H16 FEM wrinkles workflow help

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Hi all,
did anyone figure out or have any tips on getting those nice wrinkles with FEM? Sadly there is no example file and the documentation doesn't say much about it. I suspect new “hybrid object” and “hybrid configure object” has something to do with it, but I'm not sure how to set it up. I guess simulation is supposed to generate some kind of attribute similar to tension map that can be used to add wrinkles post sim.
Any tips or pointers in the right direction would be much appreciated, thanks.

Cheers,
Sasa

P.S. Congrats to SESI on yet another amazing release!
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Yes it's the new hybrid tools.
I can't help you with the setup..It's expecting both a tet mesh and a poly mesh..but it's odd that the shelf tool doesn't set up the tetrahedralization like the regular fem tools, and no videos about it so far.
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Yes, got that so far, regular tets and surface triangles for the outer shell layer, but beyond that there is no info and it isn't that straightforward (to me at least). I guess we'll have to wait for the updated docs or maybe some of the developers can chime in with some pointers or simple example. Wink-wink, nudge-nudge…
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Here's a two-stage workflow for wrinkling.
This should be a fairly re-useable setup.
I put yellow notes inside the file to explain the details.

The first stage is a quick sim that creates the overall animation without wrinkles.
This stage doesn't necessarily have to be a sim; it can also be an animation created in Houdini.
The important thing is that the animation that results from the first stage consists both tets and surface triangles.

The wrinkling is added in separately in the second stage. For wrinkling, a fairly detailed surface mesh is needed, and the tet mesh underneath must coarsen gradually as the tets approach the inside.

This version is quite hi-res: 1.1 million tets and 350 thousand surface polygons.
On loading the file, it will take a bit before everything is tetrahedralized and covered with triangles.
The embedded sim in the first stage should solve in at most a few seconds a frame.
The direct sim of skin and tissue in the second stage should take several tens of seconds per frame.

Attachments:
TwoStageWrinklingSetup.hip (421.0 KB)
BeforeWrinkling.mp4 (263.6 KB)
AfterWrinkling.mp4 (343.7 KB)

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Thanks for the detailed explanation and example file Michiel!
Really cool to know that it can be used with regular animation and not just simulation. Thanks once again, going to explore that example right now.

Cheers,
Sasa
Animator - Vimeo [vimeo.com], Behance [behance.net]
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michiel
Here's a two-stage workflow for wrinkling.
Thank you!
Would it be possible to drive a height map (for render-time displacement) instead of having to have such dense geometry in sim? Could you show how this might work? Or is that more of a tension map thing?
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Would it be possible to drive a height map (for render-time displacement) instead of having to have such dense geometry in sim? Could you show how this might work? Or is that more of a tension map thing?

The wrinkling sim needs to work directly with a mesh that consists of both tets and polygons. However, it should be possible to create texture-based representations of the wrinkle displacements afterwards, against a low-res animation of the mesh. The Bake Texture render node may be useful for this purpose.
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Here's a really simple setup I made based on Michiel's example, of an animated tube getting wrinkled via FEM. I didn't need 64-bit precision, and I didn't need a crazy dense mesh for these thicker wrinkles, so that helped with iteration speed. Fun stuff, thanks michiel!

Thanks for starting this thread sabudimir!

Attachments:
simple_tube_wrinkle.hip (197.9 KB)
tube_bend_wrinkle.jpg (256.5 KB)

I'm o.d.d.
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Nice setup Goldleaf! I tried to vary shape and bend stiffness attributes with some gradient and noise in SOPs to make wrinkles less uniform…works nicely. Just wish I had more time to play with it, it's super fun.
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I'm trying this method out, but I still can't get it to work. I cached out my first solid object sim as a .bgeo.sc then tried importing it into the hybrid object, but it's only using the lower res version. How can I switch out the low res mesh for the embedded one?
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