Mantaflow Initial velocity not working PROPERLY #84001
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Reference: blender/blender#84001
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System Information
Operating system: Windows 10 Pro
Graphics card: Geforce GTX 1070
Blender Version
Broken: 2.91.0,
0f45cab862
, master, 2020-12-20Worked: 2.82.7
Short description of error
In blender 2.91.0, mantaflow working with particles: The option of "Initial velocity" it's bearly doing nothing, if anything; even with the max setting (100). In 2.82 setting initial velocity to 1 was tremendoustly more agressive than the new version
Exact steps for others to reproduce the error
Plane with "Fluid" as Physics Properties; "Flow Source" as Particle System; "Initial velocity" active (any value)
Added subscriber: @Druzian
Added subscriber: @rjg
Changed status from 'Needs Triage' to: 'Needs User Info'
The velocity of the particle system appear to influence the smoke just fine. Does the file attached below work for you?
T84001_smoke_2.blend
If this works properly for you, please provide more detailed instructions and a minimal project that demonstrates when it doesn't work as intended.
See, in older vesions of Blender, Initial velocity has a lot more influence in smoke than at 2.91.0. Not saying that in newer versions the option has no influence, but it have an almost insiginificant one. Follow the image.
Changed status from 'Needs User Info' to: 'Needs Triage'
Added subscriber: @Fernando-Alcala
Here I compare between 0 and 100 (max) for the initial velocity. There's very little difference in using the maximum value.
230210001-0013.mp4
Added subscriber: @sebbas
If I setup two separate simulations with different particle systems that have the same parameters except for the Initial Velocity, use bake type All and bake them, the resulting simulation is significantly different for me. Perhaps this is more of an issue with a cache not being invalidated (e.g. baking it once with a low initial velocity, modifying the value and replaying it is not updating the simulation)?
I've tested this in both 2.91.0 and 2.92.0.
T84001_smoke_5.blend
@sebbas you might want to take another look at this as well.
With respect to particles, initial velocity source does change the simulation, but at an imperceptible level compared to using meshes.
no work0001-0048.mp4
Here I have both participating in the same simulation with the only difference being that one is a particle and one is a mesh. This is the first frame of the sim, source 100.
{F9536494, size=full}
And while I'm here, initial velocity normal doesn't seem to do anything useful.
normals brokeded0001-0024.mp4
Added subscriber: @lichtwerk
Changed status from 'Needs Triage' to: 'Needs User Info'
Having trouble reproducing (at least the
normal
case).@Fernando-Alcala: is this file working for you?
#84001.blend
#84001.webm
If so, please share the file thaat is failing for you.
The "issue" that I had was that the size of the simulation was too small for the timestep size. Normal 50 in meter sized sims works fine:
But when you have centimeter sized sims, you need to increase the timestepping:
@Fernando-Alcala @Druzian Am I understanding you correctly that this is considered resolved then?
Changed status from 'Needs User Info' to: 'Archived'
It's a limitation.
Fire Initial velocity issue.blend
Initial Velocity.mp4
I hope, from the bottom of my heart, that this time will be clear what I'm saying! No excuses, I have the blend file and a video showing whats the issue. Something changed in smoke simulations and I think is only when usining the INITIAL VELOCITY option. If this change was intentionaly, wasn't in the realease notes! But i suppose that it is not intentionaly once the fire and smoke simulation looks horrible compared with the last version of Blender!
Here I annex a blend file that was simulated at 2.91 and 2.82 AT THE SAME SETTINGS WITH A PROPER SIZE! If you don't belive me, download it and try it yourself!
the last time,
Vitor Druzian
@rjg Read my last comment please. I don't think it's invalid, but it's your forum, I will not change the status again
Changed status from 'Archived' to: 'Needs Triage'
Added subscriber: @EitanSomething
Changed status from 'Needs Triage' to: 'Needs User Info'
@Fernando-Alcala Please do not the status of the report, leave that to the developers and bug triagers.
Changed status from 'Needs User Info' to: 'Needs Triage'
Added subscriber: @kubagrodzki
@Druzian Hi! I also noticed some weird behaviour of "Initial Velocity" parameter. Look at my example (please don't mind the shading difference):
0001-0060.mp4
In 2.83 setting IV to 1.0 gave really huge difference, now it's almost unnoticeable. Question is: is it bug or feature? I noticed some other differences in Mantaflow behaviour in 2.9x series compared to 2.83, but we don't know what causing them.
I really don't understand Initial Velocity in 2.92. This is a ddirect quote from Manual:
I'm confused. In my example where IV is 1, smoke is definitely moving slower than the source.....
Closed as duplicate of #88257
Added subscriber: @ankitm
Added subscriber: @Cultmethod
Just wanted to comment here that something funky is definitely happening with Initial Velocity in Mantaflow. The values barely do anything and you have to set them to absurdly high values to get what you want.
Added subscriber: @Dd3d
This comment was removed by @Dd3d