20 replies to this topic

[Magnus Pettersson]

Nice tests! The flattening teapots (and elephants) seems to be a case for sidefx to take a look at!

[eetu]

I wonder if the flip volume fields are not resizing fast enough, or not with enough padding, and the flattening is some sort of boundary artifact from that?

[goldleaf]

That's a great idea, thanks eetu! I'll check it out when I can get a few minutes (getting ready to move to LA)

Edited by goldleaf, 13 April 2012 - 08:26 AM.

[johner]

goldleaf, on 12 March 2012 - 09:22 AM, said:

Has anyone experienced the flattening flip fluids before?

A few things to try to help alleviate that problem:

1) Decrease the Surface Extrapolation parameter under the Collisions tab, closer to 0.1 or so.  This controls the amount the fluid is extrapolated into the collision, in voxels, so decreasing it might make the collisions take effect slightly later.
2) Enable Collision Separation on the FLIP Object and set it to the same value as your Particle Separation.  This will give you a higher-res collision field and possibly more accurate collisions.
3) Set up your file like Igor's elephant test, where the closed bottom of the simulation volume is used as the ground plane, so collisions don't enter into the simulation at all (I'd try this first, myself).

BTW, to Igor's very well set up file, I'd only add that for very high viscosity settings, this blurb from the Viscosity Tips in the documentation is relevant:

The FLIP Solver computes the number of substeps to calculate based on velocity. While the viscosity solver should always be stable, it will be more accurate with smaller substeps. A slow moving, highly viscous sim might need more substeps than the 1 that the FLIP Solver will give it based on its velocity. Increase Minimum Substeps until you get sufficient viscosity.

[nran]

Very nice!

[eetu]

johner, on 19 March 2012 - 08:37 AM, said:

A few things to try to help alleviate that problem:

1) Decrease the Surface Extrapolation parameter under the Collisions tab, closer to 0.1 or so.  This controls the amount the fluid is extrapolated into the collision, in voxels, so decreasing it might make the collisions take effect slightly later.
2) Enable Collision Separation on the FLIP Object and set it to the same value as your Particle Separation.  This will give you a higher-res collision field and possibly more accurate collisions.
3) Set up your file like Igor's elephant test, where the closed bottom of the simulation volume is used as the ground plane, so collisions don't enter into the simulation at all (I'd try this first, myself).

Actually, I'm not sure if this is the same flattening problem, as the teapots all start to flatten out 6 frames before impact.

In case the above suggestions did not do the trick, I would be curious to know whether toggling off "Dynamically Resize Fields" or adding to the "Max Cells to Extrapolate" are of any help.

[br1]

eetu, on 27 March 2012 - 04:32 AM, said:

Actually, I'm not sure if this is the same flattening problem, as the teapots all start to flatten out 6 frames before impact.

In case the above suggestions did not do the trick, I would be curious to know whether toggling off "Dynamically Resize Fields" or adding to the "Max Cells to Extrapolate" are of any help.

I also had some flattening in my tests.  I got rid of those by increasing the substeps in the Flip solver.

[zglynn]

Good stuff guys! Lots of really great info. BTW - Goldleaf: I'm stoked for you to get here

[br1]

br1, on 03 May 2012 - 12:30 PM, said:

I also had some flattening in my tests.  I got rid of those by increasing the substeps in the Flip solver.

More feedback here after a few more tests :
Eetu's tip about increasing "Max Cells to Extrapolate" is actually quite usefull as it will allow to compute with less substeps.  I ended using only 3 substeps after increasing that value while I had to use 10 substeps before changing it.