The Coarsen Grid option operates in an opposite way to that for Refine Grid. It decreases resolution of the grid. It operates by dividing the existing number of cells in the current grid with I, J directions independently. There are two types for coarsening grid:
Coarsen grid with a selected grid segment
accuracy of a model is increased when the orthogonality of a grid is optimized. A perfect grid would have all cells perpendicular to the boundary lines. This is very difficult to achieve and thus for most EFDC models an orthogonality of under 3o is recommended. The orthogonalization tool is used to reduce the orthogonal deviation of a grid.
To view the orthogonal deviation of a grid, LMC on the grid layer in the Layer Control
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then RMC on that grid layer to show RMC's options, select Show Properties/Orthogonal Deviation as shown in Figure 1. In addition, the orthogonal deviation of a grid can be viewed from the Grid menu as shown in Figure 2.
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Figure 1 Select View orthogonal deviation of a grid segment to highlightfrom RMC's option.
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Figure 2 Grid Block Coarsening formView orthogonal deviation of a grid from Grid menu.
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Figure 3 An example of coarsening grid with a selected grid segment.
Coarsen grid with a selected grid block
Orthogonal deviation of a grid.
There are two options for orthogonalizing grid: Othogonalize entire grid and Othogonalize grid block as described below:
Othogonalize entire grid
- Select the grid layer in the Layer Control to select grid the user want to refineSelect Select object by LMC
- From Grid menu, select Orthogonalize Grid or the user can click on the Orthogonalize grid button from the main toolbar
- LMC on a grid node then hold Shift key, LMC on the second node which is not on same grid segment in I or J direction, the grid block will be highlighted as shown in 1154482393.
- From Grid menu, select Coarsen Grid option (or select Coarsen Grid button from the main toolbar), the Grid Block Coarsening form will be popup as shown in 1154482393. The user needs to enter the Coarsening Factor then click OK button. 1154482393 show examples for grid coarsening with a selected grid block.
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- as shown in Figure 4. As a result, the entire grid will be orthogonalized immediately.
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Figure 3 Orthogonal deviation of a grid.
If a global operation is selected the entire grid will be orthogonalized immediately. If a local operation is selected, the user must define two grid nodes and the area of the grid limited by the two points will be orthogonalized. Orthogonalize 1D feature is similar to the Orthogonalize Local option but is only applicable for a 1D grid region. In case the feature is applied for an improper grid region, a warning message will appear.
The change in grid orthogonality before and after applying Orthogonalize Global are shown in Figure 2 and Figure 3. It may be seen in the first image that the average orthogonality is 20.3. In the second image, after CVLGrid has automatically reduced the orthogonalization, it is only 2.6.
The change in grid orthogonality before and after applying Orthogonalize Local are shown in Figure 4 and Figure 5.
The change in grid orthogonality before and after applying Orthogonalize 1D are shown in Figure 6 and Figure 7.
Othogonalize grid block
Figure 1 Select a grid segment to highlight.
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Figure 5 Grid Block Coarsening form.
Figure 6 An example of coarsening grid with a selected grid block.Anchor Figure 6 Figure 6