CFD Online Discussion Forums - [snappyHexMesh] Disappearing geometry

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Disappearing geometry

Hello, I have a geometry of a distillation column with some pipes attached to it (photo can be found here: https://ibb.co/zFh9hgj). When I do the snappyHexMesh procedure, the pipes just disappear (the corresponding pic is here: https://ibb.co/nQsmXfM) and I don't know the reason. Can anybody tell me where I should look for the problem? Is it related to the snappyHexMesh specs, drawing, or anything else?

Thanks,
askarli.

Have you done a surface check (literally, surfaceCheck)? One possible reason is that your distillation vessel is one closed surface, and the nozzles are separate closed surfaces. The surface check should sort that out.

Presumably you have extracted the feature lines for the nozzles and are including them in the SHM dictionary?

Hi,

I did the surfaceCheck of the file and the result is shown below. Could you please have a look at it? I didn't notice any problem.

Code:

/*---------------------------------------------------------------------------*\

  =========                 |

  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox

   \\    /   O peration     | Website:  https://openfoam.org

    \\  /    A nd           | Version:  7

     \\/     M anipulation  |

\*---------------------------------------------------------------------------*/

Build  : 7-3bcbaf946ae9

Exec   : surfaceCheck dc150.stl

Date   : Jul 28 2021

Time   : 20:49:30

Host   : "sohrab-VirtualBox"

PID    : 2448

I/O    : uncollated

Case   : /home/sohrab/OpenFOAM/sohrab-7/run

nProcs : 1

sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).

fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)

allowSystemOperations : Allowing user-supplied system call operations



// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

Reading surface from "dc150.stl" ...



Statistics:

Triangles    : 197568

Vertices     : 98786

Bounding Box : (-3100.6 -2133.59 -3113.6) (3100.6 2133.59 41500)



Region        Size

------        ----

patch0        194348

patch1        300

patch2        358

patch3        463

patch4        327

patch5        124

patch6        172

patch7        287

patch8        448

patch9        222

patch10        157

patch11        140

patch12        222





Surface has no illegal triangles.



Triangle quality (equilateral=1, collapsed=0):

    0 .. 0.05  : 0.0244827

    0.05 .. 0.1  : 0.000217647

    0.1 .. 0.15  : 0.000156908

    0.15 .. 0.2  : 0.00950559

    0.2 .. 0.25  : 0.0142078

    0.25 .. 0.3  : 0.00950053

    0.3 .. 0.35  : 0.0146937

    0.35 .. 0.4  : 0.0230908

    0.4 .. 0.45  : 0.023602

    0.45 .. 0.5  : 0.0289824

    0.5 .. 0.55  : 0.032981

    0.55 .. 0.6  : 0.0283599

    0.6 .. 0.65  : 0.037749

    0.65 .. 0.7  : 0.0389132

    0.7 .. 0.75  : 0.0379211

    0.75 .. 0.8  : 0.0548216

    0.8 .. 0.85  : 0.0599945

    0.85 .. 0.9  : 0.081329

    0.9 .. 0.95  : 0.131043

    0.95 .. 1  : 0.348447



    min 4.16456e-12 for triangle 777

    max 0.995419 for triangle 105768



Dumping bad quality faces to "badFaces"

Paste this into the input for surfaceSubset





Edges:

    min 1.18216 for edge 125266 points (203.169 -3.54633 -2123.9)(203.186 -2.36429 -2123.9)

    max 38468 for edge 461 points (1821.67 1110.75 0)(1806.29 1135.59 38468)



Checking for points less than 1e-6 of bounding box ((6201.2 4267.18 44613.6) metre) apart.

Found 0 nearby points.



Surface is closed. All edges connected to two faces.



Number of unconnected parts : 1



Number of zones (connected area with consistent normal) : 1





End

Agreed - it seems to be one piece, although it is complaining about a few "bad faces" - check the folder, and you should see a file there with a list of the face numbers that it thinks are failing a quality check. Probably worth cleaning that up first. Then maybe check your SHM surface and edge settings, and possibly try with a finer background mesh (it looks pretty coarse from your picture).

Quote:

Originally Posted by Tobermory (Post 809183)

Thank you very much, I did some adjustments on the background mesh and it worked!

Regards,
askarli.