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[SOLVED]Flip Viscosity Halts Inside Collider?


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I have a working viscosity simulation.


When I replace the tube with a hollow cube, all fluid motion stops on contact with the collision surface? I have set friction to zero, but that does not seem to be the issue.


The collision object looks valid.



Does anyone know how to make FLIP work in this case? I expected the fluid to continue to ooze out and around the collision object.

How are we supposed to make our Cadbury egg simulation?


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Enabling flipsolver1->Viscosity->Slip on Collision and playing with the Slip Scale attribute seems to help a bit, but I agree that is very odd to see this happening for a fairly straightforward simulation case.  It's almost like the viscosity is getting scaled at a rapid rate despite there being nothing set up to do so in the rig. 

It's worth posting this on the SESI forums and/or sending to their techs for closer inspection if you haven't already, something does seem fishy about that behavior.

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Thanks for the replies, everyone. I also received help on Discord which provided the simplest solution. Calculate the collision object using Ray Intersect instead of providing a Volume Sample. For some reason this just fixes it..?

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Good to know, thanks for the update.  That's a weird as well as non-intuitive fix; I don't know why that would make any difference given that Volume Sample has been reliable every other time I've used it - now it definitely sounds like a bug that SideFX should check into

edit: I had to go and tinker some more to try and understand why this behavior is occurring; I've actually found that with a voxel size of 0.025 or above in the Collision Source, it works as expected.  Anything below that (even 0.0249999) causes the odd freezing behavior.  A relationship between that value and the settings in the simulation is not readily apparent to me, but I feel it is likely there is one.

Edited by ryew
further tinkering
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