A structured mesh is defined as a mesh where the inner nodes have the same number of elements around them. Another possible interpretation of a structured mesh is that it follows a given topological pattern that is reproduced in all the directions of space.
The size of the elements can be defined in a different way than for a non-structured mesh. In this case, the mesh can also be defined by the number of elements that are required on every line. This number must be the same for all lines that are opposite each other on each surface. When meshing volumes, this definition must be the same for opposite surfaces. If the number of elements is not the same, GiD will try to compatibilize them just before the meshing process. If a mesh size is assigned, GiD will assign automatically a number of elements to the lines in order to reach that element size approximately.
To create a structured mesh, choose Structured -> Volumes/Surfaces/Lines. After selecting escape, the or number of elements per line or the size is given (depending on the option chosen: 'Assign number of cells' or 'Assign size'). Later, lines can be selected and related lines (when dealing with surfaces or volumes) are added or deleted from the group. This process can be repeated as many times as necessary until all lines have a new value. Lines with no numbering given will have two elements over them. All non-selected lines will also have two elements by default.
In the case of surfaces, structured meshes can be four-sided, three-sided or centered structured.
By default, the generated elements in four-sided structured meshes are triangles. In this case, triangles can be symmetrical or non-symmetrical (see Preferences ). These surfaces can also have quadrilateral elements.
Three-sided structured meshes (relating to a three-sided surface) and centered structured meshes can only be meshed with triangles. Centered structured meshes can be centered either at a point on the surface itself, or at a point located on a particular surface boundary; for this, use the Set center option. If a center is not set, GiD will locate it automatically.
When selecting this kind of structured mesh (i.e. centered), the following window appears where you need to enter the number of concentric and perimetric divisions, as well as the two weights to concentrate elements in the center of the structure or in the boundary.
In the case of volumes, a structured mesh is usually six-sided,but it can also have other configurations if center structured mesh is used in some of its faces.
By default, the generated elements in six-sided structured volume meshes will be tetrahedra. In this case, they can be symmetrical or non-symmetrical (see Preferences ). These volumes can also have hexahedral or prism elements.
In the case of a centered structured or a three-sided surface in tops, the default element type is prism, but you can also choose to use tetrahedra.
In the case of a six-sided structured volume mesh, volumes must have six contour surfaces.
It is possible to mix some entities with structured meshes and others with unstructured ones.
To convert a structured entity to a unstructured one assign an unstructured mesh to it (see Unstructured). By selecting Reset mesh data all the meshing properties of the geometrical entities are reset.
To change the default element type see Element type.
Note 1: One NURBS surface can be structured with any number of contour lines but it must have a good shape form. This means that it must have four large angles and the other angles must be small (four corners). With this criterion, the shape will be topologically similar to one quadrilateral.
Note 2: When assigning structured divisions to a line or with difficult topology, GiD may need to reassign some number of divisions to make the structured mesh conformal; this will be done automatically. If it is impossible to create compatibility between surfaces, a message is displayed.
Note 3: It is possible to assign a number of structured divisions to the boundary line of a surface or volume, and then create an unstructured mesh for the surface/volume.