I've made some code based on a one-dimensional case in "Fluid
Mechanics" by White. I've uploaded the files in pbs-f.

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"Greg M. Johnson" wrote:
> Rune wrote:
>
> >  How should the particles move when wind is used?
>
> I gave you a suggestion earlier.

And I used it. Now I'd like to know if it works. Therefore I describe the
results I get. What I'm interested in now is not the method but the result.
Which results have you get using the method?

Rune
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"Chris Huff" wrote:
> In my particle system, I consider particles as infinitely
> small points,

Me too.

> with a constant wind resistance (not related to velocity).
[description snipped]

I do just the same except that I square the resistance, after advise from
several people from this group.

With the method I've used the particles move in a straight line. (The
velocity is not constant but the direction is.) I don't know if it is
supposed to be that way. I've also seen some very complicated methods
described here which I do not plan to implement. A simulation is fine for
me. Still, I'd like the simulation to look good.

I wonder how does the particles in your patch move when under the influence
of wind? (It's not the theory I'm interested in. I'd like to know, when the
experiment is actually done, do they move in straight lines or not?)

Rune
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\ Include files, tutorials, 3D images, raytracing jokes,
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\ all be found at http://rsj.mobilixnet.dk (updated January 28)
/ Also visit http://www.povrayusers.org

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Rune <run### [at] inamecom> wrote:
> I have implemented wind in my particle system, but I'm not sure it's
working
> correctly.
>
> When I have just gravity the particles accelerate downwards. When I add
wind
> from the side, the particles move downwards and to the side, accelerating,
> but in a straight line. When I use less drag, they move less to the side
and
> when I use more drag they move more to the side. But always in a straight
> line. I'm can't figure out if it's supposed to behave that way or not? How
> should the particles move when wind is used?

That depends on how you define "wind".  In my Liquid Spray include file, I
implemented the same idea, with a constant acceleration added based on wind
direction and strength.  Additionally, particles have a mass based on their
size, so smaller particles are more affected by the wind force.   Finally,
user-controllable turbulence is factored in so that each particle's wind
force is randomised.

For the most effective wind animation I'd probably aim for a dynamic force,
rather than simulating the wind as constant, linear force.  Introducing
vortex-like turbulence should give a convincing "blown-about" appearance to
the particles' movements (imagine feathers, falling leaves, even rain to a
certain extent).  Realistic vortices are notoriously complex, but perhaps
you could base the wind on shifting bozo patterns, so the smooth noise of
the pattern leads to recognisable shifts in wind strength and direction...

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In article <3aa41d9b@news.povray.org>, "Rune" <run### [at] inamecom> 
wrote:

> With the method I've used the particles move in a straight line. (The
> velocity is not constant but the direction is.) I don't know if it is
> supposed to be that way. I've also seen some very complicated methods
> described here which I do not plan to implement. A simulation is fine for
> me. Still, I'd like the simulation to look good.

The particles should move in a curve...it sounds like you are using a 
constant acceleration for the wind, instead of subtracting the velocity.

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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