Animated stream of fluid particles

[Eucalyptus]

I've got a question that I've tried fiddling around with to create, but haven't quite gotten it the way I want and am wondering if there is a very simple solution.

I'm trying to create a stream of fluid particles that I can have shoot in a direction (say, up), and then fall to the ground. This is relatively easy, as I just use an initial velocity.

The question I have however, is if there is an easy way to create an object/emitter that allows me to control WHEN the stream shoots out. Say at frame 10, 30, 50. Or on demand, so I can keyframe it to shoot out.

In Houdini 10 there was an option I keep reading about "Stream Emission", with fluids, but I can't seem to find how to access that in H12?

Any thoughts?

(To make it more clear, I'm trying to recreate a water fountain type effect like that outside the Bellagio Hotel in Vegas, with the water jets shooting up in a pattern)

Thanks!

[Solitude]

You can do it on the 'activation' on the fluid source node in dops, but that would turn off the entire emitter. I would suggest doing it in sops before it goes to dops. You can just delete all the points or use a switch to turn the emission points on and off as needed. You can also set the initial velocity there too, on the source geometry so you can do all your initial direction there as well with v attributes. I would probably set up the entire emission system in sops, emission speed, direction and timing.

Edited November 28, 2012 by Solitude

[Eucalyptus]

Thanks for the response Solitude.

So would you use a Flip Fluid from Object type of emitter for this, or an Emit Particle Fluid emitter? or am I not following entirely haha. In my autodopnetwork there is only the flipfluidobject (the object it's emitting from), and then the flipsolver merging into the final gravity node. I can't seem to find any indication of an "activation" properties area in any network, which is what I originally was looking for and was just going to see if I could keyframe the emission.

[Solitude]

Are you using houdini 12? If you set it up with the shelf tool it'll put the nodes in place for you. There will be a node piped into the last input of the flip solver, which is the source volume node. This brings the particles in from sops, and also sets up the fluid source node on your emitter object.

[Eucalyptus]

Ahh I see. That's perfect. I imagine what you intended was for me to just keyframe the fluid between 0-1 for when I want it to spray out then yes?

Would the best way to have it shoot up initially, but then follow the rules of gravity (like a normal fountain), be to add a Drag operator between the flipfluidobject and flipsolver, and just keyframe the velocity activation there for it as well? Or is there a way to set an initial velocity, but not constant one?

Sorry if these are dumb questions - relatively new to creating more than basic fluid sims.

[Solitude]

Attached a really quick setup. I would put in more control for the emission and direction of multiple fountain emitters, but this was a quick hack (scale is way off and such). Still, it should at least give you some ideas. I put some sticky notes in there as well to explain a bit of what's going on.

Edit: Forgot sticky note in the dop net. I'm scaling the incoming initial velocities on the source volume node.

Second edit: Redid the way the emitters get their direction. Makes more sense this way.

Flip_Animated_Fountain_Emitters_h12.hipnc

Edited November 28, 2012 by Solitude

[Eucalyptus]

Wow, thanks very much for putting this together!

It doesn't really make sense to me at the moment, but I'll try to make sense of what you've done and put it to use. Seems complex to me at the moment, but I'm sure it's just understanding referencing things.

Thanks again, this is great.

[Solitude]

No prob. I also just re-uploaded a slightly modified version of how the emitters get their directions.

[Eucalyptus]

After analyzing it, it actually makes a lot more sense. It's just much more "building blocks" than I had expected haha. A steps system.

My only question was how the emitter object is cycling back and forth in direction, because it appears the target node isn't moving at all? So I'm not sure what is causing the original object to rotate back and forth. But I think maybe that's what you just mentioned in your last comment.

Just so I make sure I'm understanding it... With this sim, you've basically:

Setup your emitter object,

Give it an animation/cycle to move back and forth,

Created instances of emitter object on a line that cycle in on it's vertices/points,

Created your surface volume on emitters by using a ___________ (blank, not sure what makes a create_surface_volume in the Shelf tools... maybe a "Emit Particle Fluid"?),

Then finally just directed your source_surface in your flipsolver to the "emitters" object that was created previously, which will emit the fluid from the particles created on your instanced emitter objects?

I don't know if I'm overcomplicating this. If I'm reading it correctly, why did you turn the emitter objects into particles (create_surface_volume in emitters node) to emit the fluid particles, instead of just emitting from the emitter object itself? (the extruded circle).

Thanks again, really appreciate it. I'm digging in pretty hard to your knowledge right now haha.

[Solitude]

Sounds like you get the majority of it. You're right, I used the emit particle fluids shelf tool. This sets up everything needed to make a constant stream of particles. The create_surface_volume node is kind of the "set this stuff up as a source for dops" node. It is also used for other things as well. It will take your object, and set it up as necessary for a given task related to dops (source / sink / pump / particles / pyro). The shelf tools set it up for you, but you can also use it for other stuff as well.

To get the direction, I had initially used a 'look at' on the original object. That was then copied to the points. Afterwards, I changed that to a static 'original_object' and used a vop to create a vector from each point on the copies to the target. This made more sense to me, though this could be done a number of ways. You could create each fountain emitter with it's own object, and just animate each one by hand (if they even have to be animated rotations), or you could give each one it's own target. For emission time, you could add a spare parameter to each emitter object, and use that to control emission, by animating and then referencing that too. Again, I just came up with something fast to convey one option.

[bloomendale]

I enjoy your use of Ramps VOP the most. Simple and beautiful)

Thanks.