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Adaptive Domain creates lines in smoke
Confirmed, NormalPublicBUG

Description

System Information
Operating system: Win 10
Graphics card: Dual RTX Titans

Blender Version
Broken: Blender 2.82

Short description of error
With adaptive domain enabled, noticeable horizontal (and sometimes vertical) lines appear in the smoke

Exact steps for others to reproduce the error
Simple blend file:

  1. Create a large box and set it as a gas domain.
  2. Create a small object as the Flow (both 'smoke' and 'fire' reproduce it)
  3. Put the flow object near the bottom of the domain
  4. Enable Adaptive Domain
  5. Bake
  6. You should see lines like this:
  7. Turn off adaptive. Not only will the smoke move faster creating a totally different looking simulation (which is problem in itself) but the lines will be gone:

It's most noticeable when the domain is large, and the adaptive box is only a small portion of it.

Increasing the adaptive margin to 24 helps somewhat, but it's still there. Any higher and it defeats the purpose of adaptive - baking takes as long as just turning it off.

Sample blend:

Event Timeline

Ankit (ankitm) added a subscriber: Ankit (ankitm).EditedMon, Mar 9, 1:34 PM

https://developer.blender.org/T67356#867120 are these the same reports? does the last comment by Germano help ?

No this is separate. The lines are part of the simulation, not the shader.

It's most obvious at the end of the video above, as you can see it creates waves in the plumes.

https://docs.blender.org/manual/en/latest/physics/fluid/type/domain/gas/adaptive_domain.html?highlight=adaptive%20domain
I still think this is expected behaviour.. Adaptive domain saves some computation time by shrinking the gas boundary. Increasing margin gives more space to the gas, thus more computation, thus it undercuts the main benefit of AD: save computation time.
bottomline: it's a tradeoff between time saving and accuracy (accidental Heisenberg? )

Richard Antalik (ISS) changed the task status from Needs Triage to Needs Information from User.Tue, Mar 10, 5:19 PM

This is effect of low domain resolution most likely
https://docs.blender.org/manual/en/dev/physics/fluid/type/domain/settings.html#bpy-types-fluiddomainsettings-resolution-max

Try to increase and see if issue persists.

Please provide sample file so we can actually see problem in action.

@Richard Antalik (ISS) Changing the resolution doesn't change much. It just makes the gaps between the lines smaller:

@Ankit (ankitm) I'd be surprised if this was the expected behaviour. If it only expands after it's needed, rather than preemptively based on the movement of the smoke then it should never be used. Coz it will always interrupt the smoke and create a totally different simulation than when disabled.

@Sebastián Barschkis (sebbas) I wonder if it's related to the Adaptive Time Steps bug, not computing multiple times between frames to create the right sized adaptive domain?

Also I've attached the .blend to the OP.

Richard Antalik (ISS) changed the task status from Needs Information from User to Confirmed.Wed, Mar 11, 11:33 AM

I can confirm as well - the results are completely different with and without adaptive domain even though they should be identical.

@Gottfried Hofmann (gottfried) did you discuss it with Sebastian already?

@Gottfried Hofmann (gottfried) did you discuss it with Sebastian already?

Yes :-)

Jacques Lucke (JacquesLucke) changed the subtype of this task from "Report" to "Bug".Tue, Mar 17, 3:50 PM