Level-set Fluids Strange Behavior

[ofer]

Hello.

Im running into a strange problem with level set fluids. Im using a narrow container, like 10 x 10 x 3. I put a source inside it, and add gravity. When I play the simulation, the fluid starts flowing down, but after a few frames, instead of accumulating, it disappears, and then starts flowing to the side. Very strange. If I add some horizontal velocity to the source, it flows to the side immediately. If I add vorticles, the same.

I thought maybe its because the source geometry fills the whole width of the container, and it happens because of friction with the walls. Im still trying to solve it.

Did anyone encountered this kind of a problem?

[ofer]

I did some tests. I removed all the collision objects, and the problem remains. I increased the divisions a lot, not helping.

If I only use gravity, with no collision objects, the fluid fills the container slowly. But when I add some horizontal velocity, it drifts to the side.

[Jason]

I did some tests. I removed all the collision objects, and the problem remains. I increased the divisions a lot, not helping.

If I only use gravity, with no collision objects, the fluid fills the container slowly. But when I add some horizontal velocity, it drifts to the side.

Hey ofer,

Could you post a simple scene showing the issue? Level set fluids always have some issues with volume loss or volume gain (which is what the surfels / markers are trying to correct) so that is not terribly surprising. You can mess with the marker settings to counteract this - or perform extra SDF rebuilds and such - but the default setup seems to balance the volume loss issue with their counter-measures quite well - computation-time-wise.

[ofer]

Sure. I remember these issues from the siggraph papers. This can explain the volume loss, and I will try to play around with it, but what about the velocity drift to the side?

Here is my scene. You can see the problem when running /obj/fluid_write. There is a ROP Output node in the end. I set the source velocity to -0.2, 0, 0. If you zero it, there is volume loss.

Thanks.