From: "rick miller" <rickm@pegasuscontrols.com>
Reply-To:
personal_submersibles@psubs.org
To:
<personal_submersibles@psubs.org>
Subject: Re:
[PSUBS-MAILIST] Re Variable Ballast Calculations
Date: Sun, 13 Nov
2005 15:34:22 -0800
joe
the tanks they are refering
to are the soft ballast tanks.
which does not effect submerged displacement,
they effect surface displacement. soft ballast is normally free
flooding
the only time they effect submerged
displacement is durring emergency blow. but due to the large quantity of air
require to do this and the chance of an uncontrolled accent this is not thee
prefered method of operation.
lets look at what is
happening in the soft ballast tanks if you want to use them for a controlled
accent , for ease of the numbers we will use an accent for 66 ft or 3 atm
absolute. fixed factors accent raate is basesd upon drag and the
positive displacement. we will use an accent rate of 60 ft /min and a
positive displacement of 128 or 2 ft^3.
durring the first thirty three foot rise
you will have to vent 1 ft^3 of air thru an oriface/ valve with a
differential pressure. in most tank designs this space would be
approx 1 inch allowing for a differential pressure of .03 psi ie a really
shitty flow rate.
for the next thirty three
feet of rise you will need to vent off 2 cf of air , while the air
density has decreased the flow is not linear based sloely on density
so you would have
to throttle the vent valves in order to made any kind of controlled
accent. this could be done using control valves and a pid controller
incorporated in a plc.but that waywould increase costs
dramatically.
the cheapest way to
accomplise this is to use a small trim tank open at the bottom that has only
the capacity to give a small quanity of positive displacement. as the air in
it expands it will just blow out the bottom. this method will using more air
the a sealed trim tank if you are planing multiple accents and decents
durring a dive but eliminates the need of a high preesure tank and control
system for the water intake valve. although it would require a crew wiegh in
to establish basic trim.
a standard scuba tank is 80
cf a 3000 psi/200 bar. assuming a full tank at 1000 ft or 500 psi
abient pressure. you will have a reserve lift capacity of
tanks size = .4 cf
volume air 80 cf air compressed to five hundred
pai ==2.35 cf
an available air supply of 1.95 cf or 125 lbs
of lift.
the formula is p1v1=p2v2
size of tank
80*14.7=3000x
80*14.7/3000=x
.392= x
3000*.4=500*x
(3000*.4)/500=x
x=2.4 cf total airremember the air that will
stay in the scuba tank
2.4-.4 = 2 cf of available air.
rick miller
Original Message -----
Sent: Sunday, November 13, 2005 1:28
PM
Subject: Re: [PSUBS-MAILIST] Re
Variable Ballast Calculations
Rick,
I had read in the NAVPERS manual for fleet boats, that a submarine does
precisely that to submerge, (reduce displacement by flooding the
tanks).
As for practicality, well this is all just math for now. Incidentally,
I am not using terms correctly in these posts, ie hard, variable, soft
ballast.
Thanks
Joe
From: "rick miller" <rickm@pegasuscontrols.com>
Reply-To:
personal_submersibles@psubs.org
To:
<personal_submersibles@psubs.org>
Subject: Re:
[PSUBS-MAILIST] Re Variable Ballast Calculations
Date: Sun, 13
Nov 2005 12:16:22 -0800
joe
you dont reduce
displacement by adding water. displacement = the total volume of all non
free flooding spaces.
the introduction of large internal ballast
tanks creates a sinificant engineering problem and a possible
piont of flooding for the passenger spaces. most hard tanks are hard to
inspect for corrosion. not to try to rain on your parade, the kiss
pricipal seems to be the way to go here, if you ever want to get in the
water.
rick
m
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