NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/electron/21656

Internet Message Format | 1992-12-29 | 4.2 KB

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From: [e-mail] (Carl J Lydick)
Newsgroups: sci.electronics,sci.energy,rec.autos
Subject: Re: Flywheel batteries as EV power source
Date: 28 Dec 1992 22:11:01 GMT
Organization: HST Wide Field/Planetary Camera
Lines: 63
Distribution: world
Message-ID: <[e-mail]>
References: <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]>,<[e-mail]>
Reply-To: [e-mail]
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In article <[e-mail]>, [e-mail] (Jim Frost) writes:
=[e-mail] (Mark Wilson) writes:
=>In <[e-mail]> [e-mail] (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.

Wrong shock wave.  You see, what we've got is a highly stresed flywheel.  If
some bit of it separates, then the stress on the rest of the flywheel changes.
Because of the degree of stress involved.  This change in stress propagates as
a shock wave THROUGH THE MATERIAL OF THE FLYWHEEL.  Because of the speeds and
stresses we're talking about here, that shockwave travelling through the
flywheel is likely to be enough to cause catastrophic failure of the rest of
the flywheel.

=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.

These shock waves will all come somewhat later than the shock wave through the
flywheel that destroys it.

=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.

Ah, but here's where the shock wave comes in again:  Since it's travelling at
the speed of sound in the flywheel, and since mechanical stresses propagate
only at the speed of sound, and since the shock wave itself is likely to
destroy the flywheel, the more or less uniform disintegration may not be as
far-fetched as you seem to think.
--------------------------------------------------------------------------------
Carl J Lydick | INTERnet: [e-mail] | NSI/HEPnet: SOL1::CARL

Disclaimer:  Hey, I understand VAXen and VMS.  That's what I get paid for.  My
understanding of astronomy is purely at the amateur level (or below).  So
unless what I'm saying is directly related to VAX/VMS, don't hold me or my
organization responsible for it.  If it IS related to VAX/VMS, you can try to
hold me responsible for it, but my organization had nothing to do with it.