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<p class="MsoNormal"><span lang="EN-GB">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I am a beginner.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">While working on a larger 3D project I noticed some gaps and overlaps.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I plan to simulate the heat transfer.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I assume gaps and overlaps are to be avoided to get a good simulation. Correct?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">I tracked down the origin of the gaps and overlaps and it seems to be the extrude command causing the trouble.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">The file below draws a rectangle with a round hole in the middle. In the hole a ring (annulus) is drawn.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">If I create the ring with the BooleanDifference command (difference of two circles): all works fine. All triangles line up perfectly around the contact line of ring and hole.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">If I create the ring with the Extrude command, things don’t line up.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Of course I could opt for the booleandifference command for this problem but:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-GB">I cannot use this booleandifference solution in my 3D problem<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0cm;mso-list:l0 level1 lfo1"><span lang="EN-GB">I can imagine these holes and overlaps also being produced in other curved contact surfaces.<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Is this a bug in GMSH or the be expected in more elaborate meshes?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">How can it be resolved?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Thank you!<o:p></o:p></span></p>
<div style="mso-element:para-border-div;border:none;border-bottom:solid windowtext 1.0pt;padding:0cm 0cm 1.0pt 0cm">
<p class="MsoNormal" style="border:none;padding:0cm"><span lang="EN-GB">Bart<o:p></o:p></span></p>
<p class="MsoNormal" style="border:none;padding:0cm"><span lang="EN-GB"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span lang="EN-GB">KanR = DefineNumber[ 0.1, Name "Parameters/KanR" ];<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">KanMeshsize = DefineNumber[ 0.05, Name "Parameters/KanMeshsize" ];<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">SetFactory("OpenCASCADE");<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Rectangle(1) = {-2.5, -2.5, 0, 5, 5, 0};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Circle(5) = {0, 0, 0, KanR, 0, 2*Pi};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Curve Loop(2) = {5};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Plane Surface(2) = {2};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">BooleanDifference{ Surface{1}; Delete; }{ Surface{2}; Delete; }<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Point(15) = {0, KanR, 0};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Point(16) = {0, KanR-0.05, 0};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Line(20) = {15, 16};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Extrude {{0, 0, 1}, {0, 0, 0}, 2*Pi} {<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"> Curve{20}; <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">}<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[1] = Distance;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[1].EdgesList = {5};<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[1].NNodesByEdge = 50;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[2] = Threshold;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[2].DistMax = 2.5;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[2].DistMin = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[2].IField = 1;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[2].LcMax = 0.25;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">//+<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Field[2].LcMin = KanMeshsize ;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Background Field = 2;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Mesh.CharacteristicLengthExtendFromBoundary = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Mesh.CharacteristicLengthFromPoints = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Mesh.CharacteristicLengthFromCurvature = 0;<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
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