<html><head></head><body><p dir="ltr">The "n" is actually supposed to be the Greek letter "eta", and is labeled in the ABS rules as "usage factor". Its value is prescribed by the rules for each section / failure type. The usage factor is a multiplier applied to the critical pressure for each failure mode, to get a prescribed maximum allowable working pressure for that mode.</p>
<p dir="ltr">Sean<br>
</p>
<br><br><div class="gmail_quote">On April 23, 2014 6:50:19 PM MDT, Pete Niedermayr via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<pre class="k9mail">Thanks Jon. What is n ? Is that the safety margin ?<br /><hr /><br />On Wed, 4/23/14, Jon Wallace via Personal_Submersibles <personal_submersibles@psubs.org> wrote:<br /><br /> Subject: Re: [PSUBS-MAILIST] ABS Hull Calc<br /> To: "Personal Submersibles General Discussion" <personal_submersibles@psubs.org><br /> Date: Wednesday, April 23, 2014, 5:34 PM<br /> <br /> <br /> You have to put in some kind of value and as I recall, very<br /> small numbers can come up with some weird results. If<br /> you use 36" OD, 72" length, and .25" thickness for the<br /> shell, and then enter .1" for the stiffeners, you'll see<br /> that the bottom line calculation (line 92) is a max depth of<br /> 1 foot. However, if you look at line 51 which is the<br /> maximum Pa for inter-stiffener strength you'll note that it<br /> is 61.2 psi which matches the results of the unstiffened<br /> online calculator. Note that both of these results<br /> correspond to a "n" of
.8 which you can manipulate in the<br /> excel spreadsheet but is hard-wired in the unstiffened<br /> calculator.<br /> <br /> So I think the answer is that you have to use very small<br /> number for lines 18 through 21 (try .001) but ignore line 92<br /> and find the lowest Pa between lines 51, 56, 63, and 71 to<br /> determine the maximum allowable operating pressure.<br /> <br /> Jon<br /> <br /> <br /> <br /> <br /> On 4/23/2014 7:02 PM, Pete Niedermayr via<br /> Personal_Submersibles wrote:<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"> What do I enter if I don't want to have hull stiffners.<br /></blockquote> I want to compare results with the Psubs online calculator<br /><blockquote class="gmail_quote" style="margin: 0pt 0pt 1ex 0.8ex; border-left: 1px solid #729fcf; padding-left: 1ex;"> <br /> Thanks Pete<br /><hr /><br /> Personal_Submersibles mailing list<br /> Personal_Submersibles@psubs.org<br
/> <a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br /></blockquote> <br /><hr /><br /> Personal_Submersibles mailing list<br /> Personal_Submersibles@psubs.org<br /> <a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br /> <br /><br /><hr /><br />Personal_Submersibles mailing list<br />Personal_Submersibles@psubs.org<br /><a href="http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles">http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles</a><br /></pre></blockquote></div></body></html>