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.
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.
