r/Houdini • u/Hoddini_ash • 1d ago

Help get rising bubbles using pressure incompressibility in FLIP SOP

I’ve been sitting here for an hour trying to figure out how to get rising bubbles using pressure incompressibility in FLIP with the FLIP solver, but I honestly don’t understand it at all. Could someone help me?

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u/ChrBohm FX TD (houdini-course.com) 1d ago edited 1d ago

Generally the concept is if you just create holes in your particle grid the empty areas will rise up.

So (after activating pressure imcompressibility of course) just add a SOP Solver in the Dive Target, connect it to the Source and delete points inside of random spheres in a tank (I use a group and a blast):

http://www.houdini-course.com/static/FlipSOPBubbles.hiplc

What might have failed for you is trying to delete points in the Volume input of the solver, which can happen, since the Dive Target Output naming is misleading.

Generally I would advice using the old DOP Network for this, since the Flip SOP Solver is pretty slow in comparison. I'm generally a big friend of the SOP Solvers, but in case of the FLIP SOP the oldschool DOP network unfortunately is significantly faster in my experience.

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u/Hoddini_ash 3h ago

Thank you so much! This is very kind of you :)