Can someone explain to me what the "Time Step Critical Elements" are when running a SewerGEMS Model with the explicit solver? After a model run when looking through the summary report, there is a section titled "Time Step Critical Elements". My model shows one element listed here with a % value next to it. What is the significance of this?
Hello Joshua,
The Report tab displays the original SWMM source report, divided by category. The continuity error with your model appears to be less than zero indicating overall stability of the model.
Other factors like flow routing continuity, highest continuity errors, time-step critical elements, highest flow instability Indexes, etc.. in the report tab, these reports provide information as to which elements have not converged well or have a large continuity error. So link CH-17 could have convergence issues, please check its results, graph the elements or create a profile to understand how it is operating during the simulation.
Troubleshooting unstable SewerGEMS and CivilStorm model results using the Explicit SWMM Solver
Regards,
Sushma Choure
Bentley Technical Suppport
Answer Verified By: Joshua Hesting
Just to add - specifically regarding the section called "Time-step critical elements" in the SWMM output report - this refers to the element that was controlling the variable time-step during the simulation, when the "Use Variable Time Step?" calculation option is set to "True". You can trad more about this option in the Help documentation and in the article that Sushma mentioned. With a smaller timestep, there will tend to be fewer elements controlling the time step during the simulation.
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.