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31.5.6 Checking the Partitions

After partitioning a grid, you should check the partition information and examine the partitions graphically.



Interpreting Partition Statistics


You can request a report to be printed after partitioning (either automatic or manual) is completed. In the parallel solver, click the Print Active Partitions or Print Stored Partitions button in the Partition Grid panel. In the serial solver, click the Print Partitions button.

FLUENT distinguishes between two cell partition schemes within a parallel problem: the active cell partition and the stored cell partition. Initially, both are set to the cell partition that was established upon reading the case file. If you re-partition the grid using the Partition Grid panel, the new partition will be referred to as the stored cell partition. To make it the active cell partition, you need to click the Use Stored Partitions button in the Partition Grid panel. The active cell partition is used for the current calculation, while the stored cell partition (the last partition performed) is used when you save a case file. This distinction is made mainly to allow you to partition a case on one machine or network of machines and solve it on a different one. Thanks to the two separate partitioning schemes, you could use the parallel solver with a certain number of compute nodes to subdivide a grid into an arbitrary different number of partitions, suitable for a different parallel machine, save the case file, and then load it into the designated machine.

When you click Print Partitions in the serial solver, you will obtain information about the stored partition.

The output generated by the partitioning process includes information about the recursive subdivision and iterative optimization processes. This is followed by information about the final partitioned grid, including the partition ID, number of cells, number of faces, number of interface faces, ratio of interface faces to faces for each partition, number of neighboring partitions, and cell, face, interface, neighbor, mean cell, face ratio, and global face ratio variations. Global face ratio variations are the minimum and maximum values of the respective quantities in the present partitions. For example, in the sample output below, partitions 0 and 3 have the minimum number of interface faces (10), and partitions 1 and 2 have the maximum number of interface faces (19); hence the variation is 10-19.

Your aim is to achieve small values of Interface ratio variation and Global interface ratio while maintaining a balanced load ( Cell variation).

>> Partitions:
P   Cells I-Cells Cell Ratio  Faces I-Faces Face Ratio Neighbors
0     134      10      0.075    217      10      0.046         1
1     137      19      0.139    222      19      0.086         2
2     134      19      0.142    218      19      0.087         2
3     137      10      0.073    223      10      0.045         1
   ------
   Partition count             = 4
   Cell variation              = (134 - 137)
   Mean cell variation         = (  -1.1% -    1.1%)
   Intercell variation         = (10 - 19)
   Intercell ratio variation   = (   7.3% -   14.2%)
   Global intercell ratio      =   10.7%
   Face variation              = (217 - 223)
   Interface variation         = (10 - 19)
   Interface ratio variation   = (   4.5% -    8.7%)
   Global interface ratio      =    3.4%
   Neighbor variation          = (1 - 2)

Computing connected regions; type ^C to interrupt.
   Connected region count      = 4

Note that partition IDs correspond directly to compute node IDs when a case file is read into the parallel solver. When the number of partitions in a case file is larger than the number of compute nodes, but is evenly divisible by the number of compute nodes, then the distribution is such that partitions with IDs $0$ to $(M-1)$ are mapped onto compute node 0, partitions with IDs $M$ to $(2M-1)$ onto compute node 1, etc., where $M$ is equal to the ratio of the number of partitions to the number of compute nodes.



Examining Partitions Graphically


To further aid interpretation of the partition information, you can draw contours of the grid partitions, as illustrated in Figures  31.5.8- 31.5.12.

Display $\rightarrow$ Contours...

To display the active cell partition or the stored cell partition (which are described above), select Active Cell Partition or Stored Cell Partition in the Cell Info... category of the Contours Of drop-down list, and turn off the display of Node Values. (See Section  28.1.2 for information about displaying contours.)

figure   

If you have not already done so in the setup of your problem, you will need to perform a solution initialization in order to use the Contours panel.


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© Fluent Inc. 2006-09-20