An "inletOutlet" switch has been added to the wave velocity boundary
condition to allow the boundary to be fixed, as is possible for the
corresponding alpha condition.
A "heightAboveWave" option has been added to the wave superposition
class to calculate velocity based on the height above the wave, rather
than above the origin. This may improve initialisation but it may also
generate divergence in the initial velocity field.
The alpha condition has also been completed so that it applies a
modelled gradient when the flow points out and a wave pressure condition
is in use.
In early versions of OpenFOAM the scalar limits were simple macro replacements and the
names were capitalized to indicate this. The scalar limits are now static
constants which is a huge improvement on the use of macros and for consistency
the names have been changed to camel-case to indicate this and improve
readability of the code:
GREAT -> great
ROOTGREAT -> rootGreat
VGREAT -> vGreat
ROOTVGREAT -> rootVGreat
SMALL -> small
ROOTSMALL -> rootSmall
VSMALL -> vSmall
ROOTVSMALL -> rootVSmall
The original capitalized are still currently supported but their use is
deprecated.
The outletPhaseMeanVelocity and waveVelocity boundary conditions now
support a "ramp" keyword, for which a function can be supplied to
gradually increase the input velocity. The following is an example
specification for an outlet patch:
outlet
{
type outletPhaseMeanVelocity;
Umean 2;
ramp
{
type quarterSineRamp;
start 0;
duration 5;
}
alpha alpha.water;
}
There is also a new velocityRamping function object, which provides a
matching force within the volume of the domain, so that the entire flow
is smoothly accelerated up to the operating condition. An example
specification is as follows:
velocityRamping
{
type velocityRamping;
active on;
selectionMode all;
U U;
velocity (-2 0 0);
ramp
{
type quarterSineRamp;
start 0;
duration 5;
}
}
These additions have been designed to facilitate a smoother startup of
ship simulations by avoiding the slamming transients associated with
initialising a uniform velocity field.
This work was supported by Jan Kaufmann and Jan Oberhagemann at DNV GL.
A wavePressure boundary condition has been added, and the Airy-type wave
models have been extended to generate the unsteady pressure field. This
provides another option for specifying wave motion at a boundary.
If a waveVelocity condition is used in isolation, then any outlet flow
will be extrapolated and scaled to match the required flow rate. This is
similar to how a flowRateOutletVelocity condition works.
0/U:
<patchName>
{
type waveVelocity;
// wave parameters ...
}
0/p_rgh:
<patchName>
{
type fixedFluxPressure;
}
If a waveVelocity is used in conjunction with the new wavePressure
condition, then one will set the value and the other the gradient, as
appropriate for the direction of the flow.
0/U:
<patchName>
{
type waveVelocity;
// wave parameters ...
p p_rgh;
}
0/p_rgh:
<patchName>
{
type wavePressure;
}
This new pressure-velocity formulation is less stable, but generates
more accurate waveforms on patches where the velocity reverses. It is
also necessary for sub-surface cases where fixing the velocity around
the entire domain generates a continuity error.
This work was supported by Alice Gillespie, on behalf of M3 Wave
"pos" now returns 1 if the argument is greater than 0, otherwise it returns 0.
This is consistent with the common mathematical definition of the "pos" function:
https://en.wikipedia.org/wiki/Sign_(mathematics)
However the previous implementation in which 1 was also returned for a 0
argument is useful in many situations so the "pos0" has been added which returns
1 if the argument is greater or equal to 0. Additionally the "neg0" has been
added which returns 1 if if the argument is less than or equal to 0.
This addition allows for theoretical wave models to be utilised for
initialisation and as boundary conditions. Multiple models can be used
simultaneously, each with differing phases and orientations. If multiple
models are used the shapes and velocities are superimposed.
The wave models are specified in the velocity boundary condition. The
phase fraction boundary condition and the set utility both look up the
velocity condition in order to access the wave model. A velocity
boundary may be specified as follows:
inlet
{
type waveVelocity;
origin (0 0 0);
direction (1 0 0);
speed 2;
waves
(
Airy
{
length 300;
amplitude 2.5;
depth 150;
phase 0;
angle 0;
}
);
scale table ((1200 1) (1800 0));
crossScale constant 1;
}
The alpha boundary only requires the type, unless the name of the
velocity field is non-standard, in which case a "U" entry will also be
needed. The setWaves utility does not require a dictionary file; non-
standard field names can be specified as command-line arguments.
Wave models currently available are Airy (1st order) and Stokes2 (second
order). If a depth is specified, and it is not too large, then shallow
terms will be included, otherwise the models assume that the liquid is
deep.
This work was supported by Jan Kaufmann and Jan Oberhagemann at DNV GL.
