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[Gmsh] Error : Self intersecting surface mesh, computing intersections & Error : Impossible |
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June 29, 2009, 00:48 |
Error : Self intersecting surface mesh, computing intersections & Error : Impossible
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#1 |
Member
Velan
Join Date: Mar 2009
Location: India
Posts: 50
Rep Power: 17 |
Hi All,
I have found two mysterious problem. Let me explain what i have done. I have found one gmsh example in cfd-online and try to replicate it. http://www.cfd-online.com/Forums/ope...ary-layer.html It works fine. Then i Import the stl file and create the external domain{bounding box}. Now created the prism layer using extrusion command upto certain height. Then try to create the volume from extrusion height to external domain. But i'm facing a problem nfo : Meshing volume 1 (extruded) You are trying to generate a mixed structured/unstructured grid using the 3D Delaunay algorithm. This algorithm cannot garantee that the final mesh will be conforming. You should probably use the Frontal Netgen algorithm instead. Do you really want to continue? (To disable this warning in the future, select `Enable expert mode' in the option dialog.) [Continue] or [Cancel]? (default=Continue) Info : Meshing volume 31 (Tetgen+Delaunay) Constructing Delaunay tetrahedralization. Delaunay seconds: 0.45 Creating surface mesh. Perturbing vertices. Delaunizing segments. Constraining facets. Error: Invalid PLC. Two subfaces (4676, 2508, 2788) and (2507, 2508, 3905) are found intersecting each other. Hint: Use -d switch to find all intersecting facets. Error : Self intersecting surface mesh, computing intersections (this could take a while) Constructing Delaunay tetrahedralization. Creating initial tetrahedralization. Incrementally inserting points. 87097 Flips (T23 51371, T32 32804, T22 211, T44 2711) Delaunay seconds: 0.44 When i visualize those mesh, i found that volume was created from the surface of stl file not from surface of extrusion layer. When i try to mesh using netgen algorithm, Info : Region 31 Face 4, 1 intersect Info : CalcLocalH: 4672 Points 0 Elements 9336 Surface Elements Info : WARNING: Intersecting elements 2429 and 8321 el1 = np = 3 3904 3905 4036 el2 = np = 3 2508 2788 3275 layer1 = 1 layer2 = 1 Info : WARNING: Intersecting elements 4954 and 8321 el1 = np = 3 2507 4036 3905 el2 = np = 3 2508 2788 3275 Without prism layer, meshing was perfect. But i need to add some prism layer near the surface. Is it possible to add prism layer and volume mesh from the latest surface of prism layer ? Second problem was, Imported the stl file. Created extrusion layer and try to create again extrusion layer from the latest surface of previous extrusion layer. But i am getting error of Error : Impossible to extrude entity 3 (of type 303) So, we cant extrude layer from the lastest surface of the extrusion using stl file ? lc=50; length=1500; dec=1000; Coherence; Merge "combine.stl"; Coherence; s1 = news ; s2 = s1 -1 ; sl1 = newsl ; Surface Loop (sl1) = {s2} ; Transfinite Surface {s2}; Recombine Surface {s2}; v2[] = Extrude{Surface{s2};Layers{8,1};Recombine;}; sl2 = newsl ; Surface Loop (sl2) = {-v2[0]} ; // External Domain xmin = -length + dec; xmax = length ; ymin = -length + dec; ymax = length - dec; zmin = -length + dec; zmax = length - dec; p1 = newp ; Point (p1) = { xmin, ymin, zmin ,lc }; p2 = newp ; Point (p2) = { xmax, ymin, zmin ,lc }; p3 = newp ; Point (p3) = { xmax, ymax, zmin ,lc }; p4 = newp ; Point (p4) = { xmin, ymax, zmin ,lc }; p5 = newp ; Point (p5) = { xmin, ymin, zmax ,lc }; p6 = newp ; Point (p6) = { xmax, ymin, zmax ,lc }; p7 = newp ; Point (p7) = { xmax, ymax, zmax ,lc }; p8 = newp ; Point (p8) = { xmin, ymax, zmax ,lc }; l1 = newl ; Line(l1) = {p1, p4}; l2 = newl ; Line(l2) = {p4, p8}; l3 = newl ; Line(l3) = {p8, p5}; l4 = newl ; Line(l4) = {p5, p1}; l5 = newl ; Line(l5) = {p2, p3}; l6 = newl ; Line(l6) = {p3, p7}; l7 = newl ; Line(l7) = {p7, p6}; l8 = newl ; Line(l8) = {p6, p2}; l9 = newl ; Line(l9) = {p1, p2}; l10 = newl ; Line(l10) = {p4, p3}; l11 = newl ; Line(l11) = {p5, p6}; l12 = newl ; Line(l12) = {p8, p7}; ll1 = newll ; Line Loop (ll1) = { l1,l2,l3,l4}; s3 = news ; Plane Surface (s3) ={ll1} ; ll2 = newll ; Line Loop (ll2) = { l5,l6,l7,l8}; s4 = news ; Plane Surface (s4) ={ll2} ; ll3 = newll ; Line Loop (ll3) = { -l3,l12,l7,-l11}; s5 = news ; Plane Surface (s5) ={ll3} ; ll4 = newll ; Line Loop (ll4) = { l1,l10,-l5,-l9}; s6 = news ; Plane Surface (s6) ={ll4} ; ll5 = newll ; Line Loop (ll5) = { l4,l9,-l8,-l11}; s7 = news ; Plane Surface (s7) ={ll5} ; ll6 = newll ; Line Loop (ll6) = { -l2,l10,l6,-l12}; s8 = news ; Plane Surface (s8) ={ll6} ; sl3 = newsl ; Surface Loop (sl3) = {s3,s4,s5,s6,s7,s8} ; ps1=newreg ; Physical Surface("body") = {s2}; ps2=newreg ; Physical Surface("xmin") = {s3}; ps3=newreg ; Physical Surface("xmax") = {s4}; ps4=newreg ; Physical Surface("ymin") = {s5}; ps5=newreg ; Physical Surface("ymax") = {s6}; ps6=newreg ; Physical Surface("zmin") = {s7}; ps7=newreg ; Physical Surface("zmax") = {s8}; v3=newv ; Volume(v3) = {sl3,sl2}; v4=newv ; Physical Volume (v4) = { v3, v2[1]} ; Thanks - Ranjith |
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July 14, 2015, 05:54 |
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#2 |
Senior Member
Join Date: Mar 2015
Posts: 250
Rep Power: 12 |
Hello,
has anyone had the same problem (problem 1) and knows how to solve it? Best regards, Kate |
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October 22, 2015, 10:55 |
Failed mesh operation: Surface is self intersecting
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#3 |
New Member
Vivek Rao
Join Date: Aug 2015
Posts: 3
Rep Power: 11 |
I've had quite a few problems with self intersecting faces during parts based mesh operations in STAR-CCM+. I cut a linear pattern of spacer grids with mixing vanes through a channel to study sub-channel thermal hydraulics in modular PWRs.
One solution is to not perform the final subtraction/imprint for bodies within the CAD modeler, but as a parts based mesh operation. Surprisingly works much better since (my understanding) it uses generated mesh surfaces/volumes to perform the subtract/imprint - makes it easier to perform if you mesh is not discrete enough to completely replicate the CAD surface (is a big problem with complex geometries). Sometimes, two disconnected surfaces with the same name in the same region technically result in a non-manifold surface for the volume mesher. Try renaming all disconnected surfaces that would otherwise appear as one entity in a single region. |
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October 22, 2015, 11:05 |
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#4 |
Senior Member
Join Date: Mar 2015
Posts: 250
Rep Power: 12 |
Hi,
thank you for this contribution. That is what I experienced too. Finally I rebuilt my geometry completely from scratch in gmsh and went with a fully structured mesh. Kate |
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