rlguy
commented
2 years ago Hi, thanks for the report! I am able to reproduce these results with the .blend file and this is expected behavior.
FLIP is naturally chaotic and noisy in the velocities generated. When the ratio is set to 0.0, the noisy motion can become too much and can make the simulation unstable. A side effect of the surface tension feature is that this can add extra noise to the velocities, which can make a 100% FLIP simulation more unstable than usual.
PIC naturally dampens the fluid velocity and causes the fluid behaves like there is a small amount of viscosity in the liquid. The default ratio of 0.05 mixes 95% FLIP with 5% PIC and the purpose of the small amount of PIC mixed in is to keep the simulation from becoming too unstable.
For some extra info and explanations, this video shows some of the differences between PIC, FLIP, and APIC (Starting at 0:45): https://youtu.be/jPG5H5ZoL5Y?t=47
Hope this info helps!
System Information
Blender Version: 3.2.1, master, 2022-07-05 15:44, a2d59b2dac9e Addon Version: A FLIP Fluid Simulation Tool for Blender (v9.4.2 Experimental 07-JUL-2022) OS: Windows-10-10.0.19042-SP0 GPU: AMD Radeon HD 7560D ATI Technologies Inc. 4.5.13399 Core Profile Context 15.201.1151.1008 CPU: AMD A8-5600K APU with Radeon(tm) HD Graphics
RAM: 16 GB DDR3
Describe the bug
The liquid looks unstable. I have turned Surface Tension to Smooth mode. Set PIC/FLIP Ratio to 0. I know that at these values the liquid will be more chaotic. But it seems to me that this is too noisy result. Is this a mistake? Or is this expected behavior?
To Reproduce
test_smooth_surface_tension.zip
Screenshots
https://user-images.githubusercontent.com/7983249/182557509-109c15b7-96f6-49a0-b526-886c6d3739a8.mp4