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

/*!

\page constructing_submeshes_page Constructing sub-meshes

By purpose, the sub-mesh is an object used to assign to a sub-shape
different meshing parameters than those assigned to the main shape.

Structurally, the sub-mesh is a mesh on a certain sub-shape, or a group of
sub-shapes, possibly generated using different meshing algorithms
and/or hypotheses than those used to generate the mesh on other
sub-shapes.

Creation of a sub-mesh allows to control individually meshing of a
certain sub-shape, thus to get a locally coarser or finer mesh, to get
elements of different types in the same mesh, etc.

A sub-shape to create a sub-mesh on should be retrieved from the main shape
in one of the following ways: <ul>
<li> In Geometry module, via <em>New Entity > Explode</em> menu.</li>
<li> In Geometry module, by creation of a group (<em>New Entity >
    Group > Create Group</em> menu).</li> 
<li> In Mesh module, by
  \ref subshape_by_mesh_elem "selecting a mesh element" generated on a
  sub-shape of interest. This way is accessible if the mesh is
  already computed.</li> 
<li> In Mesh module, by clicking <em>Publish Sub-shape</em> button in a
      dialog showing \ref meshing_failed_anchor "meshing errors".</li> 
</ul>

Internally, definition of meshing parameters to apply for
discretization of a certain sub-shape, for example an edge of a
compound of solids, starts from searching an algorithm, 1D as for the
edge. The following sub-shapes are sequentially checked for presence
of a sub-mesh where 1D algorithm is assigned:
<ul>
<li> the \b edge itself</li>
<li> <b>groups of edges</b> containing the edge, if any</li>
<li> \b wires sharing the edge</li>
<li> \b faces sharing the edge</li>
<li> <b>groups of faces</b> sharing the edge, if any</li>
<li> \b shells sharing the edge</li>
<li> \b solids sharing the edge</li>
<li> <b>groups of solids</b> sharing the edge, if any</li>
<li> the <b>main shape</b></li>
</ul>
(This sequence of sub-shapes defines the priority of sub-meshes. Thus more
local, i.e. assigned to sub-shape of lower dimension, algorithms and
hypotheses have higher priority during the search of hypotheses to
apply.)

As soon as a 1D algorithm is found, the search stops and the same
sequence of sub-shapes is checked to find the main and additional 1D
hypotheses, which can be taken into account by the found 1D algorithm. 

The multi-dimensional algorithms have a higher priority than
uni-dimensional ones if they are assigned to sub-meshes of the
same priority.

If meshing parameters are defined on sub-meshes of the same priority,
for example, different 1D hypotheses are assigned to two faces sharing
an edge, the hypothesis assigned to a sub-shape with a lower ID will
be used for meshing. You can \ref submesh_order_anchor "change" mutual
priority of such concurrent sub-meshes. 

\n Construction of a sub-mesh consists of:
<ul>
<li>Selecting a mesh which will encapsulate the sub-mesh</li>
<li>Selecting a sub-shape for meshing</li>
<li>Applying one or several
\ref about_hypo_page "hypotheses" and 
\ref basic_meshing_algos_page "meshing algorithms" which will be used
for discretization of this sub-shape.</li>
</ul>

<br><em>To construct a sub-mesh:</em>
\par
From the \b Mesh menu select <b>Create Sub-mesh</b> or click <em>"Create
Sum-mesh"</em> button in the toolbar.

<center>
  \image html image33.gif
  <em>"Create Sub-mesh" button</em>
</center>

\par
The following dialog box will appear:

\par
\image html createmesh-inv2.png

It allows to define the \b Name, the parent \b Mesh and the \b
Geometry (e.g. a face if the parent mesh has been built on box) of the
sub-mesh. You can define meshing algorithms and hypotheses in the same way as
in \ref constructing_meshes_page "Create mesh" dialog. 

Later you can change the applied hypotheses or their parameters in 
\ref editing_meshes_page "Edit mesh/sub-mesh" dialog. Mesh entities
generated using changed hypotheses are automatically removed.

\anchor subshape_by_mesh_elem
If the parent mesh is already computed, then you can define the
\b Geometry by picking mesh elements computed on a sub-shape of interest
in the 3D Viewer, i.e. you do not have to extract this sub-shape
in Geometry module beforehand. To start element selection, press \a
Selection button to the right of \b Geometry label. If this button is
already down, then click it to release and then click it again. The
following pop-up menu allowing to choose a way of geometry definition will
appear.

\image html choose_geom_selection_way.png

<b>Direct geometry selection</b> enables selecting the sub-shape in the Object
Browser.
<b>Find geometry by mesh element selection</b> activates the following dialog.

\image html find_geom_by_mesh_elem.png

In this dialog, <b> Element Type </b> defines a kind of element to pick in the
Viewer.
Instead of picking an element in the Viewer, you can type its
ID in <b> Element ID</b> field. 
<b> Geometry name </b> field allows defining a name of the sub-shape, 
with which the sub-shape will appear in the Object Browser (if not yet
there).

In the Object Browser the structure of the new sub-mesh will be
displayed as follows:

\image html image10.jpg

It contains:
<ul>
<li>a sub-mesh name (\a SubMeshFace1)
<li>a reference to the geometrical object on the basis of which the
  sub-mesh has been constructed (<em>Cylindrical Face_1</em>);</li>
<li><em>Applied hypotheses</em> folder containing the references to the
hypotheses assigned to the sub-mesh;</li>
<li><em>Applied algorithms</em> folder containing the references to the
algorithms assigned to the sub-mesh.</li>
</ul>

<br><b>See Also</b> a sample TUI Script of a 
\ref tui_construction_submesh "Construct Sub-mesh" operation.

*/