Question: 

What exactly is the difference between the Flooded tank and the Damaged tank.


Answer:


1) The FLOODED tank type is simply the classical way of treating a flooded
condition: the waterplane inside the tank is coincident with the waterplane
outside the tank.  However, the most common terminology (at least in the USA)
is to call such an analysis using this mode "damage stability analysis".

2) The DAMAGED tank type is much more complicated.  It behaves the same as a
flooded tank (assuming the contents is set to sea water) only when the tank's
reference point is under water.  If its reference point is above water and its
internal contents waterplane is below the reference point it behaves as an
ordinary intact tank.  If its reference point is above the water and its
internal contents waterplane would be above the reference point, it is in a
spilling mode.