Decoupled formulation vs fully spectral

Hello

I understand that  in Mike21,  the fully spectral formulation the calculations will include processes such as refraction and shoaling, wave growth by the wind, dissipation, etc.. Therefore, I would say that the fully spectral formulation can be used to model nearshore waves. I use this calculations quite often to design armour breakwaters. However, I am not quite sure in which cases is the Directionally decoupled parametric formulation applicable. could someone please help me to understand a bit more this formulation?

Thanks!

V.

Hi vicky2507,

Here's what the manual says about that:

"As the fully spectral formulation simulates the evolution of the directional-frequency wave action spectrum this model is several times slower than the directionally decoupled parametric formulation.

Which model formulation to use?
The fully spectral formulation can in principle be used in wave studies involving wave growth, decay and transformation of wind-generated waves and swell in offshore and coastal areas. However, the computationally less demanding directionally decoupled parametric formulation is sufficient in a number of situations. Examples of such cases are:

small scale wave transformation applications, say, spatial scale is less than ~10-50 km
applications where fully developed seas are dominating
applications where swell and combined sea/swell is not important
Note, that forcing due to the wind can not be included using the instationary directionally decoupled parametric formulation. "

Also regarding what this formulation is:

"The spectral wave module includes two different formulations

Directionally decoupled parametric formulation
Fully spectral formulation
The directionally decoupled parametric formulation is based on a parameterization of the wave action conservation equation. Following Holthuijsen et al. (1989) the parameterization is made in the frequency domain by introducing the zeroth and first moment of the wave action spectrum as dependent variables.

The fully spectral formulation is based on the wave action conservation equation as described in e.g. Komen et al. (1994) and Young (1999), where the directional-frequency wave action spectrum is the dependent variable. "

I hope this solves your problem ;)

Best regards,
Ricardo Machado

Dear Vicky,

In my experience, I use fully spectral formulation with Quasi-stationary mode to simulate Extreme events for the design of Structures. This would take less time but includes all the parameters.

For storm surges, I use Fully Spectral formulation with In-stationary  formulation with a lowest possible mesh resolution to reduce the time.

While for sediment transport and couple models, I use Direction decouples with in stationary mode to reduce the time. Its again the importance of the waves in the region. I use mode in rare cases.

Based on what you are ought to achieve, you should choose the process.

Regards,
Murali

Thank you so much for your inputs. They were really helpful. I decided to use the fully spectral formulation as I need to study the combined effect of swell and wind waves.

Thanks again

Victoria