Design Report Guided Missile Submarine SSG(X) - AOE - Virginia ...

SSG(X) Design – VT Team 3 Page 63
4.4 Structural Design and Analysis
Figure 49 - SSG(X) Sail
Structural analysis focuses on the pressure hull as it is the primary load bearer. The first phase involves
determination of initial scantling values. Calculations are performed in ModelCenter using two MathCAD files –
one for internal frames (Appendix G) and one for external frames (Appendix G) – to give values for the buoyancy
factor, which is a measure of structural efficiency. Figure 50 shows the calculation of buoyancy factor for internal
frames; Figure 51 shows the calculation of buoyancy factor for external frames.
Figure 50 - Buoyancy Factor for Internal Frames
Figure 51- Buoyancy Factor for External Frames
The ModelCenter file (see Figure 52) is composed of seven modules:
• Input: Provides common values of shell plating, flange and web thicknesses, flange width, and web height.
• Mod1, Mod2, Mod3, Mod4: Calculate adequacy parameters and buoyancy factor for each module (see
4.4.1 for an explanation of module definition). These values differ between modules due to varying
quantities for length between frames and length between bulkheads
• BFwgtavg: Calculates an average buoyancy factor for the entire pressure hull weighted by the length of the
module.
• Optimizer: Minimizes structural weight by minimizing the weighted average buoyancy factor while
maintaining sufficient adequacy parameters in each module. The values of web height, flange width, web
thickness, and flange thickness are varied in order to optimize the structure. Figure 53 shows the dialog
box in which options for the optimization are set.