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convergence problem



Hi David,

greetings from Edinburgh. I have spend the time after the Golden
conference with
a nice week of mountainbiking in Utah and then returned home earlier.
Inspired by some discussions we had I have modified the pht3d code to
write one long input file for each phreeqc step rather
than processing cell after cell. It seemed indeed to speed up execution
but the difference
is by far less substantial than temporally "deactivating" the phreeqc
step in regions/cells without chemical
gradient (I think I mentioned this). For larger models the input files
can become quite big
and I had the impression that in those cases the execution was rather
slower compared to the cell-by-cell version.
I will try to compare it properly one day.

Recently I went back to this in situ reducing zone problem that I
mentioned in my talk and now included
some more metals in addition to zinc for some scenario-type modelling
but was unfortunately
running into convergence problems. Sometimes when this happened before
(very occasionally) it was
typically when a component had a very small concentration. However, in
the case now, I can't see what the problem is,
except that it is caused by Copper. When Cu is removed from the
simulation, the model converges
in the batch and in the 2D transport simulation.
I am not sure if you have any time, but if so, maybe you have an idea
what the problem is and how
I could avoid it. I have attached the input file (with Cu activated) and
the appropriate database file.

Thanks & regards
    Henning





Attachment: pht3d_datab.dat
Description: application/unknown-content-type-dat_auto_file

SOLUTION 13
#GRID 13
units mol/L
temp 25.000000
pH 6.676109 charge # comp 29
pe -2.998528 # comp 30
Acetate 7.975427e-05 # comp 1
Molasse 1.878219e-03 # comp 2
O(0) 0.000000e+00 # comp 3
As(3) 2.395640e-09 # comp 4
As(5) 2.871453e-09 # comp 5
C(4) 3.880034e-03 # comp 6
C(-4) 8.380750e-09 # comp 7
Ca 1.286009e-03 # comp 8
Cd 8.428597e-10 # comp 9
Cl 8.471532e-03 # comp 10
Cr(2) 0.000000e+00 # comp 11
Cr(3) 8.004242e-08 # comp 12
Cr(6) 0.000000e+00 # comp 13
Cu(1) 4.582913e-07 # comp 14
Cu(2) 7.206154e-07 # comp 15
Fe(2) 1.514445e-06 # comp 16
Fe(3) 0.000000e+00 # comp 17
K 1.535808e-03 # comp 18
Mg 1.486955e-03 # comp 19
N(-3) 7.330157e-05 # comp 20
N(3) 1.392629e-05 # comp 21
N(5) 0.000000e+00 # comp 22
Na 8.936836e-03 # comp 23
Ni 4.238997e-08 # comp 24
Pb 7.970436e-08 # comp 25
S(-2) 1.009645e-05 # comp 26
S(6) 2.381857e-03 # comp 27
Zn 8.247324e-07 # comp 28
Bacteria 2.422534e-05 # comp 31 imob but no napl
EQUILIBRIUM_PHASES 13
Sphalerite 0.0 3.982682e-06  # comp  32
Hematite 0.0 1.999055e-03  # comp  33
Siderite 0.0 0.000000e+00  # comp  34
Covellite 0.0 1.251397e-05  # comp  35
Greenockite 0.0 6.945988e-09  # comp  36
Galena 0.0 6.599528e-07  # comp  37
Millerite 0.0 3.290095e-07  # comp  38
Oripment 0.0 1.618014e-08  # comp  39
Realgar 0.0 0.000000e+00  # comp  40
Cr(OH)3(A) 0.0 9.326369e-07  # comp  41
KINETICS 13
Acetate # 1
-parms  3.250000e+00 1.000000e-04
-formula Acetate -1.0 Acetate -1.0  C2H3O2- 1.0  1.0 Bacteria 0.08 C5H7O2N -0.08^M

-steps 2.160000e+04 s(econds) in 1 steps

Molasse # 2
-parms  6.000000e+00
-formula Molasse -1.0 C6H12O6 0.33333 Acetate 2.0 H+ 2.0 Bacteria 0.08 C5H7O2N -0.08^M

Bacteria # 31
-parms  1.000000e-01
-formula Bacteria -1.0 C5H7O2N 1.0^M

FeS(ppt) # 42
-m 0.000000e+00
-parms  1.000000e+00 1.000000e-10

USER_PUNCH
10 PUNCH TOT("Acetate"), TOT("Molasse")
20 PUNCH TOT("O(0)"), TOT("As(3)"), TOT("As(5)"), TOT("C(4)"), TOT("C(-4)"), TOT("Ca"), TOT("Cd"), TOT("Cl"), TOT("Cr(2)"), TOT("Cr(3)"), TOT("Cr(6)"), TOT("Cu(1)"), TOT("Cu(2)"), TOT("Fe(2)"), TOT("Fe(3)"), TOT("K"), TOT("Mg"), TOT("N(-3)"), TOT("N(3)")
25 PUNCH TOT("N(5)"), TOT("Na"), TOT("Ni"), TOT("Pb"), TOT("S(-2)"), TOT("S(6)"), TOT("Zn")
30 PUNCH -LA("H+"), -LA("e-")
40 PUNCH TOT("Bacteria")
60 PUNCH EQUI("Sphalerite"), EQUI("Hematite"), EQUI("Siderite"), EQUI("Covellite"), EQUI("Greenockite"), EQUI("Galena"), EQUI("Millerite"), EQUI("Oripment"), EQUI("Realgar"), EQUI("Cr(OH)3(A)")
90 PUNCH KIN("FeS(ppt)")
END


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Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
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