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Implicit solver for Open channel network

Hello,

I'm simulating a stormwater model in sewergems platform. the network is simulating as open channel  flow. further, network is bit complex with several tributaries with several sections (unlined trapezoidal, RCU rectangular drains, box culvert, pipe culvers, but no ponds). I'm using SCS CN method. 

when I'm simulating it  in implicit solver, giving very high continuity error and taking long time to end the simulation. but when I'm simulating it with Explicit solver it simulate quickly and no continuity error. I cannot figure out which cross section or the culvert causing the issue.

But I'm giving the message "SWMM does not directly support channel elements. Non-prismatic channels are converted to SWMM style prismatic channels. The export sets the shape of the SWMM channel based on the start cross section if it exists, otherwise the stop cross section is used."

Does that means, if i use the Implicit solver for open channel network, results are unacceptable?

Thanks and Regards

Nishadi

  • Hi Nishadi,

    Each solver has its own strengths and weaknesses. You can certainly use the Explicit solver if it is working better in your model and you understand the assumptions, limitations and differences between the other solvers. See: Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)

    You may want to first take a look at the model for input issues that could be causing the Implicit solver to struggle as you may be able to get better results after addressing them. You can find guidance on that: Troubleshooting unstable SewerGEMS and CivilStorm results using the implicit solver

    Regarding the specific user notification you mentioned - this is informational and is letting you know about a limitation/assumption with the Explicit solver. It is explained in more detail here: Are Channels prismatic or non-prismatic?

    In short, you can certainly still model channels with the Explicit solver but they are treated as prismatic. Meaning, the same cross sectional shape is used for the whole length of channel, whereas with the Implicit solver it models a gradual change between two cross sections (non-prismatic). If you have gradual changes between cross sections then this would have very little impact on the results. If you have large changes in cross sectional area between cross section nodes, you may want to consider inserting additional cross sections and channels if you elect to use the Explicit solver.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

    Answer Verified By: Nishadi 

  • Dear Jesse,

    I was able to reduce the continuity error with implicit solver after referring the links you provided.

    Thanks and Regards

    Nishadi