Gaining more control over particle fluid sims

[mikelyndon]

Hey guys, I'm hoping someone can help me out. I've been trying unsuccessfully to create fluid sims and shapes similar to that of Tim Borgmann's beautiful stills. I'm trying to create a fluid with the consistency of paint and I've run into a couple of problems.

1. I'm struggling to get the 'stringy', elastic properties of paint and keep it thin and stretchy.

2. What would be the best way to direct the fluids? I'm ignoring gravity because of the shapes I'm trying to achieve. I've tried using standard particles with noise and the particleFluidSurface node to create some interesting shapes but I don't have control over the direction of the flow. I've also tried curves as attractors but the shape becomes too uniform.

I guess I want to try and have the fluid collide with a surface to create a splash but still be able to control the shape of the splash to a certain extent.

Any help would be greatly appreciated.

Mike.

paint_splat.mov

[Ezz]

Hey guys, I'm hoping someone can help me out. I've been trying unsuccessfully to create fluid sims and shapes similar to that of Tim Borgmann's beautiful stills. I'm trying to create a fluid with the consistency of paint and I've run into a couple of problems.

1. I'm struggling to get the 'stringy', elastic properties of paint and keep it thin and stretchy.

2. What would be the best way to direct the fluids? I'm ignoring gravity because of the shapes I'm trying to achieve. I've tried using standard particles with noise and the particleFluidSurface node to create some interesting shapes but I don't have control over the direction of the flow. I've also tried curves as attractors but the shape becomes too uniform.

I guess I want to try and have the fluid collide with a surface to create a splash but still be able to control the shape of the splash to a certain extent.

Any help would be greatly appreciated.

Mike.

Hi Mike.

Maybe its a good idea to use particles to "sculpt" your shapes instead of relying on simulations.

Then use the awsome particle-fluid-mesherSOP to get a polygonshape. From there on you can start

sculpting further on.

Just a thought.

Erik

[mikelyndon]

Thanks Erik. That's kind of what I've been doing already. The problem is I need to have the object animated. So unless I'm missing something, how can I sculpt the geometry while it's being animated? I tried something simple with some noise and it looked promising but I need more control over the direction of the flow. How can I create say, 5 particles side-by-side that follow the same path with trailing particles? The attachments shows my noise test.

noise.mov

[anakin78z]

Hey Mike,

I worked on this commercial a little while ago, and we had to tackle some of the same problems:

http://adsoftheworld.com/media/tv/lg_vase

Most of the fluids were created in realflow, but some of them in houdini using particle fluids. The techniques were fairly similar though. The fluids tend to blob up, so to get thin sheets we usually ran an emitter against a bowl or similar surface to get a flat fluid splashing out of it. The edges then tended to get really stringy too, which actually often became a bit of an issue, especially with houdini's fluids.

We tried various things to 'direct' the fluid... in houdini I tried setting up pop solvers to get the fluid to follow along paths, to use attractors, etc, but that would only work for a short time before things get really blobby. It works for short shots though .

One thing that ended up helping to get thin sheets of fluid is post processing the surface in houdini. I think I rayed the surface backwards against itself, then filtered that based on curvature, so flat areas got flattened more than bumpy areas, or the edges of the sheets, which created some really nice looking surfaces, and gave us better sheets than we were able to get by directing the fluids alone.

Anyhoo, hope this helps .

-z

[mikelyndon]

Hey Z,

Thanks for the tips and the link. I was starting to worry it was just me who had the blobby and stringy problem. We've also opted to use real flow and houdini which seems to be working. I'm relatively new to Houdini, would you mind explaining in more detail how you filtered based on curvature?

Mike.

[anakin78z]

Sure thing. I don't remember the exact workflow I used then, but this is the gist of it:

You can compute curvature using the measure sop. In the ray sop, turn off Transform Points and turn on Point Intersection Distance. Then, in a vop sop, if you multiply the distance value by the normal, you'll get the displacement. Remap the curvature value to something useful, then use that to scale your displacement, so that areas that have more curvature don't get displaced as much.

The result is that flat areas should get a lot of displacement (or as much as they need anyway), while curved areas, such as the edges, don't get displaced as much. Also, you'll probably want to give it a limit of how much it gets displaced, to avoid any weird behavior.

Good luck,

-z