3 \page constructing_meshes_page Constructing meshes
5 \n Construction of a mesh consists of:
7 <li>Selecting a geometrical object for meshing</li>
8 <li>Applying \subpage basic_meshing_algos_page "meshing algorithms" and
9 \subpage about_hypo_page "hypotheses" which will be used at computation of
13 <em>To construct a mesh:</em>
15 <li>In the \b Mesh menu select <b>Create Mesh</b> or click <em>"Create
16 Mesh"</em> button in the toolbar.
18 \image html image32.png
19 <center><em>"Create Mesh" button</em></center>
21 The following dialog box will appear:
23 \image html createmesh-inv.png
25 <li>For example, you need to mesh a 3d object.
26 \n First, type the name for your mesh in the "Name" box, by default,
27 it is "Mesh_1". Then select the object you wish to mesh in the Object
28 Browser and click the "Add" button.
30 \image html image120.png
31 <center><em>"Add" button</em></center>
33 Now you can define 1d Algorithm and 1d Hypotheses, which will be
34 applied to the edges of your object. (Note that any object has edges,
35 even if their existence is not apparent, for example, a sphere has 4
36 edges). Click the <em>"Add Hypothesis"</em> button to add a hypothesis.
38 \image html image121.png
39 <center><em>"Add Hypothesis" button</em></center>
41 Click the <em>"Edit Hypothesis"</em> button to define values for the
44 \image html image122.png
45 <center><em>"Edit Hypothesis" button</em></center>
47 The use of additional hypotheses is optional (i.e. you may leave
50 Proceed in the same way with 2d and 3d Algorithms and Hypotheses, note
51 that the choice of hypotheses depends on the algorithm. There must be
52 one Algorithm and one or several Hypotheses for each dimension of your
53 object, otherwise you will not get any mesh at all. Of course, if you
54 wish to mesh a face, which is a 2d object, you don't need to define 3d
55 Algorithm and Hypotheses.
56 \n In the <b>Object Browser</b> the structure of the new mesh will be
59 \image html image88.jpg
63 <li>a reference to the geometrical object on the basis of which the mesh has been constructed;</li>
64 <li><b>Applied hypotheses</b> folder containing the references to the
65 hypotheses applied to the construction of the mesh;</li>
66 <li><b>Applied algorithms</b> folder containing the references to the
67 algorithms applied to the construction of the mesh.</li>
70 There is an alternative way to create a mesh on an object simply by
71 clicking <b>Assign a set of hypotheses</b> button and selecting between
72 Automatic Tetrahedralization or Hexahedralization. The program will
73 automatically generate a 3D mesh with the most appropriate
74 settings. In the same way you can apply this functionality for meshing
75 2D objects, in which case 3D algorithms are not applied.</li>
77 \anchor preview_mesh_anchor
79 <li> After the mesh object is created and all hypotheses are assigned and
80 before the mesh computation, it is possible to see the mesh preview.
82 For this, select the mesh in the Object Browser. From the \b Mesh menu
83 select \b Preview or click "Preview" button in the
84 toolbar or activate "Preview" item from the pop-up menu.
86 \image html mesh_precompute.png
87 <center><em>"Preview" button</em></center>
89 Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog.
92 \image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"
94 \image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"
96 <b>Compute</b> button computes the whole mesh.
98 When the Preview dialog is closed, the question about the storage of temporarily
99 created mesh elements appers:
101 \image html preview_tmp_data.png
103 These elenents can be reused in the next mesh computation.
107 <li>It is equally possible to skip the Preview and \b Compute the mesh
108 after the hypotheses are assigned. For this, select your mesh in the <b>Object
109 Browser</b>. From the \b Mesh menu select \b Compute or click "Compute" button of the
112 \image html image28.png
113 <center><em>"Compute" button</em></center>
115 The Mesh Computation information box appears.
117 \image html meshcomputationsucceed.png
119 If the mesh computation failed, the information about the cause of the
122 \image html meshcomputationfail.png
124 After you select the error, <b>Show Subshape</b> button allows
125 visualizing the geometrical entity that causes it.
127 \image html failed_computation.png "Example of the invalid input mesh"
129 \note Mesh Computation Information box does not appear if you set
130 "Mesh computation/Show a computation result notification" preference
131 to the "Never" value. This option gives the possibility to control mesh
132 computation reporting. There are the following possibilities: always
133 show information box, only if an error occurs or never.
