Diffusive wave and full momentum

[Anonymous]

I am modeling a 2D system using precipitation and a stage hydrograph. When I choose the equation set as diffusion wave, it runs ok, but as I change to full momentum it crashes in the beginning. It does’t matter what computation interval I select. It crashes anyways with this error:
Error with program: RasUnsteady64.exe Exit Code = -1073741819

Some help?

[Scott Miller]

Take a look at the last three posts in this thread:
http://hec-ras-help.1091112.n5.nabble.com/Land-Cover-Manning-in-2D-Flow-Area-Destabilizes-1D-2D-Model-td5799.html#a5993

I found that there was a problem where the edges of mesh cells crossed drops in the terrain. It would cause
a very small volume (or cross sectional area) at the bottom of the stage-storage curve (or stage-area curve). I’m not sure which was more problematic, but, while Diffusion Wave would run stable, Full Momentum would crash, quickly. I found the places where this was a problem, and either adjusted the mesh cells or modified the terrain. Ultimately, Full Momentum ran more quickly than Diffusion Wave had.

You might be able to identify problem spots by observing which mesh cell iterate a lot. You might also generate a Courant number map to check for hot spots. My model did not include precipitation or any stage boundary condition, but that might not be the issue.

[ckatsoulas]

I am not 100% but with some of my runs where I also got this error code, I found that it usually occurred if my time step was way off the mark when I did a variable time step run. I think you need to play with the starting time step so that it is close enough to the calculated time step.

[Anonymous]

I need some help regarding adding the precipitation in the HEC-RAS. The constant inflow hydrographs are provided as input for the 2D domain, now the precipitation also needs to be added over the whole 2D domain. The precipitation data consisted of the single value like return period with intensity.

1- In order to add 100-year return period value of 1-hr duration (intensity) is 30mm, How we can add it?

2- What does the actual mean of time series of precipitation? Is it mean the accumulated rainfall?
for example

Date Simulation time Precipitation (mm)
11-01-2019 07:00 00:00 30
11-01-2019 08:00 01:00 30
11-01-2019 09:00 02:00 30

Does it mean the total rainfall added on the 2D flow area during the whole simulation time is 90 mm? Please elaborate?

3- If we just want to add 30mm in total for the whole simulation time of three hours (as above), then is it a right approach?

Date Simulation time Precipitation (mm)
11-01-2019 07:00 00:00 10
11-01-2019 08:00 01:00 10
11-01-2019 09:00 02:00 10

Thanks

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