# "hex" blocks that give prism and tet wedge cells

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August 28, 2012, 15:07
"hex" blocks that give prism and tet wedge cells
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Join Date: Jul 2010
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Hi;

I am doing a simple mesh using blockMesh. I define only two "hex" blocks, but I end up with cells of the type prism and tet wedge. Any idea what could be the reason for this?

Further notes:
-If I fix all the expansion ratios to 1, the mesh works fine and I do not have any errors in checkMesh -allGeometry -allTopology, so I do not think the definition of the blocks is wrong.
-The height of the first cell has to be really small (z+(1)~0.3) because I am using kwSST model with rugosity. So, I have to refine one of the blocks in the z direction. In that case, I get prism and tet wedges cells.

Here is my blockMeshDict:
Quote:
 ..... convertToMeters 1; // ******Coordinates of blocks x0 0; x1 3000; y0 -250; //Spanwise y1 250; z0 0; //Height z1 100; // Added another block to have only refinement in the bottom part to reach z+=0.3 without having really distorted cells at the top of the domain z2 500; //*****Number of cells***** Nx 250; // Number of x-cells Ny 80; // Number of y-cells Nz1 110; // Number of z-cells Nz2 35; //*****Grading values****** Gx 1.0; //x-grading Gy 1.0; //y-grading Gz1 1100920; //z-grading Equivalent to cell-to-cell expansion k : 1.13613 Gz2 1; //z-grading vertices ( (\$x0 \$y0 \$z0) //0 (\$x1 \$y0 \$z0) //1 (\$x1 \$y1 \$z0) //2 (\$x0 \$y1 \$z0) //3 (\$x0 \$y0 \$z1) //4 (\$x1 \$y0 \$z1) //5 (\$x1 \$y1 \$z1) //6 (\$x0 \$y1 \$z1) //7 (\$x0 \$y0 \$z2) //8 (\$x1 \$y0 \$z2) //9 (\$x1 \$y1 \$z2) //10 (\$x0 \$y1 \$z2) //11 ); blocks ( hex (0 1 2 3 4 5 6 7) (\$Nx \$Ny \$Nz1) simpleGrading (\$Gx \$Gy \$Gz1) hex (4 5 6 7 8 9 10 11) (\$Nx \$Ny \$Nz2) simpleGrading (\$Gx \$Gy \$Gz2) ); edges ( ); boundary ( inlet { type mappedPatch; offset (3000 0 0 ); sampleMode nearestCell; sampleRegion region0; samplePatch none; faces ( (0 4 7 3) (4 8 11 7) ); } outlet { type patch; faces ( (1 2 6 5) (5 6 10 9) ); } bottom { type wall; faces ( (0 3 2 1) ); } top { type symmetryPlane; faces ( (8 9 10 11) ); } front { type cyclic; neighbourPatch back; faces ( (0 1 5 4) (4 5 9 8) ); } back { type cyclic; neighbourPatch front; faces ( (3 7 6 2) (7 11 10 6) ); } ); mergePatchPairs ( ); // ************************************************** *********************** //
and this is the output of checkMesh -allGeometry -allTopology:

Quote:
 Mesh stats points: 2956446 faces: 8755970 internal faces: 8632150 cells: 2900000 boundary patches: 6 point zones: 0 face zones: 0 cell zones: 0 Overall number of cells of each type: hexahedra: 2888192 prisms: 11736 wedges: 0 pyramids: 0 tet wedges: 72 tetrahedra: 0 polyhedra: 0 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Topological cell zip-up check OK. Face-face connectivity OK. Number of regions: 1 (OK). Checking patch topology for multiply connected surfaces ... Patch Faces Points Surface topology Bounding box inlet 10160 10368 ok (non-closed singly connected) (0 -250 0.000715361) (0 250 500) outlet 10160 10368 ok (non-closed singly connected) (3000 -250 0.000715361) (3000 250 500) bottom 20000 20331 ok (non-closed singly connected) (0 -250 0) (3000 250 0.000715361) top 20000 20331 ok (non-closed singly connected) (0 -250 500) (3000 250 500) front 31750 32128 ok (non-closed singly connected) (0 -250 0.000715361) (3000 -250 500) back 31750 32128 ok (non-closed singly connected) (0 250 0.000715361) (3000 250 500) Checking geometry... Overall domain bounding box (0 -250 0) (3000 250 500) Mesh (non-empty, non-wedge) directions (1 1 1) Mesh (non-empty) directions (1 1 1) Boundary openness (-1.01591e-15 -3.39516e-14 0) OK. ***High aspect ratio cells found, Max aspect ratio: 2.20513e+06, number of cells 1100000 <

 January 30, 2013, 14:46 #2 Member   Join Date: Jul 2010 Posts: 37 Rep Power: 8 I was using OFv2.1.0 when I was getting the error explained in my previous post. Now, I used the same blockMeshDict in OFv2.1.1 and OFv1.7.1 and I did not have that problem!!! wyldckat likes this.

 Tags blockmesh, cell types, hex, prism, tet wedges

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