>
> Yes, I agree with you. However, my simulation is a very simplified model
> from reality :) I strive to improve that realism, but my lack of knowledge
> in physics is a big obstacle. It would be very nice to know more about
fluid
> dynamics...
>

Complex behaviour can often be incorporated in models by changing the
premises a little bit: Perturb the model a little in one direction, make the
parameters that describe the cloth vary along the surface et.c.

I really think fluid dynamics wouldn't help you very much in this case.
Computational fluid dynamics (CFD) is a vast area, and millions of CPU hours
are required for relatively small models. And modelling air flow along the
surface of a fabric sure is a complex model!

What about trying to implement velocity dependent air resistance? Assuming
that you can (or alredy have) discretizised your cloth in polygons of some
sort, and assumng that the cloth's velocity through air is slow, maybe a
model like this could be a starting point?

        F = - |v| * cos (theta) * A * constant

where v is the polygons velocity, A its area and theta v's angle with the
surface normal. F is the force the polygon "feels" from the air resistance.

This model assumes that the air is uniformly distributed with equal pressure
everywhere, through all time. This is true when there is no wind, the cloth
falls slowly and when two pieces of cloth are not very close to each other.
(In that case, air pressure will change.)

Again, I emphasize the usefulness Runge-Kutta scheme. Assuming that you are
solving with Euler by 1) calculating forces/acceleration on some set of
point masses, 2) adding acceleration * dt to the velocity of each point mass
and 3) adding velocity * dt to position, it really should be a simple task
to extend it to a fourth order scheme. With adaptive time-step, the method
is very robust! I have successfully modelled a lump of jelly (i.e. 3d-mesh
of points connected by (even nonlinear) springs.)


regards,

Simen Kvaal.

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