avoiding problems with mesh generation, pre/post-processing applications
etc. triggering inappropriate changes to the moving and topoChanged states which
are only needed for updates in solvers corresponding to mesh changes.
The topoChanged flag now indicates that the mesh topology has changed at the
start of the current time-step rather than it is changing during the run, for
subsequent time-steps without topology change it is set false until the next
topology change.
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 mesh will now be written only for the write time following mesh-motion or
topology change (refinement/unrefinement, mesh-to-mesh mapping, load-balancing
etc.) and not for all subsequent time-steps as it did previously. This reduces
storage and reconstruction effort of changing mesh cases.
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.
The topology changes occur in the intermediate steps during mesh sub-division
and addition, there is no need to update meshObjects during this phase, these
are updated at the end of the redistribution by the distribute function called
for each. The distribute functions for nearWallDist and wallDist have been
updated accordingly.
PrimitivePatch is a geometry engine. Is not used, and is not designed to
be used, as an abstract interface. That function is left to
PrimitivePatch's immediate derivations, such as polyPatch and
MeshedSurface.
fvMesh::update() now executes at the beginning of the time-step, before time is
incremented and handles topology change, mesh to mesh mapping and redistribution
without point motion. Following each of these mesh changes fields are mapped
from the previous mesh state to new mesh state in a conservative manner. These
mesh changes not occur at most once per time-step.
fvMesh::move() is executed after time is incremented and handles point motion
mesh morphing during the time-step in an Arbitrary Lagrangian Eulerian approach
requiring the mesh motion flux to match the cell volume change. fvMesh::move()
can be called any number of times during the time-step to allow iterative update
of the coupling between the mesh motion and field solution.
With fvMeshTopoChangers::meshToMesh it is now possible to map the solution to a
specified sequence of pre-generated meshes at run-time to support arbitrary mesh
changes, refinements, un-refinements, changes in region topology, geometry,
etc. Additionally mesh-motion between the sequence of meshes is supported to
allow for e.g. piston and valve motion in engines.
The tutorials/incompressible/pimpleFoam/laminar/movingCone case has been updated
to provide a demonstration of the advantages of this run-time mesh-mapping by
mapping to meshes that are finer behind the cone and coarser in front of the
cone as the cone approaches the end of the domain, thus maintaining good
resolution while avoiding excessive cell aspect ratio as the mesh is squeezed.
The dynamicMeshDict for the movingCone case is;
mover
{
type motionSolver;
libs ("libfvMeshMovers.so" "libfvMotionSolvers.so");
motionSolver velocityComponentLaplacian;
component x;
diffusivity directional (1 200 0);
}
topoChanger
{
type meshToMesh;
libs ("libmeshToMeshTopoChanger.so");
times (0.0015 0.003);
timeDelta 1e-6;
}
which lists the mesh mapping times 0.0015s 0.003s and meshes for these times in
directories constant/meshToMesh_0.0015 and constant/meshToMesh_0.003 are
generated in the Allrun script before the pimpleFoam run:
runApplication -a blockMesh -dict blockMeshDict.2
rm -rf constant/meshToMesh_0.0015
mkdir constant/meshToMesh_0.0015
mv constant/polyMesh constant/meshToMesh_0.0015
runApplication -a blockMesh -dict blockMeshDict.3
rm -rf constant/meshToMesh_0.003
mkdir constant/meshToMesh_0.003
mv constant/polyMesh constant/meshToMesh_0.003
runApplication -a blockMesh -dict blockMeshDict.1
runApplication $application
Note: This functionality is experimental and has only undergone basic testing.
It is likely that it does not yet work with all functionObject, fvModels
etc. which will need updating to support this form of mesh topology change.
so that the input is now dictionary rather than list of dictionaries which
provides support for dictionary substitutions within the motionSolver
sub-dictionaries and also simplifies lookup of specific motionSolvers within the
list. For example the dynamicMeshDict for the floatingObject case with a second
floating object would be:
mover
{
type motionSolver;
libs ("libfvMeshMovers.so" "librigidBodyMeshMotion.so");
motionSolver motionSolverList;
solvers
{
floatingObject
{
motionSolver rigidBodyMotion;
report on;
solver
{
type Newmark;
}
accelerationRelaxation 0.7;
bodies
{
floatingObject
{
type cuboid;
parent root;
// Cuboid dimensions
Lx 0.3;
Ly 0.2;
Lz 0.5;
// Density of the cuboid
rho 500;
// Cuboid mass
mass #calc "$rho*$Lx*$Ly*$Lz";
L ($Lx $Ly $Lz);
centreOfMass (0 0 0.25);
transform (1 0 0 0 1 0 0 0 1) (0.5 0.45 0.1);
joint
{
type composite;
joints
(
{
type Py;
}
{
type Ry;
}
);
}
patches (floatingObject);
innerDistance 0.05;
outerDistance 0.35;
}
}
}
anotherFloatingObject
{
.
