Smoke simulation and scaling?

I created a smoke simulation to be used in my animation, after I finished setting up the simulation I imported it into my already made scene. Unfortunately, it was way too big, so I scaled it down to the appropriate size. Now, even after re-baking and everything, I can not see the smoke in the 3d view or render. Are there settings I have to tweak to see the smoke after scaling everything down?

If the smoke sim is anything like Cloth, then the scale has a major effect on the results of the sim – maybe at a much smaller scale, the sim isn’t working the same as it was?

AFAIK Cloth, Fluids and Soft-body physics are all based on 1 BU = 1m. My experience with Cloth (in 2.49 & earlier) shows that there is no scale compensation option within the sim itself, so if the model is at a significantly different scale, the sim will not work as well. Maybe smoke suffers from a similar limitation?

My workaround for Cloth was to use rather massive values for some of the specs (my model was about 100x too big for the sim scale), like Gravity @ -100, in some cases hitting the (very annoying) built-in value limits of the sim. If your models is very small compared to the “native” scale of the smoke sim, you may have to radically adjust the sim values to get similar results.

ugh, that’s no fun.

Have any ideas what kind of values I should change? (Other than gravity) My scene requires my smoke sim to be resized to 0.025x what it was before if that helps with what calculations I’d need to do. Unfortunately, I can’t scale the entire scene up.

Sorry, I gave up smokin’ :wink: Actually, I haven’t tried the smoke sim yet, so I can’t offer any help there, just some commiseration – the Cloth scaling issue nearly sank my Kata project. Nearly. I was able to find an acceptable set of specs, but it took weeks of trials.

Wow, blender really does need a scaling factor for these sims!

Anyway, I think I might have figured out what needs to be changed, but I still have to render the animation to make sure it looks good in motion. The smoke is still not visible in the 3d view panel, but it is visible when rendered, and looks pretty close to what it used to.

f = factor by which your simulation needs scaling (in my case 0.025 or 1/40)

Gravity /= f

Step Size *= f

Texture: (if using emit, mainly for fire)
Emission /= f

Physics:Tweak *= f

Obviously there sometimes are limits (for me step size is limited, but the smallest value seems to work fine for me)

The particles don’t look right in the 3d view, but render properly, and the smoke seems to render properly as well. Now, I’ll do a test and let you know if everything renders properly in animation.

The above settings will get you really close, but you might still need to tweak them. I had to double the density and scattering of the material, and half the emit of the fire texture for it to look like the original, but now it looks pretty good.

Glad you were able to find a good set of values for your smaller scale. One of the big issues I found in trying to rescale Cloth was the hard-coded limits for some of the values – something like your “fudge factors” wouldn’t work because I couldn’t input numbers that high! But like you I did find an acceptable compromise, it just took a lot of testing, mainly because Cloth collision is such a bear to get tamed when the values get “out of scale.”

yeah, 2.5 seems to be better at that. Like, one box might only normally go up to 10, but then if you manually type in 100, it will then change it’s maximum to 200, or whatever. It seems to adjust to how you want it on a lot of the controls. Although minimums don’t seem to have the same flexibility.