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231 lines
8.9 KiB
HTML
231 lines
8.9 KiB
HTML
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<!DOCTYPE HTML PUBLIC "HTML 4.01 Transitional">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html">
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<title>Geometry module in SALOME environnement </title>
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</head>
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<body>
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<h1>SMESH starting tutorial</h1>
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<h2>2D meshing with MEFISTO</h2>
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<h3>Overview</h3>
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<p><i>Before following this tutorial you need to create or import a geometry.
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Please refere to the GEOM module documentation to do so.</i></p>
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<p>Now we have to load SMESH component. To do so : </p>
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<ul>
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<li>click on the SMESH icon or on 'SMESH' into the combo box of resources
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on botton left.</li>
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</ul>
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<p><i>SMESH is used to mesh edges, faces and volums each one thanks to a
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specialised algorithm. To mesh an entity which degree is n, one must have all
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its lower degree entities meshed. For instance, to mesh a face requires a
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previous meshing of all its edges. In the example MEFISTO meshes faces, and
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Regular_1D meshes edges. MEFISTO doesn't check how edges are meshed. The only
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test it does is to verify that edges are meshed before starting its work.
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MEFISTO requires an hypothesis : maximum area of triangles. Regular_1D
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requires one hypothesis among two: number of segments per edge <u>or</u>
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length of segment.</i> </p>
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<p>The entire operation is done by :</p>
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<ol>
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<li>init a mesh object associated to a geometrical object</li>
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<li>choosing an <u>algorithm</u> for meshing faces, here MEFISTO is
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choosen</li>
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<li>choosing an <u>algorithm</u> for meshing edges, here Regular1d is
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choosen</li>
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<li>creating <u>hypothesis</u> of calculation. We need to inform :
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<ul>
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<li>the number of segments per edge</li>
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<li>the maximum area per triangle of meshing</li>
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</ul>
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</li>
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<li>setting or attaching algorithm and hypothesis to the object loaded</li>
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<li>launching computation</li>
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<li>displaying the result in the best mode.</li>
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</ol>
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<img alt="" src="SMESHOverview.png">
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<h3>Details</h3>
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<p>Below are explained those 6 steps precisely : </p>
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<ol>
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<li><p><u>init a mesh object associated to a geometrical object :</u></p>
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<p><img src="MeshInit.png"></p>
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<ul>
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<li>In the menu bar on the top, find the <u>Mesh</u> menu and click on
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<u>Init.</u></li>
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<li>Then in the dialog box select the topology into Geometry field of
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ObjectBrowser or Viewer, give a name an click on Ok.</li>
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<li>The topology is now known inside SMESH component.</li>
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</ul>
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</li>
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<li><p>define algorithms for meshing : </p>
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<p><img src="SelectAlgorithms.png"></p>
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<ul>
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<li>In the menu bar, find <u>Hypothesis</u>, <u>Algorithm</u> then
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click on <u>Mefisto.</u></li>
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<li>Do the same to load 'Regular1D'.</li>
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<li>Remember, Regular1D is needed for edge meshing.</li>
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</ul>
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</li>
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<li><p>define <u>hypothesis</u> of calculation :<br>
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In the menu bar, find <u>Hypothesis</u> then Hypothesis and click on
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Segments. Then in the dialog box give a name for <u>hypothesis</u> and a
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value that is the number of segments per edge. Enter 7 segments for
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example.<br>
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Do the same for 'Max. Element Area' argument that is the maximum surface
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of triangles builded during meshing. Enter 2500 here.</p>
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</li>
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<li><p>Attach previous arguments (hypothesis) and algorithm to the
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topology :<br>
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Select the object in the Object Browser then using pop up menu (right
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click on object),<br>
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'Set algorithm' and 'Set Hypothesis' into specialized dialog boxes.<br>
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You can also find these methods in the menu 'Hypothesis'.</p>
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</li>
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<li><p>Selecting the mesh object before, start computation in the pop up
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menu; click on 'Compute'.</p>
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</li>
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<li><p>Update the display using '<i>Update'</i> if necessary.<br>
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Note : in <i>Preferencies</i> / <i>Mesh</i> menu there is an
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option to have an automatic update of the display after operations that
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modify it such as Compute, adding nodes<65>€<EFBFBD> If this option is not
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setted user must make an update of the display manually.<br>
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<br>
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You may also adjust the display '<i>Properties' / 'Display Mode</i>' has
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you prefer ; shading, wireframe or shrink,<br>
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and adjust color and size attributs in a specific dialog box shown
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below.</p>
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<p><img src="SetColor.png"></p>
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</li>
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</ol>
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<h3>Final result of meshing</h3>
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<p>At this final step you can observe the result of 2D meshing of faces by
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MEFISTO.</p>
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<p>Note : it is possible to change an hypothesis by mean the pop up then
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<i>Edit</i> and finally compute again.</p>
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<p><img src="MeshResult.png"></p>
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<h2>Meshing with global and local hypothesis</h2>
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<h3>details</h3>
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<p><i>We would now make a mesh as before but with a local modification of
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parameter (hypothesis) on an edge. We first have to explode the initial
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topology in GEOMETRY component. This operation will give us access to sub
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shapes edges of geom.brep.</i></p>
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<ol>
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<li><p>import or create a geometry as before</p>
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</li>
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<li><p>call 'Explode' method found in 'New Entity' on the menu bar ;
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(remember the tip about Automatic/Store !) </p>
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<p><img src="SubShapesSelection.png"></p>
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</li>
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<li><p>select the main object, choose 'Edge' in the combo box and click on
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Ok.<br>
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<u>Note</u> : do not click on 'select sub shape' at anytime. This
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function is used with OCC viewer for individual sub shape selection not
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yet available with VTK.<br>
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<br>
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Now the object browser contents all edges as sub shapes of the main
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topology. Select the first edge <i>Edge_ 1</i> and display only it.
