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In order to introduce the effects of the small scale structures resolved by the fine model back in the coarser model, a feed-back of all the variables is done by replacing the coarse model values with averaged values from the fine model.

Each coarse point value of the nested area is replaced with the algebraic mean value of the fine grid points corresponding to this coarse cell. In order not to reintroduce numerical noise due to the interpolation back in the main model, the feed-back interface is different from the interpolation one as shown at figure 4.5.

Figure 4.5: Position of the feed-back area

Wed Jun 10 10:53:44 DFT 1998