\page extrusion_page Extrusion
\n Extrusion is used to build mesh elements of plus one
-dimension than the input ones. Boundary elements around elements of
-plus one dimension are additionally created. All created elements
-can be automatically grouped.
+dimension than the input ones. Boundary elements around generated
+mesh of plus one dimension are additionally created. All created
+elements can be automatically grouped. Extrusion can be used to create
+a \ref extrusion_struct "structured mesh from scratch".
+
+\image html extrusion_box.png "If you extrude several quadrangles, you get exactly the same mesh as if you meshed a geometrical box (except for that the initial quadrangles can be incorrectly oriented): quadrangles and segments are created on the boundary of the generated mesh"
+
<p>Any node, segment or 2D element can be extruded. Each type of
elements is extruded into a corresponding type of result elements:
<table>
<tr><td>Hexagonal polygon </td><td> Hexagonal prism </td></tr>
</table>
+When 2D elements are extruded, in addition to 3D elements segments are
+created on ribs of the result 3D mesh. Free edges of input 2D elements
+generate logically horizontal rib segments. Logically vertical rib
+segments are generated from nodes belonging to a sole input 2D element
+(a figure below illustrates this rule).
+
+\image html extru_rib_segs.png "Two triangles extruded: no vertical rib segments generated from nodes #2 and #3 as they are shared by both triangles"
+
<em>To use extrusion:</em>
<ol>
<li>From the \b Modification menu choose the \b Extrusion item or click
<em>"Extrusion" button</em>
</center>
-The following dialog common for line and planar elements will appear:
+The following dialog will appear:
\image html extrusionalongaline1.png
-\image html extrusionalongaline2.png
-
</li>
<li>In this dialog:
<ul>
- <li>Select the type of elements which will be extruded (nodes, 1D or
- 2D elements).</li>
- <li>Specify the IDs of the elements which will be extruded by one
- following means:
+ <li>Use \a Selection button to specify what you are going to
+ select at a given moment, \b Nodes, \b Edges or \b Faces.
+ \image html image120.png
+ <center><em>"Selection" button</em></center>
+ </li>
+ <li>Specify \b Nodes, \b Edges and \b Faces, which will be extruded, by one
+ of following means:
<ul>
- <li><b>Select the whole mesh, submesh or group</b> activating this
- checkbox.</li>
+ <li><b>Select the whole mesh, sub-mesh or group</b> activating the
+ corresponding check-box.</li>
<li>Choose mesh elements with the mouse in the 3D Viewer. It is
possible to select a whole area with a mouse frame.</li>
- <li>Input the element IDs directly in <b>ID Elements</b>
- field. The selected elements will be highlighted in the viewer.</li>
+ <li>Input the element IDs directly in <b>Node IDs</b>, <b>Edge
+ IDs</b> and <b>Face IDs</b> fields. The selected elements will
+ be highlighted in the viewer, if the mesh is shown there.</li>
<li>Apply Filters. <b>Set filter</b> button allows to apply a
filter to the selection of elements. See more about filters in
the \ref filtering_elements "Selection filters" page.</li>
</ul>
</li>
- <li>If the <b>Extrude to Distance</b> radio button is selected</li>
- <ul>
- <li>specify the distance at which the elements will be extruded.</li>
- </ul>
- <li>If the <b>Extrude Along Vector</b> radio button is selected</li>
- <ul>
- <li>specify the coordinates of the vector along which the elements
- will be extruded, or select the face (the normal to the face will
- define the vector),</li>
- <li>specify the distance of extrusion along the vector.</li>
+ <li>If the <b>Extrusion to Distance</b> radio button is selected
+ - specify the translation vector by which the elements will be extruded.
