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Hello psubbers.
I have a question on the whole "crush depth" thing.( actually, a couple of
questions.)
First, how can you factor in all the variables of hatch design,
window design, thru-hull pens, weld attachments, stresses built in from
weldments, additional reinforcing around penetrations, and god knows what else I
might put on this thing, and still come up with an accurate guess ( and guess it
must surely be ) of when my negative pressure envelope is gonna come crashing in
on me?
Doesn't any one of these ( or other ) changes to a tank type shape create a
need for a separate calculation on each area's configuration and ability to
withstand pressure until the time of failure?
And doesn't the plastic deformation of an area of the hull, due to reaching
that moment of failure, change the whole calculation for the adjacent areas, and
this must be factored into the failure threshold of each area
affected by the point of failure.
I'm a welder, not a mathematician. Does anybody have a simple
calculation of the " plain" tank for the Kittredge design?
If a guy has a tank 48" round, quarter inch thick, hemisphere ends,
no stiffeners, basically your average propane tank, how deep can it go before it
crushes.
My thoughts on this are, Find the weakest point in the envelope, and that's
your crush depth.
Pumping a pressure tank down with a vacuum pump won't work. The dynamics of
the steel, method of fabrication, weld quality, inherent stresses, and
flaws in the material or welds, all change the way steel reacts to external or
internal pressure variations.
Destructive testing is the best way to determine "crush depth" but
it's just too expensive to do.
And even if you do it, and get the golden guarantee, knowing just where
that hull is gonna implode, now we have to calculate what the new stress of the
dive cycle has had on the individual hull components, to find the new crush
depth.
What percentage of safety factor is acceptable, ( how much risk are you
willing to accept )
If you're cruising along, and crash into a rock, cause the surge/current
pushed you, and get a dent in your hull, do we have to recalculate
everything?
Too much math.
I'm looking for a depth, that a simple tank will go to, without getting
really flat.
Anybody got any ideas?
Frank D.
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