MIKE 21 BW, User Manual, Page: 83 / 196

2DH Boussinesq Wave Module - Examples
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stability reasons it is sometimes necessary to use the slightly more dissipa-
tive simple upwind scheme. As long as the waves are properly resolved the
dissipation is usually small.
The time step is set to 0.14 s.
The roller velocity type is set to 3 and the predominant wave direction is set to
270 ºN. Hence we assume the breaking waves (rollers) will mainly propagate
in the positive x-direction, which is a good approximation in this example. The
remaining parameters are set as recommended in the User Guide and Online
help including the time scale for the roller which is set to T/5= 2.14 s.
Except for the slot depth, which is set to 13.2 m and the slot friction coefficient
is 0.01 default parameters are used for modelling of the moving shoreline.
Model run
Before you execute the MIKE 21 BW model simulations you have to provide
internal wave boundary data. Simply drag and drop the file 'Detached_break-
water.21t' into your MIKE Zero shell, go to the 'waves' entry, select the
'Detached breakwater - H= 3.2m, T= 10.7s, h= 13.2m' (for regular wave gen-
eration) and 'Detached breakwater - Hm0= 4.6m, Tp= 10.7s, h= 13.2m' (for
random wave generation) and click on run button.
The length of the simulation is 42 minutes (corresponding to 18001 time
steps or approximately 235 (peak) wave periods).
The computation time depends on the speed of your PC. For a laptop IBM
T40 Pentium M (Centrino, 1.6 GHz and 1GB DDR RAM) the required system
time is approximately 13 hours (the system CPS is approximately 130,000
points/second).
You may reduce the length of the simulations in order to reduce the overall
CPU time.
Model results
Figure 4.54 shows 2D visualisation of the simulated instantaneous surface
elevation for the two wave situations. The most visible wave phenomena are
refraction, shoaling, diffraction, nonlinear wave-wave interaction (generation
of higher harmonic waves), wave breaking and run-up. You can make a simi-
lar plot by loading (drag and drop) the PFS-file 'MzPlot.Elevation.Regular.plc'
or 'MzPlot.Elevation.Directional.plc' into the MIKE Zero shell during or after
model execution.
Figure 4.55 shows 3D visualisations of the simulated instantaneous surface
elevation. The surface rollers are shown in white. You can make a similar plot
by loading (double-click) the PFS-file 'Anim Regular Waves with Roller.lyt’ (or
‘Anim Directional Waves with Roller.lyt’) into the MIKE Animator Plus program