Re: [PSUBS-MAILIST] uniform? acrylic viewport thickness

[Phil Nuytten <pnuytten@compuserve.com>]

Hi, Gene:
        The building analogy doesn't quite do it . . . but, good thinking,
non the less. The overall pressure on the acrylic hemi is so much greater
than the difference in pressure ( 'weight') between the apex and the base
of the hemi, that it is insignificant. You need to consider the
nonconcentric hemi as a series of layers, or horizontal slices, that
increase in thickness as they increase in diameter. The first slice would
be the top of the dome - say you cut it ( in theory) so that it was 6
inches in diameter - and the thinnnest spot (center) was 7/16 - just shy of
a half inch. If you run the numbers for 7/16th X 6.00, you will find that
it goes a hell of a lot deeper than considering the 24 inch diameter hemi
as being " only as good as the thinnest part". If you progress the
calculations for each segment, down to the base - considering that each
segment is perfectly supported by the acrylic above and below it, you will
find that a ratio of increasing thickness matched by increasing diameter
will yield a table that gives the acceptable depth after considering
whatever safety factors turns your - or the certifying agencie's - cranks.
As usual, the more more slices, the higher the resolution of the results.
As I said, a 'trick of the trade'  that seems to be virtually unknown to
laymen - even tho' it makes good sense when some one draws it to your
attention!
Phil Nuytten 





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