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# Mesh generation and data (boundary conditions, materials, etc)

Questions about mesh generation of any element types.

#### Is it possible to extract information about boundary edges and faces?

If you need the boundary edges or the faces of surface elements or volume elements you can do it in several ways:

- Give a mesh criteria of type "mesh" to the lines or surfaces that are the boundaries of your surface or body. After generation, you will have linear or triangle or quadrilateral elements apart from the main ones.
- Assign a condition "over face elems" to the line or surface that is the boundary. You can then list the element faces with this condition in the '.bas' file with the order *globalnodes or *localnodes.

#### Do you have any plans to allow geometric information to be incorporated into the customization files, so that mesh optimisation can be coupled to the solver?

There is now one feature in GiD (field #FUNC# in conditions definition) that allows to write the number of every geometric entity for every element in the mesh. Then, you can get the geometry with any command like `write ASCII` or whit the order `*tcl` inside the bas file, and you have the relationship.

To do remeshing, it is available to read a background mesh file (of triangles or tetrahedras), containing the description of the new mesh sizes desired.

To do optimisation of shapes is a more difficult problem. We are thinking on several ways to do it. One of them would be that the solver gave, as output, one description of the desired movement of the mesh and then, apply this movement to the geometry. We would appreciate any feedback that you can give to us.

#### Can GiD generate 10-noded tetrehedra?

The current version supports 10-noded tetrahedra.

#### Can GiD mesh complex structured volumes?

Structured meshes can be done with complex surfaces but not with complex volumes (they can only have 6 faces or surfaces). Probably, in the near future we will add the same capabilities to the volumes that we have now for the surfaces.

The most powerful part of GiD for CFD analysis is the tetrahedra mesh generation. It permits to concentrate elements near the object of study (ship, plane or any other), and let them grow fast or slow.

#### What methods are used to define element sizes?

- The easiest meshing is defining a global size and small elements for features are automatically calculated.
- User can define a cordal error (geometry - mesh error)
- User can manually define sizes over geometrical entities. This sizes can be automatically corrected to allow meshing checking Preferences->Meshing->Automatic correct sizes.
- The transition between sizes is controlled by a factor that the user can define (Preferences->Meshing->Size transition).

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