Hello all, I hope you are all well. This is not strictly a deal.II question, but I thought I could benefit for the huge amount of expertise present on this board. I am currently launching large (at least from my POV) tasks on our HPC cluster. The task generally contain on the order of 50M to 100M DOFs and are transient DNS problems.
Right now we are solving the Navier-Stokes equations in a GLS formulation. For steady-state problems, it is reasonably pertinent to use expensive preconditioners (like AMG with ILU-smoother/coarsener or straight ILU(1) or ILU(2)) because we do not do a large number of iterations. However, in the present case we wish to use a very small time-step (even though we are using a high-order L-Stable SDIRK33 time integration). In this case, even using ILU(1) is extremely expensive (e.g. it takes 2X more time than to assemble the matrix and it really doubles up the iteration time). Consequently, we are using ILU(0), which in the present case is performing relatively well (say between 40-100 iterations per newton step). I was wondering if there were any other suggestions in terms of preconditioner that we could use? Our system : GLS stabilized Navier-Stokes, monolithic matrix formulation (single matrix for u,v,w,p). The matrix is non-symmetric. 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. Our current preconditioner : ILU(0) Library used : Trilinos through the deal.II wrappers Element order : Q2-Q2, Q3-Q3 or Q4-Q4. Any suggestions would be appreciated. I am doing all I can right now to speed-up matrix assembly, but in general we only need to assemble the matrix every 3-5 time steps, so I am just trying to find a good compromise between a good preconditioner that is not crazy expensive. Would I be better to accept having a poorer jacobian matrix, use a more expensive preconditioner and keeping it for a longer time (say 10-20 time-steps)? -- 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 dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/773f2720-0443-4762-b8dc-46814c4b5ae9n%40googlegroups.com.
