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>Select <b>Mesh Type</b> in the corresponding list from <b>Any, Hexahedral, Tetrahedral, Triangular </b> and \b Quadrilateral (there can be less items for lower dimensions).
34 Selection of a mesh type hides any algorithms that are not able to create elements of this type.</li>
36 <li>Apply \subpage basic_meshing_algos_page "meshing algorithms" and
37 \subpage about_hypo_page "hypotheses" which will be used to compute
40 "Create mesh" dialog box contains several tab pages titled \b 3D,
41 \b 2D, \b 1D and \b 0D. The title of each page reflects the
42 dimension of the CAD model (geometry) the algorithms listed on
43 this page affect and the maximal dimension of elements the algorithms
44 generate. For example, \b 3D page lists the algorithms that affect
45 3D geometrical objects (solids).
48 - Some page(s) can be disabled if the source geometrical
49 object does not include shapes (sub-shapes) of the corresponding
50 dimension(s). For example, if the input object is a geometrical face,
51 \b 3D page is disabled.
52 - Some algorithms affect the geometry of several dimensions,
53 i.e. "1D-2D" or "1D-2D-3D". If such an algorithm is selected by the
54 user, the dialog box pages related to the corresponding lower level
55 dimensions are disabled.
56 - \b 0D page does not refer to the 0D elements, but to 0D
57 geometry (vertices). Mesh module does not provide algorithms that
58 produce 0D elements. Currently \b 0D page provides only one
59 algorithm "Segments around vertex" that allows specyfying the required
60 size of mesh edges about the selected vertex (or vertices).
62 For example, you need to mesh a 3D object.
64 First, type the name of your mesh in the \b Name box, by default,
65 it is "Mesh_1". Then select the geometrical object you wish to
66 mesh in the Object Browser and click "Select" button near \b Geometry
67 field (if the name of the object has not yet appeared in \b Geometry field).
70 \image html image120.png
71 <em>"Select" button</em>
74 Now you can define 3D Algorithm and 3D Hypotheses, which will be
75 applied to the solids of your geometrical object. Click the <em>"Add
76 Hypothesis"</em> button to add a hypothesis.
79 \image html image121.png
80 <em>"Add Hypothesis" button</em>
83 Click the <em>"Edit Hypothesis"</em> button to change the values for the
87 \image html image122.png
88 <em>"Edit Hypothesis" button</em>
91 Most 2D and 3D algorithms can work without hypotheses using default meshing parameters. Some algorithms do not require any hypotheses. After selection of an algorithm "Hypothesis" field of
92 the dialog can contain:
94 <li> <em>\<Default\></em> if the algorithm can work using default
96 <li> <em>\<None\></em> if the algorithm requires a hypothesis defining
98 <li> If the algorithm does not use hypotheses, this field is grayed.</li>
100 After selection of an algorithm <b>Add. Hypothesis</b> field can contain:
102 <li> <em>\<None\></em> if the algorithm can be tuned
103 using an additional hypothesis.</li>
104 <li> If the algorithm does not use additional hypotheses, this field is grayed.</li>
107 Proceed in the same way with 2D and 1D Algorithms and Hypotheses that
108 will be used to mesh faces and edges of your geometry. (Note
109 that any object has edges, even if their existence is not
110 apparent, for example, a sphere has 4 edges). Note that the
111 choice of hypotheses and lower dimension algorithms depends on
112 the higher dimension algorithm.
