MIKE 21 BW, User Manual, Page: 119 / 196

Basic Parameters
119
Remarks and Hints
Time domain wave modelling including wave breaking and moving shoreline
is a difficult numerical task. You may sometimes see numerical instabilities
and eventually blow-up in some of your applications. In such case please fol-
low the guideline given in Section 5.5.4.
We strongly recommend you to carefully walk through the application exam-
ples included in this installation prior to your first application with wave break-
ing and moving shoreline.
5.2.3 Type of equation
You can choose between the following two types of equations:

Classical Boussinesq equations

Enhanced Boussinesq equations
The classical Boussinesq equations are used if the ratio between the maxi-
mum water depth and the deep water wave length, h
max
/L
0
, is less than 0.22.
The enhanced Boussinesq equations include the so-called deep water
terms allowing to extend the model into deeper water/smaller wave period,
say, h
max
/L
0
= 0.5.
It should, however, be noted that including the deep water terms requires
substantially more
CPU time , as both the grid spacing and time step must be
reduced.
Remarks and hints
The 1DH applications requires the deep water terms to be included
For 2DH applications, including wave breaking and moving shoreline, the
deep water terms should be included for improved accuracy and numerical
stability.
Linear dispersion factor
For most practical applications a value of B = 1/15 = 0.067 is recommended.
5.2.4 Numerical parameters (2DH only)
On this dialog you specify the method for space and time integration of the
convective terms in the Boussinesq equations.