Would it be possible for PSUBS to gather donations from the members and
purchase outright a good FEA program ? It seems like such a useful tool
with pretty much universal need by anyone in the design phase. It
apparently takes a "WHOPPER" of a computer but if a computer savvy member
was willing to take on the task of running the calcs ( for a fee ? ) it
would sure be helpful. I for one would be willing to help pay for the
original program purchase and a reasonable fee could be taken by the
member doing the work so it wasn't a process where the member got abused
by hair brained ideas. Naturally it would have to be completely liability
free for the guy doing the FEA's, but for running basic hull shapes,
thicknesses, sizes and keeping it down to simple shapes and more or less
"standard" hulls etc. it would be a great resource available to "members
only" and maybe even make a little dough for the guy runnin' the numbers.
Frank D.
-----Original Message-----
From: vbra676539@aol.com
To: personal_submersibles@psubs.org
Sent: Sat, Dec 11, 2010 7:04 am
Subject: Re: [PSUBS-MAILIST] Design depth
It would be interesting to see a work-up and FE-calculations on Gamma, as
it has some odd stress points in the battery box and, of course, the
drilled through viewports. It works, and has done so for many years, but
I'd love to see modern computer technology applied to see in realtime what
Doug Privitt actually did. Vance
-----Original Message-----
From: MerlinSub <MerlinSub@t-online.de>
To: personal_submersibles <personal_submersibles@psubs.org>
Sent: Fri, Dec 10, 2010 11:24 pm
Subject: Re: [PSUBS-MAILIST] Design depth
Hi Vance,
we finalise just the FE-calculations for the Javasub (3+1seater) and the
orthsub (3seats).
oth boats have the same design - Java is just a little longer.
Resulst are crush at 900m (3000 feet), work depth 400 (1300 feet) test at
500 1600 feet).
hell thickness is about a half inch, the first calculation by hand shows
crush t 500m
he difference between the first 500 crush and than later increase crush up
to 00 m was a
ptimize process of the stiffteners by the FE method and the fact that the
hand ethod
s far away from the optimum to find local high force spots.
Here are the Table fore classification to Germanischer Lloyd:
d x factor = td and dd x factor2 = cd
design deep - test deep - crush deep (all in feet)
164 x 1,7 279 x 3,2 525
328 x 1,4 459 x 2,4 787
656 x 1,25 820 x 2,0 1312
984 x 1,2 1180 x 1,87(!) 1840 (1968)
1312 x 1,2 1574 x 1,80(!) 2361 (2624)
1640 x 1,2 1968 x 1,76(!) 2886 (3280)
1968 x 1,2 >2362 x 1,73(!) 3404 (3936)
(!= factor shall be 2,0 if water deep is more than design deep)
br Carsten
vbra676539@aol.com> schrieb:
You guys have fallen head over heels in love with a logic trap, heavily
basted ith semantics. Give it up. Design depth is your operating depth
PLUS the ercentage required for testing. It means the depth to which the
pressure vessel ay be taken repeatedly without incurring irrecoverable
damage.
125% doesn't make some people happy. I'll just stick in my 2 cents and
tell ou that I have done a whole bunch of dives in vehicles built and
tested to that tandard. Crush depth is an arbitrary derivative of the
overall calculations, uggesting that all things being perfect, if you go
this deep (whatever THIS appens to be) then the hull MAY suffer
irreparable damage, and if it does, then HIS is the site of most probable
damage. The THIS is typically a measure of the eakest link in the design,
which is specific to the design, not general iscussion. It is NOT a weak
link, but simply the first failure point.
A C-class Perry for instance would be rated for 1200 feet maximum
operating epth. It's design depth (and unmanned test depth) would be 1500
feet and it's rush test.....hmmm, I forget. About 1800 and change, I
think. Maybe 19 and hange. That kind of thing is in the initial ABS
calculation package, if you appen to have it. However, it is not normally
in the general ABS certs. I do ot have a crush depth number for Gamma, for
instance, but do have her ertifications.
For general interest, Nekton Alpha, Beta and Gamma are all rated at 1000
feet nd were all tank tested to 1500. Crush depth was ascertained by model
testing, hich verified the calculations handily (just over 2000 feet).
Perry was doing epetitive construction on two proven primary designs
(tubular hull, internal or xternal ring stiffeners). Once proven, in other
words, all they had to do was eplicate and prove that they had done so.
As to accepting one safety factor over another, I'd say 125% should be the
ccepted norm, based on experience and history. Anything over that is a
personal hoice. I feel one way, somebody else feels another. Potato,
potahto.
Shallow boats are easy to double up on. The old Submaray, for instance,
was /8" plate and they held it to 300 feet for safety. The PC-8, on the
other hand, as also 3/8" plate and I can't even tell you how many times
I've been to her perating maximum of 800 feet. Different construction
techniques. Different esign. Different results.
Vance
-----Original Message-----
From: Jon Wallace <jonw@psubs.org>
To: personal_submersibles <personal_submersibles@psubs.org>
Sent: Fri, Dec 10, 2010 4:53 am
Subject: Re: [PSUBS-MAILIST] Design depth
Jim,
Design depth is derived from the parameters (material type, hull
hickness, number of ribs, spacing of ribs, etc) used in ABS/ASME
formulas to etermine the maximum external pressure that the submarine
can operate in. I on't think ABS or anyone else can reliably calculate
"fail depth" or "crush epth" because those depths are highly dependent
upon quality of material, abrication, vessel use/maintenance, etc. The
crush depth could be some ercentage above or below design depth, however
you could only find out efinitively by testing the vessel to
destruction. For that reason, you on't want to perform a manned dive
to 375 feet. Make sure that is an nmanned test. You'll note that ABS
Underwater Vessels Section 3.5 limits he manned test dive to the design
depth.
Jon
On 12/10/2010 9:04 AM, JimToddPsub@aol.com wrote:
Jon,
I need to read and study the whole ABS publication thoroughly,
but rom what I've read is seems that the Design Depth I would
need to laim would be 300 feet. During the survey I would need
to dive in ncrements to 375 feet (300 x 1.25). The vessel
would then be rated o 300 feet. Per ABS, Design Depth is the
depth to which the essel is "designed and approved to operate." It's
going to be pproved to 300. If I want to have it approved for
anything more han that, I'll have to have it surveyed to
125% of whatever I want ts operating depth to be.
What is surprising is that [so far] I see nothing in ABS that
pecifies how the Design Depth must be derived. It seems rather
rbitrary rather than stating something such as "60% of the
alculated fail depth."
Jim
In a message dated 12/10/2010 1:24:29 A.M. Central Standard
Time, onw@psubs.org writes:
A different approach is to say, I know I don't want to dive
eeper than 300 feet (my max operating depth) and I want a 2x
afety margin. That means using material capable of
withstanding 00 feet depth. Now with this approach you
certainly may not pass 1.25 overpressure test for a 600 foot
design depth, however ou've already self imposed a 2x safety
margin. If you wanted ABS ertification, then you simply
claim the design depth as 480 feet. ow you meet the ABS
requirement (480 x 1.25 = 600) and also are till well within your 300 foot
self-imposed depth limit.
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