114 Some algorithms generate mesh of several dimensions, while others
115 produce mesh of only one dimension. In the latter case there must
116 be one Algorithm and zero or several
117 Hypotheses for each dimension of your object, otherwise you will
118 not get any mesh at all. Of course, if you wish to mesh a face,
119 which is a 2D object, you do not need to define a 3D Algorithm and
122 In the <b>Object Browser</b> the structure of the new mesh will be
123 displayed as follows:
126 \image html image88.jpg
131 <li>a reference to the geometrical object on the basis of
132 which the mesh has been constructed;</li>
133 <li><b>Applied hypotheses</b> folder containing the references
134 to the hypotheses applied at the construction of the mesh;</li>
135 <li><b>Applied algorithms</b> folder containing the references
136 to the algorithms applied at the construction of the mesh.</li>
139 There is an alternative way to assign Algorithms and Hypotheses by
140 clicking <b>Assign a set of hypotheses</b> button and selecting among
141 pre-defined sets of hypotheses. In addition to the standard
142 sets of hypotheses, it is possible to create custom sets by editing
143 CustomMeshers.xml file located in the home directory. CustomMeshers.xml
144 file must describe sets of hypotheses in the
145 same way as ${SMESH_ROOT_DIR}/share/salome/resources/smesh/StdMeshers.xml
146 file does (sets of hypotheses are enclosed between <hypotheses-set-group>
149 \image html hypo_sets.png
150 List of sets of hypotheses. Tag <em>[custom]</em> is
151 automatically added to the sets defined by the user.
153 \note \a Automatic in the names of pre-defined sets of
154 hypotheses means only that initially \ref
155 automatic_length_anchor "Automatic Length" hypothesis was
156 included in these sets, and not that these sets are suitable for
157 meshing any geometry.
161 Consider trying a sample script for construction of a mesh from our
162 \ref tui_creating_meshes_page "TUI Scripts" section.
164 \anchor evaluate_anchor
165 <h2>Evaluating mesh size</h2>
167 After the mesh object is created and all hypotheses are assigned and
168 before \ref compute_anchor "Compute" operation, it is possible to
169 calculate the eventual mesh size. For this, select the mesh in
170 the <b>Object Browser</b> and from the \b Mesh menu select \b
171 Evaluate. The result of evaluation will be displayed in the following
174 \image html mesh_evaluation_succeed.png
176 \anchor preview_anchor
177 <h2>Previewing the mesh</h2>
179 Before \ref compute_anchor "the mesh computation", it is also possible
180 to see the mesh preview.
182 For this, select the mesh in the Object Browser. From the \b Mesh menu
183 select \b Preview or click "Preview" button in the toolbar or activate
184 "Preview" item from the pop-up menu.
187 \image html mesh_precompute.png
188 <em>"Preview" button</em>
191 Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog.
193 \image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"
195 \image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"
197 <b>Compute</b> button computes the whole mesh.
199 When the Preview dialog is closed, the question about the storage of temporarily
200 created mesh elements appears:
202 \image html preview_tmp_data.png
204 These elements can be kept in the mesh.
207 \anchor submesh_order_anchor
208 <h2>Changing sub-mesh priority</h2>
210 If the mesh contains concurrent \ref constructing_submeshes_page "sub-meshes",
211 it is possible to change the priority of their computation, i.e. to
212 change the priority of applying algorithms to the shared sub-shapes of
215 <em>To change submesh priority:</em>
217 Choose "Change submesh priority" from the Mesh menu or a pop-up
218 menu. The opened dialog shows a list of submeshes in the order of
221 There is an example of submesh order modifications taking a Mesh created on a Box
222 shape. The main Mesh object:
224 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=20</li>
225 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>Max Element Area</b>
228 The first submesh object <b>Submesh_1</b> created on <b>Face_1</b> is:
230 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=4</li>
231 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
233 The second submesh object <b>Submesh_2</b> created on <b>Face_2</b> is:
235 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=8</li>
236 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
239 And the last submesh object <b>Submesh_3</b> created on <b>Face_3</b> is:
241 <li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=12</li>
242 <li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis <b>MaxElementArea</b>=1200</li>
245 The sub-meshes become concurrent if they share sub-shapes that can be
246 meshed with different algorithms (or different hypotheses). In the
247 example, we have three submeshes with concurrent algorithms, because
248 they have different hypotheses.
