17.4.7 What is the relationship between vertices and nodes?

When you seed a model, Abaqus/CAE automatically places fully constrained seeds wherever vertices appear along the model's edges. Fully constrained seeds that appear at vertices always indicate that nodes will appear at those vertices. (Fully constrained seeds that appear at other locations along an edge of a region do not indicate the exact location of nodes; they indicate only the number of nodes along that edge.) Therefore, when you sketch a part, you should keep in mind that the location of vertices in the part influences the quality of the mesh that Abaqus/CAE can generate. (For information about altering vertex locations, see “Dragging Sketcher objects,” Section 20.17.1.)

For example, Figure 17–11 shows a sketch of a two-dimensional part.

Figure 17–11 Vertices on a two-dimensional part.

Note the locations of the nine vertices. These vertices were created by sketching several line segments along the top and bottom edges rather than one continuous line segment along each edge.

When that part or an instance of the part is seeded, square-shaped, fully constrained seeds appear at each vertex, as shown in Figure 17–12.

Figure 17–12 Fully constrained seeds appear at each vertex.

When the model is meshed, Abaqus/CAE always places nodes at the location of the fully constrained seeds that are located at vertices, as shown in Figure 17–13.

Figure 17–13 Nodes appear at the vertices.

Likewise, Figure 17–14 shows the sketch of two concentric circles that will be extruded to form a hollow cylinder.

Figure 17–14 Concentric circles with aligned vertices.

Note the location of the vertices, which the Sketcher creates at the locations you click to define the circles' perimeters.

When the cylinder is seeded, square-shaped, fully constrained seeds appear at each vertex, as shown in Figure 17–15.

Figure 17–15 Fully constrained seeds appear at each vertex.

When the model is meshed, nodes always appear at the location of the fully constrained seeds that are located at vertices, as shown in Figure 17–16.

Figure 17–16 Nodes appear at the vertices.

If you do not align the two vertices when you sketch the cylinder, you risk generating a distorted mesh. For example, the vertices of the two concentric circles are not aligned in Figure 17–17.

Figure 17–17 Concentric circles whose vertices are not aligned.

As a result, the mesh is slightly distorted on the right side, as shown in Figure 17–18.

Figure 17–18 A distorted mesh.