Friction between two colliding gass clouds

In article ,
"Joe Taicoon" writes:
I am starting a project, university computer science, in which I want to
model the formation of a solar system from an initial cloud of gass/dust.

People have been constructing star formation models since the 1960's
at least, and it is still a subject of very active research. One
paper I just happened to find in a quick search is by Banerjee &
Pudritz (2006 ApJ 641, 949). One key sentence from the Abstract
reads "Here we report on our three-dimensional, adaptive mesh,
magnetohydrodynamic simulations of collapsing, rotating, magnetized
Bonnor-Ebert spheres, whose properties are taken directly from
observations." This will give some idea of the state of the art in
this field.

Of course if all you want is an interesting computer science project,
it doesn't have to be useful for current research.

In doing so I plan on using smoothed particle hydrodynamics and consider
forces from mutual attraction and friction between colliding clouds of
particles.

This (and much of the rest of your message) sounds much closer to
galaxy collisions than star formation. That is, if anything, an even
more active "industry" today than star formation modelling. As an
example of the sort of thing that might make a good project, Antunes
& Wallin (2007 ApJ 670, 261) constructed a model of a specific pair
of interacting galaxies. An extract of their Abstract reads "In
N-body/smoothed particle hydrodynamics (SPH) simulations of
AM 0644-741, we recreate the star formation features, as well as the
underlying kinematics." In other words, they are modelling
separately stars, gas, and (probably) dark matter, and they are
superposing on their model some prescription for how many stars form
at a given gas density. This is a very simple project by today's
standards.

I have been unable to find any good documents describing how I shoud go
about calculating the friction force between two such clouds, so I post here
hoping for some good references.

The classic paper on the subject is by Toomre & Toomre (1972 ApJ 178,
623). For more, you can do an ADS search either for papers citing
that one or for Abstract keywords. (ADS is at
http://adsabs.harvard.edu , and I think there's a mirror site in
Europe.)

....
This lets the simulation run fine without having particles ejectes when they
collide.

The "softened" potential is important, but particles are ejected in
real galaxy collisions.

Though SPH started
out doing exactly what I am trying, it seems 99% of the texts dealing with
it now are all about simulating water.

The astronomy literature on the subject is vast. ADS can help you
navigate it, but you would be better off consulting an expert in the
field. You might look at author affiliations on recent papers and
see whether any authors are near you. Or go ask at the astronomy
department if your university has one. If not, you check whether
someone in the physics department is doing astrophysics.

Good luck with your project.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)