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Flame function.

Started by Vlion Nov 26, 2001 at 2:47 PM 9 replies 1k views

Original Post

Nov 26, 2001 at 2:47 PM

Hey. Has anyone worked out the equations and functions goverening flames ? For instance: Get a variable lighter from a store. Move the little button to the lowest value. Light it, and adjust it upward. Observe: The size of the visible flame increases and descreses by a set value, according to a input. So, according to the fuel amount, a set size of opening, the flame will change size. I was studying my lighter flame today, and I realized that it cannot be a standard polynomial function. Put into 2 dimensions, you have 2 y values resulting from a single X. So thats impossible to represent via computer graphics. I think it would be a parametric function, rotated along the y axis. Am I correct, incorrect ? I came, I saw, I got programmers block. ~V''''lion

v71

Nov 26, 2001 at 4:44 PM

well what you say is well know in physics dealing with a very large of interacting particles, that''s why is used a statistical velocity or stocastic methods to compute a volumetric energy, so i think that one day we''ll have a realistic gaseous or firing routine , but is not likely to come very soon, try to simulate instead....just my 2 cents

Vlion

Author

Vlion

Nov 26, 2001 at 11:45 PM

Sorry.
What I meant is that.....


Y
|       _
|      ( )
|     (   )
|     |   |
|     (   )
|      ( )
|
---------------------------X

Thats how my lighter shape looks in 2D.

But what I

m seeing is that when the gas input is smaller, the width is slighly shrunk, and the height of the flame is decreased.

I know in reality a gazillion factors affect it.
Density, element mix in air, wind, tempature, direction flame points...it goes on and on.

However.

I

m just thinking a good equation would simulate it quite well.
Because Ive hardly ever seen computer flames look partially real, Id like to have a good general equation that would work.

I came, I saw, I got programmers block.
~V''lion

Edited by - Vlion on November 26, 2001 12:45:50 AM

KwamiMatrix

Nov 30, 2001 at 4:09 PM

Differential equations govern the physics of flames. Really complicated I suppose.

Edem Attiogbe

grhodes_at_work

Mod

198

grhodes_at_work

Nov 30, 2001 at 5:24 PM

quote:
Original post by KwamiMatrix
Differential equations govern the physics of flames. Really complicated I suppose.

Edem Attiogbe

Well, true, if you want to get into all the nitty gritty detail (which game developers often don't). The Navier-Stokes equations govern the flow, but its a chemically reacting flow so you need simulated chemistry as well, not just simple equations of state such as the ideal gas law, to close the equation set. Flame simulation is some of the hardest CFD of all. (I studied under a professor at North Carolina State University who has done high-end flame physics simulation for a few years now.)

BUT, there are always simpler ways for games. Simple models such as those suggested by Vlion and v71 can produce results that are just fine.

Graham Rhodes
Senior Scientist
Applied Research Associates, Inc.

Edited by - grhodes_at_work on November 30, 2001 6:26:12 PM

Vlion

Author

Vlion

Dec 1, 2001 at 8:29 PM

Yeah.
I`m just asking if anyone has come up with a good approximation of a flame shape.

I came, I saw, I got programmers block.
~V''''lion

python_regious

103

python_regious

Dec 2, 2001 at 9:17 AM

quote:
Original post by grhodes_at_work
Well, true, if you want to get into all the nitty gritty detail

You''d have to bear electrostatic forces in mind too then

Thrump

Dec 3, 2001 at 6:15 PM

I wrote this flame function a while ago. Might be what you're looking for.

    

char *pcFlames[4]={
   "C++ is better!",
   "VB is better!",
   "You're so stupid!",
   "Shutup!"
}

char *pcNames[4]={
   "Johnny",
   "Sally",
   "Bob",
   "Mike"
}

main(void){
   while(TRUE){
       printf("%s> %s\n", pcNames[rand()%4], pcFlames[rand()%4]);
   }
}

Edited by - Thrump on December 3, 2001 7:20:43 PM

Vlion

Author

Vlion

Dec 4, 2001 at 1:21 PM

Good one Thrump.

Thats a interesting demo, but not really what I`m looknng for.
I sense a reasearch topic in the offing... :-D
~V''lion

I came, I saw, I got programmers block.
~V''''lion

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