By default, mesh seeds prescribe only a target mesh density. Abaqus/CAE generally matches the mesh seeds exactly when you are using the free meshing technique to generate triangular- or tetrahedral-shaped elements. However, in other cases Abaqus/CAE may alter the element distribution so that it can successfully generate the mesh. If you want to prevent Abaqus/CAE from altering the element distribution, you can fix a specific number of elements along an edge by constraining the seeds along that edge. You can constrain only edge seeds, not part or instance seeds.
You can assign any one of the following three states to a group of seeds along an edge:
Unconstrained
This is the default setting. The number of elements along an edge can either increase or decrease so that the mesh can become denser or coarser than is specified by the seeds. Unconstrained seeds appear as open circles.
Partially constrained
The number of elements along an edge may be increased during mesh generation but cannot be decreased. This constraint allows the mesh to become denser than is specified by the seeds but no coarser. Partially constrained seeds appear as upward-pointing triangles.
Fully constrained
The number of elements specified by constrained seeds along an edge cannot be altered by the mesh generation process. When the seeds are fully constrained, the mesh generation will attempt to allow the location of the nodes to correspond exactly to the location of the seeds. However, an exact match between the seeds and the nodal positions is not guaranteed. Fully constrained seeds appear as squares.
Abaqus/CAE always creates a fully constrained seed at each geometric vertex of a region to indicate that a finite element node will be positioned at each vertex.
In many cases the mesh generator must redistribute elements (and deviate from the number and location of the seeds) to generate a mesh successfully. For the greatest likelihood of meshing success, leave seeds unconstrained or at least avoid fully constraining large numbers of seeds in a given part or part instance so that the mesh generator has as much freedom to redistribute seeds as possible.
For detailed instructions on constraining edge seeds, see the following sections :