Thanks to Hugh Fulton, Antoine Delafargue and Alan Clifford for uncovering several errors/typos in the spreadsheet.
Specifically:
Hugh Fulton wrote:
"The ABS Hull calculator as downloaded is showing Yield strength of 70,000 psi but it should be 37,700 psi according to ASME. 70,000 is the UTS. This does not have a great effect on the Cylindrical shell calcs but certainly does on the Heads. I think it should be altered so it downloads correctly.
Please check to see if I am right. Hugh"
Concur. The base case yield stress for A516 grade 70 is now set at 37,700 psi. I have also included in the Figures tab a graph that shows the relationship between yield and ultimate (tensile) stress. My boat calcs were all done with a yield of 38,000 psi. Unfortunately, when I sent in this sheet originally I had been playing around with different ways to calculate a crush depth and inadvertently left the yield valve in the sheet as the ultimate tensile stress. Everyone needs to use the yield value for your steel as called for in the spreadsheet.
"Just another find is that Line 88 in Cylindrical Shell calcs the formulas between Column C and column D differ.
These should be the same. Affects I min. Had me going for a bit there with oversized stiffeners required.
Hugh"
Concur. D15 in cell D88 has been replaced with D12. For Non-Heavy stiffeners, the length in the equation should be Ls not Lc. Lc is used only for Heavy Stiffeners. Column C results on the 12/17/04 sheet were correct.
Alan Clifford wrote:
"In the ABS_Hull_Calculation spreadsheet, on the “Spherical and Elliptical Heads” sheet, cell C12 is labeled as a radius but contains a diameter."
Concur. For spherical heads, equations in C12 and C13 (and D12 and D13) were reversed, i.e., diameter of shell inside diameter was being calculated as outside and outside shell diameter was being calculated as inside diameter. This error only effects spherical heads not semi elliptical heads. This has been corrected as well as the label that incorrectly identified this row as a radius. This error causes only a small change in results but has been corrected.
Antoine Delafargue wrote:
to correct for that there should be an additional term in the Iz _expression_: (Lw/2+tf/2)*tf*Lf
This plays in the stiffener tripping criteria. using the original _expression_ gives a conservative view on tripping. "
Concur except that
In the function Iz to calculate the moment of Inertia of stiffener about radial axis through web mid point, the term Lf * tf * (Lw / 2 + tf / 2) ^ 2 was added to correctly calculate the moment of inertia of the flange. It was erroneously calculating the sum of the moment of inertia of the flange and web each with respect to their own centroids rather than the midpoint of the web. This was just a knucklehead error on my part trying to code a very tersely written ABS document.
-line 67, distance from outer surface of the stiffener flange to the neutral axis of the combined stiffener and effective shell section. It seems that the formula calculates the distance between the neutral axis of the section to the outer surface of the shell instead. the ABS is not clear on where exactly on the flange the distance is calculated (mid point, inner, outer surface). In doubt the conservative view would use
Centroid_of_Section(...)+line19/2+line20 or Centroid_of_Section(...)+Lw/2+tf
instead of Centroid_of_Section(...)+line19/2+line26 or Centroid_of_Section(...)+Lw/2+t
For this cell, using the original formulation is not conservative in general so it may lead to lower revised stiffener stress limits"
Concur
The equation was calcuating the distance from the centroid of the combine shell-web- flange to the outside of flange but insted of using the thickness of the flange, it was using the thickness of the shell. This has been updated.
Thanks again to Hugh Fulton, Antoine Delafargue and Alan Clifford for uncovering these speadsheet glitches.
From: Hugh Fulton <hc.fulton@gmail.com>
To: personal_submersibles@psubs.org
Sent: Sunday, April 19, 2009 5:13:36 PM
Subject: [PSUBS-MAILIST] ABS Hull Calculator concerns.
Jon, Ray,
The ABS Hull calculator as downloaded is showing Yield strength of 70,000 psi but it should be 37,700 psi according to ASME. 70,000 is the UTS.
This does not have a great effect on the Cylindrical shell calcs but certainly does on the Heads. I think it should be altered so it downloads correctly.
Please check to see if I am right. Hugh
__________ Information from ESET NOD32 Antivirus, version of virus signature database 4019 (20090418) __________
The message was checked by ESET NOD32 Antivirus.
http://www.eset.com