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Dan Wagner

Diagnosing FESWMS error...

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Hello all,

First, a little background: I'm manually spinning down a FESWMS model from a bathtub condition to a water surface elevation and flow from a known flood. The nodestrings representing boundary condition cross sections are #1-downstream end (WS elevation), #2-flux line mid-reach, and #3-upstream end (total flow nodestring).

I've spun down from a bathtub condition at elevation 975 ft to 960 ft. I've gradually upped the total flow from 5000 cfs to the flood flow (40,100 cfs) and have dropped the Vo from 300 to 150. I've had to start dropping only 1 ft in elevation at a time since 965 ft to keep the model converging (the target WS elevation is 905 ft). I've also been disabling elements that have gone dry after each iteration. I've noted that I receive warnings for the missing elements/nodes along my boundary nodestrings as a result, but FESWMS seems to run OK despite the warnings.

OK. Now that I'm at 960 ft, trying to spin down to 959 ft, I'm running into troubles. I have received the error "Total Total conveyance is zero in boundary cross section "1". How does one go about diagnosing this error, i.e., why did it occur, and how to go about proceeding?

Any ideas would be appreciated!

Thanks,

Dan

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Hello all,

First, a little background: I'm manually spinning down a FESWMS model from a bathtub condition to a water surface elevation and flow from a known flood. The nodestrings representing boundary condition cross sections are #1-downstream end (WS elevation), #2-flux line mid-reach, and #3-upstream end (total flow nodestring).

I've spun down from a bathtub condition at elevation 975 ft to 960 ft. I've gradually upped the total flow from 5000 cfs to the flood flow (40,100 cfs) and have dropped the Vo from 300 to 150. I've had to start dropping only 1 ft in elevation at a time since 965 ft to keep the model converging (the target WS elevation is 905 ft). I've also been disabling elements that have gone dry after each iteration. I've noted that I receive warnings for the missing elements/nodes along my boundary nodestrings as a result, but FESWMS seems to run OK despite the warnings.

OK. Now that I'm at 960 ft, trying to spin down to 959 ft, I'm running into troubles. I have received the error "Total Total conveyance is zero in boundary cross section "1". How does one go about diagnosing this error, i.e., why did it occur, and how to go about proceeding?

Any ideas would be appreciated!

Thanks,

Dan

Dan,

The error you are getting is because you have dry elements on your total flow string. This is a common problem for FESWMS/RMA2 models. I would recommend extending your boundaries further away to where it will be wet or trimming your mesh down in size. If this is not possible, you may try making the inflow boundary smaller (i.e. only cover the wet elements), but I am not sure how well this would work.

Cheers,

Cameron

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Dan,

The error you are getting is because you have dry elements on your total flow string. This is a common problem for FESWMS/RMA2 models. I would recommend extending your boundaries further away to where it will be wet or trimming your mesh down in size. If this is not possible, you may try making the inflow boundary smaller (i.e. only cover the wet elements), but I am not sure how well this would work.

Cheers,

Cameron

Thanks for the advice Cameron. The terrain I'm modeling has very steep slopes on the edges of the model domain at the location of the total flow string (upstream end of model). Elements have been going dry and I have been disabling them as I've dropped the water surface elevation during spindown (is this what you refer to as "trimming the mesh down in size?"). I'll try making the inflow boundary string smaller, to prevent the error from occurring again. The total flow boundary string originally included all nodes at the upstream end of the model.

Regards,

Dan

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Thanks for the advice Cameron. The terrain I'm modeling has very steep slopes on the edges of the model domain at the location of the total flow string (upstream end of model). Elements have been going dry and I have been disabling them as I've dropped the water surface elevation during spindown (is this what you refer to as "trimming the mesh down in size?"). I'll try making the inflow boundary string smaller, to prevent the error from occurring again. The total flow boundary string originally included all nodes at the upstream end of the model.

Regards,

Dan

When I say trimming the model down, i don't just mean disabling them. Usually the location of the boundaries are far enough away from the area you are interested in that if you modify the boundaries it will not effect the area you care about. I am assuming that you used the map module to create the mesh. I would trim the map coverage mesh polygon down enough to where you know it will be wet no matter what. If you placed your boundary far enough away from the area you care about this should work.

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