Convergence NOT achieved Message when computing StormCAD or SewerCAD model

  Applies To 
  Product(s): StormCAD, SewerCAD
  Version(s): CONNECT Edition, V8i
  Area:  Output and Reporting
  Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem

My scenario is not converging on a solution when once computed. I am getting a message in the calculation summary that "Convergence is NOT achieved."

Background

The calculation solver was not able to converge on a solution given the number of traversals of the network and/or other unresolved user notifications

Solution

Try to resolve all user notifications that are pertinent to the network functioning properly

  1. In the user notifications dialog box you can double click on each notification and if it relates to a single element you will be brought directly to that element in the drawing pane. If there are many of the same type, right click on one of the user notifications and choose "select all elements with message id...."

  2. Read the user notification carefully and make the necessary changes to the element properties based on the notification details

  3. Run the Validate tool to potentially identify additional problems that need to be addressed.

Make sure you have the latest version and/or patch set installed

For subscribers, the latest version and/or patch set can be downloaded by following these instructions:

http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/8175.aspx

Remove very short pipes

Pipes that are very short can tend to cause problems like this. Either correct the length, combine multiple pipes in series, or manually enter longer lengths. This can be done for example by filtering the conduit and/or channel flextable on Length (Unified) less than 5 ft, the global edit "Has User Defined Length?" to True, then global edit the user defined length field to 5 ft.

Increase the number of network traversals in the calculation options

  1. Open the calculation options for the current scenario (Analysis > Calculation Options)

  2. Try increasing the number of network traversals. Start with a large number like 50. If that doesn't work try 100. If  that doesn't work then there may be data entry issues or something else wrong with the model. If careful review does not surface the root cause, contact technical support or post on the Hydraulics and Hydrology forum. If 100 does work then increase the number until you find the lowest number that still allows the model to converge.

  3. See more about the effect of increasing the max network traversals in the article shown below under See Also. Note that is is best to find the root cause of the excessive iterations rather than simply increasing the max trials.

Utilize the Explicit Depth and Slope equations Calculation Option

In the calculation options, try setting "Use Explicit Depth and Slope Equations" to "True". This can help with circular pipes that have trouble converging. For more details on what this does, please see the Help.

Complex diversions

Check the model for complex diversion situations ("Is Diversion Link?" = "True"). For example multiple diversions in series. Reduce complexity and excessive diversions wherever possible.

A note on flooding

If you're experiencing Non-convergence and your model is severely undersized, with significant flooding occurring, please note that this can often be the cause of non-convergence. This condition makes it more difficult for the solver to converge. More recent versions of the product handle this situation a bit better when increasing the max trials option mentioned above, but it is worth considering the limitations regarding flooding with the GVF-Rational numerical solver. The HGL will be reset to the rim elevation and the flow will continue in the pipe, whereas in the real system some of the flow will be lost. See the article below for more on this.

See Also

Different results when changing Maximum Network Traversals

Understanding how Maximum Traversals help with non converging models

Why is the HGL reset to rim elevation for flooded structures?

StormCAD hangs when trying to compute, reporting that it is Not Responding

Anonymous
Recommended
Related