Forums Technical Discussion Help!—smoke sim collisions not working with vdb

Help!—smoke sim collisions not working with vdb

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NotaBunny
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Joined: 5月 2025
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Hey guys, I'm decently new to houdini(I know the ui and node structure and basic nodes) and I'm currently working on a chimney sim and the smoke isn't colliding for somereason, even though the vdb looks to be solid...

Under smoke_2
Image Not Found

Image Not Found


Thanks in advance!

Attachments:
Screenshot 2026-04-08 at 9.19.28PM.png (2.4 MB)
Screenshot 2026-04-08 at 9.19.22PM.png (4.3 MB)
Chimneysmoke_recovered.hipnc (2.7 MB)

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sepu
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Joined: 2月 2012
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You did not post the model, so I just added a tube, there is not need to convert to polys and then back to vdb again not sure what you were trying to do there, but with a simple tube its working fine.
Edited by sepu - 昨日 18:26:56

Attachments:
Chimneysmoke_recovered.hipnc (2.7 MB)
houdini_PHb0YmXelB.gif (1.2 MB)

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NotaBunny
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Joined: 5月 2025
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sepu
You did not post the model, so I just added a tube, there is not need to convert to polys and then back to vdb again not sure what you were trying to do there, but with a simple tube its working fine.
Sorry, here is the model,
Image Not Found
.

I followed what some people on reddit suggested, I think it was tosealthe holes or smth, not rlly sure lol. Ill take a look and see what I can learn from this

The geo node is Pyro_billowy_smoke and chim_2

Thanks

EDIT: Oh dang, didn't know files weren't packed with the file...
Edited by NotaBunny - 昨日 18:48:46

Attachments:
Chimney.obj (177.2 KB)

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sepu
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Here you go, you gotta expand the voxel data - basically increase the narrow band of active voxels around a surface so you get more accurate collision detection. You can see what the collision field is doing by checking the field guides. Also, your scale was super tiny.
Edited by sepu - 昨日 20:46:03

Attachments:
Screenshot 2026-04-09 at 17.20.46.png (1.6 MB)
Chimneysmoke_recovered.hipnc (2.7 MB)

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NotaBunny
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Joined: 5月 2025
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sepu
Here you go, you gotta expand the voxel data - basically increase the narrow band of active voxels around a surface so you get more accurate collision detection. Also, your scale was super tiny.

Ohhhh, I see, what scale would you recommend, and how would I check it?

Thank you so much!!!!!
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