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How to add a boudary condition of u>=0 when solve a PDE problem?

Posted 15 oct. 2010, 10:06 UTC−4 1 Reply

youf Blue
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Hi, everyone

I am working on a problem of PDE. The unexpectant minus results is got finally. Then I think it will get better if I add a boudary condition of u>=0. How to add the boudary condition?

thanks!

youf.
1 Reply Last Post 16 oct. 2010, 04:57 UTC−4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 16 oct. 2010, 04:57 UTC−4
Hi

have you tried a bolean value a u*(u>0) id if(u>0,u,0) (if you are dividing by the "if()" you can replace "0" by "eps" to try to avoid NaN's. This might work, and is probably better than an "abs()"

But you make your system nonlinear, and you might have convergence issues

--
Good luck
Ivar
Hi have you tried a bolean value a u*(u>0) id if(u>0,u,0) (if you are dividing by the "if()" you can replace "0" by "eps" to try to avoid NaN's. This might work, and is probably better than an "abs()" But you make your system nonlinear, and you might have convergence issues -- Good luck Ivar

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