Re: [PSUBS-MAILIST] acrylic cylinder

["Sean T. Stevenson" <cast55@telus.net>]

L in this case is the spacing between two adjacent stiffeners.  There is no 
consideration of total hull length.  (which makes sense, as a sufficiently stiff 
cylinder / stiffener combination can be repeated as many times as you like to 
create a hull of indeterminate length - buckling considerations aside).  Thus, 
elastic instability of a cylinder supported by stiffeners spaced L apart 
considers only two stiffeners in all cases - at either end of an otherwise 
unsupported length of cylinder.  The integer identifier above each arc segment 
on the graph is indeed the number of lobes anticipated at collapse, and you 
will note it is labeled as such in the plot on page 753.

-Sean


On July 14, 2009 08:24:39 Jon Wallace wrote:
> Sean,
>
> According to the text under 13.3.3 (pgs 726,727), the graphs are
> supposed to show the elastic instability of a cylinder supported by
> bulkheads or stiffeners spaced L apart (page 727, first sentence under
> the formula).  So aren't the curved plots showing the number of
> stiffeners present at a particular failure pressure?
>
> Jon
>
> Sean T. Stevenson wrote:
> > OK - I can understand the confusion, as Figure 13.15 puts a lot of
> > information in one diagram.  The each plotted curve corresponds to a t/D
> > value, indicated by a text label beneath each plot.  Each plot is a
> > series of joined arcs, with each curved segment corresponding to a
> > particular number of lobes expected during failure.  These are the text
> > labels above each plot - omitted on a few of the lower ones because the
> > text would be too dense, but you can count in from the edges.
> >
> > The X coordinate is L/D as you surmised, but the Y coordinate is not
> > pressure - at least, not directly.  Actually, using your L/D value, look
> > up to the appropriate t/D plot (where you will find the number of lobes
> > expected at failure) and then read across to the Y axis, to get a value
> > of "eta" used in the following equation:
> >
> > Pc = eta * 0.035
> > (Pc = eta * E * 10^-7 for non-acrylic material)
> >
> > Where Pc is the short term critical pressure in psi.
> >
> > Three separate plots are presented, but you can think of these as simply
> > stacking on top of one another.  The plot is log-log, showing two orders
> > of magnitude in X and six in Y.
> >
> > -Sean




************************************************************************
************************************************************************
************************************************************************
The personal submersibles mailing list complies with the US Federal
CAN-SPAM Act of 2003.  Your email address appears in our database
because either you, or someone you know, requested you receive messages
from our organization.

If you want to be removed from this mailing list simply click on the
link below or send a blank email message to:
	removeme-personal_submersibles@psubs.org

Removal of your email address from this mailing list occurs by an
automated process and should be complete within five minutes of
our server receiving your request.

PSUBS.ORG
PO Box 53
Weare, NH  03281
603-529-1100
************************************************************************
************************************************************************
************************************************************************