smesh/doc/salome/gui/SMESH/input/prism_3d_algo.doc

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\page prism_3d_algo_page 3D extrusion meshing algorithm

3D extrusion algorithm can be used for meshing prisms, i.e. 3D shapes
defined by two opposing faces having the same number of vertices and
edges. These two faces should be connected by quadrangle "side" faces.

The prism is allowed to have sides composed of several faces. (A prism
side is a row of faces (or one face) connecting corresponding edges of
the top and base faces). But there is a limitation that a prism 
side is allowed to be split only vertically as indicated in the
picture below. 

\image html prism_ok_ko.png
In this picture, the left prism is suitable for meshing with 3D
extrusion algorithm; it has six sides two of which are split
vertically. And the right prism can't be meshed with this
algorithm because one of the prism sides is split horizontally (a
splitting edge is highlighted).

The algorithm can propagate 2D mesh not only between horizontal
(i.e. base and top) faces of one prism but also between faces of prisms
organized in a stack and between stacks sharing prism sides.

\image html prism_stack.png
In this picture, four neighboring prism stacks, each comprising two prisms,
are shown. The shown sub-mesh is used by the algorithm to mesh
all the eight prisms in the stacks.

To use <em>3D extrusion</em> algorithm you need to assign algorithms
and hypotheses of lower dimension as follows.

\b Global algorithms and hypotheses to be chosen at 
\ref create_mesh_anchor "Creation of a mesh object" are:
<ul>
<li> 1D algorithm and hypothesis that will be applied for meshing
(logically) vertical edges of the prism (these edges connect the top and
base faces of prism).</li>
</ul>

\b Local algorithms and hypotheses to be chosen at 
\ref constructing_submeshes_page "Constructing sub-meshes" are:
<ul>
<li> 1D and 2D algorithms and hypotheses that will be applied for
meshing the top and base prism faces. These faces can be meshed
with any type of 2D elements: quadrangles, triangles, polygons or
their mix. It's enough to define a sub-mesh on either top or base face
only.</li>
<li> Optionally you can define an 1D sub-mesh on some vertical edges
of stacked prisms, which will override the global 1D hypothesis mentioned
above. In the above picture, the vertical division is not equidistant
on all the length because of a "Number Of Segments" hypothesis with
Scale Factor=3 assigned to one of edges between the shifted stacks. 
</li></ul>

\image html image157.gif "Prism with 3D extrusion meshing"

As you can see, the <em>3D extrusion</em> algorithm permits to build
in the same 3D mesh such elements as hexahedrons, prisms and
polyhedrons.

\sa a sample TUI Script of
\ref tui_prism_3d_algo "Use 3D extrusion meshing algorithm".

*/