4.2.1 Grid Module

  Grid generation and grid handling play key roles for the successful numerical simulation of the diffusion problem. The grid module should be able to handle structured (ortho-product) as well as unstructured grids.

Initially, the grid module reads the input grid information, if specified by the user, or generates a new grid, if none specified. Thereby the simulation topology and the grid type is evaluated and if both are matching the incoming grid is read into the internal structures. The initial grid must be a Delaunay mesh (cf. 4.1.1) due to the box integration method. If no initial grid is specified by the user, we use built-in grid generators to obtain the initial grid including mesh refinement to resolve the input quantities by the generated grid.

Then this initial grid is partitioned into segment and boundary grids as shown in Figure 4.2-3 to apply different model on each partial grid. Thereby the global point-list and the global element-list of the overall grid is stored in the Main-array. Now, the ref-array of each partial grid contains the grid points which belong to them.

The geometry information which is obtained from each segment grid can be classified as follows:

Grid node information:

 

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Grid node coordinates

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Grid node number boxnum

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Box volume related to grid node vol

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Distance from grid node to nearest material interface idist

Grid line information:

 

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Grid line coordinates

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Grid line number connum

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Grid line length from to (dist)

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Ratio of flux area to line length (flux). This information is used for the discretization of the diffusion current models.

  
Figure 4.2-3: Internal representation of segment and boundary grids in PROMIS-NT obtained from the input or generated overall grid.

If the segment grid information is attained, the boundary grid information structure has to be extracted from the overall grid and the previously obtained segment grids. The boundary grids are used to connect the segment grids at the material interface and for the setup of material interface models (see Section 4.4).

The geometry information acquired from the boundary grids is related to the boundary point pair int1 - int2:

Boundary point pair information:

 

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Boundary point pair coordinates

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Number of boundary point pairs intnum

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Distance to next point pair along the boundary (next)

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Distance to previous point pair along the boundary (prev)

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Interface area related to boundary discretization box (area)

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For some sophisticated boundary conditions (cf.4.1-21) the distance to next inner segment points on either side of the boundary is obtained (inner1,inner2)

Due to the segment and boundary grids it is possible for the following discretization routines to be independent from any structural grid information. Complicated grid neighboring information is maintained in several auxiliary arrays.