy implementation. The analysis with trimmed NURBS is achieved
by double mapping. The variation of the unknowns on the boundary is specified
in a local coordinate system and is completely independent of the description
of the geometry. The method is tested on a branched tunnel and the results
compared with those obtained from a conventional analysis. The conclusion is
that the proposed approach is superior in terms of number of unknowns and
effort required.
