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I guess I don't get what the problem is? You could add drag. Your example shows the default, smoke existing in the vacuum of space. Why would you expect it to slow down in a frictionless environment?

Use the distance function supplying the @P of the camera and the @P of the particle. Use the returned value to map it into a desired range which will be assigned to @pscale for the particle point. http://www.sidefx.com/docs/houdini/vex/functions/distance.html

It does work, but setting it up is a little more difficult than it should be. Pay attention to the text prompts that appear in bottom of the 3D view. Make sure your mouse is in the 3D view when you press enter, responding to the prompts. Also, the object you are using for the sink must have the top level transform set to world origin. So zero it out and the move the geometry around inside to place the sink where you want it. ap_flip_sink_working.hiplc

Ah, got it. Get rid of that condition, at the bottom of the script and it does launch. ui = TestDialog(name = 'test', title = 'Test UI') ui.show()

So where do you place huilib.py so the include from the shelf tool can find it?

Try turning off Correct collisions inside the solver (Advanced/Collisions). What is happening with the scaling version is that your density source eventually ends up inside the collision object. This causes density (or the fields specified) to immediately be removed. Try to avoid this with better shot planning.

You might want to check out this link. I think the main take away is to limit velocity, or zero it out, and just stamp density through the volume.

Not an image, like a .WAV file. I tried the menu shown, it worked. Thanks, I didn't realize Houdini could do that.

That's interesting, do you know of anyway to render the audio output?

You can always keyframe gravity, kick out a geo sequence and use ReTime to play it back as you see fit. ap_keyframed_gravity_back.hiplc

What if you move the transform after the sim?

An attribute transfer node can do that.

I think I would use both systems, Create a tube that fills the entire trench with fluid particles. then have a few emitters inside the trench to push things along. ap_River.hipnc

Just cache the final surface out one layer at a time and use the previous layer's surface as the collision object for the new layer. That is how a lot of those stacked candy or desert animations are approached.

The Ray node can sometimes be leveraged for this kind of work. It works well with points, but tends to flatten more complex geometry. ap_Knittingtest02.hipnc