Advect fluid

[Jim M]

Hi,

I am attempting to advect a particle fluid object. I can advect particles, but not particle fluids... is this a limitation and if so if some could explain I would be grateful. I basically have a drop of fluid dropping into a smoke container, the fluid affects the smokes velocity, temperature etc and I get a nice sim. Ideally I want to create a two way advection relationship. Is this a super advanced thing to do?

Is it a case of using straight particles, and saving out the smoke sim, then using the imported smoke sim to drive the particles by advection? Ideally I want the complex forces of viscosity and surface tension to act on fluid particles yet be driven by an advection field. This is tricky for me being fairly new, but I am diving right in.

I have succeeded with straight particles (in a one way relationship, using a sphere collision to drive the smoke, then an advection force to drive the particles position/force or vel)

I have not succeeded with particle fluids at all.

Also I slightly confused as to fluid types. We have Particle fluids, Flip fluids and Volume Liquid fluids. Are they all different? I understand how Particle fluids basically operate, coming from a realflow background. Are Volume Liquids voxel based, then skinned using some isosurface or something?

Thanks for any input.

J

Edited August 15, 2010 by Jim M

[Macha]

Here is one idea with a sop vector field.

It works but I wonder if somebody else can come up with a more beautiful solution. I don't really like going outside DOP to fetch something from SOP that's actually already in DOP. There are all these nice gas microsolvers that I don't know how to use (but want to use).

untitled.hipnc

Edited August 16, 2010 by Macha

[Jim M]

Here is one idea with a sop vector field.

It works but I wonder if somebody else can come up with a more beautiful solution. I don't really like going outside DOP to fetch something from SOP that's actually already in DOP. There are all these nice gas microsolvers that I don't know how to use (but want to use).

So if i understand this... you are outputting the smoke Vel to SmokeEv and then birnging that into dops as a smoke vector field?

I did it with particles, kind of by accident. By setting the merge node to source relationship, then advecting the particles. So the particles create smoke (and velocities) and are in turn advected by the smokes velocities. Its kind of unstable at the moment.

Thank you for the example, it will take me a few days to understand it I think... It looks like just the ticket though!!

PS... I looked on your vimeo channel and had to facebook the sausages anim. Top notch m8.

[mawi]

I don't really like going outside DOP to fetch something from SOP that's actually already in DOP.

There is a fetch data DOP.

Edited August 16, 2010 by mawi

[Macha]

There is a fetch data DOP.

And I spend quite some time trying to figure out how to blend velocity data from smoke on to (fluid-)particles and still didn't find a way, with this and other nodes and combinations.

If you know how please send us a file!

Edited August 16, 2010 by Macha

[Jim M]

And I spend quite some time trying to figure out how to blend velocity data from smoke on to (fluid-)particles and still didn't find a way, with this and other nodes and combinations.

Mathematically it should be straightforward?

Modulate the vector fields output by multiplying the vectors by a vector scalar variable (lets call it N and give it a value of 0.7), then add the particles vectors based on 1 minus the vector scalar variable (=0.3). Does this make sense?

The vector scalar variable is a blend factor between 0 and 1, i.e. 0 and 100%

This is my first thought, but how to do it in Houdini is above my head so far...

[EDIT] The Fieldforce DOP has a scale force, I think this might do what I am talking about. Abviously I am missing something

Edited August 16, 2010 by Jim M

[mawi]

And I spend quite some time trying to figure out how to blend velocity data from smoke on to (fluid-)particles and still didn't find a way, with this and other nodes and combinations.

If you know how please send us a file!

I was talking about going outside DOPS to fetch data that´s already in there.

So instead of picking velocity via a vector field you could fetch that directly for use in a field force.

I dont know if it´s the best way to do it. But it´s one way to do it.

advectFluid.hipnc

Edited August 16, 2010 by mawi

[Macha]

Thanks Mawi, that's what I was looking for. A more elegant solution than mine!

Jim: The trouble was that I didn't know how to grab a field value and blend it to a geometry point inside dops. Alas, the solution was much simpler than I thought. A common Houdini experience (for me), especially in dops.

Edited August 17, 2010 by Macha

[Jim M]

Thanks Mawi, that's what I was looking for. A more elegant solution than mine!

Jim: The trouble was that I didn't know how to grab a field value and blend it to a geometry point inside dops. Alas, the solution was much simpler than I thought. A common Houdini experience (for me), especially in dops.

Thanks guys.

[Pazuzu]

It's possible to Fetch data from an external DOP network? How?

Thanks!!!