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photinka
Member
Username: photinka
Post Number: 10
Registered: 02-2007
| | Posted on Wednesday, April 14, 2010 - 05:26 am: | |
The problem geometry is a sphere in a cube. (Helmholtz equation).
I need to set a boundary condition at the sphere surface like u=f(dR(u)), where u is an unknown function and f() is a nonlinear function. Can it be done in FlexPDE? Which function, value or natural, is better to use? |
rgnelson
Moderator
Username: rgnelson
Post Number: 1348
Registered: 06-2003
| | Posted on Friday, April 16, 2010 - 02:00 pm: | |
If U is declared as a VARIABLE, then you can use nonlinear expressions in a VALUE(U) statement. The meaning of NATURAL depends on the equation system, but for a Helmholtz equation it will mean the outward normal derivative of GRAD(U). Again, you can use nonlinear expressions in the NATURAL(U) statement.
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photinka
Member
Username: photinka
Post Number: 11
Registered: 02-2007
| | Posted on Thursday, April 22, 2010 - 10:54 am: | |
Is it possible to include in the boundary condition a surface integral of unknown function? |
rgnelson
Moderator
Username: rgnelson
Post Number: 1351
Registered: 06-2003
| | Posted on Thursday, April 22, 2010 - 01:09 pm: | |
Yes. Declare a GLOBAL VARIABLE whose value is the integral.
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