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Switch the boundary condition from flux to pressure head (Richards’Equation)
Posted Mar 3, 2013, 2:52 a.m. EST Version 4.3, Version 4.3a 3 Replies
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But in the new version of COMSOL 4.2 or 4.3, I can not found that kind of setting,we would like to know how to switch the boundary condition from flux to pressure head during the calculation. We started from a flux boundary for rainfall infiltration (with negative pressure head), and when the pressure head at the surface boundary becomes positive, we would like to swith it to the pressure head boundary. We have no idea how to implement it in COMSOL4.3(Richards’Equation).
Could any expert have some suggestion? I appreciate for your help.
Hello Andy Huang
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I know this discussion is quite old but I was wondering if you found a solution (or if someone else has any suggestion) as I'm having exactly the same problem. I am using the same module (Richards' equation) and the same version of COMSOL (4.3); I am analysing water flow through an embankment during a flood event and I would like to switch boundary condition from "no flow" to "pressure head" when the pressure head at the toe of the embankment becomes positive.
I would also like to automatically change the boundary condition from "hydraulic head" to "no flow" according to the elevation of the points on a boundary. I'll try to explain this point more clearly: to represent the rising water level on the river side of the embankment I am applying a boundary condition in terms of hydraulic head varying over time (i.e. the hydrograph of my flood event); anyway on the portion of the embankment boundary which is not wet by the river, i.e. when the elevation y is more than the hydraulic head that I am applying, I need a "no flow" boundary condition. I have managed to change the value of the hydraulic head according to the elevation with a simple "if" statement (if(y<H(t),H(t),0)), but in the "else" scenario I need to change the type of boundary condition rather than its value.
Is there any way to do this? I was thinkink about a "conditional enabling", where I could enable the boundary condition "no flow" on the boundary only if y>H(t) and override the hydraulic head boundary condition only in this case, but I've found nothing about it. Could anyone have suggestion about this?
I would really appreciate any help. Thank you.
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Hi,
I know this discussion is quite old but I was wondering if you found a solution (or if someone else has any suggestion) as I'm having exactly the same problem. I am using the same module (Richards' equation) and the same version of COMSOL (4.3); I am analysing water flow through an embankment during a flood event and I would like to switch boundary condition from "no flow" to "pressure head" when the pressure head at the toe of the embankment becomes positive.
I would also like to automatically change the boundary condition from "hydraulic head" to "no flow" according to the elevation of the points on a boundary. I'll try to explain this point more clearly: to represent the rising water level on the river side of the embankment I am applying a boundary condition in terms of hydraulic head varying over time (i.e. the hydrograph of my flood event); anyway on the portion of the embankment boundary which is not wet by the river, i.e. when the elevation y is more than the hydraulic head that I am applying, I need a "no flow" boundary condition. I have managed to change the value of the hydraulic head according to the elevation with a simple "if" statement (if(y<H(t),H(t),0)), but in the "else" scenario I need to change the type of boundary condition rather than its value.
Is there any way to do this? I was thinkink about a "conditional enabling", where I could enable the boundary condition "no flow" on the boundary only if y>H(t) and override the hydraulic head boundary condition only in this case, but I've found nothing about it. Could anyone have suggestion about this?
I would really appreciate any help. Thank you.
It is better to use mixed boundary condition or you can define step function for the embankment.
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