[petsc-users] PF+Navier stokes

[Matthew Knepley]

On Mon, Mar 22, 2021 at 10:04 AM Sepideh Kavousi <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

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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