This implicit isotropic damping function relaxes the velocity field towards a
specified uniform value which can be set to (0 0 0) if no flow is required.
This is particularly appropriate to damp the waves in a closed wave tank with no
mean flow.
Testing on the interFoam wave has shown that for this simple case with uniform
mean flow the new isotropicDamping fvOption provides more rapid and complete
damping than the original verticalDamping.
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);
This is to make it clear that the value supplied is the scalar mean
velocity normal to the patch, and to distinguish it from other instances
of the keyword "UMean" which take a vector quantity.
The Scaled Function1 removes the need for classes to hold both a value
and a ramping function. If it is desired to ramp up a velocity up to
(10 0 0) over the space of 5 seconds, that can be achieved as follows:
velocity
{
type scale;
scale
{
type halfCosineRamp;
duration 5;
}
value (10 0 0);
}
Also, as a result of this change, the velocityRamping fvOption has
become a general acceleration source, based on a velocity Function1. It
has therefore been renamed accelerationSource.
The onset of vertical damping can now be graduated over a distance. The
user specifies an origin and a direction along which the graduation
occurs, and a ramping function to specify the form of the graduation. An
example specification for the fvOption is:
verticalDamping1
{
type verticalDamping;
selectionMode all;
origin (1200 0 0);
direction (1 0 0);
ramp
{
type halfCosineRamp;
start 0;
duration 600;
}
lambda [0 0 -1 0 0 0 0] 1; // Damping coefficient
timeStart 0;
duration 1e6;
}
If the origin, direction or ramp entries are omitted then the fvOption
functions as before; applying the damping to the entire volume or the
specified cell set.
This work was supported by Jan Kaufmann and Jan Oberhagemann at DNV GL.
