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Update documentation: add explanation about meaning of "3D", "2D", "1D" and "0D" pages in "Create mesh" dialog box.
335 lines
13 KiB
Plaintext
335 lines
13 KiB
Plaintext
/*!
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\page constructing_meshes_page Constructing meshes
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\n Construction of a mesh on some geometry consists of:
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<ul>
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<li> \ref create_mesh_anchor "Creating of a mesh object"</li>
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<li> \ref evaluate_anchor "Evaluating mesh size"</li>
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<li> \ref preview_anchor "Previewing the mesh"</li>
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<li> \ref submesh_order_anchor "Changing submesh priority"</li>
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<li> \ref compute_anchor "Computing the mesh"</li>
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</ul>
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Mesh can be \ref use_existing_anchor "computed using your own meshing algorithms"
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written in Python.
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\anchor create_mesh_anchor
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<h2>Creation of a mesh object</h2>
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<em>To construct a mesh:</em>
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<ol>
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<li>Select a geometrical object for meshing.</li>
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<li>In the \b Mesh menu select <b>Create Mesh</b> or click <em>"Create
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Mesh"</em> button in the toolbar.
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\image html image32.png
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<em>"Create Mesh" button</em>
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The following dialog box will appear:
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\image html createmesh-inv.png
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<br>
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</li>
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<li>Apply \subpage basic_meshing_algos_page "meshing algorithms" and
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\subpage about_hypo_page "hypotheses" which will be used at computation of
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this mesh.
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"Create mesh" dialog box contains several tab pages titled \b 3D,
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\b 2D, \b 1D and \b 0D. The title of each page reflects the
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dimension of the CAD model (geometry) the algorithms listed on
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this page affect to. For example, \b 3D page lists algorithms
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that affect 3D geometrical objects (solids).
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\note
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- Some page(s) can be disabled - if the source geometrical
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object does not include shapes (sub-shapes) of the corresponding
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dimension(s). For example, if input object is a geometrical face,
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\b 3D page is disabled.
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- Some algorithms affect on geometry of several dimensions,
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i.e. "1D-2D" or "1D-2D-3D". If such algorithm is selected by the
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user, dialog box pages related to the corresponding lower level
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dimensions are disabled.
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- \b 0D page does not refer to the 0D elements, but to 0D
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geometry (vertices). Mesh module does not provide algorithms that
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produce 0D elements. Currently \b 0D page provides only one
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algorithm "Segments around vertex" that allows specyfing required
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size of mesh edges about some selected vertex(vertices).
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For example, you need to mesh a 3D object.
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First, type the name for your mesh in the \b Name box, by default,
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it is "Mesh_1". Then select the geometrical object you wish to
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mesh in the Object Browser and click "Select" button near \b Geometry
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field (if name of the object not yet appeared in \b Geometry field).
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\image html image120.png
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<em>"Select" button</em>
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Now you can define 3D Algorithm and 3D Hypotheses, which will be
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applied to solids of your geometrical object. Click the <em>"Add
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Hypothesis"</em> button to add a hypothesis.
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\image html image121.png
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<em>"Add Hypothesis" button</em>
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Click the <em>"Edit Hypothesis"</em> button to change values for the
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current hypothesis.
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\image html image122.png
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<em>"Edit Hypothesis" button</em>
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Most standard 2D and 3D algorithms can work without hypotheses
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using some default parameters. The use of additional hypotheses
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is optional (i.e. you may leave "None" in this box).
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Proceed in the same way with 2D and 1D Algorithms and Hypotheses that
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will be used to mesh faces and edges of your geometry. (Note
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that any object has edges, even if their existence is not
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apparent, for example, a sphere has 4 edges). Note that the
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choice of hypotheses and of an algorithm of lower dimension depends on
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the algorithm.
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Some algorithms generate mesh of several dimensions while others, of
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only one dimension. In the latter case there must be one Algorithm and zero or several
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Hypotheses for each dimension of your object, otherwise you will
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not get any mesh at all. Of course, if you wish to mesh a face,
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which is a 2D object, you don't need to define 3D Algorithm and
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Hypotheses.
