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Implementing a specific boundary condition in Comsol 4.3
Posted 17 juil. 2015, 09:16 UTC−4 Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.3 1 Reply
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Hi all,
I'm working with three coupled ODEs (simplified version below), and have input them using the Coefficient Form PDE model with three dependent variables.
(1) d/dx[(x^2)(-d/dx(u1)-k*u1*d/dx(u3))]=0
(2) d/dx[(x^2)(-d/dx(u2)+u2d/dx(u3))]=0
(3) d/dx[(x^2)(u3)]-m*(x^2)(u2-u1)=0
where k and m are constants. My geometry is 1D, from 1 to 2. My problem is that I'm trying to implement a certain boundary condition at endpoint 1.
At this endpoint u1=u2=0. But the third boundary condition I would like to put in is one that says, essentially, u3 at endpoint 1 must be such that the following equation holds:
(4) a*du1/dx(1)=b*du2/dx(1)
where a and b are constants, and where du1/dx(1) means d/dx(u1) evaluated at 1.
Would anyone be able to recommend a way of doing this, or a specific resource to help? Have I given enough information? Or too much? I'd greatly appreciate any help.
I'm working with three coupled ODEs (simplified version below), and have input them using the Coefficient Form PDE model with three dependent variables.
(1) d/dx[(x^2)(-d/dx(u1)-k*u1*d/dx(u3))]=0
(2) d/dx[(x^2)(-d/dx(u2)+u2d/dx(u3))]=0
(3) d/dx[(x^2)(u3)]-m*(x^2)(u2-u1)=0
where k and m are constants. My geometry is 1D, from 1 to 2. My problem is that I'm trying to implement a certain boundary condition at endpoint 1.
At this endpoint u1=u2=0. But the third boundary condition I would like to put in is one that says, essentially, u3 at endpoint 1 must be such that the following equation holds:
(4) a*du1/dx(1)=b*du2/dx(1)
where a and b are constants, and where du1/dx(1) means d/dx(u1) evaluated at 1.
Would anyone be able to recommend a way of doing this, or a specific resource to help? Have I given enough information? Or too much? I'd greatly appreciate any help.
1 Reply Last Post 17 juil. 2015, 09:55 UTC−4
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Posted:
9 years ago
Would using a "Weak Contribution" work? i.e. adding a Weak Contribution as part of the Coefficient Form PDE physic, and entering Equation 4 into the expression there. Or am I completely off?
Also, regardless of how the overall problem is done, how do implement du1/dx(1) in Comsol 4.3? (That is, d/dx(u1) evaluated at endpoint 1).
Also, regardless of how the overall problem is done, how do implement du1/dx(1) in Comsol 4.3? (That is, d/dx(u1) evaluated at endpoint 1).