An extruded region is now contiguous even when specified with multiple
face zones. Edges that border faces in different zones now extrude into
internal faces, rather than a pair of boundary faces. Different zones
now result only in different mapped patches in the extruded and primary
meshes. This means a mesh can be created for a single contiguous
extruded region spanning multiple patches. This might be necessary if,
for example, a film region is needed across multiple walls with
differing thermal boundary conditions.
Disconnected extruded regions can still be constructed by running the
extrudeToRegionMesh utility muiliple times.
The mapped patches created to couple the extruded regions now have
symmetric names similar to those created by splitMeshRegions. For
example, if the mapped patch in the primary region is called
"region0_to_extrudedRegion_f0", then the corresponding patch in the
extruded region is called "extrudedRegion_to_region0_f0" (f0, in this
example is the face zone from which the region was extruded).
Offsetting of the top patch is now handled automatically by a new
mappedExtrudedWallPolyPatch. This refers to the bottom patch and
automatically calculates the sampling offsets by doing a wave across the
extruded mesh layers. This prevents the need to store the offsets in the
patch itself, and makes it possible for the patch to undergo mesh
changes without adding additional functions to the polyPatch (mapping
constructors, autoMap and rmap methods, etc ...).
Settings for the individual non-conformal couples can now be put in a
"nonConformalCouples" sub-dictionary of the
system/createNonConformalCouplesDict. For example:
fields no;
nonConformalCouples // <-- new sub-dictionary
{
nonConformalCouple_none
{
patches (nonCouple1 nonCouple2);
transform none;
}
nonConformalCouple_30deg
{
patches (nonCoupleBehind nonCoupleAhead);
transform rotational;
rotationAxis (-1 0 0);
rotationCentre (0 0 0);
rotationAngle 30;
}
}
This permits settings to be #include-d from files that themselves
contain sub-dictionaries without the utility treating those
sub-dictionaries as if they specify a non-conformal coupling. It also
makes the syntax more comparable to that of createBafflesDict.
The new "nonConformalCouples" sub-dictionary is optional, so this change
is backwards compatible. The new syntax is recommended, however, and all
examples have been changed accordingly.
This utility now always creates two patches, and only creates duplicate
faces when they connect to different cells and point in opposite
directions. Now that ACMI has been removed, there is no need to create
duplicate faces on the same cell and with similar orientations. This is
unituitive and is now considered an invalid mesh topology.
The preferred syntax for createBaffles is now as follows:
internalFacesOnly true;
baffles
{
cyclics
{
type faceZone;
zoneName cyclicFaces;
owner
{
name cyclicLeft;
type cyclic;
neighbourPatch cyclicRight;
}
neighbour
{
name cyclicRight;
type cyclic;
neighbourPatch cyclicLeft;
}
}
}
Note that the 'patches' sub-dictionary is not needed any more; the
'owner' and 'neighbour' sub-dictionaries can be in the same dictionary
as the parameters with which faces are selected. For backwards
compatibility, however, a 'patches' sub-dictionary is still permitted,
as are keywords 'master' and 'slave' (in place of 'owner' and
'neighbour', respectively).
The 'patchPairs' syntax has been removed. Whilst consise, this syntax
made a number of assumptions and decisions regarding naming conventions
that were not sufficiently intuitive for the user to understand without
extensive reference to the code. If identical boundaries are desired on
both sides of the patch, dictionary substitution provides a more
intuitive way of minimising the amount of specifiection required. For
example, to create two back-to-back walls, the following specification
could be used:
internalFacesOnly true;
fields true;
baffles
{
walls
{
type faceZone;
zoneName wallFaces;
owner
{
name baffleWallLeft;
type wall;
patchFields
{
p
{
type zeroGradient;
}
U
{
type noSlip;
}
}
}
neighbour
{
name baffleWallRight;
$owner; // <-- Use the same settings as for the owner
}
}
}
The 'pointSync' setting in createPatchDict is now optional and defaults
to false. This setting is very rarely used. A number of unused
'createPatchDict' files have also been removed and obsolete information
has been removed from the annotated example dictionaries.
This major development provides coupling of patches which are
non-conformal, i.e. where the faces of one patch do not match the faces
of the other. The coupling is fully conservative and second order
accurate in space, unlike the Arbitrary Mesh Interface (AMI) and
associated ACMI and Repeat AMI methods which NCC replaces.
Description:
A non-conformal couple is a connection between a pair of boundary
patches formed by projecting one patch onto the other in a way that
fills the space between them. The intersection between the projected
surface and patch forms new faces that are incorporated into the finite
volume mesh. These new faces are created identically on both sides of
the couple, and therefore become equivalent to internal faces within the
mesh. The affected cells remain closed, meaning that the area vectors
sum to zero for all the faces of each cell. Consequently, the main
benefits of the finite volume method, i.e. conservation and accuracy,
are not undermined by the coupling.
