Unsteady flow instability

[Camille]

Hi,

I ran a model I build with 6 differents unsteady flow data but always with the same geometry.
The 6 differents unsteady flow data were composed of a flow hydrograph implemented at the very first cross section and a normal depth for the last cross section. No initial condition.
These 6 differents unsteady flow data were not very different from each other (here two differents flow hydrographs).

Every thing went quite well with the 5 first unsteady flow data, but with the last one, I had a very strange water surface elevation in the three first cross section when the inflow exceeded a certain value (see profile plot below). You can find an extract of the profile plot table where we can clearly see high Froude, EG slope or Velocity in the cross section 119 and very low values in the two cross sections before.

I tried to add a new cross section to reduce the distance between the cross section, I tried to maxing out the number of HTAB points for each cross section, and decrease the increment as well, I tried to change the Manning’s value, I have checked the slope of the bed river.
But I didn’t managed to fix my problem.

Does anyone know what is wrong ?

Thank you !

Camille

[Anonymous]

This could be a variety of factors, especially if the flow varies much differently from the previous 5 inflow hydrographs. Try a different initial flow for that run. Also check your simulation time d(t).

[Anonymous]

Thank you for your answer. In fact, it seems that the inflow increases to fast at the beginning of the event. I just add two values in order to remove the abrupt change of flow. Every thing is ok !

[Author]

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