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

/*!

\page additional_hypo_page Additional Hypotheses

\n <b>Additional Hypotheses</b> can be applied as a supplement to the
main hypotheses, introducing additional concepts to mesh creation.

An <b>Additional Hypothesis</b> can be defined in the same way as any
main hypothesis in \ref create_mesh_anchor "Create Mesh" or 
\ref constructing_submeshes_page "Create Sub-Mesh" dialog.

The following additional hypothesis are available:
<ul> 
<li>\ref propagation_anchor "Propagation of 1D Hypothesis on opposite edges" 
  and \ref propagofdistribution_anchor "Propagation of Node Distribution on Opposite Edges"
  hypotheses are useful for creation of quadrangle and hexahedral
  meshes.</li>
<li>\ref viscous_layers_anchor "Viscous Layers" and 
  \ref viscous_layers_anchor "Viscous Layers 2D"
  hypotheses allow creation of layers of highly stretched
  elements near mesh boundary, which is beneficial for high quality
  viscous computations.</li>
<li>\ref quadratic_mesh_anchor "Quadratic Mesh" hypothesis allows
  generation of second order meshes.</li> 
<li>\ref quadrangle_preference_anchor "Quadrangle Preference"
  enables generation of quadrangles.</li>
</ul>


\anchor propagation_anchor
<h2>Propagation of 1D Hypothesis on opposite edges</h2>

<b>Propagation of 1D Hypothesis on opposite edges</b> allows to mesh
opposite sides of a quadrangle face, and of other adjacent quadrangles,
using the same hypothesis assigned to one edge only.<br>
Thus you define a sub-mesh on an edge where you define 1D meshing
parameters and a \b Propagation hypothesis. These local meshing
parameters will be propagated via opposite sides of quadrangles to the
whole geometry, or till an edge with other local meshing parameters.

This hypothesis can be taken into account by 
\ref a1d_algos_anchor "Wire Discretization" and 
\ref a1d_algos_anchor "Composite Side Discretization" algorithms.

<b>See Also</b> a sample TUI Script of a 
\ref tui_propagation "Propagation hypothesis" operation

\anchor propagofdistribution_anchor
<h2>Propagation of Node Distribution on Opposite Edges</h2>

<b>Propagation of Node Distribution on Opposite Edges</b> allows to propagate
distribution of nodes onto an opposite edge. If a local hypothesis and
propagation are defined on an edge of a quadrangular face, the
opposite edge will have the same number of nodes and the same
relations between segment lengths, unless another hypothesis
has been locally defined on the opposite edge.
 
This hypothesis can be taken into account by 
\ref a1d_algos_anchor "Wire Discretization" and 
\ref a1d_algos_anchor "Composite Side Discretization" algorithms.

<b>See Also</b> a sample TUI Script of a 
\ref tui_propagation "Propagation hypothesis" operation

\anchor viscous_layers_anchor
<h2>Viscous Layers and Viscous Layers 2D</h2>

<b>Viscous Layers</b> and <b>Viscous Layers 2D </b> additional
hypotheses can be used by several 3D algorithms, for example
Hexahedron(i,j,k), or 2D algorithms, for example Triangle
(MEFISTO), correspondingly. These hypotheses allow creation of layers
of highly stretched elements, prisms in 3D and quadrilaterals in 2D,
near mesh boundary, which is beneficial for high quality viscous
computations.

