# Problem of calculating divergence due to wrong boundary vaule of finite area mesh

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April 24, 2015, 08:25
Problem of calculating divergence due to wrong boundary vaule of finite area mesh
#1
New Member

Lu ZHOU
Join Date: Jul 2014
Location: Lyon, France
Posts: 12
Rep Power: 12
Hi,

I am using Finite area method to simulate the scour on river bed.

When calculating the divergence of an "areaVectorField" Qsa (fac::div(Qsa)), I found out that the program suppose the Qsa value at the boundary of the finite area mesh is (0 0 0), even though I set the boundary condition of Qsa as zeroGradient in file 0/Qsa. So the divergence calculated is not correct at the boundary of finite area mesh.

I would like to ask how to solve this problem ? Or is there a way to get the label of the face cell at the boundary of the finite area mesh and correct it ? Thanks !

Lu ZHOU
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 June 17, 2015, 09:00 #2 New Member   Tian Tang Join Date: Jun 2012 Location: Copenhagen, Denmark Posts: 18 Rep Power: 14 HI LU, I am having the same problem as you described and I wonder have you figured out a solution yet? Thanks!

 June 18, 2015, 05:10 #3 New Member   Lu ZHOU Join Date: Jul 2014 Location: Lyon, France Posts: 12 Rep Power: 12 Hello, I asked someone else and the answer I got was that the boundary of finite area method did obey the zeroGradient boundary condition. So I think the problem is when we use vsm.mapToSurface(), only the internal field is mapped but not the boundary values. So I set the boundary value by myself because in my case I just need to set the boundary value to zero. I would like to find someway to modify the boundary values as a function in finite volume mesh like U.correctBoundaryCondition() but I couldn't find one. If you get some better ways to solve this please let me know. Best regards ! Lu