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Define a Mixed (cauthy) boundary condition for Richards Equation(subsurface flow) in COMSOL 4.3

Posted Nov 1, 2012, 5:01 p.m. EDT Fluid & Heat, Porous Media Flow Version 4.2, Version 4.2a, Version 4.3, Version 4.3a, Version 5.0, Version 5.1 6 Replies

Wei Shao
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I read some paper, in the old version of COMSOL, we can choose a Mixed boundary condition (mix of Dirichlet, Newman and Cauchy conditions). in order to automatically transfer the boundary condition form pressure head to Flux, or Flux to pressure head.

But in the new version of COMSOL 4.2 or 4.3, I can not found that kind of setting, could anybody tell me how to define a mixed boundary condition, for complex infiltration problem. The situation is, if the flux is very large, the surface boundary condition is set initially a Flux boundary condition, but once the surface pressure head is larger then 0, then the boundary condition should transfer from Flux boundary condition to pressure head boundary condition.

Could any expert have some suggestion? I appreciate for your help.
6 Replies Last Post Aug 20, 2015, 10:49 a.m. EDT
Jesus Lucio
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Posted: 1 decade ago Nov 3, 2012, 4:51 p.m. EDT
Hello, Wei:

I'm not an expert, but I see in PDE the boundary condition "Flux/Source", I think that is as you like. Nevertheless, if you don't find the boundary expression you need, why not to write it by yourself? For instance, if you need an equation relating both the value and the flux of the dependent variable, like p*u + q*(ux*nx+uy*ny) = 1, you can set a Dirichlet B.C. with u = 1/p - q*(ux*nx+uy*ny)/p. Other possibility is to set a Weak Boundary Cond., if available.

Bye.

Jesus.
Hello, Wei: I'm not an expert, but I see in PDE the boundary condition "Flux/Source", I think that is as you like. Nevertheless, if you don't find the boundary expression you need, why not to write it by yourself? For instance, if you need an equation relating both the value and the flux of the dependent variable, like p*u + q*(ux*nx+uy*ny) = 1, you can set a Dirichlet B.C. with u = 1/p - q*(ux*nx+uy*ny)/p. Other possibility is to set a Weak Boundary Cond., if available. Bye. Jesus.
Wei Shao
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Posted: 1 decade ago Nov 5, 2012, 9:55 a.m. EST
Thank you for your suggestion, this problem is sovled.
Thank you for your suggestion, this problem is sovled.
Andy Huang
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Posted: 1 decade ago Feb 26, 2013, 4:22 a.m. EST
to: wei shao

can you teach me how to define Mixed (cauthy) boundary condition for Richards Equation(subsurface flow) in COMSOL 4.3?

Your kind attention is greatly appreciated.
to: wei shao can you teach me how to define Mixed (cauthy) boundary condition for Richards Equation(subsurface flow) in COMSOL 4.3? Your kind attention is greatly appreciated.
Sina Back
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Posted: 1 decade ago Dec 5, 2013, 9:45 p.m. EST

Thank you for your suggestion, this problem is sovled.


HI,

could you tell me how you defined robin boundary condition?

Thank you.
[QUOTE] Thank you for your suggestion, this problem is sovled. [/QUOTE] HI, could you tell me how you defined robin boundary condition? Thank you.
xianghong guo
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Posted: 9 years ago Aug 20, 2015, 10:34 a.m. EDT
can you tell me how to define Mixed (cauthy) boundary condition for Richards Equation in COMSOL 5.0?
Thank you！
can you tell me how to define Mixed (cauthy) boundary condition for Richards Equation in COMSOL 5.0? Thank you！
Wei Shao
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Posted: 9 years ago Aug 20, 2015, 10:49 a.m. EDT
Please read the paper "Quantification of the influence of preferential flow on slope stability using a numerical modeling approach” by W. Shao et al.
This paper provides the information of setting the boundary conditons
Please read the paper "Quantification of the influence of preferential flow on slope stability using a numerical modeling approach” by W. Shao et al. This paper provides the information of setting the boundary conditons

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