3 \page constructing_meshes_page Constructing meshes
5 \n Construction of a mesh on some geometry consists of:
7 <li> \ref create_mesh_anchor "Creating of a mesh object"</li>
8 <li> \ref evaluate_anchor "Evaluating mesh size" (optional)</li>
9 <li> \ref preview_anchor "Previewing the mesh" (optional)</li>
10 <li> \ref submesh_order_anchor "Changing sub-mesh priority" (optional)</li>
11 <li> \ref compute_anchor "Computing the mesh"</li>
14 \anchor create_mesh_anchor
15 <h2>Creation of a mesh object</h2>
16 <em>To construct a mesh:</em>
18 <li>Select a geometrical object for meshing.</li>
19 <li>In the \b Mesh menu select <b>Create Mesh</b> or click <em>"Create
20 Mesh"</em> button in the toolbar.
23 \image html image32.png
24 <em>"Create Mesh" button</em>
27 The following dialog box will appear:
29 \image html createmesh-inv.png
32 <li> To filter off irrelevant meshing algorithms, you can
33 select <b>Mesh Type</b> in the corresponding list from <b>Any,
34 Hexahedral, Tetrahedral, Triangular </b> and \b Quadrilateral (there
35 can be less items for the geometry of lower dimensions).
37 Selection of a mesh type hides all meshing algorithms that can not
38 generate elements of this type.</li>
40 <li>Apply \subpage basic_meshing_algos_page "meshing algorithms" and
41 \subpage about_hypo_page "hypotheses" which will be used to compute
44 "Create mesh" dialog box contains several tab pages titled \b 3D,
45 \b 2D, \b 1D and \b 0D. The title of each page reflects the
46 dimension of the CAD model (geometry) the algorithms listed on
47 this page affect and the maximal dimension of elements the algorithms
48 generate. For example, \b 3D page lists the algorithms that affect
49 3D geometrical objects (solids) and generate 3D mesh elements
50 (tetrahedra, hexahedra etc.)
53 - Some page(s) can be disabled if the source geometrical
54 object does not include shapes (sub-shapes) of the corresponding
55 dimension(s). For example, if the input object is a geometrical face,
56 \b 3D page is disabled.
57 - Some algorithms affect the geometry of several dimensions,
58 i.e. "1D-2D" or "1D-2D-3D". If such an algorithm is selected by the
59 user, the dialog box pages related to the corresponding lower level
60 dimensions are disabled.
61 - \b 0D page does not refer to the 0D elements, but to 0D
62 geometry (vertices). Mesh module does not provide algorithms that
63 produce 0D elements. Currently \b 0D page provides only one
64 algorithm "Segments around vertex" that allows specyfying the required
65 size of mesh edges about the selected vertex (or vertices).
67 For example, you need to mesh a 3D object.
69 First, type the name of your mesh in the \b Name box, by default,
70 it is "Mesh_1". Then select the geometrical object you wish to
71 mesh in the Object Browser and click "Select" button near \b Geometry
72 field (if the name of the object has not yet appeared in \b Geometry field).
74 \image html image120.png
75 <em>"Select" button</em>
78 Now you can define 3D Algorithm and 3D Hypotheses, which will be
79 applied to the solids of your geometrical object. Click the <em>"Add
80 Hypothesis"</em> button to add a hypothesis.
82 \image html image121.png
83 <em>"Add Hypothesis" button</em>
85 Click the <em>"Plus"</em> button to enable adding more additional hypotheses.
87 Click the <em>"Edit Hypothesis"</em> button to change the values for the
90 \image html image122.png
91 <em>"Edit Hypothesis" button</em>
94 Most 2D and 3D algorithms can work without hypotheses using
95 default meshing parameters. Some algorithms do not require any
96 hypotheses. After selection of an algorithm "Hypothesis" field of
97 the dialog can contain:
99 <li> <em>\<Default\></em> if the algorithm can work using default
101 <li> <em>\<None\></em> if the algorithm requires a hypothesis defining
103 <li> If the algorithm does not use hypotheses, this field is grayed.</li>
105 After selection of an algorithm <b>Add. Hypothesis</b> field can contain:
107 <li> <em>\<None\></em> if the algorithm can be tuned
108 using an additional hypothesis.</li>
109 <li> If the algorithm does not use additional hypotheses, this field is grayed.</li>
112 Proceed in the same way with 2D and 1D Algorithms and Hypotheses that
113 will be used to mesh faces and edges of your geometry. (Note
114 that any object has edges, even if their existence is not
115 apparent, for example, a sphere has 4 edges). Note that the
116 choice of hypotheses and lower dimension algorithms depends on
117 the higher dimension algorithm.
