General Simulation Questions

[catchyid]

Hi,

This is a generic question about FumeFX simulation. My biggest challenge in simulation is to choose the right simulation parameters such as : smoke dissipation, minimum dissipation density, emission rate, etc. For example, when I see lots of smoke in the scene that I want to eliminate, I increase dissipation rate, increase minimum dissipation density, however usually I get a result that is either lots of smoke is gone or still too much smoke, so I go back and keep changing different simulation values (such as advection stride, solver quality, CFL, noise,...) hoping that I will get the result I want. I've tried to use effectors as well to control the dissipation (e.g. cylinder effector that has radial multiplier turned on), however the effect was not that clear to notice. I've been using FumeFX for couple weeks now and I have been changing simulation parameters as I mentioned above, but unfortunately everyday I work very hard but I don't get the intended result.

Now my question here is: Is there any a methodological way to tackle these kinds of problems. For example, if there was a smoke density histogram, I can easily see where maximum/minimum densities are and then choose the right dissipation rate? Or maybe there is a certain technique that should be followed to achieve certain results.

BTW, I've watched many education resources on FumeFX, however most of them cover the meaning of the interface and its primitive (and most obvious) usage.

Thanks in advance,

[sitnisati]

Hello,

You can use FumeFX' viewport numerical display of values in the grid.
I hope that can help you to numerically determine the amount of smoke you wish to tweak.

Regards,
Kresimir Tkalcec

[catchyid]

Thanks Kresimir for your quick reply.

To test smoke density and dissipation more, I did a simple test: created very dense particle system, set emission rate to "add" with value equals 1 (I assume it's 1 unit of smoke per voxel per frame?), and in the FumeFX grid (80x13x80) I set dissipation rate to 0.0 (so nothing gets dissipated), and set vorticity to 0.0, no noise, default advection.

I simulated the scene for 50 frames and I was excepting to to see smoke density reaching 50 (because 50 frames x 1 emission rate and no dissipation), then changed smoke low/high threshold rendering parameters to different ranges such as (0.0,50), (0.0,0.001) and (0.001,0.002) and rendered the scene (pls see attached).

Now my question is: why rendering of thresholds (0.0,0.001), (0.001,0.002) and (0.0,50) looked identical? Does this imply that most smoke density is in range (0.0,0.001)? should not the smoke density reach 50 since we have no dissipation and each frame we are adding 1 unit of smoke?

Thanks in advance,

[sitnisati]

Hello,

Have you checked the numeric smoke values in the viewport ?
The High Thereshold in Smoke reandering is just used for the Opacity AFC span - it won't cut the smoke in the way Low Threshold will.
Use AFC to adjust the opacity.

Kresimir Tkalcec