\ref constructing_submeshes_page "Construction of sub-meshes" are:
<ul>
<li> 1D and 2D algorithms and hypotheses that will be applied for
- meshing the top and the base prism faces. These faces can be meshed
+ meshing the top and the base prism
+ \ref submesh_shape_section "faces". These faces can be meshed
with any type of 2D elements: quadrangles, triangles, polygons or
- their mix. It is enough to define a sub-mesh on either the top or the base
- face. In the sample picture above, "NETGEN_1D2D" algorithm meshes
- "bottom disk" face with triangles. (1D algorithm is not
- assigned as "NETGEN_1D2D" does not require divided edges to create a 2D mesh.)
+ their mix. It is enough to define a sub-mesh on either the top or
+ the base face. In the sample picture above, "NETGEN_1D2D"
+ algorithm meshes "bottom disk" face with triangles. (1D algorithm
+ is not assigned as "NETGEN_1D2D" does not require divided edges to
+ create a 2D mesh.)
</li>
- <li> Optionally you can define a 1D sub-mesh on some vertical edges
- of stacked prisms, which will override the global 1D hypothesis mentioned
- above. In the <b>Prism stacks</b> picture, the
- vertical division is not equidistant on the whole length because
- a "Number Of Segments" hypothesis with Scale Factor=3 is assigned to
- the highlighted edge.
+ <li> Optionally you can define a 1D sub-mesh on some vertical
+ \ref submesh_shape_section "edges" of stacked prisms, which will
+ override the global 1D hypothesis mentioned above. In the <b>Prism
+ stacks</b> picture, the vertical division is not equidistant on
+ the whole length because a "Number Of Segments" hypothesis with
+ Scale Factor=3 is assigned to the highlighted edge.
</li></ul>
+If <em>3D extrusion</em> algorithm is assigned to a sub-mesh in a mesh
+with multiple sub-meshes, the described above approach may not work as
+expected. For example the bottom face may be meshed by other algorithm
+before <em>3D extrusion</em> have a chance to project a mesh from the
+base face. This thing can happen with vertical edges as well. All
+these can lead to either a meshing failure or to an incorrect meshing.
+
+In such a case, it's necessary to explicitly define algorithms
+that <em>3D extrusion</em> implicitly applies in a simple case:
+- assign \ref projection_1D2D algorithm to the top face and
+- assign a 1D algorithm to a group of all vertical edges.
+
\image html image157.gif "Prism with 3D extrusion meshing. Vertical division is different on neighbor edges because several local 1D hypotheses are assigned."
\sa a sample TUI Script of