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In the <b>Object Browser</b> the structure of the new mesh will be
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displayed as follows:
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\image html image88.jpg
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It contains:
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<ul>
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<li>a reference to the geometrical object on the basis of
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which the mesh has been constructed;</li>
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<li><b>Applied hypotheses</b> folder containing the references
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to the hypotheses applied at the construction of the mesh;</li>
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<li><b>Applied algorithms</b> folder containing the references
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to the algorithms applied at the construction of the mesh.</li>
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</ul>
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There is an alternative way to assign Algorithms and Hypotheses by
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clicking <b>Assign a set of hypotheses</b> button and selecting among
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pre-defined sets of hypotheses. In addition to the standard
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sets of hypotheses, it is possible to create custom sets by editing
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CustomMeshers.xml file located in the home directory. CustomMeshers.xml
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file must describe sets of hypotheses in the
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same way as ${SMESH_ROOT_DIR}/share/salome/resources/smesh/StdMeshers.xml
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file does (sets of hypotheses are enclosed between <hypotheses-set-group>
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tags).
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\image html hypo_sets.png
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List of sets of hypotheses: <em>[custom]</em>
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automatically added to the sets defined by the user
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</li>
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</ol>
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Consider trying a sample script for construction of a mesh from our
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\ref tui_creating_meshes_page "TUI Scripts" section.
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\anchor evaluate_anchor
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<h2>Evaluating mesh size</h2>
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After the mesh object is created and all hypotheses are assigned and
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before \ref compute_anchor "Compute" operation, it is possible to
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calculate the eventual mesh size. For this, select the mesh in
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the <b>Object Browser</b> and from the \b Mesh menu select \b
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Evaluate. The result of evaluation will be displayed in the following
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information box:
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\image html mesh_evaluation_succeed.png
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\anchor preview_anchor
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<h2>Previewing the mesh</h2>
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Before \ref compute_anchor "the mesh computation", it is also possible
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to see the mesh preview.
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For this, select the mesh in the Object Browser. From the \b Mesh menu
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select \b Preview or click "Preview" button in the toolbar or activate
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"Preview" item from the pop-up menu.
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\image html mesh_precompute.png
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<em>"Preview" button</em>
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Select <b>1D mesh</b> or <b>2D mesh</b> preview mode in the Preview dialog.
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\image html preview_mesh_1D.png "1D mesh preview shows nodes computed on geometry edges"
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<br>
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\image html preview_mesh_2D.png "2D mesh preview shows edge mesh elements, computed on geometry faces"
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<b>Compute</b> button computes the whole mesh.
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When the Preview dialog is closed, the question about the storage of temporarily
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created mesh elements appers:
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\image html preview_tmp_data.png
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These elements can be kept in the mesh.
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\anchor submesh_order_anchor
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<h2>Changing submesh priority</h2>
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If the mesh contains concurrent \ref constructing_submeshes_page "submeshes",
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it is possible to change the priority of their computation, i.e. to
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change the priority of applying algorithms to the shared sub-shapes of
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the Mesh shape.
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<em>To change submesh priority:</em>
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Choose "Change submesh priority" from the Mesh menu or a pop-up
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menu. The opened dialog shows a list of submeshes in the order of
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their priority.
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There is an example of submesh order modifications of the Mesh created on a Box
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shape. The main Mesh object:
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<ul>
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<li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=20</li>
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<li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>Max Element Area</b>
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</li>
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</ul>
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The first submesh object <b>Submesh_1</b> created on <b>Face_1</b> is:
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<ul>
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<li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=4</li>
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<li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>MaxElementArea</b>=1200</li>
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</ul>
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The second submesh object <b>Submesh_2</b> created on <b>Face_2</b> is:
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<ul>
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<li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=8</li>
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<li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>MaxElementArea</b>=1200</li>
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</ul>
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And the last submesh object <b>Submesh_3</b> created on <b>Face_3</b> is:
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<ul>
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<li><i>1D</i> <b>Wire discretisation</b> with <b>Number of Segments</b>=12</li>
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<li><i>2D</i> <b>Triangle (Mefisto)</b> with Hypothesis<b>MaxElementArea</b>=1200</li>
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</ul>
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The sub-meshes become concurrent if they share sub-shapes that can be
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meshed with different algorithms (or different hypothesises). In the
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example, we have three submeshes with concurrent algorithms, because
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they have different hypotheses.
