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Re: [PSUBS-MAILIST] inertia calculation for stiffeners
Yes, the depth associated with the minimum of these working pressures
corresponds to the maximum design depth.
Cliff
----- Original Message -----
From: "gordon alexander" <gordon@curio.com>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, June 22, 2004 10:47 AM
Subject: Re: [PSUBS-MAILIST] inertia calculation for stiffeners
> Okay that makes sense. Forgive me for restating/asking what should now be
> clear - I use my design depth for this P then?
> I will share my spreadsheet, which is of course for conical sections, for
> peer review when I get it closer to finished. I have spent at least 18
hours
> on it so far but it is still not organized very well. I hope this will
only
> be a few more days.
>
> Thanks Cliff,
> Gordon Alexander
>
>
>
> ----- Original Message -----
> From: "Cliff Redus" <dr_redus@devtex.net>
> To: <personal_submersibles@psubs.org>
> Sent: Tuesday, June 22, 2004 10:27 AM
> Subject: Re: [PSUBS-MAILIST] inertia calculation for stiffeners
>
>
> > Gordon
> >
> > This section of the ABS rules is poorly written. The purpose, given
your
> > design for the stiffener and your spacing between the stiffeners, is to
> > determine, what is the maximum pressure, and thus the maximum depth,
that
> > your stiffener design is good for. They look at a number of different
> > failure modes, such as reaching yield stress at a mid point between two
> > stiffeners, local buckling of the stiffener and tripping of the
stiffener.
> > For example you could propose a design of the cylindrical pressure hull
> with
> > a thick beefy wall thickness and a very light, weak T stiffener. In
this
> > case, the calculations would come back with a large allowable pressure
for
> > stress at the mid bay between the rings but a low allowable pressure for
> > local buckling of the weak stiffener ring. The process is then to vary
> > different aspects of the design such as the shell wall thickness, the
> > stiffener web thickness, the stiffener depth and the flange width to see
> how
> > these impact the predicted maximum allowable working pressure. For each
of
> > these calculations, the maximum allowable working pressure is just the
> > hydrostatic pressure of the water column that is trying to fail the
> > stiffener with a rather larger factor of safety. Your calculations for
> this
> > section should come up with a Maximum Allowable Working Pressure based
on
> > stiffener stress, a pass/fail test on Stiffener Tripping, a pass/fail
test
> > on Web Depth to web Thickness and the Maximum Allowable Pressure
> associated
> > with this stiffener from the minimum moment of inertia constraint. With
> all
> > these calculations for Maximum Allowable Working Pressure, the minimum
> valve
> > will set the maximum water pressure your design can be exposed to and
meet
> > ABS classing rules. So the reason "P" is in all these calculations is
> > because the external water pressure is what sets up the stress loading
in
> > the shell and in the stiffener.
> >
> > Cliff
> >
> >
> >
> >
> >
> >
> > ----- Original Message -----
> > From: "gordon alexander" <gordon@curio.com>
> > To: <personal_submersibles@psubs.org>
> > Sent: Monday, June 21, 2004 6:15 PM
> > Subject: [PSUBS-MAILIST] inertia calculation for stiffeners
> >
> >
> > > I have been trying to use the formulas in section 6 (Metallic Pressure
> > > Boundary Components) of the ABS "Rules for Building and Classing
> > Underwater
> > > Vehicles, Systems and Hyperbaric Facilities". I have a question for
any
> of
> > > you fellows out there who have a grasp of the inertia calculations for
> > > stiffeners in pressure boundaries. I note that the inertia formulas
for
> > both
> > > heavy and non-heavy stiffeners (19.15.1 - pg 67 and 19.15.2 - pg 68)
> > contain
> > > "P". This is the external applied pressure, no? What is it doing in a
> > > formula used to determine the failure pressures of pressure barriers?
It
> > > seems a bit circular to me at this point. My head hurts:-(
> > > Can anyone tell me what is going on here?
> > >
> > > Gordon Alexander
> > > Shakopee, MN
> > >
> > >
> > >
> > >
> > >
> > >
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