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# Populating an Unstructured Block with Cells

Often times it is thought that once an unstructured block is assembled, the grid is complete. This is true for a structured block because Pointwise automatically connects the 2-dimensional structured lines of the domains and creates the 3-dimensional block.

However, in order to populate an unstructured block with cells, an extra step is required. When an unstructured block is initialized, Pointwise's tet solver fills the block with tetrahedra.

The example below contains a section of a hub-blade geometry with a wedge-shaped far field.

There are two mechanisms by which you can initialize the mesh in an unstructured blocK: the toolbar and the menu.

## Toolbar

The first way to initialize an unstructured block is very simple and uses a toolbar button.

1. Select the block.
2. Expand Blocks in the List panel. Notice that in the far right column, the number of Cells in the block is 0.

3. Click on Initialize on the toolbar.
4. Now notice in the List panel that you have cells in the block.

Once the block is populated with cells, you can bring the block into Pointwise's Examine comamnd and look at a number of diagnostic functions to make sure that the cells meet your criteria.

The second way that an unstructured block can be initialized is through the Grid, Solve menu.

1. Select the block.
2. Grid, Solve
3. Initialize

By using the latter method for initializing the block, several attributes can be set that could be applied during initialization. In the Attributes panel, notice that there are settings for Tetrahedra, Algorithm, and Pyramid. One of the most common settings used is under the Algorithm category called Boundary Decay. Boundary decay qualitatively controls how far into the grid's interior the boundary cell size affects the interior cell size. The boundary decay factor can fall in the range [0, 1] and the default setting is 0.5.

Notice in the pictures below how the cells grow at a slower rate if the boundary decay is increased and the block is reinitialized. Note that the pictures were taken in the block Examine command with a crinkle cut and Volume as the metric.

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