flip fluid colliders jitter on deform

[whodini]

I have flip liquid particles in a complex tank or container that has an animated base. The base deforms and the liquid flows and drops around as a result but there are some weird jitter issues with the particles when the collider moves. I notice the issue after meshing or looking through the surface field as an isosurface. I made the container watertight and thick enough to play nice with flip, its a vdb volume called collision and I also trailed it and added collisionvel wand proper vector split to make it work in dops with the source volume node. Is there a way to reduce the particle flickering on animated colliders? The collider ins't moving too fast maybe dropping 1 unit over 30- 40 frames.

[lukeiamyourfather]

It might be the collision volume resolution or insufficient substeps. It doesn't have to be the exact scene file but can you post an example scene file that exhibits the issue? 

[whodini]

Here is a hip file. I made something basic. I'm not sure why my vdb collision object is behaving like this. Play through the sim and look at the base of the container the particles jitter around as the collision volume moves. The vdb collider should have enough resolution I have also doubled the res of it just to troubleshoot. I even tried switching from VDB to source volume for generating collision volume and vel fields and the issue still exists. 

flip_collision_issue.hip

flip_collision_issue_sourcevol.hip

Edited October 14, 2014 by whodini

[whodini]

Ok I ended up narrowing this down. It's my houdini build. I'm on 13.0.509. I rolled back to 13.0.484 and used the standard fluid source node to create collision and collisionvel fields and the collisions are clean and dont have the flicker or jitter issue.

 

Actually this issue stills seems present in even the current stable production build. It looks like the velocity field is spiking because the collision field is different every frame. Here's what I tried, but none are working:

 

- I've added timeblend sops after each collision volume source but still get the nasty jittering around the bottom and sides of the container.

- I've checked the collision guide in the flip object and the collisions are represented very clean and accurately but there is a still jitter

- Looked through the velocity guide and I see mostly directional vectors but some areas have lots of mangled lines where the jitter happens.

- Tried different collision methods: particles / collision volumes but jitter still occurs

Edited December 8, 2014 by whodini

[CeeGee]

Hi,

 

can you try to run my scene and see if you have problem again i playblast from bottom and looks fine.

Everything looks smooth on bottom, just movement on top.

flip_collision_igor.hip

[whodini]

Thanks Igor, I'm looking at the results now. This works!! The tetrahedralize sop and the scatter density on the points from volume helped A LOT!! I'll give this a shot a more complex scene. Thank you for all your help!

Edited December 8, 2014 by whodini

[whodini]

I'm noticing one more thing, if I set the particle separation and collision separation to low values like 0.025 with a more complex collider with curved sides I notice that the liquid loses a lot of volume almost as if it compressed or flattened.