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George,
I
would assume that the waffle pattern will indeed add some strength, but am
at a loss when it comes to calculating how much. I can't quantify it, but it
looks to me like an inefficient approach for a couple of
reasons:
- The effectiveness of your stiffeners is largely dependent on
their moment of inertia. The waffle puts the extra mass right up against the
pressure vessel skin, which minimizes moment of inertia. To use an analogy,
if you were building a conventional stiffener out of a rectangular section, you
would have two choices. If you put the wide edge against the hull, it's
easy to fabricate but also virtually useless as a stiffener, whereas if
you placed the thin edge against the hull it is strong. For the same
reason, in L or T section stiffeners the "--" goes away from the hull skin, not
against it.
- It seems to me the waffle pattern would
strengthen as much longitudinally as radially, whereas all that
really counts in a pressure vessel is the radial
strength.
- All
those sharp angles mean concentrations of tension.
On the other
hand, even if a waffle doesn't lend itself to calculation, you have the
advantage of building an ROV instead of a manned sub... There's a whole lot less
to lose if it doesn't work.
If
space is at a premium, why not an external ring stiffener?
:)
Alec
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