# Interpolation Error on FAM Mesh with Cyclic BCs

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 August 4, 2011, 08:17 Interpolation Error on FAM Mesh with Cyclic BCs #1 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,749 Rep Power: 29 Sponsored Links Hi I have tested the new cyclic boundary condition in FAM, however, I experience a problem when using it. The mesh is horizontal, 2D, and discretised equidistanly. The field, qB, I need to interpolate (actually what to evaluate the divergence, however, it does not matter), is Code: ```dimensions [0 2 -1 0 0 0 0]; internalField nonuniform List 12 ( (8.79856e-06 -1.51105e-17 -1.51894e-17) (8.79855e-06 -1.5199e-17 -1.51006e-17) (8.79855e-06 -1.51123e-17 -1.51874e-17) (8.79856e-06 -1.51697e-17 -1.51302e-17) (8.79856e-06 -1.517e-17 -1.51301e-17) (8.79857e-06 -1.50686e-17 -1.52316e-17) (8.79857e-06 -1.52095e-17 -1.50908e-17) (8.79857e-06 -1.50941e-17 -1.52062e-17) (8.79856e-06 -1.50789e-17 -1.52212e-17) (8.79856e-06 -1.5249e-17 -1.5051e-17) (8.79856e-06 -1.52412e-17 -1.50587e-17) (8.79855e-06 -1.52707e-17 -1.5029e-17) ) ; boundaryField { cyclic1 { type cyclic; value nonuniform List 2((8.79856e-06 -1.51906e-17 -1.51092e-17) (8.79856e-06 -1.51906e-17 -1.51092e-17)); } frontAndBack { type empty; } }``` which is essentially a vector in the x-direction of almost constant magnitude. Performing the interpolation yields Code: ```dimensions [0 2 -1 0 0 0 0]; internalField nonuniform List 11 ( (8.79855e-06 -1.51547e-17 -1.51432e-17) (8.79855e-06 -1.51556e-17 -1.51422e-17) (8.79856e-06 -1.5141e-17 -1.51588e-17) (8.79856e-06 -1.51698e-17 -1.51311e-17) (8.79856e-06 -1.51193e-17 -1.518e-17) (8.79857e-06 -1.5139e-17 -1.51612e-17) (8.79857e-06 -1.51518e-17 -1.51494e-17) (8.79856e-06 -1.50865e-17 -1.52146e-17) (8.79856e-06 -1.51639e-17 -1.51379e-17) (8.79856e-06 -1.52451e-17 -1.50558e-17) (8.79856e-06 -1.52559e-17 -1.50439e-17) ) ; boundaryField { cyclic1 { type cyclic; value nonuniform List 2((1.6495e-12 -1.51906e-17 -7.92696e-20) (-1.6495e-12 -1.51906e-17 8.02252e-20)); } frontAndBack { type empty; } }``` which is correct for the internal field, however, the boundary values is given a value of 0. This, of course, directly affects the magnitude of the divergence in the faces neighbouring the cyclic boundary. I have been playing a bit around with the values in the original field, and the experience is the following: Carrying out qB[0] *= -1.0 before the interpolation, results in a value on the boundary, which is the correct, however, with wrong sign. Carrying out qB[] *= -1.0 before the interpolation, results in a value on the boundary, which is the correct with the correct sign. As already seen, doing nothing, the value at the boundary is ~0.0. This suggests to me that either: part of the field is multiplied with "-1.0" before the interpolation, which hardly makes sense or the interpolation weight is for some reason wrong. All of the above is done in OpenFoam-1.6-ext. Any help on this is highly appreciated. Niels

 August 9, 2011, 06:12 #2 Senior Member   Niels Gjoel Jacobsen Join Date: Mar 2009 Location: Deltares, Delft, The Netherlands Posts: 1,749 Rep Power: 29 Has been reported in OpenFoam-extend bug-tracker: http://sourceforge.net/apps/mantisbt...view.php?id=87 Kind regards, Niels

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