Dear Mathew,
thank you for your response. I double checked and  snes is converged in all steps. following is output of -snes_converged_reason

0 TS dt 0.0001 time 0.
copy!
Write output at step= 0!
    0 SNES Function norm 1.465357113711e+01
    1 SNES Function norm 1.131764004094e+02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 5.657793773845e+01
    1 SNES Function norm 9.539766295097e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
1 TS dt 0.0002 time 0.0001
copy!
    0 SNES Function norm 1.734774181586e+02
    1 SNES Function norm 1.009139331913e+00
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
2 TS dt 0.000324496 time 0.0003
copy!
    0 SNES Function norm 1.200543689889e+01
    1 SNES Function norm 1.715000763566e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
3 TS dt 0.000471924 time 0.000624496
copy!
    0 SNES Function norm 8.374168676869e+00
    1 SNES Function norm 3.806213226152e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
4 TS dt 0.00076859 time 0.00109642
copy!
    0 SNES Function norm 9.316857431814e+00
    1 SNES Function norm 3.125732297714e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
5 TS dt 0.00153718 time 0.00186501
copy!
    0 SNES Function norm 9.820005256073e+00
    1 SNES Function norm 8.107044589689e-04
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
6 TS dt 0.00218053 time 0.00340219
copy!
    0 SNES Function norm 5.122834112454e+00
    1 SNES Function norm 1.662895139952e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
7 TS dt 0.0022609 time 0.00558272
copy!
    0 SNES Function norm 1.423878996243e+00
    1 SNES Function norm 1.329199025944e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
8 TS dt 0.0045218 time 0.00784362
copy!
    0 SNES Function norm 1.241101191899e+00
    1 SNES Function norm 1.758309073907e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 2.174982578512e+00
    1 SNES Function norm 1.977451891592e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
9 TS dt 0.00309088 time 0.0111379
copy!
    0 SNES Function norm 7.952246195856e-01
    1 SNES Function norm 3.315360582766e-04
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
10 TS dt 0.00302529 time 0.0142288
copy!
    0 SNES Function norm 7.852078318680e-01
    1 SNES Function norm 6.819399397977e-04
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
11 TS dt 0.0036818 time 0.0172541
copy!
    0 SNES Function norm 1.269332622839e+00
    1 SNES Function norm 1.508985874154e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
12 TS dt 0.00736361 time 0.0209359
copy!
    0 SNES Function norm 6.143748829896e+00
    1 SNES Function norm 2.172457806998e-01
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
13 TS dt 0.00792431 time 0.0282995
copy!
    0 SNES Function norm 2.762542847702e+01
    1 SNES Function norm 1.329294167855e+01
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 2.287537833706e+01
    1 SNES Function norm 1.608258731248e+00
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 1.279894262237e+01
    1 SNES Function norm 5.112278399366e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
14 TS dt 0.0017228 time 0.0301754
copy!
    0 SNES Function norm 4.714428103053e+00
    1 SNES Function norm 3.141482420272e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
15 TS dt 0.00174124 time 0.0318982
copy!
    0 SNES Function norm 5.161696766061e+00
    1 SNES Function norm 3.434924981822e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 1.440940181693e+01
    1 SNES Function norm 2.060277373865e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
16 TS dt 0.00143688 time 0.0334492
copy!
    0 SNES Function norm 4.954103004576e+00
    1 SNES Function norm 1.705855165536e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
17 TS dt 0.00287377 time 0.0348861
copy!
    0 SNES Function norm 1.757129021431e+01
    1 SNES Function norm 3.191948709005e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 3.031772340693e+01
    1 SNES Function norm 7.097653811013e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
18 TS dt 0.00203648 time 0.0368402
copy!
    0 SNES Function norm 1.629074198276e+01
    1 SNES Function norm 9.774829708834e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 4.007821179267e+01
    1 SNES Function norm 4.322266335869e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 2.348161408350e+01
    1 SNES Function norm 5.218780461268e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 1.789799437816e+01
    1 SNES Function norm 2.727867493741e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
19 TS dt 0.000223859 time 0.0370644
copy!
    0 SNES Function norm 1.164475864748e+00
    1 SNES Function norm 5.580165229404e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
20 TS dt 0.000209603 time 0.0372882
copy!
Write output at step= 20!
    0 SNES Function norm 7.548512298179e-01
    1 SNES Function norm 8.191710667867e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 5.113158684224e+00
    1 SNES Function norm 4.059400705957e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
    0 SNES Function norm 3.408310084009e+00
    1 SNES Function norm 5.257240981430e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
21 TS dt 7.85133e-05 time 0.0373492
copy!
    0 SNES Function norm 4.156375747211e-01
    1 SNES Function norm 3.052885436956e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
22 TS dt 9.58699e-05 time 0.0374277
copy!
    0 SNES Function norm 4.583956492983e-01
    1 SNES Function norm 1.176944126767e-01
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
23 TS dt 9.32603e-05 time 0.0375236
copy!
    0 SNES Function norm 4.969090229611e-01
    1 SNES Function norm 1.738678566558e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
24 TS dt 0.000186521 time 0.0376169
copy!
    0 SNES Function norm 6.406466977155e-01
    1 SNES Function norm 8.183507106613e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
25 TS dt 0.000213369 time 0.0378034
copy!
    0 SNES Function norm 6.235579283905e-01
    1 SNES Function norm 7.038633582283e-02
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
26 TS dt 0.000217545 time 0.0380168
copy!
    0 SNES Function norm 5.375653976237e-01
    1 SNES Function norm 7.318538883142e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1
27 TS dt 0.000384287 time 0.0382343
copy!
    0 SNES Function norm 8.638617026715e-01
    1 SNES Function norm 1.596171692523e-03
  Nonlinear solve converged due to CONVERGED_ITS iterations 1

