open TELEMAC-MASCARET The mathematically superior suite of solvers

I am doing comparison between SWAN and TOMAWAC.

The design wind is 24 m/s and the fetch is over 65 km. Based on JONSWAP, I'd have a offshore wave height of about 3 m and period of about 6.6 seconds.

The MINIMAL FREQUENCY = 0.055556 Hz, the FREQUENTIAL RATIO = 1.22 and the NUMBER OF FREQUENCIES = 24. Thus, the maximum frequency is about 5.43 Hz.

NOTE: I have tried reducing NUMBER OF FREQUENCIES.

I have prescribed 65,000 to the BOUNDARY MEAN FETCH VALUE and the corresponding wave properties. The model reached somewhat of a steady state after 2 hours of simulation time but the wave height on the west side of the boundary is about 1 m. The water depth is over 100 m deep.

Is there some parameters that I overlooked?

I have attached the model result here. The black contour line represents water depth at 50 m interval.

Hello,

the keyword BOUNDARY MEAN FETCH VALUE is used to set the boundary conditions, and not to impose the wind field over the domain. The fetch value is used to calculate the JONSWAP spectrum that is imposed at the boundaries of the domain.
From what you write, it seems that you are not forcing the model with any wind imposed over the domain. This explains why you get a wave height that decreases from East to West.

If you want to investigate the generation and the spatial evolution of waves in the presence of a constant wind blowing over a fixed fetch, you should modify your steering file as follows :
- impose wind generation and set the wind generation model you want to use
- impose a constant wind field over the whole domain
- you set non-zero boundary condition on the East boundary only if you intends to have a wave energy flux entering from the East boundary of the domain. Otherwise, you should set absorbing boundary condition over the whole contour of the domain.
- if you impose zero energy as initial conditions and you generate waves only via the wind field imposed over the domain (i.e. you do not have any energy flux entering the domain), you must use the keyword LINEAR WAVE GROWTH, and set it to 1, otherwise the model is not able to start a wave simulation from a nil wave spectrum.[/li]

Hope it helps.
Kind regards,

Giovanni

Hi Giovanni,

I did have WIND GENERATION = 1, LENEAR WAVE GROWTH = 1 and have imposed a constant wind field over the whole domain.

I got reasonable results when I impose zero energy on the boundary.
However, when I set the non-zero boundary condition (based on 24 m/s wind, 65 km fetch) on the east side, the model results somewhat suggest that the prescribed boundary conditions are not realistic and can not be sustained and hence the decay.

Edwin