OpenFlows | Water Infrastructure - WaterSight - Inconsistent Results for Affected Customers

Product(s):	WaterSight
Area:	Documentation

This article describes some potential issues the user might encounter while running operational events in WaterSight, such as Pipe breaks, fire events, pump shutdowns or valve operations.

Inconsistent Results during Pipe Break Isolation run - check valve issue

In case you are running a pipe break isolation run (the first step to identify affected customers, and before running a steady state or EPS model run) and you notice that the outage segments seem incorrectly defined, please confirm if you are using a check valve on the pipe next to a reservoir. If that is the case, adjust your WaterGEMS model by placing the check valve on the next-downstream pipe (rather than on the pipe directly adjacent to the reservoir), and then upload the updated model one again in WaterSight. This should solve the issue. We are working toward improvements of the handling of this situation.

Figure 1 - Pipe Break Isolation run results: customers with no water are displayed at red (for those withing the isolated pipe) and purple (for those downstream the isolated pipe)

Inconsistent Results during EPS runs - unbalanced time steps

In WaterSight the identification of affected customers only considers those that are directly impacted by the operational events. This means that the application always excludes chronical customers with issues - those that already had no water or low pressure before the event. The exact rules are the following:

Customers with no pressure: customers that in the baseline scenario (with no event) had pressure and during the event scenario end up with no pressure, during at least one time step of the all simulation period;
Customers with low pressure:
- All customers that in the baseline scenario (with no event) were above the minimum pressure threshold (defined in the administration) and during the event scenario end up with no pressure, during at least one time step of the all simulation period;
- All customers that were already below the minimum pressure in the baseline scenario (no event) but had a pressure decrease greater than 15% with the event, during at least one time step of the all simulation period;

Therefore in case in case you are running a pipe break simulation, fire event, pump shutdown or valve operations event for an extended period (EPS), and you obtain several customers affected that are located very far away from the event location, this might be an issue related with some unbalanced time steps during one or more instants of the EPS run.

Confirming the issue

In order to confirm this is the case, please follow the following steps:

1 - After running the EPS simulation, go to "Model Symbology" and enable visualization of pressure at the junctions and then enable the "Side-by-side view" toggle.

2 - Click in a node in the map very near one of the affected (purple customers) and look at the pressure graph. An example below.

3- The blue line represents the pressure for the baseline scenario (without event) while the red line represents the scenario with the event. In case you get a sudden pressure spike going down for short instants for one of the scenarios (but not for the other), than this instant might be the one that is being used to assess impacted customers and might be related to an unbalanced timestep.

4 - Download the hydraulic model for this operational event directly from WaterSight, by acceding Event Management >> Operational Response, and downloading it from the table.

5 - Open the model in WaterGEMS and run it. Check if you get unbalanced time steps for the same periods you get the pressure decreases in WaterSight. Check also that you obtain the same pressure results for for the same nodes with issues in WaterSight, considering the event scenario (the event scenario is automatically configured an populated under the SCADA Connect Simulator Interface of WaterGEMS).

Solving the issue

The issue can be solved by eliminating the root cause for the unbalanced time steps in WaterGEMS. Convergency errors can typically occur at pump storage or pressure/flow regulation valves. Other solutions that might help minimizing the issue pass to adjust the Calculation Options and decrease the "Accuracy" to 0.01 or to reduce the "Hydraulic timestep" (for example to 10 minutes or 5 minutes). It was also noted that selecting older Engines in the "Engine Compatibility" such as the WaterGEMS 2.00.10 might contribute to reduce the number of unbalanced time steps. Please note that reducing the Hydraulic timestep will always affect the performance of the model in WaterSight as it will take more time to run the operational events, so this should be done as last resource.

After the adjustments are done, upload the WaterGEMS model again in WaterSight (Administration >> Numerical Model).

Affected customers are not calculated

If after running a steady state or EPS run for a pipe break simulation, fire event, pump shutdown or valve operations event you get a warning message mentioning that more than 50% of the timesteps are unbalanced, than WaterSight will not calculate and display the affected customers as the results could be invalid (see above for more detail). In this case the user should improve the WaterGEMS model in order to reduce the number of unbalanced timesteps, before deciding to upload it in WaterSight.

WaterSight - Inconsistent Results for Affected Customers

Inconsistent Results during Pipe Break Isolation run - check valve issue

Inconsistent Results during EPS runs - unbalanced time steps

Affected customers are not calculated

See Also