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Mantaflow: Effect of forces increases over time.
Closed, ResolvedPublicBUG


System Information
Operating system: Windows 10
Graphics card: Nvidia GeForce GTX 650 Ti
Processor: Intel® Core™ i7-3770

Blender Version
Broken: 2.82, master. (this is a general problem with Mantaflow; previous versions of Blender with Mantaflow implementation also possess this problem)
Worked: (previous gas simulation framework)

Short description of error
The effects of external forces on smoke (vorticity, force-fields, etc.) seem to increase in strength over time, despite not being animated. I am not sure if this is intended behavior; however, it certainly hinders the use of Mantaflow and I believe it should be minimized.

Demo with vorticity. (I am using a very medium strength for vorticity. This problem becomes much more dramatic, when using greater values, such as 1.0)

Demo with a "Force" force-field.

Exact steps for others to reproduce the error

  1. Add a mesh.
  2. Press F3, type in and select "Quick Smoke"
  3. In domain settings, set vorticity to a medium value (ie: 0.3; 0.5; etc.)
  4. Bake the simulation.

Here are two .blend files, one with just the vorticity changes and one with a force field:

Event Timeline

Evan Wilson (EAW) changed the task status from Needs Triage to Confirmed.Feb 15 2020, 4:24 PM

Confirmed using 2.82 release

Bastien Montagne (mont29) changed the subtype of this task from "Report" to "Bug".

This bug seem to be squashed to me.. I tested the attached files and they are working fine to me. Can you confirm this @Iago Diogo Vasconcelos Mota (IagoMota) ?

@Everton Schneider (eversimo) That's strange. I just tested in 2.83 50ef801a79b5, the issues still persist there.

@Iago Diogo Vasconcelos Mota (IagoMota) I'm testing here with current Master (2.90 alpha) didn't test with 2.83.
With 2.90 alpha the only thing that still happens is the vorticity spreading the smoke, but I'm not sure if this is the correct behavior, maybe this is the way it works and we need to keep really low values, I think it is very exaggerated with 0.3 but not sure...

The force field example is working fine to me. The smoke is immediately influenced by the force.

@Everton Schneider (eversimo) You're right, 2.90 alpha seems to have the issue fixed with force fields. If smoke/flame Vorticity are the only properties influenced by this bug, it's probably not significant anymore, in my opinion. So, I'm glad to see this pretty much resolved!

Looks like this has been solved in rB21485e94aac.
The vorticity thing seems to be a separate issue, I'm not sure if it is a bug. If you think it is, please create a new report just for that. Reusing the same report for two bugs makes things hard to follow.