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Re: [PSUBS-MAILIST] Design depth



Thanks Sean.

I perfectly got your point. I have values for all the P.allowable ready with me for all the criteria listed in ABS guidelines. I also have my assumed design depth ready. How can I co-relate my design depth with minimum P.allowable?

Is it just,  depth = (P.allowable/density of water)

or any other equation that co-relates these two variable?

Thanks,
Jinesh

On Wed, Dec 8, 2010 at 5:47 PM, Sean T. Stevenson <cast55@telus.net> wrote:
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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