Hi,

I'm trying to achieve this kind of effect :

https://www.youtube.com/watch?v=xATZvpmsKlY [youtube.com]

Someone has an idea of how produce a big amount of smoke with such a little emitter ?

Thanks,

Tom

Increase the density.

Density is clamped to 1, so it doesn't really help.

What you need is divergence and high velocities, and you really need to substep to make it behave.

Increasing Density is not the way to do it imho. Put down the Billowy Smoke shelf example and the density introduced is held at 1 meanwhile the MultiDisplay options set the display of the smoke to 6 or higher. If you want dense smoke, increase the shading density, not the actual density of the smoke.

The actual density field is treated as a mask within the simulation. Scaling this mask above 1 is fine but understand that this multiplies the effects everywhere and just doesn't make the smoke more dense. Since it is clamped at 1 internally and treated as a mask, the edges just get sharper and can lead to aliasing in the sim.

You want lots of velocity on the emitter as eetu did in his file above. Lots of velocity means increased sub steps or slow the sim down and then play back at faster frame rates. Without enough sub steps, your smoke emission will be starved leading to a lack of density.

Default shelf tools create hollow emitters. Only the surface is set up for emission. Make it solid by turning off the hollow options in the Fluid Source SOP. That would be Minimum Distance and Empty Interior off.
Also add a good deal of initial velocity. The more you add, the more sub steps you need to add to the simulation. Don't be setting vy at 100 with 1 sub step where 100 = 100 Houdini Units Per second and your emitter is 0.5 units high. eetu did both of these things in his file.

Selective turbulence using temperature as the Control Field and only apply turbulence to the leading edges by using the control ramp is effective at adding that extra detail as the smoke evolves. eetu didn't do this but is getting a very good look using diffusion and is also using the Gas Damp DOP micro-solver to tame the large velocities from the emitter source.

The file is perfect ! Thanks eetu.

And thanks for the explanation jeff !

I just have one more question.

In the smoke solver node > advanced > advection, why did you change the advection type and the vel advection type ?

Thank you.

Lewul
In the smoke solver node > advanced > advection, why did you change the advection type and the vel advection type ?

Oh, it was just something that johner mentioned; http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=145085#145085 [sidefx.com]

I thought this would be a case where the quality of advection matters, so I just used it - I didn't do any careful testing of the actual effect it had.

Oh okay, thanks !

The default is Modified MacCormack which is slightly faster than BFECC. Both are more involved than the Single Stage advection method.

You can think of both the MacCormack and BFECC advection models as advection and feature sharpening filter. Both will try to sharpen and retain features in the smoke. The difference comes down to a personal choice. BFECC can retain features in the smoke a bit longer and can result in more swirls than MacCormack in practice but both are very similar. Different but same.

Comparing to the Single Stage advection method, there is a pretty big difference. The Single Stage is faster as it is less involved and doesn't need to construct additional temporary fields. It is also more blurry and doesn't hold on to features nearly as well. If you want a smooth type of effect, try Single Stage.

Given that it is an artistic choice between MacCormack and BFECC, you should run sims using both advection types for yourself and choose which one you like.

I presume I'm not enough “skilled” to see the difference…
Thanks for the precision Jeff !

I need your help, again !

I'm trying to achieve this effect (gunshot) :

https://www.youtube.com/watch?v=5uFarFM9sow&feature=youtu.be&t=3m25s [youtube.com]

So my method is to source by particles that have been expulsed from a little sphere. But I'm not able to reach the effect, my smoke is not spreading everywhere in big quantity.

How can I do it ?

Thanks.