Sand through water simulation

While I was at home over Easter break, I was looking at this novelty thing I got from Myrtle Beach a few years ago. It's these two panes of glass that have sand and water between them and are on a sort of pivot. When you turn it upside down, the sand runs to the bottom and it's kind of neat to watch it flow. Anyways, I'd kind of like to write a program that simulated this (mostly just because I think it'd be a neat little exercise, but I think it'd make a cool screen saver as well), but figure simulating each grain of sand is probably way too much for a PC to do. A friend told me that I should just simulate the fluid flowing, that the sand was just on for the ride, but I know essentially nothing about physics, and was wondering if someone could point me to some sort of "Physics for Computer Scientists" sort of thing or had another (potentially simpler) idea for how to do this. I'd like to really simulate it though, and not just have some image of sand that dropped from one side of the screen to the other. Thanks.

From what I've seen (which is very little), fluid mechanics is no fun at all :)

fluid mechanics == BAD

good luck with that one.

Hey now, I've got a couple degrees related to fluid dynamics (specifically density stratified turbulent flow).

What you're looking at here is a problem in two-phase CFD (Computation Fluid Dynamics). I have colleagues working a similar, though more complex, problem with breaking waves (the other phase is air in this case) using a cluster of about 100 machines. The problem breaks down well for clusters because the local solutions don't affect each other except at the domain boundaries.

In short, though, this is the kind of thing that could become a graduate thesis - not really the type of problem you can tackle on a weekend. There is a good bit of CFD code in the public domain (written in FORTRAN), but it's hard to find without spending a lot of time digging through journal articles at your local university library.