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Velocity field and fluids

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Hello there.


I have a little question. Have a character running across the screen. From this character I am meant to emit fluids. Basically two fluids. A blobby large fluids that dies off quite quickly. Then another wispier fluid that is "left behind" and lives alot longer. So far so good.


Because these two fluids are different scales and detail settings they dont move the same. The detailed sim sometimes pops out of the blobby sim before the blobby sim dies off. Killing the effect.


I was wondering. Is there a way I can have a "third" sim. Sort of a velocity only sim. Something that looks at the movement of the character. Then pushed out a velocity field. Then my blobbly and detaily sim can read that information and use that as a bases for thier movement. This way I can say for sure that both sims will have the same basic movement.





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You could splat the velocity of the character into a field and use that as an influencing force in the two sims, but from experience I'd say that approach would probably be a bit of a pain.  You can't really use custom velocity as a basis for fluid sim - as your custom velocity will almost certainly not obey the laws of fluid dynamics, it'll just cancel out or give entirely unpredictable effects when the pressure solve removes the divergence from it... the more you try to shove and pull fluid around, the more frustration it'll cause - it has a very strong will of its own :-)


If you're going for the artistic approach of layering multiple discrete sims for effect, I'd suggest it might be a better approach to try baking the blobby one first, and then filtering the surface SDF or meshed surface to be a fluid source for the detailed sim... that way you'd sort-of-inherit the behaviour of the blobby sim directly into the detail sim, and you'd only have one thing to render at the end.

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