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Packed RBD Objects and Flip Explodes

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I'm trying to create cheerios falling into milk.
I did a test with 2 toruses falling into a flip sim.

If the toruses are separate RBD hero objects, then the sim works fine.
https://drive.google.com/open?id=1Z98WekxuaIQ89vmxReqRHTgWjxgkuPUX [drive.google.com]

However, if I try using packed RBD objects, then the sim explodes.
https://drive.google.com/open?id=13U4Su0a3iVEpLx38lEuWxpORUdciKZCP [drive.google.com]

I tried reducing the flip solver interaction scale from 1 to 0.5, but that didn't help.

Do packed rbd objects interact correctly with flip correctly in houdini 16.5?

What am I missing?



Edited by syntheticperson

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I know this thread is almost two years old, but just wondering if you ever came to a solution... and if you did can you remember it from so long ago?? Ha.

I'm working on something similar and running into the exact problem. I can set up a standard RBD object and have it interact roughly how I'd like with my flip sim, but when I try to do multiples as RBD packed objects, the objects do interact, but just sink immediately whereas the non packed RBD floats at the top.

I may post some examples files in a new thread later today. I've been banging my head against the wall for several days trying to figure this out with no luck.


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Thanks, I have that set already. I'm looking for objects to sink in just a little on top of a very viscous fluid. So I believe I'd need to have the RBd density lower than the FLIP. Non Packed RBDs work pretty much as expected. When I try packed geo with the same settings it just doesn't work. All packed geo just goes directly through the flip object and collided with the surface under it.

I thought I'd stumbled on a solution by using the RBD Fracture object to get several objects in at once. That sort of works, but then the whole thing explodes and the RBD objects shoot out of the side. I don't feel like this should be this hard, but I haven't found a solution yet.

I also tried doing it all with FLIP, using two sources with differing viscosity values and densities... that was promising, but I need the objects that don't land on the flip sim to bounce, so doing it all with FLIP didn't work either.

I'm basically trying to throw frosting at a pop tart, then follow that with a spray of sprinkles. The sprinkles should stick and flow with the viscous frosting, but bounce off of the base of the pop tart.

I attached a test file, just flip source from cube and I'm dropping spheres on it. In the dopnet I'm just bypassing the different variations for testing. You'll see that the single RBD objects rest on top of the fluid, just barely sinking in. The Packed geo just goes straight through, and the RBD fractured, kinda works, then just blows up.


Any ideas are welcome, and thanks again


****Edit, the file I originally uploaded had some errors, I'm attaching a new one. I also found that if I increase the scale of the spheres the RBD fractured sim doesn't blow up or act as erratic. This isn't ideal, for my scene I'd need an absolutely giant set up to have the sprinkles at a size that they interact with the flip correctly.




Edited by jason_harmon
incorrect file

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