Set Initial State for Fluids?

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Hi all,

Is there an option in fluids (pyroFX in particular) similar to Maya where I can set the initial state? I've got some pyroFX smoke set up as a simple smokestack with a fan force affecting it. It takes like a good 500 frames or so for it to start looking the way I'd like. In Maya, I'd run the sim out to frame 500, set the initial state, and then cache say 100 or so frames and then render.

I know Houdini's workflow is a bit different…I wasn't able to find anything in the docs regarding this.
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Ah…never mind. Found my answer. From Dynamics/Optimizing a Simulation:

“You can also break up a large simulation by time. You can run the simulation up to a certain point, and save the entire simulation state to a sim file (using a File dynamics node at the end of the network). Then, you can use the same network to run the second half, but in the Initial state parameter of the DOP Network container node, load the saved midpoint sim file.” :idea:
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Hmm…ok, so another question. I've decided to break up the 500 frame simulation into two, 250-frame sims.

So far I've cached out the low-res and up res solvers and have them loading in from disk. At obj level, I can scrub around the timeline easily with no problems (even tried closing the file and reopening just to check, and it all works fine).

Following the above-mentioned advice, I added a File node to my AutoDopNetwork, and set it to “Write Files”. When I jump to frame 250, the sim proceeds to cook, and writes out a sim file for every single frame. This isn't the way it's supposed to work, is it? If the low- and up-res solvers are both already cached, why does the network need to re-cook? Shouldn't it just be able to write out a sim file for the specific frame I specify?

Actually, after going back and double-checking, it seems that any time I move the timeline, the network wants to re-cook. If I hit escape, it appears to be reading in the cache files, but there must be something that I've overlooked here. Help…?

I've attached the hipnc file (minus the cache files, obviously), for anyone who'd like to give it a go. Thanks in advance!

Attachments:
smokestack_002a.hipnc (684.6 KB)

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