Home  CFD-ACE+ User Tips Restarting a Fine Grid Case from a Coarse Grid Solution
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Restarting a Fine Grid Case from a Coarse Grid Solution |
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Many users have asked for a
method to obtain a solution on a coarse grid and then use it as the
initial guess for a finer grid. This option can be done using the
Map utility in
CFD-Toolkit.
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The steps to perform this
operation are as follows:
Create coarse grid system:
The first step is to create the coarse grid system of the
geometry in CFD-GEOM. In this example the following coarse grid
is used. Save the coarse grid system as a DTF file, such as coarse_grid.DTF.
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Set
up and run the problem: Open
the coarse_grid.DTF file in
CFD-ACE-GUI and set up the problem.
Once
the setup is complete, submit it to the solver to be run.
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Copy
the Simulation: Once the simulation has completed
running, copy the coarse_grid.DTF
file into another file, such as fine_grid.DTF.
The fine_grid.DTF has all the
settings that the coarse_grid.DTF
has, but still has the coarse grid system.
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Create
the Fine Grid: Go to CFD-GEOM and open the coarse_grid.GGD file if it is not
already open. Create the fine grid now by changing the number of
grid points. Only the number of grid points are changed and no
modifications are made to the geometry shape. Also be careful not to delete or recreate any entity. Save the DTF file
as fine_grid.DTF by selecting
the Update Grids Only
option.
Now fine_grid.DTF consists of
the finer grid system but retains all the model setup options from the
coarse grid simulation.
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Map
Solution Data: The solution data in the fine_grid.DTF file is still from
the coarse grid solution and therefore not consistent with the fine
grid system. To map the solution data from the coarse grid DTF
file to the fine grid DTF file, we can use CFD-Toolkit. The first
thing to do is launch
CFD-Toolkit. (Note: On Windows systems, choose
Start-->Run-->CFD-Toolkit.) Go to the File View/Manipulate --> Map DTF File. Once it has been
selected, the following window will
be active.
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| The source file will be coarse_grid.DTF, which
contains the solution data for the coarse grid
simulation. The destination file will be fine_grid.DTF, which
consists of the same settings as coarse_grid.DTF.
Once these files have been input, select the Zone Data option, which will map the
solution data from one file to another. There are three options
for Zone Data: Node, Cell, Face. To map the data,
select all of the options (Node, Cell, and Face). Click Map to perform the
mapping. |
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the Fine Grid Model: The last step is to run the fine_grid.DTF file. Open the
file in CFD-ACE-GUI. All the settings used to run the coarse_grid.DTF file will be
retained. The only modification needed for the model setup is the
initial condition. Go to the IC tab (shown right) and select Previous Solution. The restart
filename will be fine_grid.DTF,
since the solution data was mapped onto fine_grid.DTF. The final step
is to submit it to the solver.
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Once the run is complete, you
can import both of the files into CFD-VIEW and analyze the
results. Below are some results obtained to demonstrate the
advantage of using a finer grid. The results on the left are from
coarse_grid.DTF and the
results on the right are from fine_grid.DTF.
As you can see, a much more accurate solution is obtained using the
finer grid.
coarse_grid.DTF
fine_grid.DTF
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| The example above showed
specifically how to use the CFD-Toolkit Map
File function to interpolate solution data from a coarse grid to a fine
grid for restart purposes. You can also use the CFD-Toolkit Map
File
function to map Simulation Data, BC Data, or VC Data between any two
DTF
files. For example, you could have two totally different grid
topologies
but you know that all the Sim Data should be the same (Sim Data are
items like problem type, model options, and solver control settings).
Likewise you could have very complex VC settings that you want to copy
from one DTF file to another. When mapping BC or VC data, CFD-Toolkit lets you choose the criteria that define a "match" (e.g.,
name only,
name and type, etc.). |
If you have any questions about
this feature or would like us to discuss some other topic in the
future, please let us know.
ESI CFD Support Team
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