Hello, I want to solve Fick's second law of diffusion using the pdepe function, where w is the concentration of a species in a solid and D is the diffusion coefficient * ∂w/∂t=∂/∂x(D ∂w/∂x) I defined the following parameters * c=1 m=0 s=0 and f=D ∂w(x,t)/∂x I made a function to define D My boundary conditions are (at x=0 and x=L) * -D ∂w(0,t)/∂x=beta * -D ∂w(L,t)/∂x=0 Since boundaries are defined as p+qf=0 I've set * pl=beta * ql=1 * pr=0 * qr=1 My code seems to work just fine. The concentration w at point x=0 grows with time and numerically, the way I’ve written the code, it has no limit but physically it cannot surpass a saturation concentration Cp. Is there a way to set a maximum to the function? I do not know how to translate this to the code or even where I can add this condition.I would like a code that sets w(0,t)=Cp whenever, w(0,t) ≥Cp Thanks

pdepe function maximum value

2018 3 7

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Hello,

I want to solve Fick's second law of diffusion using the pdepe function, where w is the concentration of a species in a solid and D is the diffusion coefficient

∂w/∂t=∂/∂x(D ∂w/∂x)

I defined the following parameters

c=1 m=0 s=0 and f=D ∂w(x,t)/∂x

I made a function to define D

My boundary conditions are (at x=0 and x=L)

-D ∂w(0,t)/∂x=beta
-D ∂w(L,t)/∂x=0

Since boundaries are defined as p+qf=0 I've set

pl=beta
ql=1
pr=0
qr=1

My code seems to work just fine. The concentration w at point x=0 grows with time and numerically, the way I’ve written the code, it has no limit but physically it cannot surpass a saturation concentration Cp. Is there a way to set a maximum to the function? I do not know how to translate this to the code or even where I can add this condition.I would like a code that sets w(0,t)=Cp whenever, w(0,t) ≥Cp

Thanks

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FM 2018-3-9

Sorry to bother you again Torsten but I have a problem when I try to launch pdepe twice in a same matlab file. I launch it once with the first boundary conditions and then when the concentration reaches Cp I launch it again but with the new boundary conditions. However it stops at the first launch. If I run my code directly on the command window it works fine, (it runs pdepe twice) so I don't think there is a problem with my code. Do you know why this happens?

Thank you in advance