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Analyzing an existing drainage nework in stormCAD

Dears,

We have a project area that is part of a bigger drainage catchment where the remainder of the area is upstream of our subcatchment. We built a model using GIS information of exisitng network (invert levels and pipe sizes ) for only the portion of the network within the project area. For this area we have done calculations for a weighted C and a will be using rational method catchments and linking them to catch basins in the model.

For the upstream area we will consider the whole area at once, its drianage path and resulting Tc and IDF curve corresponding intensity (becuase of a different adjusted IDF than the one in our area that is driven by dominant landuse as per local regulation) and we will calculate a fixed inflow that we will be added to the manhole at the point where the upstream catchment connect to the network passing through our project area (this is for planning purposes not engineering design).

While in analysis mode, we get all kinds of warnings with regards to min/max velocity and slope not met as well as flooded nodes.

The main thing is that once the model is run, in the calculation summary, we get the "Convergance was NOT achieved" warning. So before using the results for reporting we want to know if the convergance warning implies the results are not reliable or what are the implications of this type of warning.... one is more used to the green light once in design mode!

 

 

  • Hello AHQ,

    For the nonconvergence issue, the following link may be helpful: communities.bentley.com/.../9684.my-scenario-is-not-converging-on-a-solution-convergence-not-achieved-in-stormcad.

    For the warnings, these are related to the model results compared to the default design constraints. Even if you are running an analysis and not a design run, these messages may appear if the constraints are violated.

    If this doesn't help, we may need to see a copy of the model files. There are two options for sharing your model on Communities, whichever you choose please be sure to zip your files first. The first option is to attach the zip file containing your model to your reply on the forum using the Advanced Reply Editor (you'll find the link below and to the right of the reply box). If your data is confidential please use the instructions in the link below to send it via Bentley Sharefile. Files uploaded to Sharefile can only be viewed by Bentley employees. Please be sure to reply on this thread with the name of the file after it has been uploaded.

    communities.bentley.com/.../7079.be-communities-secure-file-upload

    If you upload the model to Sharefile, please post here with the name of the file so that we know it is available.

    Regards,
    Scott

    Answer Verified By: A  

  • AHQ,

    I see you mentioned that many nodes are flooded - this condition often causes the "convergence was NOT achieved" warnings. I've added a note about this in the article that Scott referenced in his previous reply.


    Regards,

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

    Answer Verified By: A  

  • Thanks for the answer. I'm not concerned with the fact that warnings about violating the defined design constrains are present. The warnings are actually the results we want to report on the back of this analysis before we attempt to identify a strategy for the solution. My worry was if the note in the calculation summary about none convergence raises questions on the correctness of these same reported results.

    I did send the model but shortly after that I raised the number of max network traversals to 50 and convergence was achieved. Anyhow, if you find anything worth warning us about, we logged in our contact details up on file submission.
  • Hello AHQ,

    I would address the flooding node issue that Jesse mentioned in his post, as that is an indication that the system is undersized and may have contributed to the non-convergence as well (you may already be planning this using automated design).

    There are also use notifications indicating a few places where the invert of the conduit is below the invert of the node it is attached to. This would be an unusual system setup and should be addressed. Reviewing the elevation data would be recommended as part of this.

    Regards,
    Scott

    Answer Verified By: A  

  • Thanks Scott,
    yes, the flooding is an indication that the system is undersized and it is something we will report on.

    The notifications on IL of conduits being lower than the nodes they connect to is due to the way we extracted the IL of each catch basin from the links database using a look up function in excel but without seeking the lowest IL-in/IL out of the pipe connecting to the catch basin . It was perceived the analysis results wont be sensitive to it since each conduit is well defined with a start and stop IL (what do you think?). We did increase the max network traversals to 50 in the same model we sent you and convergence was achieved.