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Wei October 22, 2008 13:11

Mesh repair
 
After converting an old mesh created using STAR-CD 3.1 to STAR-CD 4.06 by using nastran format, there are holes at particular part of mesh.

Does STAR-CD 4.06 provide any function particularly to repair such meshing problem?

Thank you.

allan October 23, 2008 07:28

Re: Mesh repair
 
Hi

What do you mean by holes?

whitemelon October 23, 2008 08:44

Re: Mesh repair
 
Does the mesh has couple? nastran format doesn't support the couple mesh.

TG October 23, 2008 10:12

Re: Mesh repair
 
Why don't you just read/resume the 3.1 .mdl file directly into 4.06? Nastran does not understand all possible cell shapes that STAR is capable of producing. The holes might be from that.

Wei October 24, 2008 06:10

Re: Mesh repair
 
Hi Allan,

please see the figure http://www.whlam.com/engine/corruptedduct1.gif

There are missing cells at particular region forming some holes.

Wei October 24, 2008 06:29

Re: Mesh repair
 
The reason I choose nastran format is due to the saving problem of old STAR_CD 3.1 .mdl mesh in the STAR-CD 4.06. The resumed STAR-CD 3.1 mesh can not be saved using STAR-CD 4.06. To secure the STAR-CD 3.1 mesh, I therefore exported through nastran format.

It is strange. The problem of holes or more precisely the missing cells still occurs when read the .mdl file directly.

Yes, there are couple settings. Unfortunately I lost the couple settings as well.

Could you share what particular cells nastran format does not support?

Balduin Bankerotti October 24, 2008 06:36

Re: Mesh repair
 
The missing cells are trimmed cells which can are not supported within the nastran format.


Wei October 24, 2008 06:45

Re: Mesh repair
 
Should be. The trimmed cell is not widely supported by the standard file format.

In this case, any suggestion to repair it or do you think exporting the geometry and then recreating the entire mesh is a better solution?

Thank you.

Pauli October 24, 2008 10:45

Re: Mesh repair
 
NASTRAN does not support trimmed (polyhedral cells). It supports tetrahedron, hexahedron and prism cells.

Here is something you can try. In Star 3.1, use the cdsave command to export the model. In Star 4.06 use the ifile command to read in the model. I'm not sure what happens with the Star 3.1 couples. (Star 4.06 is a face based code which does not use couples.) Star 4 may do the necessary conversion. Sorry but I haven't used Star 4 much so I'm not sure about this matter.

TG October 24, 2008 12:33

Re: Mesh repair
 
I think exporting the geometry and recreating the mesh is a much better idea. The new trimmed/poly meshers in pro-STAR4 are borrowed from STAR-CCM+ and produce significantly better meshes than older version of STAR3.

Balduin Bankerotti October 24, 2008 15:00

Re: Mesh repair
 
Read the mesh into v4 and run the command "cptran". Look if the holes are still there and post the warnings/errors from the output window.


Balduin Bankerotti October 24, 2008 15:02

Re: Mesh repair
 
Read the *.mdl file !!!

whitemelon October 24, 2008 19:58

Re: Mesh repair
 
why not export the *.cel and *.vrt data?

Anton Lyaskin October 27, 2008 05:09

Re: Mesh repair
 
Because even *.cel file format was changed between 3.x and 4.x version.

Many, many thanks to CD-Adapco...

Balduin Bankerotti October 27, 2008 07:40

Re: Mesh repair
 
v4 can read the cell files from v3. But with exporting just *.cel and *.vrt you will loose the couples which are there in most proam meshes.

How would you support polyhedral cells without a possibility to write them to the *.cel file? There are also tools available to convert a v4 *.cel file back into v3 format just ignoring the polys.


Wei October 27, 2008 12:14

Re: Mesh repair
 
cptran does seem the right answer to repair the missing cells.

1) I read the v3.1 .mdl file; 2) cptran the mesh (fix the missing cells) ; 3) export as .cel, .vrt and .bnd files (resumed v3.1 .mdl can not saved directly in v4.06); 4) import to v4.06

However, when i check the mesh quality, there are some other error messages.

errornumber-command-description

69-chec- non-right-handed cells found

234-chec- cell has a greater-than-desired aspect ratio

176-chec- cells found with face warpages greater than the prescribed value

80-chec- internal face angle of a cell exceeds prescribed value

70-chec- cells found with negative volume or volume less than specified volume

406-chec- centroidal check failed. cells have centroids which reside outside their volumes.

71-chec- centroidal check failed. cells overlap.

74-chec- there are cracks (unconnected regions) in the model

265-chec- model has groups of disconnected cells.

76-chec- cell faces with very small suface areas found in the model.

Are these fatal errors or ignorable?

Balduin Bankerotti October 27, 2008 16:43

Re: Mesh repair
 
What are you doing man? You should simply take the v31 *.mdl file and read it into v406. After that you type the command "cptran all". Then there should be no holes or missing cells.

I tried it myself with an old proam mesh and it worked.

Check if there are any warnings or errors during this process and post them.

Forget the *.cel and *.vrt files!!!


Anton Lyaskin October 28, 2008 04:11

Re: Mesh repair
 
> There are also tools available to convert a v4 *.cel file back into v3 format just ignoring the polys.

BTW, what are these tools? Because sometimes I really miss such an opportunity

Cloud October 28, 2008 04:40

Re: Mesh repair
 
I agree to TG. Live the surface from 3.1, then regenerate new trimmed meshes in 4.06. Trimmed cells of v3 and v4 are quite different. Another choice, you may try to resume 3.1 to 3.26, then resume 3.26 to 4.06. But this method may not work...

Balduin Bankerotti October 28, 2008 04:45

Re: Mesh repair
 
Ask the support for the file "cell423.f" or search for star-backport.


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