[snappyHexMesh] snappyHexMesh makes too many patches from STL?

dbazz · April 26, 2022, 18:41

When trying to create a mesh with sHM from an STL file, thousands of patches and regions are generated - too many!

Adding patches for surface regions:
----------------------------------

Patch Type Region
----- ------ -------
model10m;

6 wall model10m_patch0
7 wall model10m_patch1
8 wall model10m_patch2
...
30000 wall model10m_patch30000

The meshing process should take a few minutes, but when this issue occurs, it can take hours to generate the same mesh.

I found that is issue occurs when an STL is encoded in binary. When the STL is encoded in ASCII, this issue does not occur. To prevent this issue, you can open the mesh in software like AutoCAD Fusion, import the binary STL, and save the STL as ASCII (which you can open with a simple text editor).

I have solved my own problem but I thought I should post the question and solution here, as I could not find anything to help troubleshoot the problem.

cgoessni · June 22, 2022, 02:05

Hi dbazz!

Did you find out what the problem was?

dbazz · June 22, 2022, 10:05

Yes - the STL I was working with was in binary format. It needs to be in ASCII format to be friendly with SHM tools

cgoessni · June 22, 2022, 10:56

Okay, I want to stay with the binary format, since it is much faster, smaller in file size and more precise. I can live with the many patches now, since in my case there are only two, and not 10,000s.

Thanks for your answer.

cgoessni · July 13, 2022, 08:54

Update: If you set the attribute to another value than 0, you will get as many patches as you set the number of attributes:
https://bugs.openfoam.org/view.php?id=3860

If you use numpy-stl, you can set the attribute to 0 by
mesh.attr = 0

That resolved my problem.

April 26, 2022, 18:41	snappyHexMesh makes too many patches from STL?	#1
dbazz New Member David Join Date: Dec 2021 Posts: 4 Rep Power: 4	When trying to create a mesh with sHM from an STL file, thousands of patches and regions are generated - too many! Adding patches for surface regions: ---------------------------------- Patch Type Region ----- ------ ------- model10m; 6 wall model10m_patch0 7 wall model10m_patch1 8 wall model10m_patch2 ... 30000 wall model10m_patch30000 The meshing process should take a few minutes, but when this issue occurs, it can take hours to generate the same mesh. I found that is issue occurs when an STL is encoded in binary. When the STL is encoded in ASCII, this issue does not occur. To prevent this issue, you can open the mesh in software like AutoCAD Fusion, import the binary STL, and save the STL as ASCII (which you can open with a simple text editor). I have solved my own problem but I thought I should post the question and solution here, as I could not find anything to help troubleshoot the problem.

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June 22, 2022, 02:05		#2
cgoessni New Member Clemens Goessnitzer Join Date: Nov 2021 Posts: 6 Rep Power: 4	Hi dbazz! Did you find out what the problem was?

June 22, 2022, 10:05		#3
dbazz New Member David Join Date: Dec 2021 Posts: 4 Rep Power: 4	Yes - the STL I was working with was in binary format. It needs to be in ASCII format to be friendly with SHM tools

June 22, 2022, 10:56		#4
cgoessni New Member Clemens Goessnitzer Join Date: Nov 2021 Posts: 6 Rep Power: 4	Okay, I want to stay with the binary format, since it is much faster, smaller in file size and more precise. I can live with the many patches now, since in my case there are only two, and not 10,000s. Thanks for your answer.

July 13, 2022, 08:54		#5
cgoessni New Member Clemens Goessnitzer Join Date: Nov 2021 Posts: 6 Rep Power: 4	Update: If you set the attribute to another value than 0, you will get as many patches as you set the number of attributes: https://bugs.openfoam.org/view.php?id=3860 If you use numpy-stl, you can set the attribute to 0 by mesh.attr = 0 That resolved my problem.