We are going to use the previous model named “ToMesh3.gid”, open this model.

Set in preferences

mesh type: Cartesian,

then in the cartesian branch set

mesher: Scan convert

The Shape to be meshed could be set to: From mesh or from geometry.

In case of 'From mesh' a auxiliary unstructured mesh of triangles will be generated and will be used as input for the cartesian mesher. This intermediate mesh will be deleted at the end, and in any moment will be visible for the user.

In case of 'From geometry' then the triangles of the 'render mesh' of the geometry will be used. This option could be faster if the render mesh was previously created. A drawback is that in GiD the render mesh is not conformal between entities, and has small gaps, but usually do not affect the cartesian mesher.

Usually both shapes will generate similar cartesian meshes.

Left initially all default values and generate a mesh (menu: Mesh->Generate mesh) with general size=2 units

Then automatically is calculated a grid fitted (approximately) to the bounding box of the shape, with a cell size of 2 units in all directions X Y Z, and a cartesian mesh of hexahedra is generated. Note that the green surfaces were not meshed.

Note: This mesher could only generate 3D meshes for volumes (hexahedra), or 2D meshes for surfaces, all in z=0. It cannot generate in 3D meshes of faces for surfaces

or edges for curves.

The 'lower-right' grid icon switch on/off the drawing of the underlying grid

In this case, the default Spacing was set to Variable, but the result looks very similar to a Uniform mesh (all cells seems equal-spaced in all directions)

Now assign to the volume on the left a specific size=0.8 in all directions with

Mesh->Assign cartesian size->Volumes

and select the volume number 3 (on the right of the images) finishing with a double <Esc>

and generate again a mesh with general size=2.0. You will obtain a non-uniform mesh like these:

In case of Variable spacing, the Minimum size try to avoid a too small edge size, and the Size ratio try to avoid big differences of sixes between two consecutive edges.

The grid is automatically defined when generating the mesh (based on the current geometry and mesh sizes), but the user could set its own definition:

In preferences check User defined, press Apply to accept it, and then the Grid window... button become enable, press it and a window like this will appear, filled with the current values:

The window allow to modify the location and size of the box, set the number of divisions and set the values of the ticks editing the values of the table.

The 'Auto calculate' button allow to fill automatically all fields, based on the geometry and mesh sizes (similar to the case of generating a mesh with this size)

Changing only the (lower left) corner, the box size of the amount of divisions and pressing 'Apply' will try to set the data of the row, maintaining the other data.

E.g. if we modify the Num grid Z (third value) from 24 to 10 ticks and press the Apply button of its row then the Z grid values of the table change (to have an increasing array of 10 values normalized from 0.0 to 1.0)

Then if we generate again a mesh with general size=2.0 we obtain this mesh: