GAs Advect Field

[Sella]

Hi everyone,

Anyone knows how gas advect field works and how it is implemented into DOPS? I have an animation of smoke where I control the smoke using vector fields. Also, I have a geometry that I would love to cover with the smoke I am creating but it doesn't work. If someone can help me would be great.

Thanks,

Xavi

[Macha]

From my wobbly memory: You can calculate the properties of your fields but to make them move you need them to go through a solving step that involves advecting the field, usually by the velocity field. In the simplest case the property that you advect (move) is assumed to remain constant (say density). This advection, or convection, calculation is not very precise though and errors need to be taken into account. There are various options for that in solvers. Since the fluids are assumed to be incompressible it needs to be compensated for, otherwise your smoke will explode or dissapear.

Fields can also self-advect for added realism! For example velocity can self advect, as if you would split it up in a field quantity being moved by velocity (so, itself).

I think technically you dot the gradient of the field in question with the velocity, or whatever field you want it to advect with, add to that the rate of change of the field on a static spot in space (like a voxel) and solve it for 0, with various methods (you can choose them in solver options)

Houdini-wise you should plug that into the last part of a solver, I believe, or you can plug it all into a multisolver.

Something like that. It's been a while since I looked into fluids in detail... bunker might be the man for this.

Edited February 25, 2012 by Macha