Richard, I would like to add a comment on this discussion.
I am analyzing a subsea structure, and the external water pressure should be taken into account while calculating the hoop stress.
As discussed above, we can input the difference between the internal and external pressure in the Pressure.
Alternately, according to my colleagues, we can define the global coordinates at the beginning element. And define wave in the Static Load Case Editor.
Here is the interesting part, if we only define the global coordinates, the hoop stress calculation does take the water pressure in. This only works when we define both.
I am guessing that CAESAR II treats the structure as submerged only if the wave data is difined.
Is that right?