From: jimf@centerline.com (Jim Frost)
Newsgroups: sci.electronics,sci.energy,rec.autos
Subject: Re: Flywheel batteries as EV power source
Date: 24 Dec 1992 15:55:49 GMT
Organization: CenterLine Software, Inc.
NNTP-Posting-Host: 140.239.3.202

mwilson@ncratl.AtlantaGA.NCR.COM (Mark Wilson) writes:
>In <1992Dec23.154010.13703@fcom.cc.utah.edu> bbarkey@lark.utah.edu (Brian Barkey) writes:

>|>The flywheel will try to dissipate it's energy over a span of milliseconds.
>|>
>|I guess I missed the part about dissipating energy over ms. What's the 
>|basis for this?

>Because of the speeds at which it rotates, the instant the flywheel becomes
>unbalanced it will shake itself apart.  The first failure sets up a shock wave
>that travels at the speed of sound.  The shock wave has so much energy that it
>literally vaporizes the material it is passing through.

I thought it was assumed that the flywheel operated in vacuum?  The
"shock wave" will be expanding particles thrown off from the wheel
itself, and the speed will depend on how fast the particle was moving
when the wheel disintegrated.  I suspect that'll be a whole hell of a
lot faster than the speed of sound.

I think you'll get a series of "shock waves" -- a heat wave caused by
vaporization of the flywheel and containment vessels and
supercompression of air in front of the second wavefront, containing
the particulate matter of the flywheel and containment vessel.  Sonic
shocks will follow both of these wavefronts as the air expands due to
the affects of the previous wavefronts.

Anyway a lot of people have been assuming total uniform disintegration
of the flywheel, which could possibly allow construction of a vessel
to contain the energy release.  Such disintegration is not likely to
happen in real life.  If the flywheel becomes imbalanced it'll start
to fragment (assuming the axle can withstand the strain longer than
the flywheel in the first place, which is not likely) and you'll end
up getting several small chunks of the flywheel (furthering the
imbalance) and one or two big ones hitting different parts of the
containment vessel at very localized points.  The fragmentation will
release very little energy.  Since most of the flywheel will still be
intact you'll get nearly all of the energy dissipated against a fairly
small portion of the containment vessel.  That'll result in a
concentrated, *directional* explosion.  Along the plane of the
explosion (it'll occur in an arc perpendicular to the rotational axis)
you're going to see very dramatic effects, both from surviving
particulate matter from the flywheel and its containment vessel and
from heat and air shocks.  Besides the directionality of the explosion
you should note that the entire energy of the flywheel will not be
dissipated against the containment vessel; the containment vessel
won't last long enough to completely absorb energy from the flywheel,
both because of mechanical stresses and energy release.  This depends
on just how strong the flywheel is, of course -- a fragile flywheel
would dissipate energy better since it would fragment earlier and more
completely -- but it's my assumption that the flywheel is going to be
very, very strong.  What'll happen is that a significant fraction of
the flywheel's energy will vaporize sections of the containment vessel
and sections of the flywheel will survive to be thrown free.  Both the
energy release and the surviving portions of the flywheel will be
extremely dangerous, of course.

This discussion is great, but as I mentioned before it's also moot
unless someone's figured out a way to eliminate gyroscopic effects
from the flywheel.  These would be considerable, you know.

jim frost
jimf@centerline.com
Xref: sparky sci.electronics:21464 sci.energy:6406 rec.autos.tech:17108