134 By default, the information box is always shown after mesh computation operation.
136 <b>Publish Subshape</b> button publishes the subshape, whose meshing
137 failed, in GEOM component as a child of the mesh geometry, which
138 allows analyzing the problem geometry and creating a submesh on it in
139 order to locally tune hypotheses.
141 <b>NOTE</b> It is possible to define a 1D or a 2D mesh in a
142 python script and then use such submeshes in the construction of a 3D
143 mesh. For this, there exist two algorithms: <b>Use existing edges</b> and <b>Use
144 existing faces</b>. They are not entirely usable from the GUI, so a
145 mesh created using these algorithms should be exported into a python
146 script, edited and then imported into the GUi.
148 <li>It is possible to calculate the eventual mesh size
149 before \b Compute operation. For this, select the mesh in the <b>Object
150 Browser</b> and from the \b Mesh menu select \b Evaluate. The result of
151 evaluation will be displayed in the following information box:
153 \image html mesh_evaluation_succeed.png
159 \anchor mesh_order_anchor
160 It is allowed to change submesh priority in mesh computation when
161 there are concurrent submeshes present. I.e. user can change priority of
162 applying algorithms on shared subshapes of Mesh shape.
163 <em>To change submesh priority:</em>
165 <li>From the Mesh menu choose the "Change submesh priority" on
166 selected Mesh item, or invoke from popup menu. The opened dialogue box
167 shows a list of submeshes in the order of their priority. Algorithm and its
168 hypotheses of a submesh being upper in the list are applied before those of
169 a submesh lower in the list.
171 There is an example of submesh order modifications of Mesh created on a Box
172 shape. The main Mesh object:
174 <li><i>3D</i> <b>Tetrahedron (Netgen)</b> with Hypothesis<b>Max Element Volume</b></li>
175 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>Max Element Area</b>
177 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=20</li>
179 The first submesh object <b>Submesh_1</b> created on <b>Face_1</b>
182 <li><i>2D</i> Netgen 1D-2D with Hypothesis <b>Netgen Simple parameters</b>
183 (Number of Segments = 4)</li>
185 The second submesh object <b>Submesh_2</b> created on <b>Face_2</b>
188 <li><i>2D</i> Netgen 1D-2D with Hypothesis <b>Netgen Simple parameters</b>
189 (Number of Segments = 8)</li>
192 And the last third submesh object <b>Submesh_3</b> created on <b>Face_3</b>
195 <li><i>2D</i> Netgen 1D-2D with Hypothesis <b>Netgen Simple parameters</b>
196 (Number of Segments = 12)</li>
198 The submeshes can become concurrent if their algorithms leads to mesh shared subshape
199 with different algorithms (or different algorithms parameters, i.e. hypothesises).
200 In fact, we have three submeshes with concurrent algorithms, because
201 they have different hypothesises assigned to them.
203 The first mesh computation made with:
204 \image html mesh_order_123.png
205 <center><em>"Mesh order SubMesh_1, SubMesh_2, SubMesh_3"</em></center>
206 \image html mesh_order_123_res.png
207 <center><em>"Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "</em></center>
209 The next mesh computation with:
210 \image html mesh_order_213.png
211 <center><em>"Mesh order SubMesh_2, SubMesh_1, SubMesh_3"</em></center>
212 \image html mesh_order_213_res.png
213 <center><em>"Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "</em></center>
215 And the last mesh computation with:
216 \image html mesh_order_321.png
217 <center><em>"Mesh order SubMesh_3, SubMesh_2, SubMesh_1"</em></center>
218 \image html mesh_order_321_res.png
219 <center><em>"Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "</em></center>
221 As we can see each mesh computation has different number of result
222 elements and different mesh discretisation on shared edges (edges
223 that are shared between <b>Face_1</b>, <b>Face_2</b> and <b>Face_3</b>)
225 Additionally, submesh priority (order of algorithms to be applied) can
226 be modified not only in separate dialog box, but in <b>Preview</b>
227 also. This helps to preview different mesh results, modifying submesh
229 \image html mesh_order_preview.png
230 <center><em>"Preview with submesh priority list box"</em></center>
232 If there are no concurrent submeshes under Mesh object, then user will see the
233 following information dialog box
234 \image html mesh_order_no_concurrent.png
235 <center><em>"No concurrent submeshes detected"</em></center>
236 and no mesh order list box will appear in Preview dialog box.
240 Consider trying a sample script for construction of a mesh from our
241 \ref tui_creating_meshes_page "TUI Scripts" section.