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Use the pop up 'Display only' mode for this.<br>
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You may also rename the edge to remember it for future meshing.<br>
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<i>Our scope : apply a local hypothesis on this edge.<br>
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</i></p>
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</li>
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<li><p>The job is now finished for GEOMETRY component.</p>
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</li>
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<li><p>Load SMESH component and use menus 'Mesh' and 'Init' to load the
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topology into SMESH as before.<br>
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(Already defined if you have kept the previous study.)</p>
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</li>
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<li><p>Define algorithms Regular_1D and Mefisto using menus 'Hypothesis'
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and 'Algorithm'.</p>
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</li>
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<li><p>Define hypothesis 'Segments' = 7 and 'Max. Element Area' = 2500.
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(Already defined if<69>€<EFBFBD>) </p>
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</li>
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<li><p>Define another hypothesis 'Local length' = 100 to be used only as
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local parameter for the edge.</p>
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</li>
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<li><p>Now we have to attach algorithms and hypothesis to topologies, the
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global and the sub shape edge.<br>
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For the main topology, select it and use 'Set algorithms' and 'Set
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Hypothesis' and attach :<br>
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hypothesis 'Segments' = 7 and 'Max. Element Area' = 2500.</p>
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</li>
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<li><p>To set a local parameter of meshing on the edge we do :<br>
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click on 'Mesh' menu then 'Add Sub Mesh'. On the dialog box select the
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main object then sub object edge from Object Browser and GEOMETRY field.
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Give it a local name; for example <i>myEdge</i> or anyone.</p>
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<p><img src="SubMeshContruction.png"></p>
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</li>
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<li><p>Set the algorithm used for edge meshing. Here use Regular_ 1D.
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</p>
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</li>
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<li><p>Set a local hypothesis to the edge. Use 'Local length' = 100.</p>
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</li>
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<li><p>'<i>Compute'</i> (and '<i>Update'</i> display if necessary see
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before) the main mesh object. This will compute also the edge sub
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shape.<br>
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Do not forget to activate the display mode Wireframe,
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Shading or Shrink; see in pop up menu '<i>Properties'</i>,
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'<i>Display mode'</i><EFBFBD>€<EFBFBD> </p>
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</li>
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<li><p>Move the point of view to watch the edge meshed with a local
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hypothesis 'Local length' = 100. </p>
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</li>
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</ol>
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<h3>The result of second meshing</h3>
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<p>As we see below, the effect produced by setting a local hypothesis setted
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on the edge <i>Edge_ 1.</i></p>
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<p align="left">Compare to another edge that have the same physical
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length.</p>
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<p><img src="MeshResult2.png"></p>
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<h2>Using PYTHON interpretor to import an example script</h2>
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It is easy to import an example of meshing procedure using PYTHON interpretor
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:
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<ul>
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<li>Load SMESH component with VTK viewer.</li>
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<li>Just type <i>'import geomMesh.py'</i> in the textual window of
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PYTHON.</li>
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<li>Validate with the <i>Enter</i> key.</li>
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<li>You just have to run 'Compute' then choose a display mode to see the
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result.</li>
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</ul>
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This imported example is very similar to the last exercice. It uses a local
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hypothesis on an edge too.
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<p><img src="ImportResult.png"></p>
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<h2>Control features</h2>
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<p>Test now a control function of area for mesh resulting triangles.</p>
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<p>Find <i>Control</i> on the menu bar then <i>Cells</i> and <i>Area</i>. The
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image below displays areas with a color depending on its value in the scalar
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bar shown on the left.<br>
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Scalar bar general parameters are setted in <i>Preferencies</i> /
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<i>Mesh</i> / <i>Scalar Bar</i>.</p>
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<p>Specific range parameters are changed with the pop up menu.</p>
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<p><img src="ControlFeature.png"></p>
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</body>
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</html>
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