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localstarlight

Multiple Solver Interactions

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I'm gradually trying to learn various of Houdini's solvers (primarily cloth, pyro, and bullet for now) and I'm slowly getting to grips with how they work individually. What I'm struggling to understand, and also struggling to find good learning resources for, are the ways to create interaction between multiple solvers. I'm interested in setups for one-way interaction (eg. pyro affected by bullet/rbd sims) but even more keen to understand two-way (or more) interactions. For example, how to have cloth and bullet (and perhaps pyro as well) all working mutually in a dynamic simulation, all affecting each other.

Can someone point me in the right direction towards learning how to combine different solvers together? Are there generic ways for doing this (in other words combining cloth and bullet would involve the same understanding/setup as combining pyro and cloth), or does every solver/combination have its own idiosyncrasies when trying to combine?

I found this video about combining pop and bullet solvers: https://www.sidefx.com/tutorials/combining-solvers-with-a-multi-solver/

I assume a good understanding of the multisolver is key here. But the multisolver doesn't accept the cloth solver as an input, so it seems like there must be more to it than that...

Any help much appreciated!

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Hey Steve, there's some stuff that don't interact natively (like FEM and FLIP for example) but I guess you can only find a way to make it work (because Houdini)
In this case I got a "fake interaction" by adding the near particles speed to the fem tets, check it out: 


I guess every solver/combination does have its own idiosyncrasies and, in some cases, I think it's better to even make diferent simulations for each component.

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Hey ParticleSkull, thanks for linking to your FEM+FLIP thread, very interesting!

I'm still curious why this seems like such a hard topic to find answers on. I've read a number of times people saying one of the strengths of Houdini is that it has all these different capabilities (hair, cloth, rbd, fluids, pyro etc.) in one place, rather than (a) relying on separate pieces of software, or (b) using various different plugins inside something like Maya. And yet, there seems to be precious little written about how to actually use these things together in the same sims.

My priority right now is to figure out a mutually interacting cloth + bullet sim. I can't seem to find anything about that. Not even an answer as to whether it should be possible or not. What's the point in having all these different dynamic solutions under one roof if you can't make them work together? That's a genuine, and not a rhetorical (nor intentionally facetious), question.

Has anyone managed to create a mutually interacting cloth and bullet sim?

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Check out the MultiplerSphereClothCollision example file that ships with Houdini.

On Windows the files are located here:

C:\Program Files\Side Effects Software\Houdini 16.0.632\houdini\help\examples\nodes\dop\clothobject

If you have not visited Matt's site, Tokeru, check it out. Lots of illustrated examples on various topics.

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Guest tar
36 minutes ago, localstarlight said:

I'm still curious why this seems like such a hard topic to find answers on. I've read a number of times people saying one of the strengths of Houdini is that it has all these different capabilities (hair, cloth, rbd, fluids, pyro etc.) 

 

Because it's simply not true - once upon a time all solvers might have integrated seamlessly but since then things have diverged.  Most likely people are misinformed.

Edited by tar

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Yeah and, even though the solvers are not seamlessly integrated, i think you can always find a way to "fake" this interaction.

On 3ds Max, for example, I don't even have a fluid solver to fake an interaction with a fem solver. 

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I've been messing with faux soft bodies using Bullet constraints just to get around the interaction stuff...

 

But you can also stack DOP's and create interaction that way - though this will of course get computationally expensive, quickly...

 

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Thanks everyone!

Will check out MultiplerSphereClothCollision, thanks Atom.

Johnny: those first two videos are basically exactly what I'm looking for. Thanks!

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