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How is the following user notification resolved?
"Calculated volume of gas is more than volume of tank"
In general, you will want to size the tank such that the maximum gas volume (seen in the report and user notifications) doesn't exceed the full tank volume (basically make sure the tank doesn't become empty during the surge event), and that it provides adequate protection (basically make sure the pressure doesn't drop too quickly due to the pressure/volume relationship and headloss). This can sometimes be a difficult task, because there are many factors that effect the effectiveness of the tank, including the total tank size, initial pressure and gas volume or preset pressure (which determine the relationship between change in pressure and change in volume), headloss through the inlet, etc. So, it is often a trial-and-error process. Basically adjust the tank parameters, run the simulation, check the transient envelope and max gas volume, adjust as necessary and try again.I would try to make adjustments not just to the tank size, but the other parameters as well. Pay attention to other user notifications as well, as there may be some other issue unrelated to the hydropneumatic tank. For more information on modeling hydropneumatic tanks, please see the below Technote. There is also a Hydropneumatic Tank example model, located in the Samples folder within the HAMMER installation folder.
Modeling Reference - Hydropneumatic Tanks