Variable Coefficients in Coefficient form PDE

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Hello,

I am working to solve the following two equations in the attached images in COMSOL for a non-dimensionalized reaction diffusion problem. I am using the coefficient form PDE module in COMSOL 5.3. For some reason, the result I obtain is vastly different depending on if I define the term to be inside d_a (the damping coefficient), or if i divide the whole equation by and define c (the diffusion coefficient) and f (the source term) appropriately. These two cases should be entirely equivalent, but they are significantly different. Why? Which is correct?

Thank you!



2 Replies Last Post May 22, 2020, 9:47 AM EDT
Jeff Hiller COMSOL Employee

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Posted: 2 weeks ago May 21, 2020, 6:52 PM EDT
Updated: 2 weeks ago May 21, 2020, 6:54 PM EDT

You can't simply move the (1-r^2) term inside the divergence, if I understand correctly what you're doing.

is not the same as

Jeff

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Jeff Hiller
You can't simply move the (1-r^2) term inside the divergence, if I understand correctly what you're doing. 1/(2*(1-r^2))*\nabla . \nabla \phi is not the same as \nabla . ((1/(2*(1-r^2))*\nabla \phi) Jeff

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Posted: 2 weeks ago May 22, 2020, 9:47 AM EDT
Updated: 2 weeks ago May 22, 2020, 9:47 AM EDT

aha - i'm just incapable of reading the equation in comsol properly, of course they are not the same.. thanks..

aha - i'm just incapable of reading the equation in comsol properly, of course they are not the same.. thanks..

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