From: Matthew Knepley <knepley@gmail.com>
Sent: Tuesday, April 20, 2021 7:23 AM
To: Sepideh Kavousi <skavou1@lsu.edu>
Cc: petsc-users@mcs.anl.gov <petsc-users@mcs.anl.gov>
Subject: Re: [petsc-users] convergence slow
 
On Mon, Apr 19, 2021 at 5:43 PM Sepideh Kavousi <skavou1@lsu.edu> wrote:
Hello,
I want to solve PF solidification+Navier stokes using Finite different method. The Poisson equation is much more complicated that the one for just a fluid-flow problems (because it includes different terms order parameter terms).
The code converges but the convergence rate is very slow. I have tried different options. Following is the best options I found but the convergence is still very slow. I did not include the ksp_convergence data because it takes around 1000 liner solver steps for each snes step.
I look in literature, but I did not find any data on PF+navierstokes solutions using Petsc. Do you have any suggestions how should I improve the convergence?

First question: Are your nonlinear solves converging?

  I see you have -snes_type ksponly, but it looks like your SNES iteration _diverges_ sometimes, and mostly fails to converge.
  Is this correct?

  Thanks,

      Matt
 
Best,
Sepideh


ibrun -np 136 ./one.out -ts_monitor -snes_fd_color -ts_max_snes_failures -1  -ts_type bdf -ts_bdf_adapt -snes_linesearch_type l2 -snes_type ksponly -pc_type fieldsplit -pc_fieldsplit_0_fields 0,1 -pc_fieldsplit_1_fields 2,3 -pc_fieldsplit_2_fields 4 -pc_fieldsplit_type multiplicative -fieldsplit_0_pc_type bjacobi -fieldsplit_1_pc_type bjacobi -fieldsplit_2_pc_type ilu -fieldsplit_0_ksp_type preonly -fieldsplit_1_ksp_type preonly -fieldsplit_2_ksp_type preonly -sub_pc_type ilu -sub_ksp_type preonly -snes_monitor -log_view log.txt

