Instability lid sections

[Umberto]

Hi everyone,
it’s the first time I use lid XS and i get instabilities due to something related to lids.
The model works fine since there is little water in the long pipe modelled with lids, but as the water surface increases and the flow becomes pressurized, I get abrupt high jumps in water surface elevation…than the model stops. I added Preissmann slot to all lid sections.
My time step is 0,5 seconds, but I also tried 0,1 seconds and the problem remains.
In the Profile Output Table I see that it shows negative values of Q total at certain times.
I attached the profile plot at the max WSE.
Any suggestion?

[Chris Goodell]

Looks like you’re modeling a tunnel with your lids. Make sure that the top of the lids are high enough that water can’t get above them (i.e. higher than the hydraulic grade line). Looks like that might be what’s going on here.

[Author]

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