X-Git-Url: http://git.salome-platform.org/gitweb/?p=modules%2Fsmesh.git;a=blobdiff_plain;f=doc%2Fsalome%2Fgui%2FSMESH%2Finput%2Fconstructing_meshes.doc;h=6794b398bea21a50f333c7a54e881af35a9223a5;hp=bef709906ca7c7c817eb3d57a1e4b992ed4af6b0;hb=c150e1e4c40479c83b47cfb732f240c5df3b5d62;hpb=1067ffa6e7e5c394e3a1b17219d8b355a57607cd diff --git a/doc/salome/gui/SMESH/input/constructing_meshes.doc b/doc/salome/gui/SMESH/input/constructing_meshes.doc index bef709906..6794b398b 100644 --- a/doc/salome/gui/SMESH/input/constructing_meshes.doc +++ b/doc/salome/gui/SMESH/input/constructing_meshes.doc @@ -2,17 +2,70 @@ \page constructing_meshes_page Constructing meshes -\n Construction of a mesh on some geometry consists of: +To create a mesh on geometry, it is necessary to create a mesh object by choosing +- a geometrical shape produced in the Geometry module (main shape); +- meshing parameters, including + - \ref basic_meshing_algos_page "meshing algorithms" and + - \ref about_hypo_page "hypotheses" specifying constraints to be + taken into account by the chosen meshing algorithms. + +Then you can launch mesh generation by invoking \ref compute_anchor "Compute" command. +The generated mesh will be automatically shown in the Viewer. You can +switch off automatic visualization or limit mesh size until which it is +automatically shown in \ref mesh_preferences_page (Automatic update entry). + +\note Sometimes \a hypotheses term is used to refer to both algorithms +and hypotheses. + +Mesh generation on the geometry is performed in the bottom-up +flow: nodes on vertices are created first, then edges are divided into +segments using nodes on vertices; the node of segments are then +used to mesh faces; then the nodes of faces are used to mesh +solids. This automatically assures the conformity of the mesh. + +It is required to choose a meshing algorithm for every dimension of +sub-shapes up to the highest dimension to be generated. Note +that some algorithms generate elements of several dimensions, and +others of only one. It is not necessary to define meshing +parameters for all dimensions at once; you can start from 1D +meshing parameters only, compute the 1D mesh, then define 2D meshing +parameters and compute the 2D mesh (note that 1D mesh will not be +re-computed). + +An algorithm of a certain dimension chosen at mesh creation is applied +to discretize every sub-shape of this dimension. It is possible to +specify a different algorithm or hypothesis to be applied to one or +a group of sub-shapes by creating a \ref constructing_submeshes_page +"sub-mesh". You can specify no algorithms at all at mesh object +creation and specify the meshing parameters on sub-meshes only; then +only the sub-shapes, for which an algorithm and a hypothesis (if any) +have been defined will be discretized. + +\n Construction of a mesh on a geometry includes at least two +(\ref create_mesh_anchor "mesh creation" and +\ref compute_anchor "computing") of the following steps: -Mesh can be \ref use_existing_anchor "computed using your own meshing algorithms" -written in Python. - \anchor create_mesh_anchor

