Re: [PSUBS-MAILIST] Design depth

["Sean T. Stevenson" <cast55@telus.net>]

On Wednesday 08 December 2010 17:28:22 you wrote:
> Hello People,
> 
>    I am trying to carry out design calculations for the pressure Hull,
> according to the ABS guidelines. However, I couldn't find a section in the
> Guidelines suggesting how to find design depth for the sub.
> 
> I have been using Hull Calculator (found on psubs website) as a reference
> for my calculations.  Also, I've found different criteria (equations) to
> find the design depth on different sources.
> 
> Can anyone suggest me what equation to use to find the design depth?
> 
> TIA,
> Jinesh


Design depth is an input which governs your design (i.e. you determine the 
depth capability you need and design to meet it).  If you look at the ABS 
guide, each of the metallic pressure boundary component sections (i.e. 
cylindrical sections, cones, spheres) has equations which allow you to 
calculate a P_cr, which is the short term critical pressure (minimum possible 
failure pressure) for the dominant mode of failure for the particular 
component.  In addition, you will find a usage factor which is some multiplier 
of P_cr appropriate to the failure condition.  The usage factor multiplied by 
P_cr gives the maximum allowable working pressure for the component under 
consideration.  Typically, you want to design your sub such that P_allowable 
is equivalent for each hull component - otherwise, you are making components 
heavier or more complicated than they need to be, because the lowest 
P_allowable will fail first.  The only caveat to this process is that you want 
your first failure mode (lowest P_allowable) to be a strength failure and not 
a buckling failure, since this is deterministic.  



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