[petsc-users] How to speed up geometric multigrid
Matthew Knepley
knepley at gmail.com
Mon Sep 23 11:36:39 CDT 2013
On Mon, Sep 23, 2013 at 9:34 AM, Michele Rosso <mrosso at uci.edu> wrote:
>
> On 09/23/2013 09:24 AM, Mark F. Adams wrote:
>
>
> On Sep 23, 2013, at 11:55 AM, Michele Rosso <mrosso at uci.edu> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130923/130d7e70/attachment.html>
More information about the petsc-users
mailing list