Unsteady Flow Error Message

[Taylor Sun]

I am trying to run an unsteady flow model and I keep getting the following error messages:
– “Maximum iterations of 40 at:” and then there is a list of several cross sections.
-“Minimum error exceeds allowable tolerance at” and then there is a cross section listed.

I keep getting the red bar and my model won’t run to completion.

I’ve tried several things to try and get my model to run but none of them have worked. I’ve tried:
– Deleting the cross section immediately downstream of some of the culvert/ bridge crossings (I thought maybe they were too close and causing instability).
– I have decreased the time step for the model.
– I have increased both the initial flow and minimum flows for my model. (I ran some of the reaches individually and increasing these values seemed to help some of the reaches but I’m still having issues with my downstream reaches).
– I adjusted the HTAB parameter for the maximum number of iterations (I increased it to the maximum allowable number of iterations).
– I adjusted the ineffective flow areas so that there is a smooth transition between cross sections.

I’m all out of ideas of how to fix this model.

[cameron]

Have you tried adjusting the mixed flow options or adding more cross-sections in trouble spots?

[Taylor Sun]

I already have quite a few cross sections. They are a little more concentrated around the crossings and less so in between crossings. Also I tried selecting the mixed flow regime in the unsteady analysis window and that doesn’t seem to improve anything either.

[Anonymous]

Sounds like you have tried all of the usual fixes for this type of problem, without finding a solution. Cameron’s suggestion to try mixed flow is the next thing to look at. Apparently this did not work. So, one would suspect that the computational problems arise from this being a supercritical flow reach (bed slope greater than 50 ft./mile.). If that is not the case, there is a geometric problem somewhere. If that is the case, suggest that you try using Hydrologic Unsteady Routing for this reach.
Michael

[Taylor Sun]

Thanks Michael, I’ll try the Hydrologic Unsteady Routing approach.

[Taylor Sun]

I’m not familiar with running Hydrologic Unsteady Routing but I looked over the manual and I believe that I set it up correctly but that doesn’t seem to be working either. When I press the compute button in the unsteady window the geometry Processor will run (blue line shows up) but that’s it. The model just doesn’t seem to be running. I don’t get any red bars nor does the window say that the simulation is complete. I’ve tried changing time steps and turning the mixed flow regime on and off.

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