theoretical physics of dirt roads

[nibot]

Uurgh, I've misplaced my keys... I hate it when that happens -- it makes me feel like I'm going crazy or something! I haven't been anywhere, so their disappearance is all the more frustrating. Haven't I looked everywhere? S-:

Anyway. On a completely unrelated subject, here's a question for physicists et al: What causes the 'washboard effect' on dirt roads? I've heard a bunch of qualitative / anecdotal explanations, but I want to model the effect. The car, I think, is pretty easy to model. Mass, spring, damper, wheel. But how do I model a sandy road surface?

Links that might be useful:

• Animating Sand, Mud, Snow - from Prof. O'Brien, whose area of research is physics-based models for computer graphics

This goes on my personal to-do list of hard modeling problems... the other thing on it is to do a proper fluid-dynamical simulation of a lava lamp, without resorting to tracking blob surfaces or other empirically developed (non-physical) solutions.

Comments

[bobolly.livejournal.com]

Re: bumps. I would like to know what you come up with- I've always wondered what causes the tweedy roads to do that, and why they're worse sometimes than others. There are a lot of theories, some not involving cars at all.

Re: keys. Check all your drawers. Even the backs. And all your pockets. ALL.

[mporter.livejournal.com]

Judging by this account (http://www.straightdope.com/mailbag/mwashboard.html), perhaps you could have a continuum model which treated the road as an inelastic and highly viscous fluid?

[nibot.livejournal.com]

That was my first line of thinking. But now I am lead to believe that the primary effect might be from tires scraping away at the sandy surface, which would require a different sort of model (where the volume of the roadway isn't conserved). I'm pretty much a novice at this sort of modelling, though, so I'm not sure how far I'll get.