1 .. _additional_hypo_page:
7 **Additional Hypotheses** can be applied as a supplement to the main hypotheses, introducing additional concepts to mesh creation.
9 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.
11 The following additional hypothesis are available:
13 * :ref:`propagation_anchor` and :ref:`propagofdistribution_anchor` hypotheses are useful for creation of quadrangle and hexahedral meshes.
14 * :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.
15 * :ref:`quadratic_mesh_anchor` hypothesis allows generation of second order meshes.
16 * :ref:`quadrangle_preference_anchor` hypothesis enables generation of quadrangles.
20 .. _propagation_anchor:
22 Propagation of 1D Hypothesis on opposite edges
23 ##############################################
25 **Propagation of 1D Hypothesis on opposite edges** allows to mesh
26 opposite sides of a quadrangle face and other adjacent quadrangles,
27 using the same hypothesis assigned to only one edge.
28 Thus you define a sub-mesh on the edge where you define 1D meshing
29 parameters and the **Propagation hypothesis**. These local meshing
30 parameters will be propagated via opposite sides of quadrangles to the
31 whole geometry, and this propagation stops at an edge with other local
34 This hypothesis can be taken into account by
35 :ref:`Wire Discretization <a1d_algos_anchor>` and
36 :ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms.
38 **See Also** a sample TUI Script of a :ref:`Propagation hypothesis <tui_propagation>` operation
40 .. _propagofdistribution_anchor:
42 Propagation of Node Distribution on Opposite Edges
43 ##################################################
45 **Propagation of Node Distribution on Opposite Edges** allows to propagate
46 distribution of nodes onto an opposite edge. If a local hypothesis and
47 propagation are defined on an edge of a quadrangular face, the
48 opposite edge will have the same number of nodes and the same
49 relations between segment lengths, unless another hypothesis
50 has been locally defined on the opposite edge.
52 This hypothesis can be taken into account by
53 :ref:`Wire Discretization <a1d_algos_anchor>` and
54 :ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms.
56 **See Also** a sample TUI Script of a :ref:`Propagation hypothesis <tui_propagation>` operation
58 .. _viscous_layers_anchor:
60 Viscous Layers and Viscous Layers 2D
61 ####################################
63 **Viscous Layers** and **Viscous Layers 2D** additional
64 hypotheses can be used by several 3D algorithms, for example
65 Hexahedron(i,j,k), or 2D algorithms, for example Triangle
66 (NETGEN_2D), correspondingly. These hypotheses allow creation of layers
67 of highly stretched elements, prisms in 3D and quadrilaterals in 2D,
68 near mesh boundary, which is beneficial for high quality viscous
71 .. image:: ../images/viscous_layers_hyp.png
74 .. image:: ../images/viscous_layers_2d_hyp.png
78 * **Name** - allows to define the name of the hypothesis.
79 * **Total thickness** - gives the total thickness of element layers.
80 * **Number of layers** - defines the number of element layers.
81 * **Stretch factor** - defines the growth factor of element height from the mesh boundary inwards.
82 * **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.
84 * **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.
85 * **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.
86 * **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.
88 .. image:: ../images/viscous_layers_extrusion_method.png
92 Prisms created by the tree extrusion methods at the same other parameters
94 * **Specified Faces/Edges are** - defines how the shapes specified by the next parameter are used.
95 * **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.
98 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).
101 If faces/edges without layers are specified, the element layers are
102 not constructed on geometrical faces shared by several solids in 3D
103 case and edges shared by several faces in 2D case. In other words,
104 in this mode the element layers can be constructed on boundary faces
105 and edges only, and are not constructed on internal faces and
106 edges. There is an exception to this rule: if a hypothesis is
107 assigned to a sub-mesh, the element layers can be constructed on
108 boundary faces/edges of the shape of this sub-mesh, at same time
109 possibly being internal faces/edges within the whole model.
111 * **Create groups from layers** - activates creation of a group containing elements of the layers.
113 .. image:: ../images/viscous_layers_on_submesh.png
117 2D viscous layers constructed on boundary edges of a sub-mesh on a disk face.
119 If you use **several** hypotheses to define viscous layers on faces of
120 one solid, keep in mind the following. Each hypothesis defines a set
121 of faces with viscous layers (even if you specify faces without
122 layers). The sets of faces with viscous layers defined by several
123 hypotheses should not intersect, else the module won't add an
124 hypothesis that is incompatible with another one.
125 Also you can't define different number of layers on adjacent faces
127 This logic is also valid for the 2D hypothesis.
131 .. image:: ../images/viscous_layers_mesh.png
135 A group containing viscous layer prisms.
137 **See also** a sample TUI script of a :ref:`tui_viscous_layers`.
139 .. _viscous_layers_api_anchor:
142 ####################################
144 The Viscous layer API is available on TUI. Allows to compute a shrink version of the geometry. This shrank version can be passed to any mesher and be used to
145 build the viscous layer from the mesh computed in the shrank geometry. The current implementation only support the **Face offset** method to extrude the
146 nodes from the shrank mesh to the original geometry.
148 This implementation supports 3D (Solids and Solid Compound) and 2D (Face) geometries. For the 3D case, the faces Ids are
149 used to identify the faces (perpendicular to it) where the solid is to be reduced. For the 2D case, the edges Ids can be provided but will not have any effect
150 on the geometry computation (this control is not available in the opencascade library), therefore, for this case the entire face is shrank.
152 The Viscous Layer API receive the same parameters as the Viscous Layers Hypothesis and implements four methods:
154 * The constructor ``ViscousLayerBuilder()``
155 * The parameters definitions ``setBuilderParameters(...)``
156 * The ``GetShrinkGeometry()`` method that returns the shrink version of the original geomtry.
157 * The ``AddLayers( shrinkMesh )`` method that returns the complet version of the mesh (shrink+viscous layer)
159 **See also** a sample TUI script of a :ref:`tui_viscous_layers_api`.
161 .. _quadratic_mesh_anchor:
166 Quadratic Mesh hypothesis allows to build a quadratic mesh (in which
167 links between element nodes are not straight but curved lines due to
168 presence of an additional mid-side node).
170 This 1D hypothesis can be taken into account by
171 :ref:`Wire Discretization <a1d_algos_anchor>` and
172 :ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms. To create a quadratic mes assign this hypothesis at
173 :ref:`mesh construction <constructing_meshes_page>`.
175 See :ref:`adding_quadratic_elements_page` for more information about quadratic meshes.
178 .. _quadrangle_preference_anchor:
180 Quadrangle Preference
181 #####################
183 This additional hypothesis can be used together with 2D triangulation algorithms.
184 It allows 2D triangulation algorithms to build quadrangular meshes.
186 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.
187 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.
190 *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.