Thanks Barry. Your message provides a good starting point. I will need to do more reading to understand my options.
Thanks, Manav > On Apr 7, 2015, at 3:00 PM, Barry Smith <[email protected]> wrote: > > > You cannot just use algebraic multigrid directly on the transonic Euler > flow problem discretized with SUPG you must break the problem into pieces > (probably using PCFIELDSPLIT) and then use appropriate preconditioners for > each piece. > > Barry > > Note that ILU is a bottom feeder preconditioner, it is only working because > you are using a huge fill factor (so it is a lot like a direct solver) and > even then it is working really poorly. You should google for good > preconditioners for transonic Euler flow and SUPG (and ignore anything that > mentions ILU) to get a handle on how PCFIELDSPLIT could be used for your > problem. > > >> On Apr 7, 2015, at 7:06 AM, Manav Bhatia <[email protected]> wrote: >> >> Hi, >> >> I am solving a transonic Euler flow problem discretized with SUPG. The >> mesh is made of Tet4 elements and there are about 7M dofs, which I am trying >> to solve over 192 cores. >> >> I had earlier written about the linear solver returning with Inf, and have >> since moved beyond that such that I am able to get a solution with the >> following command line parameters: >> >> -ksp_gmres_restart 100 -pc_type asm -sub_pc_type ilu -sub_pc_factor_levels >> 4 -sub_ksp_type preonly >> >> The problem now is that I am limited to very small time-steps (~10e-6), >> outside of which the solver starts to choke and the solution diverges. I >> have tried other command line options and this above combination is what >> seems to provide the best possible solution strategy, albeit constrained in >> time steps. >> >> I would appreciate any recommendations on solver configurations that may >> allow me to take larger time-steps. >> >> Would coding up AMG be a possible alternative (more robust and >> dependable)? >> >> Please let me know if you need additional information. >> >> Regards, >> Manav >> >