Creation of a mesh object

@@ -22,108 +75,178 @@ written in Python.
  • In the \b Mesh menu select Create Mesh or click "Create Mesh" button in the toolbar. +
    \image html image32.png "Create Mesh" button +
    The following dialog box will appear: \image html createmesh-inv.png
    • +
  • To filter off irrelevant meshing algorithms, you can + select Mesh Type in the corresponding list from Any, + Hexahedral, Tetrahedral, Triangular and \b Quadrilateral (there + can be less items for the geometry of lower dimensions). + + Selection of a mesh type hides all meshing algorithms that cannot + generate elements of this type.
    • +
  • Apply \subpage basic_meshing_algos_page "meshing algorithms" and - \subpage about_hypo_page "hypotheses" which will be used at computation of + \subpage about_hypo_page "hypotheses" which will be used to compute this mesh. "Create mesh" dialog box contains several tab pages titled \b 3D, \b 2D, \b 1D and \b 0D. The title of each page reflects the - dimension of the CAD model (geometry) the algorithms listed on - this page affect. For example, \b 3D page lists the algorithms - that affect 3D geometrical objects (solids). + dimension of the sub-shapes the algorithms listed on + this page affect and the maximal dimension of elements the algorithms + generate. For example, \b 3D page lists the algorithms that affect + 3D sub-shapes (solids) and generate 3D mesh elements + (tetrahedra, hexahedra etc.) + + As soon as you have selected an algorithm, you can create a + hypothesis (or select an already created one). A set of accessible + hypotheses includes only the hypotheses that can be used by the + selected algorithm. \note - - Some page(s) can be disabled if the source geometrical + - Some page(s) can be disabled if the geometrical object does not include shapes (sub-shapes) of the corresponding dimension(s). For example, if the input object is a geometrical face, \b 3D page is disabled. - Some algorithms affect the geometry of several dimensions, - i.e. "1D-2D" or "1D-2D-3D". If such an algorithm is selected by the - user, the dialog box pages related to the corresponding lower level - dimensions are disabled. - - \b 0D page does not refer to the 0D elements, but to 0D - geometry (vertices). Mesh module does not provide algorithms that + i.e. 1D+2D or 1D+2D+3D. If such an algorithm is selected, the + dialog pages related to the corresponding lower dimensions are + disabled. + - \b 0D page refers to 0D geometry (vertices) rather than + to 0D elements. Mesh module does not provide algorithms that produce 0D elements. Currently \b 0D page provides only one - algorithm "Segments around vertex" that allows specyfying the required + algorithm "Segments around vertex" that allows specifying the required size of mesh edges about the selected vertex (or vertices). For example, you need to mesh a 3D object. - First, type the name of your mesh in the \b Name box, by default, - it is "Mesh_1". Then select the geometrical object you wish to - mesh in the Object Browser and click "Select" button near \b Geometry - field (if the name of the object has not yet appeared in \b Geometry field). - + First, you can change a default name of your mesh in the \b Name + box. Then check that the selected geometrical object indicated in + \b Geometry field, is what you wish to mesh; if not, select + the correct object in the Object Browser. Click "Select" button + near \b Geometry field if the name of the object has not yet + appeared in \b Geometry field. +
    \image html image120.png "Select" button +
    Now you can define 3D Algorithm and 3D Hypotheses, which will be - applied to the solids of your geometrical object. Click the "Add - Hypothesis" button to add a hypothesis. - + applied to discretize the solids of your geometrical object using + 3D elements. Click the "Add Hypothesis" button to create + and add a hypothesis. +
    \image html image121.png "Add Hypothesis" button +
    + Click the "Plus" button to enable adding more additional hypotheses. Click the "Edit Hypothesis" button to change the values for the current hypothesis. - +
    \image html image122.png "Edit Hypothesis" button +
    - Most standard 2D and 3D algorithms can work without hypotheses - using some default parameters. The use of additional hypotheses - is optional (i.e. you may leave "None" in this box). + 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 + the dialog can contain: + + After selection of an algorithm Add. Hypothesis field can contain: + Proceed in the same way with 2D and 1D Algorithms and Hypotheses that will be used to mesh faces and edges of your geometry. (Note that any object has edges, even if their existence is not apparent, for example, a sphere has 4 edges). Note that the choice of hypotheses and lower dimension algorithms depends on - the higher dimension algorithm. + the higher dimension algorithm. + + If you wish you can select other algorithms and/or hypotheses + for meshing some sub-shapes of your CAD model by \ref constructing_submeshes_page. Some algorithms generate mesh of several dimensions, while others - produce mesh of only one dimension. In the latter case there must be one Algorithm and zero or several + produce mesh of only one dimension. In the latter case there must + be one Algorithm and zero or several Hypotheses for each dimension of your object, otherwise you will not get any mesh at all. Of course, if you wish to mesh a face, which is a 2D object, you do not need to define a 3D Algorithm and Hypotheses. - In the Object Browser the structure of the new mesh will be + In the Object Browser the structure of the new mesh is displayed as follows: - - \image html image88.jpg - - It contains: + \image html image88.jpg + It contains: There is an alternative way to assign Algorithms and Hypotheses by clicking Assign a set of hypotheses button and selecting among - pre-defined sets of hypotheses. In addition to the standard + pre-defined sets of algorithms and hypotheses. In addition to the built-in 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 - tags). - + file does (sets of hypotheses are enclosed between \ + tags). For example: +~~~~~~{.xml} + + + + + + + +~~~~~~ + If the file contents are incorrect, there can be an error at + activation of Mesh module: "fatal parsing error: error + triggered by consumer in line ..." +
    +
    \image html hypo_sets.png List of sets of hypotheses. Tag [custom] is - automatically added to the sets defined by the user + automatically added to the sets defined by the user. +
    + \note + - \a "Automatic" in the names of predefined sets of hypotheses + does not actually mean that they are suitable for meshing any + geometry. + - The list of sets of hypotheses can be shorter than in the + above image depending on the geometry dimension.
    • @@ -146,14 +269,18 @@ information box:

