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Material property dependent on solution variable
Posted 7 feb 2014, 07:45 GMT-5 Computational Fluid Dynamics (CFD), Porous Media Flow Version 4.3a, Version 4.4 5 Replies
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I'm trying to solve a 1D flow problem with Darcy's Law. The permeability of my material is supposed to be dependent on the pressure gradient in the medium. So I would first have to create a study to solve for the pressure gradient in the medium and then use the solution from the first study as an input to the second study, which calculates Darcy's law right? How would I go about setting up a study that only solves for the pressure gradient in the medium?
Thank you!
Alexandra
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Permeability is an intrinsic property of a porous material unless of course there is a change in porous structure due to some phenomenology. I am not sure of your application area.
Typically to solve pressure field you need permeability as the input parameter. So if you have an experimental relationship between permeability and total liquid pressure this could be directly entered into the governing equation of flow. Based on initial and boundary condition, and the permeability you define you can solve Darcy's equation or in other words the pressure field.
Is this what you mean?
Suresh
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thanks for your reply!
Indeed, the porosity of my material is supposed to respond to the direction of the pressure gradient. The material becomes less permeable if the pressure gradient is positive and more permeable if it is negative. You could imagine this a bit like a valve that responds to the pressure gradient in the medium (a biological valve)
Let's say the permeability is k0 if dp/dx < 0 and it is k1 if dp/dx >= 0. How would tell Comsol to solve for the pressure field?
Thanks!
Alexandra
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In the permeability field (found under Darcy's Law > Fluid and Matrix Properties), enter the following information.
k0*(d(p,x)<0)+k1*(d(p,x)>=0)
Is this what you are looking for.
Suresh
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Alexandra
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I came across this thread while looking for an answer to a similar question. I am using a thermal expansion node (within solid mechanics) to model the effects of swelling within soil, which is affected by the volumetric wetness (theta), the density (rho), the porosity (n), and the pressure head (h). Each of these should be variable and should be included already within the model, which has initial and boundary conditions for the pressure head and includes a retention model for relating this to theta. (The model involves Richards equation and Solid mechanics.)
My question has two parts: (1) How do I make sure that each of the above terms are considered as variables within the program (I can add them as variables under "global parameters" but how will it know that it's the same as the ones being solved for later) and (2) How do I use said variables in the thermal expansion node in a way that COMSOL will recognize them as already existing within the program?
Thank you!
Shoshana