A couple connects parts of mesh that are otherwise disconnected and can
be used in the following ways:
+ to simulate rotating geometries, e.g. a propeller or stirrer, in which
a part of the mesh rotates with the geometry and connects to a
surrounding mesh which is not moving;
+ to connect meshes that are generated separately, which do not conform
at their boundaries;
+ to connect patches which only partially overlap, in which the
non-overlapped section forms another boundary, e.g. a wall;
+ to simulate a case with a geometry which is periodically repeating by
creating multiple couples with different transformations between
patches.
The capability for simulating partial overlaps replaces the ACMI
functionality, currently provided by the 'cyclicACMI' patch type, and
which is unreliable unless the couple is perfectly flat. The capability
for simulating periodically repeating geometry replaces the Repeat AMI
functionality currently provided by the 'cyclicRepeatAMI' patch type.
Usage:
The process of meshing for NCC is very similar to existing processes for
meshing for AMI. Typically, a mesh is generated with an identifiable set
of internal faces which coincide with the surface through which the mesh
will be coupled. These faces are then duplicated by running the
'createBaffles' utility to create two boundary patches. The points are
then split using 'splitBaffles' in order to permit independent motion of
the patches.
In AMI, these patches are assigned the 'cyclicAMI' patch type, which
couples them using AMI interpolation methods.
With NCC, the patches remain non-coupled, e.g. a 'wall' type. Coupling
is instead achieved by running the new 'createNonConformalCouples'
utility, which creates additional coupled patches of type
'nonConformalCyclic'. These appear in the 'constant/polyMesh/boundary'
file with zero faces; they are populated with faces in the finite volume
mesh during the connection process in NCC.
For a single couple, such as that which separates the rotating and
stationary sections of a mesh, the utility can be called using the
non-coupled patch names as arguments, e.g.
createNonConformalCouples -overwrite rotatingZoneInner rotatingZoneOuter
where 'rotatingZoneInner' and 'rotatingZoneOuter' are the names of the
patches.
For multiple couples, and/or couples with transformations,
'createNonConformalCouples' should be run without arguments. Settings
will then be read from a configuration file named
'system/createNonConformalCouplesDict'. See
'$FOAM_ETC/caseDicts/annotated/createNonConformalCouplesDict' for
examples.
Boundary conditions must be specified for the non-coupled patches. For a
couple where the patches fully overlap, boundary conditions
corresponding to a slip wall are typically applied to fields, i.e
'movingWallSlipVelocity' (or 'slip' if the mesh is stationary) for
velocity U, 'zeroGradient' or 'fixedFluxPressure' for pressure p, and
'zeroGradient' for other fields. For a couple with
partially-overlapping patches, boundary conditions are applied which
physically represent the non-overlapped region, e.g. a no-slip wall.
Boundary conditions also need to be specified for the
'nonConformalCyclic' patches created by 'createNonConformalCouples'. It
is generally recommended that this is done by including the
'$FOAM_ETC/caseDicts/setConstraintTypes' file in the 'boundaryField'
section of each of the field files, e.g.
boundaryField
{
#includeEtc "caseDicts/setConstraintTypes"
inlet
{
...
}
...
}
For moving mesh cases, it may be necessary to correct the mesh fluxes
that are changed as a result of the connection procedure. If the
connected patches do not conform perfectly to the mesh motion, then
failure to correct the fluxes can result in noise in the pressure
solution.
Correction for the mesh fluxes is enabled by the 'correctMeshPhi' switch
in the 'PIMPLE' (or equivalent) section of 'system/fvSolution'. When it
is enabled, solver settings are required for 'MeshPhi'. The solution
just needs to distribute the error enough to dissipate the noise. A
smooth solver with a loose tolerance is typically sufficient, e.g. the
settings in 'system/fvSolution' shown below:
solvers
{
MeshPhi
{
solver smoothSolver;
smoother symGaussSeidel;
tolerance 1e-2;
relTol 0;
}
...
}
PIMPLE
{
correctMeshPhi yes;
...
}
The solution of 'MeshPhi' is an inexpensive computation since it is
applied only to a small subset of the mesh adjacent to the
couple. Conservation is maintained whether or not the mesh flux
correction is enabled, and regardless of the solution tolerance for
'MeshPhi'.
Advantages of NCC:
+ NCC maintains conservation which is required for many numerical
schemes and algorithms to operate effectively, in particular those
designed to maintain boundedness of a solution.
+ Closed-volume systems no longer suffer from accumulation or loss of
mass, poor convergence of the pressure equation, and/or concentration
of error in the reference cell.
