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Stephen Moroz

Cable Overheating

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Hi everyone,

For an upcoming project, I need to create the effect of an extension cable overheating. ie. holes being burnt in the plastic casing of a wire and then smoke emitting from them.

This is a good reference, particularly the shot at 1:26

https://www.youtube.com/watch?v=jGPkkOU3Uf8

The problem I am currently having is that for smoke to emit from these little holes, the source volume has to be really tiny. This requires a ridiculously low division size just to get the sim to work, making it impossible to easily preview the simulation.

I'm thinking there must be a better method for doing this, so if anyone has any suggestions, I'd be happy to hear them!

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There's a few things you could try here.

First off, for the most part the individual smoke plumes don't interact with each other much. So you might be able to get away with running each little source as its own pyro simulation, with bounding boxes big enough to contain each individual plume but not so big as to cause more computation. You could then run all these simulations simultaneously, assuming you have a render farm for that.

Second, very tiny pyro sources typically create very wispy effects. Some of the burning holes in your source video were pretty big, and you could probably safely go with a slightly larger source and then maybe mask out the very beginning of the emission in post. For smoke that is supposed to be very wispy though, you might want to start with a fairly low-res pyro sim, then emit particles from those tiny little holes and advect them through the velocity field of that low-res sim. You could then use Volume Rasterize Points to convert those particles back into a nice thin volume. This technique requires a lot of particles, though, and the rasterization process can be very slow.

Whenever you can, parallelize your simulations! Don't run everything as one big sim unless everything needs to interact with everything else. 

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On 2/13/2018 at 2:08 AM, benne5 said:

If scale is a problem you can scale up everything to do your sim.  I also recommend having a look at this http://pepefx.blogspot.com/2016/04/cigarette-smoke.html

Thanks for the recommendation! I've seen a couple people saying to simulate things at a bigger scale but this confuses me. Wouldn't using the wrong scale produce an inaccurate result?

Currently I'm trying to sim this at real-world scale (where 1 unit = 1m) and I'm having issues getting the simulation to behave correctly. (I keep getting very grainy-looking results as soon as I try to add temperature into the sim)

Edited by Stephen Moroz

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Ultimately, it always comes down to whatever achieves the desired visual results.  So it might be worth trying at several different scales.  One thing to keep in mind that if you do scale then your pyro solver settings will also need to be adjusted.  It is difficult to assess the best methods without looking at a .hip file but generally if you are seeing grainy-ness that means the resolution of your container is not high enough.  Especially when trying to achieve wispy curly smoke.  

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Cheers, I guess that makes sense. I've ended up using a scale that is 10x bigger than the real values, and I'm getting results that I'm fairly happy with. I have had to put the buoyancy to some crazy high values to get the smoke to rise quicker, but looking back at it, I probably should have just adjusted the timescale a bit to compensate for the size.

Here's a really quick slap comp of the smoke on top of the shot (just taken from a flipbook). Currently there are some substepping artefacts near the sources but I will increase the substeps for the final sim.

Any crit on this would be greatly appreciated!

Password = "wire"

 

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Looking pretty good.  Maybe add a bit of drag force so that the smoke slows as it gets further from the source.

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1 hour ago, benne5 said:

Looking pretty good.  Maybe add a bit of drag force so that the smoke slows as it gets further from the source.

Thanks, that's a good shout! I'll see if I can add that in

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