Avoiding "Mushroom Cloud" smoke look

[Eucalyptus]

Hey guys,

Just a quick question - is there any to avoid getting that "Mushroom Cloud" looking effect in a smoke sim where the smoke is rising straight up.

I've got a sim of some advected points guiding a smoke sim being used for a Candle wispy smoke, and while I'm pretty darn happy with the look of the smoke after the fact, when the sim first starts - no matter what I change - it seems to have that "mushroom cloud" look.

Any way to avoid this at the start of a sim? The candle is being blown out so I have to be able to see the smoke begin emitting from the wick.

Cheers

[Solitude]

See if animating a bit of turbulence for a few frames while it is getting blown out helps a bit. You can do this on the velocity volumes/curl noise on the source, or on the pyrosolver. It should help make it less uniform while it's initially being blown out, allowing the smoke to move around and swirl a bit before it starts to calm down and rise. ...and since it's being blown out, you'd likely have a bit of turbulence and wind anyway.

[Eucalyptus]

Would the fact that I've used your advect points suggestion from my previous thread matter in affecting this Solitude? It seems that even when I change turbulence settings by a crazy amount in the Autodopnetwork for my smoke sim, while I can see huge changes in the AutoDopNetwork visualization, nothing much changes in the Scene level visualization of viewing the import_pyro_build. I'm even reseting my simulations manually.

Nothing ever seems to work as I would expect haha.

When I add Curl Noise, or Vortex, or anything on the initial emitter [create_density_volume] outside of the DOP network, it doesn't seem to change anything at all. Something I'm missing?

Edited January 26, 2013 by Eucalyptus

[Eucalyptus]

I'll post my file and see if what I am saying makes sense.

I also wouldn't mind making the Candle itself a Static Object, so when the smoke initially gets blown out I can have it blow against and bounce off the side (which would also remove my Mushroom Cloud problem...), but it seems to just disappear when I make it a Static Object. Again, beyond my knowledge of solving.

(import_pyro_build is the Smoke visualization)

Legend on Scene Level to help explain things - give it a look if you're feeling adventurous.

Candle_18_Render.hipnc

[dark_cry]

Hi

Eucalyptus, i've not looked at your scene, but increasing a padding on resize helps me to avoid the mushroom effect. Because of zero velocity outside the container smoke tends to "drag" causing this awfull effect So try to increase the container so that vel field could be advected far enough from density.

[Solitude]

I haven't had a chance to look at the file, but on the pyro solver, under the turbulence tab, you may have to tweak (or turn off) the control field to get it to have a stronger influence. For the vel from the source, you may have to modify similar thing on the mask tab of the source (in the dop net). Vel will be masked by the density, but you can turn that off to get the vel from the source (the curl noise from sops) to be stronger as well.

[Eucalyptus]

Thanks for replies guys. Just wanted to post that I managed to fix this problem sort of unintentionally. I wasn't happy with the starting shape of my animation so I changed that a bit, and by scaling time up slightly (1.4) it got rid of the initial mushroom look entirely.

Good to know about the padding and other suggestions though - thanks!

[johnLIC]

Increasing the padding, and going much more aggressive on the curl noise seem to have helped me out. Thanks for the tips y'all.

[stooch]

Hi, disable the velocity masking field in the pyro solver options, the velocities are being multiplied by the density field, which means that immediatelly outside of the density, velocity is set to 0. to avoid this, either make a custom field or disable density masking entirely.

[DarkMatter]

One of the best method I have found to deal with this issue is to use 'Pressure' as a control field for a shaping such as Disturbance. You want to find areas of high pressure (the head of a shroom)  and set the range in your control field such that it masks only the regions of high pressure.

To visualize the Pressure field:

> drop an Apply Data DOP in between your Smoke Object and the Pyro Solver'

>  drop down a Scalar Field Visualization DOP and plug it into the green input on the Apply Data

> on your Scalar Field Visualization set the Data Name parameter to "pressure/Visualization"

>  turn on 'Use Plane' and then play with the 'Guide Range' parameters to find the pressure field range you are interested in.

Disturbance with pressure as control field:

> Drop down a Gas Disturbance microsolver and plug it into to your Velocity input on the Pyro Solver

> Under 'Control Settings' tab (on the Gas Disturbance) check 'Use Control Field' and set it to "pressure"

> Set 'Influence' to 1

> Set 'Control Range' parameter to match the 'Guide Range' on the Scale Field Visualizer ie. the pressure range you want to apply the disturbance to 

Go nuts and crank up the disturbance 'scale' just to see it working and then dial it in. Don't forget that 'Block size' on the disturbance is in world units so it's easy to work out what size you need there then it's just a matter of finding the right 'scale' on the disturbance and a narrow enough 'Control Range' to break up the mushroom but not affect the rest of the sim too much.

[Atom]

Just set vel to zero before your fluid source node.

v@v = set(0,0,0)

 

[Eucalyptus]

This was 5 years ago now. If I hadn't solved it yet I'd be in an institution.