Banding artifacts against gradual sloping obstacles

[rlguy]

• CPU: Intel i7 7700
• RAM: 32 GB
• GPU: GTX 1070, 8 GB
• OS: Windows 8.1
• Blender Version: 2.79
• Addon Version: 0.1.1

A banding effect can be seen in the fluid particles when a thin layer of fluid is sliding down a gradual sloping obstacle.

Example .blend file:
https://www.dropbox.com/s/a9om9oimpbiii0a/gradual_slope_banding_artifacts.blend?dl=0

Note: this issue is about simulation banding artifacts rather than mesh banding artifacts. Simulation banding artifacts cause particles to group and align to the grid. A fix for mesh banding artifacts can be found here: https://github.com/rlguy/Blender-FLIP-Fluids/wiki/Scene-Troubleshooting#mesh-banding-artifacts-against-curved-obstacles

[grantwilk]

Seeing similar issues in my wave simulations. Hoping this issue hasn't been forgotten :)

[rlguy]

This issue haunts me and I can assure you it has not been forgotten! I spent a few hours earlier this week to try a few things, but did not find a solution. I've come to the conclusion that I should build some debugging tools to better visualise/understand what could be causing this issue whether it be a bug or flaw in the simulation method. I've actually planned to devote the entire week of April 23rd - 27th to work on this if needed!

[zx-82]

Any updates on this ?
I am developping my own fluid simulator and am confronted with the same issue. I suspect that it is related to the "small cell" problem (common to all cut cell based liquid solvers) because along a gradual slope there will be cells (fractions) that only contain an arbitrary tiny amount of fluid. In engineering CFD codes this problem is addressed by merging "tiny cells" with neighboring cells. While solvers used in computer graphics seem to rely on Bridson's simple "clamping trick". But this will also leave some residual "stair casing", I'm afraid.

[rlguy]

There is no update on this issue and it has been at least two years since I have had a chance to look further into the problem. The "small cell" problem sounds like a good lead for something to look into for this issue. Thank you for the tip, but I am sorry to say that I do not have any advice at the moment.

Good luck with your fluid simulator development!

[zx-82]

Hi,   

I am sorry to say that I do not have any advice at the moment.

  Thanks for your reply which is actually helpful because your (and mine so far) failure to find a simple way to resolve it, indicates that this banding is indeed related to math method/algorithm. So at least no need to wasting time chasing an imaginary bug in the software.   Best Regards,   Bernhard     Gesendet: Montag, 01. November 2021 um 18:46 Uhr Von: "Ryan Guy" ***@***.***> An: "rlguy/Blender-FLIP-Fluids" ***@***.***> Cc: "zx-82" ***@***.***>, "Comment" ***@***.***> Betreff: Re: [rlguy/Blender-FLIP-Fluids] Banding artifacts against gradual sloping obstacles (#1)   There is no update on this issue and it has been at least two years since I have had a chance to look further into the problem. The "small cell" problem sounds like a good lead for something to look into for this issue. Thank you for the tip, but I am sorry to say that I do not have any advice at the moment. Good luck with your fluid simulator development! — You are receiving this because you commented. Reply to this email directly, view it on GitHub, or unsubscribe. Triage notifications on the go with GitHub Mobile for iOS or Android.

[PavelBlend]

@rlguy I turned on the enable obstacle debugging option and saw that the stripes are located near the small polygons:

This becomes even more noticeable if you create an obstacle with very small polygons.