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Controlling particle birthrate to create jets of steam

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Xavier Bonet
Controlling particle birthrate to create jets of steam
on Mar 19, 2019 at 1:22:25 am
Last Edited By Xavier Bonet on Mar 19, 2019 at 1:30:00 am

I need to create jets or spurts of smoke/steam coming out of an industrial chimney at regular intervals, as if a mechanical process is going on that emits these jets with some force. I'm trying everything I can think of because the C4D particle emitter itself doesn't have much room to configure what it does—at least I don't seem to find anything but the speed of the emitted particles and certain variations—even the birthrate is unavailable to keyframe. Coming from After Effects, where emitters have every possible tweak built into them, I'm a little at a loss with the emitter in C4D.
The closest I've arrived at achieved sort of what I need is by placing a wind simulator that produces spurts of wind that drive the smoke particles upward. But the effect isn't exactly what I need, for several reasons: (a) when there's no wind, the same amount of particles are emitted and, because they have no speed, they just gather around at the mouth of the flue, whereas a sudden jet of steam should mean there're 0 particles emitted normally and then there are, say, 100 emitted at once—then back down to 0; (b) the wind doesn't only affect the particles being emitted at that time or, rather, those that are "inside" the flue, but it affects all particles, even the ones previously emitted, so you have those particles being shot up again together with the new ones...
These are the two major drawbacks of the strategy I've come upon but, really, I'm thinking this is in essence a very "workaround-ish" way of achieving something I'm thinking should be very easily achieved by some other means... as being able to control the particle birthrate at any given time seems like a basic necessity, right?
Anyway, hope someone can point me to the right direction with this issue! Thanks in advance!

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Jim Scott
Re: Controlling particle birthrate to create jets of steam
on Mar 19, 2019 at 3:35:47 am

For spurts of particles, keyframe particle visibility on and off (100% for 30 frames, then 0% for 30 frames, ie.).

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Steve Bentley
Re: Controlling particle birthrate to create jets of steam
on Mar 19, 2019 at 4:31:27 am

Use the emission velocity to get the particles to where they're going, then use the wind to push the particles downrange (if that's desired) and use air resistance to slow the particles down. Steam tends to shoot out very fast, then slow down pretty fast creating bunched up clouds as all he energy gets sucked out of it and it turns into water vapour.
Not sure how accurate you need to be but remember, steam is invisible and only becomes visible as the water condenses out as it hits cooler air.
Normally I would attack this with a number of synced particle systems where the particles (or more accurately the voxels) are different sizes.
So you use emitter A to shoot out very small semitransparent "droplets", Emitter B shoots out larger foggier blobs that move slower than A. And emitter C shoots out much larger, rotating, growing, and slower moving fluffy things that shadow each other. Even though they all emit from the same place, B becomes visible later in its life and C becomes visible even later than that ("later" for a particle can also mean farther along its path of travel). To the viewer this will look like one single stream where the particles change shape as they go.
A also dies earlier than B, and B dies earlier than C, while C has a nice long life.
You can have C (and to a lesser extent B) be more effected by air resistance but sometimes this is actually harder to get right. Instead, give C a lower initial velocity and start emitting it sooner so it can get out ahead of stream A before C becomes visible.

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