CFD Online Discussion Forums - OpenFOAM simulation stops with no error when increasing mesh element density

CFD Online Discussion Forums (https://www.cfd-online.com/Forums/)

- OpenFOAM Running, Solving & CFD (https://www.cfd-online.com/Forums/openfoam-solving/)

- - OpenFOAM simulation stops with no error when increasing mesh element density (https://www.cfd-online.com/Forums/openfoam-solving/232023-openfoam-simulation-stops-no-error-when-increasing-mesh-element-density.html)

OpenFOAM simulation stops with no error when increasing mesh element density

Hi all,

I've got a curious error in my simulation. The simulation will stop running at an early time step and exit without giving an error or explaining why. I began running this in parallel and the only erroneous line displayed was:

Code:

[58] #0 Foam::error::printStack(Foam::Ostream&)

I tried running this in series and instead I just got no message whatsoever about why the simulation stopped running.

This error only occurred when I increased my mesh element density from 175x315x42 to 200x360x48. The simulation worked for the former but not the latter which leads me to believe that it is a meshing problem. But when I use checkMesh it says that it only failed one test and I believe it was because of concave faces/cells.

I've attached my case below (some files, like the stl file, were removed due to the max file size) so if anyone could give me any indication as to why this is happening I would greatly appreciate it.

Thanks,
Dan

Hi Dan,

have a look at your writePrecision in controlDict and than have a look at your numbers in blockMeshDict.
You use locations like 1e-7 with a writePrecision of 7 this might cause trouble when changing your grid width.

You might want to set your write precision higher and do another test run.

Greetings,
Teresa

Hi Teresa,

I changed the 1e-7 to 1e-5 in my blockMeshDict but my simulation still exited at the exact same time step as before :/

Do you have any other suggestions? This might have something to do with my STL file/snappyHexMesh because I found that when I increased my mesh element density from 150x270x36 to 175x315x42 I seemed to "lose" my refinement region (see attachments). I can't upload my stl file here since it exceeds the max file size so images are the best I can do right now.

Hey Dan,

you could try using a different STL

Your bounding box within the snappyHexMesh
boundingBox : (-2.186298e-09 3.544467e-19 -9.674712e-19) (0.05 0.05 0.012)

and there is a warning

--> FOAM Warning :
From function void Foam::snappySnapDriver::doSnap(const Foam::dictionary&, const Foam::dictionary&, bool, Foam::scalar, Foam::scalar, const Foam::snapParameters&)
in file snappyHexMeshDriver/snappySnapDriver.C at line 2844
Did not successfully snap mesh. Continuing to snap to resolve easy
surfaces but the resulting mesh will not satisfy your quality constraints

Maybe checkMesh can give you some new hints.

Regards
Teresa

Unfortunately I need to use this STL as my project revolves around lattices.

I ran checkMesh and this is the output:

Code:

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

| =========                 |                                                 |

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

|  \\    /   O peration     | Version:  v1812                                 |

|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |

|    \\/     M anipulation  |                                                 |

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

Build  : v1812 OPENFOAM=1812

Arch   : "LSB;label=32;scalar=64"

Exec   : checkMesh -allGeometry -allTopology

Date   : Nov 27 2020

Time   : 11:29:16

Host   : DUIP74162

PID    : 2815

I/O    : uncollated

Case   : /home/ppydp7/computationalWorkPC/CFD/OpenFOAM/computationalTime/gyroidMatrix/meshElementSize/cubeCell/200x360x048_HPC

nProcs : 1

trapFpe: Floating point exception trapping enabled (FOAM_SIGFPE).

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

allowSystemOperations : Allowing user-supplied system call operations



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

Create time



Create mesh for time = 0



Enabling all (cell, face, edge, point) topology checks.



Enabling all geometry checks.



Time = 0



Mesh stats

    points:           3555489

    faces:            10466880

    internal faces:   10269006

    cells:            3455981

    faces per cell:   6

    boundary patches: 7

    point zones:      0

    face zones:       1

    cell zones:       2



Overall number of cells of each type:

    hexahedra:     3455981

    prisms:        0

    wedges:        0

    pyramids:      0

    tet wedges:    0

    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

    maxY                9600     9849     ok (non-closed singly connected)   (1e-05 0.07 1e-05) (0.05 0.07 0.012)

    minX                16944    17689    ok (non-closed singly connected)   (1e-05 -0.02 1e-05) (1e-05 0.07 0.012)

