[BUG] Netgen mesh size drifting

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kds
Posts: 8
Joined: Sun May 30, 2021 4:45 pm

[BUG] Netgen mesh size drifting

Post by kds »

Hi All,
Since 0.19 on win10, I do encounter some challenges with Netgen mesher. It seems mesh triangle size ius drifting along meshing progress towards z (for instance). See below picture comparing both 0.18 and 0.19 with exactly same design and same mesh parameters.
0.18
0.18
0.18
maillage netgen 0.18.png (42.24 KiB) Viewed 1374 times
0.19
0.19.2
0.19.2
maillage netgen 0.19.2.png (78 KiB) Viewed 1374 times
To be noted that the computing time is significantly shorter for 0.19...but leading to terrible mesh. The number of vertex element is indeed like 1/10 th of what it is for 0.18.
A work around is to increase largely the resulting number of vertex elements by tuning parameters, but all-in-all default values for "ultra fine" do not lead to usable mesh for 3d printing.

Simple shape like dummy cylinder will show same results. Any idea what has changed between 0.18 and 0.19.2 and netgen version linked to them?
Attachments
cylindre 0.19.FCStd
Cylinder FC 0.19
(9.47 KiB) Downloaded 16 times
cylindre 0.18.FCStd
Cylinder FC 0.18
(7.62 KiB) Downloaded 17 times
Last edited by kds on Sun Jul 25, 2021 3:31 pm, edited 2 times in total.
user1234
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Posts: 3348
Joined: Mon Jul 11, 2016 5:08 pm

Re: Netgen mesh size drifting

Post by user1234 »

Sorry for late reply. Here https://forum.freecadweb.org/viewtopic.php?&t=56401 you can read the answer. I also had issues with round objects.

Greetings
user1234
kds
Posts: 8
Joined: Sun May 30, 2021 4:45 pm

Re: Netgen mesh size drifting

Post by kds »

Hi,
Thanks for the tip.
Still this is a workaround.
But anyway I believe this is quite a different issue here: as you can see the shaft is not even reducing hen approaching the opposite edge.
and all this was working very well with 0.18. Something got broken with 0.20
user1234
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Joined: Mon Jul 11, 2016 5:08 pm

Re: [BUG] Netgen mesh size drifting

Post by user1234 »

Sorry i misread it, netgen not gmsh. Now i know why i not wrote anything before.
kds wrote: Tue Jun 15, 2021 5:57 pmusable mesh for 3d printing
Netgen is for FEM. There is a mesh workbench. There are also export functions for exporting meshes for printing.

Greetings
user1234
kds
Posts: 8
Joined: Sun May 30, 2021 4:45 pm

Re: [BUG] Netgen mesh size drifting

Post by kds »

Not sure what you mean, but yes, Netgen is a meshing tool, like others are.
Resulting mesh indeed can be used to solve various physical problems by FEM... or 3D printing.

None-the-less, NETGEN is not meshing properly anymore which is what it is meant for, isn't it?
user1234
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Posts: 3348
Joined: Mon Jul 11, 2016 5:08 pm

Re: [BUG] Netgen mesh size drifting

Post by user1234 »

kds wrote: Wed Jul 07, 2021 9:46 am None-the-less, NETGEN is not meshing properly anymore which is what it is meant for, isn't it?
True, just odd, i never saw anyone uses a FEM mesher for printing. But i am OK with that. I have not compiled FreeCAD with netgen. So i can not help. Also then it is mostly a netgen issue, not a FreeCAD. But to verify that you should post a file and the version (big red banner above) you using, else nobody is able help.

Greetings
user1234
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M4x
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Posts: 1474
Joined: Sat Mar 11, 2017 9:23 am
Location: Germany

Re: [BUG] Netgen mesh size drifting

Post by M4x »

If you'd post an.example, I'd be happy to verify the potential issue.
kds
Posts: 8
Joined: Sun May 30, 2021 4:45 pm

Re: [BUG] Netgen mesh size drifting

Post by kds »

Thanks for the offer!

Actually, even with basic cylinder, one can experience the differnce.
I have attached 2 FCstd files for same basic cirucalar cylinder shape.
One was created under 0.18 and one under 0.19 so you can play with respectively under Freecad 0.18 and 0.19.

Then generate netgen mesh under 0.18 with any pre-settings, for instance "fine" , same under 0.19... and differences of mesh results will appear obvious.
Attachments
cylindre 0.19.FCStd
cylinder 0.18
(9.47 KiB) Downloaded 18 times
cylindre 0.18.FCStd
cylinder 0.19
(7.62 KiB) Downloaded 25 times
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