318	2010
TITLE	On Adaptive Timestepping for Weakly Instationary Solutions of Hyperbolic Conservation Laws Via Adjoint Error Control
AUTHORS	Christina Steiner, Sebastian Noelle
ABSTRACT	We study a recent timestep-adaptation technique for hyperbolic conservation laws. The key tool is a space–time splitting of adjoint error representations for target functionals due to Süli (An Introduction to Recent Developments in Theory and Numerics for Conservation Laws. Lecture Notes in Computational Science and Engineering. Springer: Berlin, 1998; 123–194) and Hartmann (A posteriori Fehlerschätzung und adaptive Schrittweiten- und Ortsgittersteuerung bei Galerkin-Verfahren für die Wärmeleitungsgleichung. Diplomarbeit, Institut für Angewandte Mathematik, Universität Heidelberg, 1998). It provides an efficient choice of timesteps for implicit computations of weakly instationary flows. The timestep will be very large in regions of stationary flow and become small when a perturbation enters the flow field. Besides using adjoint techniques that are already well established, we also add a new ingredient that simplifies the computation of the dual problem. Owing to Galerkin orthogonality, the dual solution φ does not enter the error representation as such. Instead, the relevant term is the difference of the dual solution and its projection to the finite element space, φ−φh . We can show that it is therefore sufficient to compute the spatial gradient of the dual solution, w=∇φ . This gradient satisfies a conservation law instead of a transport equation, and it can therefore be computed with the same algorithm as the forward problem, and in the same finite element space. We demonstrate the capabilities of the approach for a weakly instationary test problem for scalar conservation laws.
KEYWORDS	hyperbolic conservation laws;weakly instationary solutions;adaptive timestepping;adjoint error control
DOI	10.1002/cnm.1183
PUBLICATION	International journal for numerical methods in biomedical engineering 26(6), 790-806 (2010)