# [petsc-users] convergence slow

Sepideh Kavousi skavou1 at lsu.edu
Mon Apr 19 16:43:11 CDT 2021

```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?
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
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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20210419/b9b4dfd8/attachment.html>
```