The ability of the model to simulate interfacial waves was investigated using
standing waves. These were initialised on grids with
the same number of grid points in the horizontal and vertical directions,
the grid being orientated as shown in figure 3-3. The grid was
initialised with 
and divided into two by a horizontal line
near the centre.
The line was either taken to be at
the centre of the grid or, when a large gravitational force was being applied,
near the centre with the bottom section slightly
larger than the top.
The order parameter 
was set to +0.5 above the line and to
-0.5 below the line.
A solid boundary was set at the bottom and top
of the fluid and
continuous boundary conditions applied at the other edges.
The boundary conditions were applied at the solid boundary
using the boundary conditions of Noble et al.
[51] discussed in section 4.3.2.
The fluid was then allowed to evolve with
= 200.0 for 8,000 time-steps. This allows the fluids to
reach an equilibrium state where the density gradient in each fluid is
established. The height of the interface between the two fluids was then found, this is the mean water level (mwl).
A sinusoidal interface was enforced
between the fluids about the previous interface,
as shown in figure 7-1,
Figure 7-1: The Initialisation of a Standing Wave
and the sign of was switched in regions A and B.
The coordinate system is also shown in figure 7-1.
The sinusoidal interface has a wavelength equal to the length of the
grid and an amplitude of 
Using this initialisation method
the density gradients are set correctly and any initial y-velocity, produced
by the creation of these gradients, has been damped, by the high viscosity, to
a negligible magnitude. The shape of the interface in the horizontal direction
is sharp with width one grid space.
The form of the interface changes to the expected shape, shown in figures
4-5 and 4-6, within a few time steps.
There is also a slight
reduction in the density around the wml mark of less than
1% which is only detectable for the first few time-steps after initialisation.
For a square l by l grid with the mwl directly in the middle
and 
. Thus 
and so
the wave can be considered as being in deep water
[67].