open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

I'm currently modeling creating a wave model for and offshore estuary and experience some issues regarding the wave height. The height decreases rapidly close to the boundary and I could not figure out whats the reason for that. I tried different frequencies as well as initial height. I assume it has to do with the chosen spectrum, but I could not find any specifications about all spectrum which are defined by the Keyword TYPE OF BOUNDARY DIRECTIONAL SPECTRUM.

I'm more thank thankful for help.
Regards,
Clemens

Hi Clement,

It is actually very realistic, because you impose a wave direction of 214, which is actually exciting your domain.

I believe Tomawac is using clock wise degrees with 0 being north, which makes 214 south-west direction.

Good luck,
Patrick

Hi Patrick,

Thanks a lot, I will check on this, but I thought it would be counterclockwise like written in the manual 5.2.2.
A question regarding the direction can you maybe explain further what is meant with BOUNDARY MAIN DIRECTION 1 and 2 as well as BOUNDARY DIRECTIONAL SPREAD 1 and 2. I assume it is like minimum and maximum, right?

Regards,
Clemens

Hi Clemens,

Clockwise or counter-clockwise, in both cases your angle should be between 0-90 or 270-360 to let the waves go into your domain.
Unfortunately, I can't answer your question about direction and spread, i'm learning tomawac as you do and your case is interesting as it might be something I might do in the future.
Regards,
Patrick

Hi Patrick,

I could find the solution. TELEMAC is using the direction as propagation direction of the wave and not as I thought as direction of origin. Since I changed that everything looks good. Thanks for the help.

Regards,
Clemens

Hi,

In addition of Patrick's answer, a TMA spectrum (initials of Texel, MARSEN and ARSLOE experiments) is an extension of Jonswap spectrum for limited fetch and finite (shallow) depth.
As a Jonswap spectrum, it allows you defining a bimodal sea state (with 2 directional peaks, swell and wind sea for instance) that you can prescribe with the keywords BOUNDARY MAIN DIRECTION 1 and 2. Each system has its own directional spreading (BOUNDARY DIRECTIONAL SPREAD 1 and 2). Then the angular repartition of the spectrum is computed according to the BOUNDARY ANGULAR DISTRIBUTION FUNCTION. You can have a look at the section 8.4 of the manual for the mathematical formulations.

Regards,
Laurent

Hello,
I'm new in numerical modelling. I have a few questions that may be stupid.

1) What is the difference between the INITIAL MAIN DIRECTION 1&2 and the NUMBER OF DIRECTIONS and the BOUNDARY MAIN DIRECTION 1&2 ?

2)I want to model the waves entering in an estuarian region, is the best way using the TMA spectrum ?

Regards,
Cyril

Hello Cyril,

"Main directions 1&2" corresponds to the directions of the 2 modes of the spectrum (typically, mode 1: swell and mode 2: wind sea, but it can be something else according to your site). "Initial" means that theses directions will be applied for all the spectra of your mesh, at the first time step only. "Boundary" refers only to the spectra located on your liquid boundaries, but for every time steps.

The number of direction refers to the discretization of your spectra in direction. The range [0 360°] will be split in as number of directions as you ask for with this keyword.

I don't really know what is the best way to your case, it depends on the characteristics of the sea states in your area, the availability of data, what you really want to represent.. You need first to have a good knowledge of the sea states in your region (offshore incoming swell(s), locally-generated wind sea, influence of tide near the coast...). If spectra measurements are available, you can look at their shapes (1 or 2 modes) and see if TMA or Jonswap (maybe more frequently used) are in agreement and which parametrisation is suited. But these parametric spectra only are theoretical representation of a real sea state.
You can also check the availability of numerical databases offshore your area that can be used on your model boundaries.
Once your boundary conditions chosen, a good parametrisation of the source terms is really important and have a significant influence on your coastal results.

I hope it helps.
Laurent

Hello Laurent,
Thanks for that answer, it helped me indeed !
The data I have are :
1) peak frequency
2) significant weive height
3) main direction
4) spread
When you say "source term", do you mean for example the wind ?
Cyril

Hello Cyril,

Yes, the energy induced by the wind is often the prevailing source term for the wave energy spectrum.
You can have a look to the section 3.3 of the tomawac user manual for a detail list of the processes modelled in tomawac.

Regards,
Laurent