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

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\page adding_quadratic_elements_page Adding Quadratic Elements

\n MESH module allows you to work with <b>Quadratic Elements</b>.

Quadratic elements are defined by the same corner nodes as the
corresponding linear ones, but in addition they have \a midside nodes
located between the corner nodes on element sides.

If a quadratic 2D element has an additional node at the
element center, it is a bi-quadratic element (both TRIA7 and
QUAD9 elements are supported). If a quadratic hexahedral element has 7
additional nodes: at the element center and at the center of each
side, it is a tri-quadratic element (or HEXA27).

The convention of nodal connectivity of elements used in SALOME is
the MED library convention. You can consult the description of nodal
connectivity of elements in the documentation on MED library or 
<a href="http://www.code-aster.org/outils/med/html/connectivites.html">
  here </a>.

There are several ways to create quadratic elements in your mesh:
- manually (this way is described below);
- use \ref quadratic_mesh_anchor "Quadratic Mesh" hypothesis to
generate a quadratic mesh on your geometry;
- convert an existing linear mesh to a quadratic one 
(see \ref convert_to_from_quadratic_mesh_page).

<em>To add a quadratic element to your mesh:</em>
<ol>
<li>Select your mesh in the Object Browser or in the 3D viewer.</li>

<li>From the \b Modification menu choose the \b Add item and select
one of the following:

\image html image152.png

\note All dialogs for quadratic element adding to the mesh
provide the possibility to automatically add an element
to the specified group or to create the group anew using
<b>Add to group</b> box, that allows choosing an existing group for
the created node or element or giving the name to a new group. By
default, the <b>Add to group</b> check box is switched off. If the user
swiches this check box on, the combo box listing all currently
existing groups of the corresponding type becomes available. By
default, no group is selected. In this case, when the user presses
<b>Apply</b> or <b>Apply & Close</b> button, the warning message box
informs the user about the necessity to input a new group name. The
combo box lists both \ref standalone_group "standalone groups"
and \ref group_on_geom "groups on geometry". If the user chooses a
group on geometry, he is warned and proposed to
\ref convert_to_standalone "convert this group to standalone".
If the user rejects conversion operation, it is cancelled and
a new quadratic element is not created.


To create any <b>Quadratic Element</b> specify the nodes which will form your
element by selecting them in the 3D viewer with pressed Shift
button. Their numbers will appear in the dialog box as <b>Corner Nodes</b>
(alternatively you can just input numbers in this field without
selection). The edges formed by the corner nodes will appear in the
table. To define the middle nodes for each edge, double-click on the
respective field and input the number of the node (or pick the node in
the viewer). For bi-quadratic and tri-quadratic elements, your also
need to specify central nodes.
As soon as all needed nodes are specified, a preview of a new
quadratic element will be displayed in the 3D viewer. Then
you will be able to click \b Apply or <b>Apply and Close</b> button to
add the element to the mesh.

\image html aqt.png

\b Reverse button reverses the element.
</li>
</ol>



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