[PSUBS-MAILIST] help interpreting ABS rules

[Sean T Stevenson via Personal_Submersibles]

"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 <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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