Thick Smoke Dissipation

[bhm]

Hi!

I am currently trying to create a huge smoke simulation like from a burning oil rig. Unfortunately I could not find any way to control the dissipation rate of the smoke. So I have not been able to keep the smoke in a specific boundary, it just grows and grows... I guess I could use a fixed container and blend it out via maps during rendering, but is there no way to tell Pheonix during simulation how fast the smoke should dissipate? Or didn't I find the right parameters yet?

Thanks in advance,
Bjoern

[Ivaylo Katev]

not directly, but there are several parameters related to the dissipation rate.
- the advection step the lower is the a.s. the higher is the dissipation per unit time.
- the vorticity - higher vorticity = higher dissipation
- the randomization - same as the vorticity
but the growing of the smoke is a different thing , it is controlled by the temperature, the smoke buoyancy and the scene scale.
if you target is to dissipate the smoke before it reach the upper bound of the box, you can "cheat" using the temperature as smoke. unlike the smoke (the smoke is a conservable value) , the temperature can disappear using the cooling option.

regards,
ivo

[bhm]

Thanks a lot for the quick reply! Definitively got me a step further!

[Sascha Selent]

not directly, but there are several parameters related to the dissipation rate.
- the advection step the lower is the a.s. the higher is the dissipation per unit time.
- the vorticity - higher vorticity = higher dissipation
- the randomization - same as the vorticity
but the growing of the smoke is a different thing , it is controlled by the temperature, the smoke buoyancy and the scene scale.
if you target is to dissipate the smoke before it reach the upper bound of the box, you can "cheat" using the temperature as smoke. unlike the smoke (the smoke is a conservable value) , the temperature can disappear using the cooling option.

regards,
ivo

Hi Ivaylo.

This sounds interesting. I have the opposite problem: I need to do a big simulation starting from a little source with large smoke distribution - it's a fire starting from a cooking place that shall distribute smoke in a big building - starting in the kitchen with the smoke filling the ceiling then moving through the dooropening to next floor - that means the smoke needs a very long lifetime. In fact I would like to keep all the smoke alive till the end of my animation. Is it possible to do this? What would be the best approach to do this? How can I manipulate the time when the smoke disappears¿

[Sascha Selent]

Sorry, I couldn't finish the post, I'm writing on a tablet and this is horrible....

Anoher question is: I have a scene with 0,1 unit =1 inch. Maybey this can make trouble? Is there an "ideal" scene scale for optimal real world size results?

Thank you and kind regards.

Sascha

[Paul Oblomov]

Some screenshots would be great Or you can find me in skype (my nick with no spaces), I can probably help ya... Maybe some guiding emmiters will help ya.

[Sascha Selent]

Some screenshots would be great Or you can find me in skype (my nick with no spaces), I can probably help ya... Maybe some guiding emmiters will help ya.

Paul!

That sound really cool! Thank you for your offer. I'm not in office at the weekend, but I'll provide screenshots monday morning. And I'll make Skype contact.

Thank you very much in advance!

Sascha

[Sascha Selent]

Smoke distribution in building

Hi Paul.

Here we go. I provided some screenshots to illustrate what SHALL go on

The first shows my source (it's a dummy object, just a circle to have something to emit), the building structure and some red arrows illustrating where the smoke shall go. It also shows a very ineffective grid covering the whole building - what I think can be done better. This is just a first attempt to see what's going on.

The next screenshot shows a reduced grid for testing purposes. It's the testing for the settings needed to fill the upper half of the room with smoke and to let the smoke leave the room through the dooropening furtheron filling the upper half of the floor and everything further up...

----------

This is what I got so far:

It's hard to keep the smoke at the ceiling. It diffuses strongly and quickly fills the whole room. Pincipally for me it's hard to keep a thick smoke compact travelling through space (I think the vorticity is too high).

It seems to be hard for the smoke to find it's way through the dooropening. The whole room is filled up with smoke, before it starts to flood the floor.