250 The first mesh computation is made with:
252 \image html mesh_order_123.png
253 <em>"Mesh order SubMesh_1, SubMesh_2, SubMesh_3"</em></center>
255 \image html mesh_order_123_res.png
256 <em>"Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "</em></center>
258 The next mesh computation is made with:
260 \image html mesh_order_213.png
261 <em>"Mesh order SubMesh_2, SubMesh_1, SubMesh_3"</em></center>
263 \image html mesh_order_213_res.png
264 <em>"Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "</em></center>
266 And the last mesh computation is made with:
268 \image html mesh_order_321.png
269 <em>"Mesh order SubMesh_3, SubMesh_2, SubMesh_1"</em></center>
270 <center>\image html mesh_order_321_res.png
271 <em>"Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "</em></center>
273 As we can see, each mesh computation has a different number of result
274 elements and a different mesh discretization on the shared edges (the edges
275 that are shared between <b>Face_1</b>, <b>Face_2</b> and <b>Face_3</b>)
277 Additionally, submesh priority (the order of applied algorithms) can
278 be modified not only in a separate dialog box, but also in
279 the <b>Preview</b>. This helps to preview different mesh results,
280 modifying the order of submeshes.
282 \image html mesh_order_preview.png
283 <em>"Preview with submesh priority list box"</em></center>
285 If there are no concurrent submeshes under the Mesh object, the user
286 will see the following information.
288 \image html mesh_order_no_concurrent.png
289 <em>"No concurrent submeshes detected"</em></center>
292 \anchor compute_anchor
293 <h2>Computing the mesh</h2>
295 It is equally possible to skip \ref evaluate_anchor "the Evaluation"
296 and \ref preview_anchor "the Preview" and to \b Compute the mesh after
297 the hypotheses are assigned. For this, select your mesh in
298 the <b>Object Browser</b>. From the \b Mesh menu select \b Compute or
299 click "Compute" button of the toolbar.
302 \image html image28.png
303 <em>"Compute" button</em>
306 After the mesh computation finishes, the Mesh Computation information
307 box appears. In case of a success, the box shows
308 information on number of entities of different types in the mesh.
310 \image html meshcomputationsucceed.png
312 If the mesh computation failed, the information about the cause of the
313 failure is provided in \b Errors table.
315 \image html meshcomputationfail.png
317 After you select the error, <b>Show Sub-shape</b> button allows
318 visualizing in magenta the geometrical entity that causes the error.
320 \image html failed_computation.png
321 <em>3D algorithm failed to compute mesh on a box shown using <b>Show
322 Sub-shape</b> button</em>
324 <b>Publish Sub-shape</b> button publishes the sub-shape, whose meshing
325 has failed, in GEOM component as a child of the mesh geometry, which
326 allows analyzing the problem geometry and creating a submesh on it in
327 order to locally tune the hypotheses.
329 If the failure is caused by an invalid input mesh and the algorithm has
330 found which mesh entities are bad, <b>Show bad Mesh</b>
331 button appears in the dialog. Clicked, it shows the bad mesh entities in
332 the Viewer in magenta. Sometimes the shown mesh entities are too small
333 or/and hidden by other mesh elements. They can be seen after
334 switching the mesh to Wireframe visualization mode or switching off
335 the visualization of faces and volumes (if any).
337 <b>Bad Mesh to Group</b> button creates groups of bad mesh entities
338 to facilitate their analysis.
340 \image html show_bad_mesh.png
341 <em>Edges bounding a hole in the surface are shown in magenta using <b>Show
342 bad Mesh</b> button</em>
344 \note Mesh Computation Information box does not appear if you set
345 "Mesh computation/Show a computation result notification" preference
346 to the "Never" value. This option gives the possibility to control mesh
347 computation reporting. There are the following possibilities: always
348 show the information box, show only if an error occurs or never.
349 By default, the information box is always shown after mesh computation operation.