I
made this example to show how oscillations occur for legitimate reasons and
the best ways to test the oscillations in InfoSWMM and SWMM 5:
Oscillations
due to downstream obstructions, downstream mixed solutions and downstream
boundary conditions:
In
this case the oscillation in some links is due to the culvert comparison which
limits the flow based on the inlet equation. You can see the flow changes
if you turn on show control actions in the run manager. The program will
then show the changes in the HTML report file. The flow oscillation is
due to the water being stored at the upstream node of the culvert followed by
the excess flow going into the culvert.
How
to check the validity of the solution: Use a Map Display of the Link
Result Variable Link Volume. If you do a map display of the link total
volume you will see that the total volume passing through each link is in
balance. You were using a 30 minute report time step, you can see and
understand the oscillations better if you use a 1 minute report
step. In the culverts even though the flow in the culvert
oscillates the mean flow is being passed downstream – that is why the
downstream flows are constant. I am trying a different way of modeling
the steady state flow = this model does not have a continuity error but since
the inflow to the culvert is oscillating between two solutions you are getting
an uncertain flow.
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| Figure 1 Control Actions |
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| Figure 2 Mass Balance |