+ Partially overlapped simulations are now possible on surfaces that are
not perfectly flat. The projection fills space so no overlaps or
spaces are generated inside contiguously overlapping sections, even if
those sections have sharp angles.
+ The finite volume faces created by NCC have geometrically accurate
centres. This makes the method second order accurate in space.
+ The polyhedral mesh no longer requires duplicate boundary faces to be
generated in order to run a partially overlapped simulation.
+ Lagrangian elements can now transfer across non-conformal couplings in
parallel.
+ Once the intersection has been computed and applied to the finite
volume mesh, it can use standard cyclic or processor cyclic finite
volume boundary conditions, with no need for additional patch types or
matrix interfaces.
+ Parallel communication is done using the standard
processor-patch-field system. This is more efficient than alternative
systems since it has been carefully optimised for use within the
linear solvers.
+ Coupled patches are disconnected prior to mesh motion and topology
change and reconnected afterwards. This simplifies the boundary
condition specification for mesh motion fields.
Resolved Bug Reports:
+ https://bugs.openfoam.org/view.php?id=663
+ https://bugs.openfoam.org/view.php?id=883
+ https://bugs.openfoam.org/view.php?id=887
+ https://bugs.openfoam.org/view.php?id=1337
+ https://bugs.openfoam.org/view.php?id=1388
+ https://bugs.openfoam.org/view.php?id=1422
+ https://bugs.openfoam.org/view.php?id=1829
+ https://bugs.openfoam.org/view.php?id=1841
+ https://bugs.openfoam.org/view.php?id=2274
+ https://bugs.openfoam.org/view.php?id=2561
+ https://bugs.openfoam.org/view.php?id=3817
Deprecation:
NCC replaces the functionality provided by AMI, ACMI and Repeat AMI.
ACMI and Repeat AMI are insufficiently reliable to warrant further
maintenance so are removed in an accompanying commit to OpenFOAM-dev.
AMI is more widely used so will be retained alongside NCC for the next
version release of OpenFOAM and then subsequently removed from
OpenFOAM-dev.
motionSmootherAlgoCheck::checkMesh is used by snappyHexMesh to check the mesh
after snapping and morphing. The minVol test which checks for collapsed cells
is now relative to the cube of the minimum bounding box length so that it is
less dependent on the size of the geometry and less likely to need changing for
very small geometries.
The default value is set in
etc/caseDicts/mesh/generation/meshQualityDict
etc/caseDicts/mesh/generation/meshQualityDict.cfg
//- Minimum cell pyramid volume relative to min bounding box length^3
// Set to a fraction of the smallest cell volume expected.
// Set to very negative number (e.g. -1e30) to disable.
minVol 1e-10;
The unused minArea and minTriangleTwist tests have been removed
also adding optional "libs" entry to renumberMeshDict so that the
libzoltanRenumber.so can be loaded at run-time rather than having to recompile
and relink the renumberMesh utility to support it.
When snappyHexMesh is run in parallel it re-balances the mesh during refinement
and layer addition by redistribution which requires a decomposition method
that operates in parallel, e.g. hierachical or ptscotch. decomposePar uses a
decomposition method which operates in serial e.g. hierachical but NOT
ptscotch. In order to run decomposePar followed by snappyHexMesh in parallel it
has been necessary to change the method specified in decomposeParDict but now
this is avoided by separately specifying the decomposition and distribution
methods, e.g. in the incompressible/simpleFoam/motorBike case:
numberOfSubdomains 6;
decomposer hierarchical;
distributor ptscotch;
hierarchicalCoeffs
{
n (3 2 1);
order xyz;
}
The distributor entry is also used for run-time mesh redistribution, e.g. in the
multiphase/interFoam/RAS/floatingObject case re-distribution for load-balancing
is enabled in constant/dynamicMeshDict:
distributor
{
type distributor;
libs ("libfvMeshDistributors.so");
redistributionInterval 10;
}
which uses the distributor specified in system/decomposeParDict:
distributor hierarchical;
This rationalisation provides the structure for development of mesh
redistribution and load-balancing.
The code relating to extending refinement to the span of the facet/triangles
intersected by the refinement distance referred to in report
https://bugs.openfoam.org/view.php?id=3361
and temporarily removed may now be selected by the optional
castellatedMeshControls:extendedRefinementSpan entry in snappyHexMeshDict. It
in not clear if this control is generally beneficial and very few users have
reported a preference and too few example cases have been provided to make a
balanced judgement so it has been decided to reinstate the previous default
behaviour and default extendedRefinementSpan to true.
for consistency with the regionToCell topo set source and splitMeshRegions and
provides more logical extension to the multiple and outside point variants insidePoints,
outsidePoint and outsidePoints.
