17.8.1 What is structured meshing?

The structured meshing technique generates structured meshes using simple predefined mesh topologies. ABAQUS/CAE transforms the mesh of a regularly shaped region, such as a square or a cube, onto the geometry of the region you want to mesh. For example, Figure 17–41 illustrates how simple mesh patterns for triangles, squares, and pentagons are applied to more complex shapes.

Figure 17–41 Two-dimensional structured mesh patterns.

You can apply the structured meshing technique to regions that have been assigned the Quad or Quad-dominated element shape option for simple two-dimensional regions (planar or curved) or the Hex or Hex-dominated element shape option for simple three-dimensional regions. For more information about assigning element shapes to a region, see “Choosing an element shape,” Section 17.15.2.

When you mesh a region using any meshing technique, the nodes on the boundary of the mesh are always located on the boundary of the geometric region. However, when ABAQUS/CAE creates a mesh using the structured meshing technique, it is possible for nodes in the interior of the mesh to fall outside the region's geometry, which results in a distorted, invalid mesh. This problem typically occurs near concave boundaries.

For example, the region in Figure 17–42 has five sides; therefore, when ABAQUS/CAE meshes this region using the structured meshing technique, it applies the mesh pattern for a regular pentagon to the region.

Figure 17–42 The mesh pattern for a regular pentagon is applied to the region.

However, if you seed the region so that the number of elements is reduced, as shown in Figure 17–43, a distorted mesh results due to the concavity at the highly curved edge. Nodes from the interior of the mesh pattern (indicated by closed circles in Figure 17–44) fall outside the region's geometry, while nodes on the boundary of the mesh (indicated by open circles in Figure 17–44) remain on the boundary of the region's geometry.

Figure 17–43 Seeds prescribing a coarser mesh.

Figure 17–44 Nodes from the interior of the mesh fall outside the region's geometry.

When interior nodes fall outside the region's geometry, you can try the following techniques to improve the mesh:

Change the mesh seeds and remesh. For example, the number of elements along the highly curved edge in Figure 17–42 is greater than in Figure 17–44.
Partition the part instance into smaller, more regularly shaped regions. For example, the model was partitioned into three regions in Figure 17–45.
Figure 17–45 Partition the region.
Select a different meshing technique. This option is most useful for two-dimensional regions, where you can switch from structured meshing to free meshing and still retain quadrilateral elements in the mesh. (Three-dimensional free meshing is limited to tetrahedral elements. For more information, see “Free meshing,” Section 17.9.) Figure 17–46 shows the region meshed using the free meshing technique.
Figure 17–46 Mesh the region using the free meshing technique.
The mesh in Figure 17–46 is not symmetric, which is typical of free meshes.