Does smoke have mass?

[cspears2002]

A colleague and I were discussing smoke in Houdini at work. We were wondering if smoke in Houdini has a parameter that represents the smoke's mass. We looked in the smoke object and smoke solver and could not see anything. I suggested that we might have to somehow create the attribute ourselves. Am I off base here? My reasoning is that heavy, sooty smoke will have more mass and therefore respond to forces differently than light smoke that consists primarily of water vapor.

[mightcouldb1]

You can recreate the effect of heavy smoke by using viscosity, cooling rate, and temperature. You can adjust the density with a shader. There isn't a parameter to input mass explicitly, but you could create that parameter if you really wanted to. I think that the artistic model is fine, because not everyone is working in a controlled environment where all models are modeled to real world scale, all forces are real world scale, etc.

Edit: All mater has mass.

Edited May 20, 2010 by mightcouldb1

[sam.h]

Isn't that what the density field is defining?

[static]

From what I've learned, density is used exclusively for shading and doesn't have an impact on how your fluid moves (think of it more like an alpha attribute). You could create your own scalar field for 'mass' and simply base it off density, but you would need to edit the pyrosolver to use this field to modify your fluid forces. The other option is to simply fake it, using the attributes mightcouldb suggested above.

[Marc]

This is not quite the same thing, but it may help:

We did a fair amount of dust here recently which has a similar problem, and one thing I found helpful was setting the ambient temperature using the 'Gas Bouyancy' DOP (if you're using pyro, it's in the 'temp_velocity_update' network box). From what I could figure out, the ambient temperature of a fluid box is 0, which means that even if you play with the cooling rate and temp options, you're never going to get a negative bouyancy since your temp will only go as low as 0. Increasing the ambient temp means that at some point when your temp cools down then you'll start getting negative bouyancy... which is expected in the case of heavy dust.

Anyway, as I say... not quite the same as your question, but it may add something .

Cheers

M