I have to work with very very low thresholds to make the smoke visible in previews leading to very flickering previews, but I think this is setup related. I think my actual setup produces too much thin smoke to be visible in preview. The problem is in the rendering it flickers too (it´s not youtube, it´s in the uncompressed footage too)... Have to check the transparency...

Buffered conservation mode leads to disapperaring when colliding with the ceiling geometry... (?) ...I have no clue why...

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Here the preview:
http://youtu.be/ZgEuoylYciA

Here the testrender (shading is a different thing, not the point here):
http://youtu.be/AYARWLYBR8E

I think this setup so far is not too bad, but still not filling my purposes. What I need now is...

• to keep the smoke thicker and more compact (I think it is important to firstly eliminate vorticity to get the basic distribution first...)
• to concentrate the smoke more at the ceilings and keep it mostly there
• and then of course an effective setup with low simtimes. Here I would like to try the "finesmoke.max" approach using particles, but I'm not sure if it will work - this sample uses temperature only as smoke replacement - maybe this is the way to go?

I also want to try to use several grids to let the particles travel from one to another, I think - looking at the "cascade.max" sample - this should be possible.

So, if you have any hints for me and tips and tricks I would really appreciate this.

Thank you and kind regards.

Sascha

[Ivaylo Katev]

the only problem that i see here is the huge container that you need, the smoke behavior should be not a problem. i'm skeptical about the use of particle smoke, you will need a really huge particle count.

[Sascha Selent]

Ivaylo!

Thanks for answering.

the only problem that i see here is the huge container that you need

What do you mean here? Does that problem mean "it will not be possible to do that" or does it mean "simulation times will be huge"? The smoke quality is not that critical, beacuse it will not be a "realistic" animation, it will only be a stylized taste of smoke. But I need the desired distribution... - fill the ceiling, distribute to the corridor through the upper dooropening...

the smoke behavior should be not a problem

That sounds promising, but I don´t get a controlable result. Right now I fail to fill a volume with smoke... - I will attach a basic scene with my setup, maybe you can take a look and help me with the settings? Right now I crank a lot of smoke into the scene, but it sticks at the ceiling and does not fill the volume any further... - it feels as if the smoke has no mass, no density and cannot displace itself... - ...as if using smoke buoyancy is not a good idea... anyway, maybe you take a look?

i'm skeptical about the use of particle smoke, you will need a really huge particle count.

Right now I´m not able to test this because I fail to get my desired distribution in any way...

Btw. I´m on max 2012 with PHX 2.00.00 - This wouldn´t make any problems, does it?

Thank you and kind regards.

Sascha

[Ivaylo Katev]

well, if the smoke quality is not a problem, then it can be achieved.
some tips:
- increase the conservation, 40-100 may be better
- be sure that there are holes in the building, otherwise there will be no outgoing path for the air and the smoke will be unable to replace it.

[Sascha Selent]

Ivaylo...

increase the conservation, 40-100 may be better

Yeah, will do that...

increase the conservation, 40-100 may be better
- be sure that there are holes in the building, otherwise there will be no outgoing path for the air and the smoke will be unable to replace it.

Goosh, that sound logical! If it´s really physical it must have some way to get out... I´ll try it!

What about conservation method? Which would be the best choice for this kind of distribution?

Thank you.

Sascha

[Ivaylo Katev]

the default conservation method is better.

[Ivaylo Katev]

one more very important suggestion - use FT advection method!
it conserves the smoke strongly, unlike the classic method

[Sascha Selent]

if the conservation is important (i'm not sure about this, just a guess) then the default one is better. if the conservation is not important, i.e. if the smoke propagates anyway try with buffered, it produces more fine details

Yes, conservation is important (if conservation means that the mass of the smoke shall be preserverd) - I´ll stick with smooth...

and one more thing - decrease the vorticity to 0.1

Yeah, did that already...

Ooops, where did your post go? Anyway...

use FT advection method!

Yes, I´ll do that.

And: do you believe that my scene units make problems? Are the results comparable between different system units if you use the same metric units?

Thank you very very much! I love the Chaos forum

Sascha