.
.
}
}
}
This new mapping structure is designed to support run-time mesh-to-mesh mapping
to allow arbitrary changes to the mesh structure, for example during extreme
motion requiring significant topology change including region disconnection etc.
The polyTopoChangeMap is the map specifically relating to polyMesh topological
changes generated by polyTopoChange and used to update and map mesh related
types and fields following the topo-change.
This is a map data structure rather than a class or function which performs the
mapping operation so polyMeshDistributionMap is more logical and comprehensible
than mapDistributePolyMesh.
Moving mesh cases running with 2nd-order ddt schemes can now run with
re-distribution. This does not include support for topology change including
mesh refinement which will require special complex handling for 2nd-order time
schemes.
A single transform method has been written to govern meshWave transfers
through transformed interfaces. This allows the transformer class to
take care of the different types of transform (e.g., displacement vs
positions), rather than having the waved data do it manually. It also
simplifies the creation of data classes and removes a large number of
functions that do nothing.
Propagation through AMI interfaces and the transformation of wall
normals through has also been corrected.
The template parameters were only ever polyBoundaryMesh and
processorPolyPatch. Un-templating makes mainteance and bug-fixing
quicker as it means minor modifications no longer cause a full rebuild
of OpenFOAM.
This means the field gets decomposed and reconstructed in the same way
as any other point field, and prevents issues with restart of cases
which feature both mesh motion and topology change.
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
Basic support is now provided for dynamic mesh redistribution, particularly for
load-balancing. The mesh distributor is selected in the optional 'distributor'
entry in dynamicMeshDict, for example in the
multiphase/interFoam/RAS/floatingObject tutorial case when run in parallel using
the new Allrun-parallel script
distributor
{
type decomposer;
libs ("libfvMeshDistributors.so");
redistributionInterval 10;
}
in which the 'decomposer' form of redistribution is selected to call the mesh
decomposition method specified in decomposeParDict to re-decompose the mesh for
redistribution. The redistributionInterval entry specifies how frequently mesh
redistribution takes place, in the above every 10th time-step. An optional
maxImbalance entry is also provided to control redistribution based on the cell
distribution imbalance:
Class
Foam::fvMeshDistributor::decomposer
Description
Dynamic mesh redistribution using the decomposer
Usage
Example of single field based refinement in all cells:
\verbatim
distributor
{
type decomposer;
libs ("libfvMeshDistributors.so");
// How often to redistribute
redistributionInterval 10;
// Maximum fractional cell distribution imbalance
// before rebalancing
maxImbalance 0.1;
}
\endverbatim
Currently mesh refinement/unrefinement and motion with redistribution is
supported but many aspects of OpenFOAM are not yet and will require further
development, in particular fvModels and Lagrangian.
Also only the geometry-based simple and hierarchical decomposition method are
well behaved for redistribution, scotch and ptScotch cause dramatic changes in
mesh distribution with a corresponding heavy communications overhead limiting
their usefulness or at least the frequency with which they should be called to
redistribute the mesh.
To support mesh redistribution for load-balancing etc. all MeshObjects requiring
a special updateMesh(const mapPolyMesh&) function will also require a
distribute(const mapDistributePolyMesh&) to handle the redistribution of
no-field and unregistered mesh-related state data.
Fortunately there are not many MeshObjects requiring a special distribute(const
mapDistributePolyMesh&) implementation but it will take some time to implement
and test all those that do; this patch provides those for displacement-based
mesh-movers.
for e.g. load-balancing. The fvMeshDistributor is selected via the new optional
distributor entry in dynamicMeshDict, e.g.
distributor
{
type decomposer;
libs ("libfvMeshDistributors.so");
}
Note that currently only the framework is included in this commit, the
fvMeshDistributors library is not yet fully functional and hence not released
yet.
The floatingObject tutorial has been update to demonstrate this functionality by
adding the following topoChanger entry to dynamicMeshDict:
topoChanger
{
type refiner;
libs ("libfvMeshTopoChangers.so");
// How often to refine
refineInterval 1;
// Field to be refinement on
field alpha.water;
// Refine field in between lower..upper
lowerRefineLevel 0.001;
upperRefineLevel 0.999;
// Have slower than 2:1 refinement
nBufferLayers 1;
// Refine cells only up to maxRefinement levels
maxRefinement 1;
// Stop refinement if maxCells reached
maxCells 200000;
// Flux field and corresponding velocity field. Fluxes on changed
// faces get recalculated by interpolating the velocity. Use 'none'
// on surfaceScalarFields that do not need to be reinterpolated.
correctFluxes
(
(phi none)
(nHatf none)
(rhoPhi none)
(alphaPhi.water none)
(meshPhi none)
(ghf none)
);
// Write the refinement level as a volScalarField
dumpLevel true;
}
Note that currently only single rigid body motion is supported (but multi-body
support will be added shortly) and the Crank-Nicolson scheme is not supported.
replacing the virtual functions overridden in engineTime.
