Applies To
	Product(s):	HAMMER
	Version(s):	V8i, CONNECT Edition
	Area:	Calculations
	Original Author:	Jesse Dringoli, Bentley Technical Support Group

Problem

The following warning message is displayed in the user notification window after computing a transient simulation:

"Tank elevation is different than the tank base elevation. If this is an elevated tank, the transient analysis results will be more accurate if the tank inlet pipe is modeled explicitly."

Solution

This message is an informational warning, not an error. The calculations will not be stopped, but your results may not be accurate. The reason is because in this case, the time that it takes for a transient wave to travel from the bottom of the elevated tank to the top will not be accounted for.

To help visualize this, please refer to the diagram below. The "Elevation (Base)" field in the tank properties represents the bottom of the tank itself, whereas the "Elevation" field in the "Physical" section of the properties represents the ground elevation. If your "Elevation" field is lower than then "Elevation (base)", it implies that the tank is elevated and therefore a distance of piping extends from the ground to the bottom of the tank. This distance of pipe is not accounted for automatically. In the Steady State/EPS solver (or in our WaterCAD or WaterGEMS products), this extra pipe does not need to be explicitly modeled, but it may make a difference for a transient analysis.

Since this is an informational warning, you can choose to ignore it if you do not feel a significant difference will occur in your results. If you choose to model the pipe explicitly, you can still keep the base and physical elevations as-is and ignore the warning.

However, if you'd like to model the pipe explicitly to account for the wave speed, etc, the recommended approach would be to model the vertical pipe that extends from the ground to the bottom of the tank. To do this, try the following steps. Place a junction where the vertical pipe is connected to the underground pipe main. Enter the correct node elevation for this connection, then connect the vertical pipe to the tank. For "Elevation (Ground)" on the tank, enter the elevation where the vertical pipe connects to the tank.

With the correct elevations entered, set the pipe to use a user-defined length. With the correct data entered, the program will correctly calculate the modeling effects as a vertical pipe. While the pipe will be correctly modeled as a vertical pipe, the appearance in the drawing will be two-dimensional, or a plan view, of the system.

Note that the profile may not correctly display the vertical pipe. However, the results from the analysis will be accurate.