For a set to zone conversion the name of the zone is now specified with the
'zone' keyword.
For a patch to set conversion the name of the patch is now specified with the
'patch' keyword.
Backward-compatibility is supported for both these changes.
Additionally the file name of a searchableSurface file is specified with the
'file' keyword. This should be 'surface' but that keyword is currently and
confusingly used for the surface type rather than name and this cannot be
changed conveniently while maintaining backward compatibility.
and only needed if there is a name clash between entries in the source
specification and the set specification, e.g. "name":
{
name rotorCells;
type cellSet;
action new;
source zoneToCell;
sourceInfo
{
name cylinder;
}
}
When using 'simple' or 'hierarchical' decomposition it is useful to slightly rotate a
coordinate-aligned block-mesh to improve the processor boundaries by avoiding
irregular cell distribution at those boundaries. The degree of slight rotation
is controlled by the 'delta' coefficient and a value of 0.001 is generally
suitable so to avoid unnecessary clutter in 'decomposeParDict' 'delta' now
defaults to this value.
The FOAM file format has not changed from version 2.0 in many years and so there
is no longer a need for the 'version' entry in the FoamFile header to be
required and to reduce unnecessary clutter it is now optional, defaulting to the
current file format 2.0.
the previous naming tan1, tan2, normal was non-intuitive and very confusing.
It was not practical to maintain backward compatibility but all tutorials and
example refineMeshDict files have been updated to provide examples of the
change.
Specifying a plane with which to subset feature edges is now done using
the same dictionary syntax used elsewhere in OpenFOAM. For example, in
system/surfaceFeaturesDict:
subsetFeatures
{
// Include only edges that intersect the plane
plane
{
planeType pointAndNormal;
point (0 0 0);
normal (1 0 0);
}
...
}
Originally the only supported geometry specification were triangulated surfaces,
hence the name of the directory: constant/triSurface, however now that other
surface specifications are supported and provided it is much more logical that
the directory is named accordingly: constant/geometry. All tutorial and
template cases have been updated.
Note that backward compatibility is provided such that if the constant/geometry
directory does not exist but constant/triSurface does then the geometry files
are read from there.
End points of topoSet cylinder sources should now be specified as
"point1" and "point2", which is consistent with other parts of the code.
The previous keywords, "p1" and "p2" have been retained for backwards
compatibility but may be removed in future.
To handle the additional optional specification for the closeness calculation
these settings are now is a sub-dictionary of surfaceFeaturesDict, e.g.
closeness
{
// Output the closeness of surface elements to other surface elements.
faceCloseness no;
// Output the closeness of surface points to other surface elements.
pointCloseness yes;
// Optional maximum angle between opposite points considered close
internalAngleTolerance 80;
externalAngleTolerance 80;
}
For complex geometries the calculation of surface face and point "closeness" can
be quite time consuming and usually only one or other is required; the new
options allow the user to specify which should be calculated and written.
which are now read directly from the thermophysicalProperties dictionary for
consistency with non-reacting mixture thermodynamics. The species thermo and
reactions lists can still be in separate files if convenient and included into
the thermophysicalProperties file using the standard dictionary #include.
With the inclusion of boundary layer modelling in the gas, the
separation of wave perturbation from and mean flow became less useful,
and potentially prevents further extension to support similar boundary
layer modelling in the liquid.
The mean velocity entry, UMean, is now needed in the
constant/waveProperties file rather than in the waveVelocity boundary
condition.
In order to increase the flexibility of the wave library, the mean flow
handling has been removed from the waveSuperposition class. This makes
waveSuperposition work purely in terms of perturbations to a mean
background flow.
The input has also been split, with waves now defined as region-wide
settings in constant/waveProperties. The mean flow parameters are sill
defined by the boundary conditions.
The new format of the velocity boundary is much simpler. Only a mean
flow velocity is required.
In 0/U:
boundaryField
{
inlet
{
type waveVelocity;
UMean (2 0 0);
}
// etc ...
}
Other wave boundary conditions have not changed.
The constant/waveProperties file contains the wave model selections and
the settings to define the associated coordinate system and scaling
functions:
In constant/waveProperties:
origin (0 0 0);
direction (1 0 0);
waves
(
Airy
{
length 300;
amplitude 2.5;
phase 0;
angle 0;
}
);
scale table ((1200 1) (1800 0));
crossScale constant 1;
setWaves has been changed to use a system/setWavesDict file rather than
relying on command-line arguments. It also now requires a mean velocity
to be specified in order to prevent ambiguities associated with multiple
inlet patches. An example is shown below:
In system/setWavesDict:
alpha alpha.water;
U U;
liquid true;
UMean (1 0 0);