    Previewing the mesh

    Before \ref compute_anchor "the mesh computation", it is also possible -to see the mesh preview. +to see the mesh preview. This operation allows to incrementally +compute the mesh, dimension by dimension, and to discard an +unsatisfactory mesh. For this, select the mesh in the Object Browser. From the \b Mesh menu select \b Preview or click "Preview" button in the toolbar or activate "Preview" item from the pop-up menu. +
    \image html mesh_precompute.png "Preview" button +
    Select 1D mesh or 2D mesh preview mode in the Preview dialog. @@ -172,46 +299,46 @@ These elements can be kept in the mesh. \anchor submesh_order_anchor -

    Changing submesh priority

    +

    Changing sub-mesh priority

    -If the mesh contains concurrent \ref constructing_submeshes_page "submeshes", +If the mesh contains concurrent \ref constructing_submeshes_page "sub-meshes", 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: +To change sub-mesh priority: -Choose "Change submesh priority" from the Mesh menu or a pop-up -menu. The opened dialog shows a list of submeshes in the order of +Choose "Change sub-mesh priority" from the Mesh menu or a pop-up +menu. The opened dialog shows a list of sub-meshes in the order of their priority. -There is an example of submesh order modifications taking a Mesh created on a Box +There is an example of sub-mesh order modifications taking a Mesh created on a Box shape. The main Mesh object: -The first submesh object Submesh_1 created on Face_1 is: +The first sub-mesh Submesh_1 created on Face_1 is: -The second submesh object Submesh_2 created on Face_2 is: +The second sub-mesh Submesh_2 created on Face_2 is: -And the last submesh object Submesh_3 created on Face_3 is: +And the last sub-mesh Submesh_3 created on Face_3 is: The sub-meshes become concurrent if they share sub-shapes that can be meshed with different algorithms (or different hypotheses). In the -example, we have three submeshes with concurrent algorithms, because +example, we have three sub-meshes with concurrent algorithms, because they have different hypotheses. The first mesh computation is made with: @@ -238,18 +365,18 @@ And the last mesh computation is made with: "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 +elements and a different mesh discretization 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 +Additionally, sub-mesh 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. +modifying the order of sub-meshes.
    \image html mesh_order_preview.png -"Preview with submesh priority list box"
    +"Preview with sub-mesh priority list box" -If there are no concurrent submeshes under the Mesh object, the user +If there are no concurrent sub-meshes under the Mesh object, the user will see the following information.
    \image html mesh_order_no_concurrent.png @@ -262,39 +389,46 @@ will see the following information. It is equally possible to skip \ref evaluate_anchor "the Evaluation" and \ref preview_anchor "the Preview" and to \b Compute the mesh after the hypotheses are assigned. For this, select your mesh in -the Object Browser. From the \b Mesh menu select \b Compute or -click "Compute" button of the toolbar. +the Object Browser. From the \b Mesh menu or the context menu +select \b Compute or click \a "Compute" button of the toolbar. +
    \image html image28.png "Compute" button +
    -The Mesh Computation information box appears. +After the mesh computation finishes, the Mesh Computation information +box appears. If you close this box and click "Compute" button again, +without previously changing meshing parameters, the mesh will NOT be +re-computed and the Mesh Computation information box will be shown +with the same contents. (To fully re-compute the mesh, invoke +\ref clear_mesh_anchor "Clear Mesh Data" command before). + +\anchor meshing_result_anchor +If the mesh computation has been a success, the box shows information +on the number of entities of different types in the mesh. \image html meshcomputationsucceed.png -If the mesh computation failed, the information about the cause of the -failure is provided. +\anchor meshing_failed_anchor +If the mesh computation has failed, the information about the cause of the +failure is provided in \b Errors table. \image html meshcomputationfail.png -After you select the error, Show Sub-shape button allows -visualizing in magenta the geometrical entity that causes it. +After you select an error in \b Errors table, Show Sub-shape button allows +visualizing in magenta the geometrical entity meshing of which failed +(Name of this entity or its ID and type is shown in \a Sub-shape column). +
    \image html failed_computation.png 3D algorithm failed to compute mesh on a box shown using Show Sub-shape button - - -\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 the information box, show 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 -has failed, in GEOM component as a child of the mesh geometry, which -allows analyzing the problem geometry and creating a submesh on it in +has failed, in the Geometry component as a child of the main shape, which +allows analyzing the problematic geometry and creating a sub-mesh on it in order to locally tune the hypotheses. If the failure is caused by an invalid input mesh and the algorithm has @@ -305,35 +439,45 @@ or/and hidden by other mesh elements. They can be seen after switching the mesh to Wireframe visualization mode or switching off the visualization of faces and volumes (if any). +Bad Mesh to Group button creates groups of bad mesh entities +to facilitate their analysis. + +
    \image html show_bad_mesh.png -Too close nodes causing meshing failure are shown in magenta using Show +Edges bounding a hole in the surface are shown in magenta using Show bad Mesh button -

