Graded mesh refinement and error estimates of higher order for DGFE solutions of elliptic boundary value problems in polygons (Q2910804)

Error estimates for discontinuous Galerkin finite element (DGFE) solutions are well investigated if one assumes that the exact solution is sufficiently regular. In this article, a Dirichlet and a mixed boundary value problem for a linear elliptic equation in a polygon is considered. It is well known that the first derivatives of the solutions develop singularities near reentrant corner points or points where the boundary conditions change. On the basis of the regularity results formulated in Sobolev-Slobodetskii spaces and weighted spaces of Kondratiev type, error estimates of higher order are proved for DGFE solutions using a suitable graded mesh refinement near boundary singular points.NEWLINENEWLINEThe main tools are as follows: regularity investigation for the exact solution relying on general results for elliptic boundary value problems, error analysis for the interpolation in Sobolev-Slobodetskii spaces, and error estimates for DGFE solutions on special graded refined meshes combined with estimates in weighted Sobolev spaces. The main result is that there exist a local grading of the mesh and a piecewise interpolation by polynoms of higher degree such that the same order \(O(h^{\alpha })\) of approximation is obtained as in the smooth case.