[petsc-users] PF+Navier stokes

[Sepideh Kavousi]

I found some discussions in the following link and  https://lists.mcs.anl.gov/pipermail/petsc-users/2010-May/006422.html and the following paper: https://www.sciencedirect.com/science/article/pii/S0021999107004330
But I am engineer and the discussions are confusing for me. Would you please tell me what is the correct path to follow?
Should I go ahead and apply SIMPLER algorithm for this problem, or I should learn to apply fieldsplit to determine individual preconditioning on each unknown?
Best,
Sepideh
________________________________
From: Matthew Knepley <knepley at gmail.com>
Sent: Monday, March 22, 2021 9:15 AM
To: Sepideh Kavousi <skavou1 at lsu.edu>
Cc: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] PF+Navier stokes

On Mon, Mar 22, 2021 at 10:04 AM Sepideh Kavousi <skavou1 at lsu.edu<mailto:skavou1 at lsu.edu>> wrote:
Hello,
I want to solve PF solidification+Navier stokes using Finite different method, and I have a strange problem. My code runs fine for some system sizes and fails for some of the system sizes. When I run with the following options:
mpirun -np 2 ./one.out -ts_monitor -snes_fd_color -ts_max_snes_failures -1  -ts_type bdf -ts_bdf_adapt -pc_type bjacobi  -snes_linesearch_type l2 -snes_type ksponly -ksp_type gmres -ksp_gmres_restart 1001 -sub_pc_type ilu -sub_ksp_type preonly -snes_monitor -ksp_monitor -snes_linesearch_monitor -ksp_monitor_true_residual -ksp_converged_reason -log_view

    0 SNES Function norm 1.465357113711e+01
    0 SNES Function norm 1.465357113711e+01
    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to SUBPC_ERROR
    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to SUBPC_ERROR
    0 SNES Function norm 1.465357113711e+01
    0 SNES Function norm 1.465357113711e+01
    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to SUBPC_ERROR
    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to SUBPC_ERROR
    0 SNES Function norm 1.465357113711e+01
    0 SNES Function norm 1.465357113711e+01
^C    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to SUBPC_ERROR
    0 SNES Function norm 1.465357113711e+01
    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to SUBPC_ERROR
    0 SNES Function norm 1.465357113711e+01

Even setting pc_type to LU does not solve the problem.
0 TS dt 0.0001 time 0.
copy!
copy!
Write output at step= 0!
Write output at step= 0!
    0 SNES Function norm 1.465357113711e+01
    0 SNES Function norm 1.465357113711e+01
    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to FACTOR_NUMERIC_ZEROPIVOT
    Linear solve did not converge due to DIVERGED_PC_FAILED iterations 0
                   PC_FAILED due to FACTOR_NUMERIC_ZEROPIVOT

I guess the problem is that in mass conservation I used forward discretization for u (velocity in x) and for the moment in x , I used forward discretization for p (pressure) to ensure non-zero terms on the diagonal of matrix. I tried to run it with valgrind but it did not output anything.

Does anyone have suggestions on how to solve this issue?

Your subproblems in Block_jacobi are singular. With multiphysics problems like this, definition of blocks can be
tricky. I would first try to find a good preconditioner for this system in the literature, and then we can help you
try it out.

  Thanks,

      Matt


Best,
Sepideh


--
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

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