+ </li>
+ <p><br></p>
+
+\image html extrusionalongaline2.png
+
+ <li>If the <b>Extrusion Along Vector</b> radio button is selected
+ <ul>
+ <li>specify the coordinates of the \b Vector along which the elements
+ will be extruded, either directly or by selecting the mesh face (the
+ normal to the face will define the vector),</li>
+ <li>specify the \b Distance of extrusion along the vector (it can
+ be negative).</li>
+ </ul>
+ </li>
+ <p><br></p>
+
+\image html extrusionalongaline3.png
+
+ <li>If the <b>Extrusion By Normal</b> radio button is selected,
+ every node of the selected faces is extruded along the \a average
+ of the \a normal vectors to the faces sharing the node. (Nodes and
+ edges cannot be extruded in this mode.)
+ <ul>
+ <li>Specify the \b Distance of extrusion (it can be negative),</li>
+ <li>Use <b>Along average normal</b> check-box to specify along
+ which vector the distance is measured.
+ <ul>
+ <li>If it is \a activated the distance is measured along the
+ average normal mentioned above. </li>
+ <li>If it is \a deactivated every node is extruded along the
+ average normal till its intersection with a virtual plane obtained
+ by translation of the face sharing the node along its own normal
+ by the \b Distance.</li>
+ </ul>
+ The picture below shows a cross-section of a 2D mesh extruded
+ with <b>Along average normal</b> activated (to the left) and
+ deactivated (to the right).
+
+ \image html extrusionbynormal_alongavgnorm.png "'Along average normal' activated (to the left) and deactivated (to the right)"
+ <p></li>
+
+ <li><b>Use only input elements</b> check-box specifies what
+ elements will be used to compute the average normal.<ul>
+ <li> If it is \a activated only selected faces, among faces
+ sharing the node, are used to compute the average normal at
+ the node. </li>
+ <li>Else all faces sharing the node are used.</li></ul>
+
+ The picture below shows a cross-section of a 2D mesh the upper
+ plane of which is extruded with <b>Use only input elements</b>
+ activated (to the left) and deactivated (to the right).
+
+ \image html extrusionbynormal_useonly.png "'Use only input elements' activated (to the left) and deactivated (to the right)"
+ <p></li>
+ </li>
</ul>
- <li>Specify the number of steps.</li>
+
+ <li>Specify the <b>Number of steps</b>.</li>
<li>If you activate <b>Generate Groups</b> check-box, the <em>result elements</em>
- created from <em>extruded elements</em> contained in groups will be
+ created from <em>selected elements</em> contained in groups will be
included into new groups named by pattern "<old group
- name>_extruded" and "<old group name>_top". For example if an
- extruded quadrangle is included in \a Group_1 group then result
- hexahedra will be included in \a Group_1_extruded group and a
- quadrangle created at the "top" of extruded mesh will
- be included in \a Group_1_top group. <br>This check-box is active
- only if there are some groups in the mesh.</li>
+ name>_extruded" and "<old group name>_top". For example if a
+ selected quadrangle is included in \a g_Faces group (see figures
+ below) then result hexahedra will be included in \a
+ g_Faces_extruded group and a quadrangle created at the "top" of
+ extruded mesh will be included in \a g_Faces_top group. <br>
+\image html extrusion_groups.png
+\image html extrusion_groups_res.png
+ <p> This check-box is active only if there are some groups in the mesh.
+ </li>
</ul>
<li>Click \b Apply or <b> Apply and Close</b> button to confirm the operation.</li>
</ol>
+<p>
+
+\anchor extrusion_struct
+<h2>Example: creation of a structured mesh from scratch</h2>
-\image html image77.jpg "The mesh with an edge selected for extrusion"
+\image html image75.jpg "A node is extruded into a line of segments"
+<br>
+\image html image76.jpg "The line of segments is extruded into a quadrangle mesh"
+<br>
+\image html image77.jpg "The quadrangle mesh is revolved into a hexahedral mesh"
-\image html image76.jpg "The mesh with extruded edge"
<br><b>See Also</b> a sample TUI Script of an
\ref tui_extrusion "Extrusion" operation.
