
Reference Manual
182
MIKE 21 BW - © DHI
5.5.11 Linear dispersion relation
For small amplitude waves, non-linear effects can be neglected and analyti-
cal methods can be used to derive the linear dispersion relation.
The phase celerity using Stokes first order theory is given by
(5.20)
where
c
is the celerity (= L/T), k the wave number (= 2
/L),
h
the water depth,
and
g
is the gravitational acceleration (= 9.81 m/s
2
). L and T are the wave
length and wave period, respectively.
Boussinesq equations
You can use this dispersion relation as a good approximation to the phase
celerity of the Boussinesq equations used in MIKE 21 BW as long as you fulfil
the requirements:
Classical Boussinesq equations: h
max
/L
0,min
< 0.22
Enhanced Boussinesq equations: h
max
/L
0,min
< 0.50
Here h
max
denotes the maximum water depth in the model domain, and L
0,min
the minimum wave length in deep water (= gT
2
/2
). T is the minimum wave
period. A comparison between the phase celerity derived for the Boussinesq
equations and Stokes first order theory is shown in Madsen et al (1991) and
Madsen and Sørensen (1992), see Scientific Documentation.
5.5.12 Mesh generation
You can use the MIKE 21 BW 1DH module for either structured or unstruc-
tured meshes. An unstructured mesh is recommended for detailed modelling
of surf and swash zone dynamics as this allows you to use a high spatial res-
olution in areas of particularly interest. An extracted profile from a e.g. a dfs2
bathymetry file can be used directly in MIKE 21 BW 1DH as a structured
mesh having a constant resolution/grid spacing.
If you would like to increase the spatial resolution in local areas (see e.g. the
example below) you first have to use the MIKE 21 Toolbox program “Mesh
Generation for MIKE 21 BW” for generation of an unstructured mesh. Based
on the structured data (dfs1-type data file) this tool generates a new file con-
taining two items; Item 1: co-ordinate (in length unit) of the node in the mesh
and Item 2: the corresponding water depth in the node. The second item is
used as the bathymetry mesh.
c
g tanh(kh)
k
------------------------
=
Содержание 21 BW
Страница 1: ...MIKE 2017 MIKE 21 BW Boussinesq Waves Module User Guide...
Страница 2: ...2...
Страница 4: ...4 MIKE 21 BW DHI...
Страница 13: ...General Description 13 Figure 2 4 Simulation of wave penetration into Frederikshavn harbour Denmark...
Страница 16: ...Introduction 16 MIKE 21 BW DHI...
Страница 75: ...2DH Boussinesq Wave Module Examples 75 Figure 4 45 Visualisation 2D of instantaneous surface elevation...
Страница 185: ...Entries Arranged Alphabetically 185 Figure 5 58 Application of different time extrapolation factors...
Страница 190: ...Reference Manual 190 MIKE 21 BW DHI...
Страница 192: ...Scientific Documentation 192 MIKE 21 BW DHI...
Страница 193: ...193 INDEX...