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davidyannick

Vellum fluid and cog wheel

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There should be, I think, but I haven't had time to really play with the new vellum constraint types in 19 so others might have better tips. And right at this moment, configure fluid seems to crash Houdini... but...

Obviously, you could hand animate the cog and then use it as an animated collider object. Honestly, that's probably what I would do unless you are doing something fancy with the way it interacts with the fluid. Easier to fake it.

But, if you want them to interact, you *should* be able to add the cog as a rigid body to the simulation and they should interact. Instead of wiring it in as a collider, add a vellum constraints SOP set to "shape match" after your polyfill and then merge together both the GEO and the CONSTRAINTS with those coming from the vellum fluid and add the results to the solver. You'll probably have to play with the masses and find a way to pin the cog so it doesn't fall down.

But it should work...

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9 hours ago, madebygeoff said:

There should be, I think, but I haven't had time to really play with the new vellum constraint types in 19 so others might have better tips. And right at this moment, configure fluid seems to crash Houdini... but...

Obviously, you could hand animate the cog and then use it as an animated collider object. Honestly, that's probably what I would do unless you are doing something fancy with the way it interacts with the fluid. Easier to fake it.

But, if you want them to interact, you *should* be able to add the cog as a rigid body to the simulation and they should interact. Instead of wiring it in as a collider, add a vellum constraints SOP set to "shape match" after your polyfill and then merge together both the GEO and the CONSTRAINTS with those coming from the vellum fluid and add the results to the solver. You'll probably have to play with the masses and find a way to pin the cog so it doesn't fall down.

But it should work...

I've tried with Shapematch but indeed I can't find a way to pin the wheel, with RBD it's quite easy but in this case with vellum I really don't know, thanks for your tips :)

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Yeah, you'll have to get a little creative with the COG. A few thoughts off the top of my head:

1 -- The first is to add a static collider that fits inside the interior or the cog. Make a hole in the center of the cog and then run a tube through it, kind of like an axle running through. Then make that a collision object. It'll work, but now you've added another object to your sim, adding time and an opportunity for simulation weirdness.

2 -- Vellum respects pretty much all the POP attributes. There's called "stopped" that will control the movement of points. If you set it to 1 for instance (i@stopped = 1 in a point wrangle), your point will rotate, but stay fixed in space. Maybe you could make another object, let's say call it "cog_pin", make it a single point and set i@stopped = 1 on that object/point. Then constrain your cog to that point. But getting the constraints to work properly, so that the Cog still turns, but doesn't fall. would probably be a pain in the butt.

https://www.sidefx.com/docs/houdini/vellum/vellumattributes.html

3 -- Now that I think about it, maybe if your cog geo had a single point at its center, you could stop just that point. The fluid would interact with the rest of the geo, that point wouldn't translate in space, and the shape match would hopefully hold the whole thing together?... Or your simulation may explode with conflicting forces :)

4 -- Once again, I'd probably just animate the wheel to do whatever it is you want it to do and then sim the water on top of that... Not the answer you are looking for, but it'll work.

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