> The task generally contain on the order of 50M to 100M DOFs and are > transient DNS problems.
With this you are likely at a point where factorizations (even ILU) not work very well. Even if you can afford a Block ILU, you likely run on 100+ cores, which means the quality of the preconditioner will deteriorate quite a lot just based on the number of processors. You likely need something that puts more effort into the parallel aspect. > Our solver : Either GMRES or BiCGStab. In our case it seems GMRES is a bit > faster (around 20%) because the iterations are cheaper. I have tried all of > the solvers in the TrilinosWrappers except FGMRES actually. My general advice is to work on the preconditioner to have a method in the 10-40 iterations range. Then, it doesn't really matter which Krylov method you use. Just use FGMRES (if you need flexibility), CG (for SPD), MINRES (for symmetric), or GMRES (for everything else). Switching between different Krylov methods is unlikely to make a big difference unless you are in the 100k+ core range or need too many iterations. > Our current preconditioner : ILU(0) > Element order : Q2-Q2, Q3-Q3 or Q4-Q4. Are you just applying ILU to the whole system? My general advice is to exploit the block structure of your PDE first and then apply ILU or AMG to individual blocks. Time dependent Navier-Stokes with small time steps is a relatively easy case. Let me know if you want more details. -- Timo Heister http://www.math.clemson.edu/~heister/ -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/CAMRj59F3qW2JaArsr1rBP_oFDAet%2BKmWxCsxjRXNVUZPR7fO7Q%40mail.gmail.com.
