Volume Pressure Question

[Fabiano Berlim]

I'm trying to understand how pressure attribute affects volume.

I was expecting volumes to avoid the high density areas and escape to lower density areas.

So, to test it, I zero out temperature and start emitting volume from a stopped source. But volume just stay still.

I also tried to modify data inside pressure. Nothing.

Any clue?

[chimeric]

I am not sure about pressure but have you tried using divergence instead?

[Fabiano Berlim]

I am not sure about pressure but have you tried using divergence instead?

You're right. Thanks! Divergence can give me some cool effects.

I've found this inside houdini manual.

"You could also try using a compressible fluid to allow the fluid to expand in the center. You can do this by setting the divergence field to the amount of compression/expansion you want to occur in each voxel."

This an example of a volume doing compression and expansion.

divergence.hipnc

And back to the post topic.

If expansion and compression is done with divergence. What about pressure?

[~nature~]

You're right. Thanks! Divergence can give me some cool effects.

I've found this inside houdini manual.

"You could also try using a compressible fluid to allow the fluid to expand in the center. You can do this by setting the divergence field to the amount of compression/expansion you want to occur in each voxel."

This an example of a volume doing compression and expansion.

divergence.hipnc

And back to the post topic.

If expansion and compression is done with divergence. What about pressure?

To my understanding,

Pressure is here to ensure the divergence (free) in the equation and output in the node Gas Project Non Divergent, the purpose of this pressure field may be later used as reference or to exert the feedback force to the objects which interact with the fluid.

Cheers.

[Fabiano Berlim]

To my understanding,

Pressure is here to ensure the divergence (free) in the equation and output in the node Gas Project Non Divergent, the purpose of this pressure field may be later used as reference or to exert the feedback force to the objects which interact with the fluid.

Cheers.

I suppose you're right. But the volume also seems to be affected to pressure. In this file you can see that the pressure in the side of the box is negative. That causes the volume to expand to there. But not like divergence. Divergence is like a gas that heats and expands. It's volume get higher. So to simulate that, I suppose that houdini add more density to it. While pressure keep the density constant.

pressure_visualization.hipnc

Well. Just a theory. I'm not really sure.

[~nature~]

Hi, Fabiano, here is the invaluable reference which would be helpful if you are interested in understanding what is going on under the hood. it explains how the pressure and divergence work and houdini must follow the principle.

http://www.cs.ubc.ca/~rbridson/fluidsimulation/fluids_notes.pdf

Cheers

[Fabiano Berlim]

Hi, Fabiano, here is the invaluable reference which would be helpful if you are interested in understanding what is going on under the hood. it explains how the pressure and divergence work and houdini must follow the principle.

http://www.cs.ubc.ca/~rbridson/fluidsimulation/fluids_notes.pdf

Cheers

That's awesome!!! Thanks a lot!!!