4.2.2 Structured grids

Extrude { expression-list } { extrude-list layers }

Extrudes both the geometry and the mesh using a translation (see section Extrusions). The layers option determines how the mesh is extruded and has the following syntax:

layers: Layers { expression } | Layers { { expression-list }, { expression-list } } | Recombine; …

In the first Layers form, expression gives the number of elements to be created in the (single) layer. In the second form, the first expression-list defines how many elements should be created in each extruded layer, and the second expression-list gives the normalized height of each layer (the list should contain a sequence of n numbers 0 < h1 < h2 < … < hn <= 1). See ‘t3.geo’, for an example.

For line extrusions, the Recombine option will recombine triangles into quadrangles when possible. For surface extrusions, the Recombine option will recombine tetrahedra into prisms, hexahedra or pyramids.

Please note that, starting with Gmsh 2.0, region numbers cannot be specified explicitly anymore in Layers commands. Instead, as with all other geometry commands, you must use the automatically created entity identifier created by the extrusion command. For example, the following extrusion command will return the id of the new “top” surface in num[0] and the id of the new volume in num[1]:

num[] = Extrude {0,0,1} { Surface{1}; Layers{10}; };

Extrude { { expression-list }, { expression-list }, expression } { extrude-list layers }

Extrudes both the geometry and the mesh using a rotation (see section Extrusions). The layers option is defined as above.

Extrude { { expression-list }, { expression-list }, { expression-list }, expression } { extrude-list layers }

Extrudes both the geometry and the mesh using a combined translation and rotation (see section Extrusions). The layers option is defined as above.

Extrude { Surface { expression-list }; layers }

Extrudes a boundary layer along the normals of the specified surfaces.

Transfinite Line { expression-list } = expression < Using Progression | Bump expression >;

Selects the lines in expression-list to be meshed with the 1D transfinite algorithm. The expression on the right hand side gives the number of nodes that will be created on the line (this overrides any characteristic length prescription—see Characteristic lengths). The optional argument `Using Progression expression' instructs the transfinite algorithm to distribute the nodes following a geometric progression (Progression 2 meaning for example that each line element in the series will be twice as long as the preceding one). The optional argument `Using Bump expression' instructs the transfinite algorithm to distribute the nodes with a refinement at both ends of the line.

(A deprecated synonym for Progression is Power.)

Transfinite Surface { expression } = { expression-list } < Left | Right | Alternate > ;

Selects the surface expression to be meshed with the 2D transfinite algorithm. The expression-list should contain the identification numbers of three or four points on the boundary of the surface, defining the corners of the transfinite interpolation. If no identfication numbers are given, the transfinite algorithm will try to find the corners automatically. The optional argument specifies the way the triangles are oriented when the mesh is not recombined.

Transfinite Volume { expression } = { expression-list };

Selects a five- or six-face volume expression to be meshed with the 3D transfinite algorithm. The expression-list should contain the identification numbers of the six or eight points on the boundary of the volume that define the corners of the transfinite interpolation.