The sub-loops of the solution control are now named more consistently,
with ambiguously named methods such as finalIter replaced with ones
like finalPimpleIter, so that it is clear which loop they represent.
In addition, the final logic has been improved so that it restores state
after a sub-iteration, and so that sub-iterations can be used on their
own without an outer iteration in effect. Previously, if the
non-orthogonal loop were used outside of a pimple/piso iteration, the
final iteration would not execute with final settings.
A new constraint patch has been added which permits AMI coupling in
cyclic geometries. The coupling is repeated with different multiples of
the cyclic transformation in order to achieve a full correspondence.
This allows, for example, a cylindrical AMI interface to be used in a
sector of a rotational geometry.
The patch is used in a similar manner to cyclicAMI, except that it has
an additional entry, "transformPatch". This entry must name a coupled
patch. The transformation used to repeat the AMI coupling is taken from
this patch. For example, in system/blockMeshDict:
boundary
(
cyclic1
{
type cyclic;
neighbourPatch cyclic2;
faces ( ... );
}
cyclic2
{
type cyclic;
neighbourPatch cyclic1;
faces ( ... );
}
cyclicRepeatAMI1
{
type cyclicRepeatAMI;
neighbourPatch cyclicRepeatAM2;
transformPatch cyclic1;
faces ( ... );
}
cyclicRepeatAMI2
{
type cyclicRepeatAMI;
neighbourPatch cyclicRepeatAMI1;
transformPatch cyclic1;
faces ( ... );
}
// other patches ...
);
In this example, the transformation between cyclic1 and cyclic2 is used
to define the repetition used by the two cyclicRepeatAMI patches.
Whether cyclic1 or cyclic2 is listed as the transform patch is not
important.
A tutorial, incompressible/pimpleFoam/RAS/impeller, has been added to
demonstrate the functionality. This contains two repeating AMI pairs;
one cylindrical and one planar.
A significant amount of maintenance has been carried out on the AMI and
ACMI patches as part of this work. The AMI methods now return
dimensionless weights by default, which prevents ambiguity over the
units of the weight field during construction. Large amounts of
duplicate code have also been removed by deriving ACMI classes from
their AMI equivalents. The reporting and writing of AMI weights has also
been unified.
This work was supported by Dr Victoria Suponitsky, at General Fusion
The built-in explicit symplectic integrator has been replaced by a
general framework supporting run-time selectable integrators. Currently
the explicit symplectic, implicit Crank-Nicolson and implicit Newmark
methods are provided, all of which are 2nd-order in time:
Symplectic 2nd-order explicit time-integrator for 6DoF solid-body motion:
Reference:
Dullweber, A., Leimkuhler, B., & McLachlan, R. (1997).
Symplectic splitting methods for rigid body molecular dynamics.
The Journal of chemical physics, 107(15), 5840-5851.
Can only be used for explicit integration of the motion of the body,
i.e. may only be called once per time-step, no outer-correctors may be
applied. For implicit integration with outer-correctors choose either
CrankNicolson or Newmark schemes.
Example specification in dynamicMeshDict:
solver
{
type symplectic;
}
Newmark 2nd-order time-integrator for 6DoF solid-body motion:
Reference:
Newmark, N. M. (1959).
A method of computation for structural dynamics.
Journal of the Engineering Mechanics Division, 85(3), 67-94.
Example specification in dynamicMeshDict:
solver
{
type Newmark;
gamma 0.5; // Velocity integration coefficient
beta 0.25; // Position integration coefficient
}
Crank-Nicolson 2nd-order time-integrator for 6DoF solid-body motion:
The off-centering coefficients for acceleration (velocity integration) and
velocity (position/orientation integration) may be specified but default
values of 0.5 for each are used if they are not specified. With the default
off-centering this scheme is equivalent to the Newmark scheme with default
coefficients.
Example specification in dynamicMeshDict:
solver
{
type CrankNicolson;
aoc 0.5; // Acceleration off-centering coefficient
voc 0.5; // Velocity off-centering coefficient
}
Both the Newmark and Crank-Nicolson are proving more robust and reliable
than the symplectic method for solving complex coupled problems and the
tutorial cases have been updated to utilize this.
In this new framework it would be straight forward to add other methods
should the need arise.
Henry G. Weller
CFD Direct
