+.. _additional_hypo_page:
+
+*********************
+Additional Hypotheses
+*********************
+
+**Additional Hypotheses** can be applied as a supplement to the main hypotheses, introducing additional concepts to mesh creation.
+
+An **Additional Hypothesis** can be defined in the same way as any main hypothesis in :ref:`Create Mesh <create_mesh_anchor>` or :ref:`Create Sub-Mesh <constructing_submeshes_page>` dialog.
+
+The following additional hypothesis are available:
+
+* :ref:`propagation_anchor` and :ref:`propagofdistribution_anchor` hypotheses are useful for creation of quadrangle and hexahedral meshes.
+* :ref:`Viscous Layers <viscous_layers_anchor>` and :ref:`Viscous Layers 2D <viscous_layers_anchor>` hypotheses allow creation of layers of highly stretched elements near mesh boundary, which is beneficial for high quality viscous computations.
+* :ref:`quadratic_mesh_anchor` hypothesis allows generation of second order meshes.
+* :ref:`quadrangle_preference_anchor` hypothesis enables generation of quadrangles.
+
+
+
+.. _propagation_anchor:
+
+Propagation of 1D Hypothesis on opposite edges
+##############################################
+
+**Propagation of 1D Hypothesis on opposite edges** allows to mesh
+opposite sides of a quadrangle face and other adjacent quadrangles,
+using the same hypothesis assigned to only one edge.
+Thus you define a sub-mesh on the edge where you define 1D meshing
+parameters and the **Propagation hypothesis**. These local meshing
+parameters will be propagated via opposite sides of quadrangles to the
+whole geometry, and this propagation stops at an edge with other local
+meshing parameters.
+
+This hypothesis can be taken into account by
+:ref:`Wire Discretization <a1d_algos_anchor>` and
+:ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms.
+
+**See Also** a sample TUI Script of a :ref:`Propagation hypothesis <tui_propagation>` operation
+
+.. _propagofdistribution_anchor:
+
+Propagation of Node Distribution on Opposite Edges
+##################################################
+
+**Propagation of Node Distribution on Opposite Edges** 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:`Wire Discretization <a1d_algos_anchor>` and
+:ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms.
+
+**See Also** a sample TUI Script of a :ref:`Propagation hypothesis <tui_propagation>` operation
+
+.. _viscous_layers_anchor:
+
+Viscous Layers and Viscous Layers 2D
+####################################
+
+**Viscous Layers** and **Viscous Layers 2D** 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:: ../images/viscous_layers_hyp.png
+ :align: center
+
+.. image:: ../images/viscous_layers_2d_hyp.png
+ :align: center
+
+
+* **Name** - allows to define the name of the hypothesis.
+* **Total thickness** - gives the total thickness of element layers.
+* **Number of layers** - defines the number of element layers.
+* **Stretch factor** - defines the growth factor of element height from the mesh boundary inwards.
+* **Extrusion method** (available in 3D only) - defines how positions of nodes are found during prism construction and how the creation of distorted and intersecting prisms is prevented.
+
+ * **Surface offset + smooth** method extrudes nodes along the normal to the underlying geometrical surface. Smoothing of the internal surface of element layers is possible to avoid creation of invalid prisms.
+ * **Face offset** method extrudes nodes along the average normal of surrounding mesh faces to the intersection with a neighbor mesh face translated along its own normal by the thickness of layers. The thickness of layers can be limited to avoid creation of invalid prisms.
+ * **Node offset** method extrudes nodes along the average normal of surrounding mesh faces by the thickness of layers. The thickness of layers can be limited to avoid creation of invalid prisms.
+
+ .. image:: ../images/viscous_layers_extrusion_method.png
+ :align: center
+
+ .. centered::
+ Prisms created by the tree extrusion methods at the same other parameters
+
+* **Specified Faces/Edges are** - defines how the shapes specified by the next parameter are used.
+* **Faces/Edges with/without layers** - 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 (**Specified Faces/Edges are**). Faces (or edges) can be selected either in the Object Browser or in the VTK Viewer. **Add** button becomes active as soon as a suitable sub-shape is selected.
+
+ .. note::
+ A mesh shown in the 3D Viewer can prevent selection of faces and edges, just hide the mesh to avoid this. If a face, which should be selected, is hidden by other faces, consider creating a group of faces to be selected in the Geometry module. 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 :ref:`Sub-shapes preview chunk size <chunk_size_pref>` 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.
+
+* **Create groups from layers** - activates creation of a group containing elements of the layers.
+
+ .. image:: ../images/viscous_layers_on_submesh.png
+ :align: center
+
+ .. centered::
+ 2D viscous layers constructed on boundary edges of a sub-mesh on a disk face.
+
+ If you use **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.
+ Also you can't define different number of layers on adjacent faces
+ of a solid.
+ This logic is also valid for the 2D hypothesis.
+
+
+
+.. image:: ../images/viscous_layers_mesh.png
+ :align: center
+
+.. centered::
+ A group containing viscous layer prisms.
+
+**See also** a sample TUI script of a :ref:`tui_viscous_layers`.
+
+
+.. _quadratic_mesh_anchor:
+
+Quadratic Mesh
+##############
+
+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 mid-side node).
+
+This 1D hypothesis can be taken into account by
+:ref:`Wire Discretization <a1d_algos_anchor>` and
+:ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms. To create a quadratic mes assign this hypothesis at
+:ref:`mesh construction <constructing_meshes_page>`.
+
+See :ref:`adding_quadratic_elements_page` for more information about quadratic meshes.
+
+
+.. _quadrangle_preference_anchor:
+
+Quadrangle Preference
+#####################
+
+This additional hypothesis can be used together with 2D triangulation algorithms.
+It allows 2D triangulation algorithms to build quadrangular meshes.
+
+Usage of this hypothesis with :ref:`Quadrangle: Mapping <quad_ijk_algo_page>` meshing algorithm is obsolete since introducing :ref:`Quadrangle parameters <hypo_quad_params_anchor>` hypothesis.
+Usage of this hypothesis with :ref:`Quadrangle: Mapping <quad_ijk_algo_page>` meshing algorithm corresponds to specifying *Quadrangle Preference* transition type of :ref:`Quadrangle parameters <hypo_quad_params_anchor>` hypothesis.
+
+.. note::
+ *Quadrangle Preference* transition type can be used only if the total quantity of segments on all sides of the face is even (divisible by 2), else *Standard* transition type is used.
