[PSUBS-MAILIST] help interpreting ABS rules

Tue Apr 21 21:57:47 EDT 2015

21.13 Heavy Stiffeners Stiffeners used for purposes of reducing the
compartment length Lc within which overall buckling performance is checked
are termed heavy stiffeners and are to be designed to meet the requirements
for heavy stiffeners in 6/21.17.2. 

  _____  

From: Personal_Submersibles [mailto:personal_submersibles-bounces at psubs.org]
On Behalf Of Jon Wallace via Personal_Submersibles
Sent: Tuesday, April 21, 2015 7:49 PM
To: Personal Submersibles General Discussion
Subject: Re: [PSUBS-MAILIST] help interpreting ABS rules

Ok, missed the section on calculating "I".  I looked at the doc more tonight
and it seems to me that your original conclusion of using Heavy Stiffeners
is correct.  Section 19.11 defines Heavy Stiffeners as the stiffeners to be
used for purposes of checking overall buckling performance.  Section 19.13
requires "heavy support members" which I believe equates to "Heavy
Stiffeners".  In Section 19.15.2, Lc is used to calculate "I".  Doesn't this
all point to using 19.15.2 to calculate "I" ?

Jon

On 4/21/2015 7:48 PM, Sean T Stevenson via Personal_Submersibles wrote:

"I" is calculated differently for non-heavy stiffeners (19.15.1(d)) than for
heavy stiffeners (19.15.2(d)).  It is entirely contextual as to which "I" to
use.

Sean

On April 21, 2015 1:08:02 PM MDT, Jon Wallace via Personal_Submersibles
<mailto:personal_submersibles at psubs.org> <personal_submersibles at psubs.org>
wrote: 

Given that there is copious distinction throughout the document
differentiating heavy and non-heavy stiffeners, it could be that
non-distinction in the definitions of equation variables means application
to both.  I notice that none of the variable definitions referencing
stiffeners differentiates between heavy or non-heavy.  What is the effect in
the equation of assuming "I" refers to all stiffeners?

Jon

+++++++++++++++++++++++++++++++++

SEAN STEVENSON WROTE:

I found a bit of time this weekend to work on the hull optimization

software, and was just revisiting the "Overall Buckling Strength"

calculation in Section 6/19.13 of the 2014 ABS Rules for Building and

Classing Underwater Vehicles, Systems and Hyperbaric Facilities, when I

noticed the following:

The limit pressure corresponding to the overall buckling mode between

heavy support members is obtained from the following

equation:

Pn = (E*t/R)*A_1 + E*I*A_2/L*R^3

The section goes on to define some of those terms, but what caught my

attention was the "I" in the second term of this equation.  The

nomenclature "I" does not distinguish between "I" for a heavy stiffener

or a regular stiffener in the rules - it is contextual.  Given the

purpose of the section, I had assumed that it meant "I" for a heavy

stiffener, but the term in question also contains the term "L", or

distance between stiffeners, which is distinct from "L_c", or distance

between heavy stiffeners, leading to some ambiguity.  If the second term

is a correction for stiffness of the section in between heavy

stiffeners, the "I" could very well be the "I" for a regular stiffener

in between, but it isn't clear to me.

Thoughts?

Sean

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