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saving data in paraview

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Old   May 22, 2014, 10:57
Default saving data in paraview
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Dear Foamers,

I've calculated kinetic energy from vector field U in paraview with the calculator.
Afterwards I've saved the data (vectorfield U and computed scalarfield K). Before saving process is finished the user needs to choose the field association:
Points, Cells or Field Data.

If I choose 'Points' or 'Cells' I receive four csv.files. The first file contains values of the internal flow field.
The other three files contain values from patches, but not for all patches.

In my test case I've a flow channel with cyclic inlet/outlet (flow-direction) and cyclic patches in spanwise direction. top and bottom patches are defined as walls. To be able to do grading I've created the mesh with two blocks. That way flow domain is horizontally subdivided (at y = 1/2*channel height). Total number of patches = 10.

I've compared number of cells on the patches with number of file entries in the three additional data files. It seems that two of these three additional files contain values for one inlet and one outlet patch (in total I've two inlet and two outlet patches) and the last file contains values of only one wall patch (bottom or top).

I've no symmetry plane defined. Why do I not receive a data file for each patch?

What is the difference between the Field Association options 'Points', 'Cells' and 'Field Data'?
I thought 'Points' give values at cell centroids. But this idea must be wrong because the file contains U component values equal to zero. That indicates that 'Points' lie on the wall where U is zero.
If I choose 'Cells' the data files contain only the components of velocity vector U but no the scalar values of kinetic energy K. Does 'Cells' imply vector components?
And if I choose 'Field Data' the csv files are empty.

Could anybody explain me the options 'Cells' and 'Field Data' ?


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Old   May 25, 2014, 07:14
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Greetings Aylalisa,

A detailed explanation on the topic of point data vs cell data is given here: studying a valve case post #12

As for "Field data": I haven't fully figure out what it's for, but AFAIK it's not commonly used for OpenFOAM cases.

As for the various CSV files: I believe that you're getting one file per loaded block. In other words, the readers for opening OpenFOAM cases in ParaView, usually associate 1 data block per mesh part, as shown in the attached picture.
If you're not getting all of the CSV files for all of the patches you want, it's very likely that you didn't choose to load all of the mesh parts that your case provides.

Best regards,
Bruno
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Old   May 28, 2014, 08:56
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Hello Bruno,

thank you for your support!

Quote:
As for the various CSV files: I believe that you're getting one file per loaded block. In other words, the readers for opening OpenFOAM cases in ParaView, usually associate 1 data block per mesh part, as shown in the attached picture.
If you're not getting all of the CSV files for all of the patches you want, it's very likely that you didn't choose to load all of the mesh parts that your case provides.
You are right, I chose only three mesh parts including the internal mesh and therefore received 'only' four data files!

With help of the documentation I understand 'point data' and 'cell data'.


I wonder why the files, generated by selecting 'field data', are empty , that makes it hard to derive their meaning.


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Old   May 31, 2014, 11:38
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Quote:
Originally Posted by aylalisa View Post
I wonder why the files, generated by selecting 'field data', are empty , that makes it hard to derive their meaning.
If there are no fields in "field data", then is nothing to export to CSV file.

I've done a quick search and it's explained here: http://www.paraview.org/Wiki/VTK/Tut...rage#FieldData - and I quote:
Quote:
FieldData

Arrays attached to the FieldData of a dataset describe global properties of the data. That is, if you want to save the time at which the data were recorded, you would put that value in the FieldData. If you wanted to name the data set, you would also put that in the FieldData. There are no restrictions about the length of arrays that are added to the FieldData.
This simply isn't used by OpenFOAM, when converting data to VTK format.
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