
Reference Manual
134
MIKE 21 BW - © DHI
Recommended values
The relationship between the depth averaged velocity, U, and the velocity at
the bed, U
b
, can vary from unity by as much as 30% for high waves and 50%
for high waves in relatively deep water.
Example
Wave height, H = 2.0 m; wave period, T = 8.0 s; water depth, h = 10.0 m; and
roughness height, k
N
= 0.001 m (a
b
/k
N
= 1000). With U/U
b
= 1.3, we get f
w
=
0.01, which corresponds to an equivalent Chezy number of C = 58.
Manning number
You can convert a Chezy number, C, to a Manning number, M, using the fol-
lowing relationship
(5.4)
where the Manning number has the unit [m
1/3
/s], and
h
is the water depth.
Please note that the Manning number used in MIKE 21 BW is the reciprocal
value of the Manning number described in some hydraulic text books.
5.3.6
Eddy viscosity
The decomposition of the prognostic variables into a mean quantity and a tur-
bulent fluctuation leads to additional stress terms in the governing equations
to account for the non-resolved processes both in time and space. By the
adoption of the eddy viscosity concept these effects are expressed through
the eddy viscosity and the gradient of the mean quantity. Thus the effective
shear stresses in the momentum equations contain the laminar stresses and
the Reynolds stresses (turbulence).
The eddy viscosity can be specified in three different ways:
No eddy
Constant eddy formulation
Spatial varying formulation
The eddy viscosity is calculated using two different formulations:
Eddy coefficient
Smagorinsky coefficient
For the case with values varying in domain you have to prepare a data file
containing the eddy viscosity coefficient or the Smagorinsky coefficient before
M
C
h
1 6
----------
=
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...