119 If you wish you can select different algorithms and/or hypotheses
120 for meshing some parts of your CAD model by \ref constructing_submeshes_page.
122 Some algorithms generate mesh of several dimensions, while others
123 produce mesh of only one dimension. In the latter case there must
124 be one Algorithm and zero or several
125 Hypotheses for each dimension of your object, otherwise you will
126 not get any mesh at all. Of course, if you wish to mesh a face,
127 which is a 2D object, you do not need to define a 3D Algorithm and
130 In the <b>Object Browser</b> the structure of the new mesh will be
131 displayed as follows:
134 \image html image88.jpg
139 <li>a mesh name (<em>Mesh_mechanic</em>);
140 <li>a reference to the geometrical object on the basis of
141 which the mesh has been constructed (\a mechanic);</li>
142 <li><b>Applied hypotheses</b> folder containing the references
143 to the hypotheses applied at the construction of the mesh;</li>
144 <li><b>Applied algorithms</b> folder containing the references
145 to the algorithms applied at the construction of the mesh.</li>
148 There is an alternative way to assign Algorithms and Hypotheses by
149 clicking <b>Assign a set of hypotheses</b> button and selecting among
150 pre-defined sets of hypotheses. In addition to the standard
151 sets of hypotheses, it is possible to create custom sets by editing
152 CustomMeshers.xml file located in the home directory. CustomMeshers.xml
153 file must describe sets of hypotheses in the
154 same way as ${SMESH_ROOT_DIR}/share/salome/resources/smesh/StdMeshers.xml
155 file does (sets of hypotheses are enclosed between <hypotheses-set-group>
158 \image html hypo_sets.png
159 List of sets of hypotheses. Tag <em>[custom]</em> is
160 automatically added to the sets defined by the user.
162 \note \a Automatic in the names of pre-defined sets of
163 hypotheses means only that initially \ref
164 automatic_length_anchor "Automatic Length" hypothesis was
165 included in these sets, and not that these sets are suitable for
166 meshing any geometry.
170 Consider trying a sample script for construction of a mesh from our
171 \ref tui_creating_meshes_page "TUI Scripts" section.
173 \anchor evaluate_anchor
174 <h2>Evaluating mesh size</h2>
176 After the mesh object is created and all hypotheses are assigned and
177 before \ref compute_anchor "Compute" operation, it is possible to
178 calculate the eventual mesh size. For this, select the mesh in
179 the <b>Object Browser</b> and from the \b Mesh menu select \b
180 Evaluate. The result of evaluation will be displayed in the following
183 \image html mesh_evaluation_succeed.png
185 \anchor preview_anchor
186 <h2>Previewing the mesh</h2>
188 Before \ref compute_anchor "the mesh computation", it is also possible
189 to see the mesh preview.
191 For this, select the mesh in the Object Browser. From the \b Mesh menu
192 select \b Preview or click "Preview" button in the toolbar or activate
193 "Preview" item from the pop-up menu.
196 \image html mesh_precompute.png
197 <em>"Preview" button</em>
200 Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog.
202 \image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"
204 \image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"
206 <b>Compute</b> button computes the whole mesh.
208 When the Preview dialog is closed, the question about the storage of temporarily
209 created mesh elements appears:
211 \image html preview_tmp_data.png
213 These elements can be kept in the mesh.
216 \anchor submesh_order_anchor
217 <h2>Changing sub-mesh priority</h2>
219 If the mesh contains concurrent \ref constructing_submeshes_page "sub-meshes",
220 it is possible to change the priority of their computation, i.e. to
221 change the priority of applying algorithms to the shared sub-shapes of
224 <em>To change submesh priority:</em>
226 Choose "Change submesh priority" from the Mesh menu or a pop-up
227 menu. The opened dialog shows a list of submeshes in the order of
230 There is an example of submesh order modifications taking a Mesh created on a Box
231 shape. The main Mesh object:
233 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=20</li>
234 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>Max Element Area</b>
237 The first submesh object <b>Submesh_1</b> created on <b>Face_1</b> is:
239 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=4</li>
240 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
242 The second submesh object <b>Submesh_2</b> created on <b>Face_2</b> is:
244 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=8</li>
245 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
248 And the last submesh object <b>Submesh_3</b> created on <b>Face_3</b> is:
250 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=12</li>
251 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
254 The sub-meshes become concurrent if they share sub-shapes that can be
255 meshed with different algorithms (or different hypotheses). In the
256 example, we have three submeshes with concurrent algorithms, because
257 they have different hypotheses.
