### GWF-GNC #### Structure of Blocks _FOR EACH SIMULATION_ ``` BEGIN OPTIONS [PRINT_INPUT] [PRINT_FLOWS] [EXPLICIT] END OPTIONS ``` ``` BEGIN DIMENSIONS NUMGNC NUMALPHAJ END DIMENSIONS ``` ``` BEGIN GNCDATA ... END GNCDATA ``` #### Explanation of Variables ##### Block: OPTIONS * `PRINT_INPUT` keyword to indicate that the list of GNC information will be written to the listing file immediately after it is read. * `PRINT_FLOWS` keyword to indicate that the list of GNC flow rates will be printed to the listing file for every stress period time step in which "BUDGET PRINT" is specified in Output Control. If there is no Output Control option and "PRINT_FLOWS" is specified, then flow rates are printed for the last time step of each stress period. * `EXPLICIT` keyword to indicate that the ghost node correction is applied in an explicit manner on the right-hand side of the matrix. The explicit approach will likely require additional outer iterations. If the keyword is not specified, then the correction will be applied in an implicit manner on the left-hand side. The implicit approach will likely converge better, but may require additional memory. If the EXPLICIT keyword is not specified, then the BICGSTAB linear acceleration option should be specified within the LINEAR block of the Sparse Matrix Solver. ##### Block: DIMENSIONS * `numgnc` is the number of GNC entries. * `numalphaj` is the number of contributing factors. ##### Block: GNCDATA * `cellidn` is the cellid of the cell, n, in which the ghost node is located. For a structured grid that uses the DIS input file, CELLIDN is the layer, row, and column numbers of the cell. For a grid that uses the DISV input file, CELLIDN is the layer number and CELL2D number for the two cells. If the model uses the unstructured discretization (DISU) input file, then CELLIDN is the node number for the cell. * `cellidm` is the cellid of the connecting cell, m, to which flow occurs from the ghost node. For a structured grid that uses the DIS input file, CELLIDM is the layer, row, and column numbers of the cell. For a grid that uses the DISV input file, CELLIDM is the layer number and CELL2D number for the two cells. If the model uses the unstructured discretization (DISU) input file, then CELLIDM is the node number for the cell. * `cellidsj` is the array of CELLIDS for the contributing j cells, which contribute to the interpolated head value at the ghost node. This item contains one CELLID for each of the contributing cells of the ghost node. Note that if the number of actual contributing cells needed by the user is less than NUMALPHAJ for any ghost node, then a dummy CELLID of zero(s) should be inserted with an associated contributing factor of zero. For a structured grid that uses the DIS input file, CELLID is the layer, row, and column numbers of the cell. For a grid that uses the DISV input file, CELLID is the layer number and cell2d number for the two cells. If the model uses the unstructured discretization (DISU) input file, then CELLID is the node number for the cell. * `alphasj` is the contributing factors for each contributing node in CELLIDSJ. Note that if the number of actual contributing cells is less than NUMALPHAJ for any ghost node, then dummy CELLIDS should be inserted with an associated contributing factor of zero. The sum of ALPHASJ should be less than one. This is because one minus the sum of ALPHASJ is equal to the alpha term (alpha n in equation 4-61 of the GWF Model report) that is multiplied by the head in cell n. #### Example Input File ``` BEGIN OPTIONS PRINT_INPUT PRINT_FLOWS END OPTIONS BEGIN DIMENSIONS NUMGNC 24 NUMALPHAJ 1 END DIMENSIONS BEGIN GNCDATA 10 41 9 0.333333333333 10 43 11 0.333333333333 11 44 10 0.333333333333 11 46 12 0.333333333333 12 47 11 0.333333333333 12 49 13 0.333333333333 16 41 9 0.333333333333 16 59 20 0.333333333333 17 49 13 0.333333333333 17 67 21 0.333333333333 20 68 16 0.333333333333 20 86 24 0.333333333333 21 76 17 0.333333333333 21 94 25 0.333333333333 24 95 20 0.333333333333 24 113 28 0.333333333333 25 103 21 0.333333333333 25 121 32 0.333333333333 29 113 28 0.333333333333 29 115 30 0.333333333333 30 116 29 0.333333333333 30 118 31 0.333333333333 31 119 30 0.333333333333 31 121 32 0.333333333333 END GNCDATA ```