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Animation and particles leaking

Posted: Tue Feb 06, 2018 3:11 pm
by Dakiz
Hello there ! :)

I have been having an issue for a while now and I really don't see the end of it.
For a personal project, I have a shot where a vial falls from a table, but stops mid air thanks to some sort of magic spell. I built the vial at the right scale and animated it in Maya, then exported the animation in an alembic file. The vial is supposed to be filled up to the 3/4th of a waterish liquid. Basically, all I'm trying to do is to simulate a simple fluid inside the vial while it falls.

Thing is, no matter how I try, I always end up with particles leaking through the geo during the animation.

I tried :
-Thickening the walls of the vial
-MIN/MAX Substeps tweaking
-Scale the geo up to meters wide proportion (since fluid sim usually don't like tiny scale sims, the vial is ~ 7cm long and 3cm wide)
-tweak the time factor
-Collider daemon tweaking
-A few other things that I'm forgetting right now...

I tried all those options both in the standalone version and the C4D plug-in but no luck (even though it seems that I am having better results in the C4D version so far)... I'm a bit out of idea so here is my call for help.

If you're interested in having a look, here are the alembic files (normal animation, normal animation but with a proxy geo of the vial and one that is 2x slower with proxy)

I thank you in advance !


Re: Animation and particles leaking

Posted: Thu Feb 08, 2018 1:57 pm
by ChristianZ

I assume you have not forgotten to turn on "Continous collision detection".All your measures make sense.

But the timing of the alembic still looks quite fast. I would think that further slowing of the motion should make it work.

Re: Animation and particles leaking

Posted: Thu Feb 08, 2018 9:13 pm
by Dakiz
Hi ChristianZ !

Thanks for your answer! I'll try to make it 4x times slower (just so I can make sure this is a viable solution :) ). If I do so, would it be good to adjust the realflow time factor in consequence or would that just keep me at the same state than previously (make the animation 4x slower, set the time factor at .25) ? Or should I just make it a respond a bit faster than it should to make sure it follows the animation correctly ?

Thanks again!

Re: Animation and particles leaking

Posted: Fri Feb 09, 2018 8:59 pm
by ChristianZ
I see... maybe better to make the time factor (fps) so that the liquid is not over-reacting to the objects. Alternatively you could use a strong drag-force to calm the liquids behavior.

Re: Animation and particles leaking

Posted: Sun Feb 11, 2018 11:26 am
by ChristianZ
This is an interesting challenge and out of curiosity, I tried something similar: a filled paper cup falls on a surface and spills its content.
In this project I found that leaking was not such a problem, but over-shooting behavior of the liquid.
First, I tried to simulate the dynamics of the cup and liquid at the same time in RF. So, I filled the cup, then turned dynamics of the cup on and started the timeline. However, the liquid then always over-reacted and spilled or leaked already in the falling phase.
In a second attempt I first simulated only the empty cap at very high FPS so that everything was super-slow-motion. Stored this animation by setting the cup to cache and then filled this object with particles and started the sim again. In this way it worked better.

cup object: cell size=0.01, volume mode=shell, mass=40, collision geometry mesh, collision side=outside
liquid: SPH dyverso, resolution=1600, surface tension=3000, density=2000
gravity=12, k-speed daemon and sheeter used
simulation parameters: 1200 FPS

Super slow preview movie:

Re: Animation and particles leaking

Posted: Tue Feb 20, 2018 9:29 am
by Dakiz
Hi Christian !

Sorry I was away for a shooting, I'm getting back to it today and will give you my results ! Seems like the over-shooting behavior you're describing fits to what happens with my particles. Interesting ! I'm going to troubleshoot according to your suggestions ! Thanks sir !