Exploding FLIP sim

[lloydwood]

I am having problems with unstable FLIP behaviour and wondered whether anybody might be able to point me in the right direction.

 

The shot is an animated object rising from a FLIP tank.

 

I have uploaded two movies (pass: od_vid):

 

https://vimeo.com/125380671

 

This is the behaviour I want. The box rises out with the FLIP fluid sticking and dripping off.

 

https://vimeo.com/125380672

 

This is the unstable behaviour. There is a point where the surface tension of the FLIP fluid seems to break causing an explosion effect rather than the FLIP fluid running over the object

 

The settings for both sims are the same in H14. Stick on collision is on (stick_scale: 0.3, normal_scale: 1, tangent_scale: 0.1). Substeps are at the default.

 

The only real difference between the collision meshes is that one is simple and one is hi-res. The hi-res one is generated with a VDB converted to polys.

 

Unfortunately I can't really attach the hip because there is a lot of cached geometry involved. What I really would like to know is what settings could cause this behaviour and what I could try to get closer to the box result.

 

 

[Diego A Grimaldi]

Without looking at the file is not too easy but lets see if I can help you anyway. I'm assuming you didn't change anything in the fluid source like adding curl noise to the velocity emission or anything like that, but if you did that may be partially influencing it.
Asides for that, things that you can tweak to make it less explosive:

In the flip solver:

Turn off droplets if you had it on, velocity smoothing bring it up to .3 - .5 instead of the default .1

In the flip obj, under physical tab bring the density up to maybe 1200 or 1500.

Maybe bring the time scale down slightly on the solver

 

Those are things I can think of on top of my head but I'm sure there's more you could do

 

Also check the collision mesh under your static object and see if it has anything funky.

 

Good luck.