Houdini viscosity FLIP stick on object

[blackchicken]

Hello

is there some parameter which I could drive FLIP particles stickines? If I add viscosity a lot of particles stick on colliding object. But what if I want viscose fluid bud no "friction" "sticky" behavior? Ofcourse I have fricton 0 on fluids and colliding object. Thanks a lot.

[Annon]

Not sure about H12, but I think the answer is still the same.

You'd going to have to do something yourself in DOP/Pops or DOP/Sops.

Volume gradient will get your the direction to the surface, volume sample will get you the distance. From there you can do what you want.

[blackchicken]

Thanks for repply Christian, Im not very familiar with dops, is there on odfroce some hip which I could explore? Thanks a lot BC

[rayman]

Hi,

I`m having the same problem with flip and viscosity. Can you help me?

[danw]

The last version of Naiad had something like this implemented, named "Sticktion" - it doesn't actually relate to viscosity at all as I understand it - it's more a general stickiness/surface-tension-trick, and it'll work for non-viscous fluids as well.

In vague terms, it allowed free movement tangentially to a surface, but would damp the velocity of the fluid only along the vector away from the surface - within a specified distance from the surface. The effect was that fluid could run underneath overhangs and "cling" to the surface.

I'm not at all familiar with Houdini FLIP fluids yet, so I don't know where to start creating the same effect, but I get the impression it shouldn't actually be that hard. You can get the vector to a collision surface by taking the gradient of the SDF, and you get the distance for free. I would guess you'd need to take a dot-product between the velocity and the surface gradient vector, and apply less damping as it approached zero - ie, when they're perpendicular... and more as it approaches 1 - ie, when the velocity points directly away from the surface. (...or -1, if the gradient vector points inward... I always get SDFs back to front)

Edit: whoops, just realised this thread was resurrected from a year ago... well, might be useful to someone I guess :-P

Edited February 28, 2013 by danw

[mawi]

For knowledge there is stick on collision parameters in flipsolver/volume motion/collisions,,,

[Solitude]

The stick on collision works ok, but it doesn't make fluid flow around an object. Like, if you run water over a sphere some of the water will come down around the bottom of the sphere and drip off the bottom. Flip doesn't handle this at all. It will slow down when it collides, but when it comes around the bottom it doesnt stick to the surface, it just slides right off, albeit slower than if it was turned off. I usually work around it by adding in a custom velocity field from the normals of the object or field force that pulls the fluid toward the surface of the object if I need it.

Edited February 28, 2013 by Solitude