It would be useful to see the convergences inside the linear solve so perhaps start with
-ksp_monitor_true_residual -fieldsplit_u_ksp_type richardson (this is to allow the monitor below to work) -fieldsplit_u_ksp_max_its 1 -fieldsplit_u_ksp_monitor Perhaps others, Matt/Jed/Pierre/Stefano likely know better off the cuff than me. We should have a convenience option like -pc_fieldsplit_schur_monitor similar to the -pc_fieldsplit_gkb_monitor > On Apr 13, 2023, at 4:33 PM, Alexander Lindsay <[email protected]> > wrote: > > Hi, I'm trying to solve steady Navier-Stokes for different Reynolds numbers. > My options table > > -dm_moose_fieldsplit_names u,p > -dm_moose_nfieldsplits 2 > -fieldsplit_p_dm_moose_vars pressure > -fieldsplit_p_ksp_type preonly > -fieldsplit_p_pc_type jacobi > -fieldsplit_u_dm_moose_vars vel_x,vel_y > -fieldsplit_u_ksp_type preonly > -fieldsplit_u_pc_hypre_type boomeramg > -fieldsplit_u_pc_type hypre > -pc_fieldsplit_schur_fact_type full > -pc_fieldsplit_schur_precondition selfp > -pc_fieldsplit_type schur > -pc_type fieldsplit > > works wonderfully for a low Reynolds number of 2.2. The solver performance > crushes LU as I scale up the problem. However, not surprisingly this options > table struggles when I bump the Reynolds number to 220. I've read that use of > AIR (approximate ideal restriction) can improve performance for advection > dominated problems. I've tried setting -pc_hypre_boomeramg_restriction_type 1 > for a simple diffusion problem and the option works fine. However, when > applying it to my field-split preconditioned Navier-Stokes system, I get > immediate non-convergence: > > 0 Nonlinear |R| = 1.033077e+03 > 0 Linear |R| = 1.033077e+03 > Linear solve did not converge due to DIVERGED_NANORINF iterations 0 > Nonlinear solve did not converge due to DIVERGED_LINEAR_SOLVE iterations 0 > > Does anyone have an idea as to why this might be happening? If not, I'd take > a suggestion on where to set a breakpoint to start my own investigation. > Alternatively, I welcome other preconditioning suggestions for an advection > dominated problem. > > Alex
