Unstructured mesh Properties

Changing the unstructured mesh parameters
Generating the unstructured mesh

The unstructured mesh of CrysMAS consisting of irregular triangles inside each region. The unstructured mesh is required for each region there the computation is to be done. The only exception is the surface to surface radiative heat transfer in vacuum where the heat conduction is not considered. Even if the structured mesh is generated in any region, as a condition for its generation is the availability of the unstructured mesh in this region. First the unstructured mesh is generated and then the structured mesh is created which overlaps the unstructured one in the second layer.

The quality of the simulation result depends on the appropriateness of the mesh. Modifying the mesh parameters can considerably improve the computation result.

Starting from these values CrysMAS will compute the unstructured mesh:

mesh parameter

Default value

Description

Regions properties: Edge length (m)

0.1

Desired edge length inside a region.

Regions properties: Fit slope

0.3

Maximum allowed gradient of the edge length inside a region. The fit slope defines how fast the mesh size will increase towards the middle of the region. Small fit slope means small meshes.

Sometimes this value should be reduced to about 0.1 if the triangles with very small angles are created and as a consequence the node is connected with a large number of triangles.

Lines properties: Edge length (m)

0.1

Desired edge length along lines.

The influence of the fit slope is illustrated in Influence of fit slope on unstructured mesh. The parameters for edge lengths of lines and regions are identical in both cases 0.01 (vertical lines) and region edge length = 0.05.

Influence of fit slope on unstructured mesh 
  • A: Fit slope = 0.3

  • B: Fit slope = 0.1

  • A+B: Line edge length = 0.05 (horizontal lines), 0.01 (vertical lines)

  • A+B: Region edge length = 0.05

Figure 6. Influence of fit slope on unstructured mesh

If your furnace has many small regions, the mesh may become unnecessarily fine in certain regions. To reduce the computing time, you select a line and click on the respect edge length button. The program is forced to respect the edge length of the line. The effect is illustrated in Respect edge length active for highlighted line and in Respect edge length active for highlighted line.

Another application of the respect edge length item is for reduction of the view factors number by treatment of the surface to surface radiation. The consumed memory and computation time depends quadratically on the number of the radiating tile in the same radiating cavity. The radiating tile is defined by the edge of the triangle at the radiating surface. The respect edge length forces the program to preserve the larger length of radiating edges and reduce their number.

Respect edge length inactive 

Figure 7. Respect edge length inactive

Respect edge length active for highlighted line 

Figure 8. Respect edge length active for highlighted line