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Waasha

Flip sim emitting particles from below the water level

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Hello, I'd like to ask if there is a way of emiting particles into the FLIP simulation after the water level rises above the emitor.

 

I have a sim where I try to fill the container with the emitor on the bottom of it. The water rises, rises, and...when the water level reaches the emitor and the emitor "sinks", it stops. There is no new volume, added from the new particles..

 

If I animate the emittor to go up, it works as soon as it is above the water level, so the emission works all the time, but only above the water level, not below...

 

There is an option on the source volume DOP called "Kill inside", but even if I uncheck it, the particles are added, but the water level doesn't rise above the emitter..

 

Turning particle separation also doesn't help..

 

Any advice?

 

Thanks...

fill_from_bottom_V01.hipnc

Edited by Waasha

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There was a thread on this not long ago, maybe it's worth to try searching. If I remember right it was about not having enough pressure to push new liquid, maybe you have to add some divergence with your source? Also maybe reseeding could be involved too?

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It can be slightly confusing if you're used to other types of particle sim.  In a FLIP sim, when you "emit" particles inside an existing body of water, what you're actually doing is just adding resolution to the existing liquid.  (And if you have "Kill inside" enabled, it won't even do that)  With a normal zero-divergence sim, any point in the sim either already is water, or it isn't.  The only way you can emit new water into an area that is already water is to push the existing water out of the way first.

You can do that literally, by having it move away under gravity, or push it with a collider or a force, or as teratera mentions, you can use divergence to achieve the effect too.

 

Emitting divergence is effectively instructing the fluid to inflate the size of the existing water... which under normal circumstances would end up spreading the particles out too thin, so you either use reseeding to maintain the particle density, or you can emit new particles in the same area you're emitting divergence.  (Personally, I prefer to emit new particles directly, and only use reseeding to cull particles when there are too many in a voxel)

Edited by danw
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Thank you VERY much for such a detailed answer, danw. In Real Flow this isn't problem, but that's SPH. Now I understand how it works with FLIP..

 

I will look into the divergence emitting.

 

Thank you very much again!

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