[PSUBS-MAILIST] Scott's new sub

[Sean T. Stevenson via Personal_Submersibles]

On 2015-01-08 20:09, swaters at waters-ks.com via Personal_Submersibles wrote:
> I am really new to the engineering side of all this, but am working on it. I have some questions about the calc.
>
>  *It shows material weight is 16351.9 n. Which I show a newton is .224lbs making material weight 3662lbs. Is that right?
>
> *Displacement is 1899.67kg which I show a kg is .453 lbs making displacement 860.55lbs which seams wrong to me?
>
> *Boyancy is 2277.43 n which means 510 lbs? Does that mean it is positive 510 lbs boyancy with no payload and no additional weights?
>
> *at 1000m the pressure is 10.0518 MPa and max working pressure per ABS is 10.0762 MPa meaning it meets requirements. The sphere limit is 15.0391 MPa. Correct?
>
> Sorry, student learning in process.
> Thanks,
> Scott Waters

Scott, my solver works in an iterative process, increasing shell
thickness by a very small amount in each iteration.  Consequently, there
will be minor (but negligible) differences between the stop condition,
which is the pressure at the desired working depth, and the maximum
allowable working pressure at the final shell thickness, which is a
multiple of the increment.  In any case, the sphere limit pressure (~15
MPa in this example) is the theoretical "crush", or instability
pressure, and the maximum allowable working pressure is this pressure
multiplied by the usage factor, eta, which is prescribed by ABS to be
0.67 for spherical shells.  This is the minimum value, and you of course
can (and should) increase the factor of safety over and above this value.

As regards unit conversions:

1 Newton = 1 kg*m/s^2 = 0.22480894 pounds-force

1 kilogram = 2.20462262 pounds-mass

As regards terminology in my software:

"displacement volume" = volume of seawater displaced by closed sphere
"material volume" = volume of steel in hull shell
"material mass" = mass of steel in hull shell
"material weight" = force due to gravity acting on steel in hull shell
"mass of displaced seawater" = mass of seawater displaced by closed sphere
"buoyant force" = gross buoyant force due to displaced seawater
"net buoyancy" = buoyant force minus material weight (net force acting
on closed sphere)
"payload capacity" = net buoyancy divided by gravitational acceleration
= adding this mass inside the sphere will drop buoyancy to zero.

Sean