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<div class="moz-cite-prefix">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.<br>
<br>
Sean<br>
<br>
<br>
On 2015-04-21 18:48, Jon Wallace via Personal_Submersibles wrote:<br>
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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" ?<br>
<br>
Jon<br>
<br>
<br>
On 4/21/2015 7:48 PM, Sean T Stevenson via Personal_Submersibles
wrote:<br>
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cite="mid:516782a6-fb8b-4742-bd2d-a7f5369b0708@email.android.com"
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<p dir="ltr">"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.</p>
<p dir="ltr">Sean<br>
</p>
<br>
<br>
<div class="gmail_quote">On April 21, 2015 1:08:02 PM MDT, Jon
Wallace via Personal_Submersibles <a moz-do-not-send="true"
class="moz-txt-link-rfc2396E"
href="mailto:personal_submersibles@psubs.org"><personal_submersibles@psubs.org></a>
wrote:
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0.8ex; border-left: 1px solid rgb(204, 204, 204);
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<pre class="k9mail">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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