[EGajetti]

Hello everybody,
I'm trying a multi region mesh, where I have a solid part and a fluid part defined with two different .stl with patches.
I define cellZones and faceZones for the two parts so to use splitMeshRegions.
However, at the end of snappyHexMesh, all the patches are removed with the following warning:
"Removing zero-sized patches".

This is my snappyHexMeshDict:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  8
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      snappyHexMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#includeEtc "caseDicts/mesh/generation/snappyHexMeshDict.cfg"

castellatedMesh true;
snap            true;
addLayers       false;

geometry
{
	solido_semplice_patch.stl
	{
		type triSurfaceMesh;
		name solidoSemplice;
		regions
		{
			solido{name contact_solido;
				       type wall;}
			top{name topWall;
			    type wall;}
			bottom{name bottomWall;
			    type wall;}		
		}
			
	}
	fluido_semplice_patch.stl
	{
		type triSurfaceMesh;
		name fluidoSemplice;
		regions
		{
			fluido{name contactFluido;
				type wall;}
			inlet{name entrata;
				type patch;}
			outlet{name uscita;
				type patch;}
		}
	}
    
};

castellatedMeshControls
{
	// Refinement Parameters
	maxLocalCells 10000000;
	maxGlobalCells 50000000;
	minRefinementCells 0;
	maxLoadUnbalance 0.10;
	nCellsBetweenLevels 2;
	
	// Locale curvature and feature angle refinement
	resolveFeatureAngle 15;
	planarAngle 30;
	
	features
	(	
	);


	refinementSurfaces
        {

		solidoSemplice
        	{
            		level (2 2);
            		faceZone solidoSemplice; 
            		cellZone solidoSemplice; 
            		cellZoneInside insidePoint;
			insidePoint (0.0 0.006 0);
		}

       		fluidoSemplice
		{
            		level (2 2);
            		faceZone fluidoSemplice;
            		cellZone fluidoSemplice;
            		cellZoneInside insidePoint;
			insidePoint (0.0 0.0 0.000);
         	}
	  }
    refinementRegions
    {
    }

    locationInMesh (0 0 0);
    allowFreeStandingZoneFaces true;
/*
    faceZoneControls
        {
            solido_to_fluido
            {
                patchInfo
                {
                    type patch;
                }
                faceType baffle;
            }
            fluido_to_solido
            {
                patchInfo
                {
                    type patch;
                }
                faceType baffle;
            }
        }
*/
}


snapControls
{
	// Number of patch smoothing iterations before finding correspondence to surface
	nSmoothPatch 3;

	// Maximum relative distance for points to be attracted by surface. 
	// True distance is this factor times local maximum edge length. 
	//Note: changed(corrected) w.r.t 17x! (17x used 2* tolerance)
	tolerance 2.0;

	// Number of mesh displacement relaxation iterations.
	nSolveIter 20;

	// Maximum number of snapping relaxation iterations. 
	// Should stop before upon reaching a correct mesh. 
	// Increase this value to improve the quality of the body fitted mesh.
	nRelaxIter 20;

    // Feature snapping

        // Number of feature edge snapping iterations.
        // Leave out altogether to disable.
        // Increase this value to improve the quality of the edge features.
        nFeatureSnapIter 15;

        // Detect (geometric only) features by sampling the surface
        // (default=false).
        implicitFeatureSnap false;

        // Use castellatedMeshControls::features (default = true)
        explicitFeatureSnap true;

        // Detect features between multiple surfaces
        // (only for explicitFeatureSnap, default = false)
        multiRegionFeatureSnap true;
}
addLayersControls
{
	relativeSizes       true;
	expansionRatio      1.2;
	finalLayerThickness 0.5;
	minThickness        1e-3;
	layers
    {
   	}
   	// Advanced settings
	nGrow 0;
	featureAngle 130;
	maxFaceThicknessRatio 0.5;
	nSmoothSurfaceNormals 1;
	nSmoothThickness 10;
	minMedianAxisAngle 90;
	maxThicknessToMedialRatio 0.3;
	nSmoothNormals 3;
	slipFeatureAngle 30;
	nRelaxIter 5;
	nBufferCellsNoExtrude 0;
	nLayerIter 50;
	nRelaxedIter 20;
}
meshQualityControls
{
	maxNonOrtho 50;
	maxBoundarySkewness 20;
	maxInternalSkewness 4;
	maxConcave 80;
	minVol 1.00E-16;
	minTetQuality 1e-12;
	minArea -1;
	minTwist 0.05;
	minDeterminant 0.001;
	minFaceWeight 0.05;
	minVolRatio 0.01;
	minTriangleTwist -1;
	minFlatness 0.5;
	nSmoothScale 4;
	errorReduction 0.75;

