Creation and meshing of a volume

We will now present a study of entities of volume. To illustrate this, a cube and a volume mesh will be generated.

Without leaving the project, save the work done up to now by choosing Files->Save, and return to the geometry last created by choosing View->Mode→Geometry.

In order to create a volume from the existing geometry, firstly we must create a point that will define the height of the cube. This will be point 5 with coordinates (0,0,10), superimposed on point 1. To view the new point, we must rotate the figure by selecting from the Mouse Menu: Rotate→Trackball.

This option is also available in the toolbar:

Rotate the figure until the following position is achieved and press ESC:

Next, we will create the upper face of the cube by copying from point 1 to point 5 the surface created previously. To do this, select the copy command, Utilities→Copy.

In the Copy window, we define the translation vector with the first and second points, in this case (0,0,0) and (0,0,10). Option Do extrude surfaces must be selected; this option allows us to create the lateral surfaces of the cube. Fill in the rest of variables as shown in the following image.

 NOTE: In the Copy and Move windows, the button may be used to select existing points with the mouse, or alternatively enter its number in the entry field.

 NOTE: If we look at the Copy Window, we can see an option called Collapse. By activating this option, point 6 will be merged with point 5 when the entities are copied. By labeling the entities we could verify that only one point has been created.

If the user does not choose option Collapse, when the entities are copied (in this case from point 1 to point 5) GiD would create a new point (point 6) with the same coordinates as point 5.
To finish the copy command click Select, select the surface and then press ESC. We obtain the following surfaces:

Now, we can generate the volume delimited by these surfaces. To create the volume, simply select the command Geometry->Create->Volume->By contour . This option is also available in the toolbar:

Select all the surfaces and press ESC twice. GiD automatically generates the volume of the cube. The volume viewed on the screen is represented by a cube with an interior color of sky blue.

Before proceeding with the mesh generation of the volume, we should eliminate the information of the structured mesh created previously for the surface. Do this by selecting Mesh->Reset mesh data, and the following dialog box will appear on the screen:

In which the user is asked to confirm the erasure of the mesh information.

 NOTE: Another valid option would be to assign a size of 0 to all entities. This would eliminate all the previous size information as well as the information for the mesh, and the default options would become active.
Next, generate the mesh of the volume by choosing Mesh->Generate mesh. Another Auxiliary Window appears into which the size of the volumetric element must be entered. In this example, the value is 1.

The mesh generated above is composed of tetrahedral elements of four nodes, but GiD also permits the use of hexahedral, eight-nodded structured elements.
We will generate a structured mesh of the volume of the cube. This is done by selecting Mesh->Structured->Volumes->Assign number of divisions to volume lines.

Now select the volume to mesh and press ESC.
Then a window appears where the number of subdivisions for the volume limit lines should be entered.
Enter 10 and click Assign and select one of the lines in X axis, the parallel lines are also selected. Press ESC.
The same window appears again, click Assign and select one of the lines in Y axis, the parallel ones are also selected. Press ESC.
Again click Assign and select one of the lines in Z axis, the parallel ones are also selected. Press ESC.
Click Close when the window appears again.
Then, create again the mesh.

 NOTE: GiD only allows the generation of structured meshes of 6-sided volumes.

With this example, the user has been introduced to the basic tools for the creation of geometric entities and mesh generation.