MIKE 21 BW, User Manual, Page: 18 / 196

Getting Started
18 MIKE 21 BW - © DHI
– Directional spreading
– Wave-wave interaction
– Wave-current interaction
The MIKE 21 BW module can handle these phenomena with the
exception of wind-wave generation.
3.2.2 Check MIKE 21 BW capabilities
Next, check if the MIKE 21 BW module is able to solve your problem. This
you can do by turning to Chapter 2, which gives a short description of MIKE
21 BW and an overview of the type of applications for which MIKE 21 BW can
be used, and by consulting the Scientific Documentation, section 6.
3.2.3 Selecting model area spectral and temporal resolution
When selecting the model area (or profile) you must consider the area of
interest, the alignment of the model grid relative to the main direction of
approach of the incident wave trains and the position and types of model
boundaries to be used, see
Selecting the Model Area under Bathymetry .
The choice of the grid spacing and time step depends on the wave conditions
for which simulations are to be performed and the water depth in the area of
interest.

The ratio of the maximum water depth to the deep water wave length of
waves with the shortest wave period must not become larger than 0.22, if
the deep water correction terms are excluded, and 0.5, if these terms are
included. See
Linear Dispersion Relation

The grid spacing is restricted by the resolution of the shortest wave
length or the surface roller, if wave breaking is included. See
Selecting
Grid Spacing under Bathymetry

The time step is restricted by the resolution of the shortest wave period.
See
Time Step

The Courant number should be kept equal or less than unity (0.5 for the
1DH module) to avoid instability problems. See
Courant Number
In practice the choice of the grid spacing and time step is often a compromise
between low computer costs and high accuracy.
The MIKE 21 BW Model Setup Planner (Figure 5.7) is an efficient tool for the
setup of your model.