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The first mesh computation is made with:
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<center>
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\image html mesh_order_123.png
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<em>"Mesh order SubMesh_1, SubMesh_2, SubMesh_3"</em></center>
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<center>
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\image html mesh_order_123_res.png
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<em>"Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "</em></center>
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The next mesh computation is made with:
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<center>
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\image html mesh_order_213.png
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<em>"Mesh order SubMesh_2, SubMesh_1, SubMesh_3"</em></center>
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<center>
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\image html mesh_order_213_res.png
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<em>"Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "</em></center>
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And the last mesh computation is made with:
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<center>
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\image html mesh_order_321.png
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<em>"Mesh order SubMesh_3, SubMesh_2, SubMesh_1"</em></center>
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<center>\image html mesh_order_321_res.png
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<em>"Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "</em></center>
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As we can see, each mesh computation has a different number of result
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elements and a different mesh discretisation on the shared edges (the edges
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that are shared between <b>Face_1</b>, <b>Face_2</b> and <b>Face_3</b>)
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Additionally, submesh priority (the order of applied algorithms) can
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be modified not only in a separate dialog box, but also in
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the <b>Preview</b>. This helps to preview different mesh results,
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modifying the order of submeshes.
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<center>
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\image html mesh_order_preview.png
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<em>"Preview with submesh priority list box"</em></center>
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If there are no concurrent submeshes under the Mesh object, the user
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will see the following information.
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<center>
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\image html mesh_order_no_concurrent.png
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<em>"No concurrent submeshes detected"</em></center>
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\anchor compute_anchor
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<h2>Computing the mesh</h2>
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It is equally possible to skip \ref evaluate_anchor "the Evaluation"
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and \ref preview_anchor "the Preview" and to \b Compute the mesh after
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the hypotheses are assigned. For this, select your mesh in
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the <b>Object Browser</b>. From the \b Mesh menu select \b Compute or
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click "Compute" button of the toolbar.
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\image html image28.png
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<em>"Compute" button</em>
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The Mesh Computation information box appears.
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\image html meshcomputationsucceed.png
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If the mesh computation failed, the information about the cause of the
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failure is provided.
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\image html meshcomputationfail.png
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After you select the error, <b>Show Sub-shape</b> button allows
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visualizing in magenta the geometrical entity that causes it.
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\image html failed_computation.png
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<em>3D algorithm failed to compute mesh on a box shown using <b>Show
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Sub-shape</b> button</em>
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\note Mesh Computation Information box does not appear if you set
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"Mesh computation/Show a computation result notification" preference
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to the "Never" value. This option gives the possibility to control mesh
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computation reporting. There are the following possibilities: always
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show information box, only if an error occurs or never.
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By default, the information box is always shown after mesh computation operation.
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<b>Publish Sub-shape</b> button publishes the sub-shape, whose meshing
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failed, in GEOM component as a child of the mesh geometry, which
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allows analyzing the problem geometry and creating a submesh on it in
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order to locally tune hypotheses.
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If a cause of failure is an invalid input mesh and the algorithm has
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provided information on what mesh entities are bad <b>Show bad Mesh</b>
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button appears in the dialog. Clicked, it shows bad mesh entities in
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the Viewer in magenta. Sometimes the shown mesh entities are too small
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or/and hidden by other mesh elements, to see them it can be helpful to
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switch the mesh to Wireframe visualization mode or to switch off
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visualization of faces and volumes (if any).
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\anchor use_existing_anchor
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<h2>"Use existing edges" and "Use existing faces" algorithms</h2>
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It is possible to create an 1D or a 2D mesh in a python script
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(using <em>AddNode, AddEdge</em> and <em>AddFace</em> commands) and
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then use such sub-meshes in the construction of a 2D or a 3D mesh. For
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this, there exist two algorithms: <b>Use existing edges</b> and <b>Use
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existing faces</b>. Scenario of their usage is following. For
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example, you want to use standard algorithms to generate 1D and 3D
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meshes and to create 2D mesh by your python code. Then you
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<ul>
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<li> create a mesh object, assign an 1D algorithm,</li>
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<li> invoke \b Compute command, which computes an 1D mesh,</li>
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<li> assign <b>Use existing faces</b> and a 3D algorithm,</li>
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<li> run your python code, which creates a 2D mesh,</li>
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<li> invoke \b Compute command, which computes a 3D mesh.</li>
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</ul>
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Consider trying a sample script demonstrating usage of
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\ref tui_use_existing_faces "Use existing faces" algorithm for
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construction of a 2D mesh using Python commands.
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\image html use_existing_face_sample_mesh.png
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<em> Mesh computed by \ref tui_use_existing_faces "the sample script"
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shown in a Shrink mode.</em>
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*/
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