Brent,
So now with your greater understanding of the issue you can realize
some of the complexities of developing a safe solution. I believe you
could calculate this acceleration and it shouldn’t be too difficult, it
is for issues like this that I am back in school studying naval
architecture. It might be solvable with your combination of FlowWorks and
SolidWorks but not familiar with the particulars of the programs. You
have to be very careful with modeling software because you have to know more
than the program so that you can identify false solutions. While working
on a flow study of Nahant Bay north of Boston in the late 70’s, two MIT
grad students developed a theoretical flow model of the Bay looked great but
when they ran it, a 75 ft. tall water spot mysteriously appeared in the middle
of the Bay in the model. Care must be taken with finite element analysis
(FEA) and computational fluid dynamics (CFD) so that you can identify what
appears to be a correct solution that is indeed false.
I do know that FlowWorks is great for modeling complicated flows in
piping and the path water takes along a moving hull but not sure that it is
appropriate for your acceleration model (I qualify this once again in that I
have not had the opportunity to work with the program).
R/Jay
Jay K. Jeffries
Andros Is., Bahamas
A skimmer afloat is but a submarine, so poorly built it will not
plunge…
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent
Hartwig
Sent: Friday, September 05, 2008 2:41 PM
To: PSUBSorg
Subject: [PSUBS-MAILIST] Calculating Acceleration of a Subs Ascent
Hi Jay,
So size my relief
valve(s) to be able to handle the maximum expansion rate expected.
Check
It might be a
little hard to calculate the acceleration of a given sub, when dealing with
both buoyant left, hydrodynamic drag of the whole craft, being in salt or
freshwater, and distance the sub will travel before it gets to the surface. I
might of missed a couple elements.
Perhaps I can use my
FlowWorks software I've never used, in Solidworks to figure out drag.
Your resident pipe dreamer ;)'
Regards,
Szybowski
From:
bottomgun@mindspring.com
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Venting an Ambient
Date: Fri, 5 Sep 2008 06:18:22 -0400
Brent,
This goes against basic
physics. If you have only a partial fill of a volume at depth, you will
accelerate as you near the surface and pressure drops unless you can vent the
expanding air (you will find this difficult as you manage all of the surfacing
functions). You should always size your relief valves to be able to
handle the maximum expansion rate.
R/Jay
Respectfully,
Jay K. Jeffries
Andros Is., Bahamas
Talk sense to a fool and he calls
you foolish.
- Euripides
(484 BC - 406 BC)
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent
Hartwig
Sent: Friday, September 05, 2008 12:37 AM
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Venting an Ambient
I forgot to add that,
if I need to blow air into the inflatable pontoons to surface, that I can add
just enough air to make the sub start to ascend, much like some PSUBBERS
do with there MBT's. That way as I rise, the air will fill the pontoons,
hopefully slower, and also keep my sub from accelerating as fast in a dangerous
manor, and put less pressure on the interior surfaces as the air expands and
tries to get out of the expansion valves. If I'm really deep then I'll need a
better valve design to deal with the faster changing pressures inside the
pontoons when they get totally full and the sub starts to accelerate. But I
still expect to need a number of expansion valves regardless. I would
hate to have the pontoons pop when ascending, it they are my last option for
lift.
Your expanding air
filled dreamer ;)'
Regards,
Szybowski
From:
brenthartwig@hotmail.com
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] Venting an Ambient
Date: Thu, 4 Sep 2008 16:13:52 -0700
Hi Joe,
This point
you made below, is exactly what I want to figure out for my inflatable
pontoons, so I can blow them at depth if I need to in an emergency. Most
of the time I would only fill them up when I get back to the surface.
"What would a cracking pressure of 0.5 to 2 lbs translate to in hull
overpressure, and how many would be required to dump expansion in an emergency
ascent from max depth."
Your resident
pontoon dreamer ;)'
Regards,
Szybowski
From: joeperkel@hotmail.com
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Venting an Ambient
Date: Thu, 4 Sep 2008 13:59:49 +0000
Someone asked about venting an ambient.
I found some PVC check valves today which could quite possibly do the
trick but I think you would have to ask two questions.
What would a cracking pressure of 0.5 to 2 lbs translate to in hull
overpressure, and how many would be required to dump expansion in an emergency
ascent from max depth.
Otherwise, these look pretty nifty!
Joe