Goal oriented error estimators for Stokes equations based on variationally consistent postprocessing

In many flow problems, and in particular when fluid-structure interaction is considered, the important unknowns are the forces acting on the structure in certain areas. Hence, accurate values for these local quantities is essentially what one wants to get out of the flow computations. By means of variationally consistent postprocessing, where forces are computed using the weak form of the equations, we recover the requested forces. Goal oriented local error indicators are provided by solving an auxiliary problem. At the end numerical examples are presented that illustrate how this goal oriented strategy gives improved efficiency compared to traditional methods. The fluid flow is assumed to be governed by the Stokes equations.