On Mon, Sep 23, 2013 at 9:34 AM, Michele Rosso <[email protected]> wrote:
> > On 09/23/2013 09:24 AM, Mark F. Adams wrote: > > > On Sep 23, 2013, at 11:55 AM, Michele Rosso <[email protected]> wrote: > > Hi, > > I am successfully using PETSc to solve a 3D Poisson's equation with CG + > MG . Such equation arises from a projection algorithm for a multiphase > incompressible flow simulation. > I set up the solver as I was suggested to do in a previous thread(title: > "GAMG speed") and run a test case (liquid droplet with surface > tension falling under the effect of gravity in a quiescent fluid). > The solution of the Poisson Equation via multigrid is correct but it > becomes progressively slower and slower as the simulation progresses (I am > performing successive solves) due to an increase in the number of > iterations. > Since the solution of the Poisson equation is mission-critical, I need to > speed it up as much as I can. > Could you please help me out with this? > > > Just to add, it is not unusual as structures develop in your simulation > to see an increase in iterations. If you plot the material coefficients I > suspect that you will see sharper structures developing in time. Can you > look at this in some way or generate some statistics like (max) gradient of > material coefficients or even just max & min coefficients? > > Yes, I suspected that this may have been a reason. Initially both phases > are at rest, so basically no fluid structures are present, thus the > convergence is very fast(6 iterations maximum). Then vortices start > developing both inside and outside the droplet and at that point the number > of iteration increases. I noticed that the convergence rate becomes almost > steady at a certain point, I guess when the flow is fully developed. I > would like to speed up the solve for this last scenario. > Mark, is this where we do Bootstrap? :) Thanks, Matt > I run the test case with the following options: > > -pc_type mg -pc_mg_galerkin -pc_mg_levels 5 -mg_levels_ksp_type > richardson -mg_levels_ksp_max_it 1 > -mg_coarse_pc_type lu -mg_coarse_pc_factor_mat_solver_package > superlu_dist > -log_summary -ksp_view -ksp_monitor_true_residual -options_left > > Please find the diagnostic for the final solve in the attached file > "final.txt'. > Thank you, > > Michele > <final.txt> > > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
