Mantaflow - liquid sim - strange behaviour #78384

New Issue

Ignatz · 2020-06-28T15:25:27+02:00

Ignatz commented

2020-06-28 15:25:27 +02:00

System Information
Operating system: Windows 7 Pro 64-bit
Graphics card: Nvidia GeForce GTX 1060 6gig

Blender Version
Broken: 2.90.0 Alpha - 2020 - 06 - 27 - hash 59d2dd2237
Worked: - - -

Short description of error

Mantaflow liquid not behaving as expected.

Liquid streams out of in-flow object, splashes down to bottom of domain, but then rises up unexpectedly to form what appears to be a moving layer upon the surface of an invisible liquid.

Normally, I would expect the liquid to fill the domain volume from the bottom... up to the top surface of the liquid particles.

While I think this is an interesting effect in its own way, it is certainly not the behaviour that most users would expect to achieve.

Please see attached .blend file and video.

mantaflow - liquid bug.blend
mantaflow - liquid bug.mp4

**System Information** Operating system: Windows 7 Pro 64-bit Graphics card: Nvidia GeForce GTX 1060 6gig **Blender Version** Broken: 2.90.0 Alpha - 2020 - 06 - 27 - hash 59d2dd2237ce Worked: - - - **Short description of error** Mantaflow liquid not behaving as expected. Liquid streams out of in-flow object, splashes down to bottom of domain, but then rises up unexpectedly to form what appears to be a moving layer upon the surface of an invisible liquid. Normally, I would expect the liquid to fill the domain volume from the bottom... up to the top surface of the liquid particles. While I think this is an interesting effect in its own way, it is certainly not the behaviour that most users would expect to achieve. Please see attached .blend file and video. [mantaflow - liquid bug.blend](https://archive.blender.org/developer/F8651348/mantaflow_-_liquid_bug.blend) [mantaflow - liquid bug.mp4](https://archive.blender.org/developer/F8651349/mantaflow_-_liquid_bug.mp4)

Ignatz commented

2020-06-28 15:25:27 +02:00

Added subscriber: @ignatz

Ignatz commented

2020-06-29 07:36:13 +02:00

Strange volume behaviour appears to have already been spotted and corrected in the following release of 2.90.0 alpha - 2020-06-28 - hash b21ba5e579

mantaflow - liquid sim - better.mp4

Strange volume behaviour appears to have already been spotted and corrected in the following release of 2.90.0 alpha - 2020-06-28 - hash b21ba5e57974 [mantaflow - liquid sim - better.mp4](https://archive.blender.org/developer/F8652923/mantaflow_-_liquid_sim_-_better.mp4)

Philipp Oeser commented

2020-06-29 11:35:34 +02:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2020-06-29 11:35:34 +02:00

Changed status from 'Needs Triage' to: 'Resolved'

Philipp Oeser closed this issue

2020-06-29 11:35:34 +02:00

Philipp Oeser self-assigned this 2020-06-29 11:35:34 +02:00

Philipp Oeser commented

2020-06-29 11:35:34 +02:00

This looks like it can be closed then?
(feel free to comment again if issues persist though, can always reopen in that case)

This looks like it can be closed then? (feel free to comment again if issues persist though, can always reopen in that case)

Ignatz commented

2020-07-01 09:37:27 +02:00

I spoke too soon. The problem appears to still be here. Latest build: Blender 2.90.0 - June 30 - hash a3e6b7c2ce

Some other observations:

Odd mesh behaviour: When rebaking the simulation with the mesh, Blender will sometimes simply place one large mesh around the domain for the first frame, then starting the sim calculation correctly with the following frame. (see screenshot below).

