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Richard's Equation questions
Posted Mar 18, 2013, 3:02 p.m. EDT 1 Reply
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Hi,
I'm trying to use COMSOL to model water infiltration and evaporation in porous media. Few questions in this issue:
1) How do I define a boundary as open boundary for Evaporation. How do I define the evaporation rates?
2) Can I add to the model vegetation with roots uptake?
3) How can I change the soil properties? In the material library there is only 1 soil with certain compositions. For example, how can I define that there will be no organic matter in the soil?
4) When I run a simple Richard's model over long time scales (few thousands of seconds) it gives me the message that it has problem to identify the initial conditions? How can I solve it?
Many thanks,
Uri Nachshon.
I'm trying to use COMSOL to model water infiltration and evaporation in porous media. Few questions in this issue:
1) How do I define a boundary as open boundary for Evaporation. How do I define the evaporation rates?
2) Can I add to the model vegetation with roots uptake?
3) How can I change the soil properties? In the material library there is only 1 soil with certain compositions. For example, how can I define that there will be no organic matter in the soil?
4) When I run a simple Richard's model over long time scales (few thousands of seconds) it gives me the message that it has problem to identify the initial conditions? How can I solve it?
Many thanks,
Uri Nachshon.
1 Reply Last Post Apr 14, 2013, 6:54 a.m. EDT
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Posted:
1 decade ago
Yes, all your questions can be incorporated. I do not have examples for them though.
But you can refer to a COMSOL paper or a similar paper published by the same authors in a journal and is titled:
"Implementing Hydrologic Boundary Conditions in a Multiphysics Model" Ting Fong May Chui, David L. Freyberg
which talks of similar boundary conditions such as evapotranspiration. This will help you as COMSOL implementation is discussed. Root water uptake could be included as a source term.
You can define your own properties using "variables". Richard's equation only needs unsaturated hydraulic conductivity relationship and moisture retention characteristics and the rest of the parameters relates to your sink/source terms.
The error you cite is not informative enough. But it is strange that after running for so many time steps it gives out an error related to initial condition. Typically, errors concerning initial conditions are highlighted at the start of your analysis, at least for me. So I am not sure. You will have problems if your material parameters are ill-defined or sometimes if your specific moisture capacity relationship calculates zero value upon saturation.
Suresh
But you can refer to a COMSOL paper or a similar paper published by the same authors in a journal and is titled:
"Implementing Hydrologic Boundary Conditions in a Multiphysics Model" Ting Fong May Chui, David L. Freyberg
which talks of similar boundary conditions such as evapotranspiration. This will help you as COMSOL implementation is discussed. Root water uptake could be included as a source term.
You can define your own properties using "variables". Richard's equation only needs unsaturated hydraulic conductivity relationship and moisture retention characteristics and the rest of the parameters relates to your sink/source terms.
The error you cite is not informative enough. But it is strange that after running for so many time steps it gives out an error related to initial condition. Typically, errors concerning initial conditions are highlighted at the start of your analysis, at least for me. So I am not sure. You will have problems if your material parameters are ill-defined or sometimes if your specific moisture capacity relationship calculates zero value upon saturation.
Suresh