TACC:  Starting up job 7605521
TACC:  Starting parallel tasks...
nu_nd=14948.511 !
tau/w=26225.459!
initial!
0 TS dt 0.0001 time 0.
copy!
Write output at step= 0!
    0 SNES Function norm 1.465357113711e+01
    1 SNES Function norm 1.131764004117e+02
    0 SNES Function norm 5.657793773935e+01
    1 SNES Function norm 9.539772669908e-02
1 TS dt 0.0002 time 0.0001
copy!
    0 SNES Function norm 1.734774194628e+02
    1 SNES Function norm 1.009134558763e+00
2 TS dt 0.000324128 time 0.0003
copy!
    0 SNES Function norm 1.199860231725e+01
    1 SNES Function norm 1.698885201785e-02
3 TS dt 0.000470679 time 0.000624128
copy!
    0 SNES Function norm 8.344934987594e+00
    1 SNES Function norm 4.082958856578e-03
4 TS dt 0.000769357 time 0.00109481
copy!
    0 SNES Function norm 9.338443428763e+00
    1 SNES Function norm 2.472903267511e-03
5 TS dt 0.00153871 time 0.00186416
copy!
    0 SNES Function norm 9.836384162921e+00
    1 SNES Function norm 6.383053421790e-03
6 TS dt 0.00215245 time 0.00340288
copy!
    0 SNES Function norm 5.043289760603e+00
    1 SNES Function norm 2.168332362305e-03
7 TS dt 0.0022353 time 0.00555533
copy!
    0 SNES Function norm 1.421255264272e+00
    1 SNES Function norm 1.750393691475e-03
8 TS dt 0.0044706 time 0.00779063
copy!
    0 SNES Function norm 1.216746389225e+00
    1 SNES Function norm 5.339123694240e-04
    0 SNES Function norm 2.168489818312e+00
    1 SNES Function norm 1.928809773415e-03
9 TS dt 0.00310217 time 0.0110885
copy!
    0 SNES Function norm 8.021629529051e-01
    1 SNES Function norm 2.161901383228e-04
10 TS dt 0.00300302 time 0.0141906
copy!
    0 SNES Function norm 7.731190774223e-01
    1 SNES Function norm 2.807020573793e-04
11 TS dt 0.00367968 time 0.0171937
copy!
    0 SNES Function norm 1.263830181443e+00
    1 SNES Function norm 1.049133009231e-02
12 TS dt 0.00704796 time 0.0208733
copy!
    0 SNES Function norm 5.619818748359e+00
    1 SNES Function norm 1.569218805659e-01
13 TS dt 0.00742462 time 0.0279213
copy!
    0 SNES Function norm 2.268051808662e+01
    1 SNES Function norm 7.055762930884e+00
    0 SNES Function norm 2.173806325395e+01
    1 SNES Function norm 1.564571270312e+00
    0 SNES Function norm 1.208038223084e+01
    1 SNES Function norm 5.192087605517e-02
14 TS dt 0.00186927 time 0.0299244
copy!
    0 SNES Function norm 4.797722218343e+00
    1 SNES Function norm 3.975928994156e-03
15 TS dt 0.00189622 time 0.0317937
copy!
    0 SNES Function norm 5.510229536082e+00
    1 SNES Function norm 4.496811351139e-03
16 TS dt 0.00172953 time 0.0336899
copy!
    0 SNES Function norm 6.945417639798e+00
    1 SNES Function norm 4.569326335543e-03
17 TS dt 0.00218527 time 0.0354194
copy!
    0 SNES Function norm 1.351474156680e+01
    1 SNES Function norm 1.719775600164e-02
18 TS dt 0.00224386 time 0.0376047
copy!
    0 SNES Function norm 2.174969556700e+01
    1 SNES Function norm 3.814212178889e-02
    0 SNES Function norm 4.891415655138e+01
    1 SNES Function norm 6.772042718901e-02
    0 SNES Function norm 2.828143585009e+01
    1 SNES Function norm 6.965842377755e-03
    0 SNES Function norm 2.168193335917e+01
    1 SNES Function norm 2.463212234975e-03
19 TS dt 0.000205482 time 0.0378175
copy!
    0 SNES Function norm 1.409435206457e+00
    1 SNES Function norm 1.859628755245e-02
20 TS dt 0.000188785 time 0.0380229
copy!
Write output at step= 20!
    0 SNES Function norm 5.900261363044e-01
    1 SNES Function norm 2.653576084845e-02
    0 SNES Function norm 5.122905363140e+00
    1 SNES Function norm 4.297068425492e-03
    0 SNES Function norm 3.428448792746e+00
    1 SNES Function norm 1.000610664096e-02
21 TS dt 6.50511e-05 time 0.0380738
copy!
    0 SNES Function norm 3.700405789863e-01
    1 SNES Function norm 6.263642369355e-02
22 TS dt 7.93452e-05 time 0.0381388
copy!
    0 SNES Function norm 5.282939288286e-01
    1 SNES Function norm 3.003209840754e-01
23 TS dt 7.50242e-05 time 0.0382181
copy!
    0 SNES Function norm 7.079201595974e-01
    1 SNES Function norm 1.247544399226e-02
24 TS dt 0.000150048 time 0.0382932
copy!
    0 SNES Function norm 6.197633272307e-01
    1 SNES Function norm 3.176914154297e-02
25 TS dt 0.000171939 time 0.0384432
copy!
    0 SNES Function norm 5.849423362557e-01
    1 SNES Function norm 9.462256964187e-03
26 TS dt 0.000176855 time 0.0386152
copy!
    0 SNES Function norm 4.304951653234e-01
    1 SNES Function norm 3.939112950208e-03



--
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