Clumsy interface: When changing any parameters of the inflow objects, Blender does not sense this and will not automatically rebake the simulation. The user has to force this, but in the** 'replay'mode there is no"free data"** button so the user has to force this by making some sort of alteration to the domain parameters (even if entering exactly the same information into one of the fields). I'm sure this is confusing to some users.

liquid oddity.mp4

mantaflow - liquid oddity1.blend

I spoke too soon. The problem appears to still be here. Latest build: Blender 2.90.0 - June 30 - hash a3e6b7c2ce06 Some other observations: Odd mesh behaviour: When rebaking the simulation with the mesh, Blender will sometimes simply place one large mesh around the domain for the first frame, then starting the sim calculation correctly with the following frame. (see screenshot below). Clumsy interface: When changing any parameters of the inflow objects, Blender does not sense this and will not automatically rebake the simulation. The user has to force this, but in the** 'replay'**mode there is no**"free data"** button so the user has to force this by making some sort of alteration to the domain parameters (even if entering exactly the same information into one of the fields). I'm sure this is confusing to some users. ![mantaflow - liquid oddity1 - screenshot frame 01.jpg](https://archive.blender.org/developer/F8656466/mantaflow_-_liquid_oddity1_-_screenshot_frame_01.jpg) [liquid oddity.mp4](https://archive.blender.org/developer/F8656469/liquid_oddity.mp4) [mantaflow - liquid oddity1.blend](https://archive.blender.org/developer/F8656470/mantaflow_-_liquid_oddity1.blend)

Philipp Oeser commented

2020-07-01 09:52:37 +02:00

Changed status from 'Resolved' to: 'Needs Triage'

Philipp Oeser reopened this issue

2020-07-01 09:52:37 +02:00

Ignatz commented

2020-07-01 13:39:29 +02:00

Another piece of information that may prove useful to the programmer(s):

On a hunch I decided to reduce the Fluid Flow field weight setting down to0.200 and the attached video shows the result.

liquid oddity 02.mp4

Another piece of information that may prove useful to the programmer(s): On a hunch I decided to reduce the **Fluid Flow field weight** setting down to**0.200** and the attached video shows the result. [liquid oddity 02.mp4](https://archive.blender.org/developer/F8656787/liquid_oddity_02.mp4)

Germano Cavalcante commented

2020-07-02 15:12:02 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2020-07-02 15:12:02 +02:00

Changed status from 'Needs Triage' to: 'Needs User Info'

Germano Cavalcante commented

2020-07-02 15:12:02 +02:00

I cannot reproduce this with either the current development version of Blender.

Please try the latest daily build: https://builder.blender.org/download/

If the problem persists, please give us more clear instructions on how to reproduce it from scratch.

I cannot reproduce this with either the current development version of Blender. Please try the latest daily build: https://builder.blender.org/download/ If the problem persists, please give us more clear instructions on how to reproduce it from scratch.

Sebastián Barschkis commented

2020-07-02 17:37:09 +02:00

Added subscriber: @sebbas

Sebastián Barschkis commented

2020-07-02 17:37:09 +02:00

To me it also looks like this is fixed already. Not sure which commit actually did that though.

@ignatz Yes, the issue with flow objects not resetting the simulation is a known issue. This should probably be noted somewhere (or even better, fixed :)

To me it also looks like this is fixed already. Not sure which commit actually did that though. @ignatz Yes, the issue with flow objects not resetting the simulation is a known issue. This should probably be noted somewhere (or even better, fixed :)

Ignatz commented

2020-07-02 18:02:07 +02:00

Now using version 2.90.0 alpha - 2020-07-01 - hash 52b125a790

Tried about ten different times with various inflow objects at different positions, angles and inflow volumes, but I can no longer recreate the problem.

Cannot figure out what has changed, but if the problem doesn't show up it is just fine by me. :-)

Now using version 2.90.0 alpha - 2020-07-01 - hash 52b125a790e3 Tried about ten different times with various inflow objects at different positions, angles and inflow volumes, but I can no longer recreate the problem. Cannot figure out what has changed, but if the problem doesn't show up it is just fine by me. :-)

Sebastián Barschkis commented

2020-07-02 18:06:48 +02:00

Changed status from 'Needs User Info' to: 'Resolved'

Sebastián Barschkis closed this issue

2020-07-02 18:06:48 +02:00

Sebastián Barschkis commented

2020-07-02 18:06:48 +02:00

That's great to hear! Thanks for reporting, closing for now!

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Mantaflow - liquid sim - strange behaviour #78384