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modify splash in FLIP sim by sink, pump, or pop-nodes

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Hi, I have general questions about FLIP. For instance, there are splashes like an attached picture.
If I want to change velocity or delete splash/spray, I think there are 3ways. The FLIP concept could make it tricky because FLIP contains particle and volume fields together. Thus, questions are:

1 - in general, if I want to change velocity or delete splash, do I need to modify the both of particles and field together? Or just modify one of them?

2 - It's kind of similar question as #1, but, when we use sinkFLIP and pump and sourceFLIP; 
 2a  - pump seems to add velocity, but it's strange why source volume sets copy, and velocity sets normalized?? It should set source Volume none, and set velocity normalize OFF. Also, why don't we use pop node to change particle velocity directly??

 2b - sink seems to just kill particle, but why sourceVolume is maximum? It should be subtract although it's not exist.. And there is still surface volume exists after deleting particle...  Can't we use just pop kill to remove waterVolume/splash?

 3c - sourceFLIP looks just adding particle. I guess we can add velocity with particle together, then when it passes solver, it create water volume (surface field and vel field), then why don't we just use pop-source to add particle with velocity??

3 - There is FLIP solver > particle motion > Droplets > and min/max particle Density. However, there is no density attribute. What density talks about and how they calculate density??

Thanks for reading a lot of questions!!


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1 - to change the FLIP velocity you can update the velocity field (vel) or the particles velocity (v) with a gasfield wrangle (or VOP)
// update particles vel (eg: add some vel in X)
v@v += {0.1,0,0};

// update velocity field (eg: add some vel in X)
v@vel += {0.1,0,0}; 

to delete the particles, you can use a geometry wrangle (or VOP)
// example to delete droplets
if(f@droplet>0) removepoint(0,@ptnum);

3 - density is the number of particle per voxel. A gasparticlecount microsolver creates a particlecount field and the values are normalized to create the f@droplet attribute.

hope that helps...

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Thank you, Bunker, for your tips.

1 - It sounds that we don't have so much chance to use pump and sink node operations.

3 - I will use droplet feature to just detect it, and use wrangle to control droplet externally.

And, I am still wondering theoretical aspect like a my #1 question. Houdini'd FLIP is designed to modify the both of particles and field together, or just modify one of them.

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1 - no, I don't use sinks or pumps :)
#1 just one other them. 

Edited by bunker

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