MIKE 21 BW, User Manual, Page: 179 / 196

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179
1. Define the minimum (h
min
) and maximum (h
max
) water depth in your
model area.
2. Define the minimum wave period in the spectrum which you would like to
resolve in the model
(5.15)
where

= 0.22 for the classical equations, and

= 0.5 for en enhanced
equations (see Minimum wave period p. 183).
3. Find the grid spacing so that the minimum wave length is resolved by at
least 7 grid points, i.e.
(5.16)
Here L
min
is the wave length corresponding to T
min
and h
min
. The wave
length can be calculated from the Linear dispersion relation.
In case of breaking waves and moving shoreline boundary 20-40 grid
points are required for the most energetic waves (20 points are assumed
in the MIKE 21 BW Model Setup Planner) for the minimum wave period.
4. Find the time step for the numerical time integration. Beside fulfilling the
CFL criterion (first expression in bracket), the minimum wave period has
to be resolved by a minimum of 7 (classical equations), or 35 (enhanced
equations), time steps, i.e.
(5.17)
In case of breaking waves and moving shoreline boundary the time step
is often 0.02-0.1 s in 2DH applications.
In 1DH applications the Courant number needs to be less than about 0.5
and the time step is most often within the range 0.001-0.1s depending on
the spatial resolution.
5. Find the simulation duration. Most often the simulation time is longer
than 20 minutes, see section 5.2.6 Simulation period.
6. Then you have to decide whether you should apply long crested (unidi-
rectional waves) or short crested (directional) input at the internal gener-
ation line.
h
max
L
0 min

---------------  
T
min
2

h
max
g

-------------------
 
L
min
x

---------- 7

t

x

gh
max
--------------------
T
min
7
----------- or
T
min
35
-----------
{ , }
