Velocity and other results fields in a Diversion pipe

  Applies To 
  Product(s): StormCAD, CivilStorm, SewerGEMS
  Version(s): 08.11.03.XX and greater
  Area:  Calculations, Results and Output
  Original Author: Jesse Dringoli, Bentley Technical Support Group

Problem

Velocity results show as zero for a conduit set as a Diversion.

Solution

Velocity and hydraulic grade

When modeling a diversion in a conduit, diverted flow (based on the rating table) is passed on to the next downstream element. The GVF-Rational (StormCAD) numerical solver approximates the hydraulic grades (and thus velocities) through a profile of a diversion link with a Gradually Varied Flow backwater calculation based on the downstream HGL. Because of this, the "Velocity" result (which is the average velocity) may not be applicable. Instead, you would refer to both the "Velocity (in)" and "Velocity (out)".

An alternative option would be to change the average velocity method to "simple average" and then the "velocity" result will show the average between the velocity in and velocity out.

Bend Angle and Subnetwork Outfall

Similarly, other calculated fields such as the bend angle (used with certain structure loss methods) and the "subnetwork outfall" are not supported with diversion conduits and will not be calculated.

Another possible workaround would be to use a very short length of pipe for the diversion pipe, and use a longer "real" pipe (not set as a diversion) immediately downstream of it to model the majority of the length of the actual pipe. (since results will be calculated for that element).

Downstream Outfall Flow

In version 10.02.03.03 and earlier, flow from a diversion pipe was not accounted for in the calculated flow result in the downstream outfall. Starting with version 10.03.00.XX (due to be available February2020) this will be resolved and the flow will be included.

See Also

Modeling a flow split (diversion) with the SewerCAD or StormCAD numerical solver

Velocity Calculations and the Average Velocity Methods in SewerCAD and StormCAD

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