[PSUBS-MAILIST] help interpreting ABS rules

[Sean T. Stevenson via Personal_Submersibles]

Jon - that was my original thinking, but then I noticed that the second
term in the Pn equation in 6/19.13 contains the L term, or distance
between non-heavy stiffeners, leading me to believe that this second
term might be a correction factor for stiffness of the reinforced shell
in between the heavy stiffeners, in which case it would make sense that
the I term is the non-heavy I.  Conceptually this makes sense because
the section is dealing with overall buckling across the length between
heavy stiffeners, which is resisted by the mechanical properties of the
shell reinforced with non-heavy stiffeners.  Only the mention of heavy
stiffeners as the limiting extents of the collapse led me to originally
assume the heavy I, which I am now unsure of.

Sean


On 2015-04-21 18:48, Jon Wallace via Personal_Submersibles wrote:
>
> 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 <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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