Structured |
Menu: Mesh->Structured
A structured mesh is defined as a mesh where all the nodes have the same number of elements around them.
The size of the elements is defined in a different way than for a non-structured mesh. In this case, the mesh is not defined by the size but 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.
To create a structured mesh, choose Structured -> Volumes/Surfaces/Lines. After selecting escape, the number of elements per line is given. 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.
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By default, the generated elements in four-sided structured meshes are quadrilaterals, but they can be triangles. In this case, triangles can be symmetrical or non-symmetrical (see Preferences -> Meshing).
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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.
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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.
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In the case of volumes, a structured mesh is usually six-sided,but it can also be five-sided.
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By default, the generated elements in six-sided structured volume meshes will be hexahedra, but they can be tetrahedra or prisms. In the case of tetrahedra, they can be symmetrical or non-symmetrical (see Preferences -> Meshing).
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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 non-structured one, select reset (see Reset mesh data ) or assign an unstructured mesh to it (see Unstructured ).
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.
Element concentration |
Menu: Mesh->Structured->Lines
By default, all partitions in one structured line have the same approximate length. This command lets you select one line, which will be shown in the graphical window with an arrow indicating its direction. You then have to enter a positive or negative weight. If the weight is positive the elements will be concentrated towards the extremities of the line; if negative, the elements will be repelled.
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As the magnitude of the weight increases, the difference between element sizes will be greater.