Now, run Shells again, for an actual dynamical simulation experiment! Check the table under Step 16, and be sure that all input and output files are linked to the job, either by providing file names at run time, or by assigning them in a batch file.
Shells should provide a table called "Iteration History" as part of its text output in the t______.out file (Fortran device 6), and it should look something like this:
ITERATION HISTORY:
RELATIVE
CORRE- MAXIMUM MEAN
RELATIVE LATION VERTICALLY VERTICALLY
MAXIMUM MEAN WITH INTEGRATED INTEGRATED
ITER- RMS VELOCITY VELOCITY LAST STRESS STRESS
ATION VELOCITY CHANGE CHANGE CHANGE ERR0R ERR0R
1 6.671025E-11 1.4950E-10 1.000000 ---- 1.7092E+16 .993490
2 6.304374E-11 4.0193E-11 .137291 -.63 3.6075E+13 .378274
3 6.171746E-11 1.8318E-11 .066566 .76 4.7169E+13 .346676
4 6.110019E-11 9.6699E-12 .054420 .94 4.3406E+13 .339420
5 6.097313E-11 6.9601E-12 .042287 .99 3.5744E+13 .321039
6 6.104579E-11 4.8806E-12 .030164 .99 3.5259E+13 .288665
7 6.111884E-11 3.6560E-12 .021870 .99 3.2814E+13 .249889
8 6.116438E-11 2.7920E-12 .016233 1.00 3.4038E+13 .210514
9 6.120358E-11 2.2050E-12 .012962 1.00 1.8886E+13 .177277
10 6.123600E-11 1.7543E-12 .010455 1.00 2.0459E+13 .151851
11 6.124162E-11 1.3929E-12 .008227 1.00 2.8621E+13 .129272
12 6.124802E-11 1.2190E-12 .006900 1.00 2.5601E+13 .111101
13 6.124833E-11 1.1118E-12 .005794 1.00 1.8946E+13 .097004
14 6.123912E-11 1.0577E-12 .005094 1.00 1.2855E+13 .085483
15 6.123926E-11 9.6767E-13 .004568 1.00 1.0113E+13 .074999
16 6.123978E-11 8.6750E-13 .003997 1.00 8.9478E+12 .064639
17 6.124278E-11 7.5090E-13 .003491 1.00 9.2755E+12 .057505
18 6.125361E-11 6.4242E-13 .003049 1.00 7.3854E+12 .050013
19 6.127198E-11 5.5315E-13 .002617 1.00 6.6525E+12 .044480
20 6.129393E-11 4.7318E-13 .002212 1.00 5.3433E+12 .039265
21 6.131728E-11 4.0393E-13 .001880 1.00 6.8598E+12 .034951
22 6.134085E-11 3.4605E-13 .001606 1.00 8.2828E+12 .031143
23 6.136439E-11 2.9741E-13 .001391 1.00 7.3014E+12 .027845
24 6.138654E-11 2.5652E-13 .001205 1.00 6.0201E+12 .025084
25 6.140663E-11 2.2168E-13 .001046 1.00 5.5352E+12 .022969
26 6.142430E-11 1.9390E-13 .000916 1.00 5.1053E+12 .021258
27 6.143915E-11 1.7637E-13 .000805 1.00 4.6690E+12 .019945
28 6.145105E-11 1.8290E-13 .000706 1.00 4.1747E+12 .018810
29 6.146025E-11 1.9527E-13 .000624 1.00 4.8535E+12 .017693
30 6.146818E-11 2.0409E-13 .000568 1.00 6.0509E+12 .016545
31 6.147545E-11 2.0975E-13 .000523 1.00 4.0108E+12 .014991
32 6.148303E-11 2.1244E-13 .000495 1.00 3.9696E+12 .013836
33 6.149065E-11 2.1109E-13 .000467 1.00 3.8282E+12 .012943
34 6.149793E-11 2.0582E-13 .000437 1.00 3.6485E+12 .012218
35 6.150450E-11 1.9935E-13 .000399 1.00 4.1463E+12 .011425
36 6.151064E-11 1.9136E-13 .000369 1.00 4.7319E+12 .010748
37 6.151652E-11 1.8137E-13 .000342 1.00 3.3119E+12 .009961
38 6.152232E-11 1.7012E-13 .000318 1.00 3.9367E+12 .009267
39 6.152796E-11 1.5838E-13 .000295 1.00 3.9631E+12 .008742
40 6.153339E-11 1.4642E-13 .000274 1.00 1.9996E+12 .008194
41 6.153864E-11 1.3427E-13 .000257 1.00 1.8821E+12 .007794
42 6.154367E-11 1.2248E-13 .000242 1.00 1.8185E+12 .007416
43 6.154861E-11 1.1111E-13 .000229 1.00 1.9659E+12 .007063
44 6.155340E-11 1.0026E-13 .000218 1.00 1.7831E+12 .006717
45 6.155805E-11 9.0069E-14 .000207 1.00 1.5092E+12 .006341
46 6.156260E-11 8.0702E-14 .000197 1.00 1.4318E+12 .006023
47 6.156717E-11 7.2161E-14 .000189 1.00 1.3508E+12 .005732
48 6.157177E-11 6.4406E-14 .000180 1.00 1.3697E+12 .005473
49 6.157626E-11 5.7332E-14 .000173 1.00 1.6307E+12 .005227
50 6.158074E-11 5.0900E-14 .000165 1.00
ITERATION LIMIT REACHED BEFORE CONVERGENCE.
---------------------------------------------------------------------- |
All units are SI, so the "RMS velocity" and "Maximum velocity change" are in m/s (typically a very small number), and the "Maximum vertically-integrated stress error" is in Pa m, or N/m (a very large number).
If we graph the two dimensionless measures of this table using a logarithmic scale, we should see steady progress:
If you do not get steady convergence, the most likely causes are:
The solution to the problem you have posed includes one or more "landslides" (localized flows down a topographic gradient) with very high steady-state velocities. The symptom of this is that the RMS velocity (column 2 in the table above) increases in each iteration, in a pattern of quasi-exponential growth. The solution to such cases is to plot the velocity solution (even though it is not converged) to see where the landslide(s) is/are. Then, you can strengthen the lithosphere either locally (by moderating the heat-flow or topography) or globally (by changing rheologic constants).
If there is steady convergence at first, and then a transition to a limiting "noise level" of velocity change and/or stress error, then actually this is normal. (It is just that we usually stop the program before this level is reached.) The "noise level" is largely determined by input parameter OKDELV, which is a velocity (in m/s) precision that we hope to reach, but may not. If this parameter is too large, then convergence will be rapid, but the solution will not be accurate. (This is because the maximum limit on viscosity will be set rather low, and thus the viscosity limit rather than the desired flow law will determine the strain rate at many points.) However, if this parameter is made very small, later iterations may be "wasted" in the sense that the computer runs on but the solution no longer improves.