Flip Pour with Penetrating Objects (chocolate and nuts)

[ObiNon]

Hi I am trying to create a pour of chocolate and have some nuts fall into it. The problem I have is that the chocolate is very viscous, and the nut bounces off of it when they hit it. (I set the nuts and fluids bounce to 0 and cranked up the friction ... did not seem to do anything.) The nuts deform the stream of chocolate instead of getting submerged into and riding along with it. 

Any thoughts ?

Right now the scene is just a simple flip sim from an object with an alembic nut rbd (could be a sphere) falling into the fluid stream. Nothing fancy at all yet.

[rbowden]

Have you tried changing the density of your nut geo in the rbd object? Dunno if that will fix your problem or not since I don't have your file but, that is where I would start. Maybe this topic could help you also:

http://forums.odforce.net/topic/23279-exploding-rbds-in-flip-fluid/

 

[ObiNon]

yeah ... I am playing with the nut physical properties right now ... lots of trial and error. Here is a flipbook of an example of the problem ... this one the fluid is not getting deformed at all. (rbd doesn't have enough mass)

 

liquid_test.mp4

Edited October 17, 2016 by Mdonovan
video

[rbowden]

Are you running the flip sim first and then trying to run your rbds on that cache or are you doing a two-way interaction between flip and the rbd objects? (meaning are you running the sim of the rbd and the flip at the same time).

 

[ObiNon]

they are in the same dop - nothing fancy - it is alembic geo .. im going to test with a native sphere.

viscosity_test.[1-190].mp4 

- Here you can see that even with bounce turned completely to 0 on both the fluidobject and the pistachio ... the nut still bounces sky high.

Edited October 17, 2016 by Mdonovan
video

[rbowden]

Did a super quick test with a native sphere and it works fine. I am attaching the example file I used so you can take a look.

fluid_rbd_interaction_RB.hip

[ObiNon]

this is from sidefx support : seems like having different creation frames was one of the reason for the problem.

Warning: Getting RBD & FLIP to interact is not a stable proposition.

 

The following changes were needed to get this working:

1) When two objects are in Mutual Collision they still have an implicit order defined by object creation time. Normally this makes the left input show up first, but in this case the pistachio is only built on frame 100, so it ends up running after the flip solver. This means the usual feedback was not working for you, but the pistachio was colliding with the flip as a hard surface. The work around is to create the pistachio on frame 1 but have it inactive until 100.

 

2) The FLIP solver's Volume::Solver::Feedback Scale has to be changed to 1 from the default 0 so it applies feedback forces.

 

3) The FLIP feedback forces are based on pressure gradients so require sufficient grid resolution to work. The setup there had too few particles for this to resolve nicely. I switched to a 0.05 particle separation and got good collisions.

 

If you change things, you may have to tweak the feedback scale to balance how much force is used to stop & float the pistachio. In this case I was lucky that 1.0 worked out of the box, often I have more rounds of tweaking to get it good.

 

Edited October 19, 2016 by Mdonovan