background, see the User Bulletin entitled "TANKTYPE"
and also the sample run file entitled "BUBBLE".)
As bubble tanks
are implemented in GHS, they cannot have more air pressure at a
given load volume than would result in one atmosphere if the load
were reduced to zero. If you give a pressure in a LOAD command such
that the pressure would be greater than one atm. at zero load, it
reduces the pressure. You can see this in the zero nominal load
which is shown in response to the plain LOAD command. If it allowed
greater pressures, it would present a problem whenever the depth
decreases beyond the point where the load goes to zero and the pressure
is still more than 1 atm. Since the load cannot go negative it would
have to remain at zero and violate the gas constant (i.e. spill
There are some
proposals for extending the ability to handle higher pressures:
1. Extend the
Bubble type to allow a mode where air spills when the load goes
to zero but is "replenished" as the depth increases to
the point where the original gas constant can be supported. Since
it's not a sealed tank and it's not one where the air pressure is
maintained at a constant, there is a question as to whether this
would model something that could happen in the real world. (If anyone
has advice on this, please let us know.)
2. Provide a
mode where air is allowed to spill and thereafter remain spilled.
This would model something that could happen in the real world.
It presents a difficulty to the solving process in that it presents
an irreversible discontinuity which is hard to deal with in the
solvers and in interpreting the righting arm curve.