[Beowulf] Moores Law is dying

Robert G. Brown rgb at phy.duke.edu
Fri Apr 10 10:38:21 EDT 2009


On Fri, 10 Apr 2009, Lux, James P wrote:

> ...I don't know that they're harmonics, per se, but just the
> phenomenon of aerodynamic flutter, which was very poorly understood and
> is basically a resonance thing. (the nonlinearities in the state

Um, "basically a resonance thing" = "harmonics" in a linearization
around the resonance in question, right...;-)

> equation for air doesn't help with understanding, of course).  Flutter
> can occur at lower speeds, too (it's what sets Vne on some small
> planes), but at lower speeds, how to deal with it is easier to solve
> empirically AND it's testable by gradually creeping up on it and waiting
> for the evil moment.  When you get close to sonic speed (and actually,
> it's localized sonic speed over part of the airframe that's troubling),
> then you get very fast changes.  One needs to be a manly man test pilot.

Yep!

> BTW, demonstrating sonic flow is easy.  Your run of the mill air
> nozzle is probably in "choked flow" with a shock wave in the throat.  If
> you have a usual shop air compressor, and the air is damp (bad for the
> tank, but good for the demo), and vent it through something like an 1/8"
> hole, you'll probably see a nice Mach cone, as the rapid change in
> pressure causes the water to condense.  An old style non-OSHA safe air
> blowing nozzle does nicely, so does a 1/4" or 1/2" ball valve feeding a
> pipe cap with a hole drilled in it.

I have no idea what you just said here, but it sounds very cool!  Maybe
I'll as my lab guy who does understand this sort of thing to look into
it for the appropriate part of physics 41.  (Well, OK, I do KINDA
understand, but not well enough to visualize what you're shooting for.)

   rgb

Robert G. Brown                            Phone(cell): 1-919-280-8443
Duke University Physics Dept, Box 90305
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Web: http://www.phy.duke.edu/~rgb
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