Thick Smoke Dissipation

[Sascha Selent]

the most common reason is the use of inscribed geometry representation

I use "center" - shall I better use "circumscribed"? Remind, I use the setup you provided in the "block.max"-sample.

And you are fast!

Thank you.

Sascha

[Ivaylo Katev]

circumscribed is better, inscribed is used for liquids with thick walls

[Sascha Selent]

Work in progress

Ivaylo

It starts working, but I have to crank up the discharge to 4000 - isn´t it a little like a jet engine?

Sascha

[Ivaylo Katev]

the discharge is measured in scene units per second, for big scale scenes you need bigger discharge in order to achieve the same effect.

[Sascha Selent]

Discharge

the discharge is measured in scene units per second, for big scale scenes you need bigger discharge in order to achieve the same effect.

Can you please explain this more? The documentation says "The speed (not the quantity) of the discharged fluid. The quantity of the fluid will be equal to this parameter multiplied by the object's surface."

So I have system unit scale 1 Unit = 0,1 inch - that means my object emits with 400 inches per second - but what means the surface multiplier? And isn´t 400 inches per second still very much? In a default scene (1 unit = 1 inch) a PHXSource starts with discharge 40. I have 100 times more if I calculate right...

In my scene I do 2 diffenrent simulations: the biiig smoke simulator with discharge 4000 and a small hires simulator for the fire with discharge 400 (which fits the default of 40 with my scene units set to 1 unit = 0,1 inches). If I use a small discharge to get a nice fire I do not get enough smoke to fill the scene unless I crank up the smoke multiplier - which produces some weird dense smoke that is really hard to shade.

So what would be the right way to achieve this: a nice small fire on the cooking place burning on and on producing THAT MUCH smoke that the whole building will be filled up? Do I have to crank up the discharge or better the smoke multiplier? Or do I have to try to achieve this with the transparency in the simple smoke? Or is it a mixture of all?

Thank you again.

Sascha

btw.: What do you think about my smoke?

[Ivaylo Katev]

that means my object emits with 400 inches per second - but what means the surface multiplier?

the surface multiplier means that your source produces 400*S cubic inches per second, where S is the surface of the emitter.

And isn´t 400 inches per second still very much?

yes, it sounds like a big value, but if your source has small surface (your case seems to be like this) the total volume of the produced smoke isn't so big.
i think the best way to do this is to use smaller discharge and high smoke value of the source. to limit the density you can use curve based transparency (not simple smoke).

[Sascha Selent]

to limit the density you can use curve based transparency (not simple smoke).

Yeah, I tried that, but for me it´s hard to understand whats going on with the curve...

For example: what would the curve look like to reproduce the simple smoke behavior? A straight line between lets say 0,0 / 0,0 and 1,0 / 0,1?

What do x and y stand for? Is x the density value given by the simulation and y the transparency at a given density?

I would like to understand what the curve exactly does and what will happen when I start to move the points around...

Thaaaaankyouagain

[Ivaylo Katev]

For example: what would the curve look like to reproduce the simple smoke behavior? A straight line between lets say 0,0 / 0,0 and 1,0 / 0,1?

not exactly, but it's near, it should be curved in negative direction.

Is x the density value given by the simulation and y the transparency at a given density?

yes, it is. with the additional note that y meaning can be switched between transparency/opacity. the "density value" is actually one of the channels exported by the simulator, it can be temperature, smoke, even velocity. i.e. you can make the faster parts of you simulation to look dense
i would recommend you to use the curve of the scene "nuke.max". you can do this exporting/importing it with the right button

[Sascha Selent]

I´ll check this tomorrow...

EDIT: Learning A LOT about Phoenix! Thank you Ivaylo.

[Sascha Selent]

Work in progress

Ivaylo

Take a look

The smoke with a lowResGrid (16mio) - sim time is too long, I´ll further reduce the resolution and bring up the vorticity and the random amount a bit.

[Sascha Selent]

Work in progress

And this is what I mix up: A huge loResGrid for the smoke with a small hiResGrid for the fire - with very different setting, but I think the result will fit my needs...

Sascha

[Ivaylo Katev]

you can try to decrease the upper SPF limit for faster sim. and you can experiment with some randomization too

[Sascha Selent]

MORNING

Early Bird, eh? What time is it in Bulgaria?

you can try to decrease the upper SPF limit for faster sim. and you can experiment with some randomization too

Yeah, I slightly bring up randomization, but I think I have to use it carefully, because it diffuses the smoke quite much and releases it from the ceiling. I have to test very much, so I´ll try your SPF-hint to speed up simulation. What do you think would be a good value for the upper SPF limit?

If I reduce it from 10 to 5 it doesn´t seem to have any impact...

[Sascha Selent]

Work in progress

The same with lower resolution (8mio). Behaves slightly different...

...but simulates muuuch faster - about 6-7 hours for that - the 16mio grid would simulate over 2 days... - ...I would think that the upper SPF limit would more affect a higher grid resolution, ist that right?

[Ivaylo Katev]

Early Bird, eh? What time is it in Bulgaria?

first in the office! actually it was about 9:30 am not a big deal

to the work: the upper SPF limit is important if you SPF value reaches it. otherwise it is not used, and the result will be the same.