}

mergeTolerance 1e-6;

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

And this is my log.snappyHexMesh:

/*---------------------------------------------------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  8
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
Build  : 8-1c9b5879390b
Exec   : snappyHexMesh -parallel -noFunctionObjects -overwrite
Date   : Dec 23 2022
Time   : 18:41:50
Host   : "server1"
PID    : 7783
I/O    : uncollated
Case   : /mnt/d/OpenFOAM/noTPMS
nProcs : 6
Slaves : 
5
(
"server1.7784"
"server1.7785"
"server1.7786"
"server1.7787"
"server1.7788"
)

Pstream initialized with:
    floatTransfer      : 0
    nProcsSimpleSum    : 0
    commsType          : nonBlocking
    polling iterations : 0
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

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Create time

Create mesh for time = 0

Read mesh in = 0.01 s

Overall mesh bounding box  : (-0.008 -0.008 -0.009) (0.008 0.008 0.009)
Relative tolerance         : 1e-06
Absolute matching distance : 2.891366459e-08

Reading refinement surfaces.
Read refinement surfaces in = 0.02 s

Reading refinement shells.
Read refinement shells in = 0 s

Setting refinement level of surface to be consistent with shells.
Checked shell refinement in = 0 s

Reading features.
Read features in = 0 s


Determining initial surface intersections
-----------------------------------------

Edge intersection testing:
    Number of edges             : 14656
    Number of edges to retest   : 14656
    Number of intersected edges : 1704
Calculated surface intersections in = 0 s

Initial mesh : cells:4608  faces:14656  points:5491
Cells per refinement level:
    0	4608

Adding patches for surface regions
----------------------------------

Patch Type                Region                        
----- ----                ------                        
solidoSemplice:

1     wall                bottomWall                    
2     wall                bottomWall_slave              
3     wall                contact_solido                
4     wall                contact_solido_slave          
5     wall                topWall                       
6     wall                topWall_slave                 

fluidoSemplice:

7     wall                contactFluido                 
8     wall                contactFluido_slave           
9     wall                entrata                       
10    wall                entrata_slave                 
11    wall                uscita                        
12    wall                uscita_slave                  

Added patches in = 0.02 s
...

...
Removing zero-sized patches:
    bottomWall type wall at position 1
    bottomWall_slave type wall at position 2
    contact_solido type wall at position 3
    contact_solido_slave type wall at position 4
    topWall type wall at position 5
    topWall_slave type wall at position 6
    contactFluido type wall at position 7
    contactFluido_slave type wall at position 8
    entrata type wall at position 9
    entrata_slave type wall at position 10
    uscita type wall at position 11
    uscita_slave type wall at position 12

Snapped mesh : cells:125960  faces:401284  points:149373
Cells per refinement level:
    0	584
    1	18880
    2	106496
Writing mesh to time constant
Wrote mesh in = 0.25 s.
Mesh snapped in = 3.4 s.
Checking final mesh ...
Checking faces in error :
    non-orthogonality > 50  degrees                        : 0
    faces with face pyramid volume < 1e-16                 : 0
    faces with face-decomposition tet quality < 1e-12      : 0
    faces with concavity > 80  degrees                     : 0
    faces with skewness > 4   (internal) or 20  (boundary) : 0
    faces with interpolation weights (0..1)  < 0.05        : 0
    faces with volume ratio of neighbour cells < 0.01      : 0
    faces with face twist < 0.05                           : 0
    faces on cells with determinant < 0.001                : 0
Finished meshing without any errors
Finished meshing in = 7.33 s.
End

Finalising parallel run

I think the problem lies in the fact that snappy maintains also the leaving between the stl and the residual blockMesh as region.
I also attach pictures of the domain.

How can I do to fix that issue?
Thank in advance,
Greetings,
Eleonora