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Model formulations

DF

Model formulations

Capillary Posts: 4 Join Date: 1/5/13
Dear all,

As I am studying the results of my XBeach runs, I am experiencing some difficulties. If someone has some knowledge he wishes to share about these topics, I would be very pleased.

* The exchange of energy inbetween short wave enveloppes and the low frequency waves. I know this topic is still under research (Battjes 2004, ...), but I am curious on what exact model is used in the latest version (easter 2012).

* Triad interaction. Same as above.

* Wind. As stated in the user manual, a wind variable is included in the momentum balance. Although I am not sure if it is included in the GLM formulations of the manual (p2-16). I suggest it is taken into account by the surface shear stress (tau_sx, tau_sy)

Kind regards,
Dries Fonderie
U

RE: Model formulations

Hi Dries,

It's been some time since you posted your question, but maybe I can still help you out a bit.

For the interaction between the short waves and long waves I suggest you to take a look in the XBeach paper (Roelvink et al., 2009), which you can find here: http://oss.deltares.nl/web/xbeach/publications. In the paper all equations are written down and explained in a clear way. Following section 3.2 you can see that XBeach uses a wave action balance (eq 0.1) in combination with a roller balance (eq 0.12). These induce a respectively wave-induced and roller-induced radiation stress component, which is translated into a wave force (eq. 0.18). The wave force is direct input into the nonlinear shallow water equations (0.21 - 0.23).

As far as I know the short wave part of XBeach does not include nonlinear wave processes such as triads (in contrary to SWAN).

Finally, about the wind you are right, it is included as a surface shear stress in the GLM equations (term tausx and tausy in eq.0.21-0.23).

Cheers,
Arnold
DF

RE: Model formulations

Capillary Posts: 4 Join Date: 1/5/13
Thanks Arnold!