# Nonconvergence in a multiple region Laplacian problem

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 June 7, 2006, 10:10 Hi K.! I didn't go through #2 Assistant Moderator   Bernhard Gschaider Join Date: Mar 2009 Posts: 4,008 Rep Power: 43 Hi K.! I didn't go through it in detail (and I don't know where exactly in your code this should be corrected), but is it possible, that the other diffeence between your two grids is that in the first case the grid-spacing on the left and the right of the boundary is the same while in the second case they differ by a factor of 2? Have you checked the obundary conditons for T for the non-interface boundaries? __________________ Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

 June 7, 2006, 12:08 Hi Bernhard, Thanks for the #3 New Member   kmurphy Join Date: Mar 2009 Posts: 10 Rep Power: 10 Hi Bernhard, Thanks for the reply. I was worried about the boundary between the two meshes, i.e., whether the faces of the corresponding cells on the commom boundary of both meshes were aligned, and so I wrote code to: Determine the two unit normals fields, using .Sf(), and compare to ensure that the normal for corresponding faces were pointing to opposite directions. Determine the face centres, using .Cf(), and compare to ensure that the face centres for corresponding faces were equal. However, the cell volumes (or just areas since it is a 2D problem) may well be different on either side of the common boundary of the two meshes. In the 1D case I ran a few experiments with different size cells on either side of the boundary (while keeping the boundary faces aligned). Varying the cell volume on either side of the boundary had no effect so I assumed that this was not the source of the problem. (Bad idea?) If the relative cell volumes did have an effect how do I add a correction for this when transferring the gradient information between meshes (I think that the transfer of potential information is OK - it is only one line!). The boundaries conditions for the non-interface are that T is zero. KM

 June 7, 2006, 13:56 OK. The mesh stuff was only a #4 Assistant Moderator   Bernhard Gschaider Join Date: Mar 2009 Posts: 4,008 Rep Power: 43 OK. The mesh stuff was only a guess. Sorry for asking. About the BC: it's zero, not zeroGradient? (sorry for asking, but I want to be sure) Does the solution get unbounded in the whole domain or only near your interface? Can you provide us a picture? __________________ Note: I don't use "Friend"-feature on this forum out of principle. Ah. And by the way: I'm not on Facebook either. So don't be offended if I don't accept your invitation/friend request

 June 8, 2006, 04:40 are you sure about the code pa #5 Senior Member   Daniele Panara Join Date: Mar 2009 Posts: 101 Rep Power: 10 are you sure about the code part that compute the normals? Can you explain better the jump condition? and your BC? In my experience such a problem can appear if you wrong the sign of the heat flux (scalar gradient). Are the heat fluxes pointing in the same direction at the boundary (going in or out from the circle)? Daniele

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