HI Tangfei,

In the attached test case which has all boundary conditions I have modified the PRIMCOEFF to a non-unit value and modified the exact value accordingly. It seems to run with a non-unit value. 

Cheers,
Spencer.

Spencer Sherwin FREng, FRAeS
Head of Aerodynamics Section,
Director of Research Computing Service,
Professor of Computational Fluid Mechanics,
Department of Aeronautics,
s.sherwin@imperial.ac.uk                                   South Kensington Campus,
Phone: +44 (0)20 7594 5052                              Imperial College London,
Fax:   +44 (0)20 7594 1974                               London, SW7 2AZ,  UK
http://www.imperial.ac.uk/people/s.sherwin/

On 11 Jul 2020, at 13:16, zhangtengfei@sjtu.edu.cn wrote:

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Dear all,

I am using the robin boundary condition in Nektar+ but have some problems understanding how it works.

The b.c. I want to impose is 
  D* gradient {u} + 0.5 * u = 0
in which D is the diffusion constant (same as the D value used in the adjacent element), u is the unknown field.

To do this I normalize the b.c. into the form of  
gradient {u} + 0.5 / D * u = 0,
and specify the robin boundary condition as 
<R VAR="u"  PRIMCOEFF="0.5/D" />

This setting does not yield the correct answer, unless the special case that D = 1.0. Could anyone please tell me what is wrong here?

Thanks,

Tengfei Zhang
 
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