Smoke grenade/ Smoke canister adaptive grid issues

[Bertjenkins]

Hi,

I'm doing a quick smoke canister animation and i want the canister/grenade to continually emit smoke as someone throws it. The adaptive grid seems to always cut off at about 70 frames. Is this because the memory has run out? I wonder what's the best way to approach this...at the moment i'm using the cold smoke setting (the grid threshold is set at 0.002). Any help would be much appreciated.

[Svetlin.Nikolov]

Hey, can you check the Phoenix log for any warning/error messages, or send it over right after you've simulated?

[Bertjenkins]

Thanks for the swift reply. I've done this type of thing before, I just haven't used phoenix for a while. No error messages. Just when the object speeds up the adaptive grid cant keep up. I changed the step size which helped. I just wanted to know if it's best to make a huge grid and leave it or use an adaptive grid. Should i use cold smoke for a smoke canister feel? Which general settings etc? The speed of the sim differs wildly when you change the smallest of parameters. Just wondered if there was a basic tutorial on trails/ single object emitting smoke as it travels through air and what to watch out for as I don't have much time to get this working...I've done this size of smoke trail before it's just stubbornly not working...

[georgi.zhekov]

Hey,

If the adaptive grid can't keep up you might need to increase the Extra margin option in the Grid rollout. This will give the fluid a bit more room and the grid should be able to expand.

If the simulation manages to keep up but the grid is not expanding then you might be running out of RAM. You can check this in the Windows Task manager. Then a solution would be to either decrease the grid resolution or try using non-adaptive grid.

Another thing that you can try and might work depending on the trajectory and the speed of your canister is to parent the Phoenix simulator to the emitter object. This way you won't need such a big grid, though note that this might blur the simulation too fast and might not look good.

As for the smoke look - it all depends on the results you're after. The cold smoke preset uses a Temperature of 10 in the Source settings - this would make the smoke "heavy" and it will go down. If you wish a more neutral smoke you can try setting the Temperature to 300 and then use a Phoenix Plain Force to act as a wind or adding Turbulence Force to give it a bit more interesting motion.

You can also play around with the Conservation settings in the Dynamics rollout of the Simulator. Using Direct symmetric or the PCG methods would give a different look to the smoke. If you need more swirls you can increase the Conservation quality, but note that this will increase the simulation time. You can find more about the conservation here - https://docs.chaosgroup.com/display/...Smoke+Dynamics

Hope this helps!

[Bertjenkins]

I found the best results through doing some tests with spheres of varying sizes using the sphere scale to build density first. If the trajectory was on a simple path (a narrow long grid) it seems to work much better than moving xy/zx etc. I actually found the rough sim with the standard settings just adjusting the source and the density, then adjusting the temperature to stop it falling/rising too rapidly. I'll let you know how i get in with the finessing....

[Bertjenkins]

Thanks For the reply! Sorry sent the last one before I'd seen all that. All very useful stuff

[Bertjenkins]

The animation looks great in the viewport. However I need to render in arnold on this project. The whole open vdb conversion is a bit tricky and the sim in arnold looks totally different to the viewport. Does the latest version of pheonix support arnold natively? Or do you intend to in future?

[Bertjenkins]

One thing I don't quite understand is replicating the phoenix viewport smoke look in arnold. It's just very diffuse thick smoke like the canisters produce. In arnold it seems to go very black and adjusting the volume shader seems to make it quite fake. For basic smoke am i to assume i don't need temperature data? Do I tick RGB and Temperature? When i render in arnold it looks different, i'm wondering if this i because i only simmed the smoke channel (ie default values), an dnot RGB or temperature. Do I need these? Or maybe because i am using blackbody in the arnold volume shader emission channels and there is no temperature data? (ie is there any emission involved in basic smoke?)

[Bertjenkins]

For anyone else stumbling upon this, in the arnold volume shader, once you adjust the scatter color - keep the weight at 1 but change the HSV value of the colour up to quite a high number above 1, ie in the 20's etc, the smoke starts to brighten up and look much more like the viewport preview.

[Svetlin.Nikolov]

Ah yes... since Arnold does not support native Phoenix rendering like Corona, V-Ray and Octane do, you gotta dial in settings that try to mimic the Phoenix shader.

One workflow that I've been using from time to time when equalizing shader settings between different engines is:
1. Equalize the Smoke Alpha - turn off any emission/fire, leave just the smoke and equalize what shows up in the alpha channel.
2. Then equalize the Smoke Color - keep the emissive/fire off and adjust the scattering, absorption/diffuse, etc.
3. and 4 - then turn off the smoke and do the same two steps for the fire/emission.

Overall this approach applies to any pair of render engines out there and should help prevent situations when you've just made it 90% equal and the final 10% suddenly break everything

Cheers!