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In SnappyHexMesh, which external mesher can be usable for background mesh?

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Old   January 17, 2024, 12:52
Default In SnappyHexMesh, which external mesher can be usable for background mesh?
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Hi everyone.

I am very new in openFoam. I try to do a ventilation project for a room. Inside geometry is okay but room geometry(my background mesh) is hard to make with blockMesh (the room has chamfered like edges).

Do you have any advice about which mesher without blockMesh can I use for the room geometry?

Good day.
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Old   January 18, 2024, 03:24
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Hello,

You can use a STL file for your room geometry and use a simple blockMesh encapsulating it.

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Yann
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Old   January 18, 2024, 04:59
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Thank you for your advice.
But I am afraid I could not express myself properly. The room geometry is encapsulater one. I use STL file for inside furniture but room geometry is hard to be maked by blockmesh.

Regards,
Xbrt.
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Old   January 18, 2024, 05:07
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Can you elaborate about what you are trying to achieve?
Like a simple drawing?

You can have STL files for the furniture, another STL for the room geometry, and have a bigger blockMesh encapsulating all your stl files to use as background mesh. snappyHexMesh will use the locationInMesh coordinate to know what part of the mesh has to be kept and which ones will be removed.
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Old   January 18, 2024, 05:21
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Yes , my furniture is STL but the bigger geometry that is encapsulate the furniture is room. The room is hard to be maked with blockmesh. I wonder if there is any alternative.
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Old   January 18, 2024, 05:26
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Alright, this is my point: make the room as a STL file too, and use a blockMesh bigger than the room.

Your blockMesh can be made of one single block and the boundaries do not really matter as the blockMesh part outside of the room will be removed by snappy. You will end up with the inside of your room meshed and the boundaries will be the one defined in the room STL.

EDIT: added drawing
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Old   January 18, 2024, 05:37
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Ah, I now understand it. I will try to do. Thank you for your time and your information. I will put here the solution that maybe others can find it useful.

Have a nice day.
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Old   January 19, 2024, 07:54
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Hi again. I run this snappyHexMesh file and computer do not mesh my interior (table and lamps). How can I fix this?

geometry
{
room.stl
{
type triSurfaceMesh;
name room.stl;



regions
{

inlet
{
name inlet.stl;
}

outlets
{
name outlets.stl;
}

sidewalls
{
name sidewalls.stl;
}

upperwall
{
name upperwall.stl;
}
downwall
{
name downwall.stl;
}
}
}
lamps.stl
{
type triSurfaceMesh;
name lamps.stl;
}

table.stl
{
type triSurfaceMesh;
name table.stl;
}




/*
refinementBox1
{
type searchableBox;
min (-2 -2 -2);
max (2 2 2);
}
*/

};


castellatedMeshControls
{


maxLocalCells 100000;


maxGlobalCells 2000000;


minRefinementCells 0;


maxLoadUnbalance 0.10;



nCellsBetweenLevels 2;



features
(
{
file "room.eMesh";
level 0;
}
{
file "lamps.eMesh";
level 0;
}
{
file "table.eMesh";
level 0;
}
);


refinementSurfaces
{
room.stl
{

level (2 2);

regions
{

inlet
{
level (2 4);
patchInfo { type patch; }
}

outlets
{
level (2 4);
patchInfo { type patch; }
}

sidewalls
{
level (2 4);
patchInfo { type wall; }
}

upperwall
{
level (2 4);
patchInfo { type wall; }
}

downwall
{
level (2 4);
patchInfo { type wall; }
}
}
}


}


resolveFeatureAngle 60;



refinementRegions
{

}

locationInMesh (7.5 3 6);


}
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File Type: jpg geo.JPG (14.1 KB, 8 views)
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Old   January 19, 2024, 08:32
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Hello,

Where is located your locationInMesh point? this is the parameter defining which volume your want to keep in your mesh.

Yann
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Old   January 19, 2024, 10:05
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As Yann points out, locationInMesh must be set correctly.
Some additional hints:
1) usually we set the locationInMesh with some double components like (0.212 -11.991 2.2188). The reason is, that, if it lands on a cell node, snappy potentially makes strange things. This is probably not causing your isssue, just FYI.
2) Snappy works best with a uniform background mesh. Yours is very flat already, it is going to have a hard time creating a good quality mesh with this as an input. You need to really know what you are doing to use that kind of anisotropy.
3) I recommend not setting the min/max level for a region greater than 1 apart. The best would be to use one specific level for your region like (3 3) or (4 4).
4) Your global settings for maxGlobal and maxLocal cells might cause snappy to stop refining midway through the process and that might lead to some things missing. Make sure you are below these levels or increase these values if your computer can handle it.
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Old   January 19, 2024, 10:06
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It was 1st. point. After your answer I change it to 2nd. location. But now it does not run even.
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Old   January 19, 2024, 10:25
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2nd location is the way to go.

Quote:
Originally Posted by Xbrt View Post
IBut now it does not run even.
This does not give any useful information to help you. What error do you get? Do you have the snappyHexMesh log?

Yann
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Old   January 19, 2024, 11:00
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I correct the error but my outer mesh and interiors gone.
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Old   January 19, 2024, 11:01
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Quote:
Originally Posted by AtoHM View Post
As Yann points out, locationInMesh must be set correctly.
Some additional hints:
1) usually we set the locationInMesh with some double components like (0.212 -11.991 2.2188). The reason is, that, if it lands on a cell node, snappy potentially makes strange things. This is probably not causing your isssue, just FYI.
2) Snappy works best with a uniform background mesh. Yours is very flat already, it is going to have a hard time creating a good quality mesh with this as an input. You need to really know what you are doing to use that kind of anisotropy.
3) I recommend not setting the min/max level for a region greater than 1 apart. The best would be to use one specific level for your region like (3 3) or (4 4).
4) Your global settings for maxGlobal and maxLocal cells might cause snappy to stop refining midway through the process and that might lead to some things missing. Make sure you are below these levels or increase these values if your computer can handle it.
Thank you for advices
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Old   January 19, 2024, 11:04
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Well, outer mesh gone was pretty much the point since you want to simulate the flow inside the room right?

What do you mean by "interiors gone" ? No furniture at all or no mesh inside furniture?
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Old   January 19, 2024, 11:20
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in solutions I plan to see flow around table and lamps. But my STL files that located in triSurfacedMesh do not be meshed
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Old   January 19, 2024, 11:32
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OK then. Can you post your snappyHexMeshDict and your snappyHexMesh log?
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Old   January 19, 2024, 13:52
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Sorry for late answer. I cannot enter the forum for a gap
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File Type: txt log.txt (35.5 KB, 1 views)
File Type: txt snappy.txt (16.6 KB, 2 views)
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Old   January 19, 2024, 16:30
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Thanks for the files.

You need to define surface refinement for your lamps and table in the refinementSurfaces section. For now only room is defined and this is why only room is meshed.

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Old   January 20, 2024, 07:29
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Quote:
Originally Posted by Yann View Post
Thanks for the files.

You need to define surface refinement for your lamps and table in the refinementSurfaces section. For now only room is defined and this is why only room is meshed.

Yann
Thank you very much. Would you consider mentoring me on this project for fee?
I have very limited time until deadine and I am stucked.
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