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Rony Melo (rgmmelo)
New member
Username: rgmmelo

Post Number: 1
Registered: 08-2007
Posted on Thursday, September 06, 2007 - 07:02 pm:   

hi... I'm a new flexpde's user and don't know how I set danckwerts boundary conditions. I've this boundary:
c1*dc/dz(z=0)=c2*(c(0+)-c0), when I use finite difference method I approximate of that way: c(0+)= ( c(j+1)+ c(j))/2
can anybody help me?
in this website explains better my boundary conditions : http://www.engin.umich.edu/~CRE/course/lectures/fourteen/index.htm
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Robert G. Nelson (rgnelson)
Moderator
Username: rgnelson

Post Number: 949
Registered: 06-2003
Posted on Saturday, September 08, 2007 - 01:00 pm:   

IF
the second-order part of your PDE is "Div(-C1*grad(C))", and
IF
z=0 is the planar bottom boundary,
THEN
c1*dc/dz looks like the Natural BC for your equation.
IN THAT CASE,
NATURAL(C)= c2*(c-c0)
implements the BC you mention.

I have no idea what your statement
c(0+)=(c(j+1)+c(j))/2 means.
It's just an average, and j is undefined.
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Robert G. Nelson (rgnelson)
Moderator
Username: rgnelson

Post Number: 950
Registered: 06-2003
Posted on Saturday, September 08, 2007 - 01:01 pm:   

PS
See NATURAL in the Help Index.
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Rony Melo (rgmmelo)
New member
Username: rgmmelo

Post Number: 2
Registered: 08-2007
Posted on Sunday, September 23, 2007 - 11:48 am:   


thanks nelson, i'll read help again

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