<!doctype HTML public "-//W3C//DTD HTML 4.0 Frameset//EN"> <html> <!--(==============================================================)--> <!--(Document created with RoboEditor. )============================--> <!--(==============================================================)--> <head> <title>About meshes</title> <!--(Meta)==========================================================--> <meta http-equiv=content-type content="text/html; charset=windows-1252"> <meta name=generator content="RoboHELP by eHelp Corporation - www.ehelp.com"> <meta name=generator-major-version content=0.1> <meta name=generator-minor-version content=1> <meta name=filetype content=kadov> <meta name=filetype-version content=1> <meta name=page-count content=1> <meta name=layout-height content=1398> <meta name=layout-width content=700> <!--(Links)=========================================================--> <link rel='stylesheet' href='../default_ns.css'> <script type="text/javascript" language="JavaScript" title="WebHelpSplitCss"> <!-- if (navigator.appName !="Netscape") { document.write("<link rel='stylesheet' href='../default.css'>");} //--> </script> <style type="text/css"> <!-- img_whs1 {border-style: none; border: none; width: 30px; height: 30px; float: none;} ul.whs2 {list-style: disc;} p.whs3 {text-indent: 8px;} p.whs4 {text-indent: 48px;} h4.whs5 {text-indent: 1px;} p.whs6 {text-indent: 1px;} img_whs7 {border-style: none; border: none; width: 36px; height: 38px; float: none;} p.whs8 {font-weight: bold; text-indent: 1px;} --> </style> <script type="text/javascript" language="JavaScript" title="WebHelpInlineScript"> <!-- function reDo() { if (innerWidth != origWidth || innerHeight != origHeight) location.reload(); } if ((parseInt(navigator.appVersion) == 4) && (navigator.appName == "Netscape")) { origWidth = innerWidth; origHeight = innerHeight; onresize = reDo; } onerror = null; //--> </script> <style type="text/css"> <!-- div.WebHelpPopupMenu {position:absolute; left:0px; top:0px; z-index:4; visibility:hidden;} --> </style> <script type="text/javascript" language="javascript1.2" src="../whmsg.js"></script> <script type="text/javascript" language="javascript" src="../whver.js"></script> <script type="text/javascript" language="javascript1.2" src="../whproxy.js"></script> <script type="text/javascript" language="javascript1.2" src="../whutils.js"></script> <script type="text/javascript" language="javascript1.2" src="../whtopic.js"></script> </head> <!--(Body)==========================================================--> <body> <script type="text/javascript" language="javascript1.2"> <!-- if (window.gbWhTopic) { if (window.addTocInfo) { addTocInfo("SMESH module\nCreating meshes\nAbout meshes"); addButton("show",BTN_TEXT,"Show","","","","",0,0,"","",""); } if (window.writeBtnStyle) writeBtnStyle(); if (window.writeIntopicBar) writeIntopicBar(1); if (window.setRelStartPage) { setRelStartPage("../smesh.htm"); autoSync(0); sendSyncInfo(); sendAveInfoOut(); } } else document.location.reload(); //--> </script> <h1>About meshes</h1> <p><img src="../i_blue.jpg" x-maintain-ratio="TRUE" width="30px" height="30px" border="0" class="img_whs1"> <span style="font-weight: bold;"><B>MESH</B></span> represents a discretization of a geometrical CAD model into a set of entities with a simple topology. In SMESH there are two options of creation of meshes, you can:</p> <p> </p> <ul type="disc" class="whs2"> <li class=kadov-p><p>generate meshes on the basis of geometrical shapes produced in the GEOM module, </p></li> <li class=kadov-p><p>create your own meshes using the SMESH functions destined for modification of generated meshes. More about this functionality of SMESH see in the chapter "Modifying meshes". </p></li> </ul> <p> </p> <p>The topology of a mesh is described by the relationships between its entities including:</p> <p class="whs3"> </p> <ul type="disc" class="whs2"> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>Node</B></span> � 0D element of a mesh presented by a point with coordinates (x, y, z).</p></li> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>Edge</B></span> � 1D element of a mesh defined by two nodes.</p></li> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>Face</B></span> � 2D element of a mesh defined by three or four edges (closed contour).