    maxX                16989    17689    ok (non-closed singly connected)   (0.05 -0.02 1e-05) (0.05 0.07 0.012)

    minY                9600     9849     ok (non-closed singly connected)   (1e-05 -0.02 1e-05) (0.05 -0.02 0.012)

    minZ                72000    72561    ok (non-closed singly connected)   (1e-05 -0.02 1e-05) (0.05 0.07 1e-05)

    maxZ                72000    72561    ok (non-closed singly connected)   (1e-05 -0.02 0.012) (0.05 0.07 0.012)

    gyroidMatrix        741      2360     ok (non-closed singly connected)   (1e-05 7.811226e-08 0.0008573088) (0.05 0.04999995 0.01114398)



Checking faceZone topology for multiply connected surfaces...

    FaceZone            Faces    Points   Surface topology                   Bounding box

    block_to_air        448857   450410   ok (non-closed singly connected)   (1e-05 -2.590211e-05 1e-05) (0.05 0.05002226 0.012)



Checking basic cellZone addressing...

    CellZone            Cells        Points       Volume       BoundingBox

    block               672595       936490       1.060277e-05 (1e-05 -2.590211e-05 1e-05) (0.05 0.05002226 0.012)

    air                 2783386      3069409      4.334144e-05 (1e-05 -0.02 1e-05) (0.05 0.07 0.012)



Checking geometry...

    Overall domain bounding box (1e-05 -0.02 1e-05) (0.05 0.07 0.012)

    Mesh has 3 geometric (non-empty/wedge) directions (1 1 1)

    Mesh has 3 solution (non-empty) directions (1 1 1)

    Boundary openness (-1.762469e-15 -3.517342e-16 6.255808e-15) OK.

    Max cell openness = 4.243169e-16 OK.

    Max aspect ratio = 12.8433 OK.

    Minimum face area = 1.896463e-09. Maximum face area = 1.540076e-07.  Face area magnitudes OK.

    Min volume = 1.449772e-12. Max volume = 3.802479e-11.  Total volume = 5.394421e-05.  Cell volumes OK.

    Mesh non-orthogonality Max: 65.64012 average: 10.60025

    Non-orthogonality check OK.

    Face pyramids OK.

 ***Max skewness = 4.757959, 35 highly skew faces detected which may impair the quality of the results

  <<Writing 35 skew faces to set skewFaces

    Coupled point location match (average 0) OK.

    Face tets OK.

    Min/max edge length = 2.048068e-05 0.0005143614 OK.

   *There are 1230 faces with concave angles between consecutive edges. Max concave angle = 42.74695 degrees.

  <<Writing 1230 faces with concave angles to set concaveFaces

    Face flatness (1 = flat, 0 = butterfly) : min = 0.7928011  average = 0.9981342

   *There are 3 faces with ratio between projected and actual area < 0.8

    Minimum ratio (minimum flatness, maximum warpage) = 0.7928011

  <<Writing 3 warped faces to set warpedFaces

    Cell determinant (wellposedness) : minimum: 0.008020489 average: 0.9545793

    Cell determinant check OK.

 ***Concave cells (using face planes) found, number of cells: 39349

  <<Writing 39349 concave cells to set concaveCells

    Face interpolation weight : minimum: 0.081386 average: 0.4851155

    Face interpolation weight check OK.

    Face volume ratio : minimum: 0.07626664 average: 0.9306736

    Face volume ratio check OK.



Failed 2 mesh checks.



End

I believe the failed checks to be the concave cells (which doesn't matter I think?) and the max skewness (which curiously I didn't have when I had my blockMeshDict at 1e-7).

I'm not particularly sure where to go from here now however.

Thank you for the help so far.

Hi,

even if you have to use this stl in the end you might want to use a different one now to check if the stl is a problem.
You can change your current STL to less features, different resolution and so on as well.

You might get better results with snappyHexMesh using the same grid with in all directions.

If snappyHexMesh refines your cells even more you should change the writingPrecision accordingly (instead of your points in the blockMesh).

Getting a nice mesh is worth the time and effort in many if not most cases.

Good luck,
Teresa

Thanks Teresa! I'm definitely going to have to work on my mesh a bit more then and make sure that it's as good as I can get it. Thanks for all of your help so far!

If I make any breakthroughs I'll post here again :)

You have an intresting geometry! I usually encounter problems when the stl is not refined enough. You can have really bad cells. First of all try checkMesh, see your elements if they are in good shape or not. If they are not, I suggest you to refine your stls surface quality.