\image html viscous_layers_hyp.png

\image html viscous_layers_2d_hyp.png

<ul>
<li><b>Name</b> - allows to define the name of the hypothesis.</li>
<li><b>Total thickness</b> - gives the total thickness of element layers.</li>
<li><b>Number of layers</b> - defines the number of element layers.</li>
<li><b>Stretch factor</b> - defines the growth factor of element height
  from the mesh boundary inwards.</li>
<li><b>Extrusion method</b> (available in 3D only) - defines how
  position of nodes are found during prism construction and how
  creation of distorted and intersecting prisms is prevented.
<ul><li><b>Surface offset + smooth</b> method extrudes nodes along normal
    to underlying geometrical surface. Smoothing of internal surface of
    element layers is possible to avoid creation of invalid prisms.</li>
  <li><b>Face offset</b> method extrudes nodes along average normal of
    surrounding mesh faces till intersection with a neighbor mesh face
    translated along its own normal by the layers thickness. Thickness
    of layers can be limited to avoid creation of invalid prisms.</li>
  <li><b>Node offset</b> method extrudes nodes along average normal of
    surrounding mesh faces by the layers thickness. Thickness of
    layers can be limited to avoid creation of invalid prisms.</li> 
\image html viscous_layers_extrusion_method.png "Prisms created by the tree extrusion methods at the same other parameters"
</ul></li>
<li><b>Specified Faces/Edges are</b> - defines how the shapes specified by
  the next parameter are used.
<li><b> Faces/Edges with/without layers</b> - 
  defines geometrical faces or edges on which element layers
  either should be or should not be constructed, depending on the
  value of the previous parameter (<b>Specified Faces/Edges are</b>). 
  Faces (or edges) can be selected either in the Object Browser or in
  the VTK Viewer.
  \note A mesh shown in the 3D Viewer can prevent selection of faces
  and edges, just hide the mesh to avoid this. Sometimes a face to
  select is hidden by other faces, in this case consider creating a
  group of faces you want to select in the Geometry module.<br>
  To avoid a long wait when a
  geometry with many faces (or edges) is displayed, the number of faces
  (edges) shown at a time is limited by the value of "Sub-shapes
  preview chunk size" preference (in Preferences/Mesh/General tab).


  If faces/edges without layers are specified, the element layers are
  not constructed on geometrical faces shared by several solids in 3D
  case and edges shared by several faces in 2D case. In other words,
  in this mode the element layers can be constructed on boundary faces
  and edges only, and are not constructed on internal faces and
  edges. There is an exception to this rule: if a hypothesis is
  assigned to a sub-mesh, the element layers can be constructed on
  boundary faces/edges of the shape of this sub-mesh, at same time
  possibly being internal faces/edges within the whole model.
  \image html viscous_layers_on_submesh.png 2D viscous layers constructed on boundary edges of a sub-mesh on a disk face.

  If you use \b several hypotheses to define viscous layers on faces of
  one solid, keep in mind the following. Each hypothesis defines a set
  of faces with viscous layers (even if you specify faces without
  layers). The sets of faces with viscous layers defined by several
  hypotheses should not intersect, else the module won't add an
  hypothesis that is incompatible with another one. <br>
  Also you can't define different number of layers on adjacent faces
  of a solid.<br>
  This logic is also valid for the 2D hypothesis.
</li>
</ul>

\image html viscous_layers_mesh.png A group containing viscous layer prisms.

<br><b>See also</b> a sample TUI script of a \ref tui_viscous_layers
"Viscous layers construction".


\anchor quadratic_mesh_anchor
<h2>Quadratic Mesh</h2>

Quadratic Mesh hypothesis allows to build a quadratic mesh (in which
links between element nodes are not straight but curved lines due to
presence of an additional midside node).

This 1D hypothesis can be taken into account by 
\ref a1d_algos_anchor "Wire Discretization" and 
\ref a1d_algos_anchor "Composite Side Discretization" algorithms. To
make a quadratic mesh assign this hypothesis at 
\ref constructing_meshes_page "mesh construction".

See \ref adding_quadratic_elements_page
for more information about quadratic meshes.


\anchor quadrangle_preference_anchor
<h2>Quadrangle Preference</h2>

This additional hypothesis can be used together with 2D triangulation algorithms.
It allows 2D triangulation algorithms to build quadrangular meshes.

When used with "Quadrangle (Mapping)" meshing algorithm, that is obsolete
 since introducing \ref hypo_quad_params_anchor "Quadrangle parameters" 
hypothesis, this hypothesis has one restriction on its work: the total quantity of 
segments on all four sides of the face must be even (divisible by 2).

*/