Re: Q: For Sy Liebergot (Yeah, it's new safe CT-free topic fodder!)

>>From Craig Fink:
> On Fri, 06 May 2005 08:34:51 -0700, Stuf4 wrote:
>
> > I also find this statement as curious:
> >
> > "The g-force was so great that the reactant feed valves feeding
Fuel
> > cells 1 & 3 were shocked closed, causing both to fail within about
a
> > minute."
> >
> > Was it g-force that caused the valve closure? My understanding is
that
> > the hardware was thoroughly ground tested to withstand more g's
than
> > even that experienced during launch vibration, to include harmonic
> > resonance analysis.
>
>
> I don't find it curious.
>
> Impacts can be thought of in terms of g-force also. Slap your hand
to the
> table as hard as you can, it's probably just pulled 50 to 100 g's. I
would
> think they really had no idea about what the damage to the feed
valves
> were. Did it bend them? Don't know. Did something impact them? Who
knows.
> Did the pipes bend? Who cares. A detailed study of the Service module
> wasn't done, just some pictures. Why would you think vibrations
testing
> (like shaking your had in the air) would be applicable to impact
testing
> (like slapping the table)? Just because something was vibration
tested,
> doesn't mean you can take a hammer to it.

First, let's be clear that "g-force" is a confused term. Force is
force, while "g" refers to acceleration. Using that popular
terminology can be seen as presenting a lack in caring (or
understanding) of accurate physics. That is one reason for my
questioning the use of that term.

"Slap your hand to the table as hard as you can, it's probably just
pulled 50 to 100 g's."

Your statement here serves as a perfect example to point to my more
fundamental objection to that "g-force" statement. When analyzing the
breaking of structures, energy is a far more important parameter than
either acceleration or force. To say that your fingers pulled 50-100
g's tells you nothing about whether or not you broke your fingers
during that impact. It may sound impressive to cite such facts, but
those facts have little relevance to the question of failure (or valve
closing, in this case).

Critical distinctions are made between "instantaneous g" versus
"sustained g". Again, the reason is because the energy involved is
radically different.

This is from a prior discussion about acceleration rate, or "a dot":
------
> [1] Anyone who believes that technical words retain their everyday
> meaning isn't familiar with "jerk".

(Engineers are taught that jerk is a dot, so to speak.)
------
(http://groups-beta.google.com/group/sci.space.history/msg/cb66658fffc10d2c?hl=en)


We could continue on the topics of impulse, momentum, jerk, etc, but
the primary point that I was trying to make is that I am not aware of
any testing that was done on the O2/H2-FuelCell system to demonstrate
its capability to withstand something like an O2 tank rupture. By "any
testing", I include preflight certification testing as well as
post-mishap testing done by the board.


~ CT

.

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