I've been trying to get a grasp on the FLIP workflow for the past 2 weeks or so and one thing i'm having
trouble wrapping my head around is how to have my RBD toy object react elegantly to the FLIP simulation. It always
seems to move in an erratic way with lots of weird little jitters and bumps yet the FLIP fluid beneath it appears to be
pretty smooth.

My scene scale is realistic. The baby pool is 3m in diameter

I've tried lowering my collision separation to match my particle separation (currently 0.01). I had to lower this considerably to keep the water from leaking out of the bottom of the pool.

Feedback scale is set to 1.

The Density of the toy is lower than the water (50 vs 1000)

I've tried increasing the overall substeps to 2 on the dopnet itself but it did not seem to make a difference.

I used a convex decomposition on the toy to turn it into a bunch of packed convex pieces. It's set to convex hull in the RBD Packet Object bullet data options. Maybe this is the problem here? I don't see a way to create a volume representation of the toy.

The pool and the ground are both static objects prepared as an SDF in SOPs and set to “Volume Sample”. I increased their uniform subdivisions to 60.

I've attached the file if anyone has time to help me investigate.

Cheers!

https://streamable.com/s/7pwh4/mwtako [streamable.com]

Hello.

The problem is packed object don't interact correctly with flip. You could try with rbdobject rather than rbdpackedobject, This should work.

This definitely seems to be the case however I've come across a few issues when using the rbd object. I've created two separate collisions outputs for the rubber toy in SOPs to prepare for both bullet and FLIP. I fractured my rubber toy to ensure that my bullet representation is made up of concave pieces for a more accurate solve. I also made a separate SDF output with what seems like enough resolution.

If I set the volume collision mode in my rubber toy rbdobject to “Volume Sample” and point it to my SDF it seems to freak out and disappear from the sim altogether.

If I use the default “Ray Intersect” mode it seems to work ok except for the fact that it's now using my fractured geometry to automatically convert to an sdf and looks porous and strange.

See below:

https://streamable.com/v1y28 [streamable.com]