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

Posted Oct 15, 2010, 10:06 a.m. EDT 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 Oct 16, 2010, 4:57 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Oct 16, 2010, 4:57 a.m. EDT
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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