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CFD-VisCART is best suited for aerodynamic and
automotive underhood applications involving extremely
complex geometries. When generating the mesh, you
might encounter negative volumes in the mesh.
CFD-ACE-SOLVER is not capable of handling such
meshes, and thus these deficiencies in the mesh must
be removed before submitting it to the solver. This
user tip will discuss how to locate these problem
cells from CFD-VisCART output.
As shown in a previous user tip, CFD-VisCART offers
some automatic clean up tools to check and improve
the quality of the grid and in particular to remove
those negative volume cells. CFD-VisCART v2006
extended this capability by automatically removing
skewed cells and negative volume cells. When using
these tools, you will get a message detailing the
number of problem cells.
Total Negative Volume Cells: 0
However, when dealing with very complex geometries,
these tools might not be sufficient to remove all of
them and you can still face the warning message shown
in Figure 1.
Figure 1. Warning message that negative volumes have
been encountered.
In this situation, if the "Remove" button suggested
by the warning message cannot repair all the
offending cells, there are several options to improve
the grid and get rid of these negative volumes cells.
The most common one being the addition of some local
refinement sources (e.g. surface or box sources).
Previously, CFD-VisCART was indicating only the
number of offending cells and their volumes.
Therefore the user had to guess where the problem
location was and add some refinement sources,
regenerate the mesh and verify that it fixed the problem.
In order to help this process, the log file created
by CFD-VisCART was improved so that it gives the
location of the negative volume cells. So, by opening
the file called VisCART.log, which is always created in
your working directory, you can check the positions
of the offending cells, as shown in Figure 2. You can
also view the log file by clicking the VisCART log
button in the toolbar.
Figure 2. CFD-VisCART log file detailing the
locations of the negative volume cells.
Now, you can simply go back to CFD-VisCART and create
a source around the locations indicated in the log
file. It avoids the trial and error process that was
required previously, and saves you some significant
time for your mesh generation.
In addition to this, two new options were recently
added in order to help users when they share files
and use multiple versions of CFD-VisCART. The first
one allows you to get the version number of the
CFD-VisCART you are using. In a command line, type:
CFD-VisCART -v
On Unix/Linux, it will simply output in the shell the
following information:
CFD-VisCART V2006.0.56 DTF V7.2.2 Build date
11/09/2005 12:07:31
On Windows, this is slightly different. It will
create a file called CFD-VisCART.version in your
working directory with the same information.
The second command allows you to check the version of
CFD-VisCART that was used to create the VGD file.
This can be useful to check the compatibility between
files among several users for instance. Also in a
command line, type:
CFD-VisCART -fv file.VGD
Again, it will be slightly different between
Unix/Linux and Windows. On Unix/Linux, you will get
the information written to the shell:
VGD Version: 2006.0.56
On Windows, it will
create a file called CFD-VisCART.fversion in your
working directory with the same information.
Emmanuel Bot
Applications Engineer
ESI CFD Customer Support
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