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How can a user fix the WaterGEMS/WaterCAD error message"Network Unbalanced"?

Applies To

Product(s): Bentley WaterGEMS, Bentley WaterCAD

Version(s): 08.11.xx.xx

Environment: N/A

Area: Modeling

Subarea:

Original Author: Scott Kampa, Bentley Technical Support Group

Error or Warning MessageHow can a user fix the WaterGEMS/WaterCAD error message "Network Unbalanced"?

ExplanationThe "Network Unbalanced" user notification means that for a particular timestep the program could not convergeon a balanced solution within the maximum number of trials. Between calculation iterations, the program checksthe relative change in flow, which has a default value is 0.001. If the relative flow change is below the "Accuracy"value designated in the calculation options, the timestep is balanced or is said to have converged. If the relativeflow change is greater than the Accuracy value, the program will try another iteration. If the program reaches themaximum number of trials without finding a solution, the "Network Unbalanced" user notification is generated.

How to AvoidThere are some things that a user can try to resolve the issue.

First, you can try increasing the number of trials. To do this, go to Analysis > Calculation Options. Under the"Steady State/EPS Solver" section, double-click on the active calculation option to view the properties. Find theproperty field "Trials" and set this to a higher value. In many instances, this is enough to allow the program to finda viable solution.

If that doesn't work, you can also try to increase the Accuracy field (also in Calculation Options properties) to ahigher value, such as 0.01. This will mean that the relative flow change between iterations can be higher, whichmay allow the program to find a solution. You do not want the accuracy value to be too high though, or it maycompromise the results.

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You can also try changing the Engine Compatibility field. The latest solver is "WaterGEMS 2.00.12". If you areusing an older solver, using the latest may help as well.

If the issue still occurs, here are some steps to considerwhen looking for the possible cause of the error message.

Check to make sure that your data for all elements is inputcorrectly. Pay close attention to logical controls, valvesettings and valve status, empty or full tanks, and nearzero flows as these are common causes of the issue.

If you have a check valve on the pipe directly downstreamof a pump, consider removing the check valve. InWaterGEMS and WaterCAD, a pump will not allow reverseflow. A check valve on the downstream pipe is redundantand can sometimes impact the model calculations.

For EPS simulations you might find more clues to solvingyour problem by opening the .RPC file. This file contains alog of the trials that the program runs through when it istrying to converge on a solution. In order to open this filebrowse to the folder where your model is saved; that iswhere the .RPC file will be. You can open this file in a texteditor, such as Notepad.

With this file open you should look down the trial list untilyou start to see the trials where there are elements that areconstantly changing status (for valves a status change may be going from "active" to "closed" or vice versa andfor pumps it could be going from "On" to "Off") over consecutive trials. The elements that have a constantlytoggling status could be a clue to where your problem lies. If this happens often for certain elements then yourmodel may be to tightly constrained or controlled and you should attempt to simplify the model where possible.

See Also"Network Unbalanced" problems with zero flow/ static conditions (Solution 500000060448)

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How can a user fix the WaterGEMS/WaterCAD error message "Network Unbalanced"?Error or Warning MessageExplanationHow to AvoidSee Also