Home  Blog Changing Solver Control Parameters on the Fly via the MOD File
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Changing Solver Control Parameters on the Fly via the MOD File |
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The MOD file can be used to
change some solver control parameters while the solver is running. The
idea is
that some solution control and output control parameters can be
modified by creating a modelname.MOD
file, without stopping and
restarting the simulation. The MOD file should be in the directory
where
your modelname.DTF file is
located (where the solver is running).
The flow solver checks for the presence of a modelname.MOD file at the
beginning of each solution iteration. If that file exists, the
solver will open
the file, read and process any commands found in that file, echo the
commands to a file named modelname.HIS,
and finally delete the original modelname.MOD
file. The MOD file is a plain text file
created by the user (with Notepad or some other text editor; do
not use Microsoft Word). Please note that the text file should be in ASCII format only.
Here is the simple example of using a MOD file. Lets say you are
running a steady state case.
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The output
settings
are:
- Number of Iterations = 1000
- Output = End of Simulation
Let's say the solver has completed 500 iterations and you wish to post
process
your results in CFD-VIEW. Because you have selected the “End of
Simulation” output option, you will not have any solution data until
the solver is finished. Rather than stopping the simulation, you can use a
MOD file.
Following are some simple steps for using the MOD file:
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Create modelname.MOD
file using Notepad or some other text
editor and put it in the same directory where your modelname.DTF file is.
Note: If you are using
Notepad to create the MOD file, make sure the file is saved as *.MOD
without the .txt
extension. If the .txt
extension is in the file name, the solver will not recognize the file
as a MOD file.
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Write the command keyword “SAVE_CONTINUE” in modelname.MOD file as
shown.
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The solver checks for the presence of a modelname.MOD
file at the beginning
of each solution iteration. It will open the modelname.MOD
file,
read and process the command “SAVE_CONTINUE” (in this case saving the
data/results to modelname.DTF),
create a history file named modelname.HIS,
and delete the original modelname.MOD
file. You can now open that DTF file in
CFD-VIEW
and post-process the results.
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Once the MOD file has been processed, the history file, modelname.HIS, provides
information about
changes that were made to the solver during the run.
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The user can
also change the control parameters at a
desired iteration or time step by using the ‘perform_at_iteration’
and ‘perform_at_time_step’
commands, respectively. These commands should precede the command the
user wants to execute at
that iteration or time.
Given below
is an example of a MOD file that tells the solver to change the
enthalpy under-relaxation at the 250th iteration and at the
500th iteration.
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The solver has many MOD
file commands available that are useful in many situations. A
list of the available commands can be
found here.
If you have any questions about this feature or would like us to
discuss other topics in the future, please let us know.
Regards,
Kartik Shah
ESI CFD Support Team
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