"Simulation Health: The results show flow continuity issues, please try a shorter time step" when shortest time step is already selected in InfoDrainage

Autodesk Support

Oct 25, 2024


Products and versions covered


Issue:

"Simulation Health: The results show flow continuity issues; please try a shorter time step" when the shortest time step is already selected in InfoDrainage.

Causes:

A continuity error refers to the overall computational balance error of the system, encompassing the total inflow and outflow, flow losses caused by overflows, and volume changes between initial and final storage. It serves as an indication of the hydraulic stability of the results. There can be multiple reasons for the simulation health error. Some common reasons include:

  • Models with very long connections (over 100 m/328 ft) 
  • Misconnections or unconnected links, nodes, or stormwater controls. 
  • Sudden, large flow changes that are the result of an input error.
  • Very small manholes (diameter less than 0.6 m/2 ft)
  • Backflow to underdrains
  • An unnecessary stormwater control has been added that is receiving little to no flow

Solution:

Audit for common causes of continuity errors and optimize the model within InfoDrainage:

  • Split up longer connections into smaller sections, especially if long connections are steep and/or have high incoming flow. 
  • Use profile view to check that all conduits (links), nodes (such as manholes), and stormwater controls are properly connected. 
  • Double-click junctions and check the inlet and outlet tabs to verify that the correct connections are included.
  • Consider swapping out very short pipes (less than 5 m/16 ft) for no-delay connections.
  • Increase the runtime of storm durations that experience the simulation health warning.
  • Check for any sudden, large flow changes and confirm that they are realistic and not the result of an input error.
  • Increase the diameter of manholes to greater than 0.6 m/2 ft
  • In the event of backflow to underdrains, try changing to a no delay connection.
  • Remove or resize excessive stormwater controls


To narrow it down and identify the specific elements where the highest continuity errors are occurring in the model, use the.RPT and.INP files:

  1.  Enable.RPT and.INP files: How to enable .RPT and .INP files for InfoDrainage (autodesk.com)
  2. Run the simulation in InfoDrainage.
  3. A folder containing.RPT and.INP files will be created in the same location where the.iddx is saved. 
  4. Open the RPT file for the storm resulting in the simulation health warning.
  5. Search the RPT file for "Highest Continuity Errors."
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  6. Copy the string of characters and open the corresponding. INP file.
  7. Search the .INP file for the string of characters to locate the element ID .inp file search
  8. Use the element ID (in the above example, "Swale 2_Outlet") to locate the element in InfoDrainage and troubleshoot the causes of continuity errors listed above. 

Products:

InfoDrainage;


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