[Mantaflow] the number of particles increases over time #76691

Closed
opened 2020-05-12 17:06:11 +02:00 by Pavel Blend · 12 comments

System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: AMD Radeon HD 7560D ATI Technologies Inc. 4.5.13399 Core Profile Context 15.201.1151.1008

Blender Version
Broken: version: 2.83 (sub 15), branch: master, commit date: 2020-05-11 19:18, hash: 8956e9e5f6
Worked: (newest version of Blender that worked as expected)

Short description of error
If particles come into contact with obstacles, then the number of particles increases.

Exact steps for others to reproduce the error
Bake this scene.
mantaflow_particles_test.zip

**System Information** Operating system: Windows-10-10.0.18362-SP0 64 Bits Graphics card: AMD Radeon HD 7560D ATI Technologies Inc. 4.5.13399 Core Profile Context 15.201.1151.1008 **Blender Version** Broken: version: 2.83 (sub 15), branch: master, commit date: 2020-05-11 19:18, hash: `8956e9e5f6` Worked: (newest version of Blender that worked as expected) **Short description of error** If particles come into contact with obstacles, then the number of particles increases. **Exact steps for others to reproduce the error** Bake this scene. [mantaflow_particles_test.zip](https://archive.blender.org/developer/F8530937/mantaflow_particles_test.zip)
Author

Added subscriber: @Pavel_Blend

Added subscriber: @Pavel_Blend
Member

Added subscriber: @sebbas

Added subscriber: @sebbas

Added subscriber: @mano-wii

Added subscriber: @mano-wii

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

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

I can confirm.
It is as if the volume of the liquid gradually increases although it does not have an outflow.
Problem seen in 2.90 f9d0f59bed and 2.83 50ef801a79

I can confirm. It is as if the volume of the liquid gradually increases although it does not have an outflow. Problem seen in 2.90 `f9d0f59bed` and 2.83 `50ef801a79`
Member

Added subscriber: @JacquesLucke

Added subscriber: @JacquesLucke
Member

I've seen a similar report somewhere else before, but can't find it right now. I can also reproduce the issue.

@sebbas do you know if this is a bug in our code or more likely an issue with the solver?

I've seen a similar report somewhere else before, but can't find it right now. I can also reproduce the issue. @sebbas do you know if this is a bug in our code or more likely an issue with the solver?

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

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

The solver has certain metrics to adjust the number of particles in the scene (e.g. parameters "Particles Maximum", "Particles Minimum", "Narrow Band Width"). Based on these parameters, the amount of particles is allowed to increase/decrease.
In a very splashy scene ("FLIP Ratio" near 1) with high external velocities, like the one you created, this adjustment is not enough. As there is no upper threshold, the number of particles can blow up.

To fix this, there is now a "System Maximum" variable with which one can set the maximum number of allowed particles in the simulation (e76f64a532).

Can you try and see if this helps you solve the issue?

The solver has certain metrics to adjust the number of particles in the scene (e.g. parameters "Particles Maximum", "Particles Minimum", "Narrow Band Width"). Based on these parameters, the amount of particles is allowed to increase/decrease. In a very splashy scene ("FLIP Ratio" near 1) with high external velocities, like the one you created, this adjustment is not enough. As there is no upper threshold, the number of particles can blow up. To fix this, there is now a "System Maximum" variable with which one can set the maximum number of allowed particles in the simulation (e76f64a5329d). Can you try and see if this helps you solve the issue?

Note: One of the caveats of this approach is that "System Maximum" is an absolute number. I.e. it does not scale when the resolution of the domain changes.
For now, this number needs to be estimated. In the future, it would be nice to have a volume based solution (number of particles can vary, but volumes stays constant).

Note: One of the caveats of this approach is that "System Maximum" is an absolute number. I.e. it does not scale when the resolution of the domain changes. For now, this number needs to be estimated. In the future, it would be nice to have a volume based solution (number of particles can vary, but volumes stays constant).

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

Changed status from 'Needs User Info' to: 'Resolved'
Sebastián Barschkis self-assigned this 2020-08-03 10:52:07 +02:00

Closing for now. If you still encounter a situation with exploding particles, feel free to reopen!

Closing for now. If you still encounter a situation with exploding particles, feel free to reopen!
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Reference: blender/blender#76691
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