MIKE 21 BW, User Manual, Page: 122 / 196

Reference Manual
122 MIKE 21 BW - © DHI
tions explicitly. This can be due to internal boundaries, a boundary stretching
over a series of small islands, etc.
The model requires you to specify either the surface elevation or the flux at all
open boundaries.
Recommendations
As open boundaries are treated as fully reflective in MIKE 21 BW it is recom-
mended to use internal wave generation. In 2DH applications involving wave-
current interaction an open boundary may be used, e.g. an open flux bound-
ary.
5.2.6 Simulation period
On the Simulation Period dialog you specify information on

Number of time steps

Time step interval

Warm-up Period
Furthermore, you must specify the date and time for the simulation.
Number of time steps
The number of time steps is the total simulation time divided by the time step.
The total simulation time should allow for waves to reach all model areas and
from this time (start-up period) the simulation should continue at least 15-20
min. for calculation of statistical parameters such as the significant wave
height, H
m0
. If the study includes investigation of e.g. long periodic wave dis-
turbance (e.g. harbour resonance and seiching or wave-induced currents) the
simulation time should be longer.
For typical short wave applications the simulation time is 20 - 30 minutes.
The figure below shows a typical surface elevation time series extracted from
inside a harbour. Note that no elevations are present in the beginning as no
waves have reached the basin of the harbour. Therefore, this period should
not be included in the calculation of the wave statistics.