259 The first mesh computation is made with:
261 \image html mesh_order_123.png
262 <em>"Mesh order SubMesh_1, SubMesh_2, SubMesh_3"</em></center>
264 \image html mesh_order_123_res.png
265 <em>"Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "</em></center>
267 The next mesh computation is made with:
269 \image html mesh_order_213.png
270 <em>"Mesh order SubMesh_2, SubMesh_1, SubMesh_3"</em></center>
272 \image html mesh_order_213_res.png
273 <em>"Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "</em></center>
275 And the last mesh computation is made with:
277 \image html mesh_order_321.png
278 <em>"Mesh order SubMesh_3, SubMesh_2, SubMesh_1"</em></center>
279 <center>\image html mesh_order_321_res.png
280 <em>"Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "</em></center>
282 As we can see, each mesh computation has a different number of result
283 elements and a different mesh discretization on the shared edges (the edges
284 that are shared between <b>Face_1</b>, <b>Face_2</b> and <b>Face_3</b>)
286 Additionally, submesh priority (the order of applied algorithms) can
287 be modified not only in a separate dialog box, but also in
288 the <b>Preview</b>. This helps to preview different mesh results,
289 modifying the order of submeshes.
291 \image html mesh_order_preview.png
292 <em>"Preview with submesh priority list box"</em></center>
294 If there are no concurrent submeshes under the Mesh object, the user
295 will see the following information.
297 \image html mesh_order_no_concurrent.png
298 <em>"No concurrent submeshes detected"</em></center>
301 \anchor compute_anchor
302 <h2>Computing the mesh</h2>
304 It is equally possible to skip \ref evaluate_anchor "the Evaluation"
305 and \ref preview_anchor "the Preview" and to \b Compute the mesh after
306 the hypotheses are assigned. For this, select your mesh in
307 the <b>Object Browser</b>. From the \b Mesh menu select \b Compute or
308 click "Compute" button of the toolbar.
311 \image html image28.png
312 <em>"Compute" button</em>
315 After the mesh computation finishes, the Mesh Computation information
316 box appears. In case of a success, the box shows
317 information on number of entities of different types in the mesh.
319 \image html meshcomputationsucceed.png
321 If the mesh computation failed, the information about the cause of the
322 failure is provided in \b Errors table.
324 \image html meshcomputationfail.png
326 After you select the error, <b>Show Sub-shape</b> button allows
327 visualizing in magenta the geometrical entity that causes the error.
329 \image html failed_computation.png
330 <em>3D algorithm failed to compute mesh on a box shown using <b>Show
331 Sub-shape</b> button</em>
333 <b>Publish Sub-shape</b> button publishes the sub-shape, whose meshing
334 has failed, in GEOM component as a child of the mesh geometry, which
335 allows analyzing the problem geometry and creating a submesh on it in
336 order to locally tune the hypotheses.
338 If the failure is caused by an invalid input mesh and the algorithm has
339 found which mesh entities are bad, <b>Show bad Mesh</b>
340 button appears in the dialog. Clicked, it shows the bad mesh entities in
341 the Viewer in magenta. Sometimes the shown mesh entities are too small
342 or/and hidden by other mesh elements. They can be seen after
343 switching the mesh to Wireframe visualization mode or switching off
344 the visualization of faces and volumes (if any).
346 <b>Bad Mesh to Group</b> button creates groups of bad mesh entities
347 to facilitate their analysis.
349 \image html show_bad_mesh.png
350 <em>Edges bounding a hole in the surface are shown in magenta using <b>Show
351 bad Mesh</b> button</em>
353 \note Mesh Computation Information box does not appear if you set
354 "Mesh computation/Show a computation result notification" preference
355 to the "Never" value. This option gives the possibility to control mesh
356 computation reporting. There are the following possibilities: always
357 show the information box, show only if an error occurs or never.
358 By default, the information box is always shown after mesh computation operation.