Version: 6.5.0
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Constructing meshes


Construction of a mesh consists of:

To construct a mesh:

  1. In the Mesh menu select Create Mesh or click "Create Mesh" button in the toolbar.

    image32.png
    "Create Mesh" button

    The following dialog box will appear:

    createmesh-inv.png
  2. For example, you need to mesh a 3d object.
    First, type the name for your mesh in the "Name" box, by default, it is "Mesh_1". Then select the object you wish to mesh in the Object Browser and click the "Add" button (if name of the object not yet appeared in Geometry field).

    image120.png
    "Add" button

    Now you can define 1d Algorithm and 1d Hypotheses, which will be applied to the edges of your object. (Note that any object has edges, even if their existence is not apparent, for example, a sphere has 4 edges). Click the "Add Hypothesis" button to add a hypothesis.

    image121.png
    "Add Hypothesis" button

    Click the "Edit Hypothesis" button to define values for the current hypothesis.

    image122.png
    "Edit Hypothesis" button

    The use of additional hypotheses is optional (i.e. you may leave "None" in this box).

    Proceed in the same way with 2d and 3d Algorithms and Hypotheses, note that the choice of hypotheses depends on the algorithm. There must be one Algorithm and zero or several Hypotheses for each dimension of your object (most standard 2D and 3D algorithms can work without hypotheses using some default parameters), otherwise you will not get any mesh at all. Of course, if you wish to mesh a face, which is a 2d object, you don't need to define 3d Algorithm and Hypotheses.
    In the Object Browser the structure of the new mesh will be displayed as follows:

    image88.jpg

    It contains:

    • a reference to the geometrical object on the basis of which the mesh has been constructed;
    • Applied hypotheses folder containing the references to the hypotheses applied to the construction of the mesh;
    • Applied algorithms folder containing the references to the algorithms applied to the construction of the mesh.


    There is an alternative way to create a mesh on an object simply by clicking Assign a set of hypotheses button and selecting among pre-defined sets of hypotheses. In addition to the standard sets of hypotheses, it is possible to create custom sets by editing CustomMeshers.xml file located in the home directory. CustomMeshers.xml file must describe sets of hypotheses in the same way as ${SMESH_ROOT_DIR}/share/salome/resources/smesh/StdMeshers.xml file does (sets of hypotheses are enclosed between <hypotheses-set-group> tags).

    hypo_sets.png
    List of sets of hypotheses: [custom] is automatically added to the sets defined by the user

  3. After the mesh object is created and all hypotheses are assigned and before the mesh computation, it is possible to see the mesh preview.

    For this, select the mesh in the Object Browser. From the Mesh menu select Preview or click "Preview" button in the toolbar or activate "Preview" item from the pop-up menu.

    mesh_precompute.png
    "Preview" button

    Select 1D mesh or 2D mesh preview mode in the Preview dialog.

    preview_mesh_1D.png
    1D mesh preview shows nodes computed on geometry edges
    preview_mesh_2D.png
    2D mesh preview shows edge mesh elements, computed on geometry faces

    Compute button computes the whole mesh.

    When the Preview dialog is closed, the question about the storage of temporarily created mesh elements appers:

    preview_tmp_data.png

    These elenents can be reused in the next mesh computation.

  4. It is equally possible to skip the Preview and Compute the mesh after the hypotheses are assigned. For this, select your mesh in the Object Browser. From the Mesh menu select Compute or click "Compute" button of the toolbar.

    image28.png
    "Compute" button

    The Mesh Computation information box appears.

    meshcomputationsucceed.png

    If the mesh computation failed, the information about the cause of the failure is provided.

    meshcomputationfail.png

    After you select the error, Show Sub-shape button allows visualizing the geometrical entity that causes it.

    failed_computation.png
    Example of the invalid input mesh
    Note
    Mesh Computation Information box does not appear if you set "Mesh computation/Show a computation result notification" preference to the "Never" value. This option gives the possibility to control mesh computation reporting. There are the following possibilities: always show information box, only if an error occurs or never. By default, the information box is always shown after mesh computation operation.

    Publish Sub-shape button publishes the sub-shape, whose meshing failed, in GEOM component as a child of the mesh geometry, which allows analyzing the problem geometry and creating a submesh on it in order to locally tune hypotheses.

    NOTE It is possible to define a 1D or a 2D mesh in a python script and then use such submeshes in the construction of a 3D mesh. For this, there exist two algorithms: Use existing edges and Use existing faces. They are not entirely usable from the GUI, so a mesh created using these algorithms should be exported into a python script, edited and then imported into the GUi.

  5. It is possible to calculate the eventual mesh size before Compute operation. For this, select the mesh in the Object Browser and from the Mesh menu select Evaluate. The result of evaluation will be displayed in the following information box:

    mesh_evaluation_succeed.png

  6. If the mesh contains concurrent submeshes, it is possible to change the priority of their computation, i.e. to change the priority of applying algorithms to the shared sub-shapes of the Mesh shape.

    To change submesh priority:

  7. Choose "Change submesh priority" from the Mesh menu or a popup menu. The opened dialogue shows a list of submeshes in the order of their priority.

    There is an example of submesh order modifications of the Mesh created on a Box shape. The main Mesh object:

    • 1D Wire discretisation with Number of Segments=20
    • 2D Triangle (Mefisto) with HypothesisMax Element Area

    The first submesh object Submesh_1 created on Face_1 is:

    • 1D Wire discretisation with Number of Segments=4
    • 2D Triangle (Mefisto) with HypothesisMaxElementArea=1200

    The second submesh object Submesh_2 created on Face_2 is:

    • 1D Wire discretisation with Number of Segments=8
    • 2D Triangle (Mefisto) with HypothesisMaxElementArea=1200

    And the last submesh object Submesh_3 created on Face_3 is:

    • 1D Wire discretisation with Number of Segments=12
    • 2D Triangle (Mefisto) with HypothesisMaxElementArea=1200

    The submeshes become concurrent if they share sub-shapes that can be meshed with different algorithms (or different hypothesises). In the example, we have three submeshes with concurrent algorithms, because they have different hypotheses.

    The first mesh computation is made with:

    mesh_order_123.png
    "Mesh order SubMesh_1, SubMesh_2, SubMesh_3"
    mesh_order_123_res.png
    "Result mesh with order SubMesh_1, SubMesh_2, SubMesh_3 "

    The next mesh computation is made with:

    mesh_order_213.png
    "Mesh order SubMesh_2, SubMesh_1, SubMesh_3"
    mesh_order_213_res.png
    "Result mesh with order SubMesh_2, SubMesh_1, SubMesh_3 "

    And the last mesh computation is made with:

    mesh_order_321.png
    "Mesh order SubMesh_3, SubMesh_2, SubMesh_1"
    mesh_order_321_res.png
    "Result mesh with order SubMesh_3, SubMesh_2, SubMesh_1 "

    As we can see, each mesh computation has a different number of result elements and a different mesh discretisation on the shared edges (the edges that are shared between Face_1, Face_2 and Face_3)

    Additionally, submesh priority (the order of applied algorithms) can be modified not only in a separate dialog box, but also in the Preview. This helps to preview different mesh results, modifying the order of submeshes.

    mesh_order_preview.png
    "Preview with submesh priority list box"

    If there are no concurrent submeshes under the Mesh object, the user will see the following information.

    mesh_order_no_concurrent.png
    "No concurrent submeshes detected"

Consider trying a sample script for construction of a mesh from our TUI Scripts section.

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