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Hi Dr. Parkhurst,
I have a questions about PHAST.
The question relates to the choice of a time-step
when simulating an ion exchange problem.
I have included the input file of the problem
and a graph for Cl- concentrations vs distance (the results are
similar for Ca, Na and K).
I'm comparing the results with MIN3P and I get a
good match with a time step of 0.5 days.
I don't know why, when using a small time
step, I get oscillations. The smaller the time step the larger the
oscillations. I would have thought, due to the Courant conditions, the
results would be more precise with a smaller time steps.
If you could solve this for me, or give me an
indication of how best to choose a time step when setting up a new problem,
I would appreciate it.
Best regards,
Angus
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Attachment:
ionx.chem.dat
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ionx.trans.dat
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Attachment:
phast-timestep.wmf
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