On 09/23/2013 09:24 AM, Mark F. Adams wrote:
On Sep 23, 2013, at 11:55 AM, Michele Rosso <[email protected]
<mailto:[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.
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>
