The Virtual Topology toolset is available only in the Mesh module. You can apply virtual topology to parts, or you can apply it to independent instances in the assembly. The Virtual Topology toolset allows you to do the following:
Combine faces or edges
You can select two or more faces or edges that ABAQUS/CAE will combine into a single virtual face or virtual edge. If you combine two faces, any edges between the faces are ignored when ABAQUS generates the mesh. Similarly, if you combine two edges, any vertices between the edges are ignored when the mesh is generated.
Ignore an edge or a vertex
You can select edges or vertices that ABAQUS/CAE will ignore. Ignoring an edge between two faces is the equivalent of combining the faces. Similarly, ignoring a vertex between two edges is the equivalent of combining the edges; however, you will find the combine tools useful when you have a large number of faces and edges to combine. Using ignore to create virtual topology has the same effect as using combine to create virtual topology—ignored edges or vertices are not considered when ABAQUS generates the mesh.
To preserve mesh quality, edges and faces to be combined should have shallow included angles that are close to 180°. The recommended angle is between 120° and 240°. You can use the angle method to choose only adjacent faces with shallow included angles. For more information, see “Using the angle method to select multiple objects,” Section 6.2.3. If the included angle at some edges or vertices lies outside this range, ABAQUS/CAE displays a warning and allows you to remove those edges or vertices from your selection. If you choose to retain the sharp edges, the resulting mesh may not lie on a smooth surface. Figure 49–4 illustrates a mesh on a virtual surface that is not smooth.
Figure 49–4 When you apply virtual topology to sharp edges and vertices, the resulting mesh can deviate substantially from the original surface.
You can ignore an edge only if that edge is shared by two adjacent faces or if it is embedded in a face. For example, you cannot ignore the free edge of a shell or an edge shared by three faces, as shown in Figure 49–5.
Similarly, you can ignore a vertex only if that vertex is shared by two adjacent edges or embedded in a face. For example, you cannot ignore the vertex at the free end of a wire or where a wire intersects with a face, as shown in Figure 49–6.ABAQUS/CAE does not support all of the meshing techniques on regions that contain virtual topology (combined faces or combined edges). Specifically, ABAQUS/CAE does not support the following:
Two-dimensional free meshing with quadrilateral or quadrilateral-dominated elements using the medial axis algorithm.
Three-dimensional swept meshing using the medial axis algorithm.
Two-dimensional structured meshing if the region to be meshed is not bounded by four corners.
Three-dimensional structured meshing if the region to be meshed is not bounded by six sides.
If you need to apply virtual topology to a dependent instance, you can create a copy of the original part and then create an independent instance of the copy. You can then replace the dependent instance with the new independent instance and apply virtual topology to the replacement. For more information, see “What is the difference between a dependent and an independent part instance?,” Section 13.3.2.
You may be able to make a part swept meshable by combining multiple faces on the target side into a single face; for more information, see “Swept meshing of three-dimensional solids,” Section 17.10.3. However, if you combine many faces into a single face, the meshing procedure may be slower and the resulting mesh may not be acceptable. If you try to combine a large number of faces into a single face, ABAQUS/CAE displays a warning and allows you to change your selection. ABAQUS/CAE calculates the number of faces being combined from the cumulative number of faces in your selection. For example, if you try to combine two faces each of which already contains five combined faces, the cumulative number of faces will be ten.
