On Thu, 18 Apr 2013, Manav Bhatia wrote: > I use a constant time step of 0.05 sec with a backwards Euler > implicit time scheme. Of course, the local CFL increases to > large numbers as the mesh is refined, since I do not change the > time step. > > Do you typically change the time step post refinement? Or use > local time stepping?
I don't know how well Ben's and my experiences will carry over to your code - we're using SUPG rather than GLS, so we ought to be getting a better conditioned matrix at the cost of more finicky stability. Don't GLS matrix condition numbers grow like h^-4 instead of h^-2? But with that in mind: I definitely reduce the time step post-refinement, and not just by a factor of 2. Otherwise it gets too hard for our scheme to handle sudden sharpening of shocks in hypersonic real gas flows. Usually our adaptive time stepper ramps up the time step afterwards pretty aggressively, though, successfully. Also, problems with no shock or with no sensitive chemistry are more robust. I'd be a little surprised if the time step size was the root of your linear solver convergence problem, but that's such an easy thing to check that I would definitely give a reduced time step a try. --- Roy ------------------------------------------------------------------------------ Precog is a next-generation analytics platform capable of advanced analytics on semi-structured data. The platform includes APIs for building apps and a phenomenal toolset for data science. Developers can use our toolset for easy data analysis & visualization. Get a free account! http://www2.precog.com/precogplatform/slashdotnewsletter _______________________________________________ Libmesh-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/libmesh-users
