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Boundary condition is a PDE, rather than a constant!

Posted 23 feb 2017, 18:15 GMT-5 Fluid & Heat, Modeling Tools & Definitions, Parameters, Variables, & Functions 1 Reply

Guanlong Guo
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Dear all:

In my model for fluid flow in porous media, I want to set gas pressure as boundary condition at one end of the soil specimen. In the experiment, the gas pressure is applied on the specimen by compressing a certain amount of gas, just like a syringe. At the same time the gas will flow through the specimen following Darcy's law.

According to the condition, I derived a differential equation to solve the gas pressure, but I have no ideas how to applied it on the specimen in Comsol. The equation is like: d(PV)=APv, where P is the gas pressure, V is the gas volume, A is the area of the cross-section of the specimen, v is the Darcy's velocity, which is v=k*grad(P). This seems complicated to apply it on the boundary. If you have any ideas or any experience about such a problem, could you please share them with me? I really appreciate your assistance and time.

Thank you!

1 Reply Last Post 30 mar 2017, 14:28 GMT-4
COMSOL Moderator

Hello Guanlong Guo

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Mohammad Amin Kazemi
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Posted: 8 years ago 30 mar 2017, 14:28 GMT-4
Guanlong
I'm not sure if you are still seeking to an answer.
Anyway, I think you need to define a separate differential equation physics which is solved simultaneously with your flow field. For this purpose, you may add a coefficient form PDE to your model and name the variable whatever you want, let's say Pg.
Then add a pressure boundary condition to the flow physics and in the pressure field, type Pg. This should work.
Amin,
Guanlong I'm not sure if you are still seeking to an answer. Anyway, I think you need to define a separate differential equation physics which is solved simultaneously with your flow field. For this purpose, you may add a coefficient form PDE to your model and name the variable whatever you want, let's say Pg. Then add a pressure boundary condition to the flow physics and in the pressure field, type Pg. This should work. Amin,

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