I simulated a sewer system in SewerGEMS with the calculation options Covex, Dynamic wave and SWMM Solvers. In the simulation with the Dynamic Wave option, it notifies me that I have a froude number greater than 1, what does that mean?Another doubt that I have is that with the Dynamic Wave option the flow rate through the outfall is 18.27 l / s but in the Convex and SWMM Solvers options the flow that comes out is 18 l / s. Why this difference in flow? .I attach the model in SewerGEMS to be reviewed.
Every solver in SewerGEMS is different in its own way, implicit and explicit are dynamic routing solvers, whereas convex and rational solvers solve for the peak flow conditions, so results will not be same in either of the solvers.
When there is notification about change in flow from subcritical to supercritical, it means that conduit is flowing under pressure. I will have a look at your model and comment further for this particular model.
Below is information about, how each of the solver works and why do we get different results.
Model results are different between the GVF-Convex and the Implicit/Explicit solvers
Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)
Bentley Technical Suppport
Answer Verified By: Alexander Benites
Thank you Sushma,
I verify that Depht/Rise in all conduits are less than 100% which means that the pipes are not working under pressure. Or I'm wrong?. I also see that the Depht/Rise relationship in Dynamic Wave and SWMM Solvers are very different.I would like you to explain this
The depth/rise varies from solver to solver.
For Implicit Solver - depth/rise is active depth in the middle of the conduit or channel by rise.
For GVF-Convex and GVF-Rational Solver - depth/rise is the average depth in the link by rise.
For Explicit (SWMM) Solver - depth/rise is depth calculated by Explicit engine by rise.
You can find the differences in the different solvers and how they operate from the links provided in the earlier response,
Hope this helps.
Bentley Technical Support
You are right pipes aren't working under pressure in your case.
The notification about "A supercritical to subcritical transition is occuring during this time-step" means that a hydraulic jump may be occuring, which you might want to be aware of.
And notification about "One or more elements had a Froude number greater than 1 during this time-step." means that supercritical flow occurs in the pipe at some point, which you might want to be aware of.
It is basically implying this transition in conduit CO-10(2), in your case, as seen in the below screenshot.