Boundary Conditions: Pressure head vs. Pervious Layer

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Carolyne Bocovich

Carolyne Bocovich

June 12, 2014 5:36pm UTC

Boundary Conditions: Pressure head vs. Pervious Layer

We are creating a 2D, steady state, Darcy model of a clayey embankment acting as a dam with a sand foundation. Upstream of the dam is at a higher water level then downstream, both are constant.

A conditional boundary condition is being used to define pressure head as zero above the water level along the embankment boundary. Below the water level ("load") the pressure head takes into account the y-coordinate (elevation) with respect to the water level. The code to describe this is: "0 + (load-y)*(load >= y)".

Using the pressure head boundary condition along the embankment forces the pressure head at the boundary to be zero. The Phreatic line is forced to the embankment surface because of this boundary condition. We would like the model to calculate the steady state phreatic line within the embankment.

What is the best way to define the boundary condition to allow the model to calculate the zero pressure head within the embankment?

Is the pervious layer boundary condition more applicable to this situation? How is the pervious layer boundary different from the pressure head boundary condition? How do I appropriately apply the conductance and how is Comsol using the conductance value in the model?

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