Author Topic: Free Surface Setting - Constrained head  (Read 45 times)

Matteo.F

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Free Surface Setting - Constrained head
« on: September 10, 2019, 08:44:41 pm »
Hello,

I am here to ask a question about the free surface setting called "constrained head".

I have a model with that setting applied to the top of the model domain (including the prevent inflow option). As far as I understood, that setting should enable the activation of hydraulic head BC with a max flow rate set to 0 at any node where groundwater level reaches the topographic surface, in order to remove exceeding water.

However, some nodes show a hydraulic head value higher than the topographic elevation. Why does it happen? Shouldn't this setting allow the hydraulic head value be at most equal to the topopgrahic elevation?

Thanks in advance,
Matteo

Peter Schätzl

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Re: Free Surface Setting - Constrained head
« Reply #1 on: September 11, 2019, 08:40:46 am »
Matteo,

in general you are right, the setting enables a head bc with max Q = 0. This BC is applied iteratively, as setting the bc at one node may influence the neighboring ones. To avoid endless iteration, though, there's a max. number of loops - if I remember correctly this is 30. Whatever nodes remain not matching the conditions after this number of iterations can show a higher head.

Hope this helps to understand what's going on.

Cheers,
Peter
Expert / Advisor
DHI WASY GmbH
Berlin - Germany

Matteo.F

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Re: Free Surface Setting - Constrained head
« Reply #2 on: September 11, 2019, 09:37:43 am »
Hi Peter,

Thank you for the quick reply.

Yes, that helps me understanding more what FEFLOW does.

According to this, the hydraulic head values higher than elevation that come out from calculation should be taken just as a qualitative indicator (in those nodes flooding has occured) and not as a quantitative indicator (the higher the hydraulic head is compared to the elevation, the higher is the amount of flooding water in that node), is that right?

Thanks,
Matteo