    - -\anchor use_existing_anchor -

    "Use existing edges" and "Use existing faces" algorithms

    - -It is possible to create a 1D or a 2D mesh in a python script -(using AddNode, AddEdge and AddFace commands) and -then use such sub-meshes in the construction of a 2D or a 3D mesh. For -this, there exist two algorithms: Use existing edges and Use - existing faces. -For example, you want to use standard algorithms to generate 1D and 3D -meshes and to create 2D mesh by your python code. Then you -
      -
    • create a mesh object, assign a 1D algorithm,
      • -
    • invoke \b Compute command, which computes a 1D mesh,
      • -
    • assign Use existing faces and a 3D algorithm,
      • -
    • run your python code, which creates a 2D mesh,
      • -
    • invoke \b Compute command, which computes a 3D mesh.
      • -
    +
    -Consider trying a sample script demonstrating the usage of -\ref tui_use_existing_faces "Use existing faces" algorithm for -construction of a 2D mesh using Python commands. +\note Mesh Computation Information box does not appear if you set +\ref show_comp_result_pref "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 the information box, show only if an error occurs or never. +By default, the information box is always shown after mesh computation operation. -\image html use_existing_face_sample_mesh.png - Mesh computed by \ref tui_use_existing_faces "the sample script" - shown in a Shrink mode. +

    +\anchor edit_anchor +

    Editing the mesh

    + +It is possible to \ref modifying_meshes_page "edit the mesh" of a +lower dimension before generation of the mesh of a higher dimension. + +For example you can generate a 2D mesh, modify it using e.g. +\ref pattern_mapping_page, and then generate a 3D mesh basing on the +modified 2D mesh. The workflow is as follows: +- Define 1D and 2D meshing algorithms. +- Compute the mesh. 2D mesh is generated. +- Apply \ref pattern_mapping_page. +- Define 3D meshing algorithms without modifying 1D and 2D algorithms +and hypotheses. +- Compute the mesh. 3D mesh is generated. + +\note Nodes and elements added \ref adding_nodes_and_elements_page +"manually" cannot be used in this workflow because the manually created +entities are not attached to any geometry and thus (usually) cannot be +found by the mesher paving a geometry. + +See Also a sample TUI Script demonstrates the possibility of +\ref tui_editing_while_meshing "Intermediate edition while meshing" */