Forums Technical Discussion Velocity Problems in basic Flip Simulation

Velocity Problems in basic Flip Simulation

   2582   2   0
User Avatar
Fele
Member
36 posts
Joined: 11月 2013
Offline
 
Hello!

I am having two issues with a pretty basic Flip Simulation (Shelf Tool Emit).

I am getting random velocity spikes inside the fluid as soon as the fluid settles. Little flashes with high velocities in small areas only for one frame. Gets very noticeable with the Particle Fluid Surface Preview, but also inside the DOP if you look carefully.

The other issue is the fluid behavior inside volume. When using the solvers boundaries, everything looks fine. But as soon as I use my own volume for collisions, the fluid becomes very jagged and I am getting also strange velocity spikes and particles sometimes escape the container.


Would be great if someone knows what's causing this. (Hip file attached below)

Thanks
Felix
Edited by Fele - 2023年3月19日 11:41:13

Attachments:
collisions.jpg (616.7 KB)
spikes.jpg (367.1 KB)
flip_problems.hiplc (2.3 MB)

 Report
User Avatar
Enivob
Member
2626 posts
Joined: 6月 2008
Offline
 
One thing to try is supplying an alternate collision object. Instead of placing your FLIP source inside the collision object and inverting the SDF, try building walls around the source and running non-inverted. When I turn off Oversampling At Boundaries on the Reseeding tab, I notice the white velocity spikes go away. My guess is when old particles die in a voxel, and are reseeded, the new particles might intersect momentarily, generating a velocity boost that reveals itself as those white spikes.

Attachments:
ap_flip_problems.hiplc (2.3 MB)
flip_vel_issue.gif (1.3 MB)

Using Houdini Indie 20.0
Windows 11 64GB Ryzen 16 core.
nVidia 3050RTX 8BG RAM.
 Report
User Avatar
jacob clark
Member
665 posts
Joined: 7月 2005
Offline
 
If you don't need Reseeding turn this option off as it can definitely cause strange spikes in your simulation.
 Report
  • Quick Links