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----- Original Message -----
From: rick
miller
Sent: Monday, March 06, 2006 1:27 PM
Subject: Fw: [PSUBS-MAILIST] Free Surfaces solution! Joe
your center of gravity vrs
center of buoyancy difficulties are probably based upon your aircraft
experience. in an aircraft the center of buoyancy is the center of lift of
the wing and does not greatly change do to attitude. where as in a vessel the cb
is constantly changing due to attitude and store consumption. your center of
buoyancy is based on the displacement vrs weight. in a sub where you have a
minimum of four different configurations you must figure for all of them i.e.,
surface ,negative , neutral, positive.
then you must work out the
stability of the vessel its tendency to right its self after a roll. most
commonly a problem at the surface. because unlike a aircraft where the plane of
the lifting force follows the attitude of the aircraft the force of buoyancy is
always straight up.
for smaller subs with minimum
consumables HP air the best way to deal with this is to keep the stores as
close to the center of buoyancy as possible. the biggest item for change is in
the hard ballast tanks. a spherical tank place at the center of buoyancy on the
longitudinal axis will minimize the free surface effect . as the bow goes
down. the water in the tank shifts fwd but the tank shifts aft in respect to the
center of buoyancy canceling the shift. an 18 sphere at the center will give you
up to 110 lbs buoyancy without having a free surface problem.
go to link to see drawing of this http://www.frappr.com/?a=myfrappr&id=386116
spherical tanks will self level. square tanks will
go 45 degress down 45 degress up or level these are the equalibrium states.
cylinder tanks will have equalibrium points farther off as then
square tanks.
fianl conclusion any tank
exposed to free surface effect should be spherical.
Rick m
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