Now the userTime conversion function in Time is specified in system/controlDict
such that the solver as well as all pre- and post-processing tools also operate
correctly with the chosen user-time.
For example the user-time and rpm in the tutorials/combustion/XiEngineFoam/kivaTest case are
now specified in system/controlDict:
userTime
{
type engine;
rpm 1500;
}
The default specification is real-time:
userTime
{
type real;
}
but this entry can be omitted as the real-time class is instantiated
automatically if the userTime entry is not present in system/controlDict.
Mesh motion and topology change are now combinable run-time selectable options
within fvMesh, replacing the restrictive dynamicFvMesh which supported only
motion OR topology change.
All solvers which instantiated a dynamicFvMesh now instantiate an fvMesh which
reads the optional constant/dynamicFvMeshDict to construct an fvMeshMover and/or
an fvMeshTopoChanger. These two are specified within the optional mover and
topoChanger sub-dictionaries of dynamicFvMeshDict.
When the fvMesh is updated the fvMeshTopoChanger is first executed which can
change the mesh topology in anyway, adding or removing points as required, for
example for automatic mesh refinement/unrefinement, and all registered fields
are mapped onto the updated mesh. The fvMeshMover is then executed which moved
the points only and calculates the cell volume change and corresponding
mesh-fluxes for conservative moving mesh transport. If multiple topological
changes or movements are required these would be combined into special
fvMeshMovers and fvMeshTopoChangers which handle the processing of a list of
changes, e.g. solidBodyMotionFunctions:multiMotion.
The tutorials/multiphase/interFoam/laminar/sloshingTank3D3DoF case has been
updated to demonstrate this new functionality by combining solid-body motion
with mesh refinement/unrefinement:
/*--------------------------------*- C++ -*----------------------------------*\
========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Version: dev
\\/ M anipulation |
\*---------------------------------------------------------------------------*/
FoamFile
{
format ascii;
class dictionary;
location "constant";
object dynamicMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
mover
{
type motionSolver;
libs ("libfvMeshMovers.so" "libfvMotionSolvers.so");
motionSolver solidBody;
solidBodyMotionFunction SDA;
CofG (0 0 0);
lamda 50;
rollAmax 0.2;
rollAmin 0.1;
heaveA 4;
swayA 2.4;
Q 2;
Tp 14;
Tpn 12;
dTi 0.06;
dTp -0.001;
}
topoChanger
{
type refiner;
libs ("libfvMeshTopoChangers.so");
// How often to refine
refineInterval 1;
// Field to be refinement on
field alpha.water;
// Refine field in between lower..upper
lowerRefineLevel 0.001;
upperRefineLevel 0.999;
// Have slower than 2:1 refinement
nBufferLayers 1;
// Refine cells only up to maxRefinement levels
maxRefinement 1;
// Stop refinement if maxCells reached
maxCells 200000;
// Flux field and corresponding velocity field. Fluxes on changed
// faces get recalculated by interpolating the velocity. Use 'none'
// on surfaceScalarFields that do not need to be reinterpolated.
correctFluxes
(
(phi none)
(nHatf none)
(rhoPhi none)
(alphaPhi.water none)
(meshPhi none)
(meshPhi_0 none)
(ghf none)
);
// Write the refinement level as a volScalarField
dumpLevel true;
}
// ************************************************************************* //
Note that currently this is the only working combination of mesh-motion with
topology change within the new framework and further development is required to
update the set of topology changers so that topology changes with mapping are
separated from the mesh-motion so that they can be combined with any of the
other movements or topology changes in any manner.
All of the solvers and tutorials have been updated to use the new form of
dynamicMeshDict but backward-compatibility was not practical due to the complete
reorganisation of the mesh change structure.
used to check the existence of and open an object file, read and check the
header without constructing the object.
'typeIOobject' operates in an equivalent and consistent manner to 'regIOobject'
but the type information is provided by the template argument rather than via
virtual functions for which the derived object would need to be constructed,
which is the case for 'regIOobject'.
'typeIOobject' replaces the previous separate functions 'typeHeaderOk' and
'typeFilePath' with a single consistent interface.
topoSet is a more flexible and extensible replacement for setSet using standard
OpenFOAM dictionary input format rather than the limited command-line input
format developed specifically for setSet. This replacement allows for the
removal of a significant amount of code simplifying maintenance and the addition
of more topoSet sources.
to differentiate between flux field which require face-flipping and
non-extensive surface fields which do not. Currently flux fields are
distinguished by being surfaceScalarField with dimensions of either volumetric
or mass flux.
This change corrects the handling of the surfaceVectorField Uf which was
previously mapped incorrectly on faces requiring the flipping of the flux
orientation.
