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168 lines
8.4 KiB
ReStructuredText
168 lines
8.4 KiB
ReStructuredText
.. _additional_hypo_page:
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*********************
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Additional Hypotheses
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*********************
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**Additional Hypotheses** can be applied as a supplement to the main hypotheses, introducing additional concepts to mesh creation.
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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.
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The following additional hypothesis are available:
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* :ref:`propagation_anchor` and :ref:`propagofdistribution_anchor` hypotheses are useful for creation of quadrangle and hexahedral meshes.
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* :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.
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* :ref:`quadratic_mesh_anchor` hypothesis allows generation of second order meshes.
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* :ref:`quadrangle_preference_anchor` hypothesis enables generation of quadrangles.
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.. _propagation_anchor:
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Propagation of 1D Hypothesis on opposite edges
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##############################################
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**Propagation of 1D Hypothesis on opposite edges** allows to mesh
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opposite sides of a quadrangle face and other adjacent quadrangles,
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using the same hypothesis assigned to only one edge.
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Thus you define a sub-mesh on the edge where you define 1D meshing
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parameters and the **Propagation hypothesis**. These local meshing
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parameters will be propagated via opposite sides of quadrangles to the
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whole geometry, and this propagation stops at an edge with other local
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meshing parameters.
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This hypothesis can be taken into account by
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:ref:`Wire Discretization <a1d_algos_anchor>` and
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:ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms.
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**See Also** a sample TUI Script of a :ref:`Propagation hypothesis <tui_propagation>` operation
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.. _propagofdistribution_anchor:
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Propagation of Node Distribution on Opposite Edges
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##################################################
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**Propagation of Node Distribution on Opposite Edges** allows to propagate
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distribution of nodes onto an opposite edge. If a local hypothesis and
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propagation are defined on an edge of a quadrangular face, the
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opposite edge will have the same number of nodes and the same
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relations between segment lengths, unless another hypothesis
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has been locally defined on the opposite edge.
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This hypothesis can be taken into account by
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:ref:`Wire Discretization <a1d_algos_anchor>` and
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:ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms.
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**See Also** a sample TUI Script of a :ref:`Propagation hypothesis <tui_propagation>` operation
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.. _viscous_layers_anchor:
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Viscous Layers and Viscous Layers 2D
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####################################
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**Viscous Layers** and **Viscous Layers 2D** additional
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hypotheses can be used by several 3D algorithms, for example
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Hexahedron(i,j,k), or 2D algorithms, for example Triangle
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(MEFISTO), correspondingly. These hypotheses allow creation of layers
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of highly stretched elements, prisms in 3D and quadrilaterals in 2D,
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near mesh boundary, which is beneficial for high quality viscous
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computations.
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.. image:: ../images/viscous_layers_hyp.png
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:align: center
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.. image:: ../images/viscous_layers_2d_hyp.png
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:align: center
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* **Name** - allows to define the name of the hypothesis.
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* **Total thickness** - gives the total thickness of element layers.
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* **Number of layers** - defines the number of element layers.
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* **Stretch factor** - defines the growth factor of element height from the mesh boundary inwards.
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* **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.
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* **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.
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* **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.
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* **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.
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.. image:: ../images/viscous_layers_extrusion_method.png
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:align: center
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.. centered::
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Prisms created by the tree extrusion methods at the same other parameters
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* **Specified Faces/Edges are** - defines how the shapes specified by the next parameter are used.
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* **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.
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.. note::
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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).
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If faces/edges without layers are specified, the element layers are
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not constructed on geometrical faces shared by several solids in 3D
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case and edges shared by several faces in 2D case. In other words,
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in this mode the element layers can be constructed on boundary faces
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and edges only, and are not constructed on internal faces and
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edges. There is an exception to this rule: if a hypothesis is
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assigned to a sub-mesh, the element layers can be constructed on
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boundary faces/edges of the shape of this sub-mesh, at same time
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possibly being internal faces/edges within the whole model.
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.. image:: ../images/viscous_layers_on_submesh.png
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:align: center
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.. centered::
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2D viscous layers constructed on boundary edges of a sub-mesh on a disk face.
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If you use **several** hypotheses to define viscous layers on faces of
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one solid, keep in mind the following. Each hypothesis defines a set
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of faces with viscous layers (even if you specify faces without
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layers). The sets of faces with viscous layers defined by several
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hypotheses should not intersect, else the module won't add an
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hypothesis that is incompatible with another one.
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Also you can't define different number of layers on adjacent faces
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of a solid.
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This logic is also valid for the 2D hypothesis.
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.. image:: ../images/viscous_layers_mesh.png
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:align: center
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.. centered::
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A group containing viscous layer prisms.
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**See also** a sample TUI script of a :ref:`tui_viscous_layers`.
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.. _quadratic_mesh_anchor:
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Quadratic Mesh
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##############
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Quadratic Mesh hypothesis allows to build a quadratic mesh (in which
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links between element nodes are not straight but curved lines due to
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presence of an additional mid-side node).
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This 1D hypothesis can be taken into account by
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:ref:`Wire Discretization <a1d_algos_anchor>` and
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:ref:`Composite Side Discretization <a1d_algos_anchor>` algorithms. To create a quadratic mes assign this hypothesis at
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:ref:`mesh construction <constructing_meshes_page>`.
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See :ref:`adding_quadratic_elements_page` for more information about quadratic meshes.
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.. _quadrangle_preference_anchor:
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Quadrangle Preference
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#####################
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This additional hypothesis can be used together with 2D triangulation algorithms.
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It allows 2D triangulation algorithms to build quadrangular meshes.
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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.
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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.
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.. note::
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*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.
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