</p></li> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>Volume</B></span> � 3D element of a mesh defined by several faces.</p></li> </ul> <p class="whs3"> </p> <p class="whs4">These entities are considered as topological entities and they don't imply any geometric representation. Only <span style="font-weight: bold;"><B>Nodes</B></span> reference geometric representations of points with definite coordinates. <span style="text-indent: 8px;">The node entity will contain additional information about its position in the space and its relations with the meshed CAD model. Its position could be described in the following way:</span></p> <p class="whs4"> </p> <ul type="disc" class="whs2"> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>2D position</B></span>. It is a free position defined by only two coordinates x,y.</p></li> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>3D position</B></span>. It is a free position defined by three coordinates x,y and z.</p></li> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>Surface position</B></span>. It characterizes the position of a node on a geometric surface and is defined by the u,v position in the parametric space of the corresponding surface.</p></li> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>Line position</B></span>. It characterizes the position of a node on a geometric curve and is defined by the u parameter and the corresponding curve.</p></li> <li class=kadov-p><p class="whs3"><span style="font-weight: bold;"><B>Vertex position</B></span>. It characterizes the position of a node on a geometric point of the meshed CAD model and is defined by the x,y,z coordinates of the corresponding vertex.</p></li> </ul> <p class="whs3"> </p> <p class="whs3"> </p> <h4 class="whs5">Connections</h4> <p class="whs6">Each mesh entity bounds 0 or more mesh entities of higher dimension. In the same way each mesh entity is bounded by 0 or more mesh entities of lower dimension:</p> <p class="whs6"> </p> <ul type="disc" class="whs2"> <li class=kadov-p><p class="whs6">A node bounds edges, faces and volumes</p></li> <li class=kadov-p><p class="whs6">An edge bounds faces, and volumes</p></li> <li class=kadov-p><p class="whs6">A face bounds volumes</p></li> <li class=kadov-p><p class="whs6">A volume is bounded by faces, edges and nodes</p></li> <li class=kadov-p><p class="whs6">A face is bounded by edges, and nodes</p></li> <li class=kadov-p><p class="whs6">An edge is bounded by nodes</p></li> </ul> <p class="whs6"> </p> <p class="whs6">You can notice that there are two types of connections: <span style="font-weight: bold;"><B>inverse</B></span> and <span style="font-weight: bold;"><B>direct</B></span> connections.</p> <p class="whs6"> </p> <h4 class="whs5">Inverse connections</h4> <p class="whs6"> </p> <p class="whs6">This relationship has a particularity that the order of bounded entities has not a direct meaning. Also the number of bounded entities is not fixed.</p> <p class="whs6"> </p> <p class="whs6"><img src="../pics/exemple.gif" x-maintain-ratio="TRUE" width="36px" height="38px" border="0" class="img_whs7"> The edges surrounding a node. The 3rd edge has no more sense that the 5th one.</p> <p class="whs6"> </p> <p class="whs8">Direct connections</p> <p class="whs6"> </p> <p class="whs6">This relationship has a particularity that the order of bounding entities is meaningful. The number of bounding entities is fixed and depends on the type of the entity (hexahedron, tetrahedron,�).</p> <p class="whs6"> </p> <p class="whs6"><img src="../pics/exemple.gif" x-maintain-ratio="TRUE" width="36px" height="38px" border="0" class="img_whs7"> An edge is composed of two nodes. A face is composed of 3 or 4 edges depending if we are dealing with triangles or quadrangles.</p> <p class="whs6"> </p> <p class="whs6">The connections are not only restricted to entities of one dimension higher or lower. For example some algorithms may be interested to retrieve all the faces surrounding a node.</p> <p class="whs6"> </p> <p class="whs6"> </p> <p class="whs6"> </p> <script type="text/javascript" language="javascript1.2"> <!-- if (window.writeIntopicBar) writeIntopicBar(0); //--> </script> </body> </html>