Condensing/Compressing smoke

[Badbullet]

What I'm trying to do is make smoke appear from the environment, like a weak fog, that gets attracted to another object and gets thicker and denser as it collects around it.

In my test I have a large box that is set up to Volume Inject on one frame, only the Smoke channel is used, set to .5. I have a sphere that I have setup with a Body Force to suck in all of that smoke and have it condense around the sphere. What I'm assuming should happen is that the smoke should compress, or condense together to a higher value as it all collects in this smaller area. But it doesn't. In fact, it never seems to get higher than the value that is set in the source, but seems to gets eaten by the body force.

Is there a special Conservation and Material Transfer setup that would make this work? Or does Phoenix not make already existing smoke denser as it is compressed into a smaller area?

[Svetlin.Nikolov]

Hey,

This is one of the worst enemies of grid-based fluid solvers Fluids must not dissipate and must not build up over time, so neither advection or conservation method would deliberately aid this, just the opposite.

We are working on a tool that would make it much easier to explicitly tell the simulation do that. However, until then, maybe you can work around it at render time - for example, you could map the smoke opacity in the volumetric options with a V-Ray distance texture and make it more opaque near the attracting geometry?

[Badbullet]

I will give that a try. It will make coloring the smoke based on the smoke value a bit tricky, but if it is all I have.

[Svetlin.Nikolov]

Yup, it's definitely gonna be better to be able to do this at simulation time so you can get a more natural looking sim...

[Badbullet]

Distance texture doubled the render time. Since I'm going to a near sphere shape, falloff set to Distance Blend was much faster, and easier to tweak the fading out.