Talks and Poster Presentations (with Proceedings-Entry):

M. Feischl, M. Karkulik, J. Melenk, D. Praetorius:
"Residual a-posteriori error estimates in BEM: convergence of h-adaptive algorithms";
Talk: IABEM 2011 Conference, Brescia; 09-05-2011 - 09-08-2011; in: "Proceedings of IABEM 2011", (2011), 135 - 140.

English abstract:
Galerkin methods for FEM and BEM based on uniform mesh refinement have a guaranteed rate of convergence. Unfortunately, this rate may be suboptimal due
to singularities present in the exact solution. In numerical experiments, the optimal rate of convergence is regained when
algorithms based on a-posteriori error estimation and adaptive mesh-refinement are used.
This observation was proved mathematically for the FEM in the last few years, cf. [Cascon, Kreuzer, Nochetto, Siebert, 2008]
In constrast, the
mathematical understanding of adaptive strategies is wide open in BEM.
One reason for this is the non-locality of the boundary integral operators involved and
the appearance of fractional-order or negative Sobolev norms.

In our prior works on adaptive BEM [Aurada, Ferraz-Leite, Goldenits, Karkulik, Mayr, Praetorius, 2001], we considered (h-h/2) error estimators. Reliability of such estimators is,
however, equivalent to the so-called saturation assumption. Although
this is widely believed to hold in practice, it still remains mathematically open. For this reason, these
convergence results are not fully satisfactory.

In our talk, we consider weighted residual error estimators for
some weakly-singular integral equations in 2D or 3D. These estimator are reliable,
irrespective of the saturation
assumption. We prove a certain (local) inverse-type estimate which
allows us to conclude that the discrete solutions generated by the usual h-adaptive
algorithm converge towards the exact solution
of the integral equation.

In a second step we prove quasi-optimality in a certain approximation class.
From this, we infer that the rate of convergence of adaptive mesh-refinement
is at least as good as for uniform approaches.

Electronic version of the publication:

Created from the Publication Database of the Vienna University of Technology.