Menu: Mesh->Mesh criteria
GiD provides four different criteria to generate the mesh. The Default option set all the other ones to the default value.
Mesh Menu>Mesh criteria>Default
To set all default mesh criteria to the selected entities
Mesh Menu>Mesh criteria>Mesh NoMesh
The Mesh option lets you choose the entities to be meshed, while the No Mesh option does the opposite. By default, the No Mesh option is set.
Default mesh set this flag as default, not explictly set to Mesh or No mesh.
It has to be considered that the mesh of an entity can be generated by GiD in order to generate the mesh of a higher level entity (for instance, to generate the mesh of a volume, the mesh of its surfaces is generated first). In this cases, the mesh of the lower entity (in the example, the surface one), is deleted automatically after generating the higher level one.
Some example:
- If the model has one volume, and nothing is assigned (No Mesh option is set by default), after generating the mesh the user will get the tetrahedra mesh (or hexahedra), but not the surfaces meshes (triangles or quadrilateral). In order to get the surfaces meshes (which are the triangles skin of the tetrahedra), the user may set 'Mesh' option to the surfaces previously to generating the mesh.
- If a surface does not belong to any volume, its mesh will always appear after mesh generation, unless 'No Mesh' option has been assigned to it.
- Analogously, the mesh of a line will not appear if it belongs to a surface, and the 'Mesh' option has not been set explicitly to the line.
Mesh Menu>Mesh criteria>Skip
The Skip option forces GiD to skip a geometrical entity when meshing (so the entity will not have mesh), while the No Skip option forces GiD not to skip the geometrical entity (so the entity will have mesh) when the 'Skip entities automatically' option is set (see Preferences ). By default, any entity is skipped.
The 'Automatic skip' option lets GiD decide if the geometrical entity should be skipped or not skipped accordingly with the parameters in the preferences window (allow or not to 'join' entities in different layers, and the tangency between entities: those entities that are tangent enough will be skipped when meshing.
Entities with some group, condition or material assigned are never skipped. Entities belonging to different groups are never meshed together.
Using the 'Skip by...' option user can apply some of the useful following criteria to select the entities to be skipped, not to be skipped or to be skipped automatically.
- Tangency limit angle: This criteria select the lines between surfaces in which angles between normals in the surfaces are lower than the value.
- Take care layers: If this is set, lines between surfaces which are in different layers won't be selected.
- Take care curvatures: This ratio means the diference between curvatures in the surfaces that share a line. If the ratio between the curvatures exceeds this value, the shared line is not considered to be selected. As an example, if this value is 0.1 (10%), the only lines which will be selected will be the ones in which the two surfaces that share the line have almost the same curvature (only a 10% of difference is accepted ). As this number increases, probably more lines will be selected.
- Lines of surfaces smaller than: All the lines of surfaces which have some line smaller than this value will be selected.
Window to assign skip criteria to lines.
- By clicking Select by criteria all the selected criteria are used to select the lines.
- Modify selection allows the user to modify manually the selection made.
- When Apply is clicked the marked option (Skip, No skip or Automatic skip) is aplied to the selected lines.
Mesh Menu>Mesh criteria>Force points to
The 'Force points to' option forces the selected points to belong to the surface or volume mesh, even though they do not necessarily belong to the surface or the volume topologically. By default no point is forced to any surface or volume mesh.
Model of a surface and a line, with no topological relationship. Surface and line are isolated.
Mesh of the model assigning to one point of the isolated line the 'Force' option to the surface. It can be seen that the final surface mesh contains the node corresponding to the point set.
Mesh Menu>Mesh criteria>Duplicate
Use the Duplicate option when you want to create a discontinuity in the mesh in a particular place by duplicating nodes. This is interesting, for example, when dealing with very thin shapes where it is difficult to represent the domain with two overlapped surfaces, and it is easier to have a single surface marked with this meshing option (like sails embedded in a volume, material cracks, etc.).
Marked lines and the deformated mesh after an structural analysis
It is possible to mark lines embedded in a 2D domain, or surfaces in the case of 3D domains.