Difference between revisions of "OpenFOAM/C3/Creating-a-sphere-in-GMSH/English"

• Create a circular arc
• Create ruled surfaces
• and basic manipulations using the file with extension .geo

• Ubuntu Linux Operating system 14.04
• GMSH version 2.8.5

If not, refer to the GMSH spoken tutorials in the OpenFOAM series on this website.

• The origin of the sphere is at (0,0,0).
• And the other points of the sphere are as displayed.

In terminal type gmsh sphere1.geo and press enter

To open the terminal, press Ctrl+Alt+T keys.

Now type gmsh sphere1.geo and press Enter

GMSH is opened.

To create the points of the sphere, kindly refer to the tutorial mentioned earlier.

In GMSH, a circular arc is strictly created less than Pi.

Then, select this point here as the center point. Please note: This is the point with the coordinates (0,0,0).

And finally, I will select a point on the top-side as the end point of the arc.

Remember to keep the same centre point for all the arcs.

and then selecting respective edges

Select the bounding edges for the surface, as demonstrated here.

Notice that the selected edges are now in red colour.

You can see that the surface has been created.

This is indicated by the dotted line, as shown here.

Locate and open the file sphere1.geo using gedit Text Editor.

• Geometrical entity, identification number inside the parenthesis
• which equals to an expression.

Simultaneously highlighting the syntax

• Point, identification number inside parenthesis, which is usually the next integer starting from 1
• equals to X,Y,Z coordinates and the value of mesh element size inside braces.

The size of the mesh elements will then be computed by linearly interpolating these values on the initial mesh.

This is for specifying the value of mesh element size of the sphere.

and typing Mesh.CharacteristicLengthFromCurvature = 0.05;

For this purpose, we shall use the line,

Mesh.CharacteristicLengthFromCurvature = 0.05;

will adapt the mesh with respect to the curvature of the geometrical entities.

For this, at the end of the file, type

• Surface Loop followed by its identity
• which is the next integer inside parenthesis
• which equals the identities of all the surfaces of the sphere within braces.

Here, the identities are 14, 16, 18, 20, 22, 24, 26 and 28.

Select Physical Groups >> Add >> Surface option --> select all the surfaces --> Press E

In the left-hand-side menu, click on Physical Groups, then Add, and then Surface.

Select all the surfaces of the sphere.

Press E on the keyboard to execute this selection.

Right at the bottom, notice that a new line of code has been added.

This will help us to easily identify the boundaries of the sphere while post processing or otherwise.

• Create curved lines and surfaces
• Create a sphere and
• and basic manipulations using the file with extension .geo

Create a sphere with a larger radius.

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