My learning curve is
flattened again, too many distractions, Please help me with some basics
here.
#1 One submerges a
bubble of air (enclosed in any material) and open to ambient pressure to
1atm . Equal forces of pressure are applied to either side of the material. I
assume that the lifting force of the air in pounds of buoyancy is not
cancelled out by the equalization of that pressure. That the material is
subjected to a stress in psi equal to that force. Then if one were to apply an
opposing force ,as in ballast, that the material is then subjected to both
forces. Is this a correct assumption?
No. Boyle's Law states that a given volume
of air will compress to half its original volume for every atmosphere of
pressure applied or P1V1=P2V2
At ~33 feet seawater, the dived volume is half
its original surface volume and is now half as buoyant. The forces
applied to either side are indeed cancelled out but not the forces applied
above and below the air bubble. They ae unequal and this is where
buoyancy comes from.
#2 One submerges a piece of marine ply to one atm. Is
the cellular structure of the wood irreversibly compressed creating a
permanent change in density and therefore buoyancy?
Yes, to some degree it does. Elasticity of wood, or
the ability to bounce back from an applied force, is limited. To what
degree this is important is debatable. If we are talking continental
shelf pressures, probably not a heck of a lot. If you fall off the edge,
eventually I could see it playing a role.
At a practical level I believe it's a moot point,
especially within the first two hundred feet. It depends on the wall
thickness, whether you've used cold moulding, the pressure hull shape,
pressure focal points, etc.
Rick
Vancouver