Limitations of Bubble-Type Tank Loads
(For 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.
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.
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Creative Systems, Inc.