open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi all,

I was hoping to get some guidance on my wave modeling for Terrigal Bay (NSW, Aust.). I have a 2d telemac coupled with tomawac (with temporal varying wave heights on the oceanic boundary). The telemac model seems to run fine, i.e., tidal comparison with observations are good, and tomawac seems to predict the right order of magnitude of the significant wave heights (hsig) near shore compared to RDI ADCP (with waves) observations.

My issue is that the model output of the hsig is "choppy" after it refracts around a headland. Please view the attached image. (Right) is time-varying swells from mostly SE, (Left) static swell conditions with average hsig from SE direction.

Telemac dt=10
Coupling period with tomawac=36
Tomawac dt=360
Number of breaking timesteps=10
All wave dissipation sinks are ON at default values.

I'm wondering if anyone has any previous experience on why this choppy behaviour is happening and any potential solutions? I suspect that my coupling period & tomawac dt might be on the high side, but I was hoping to get some confirmation by more experienced tomawac-ers before I start up a long simulation to test it.

Thanks,
Shiv
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Note: The area between the wave rays (blue zone) near the coastline has reefs, but otherwise the bathymetry is fairly smooth. I have increased the ND (# of directions) 12 to 36 and it just increases the number of wave rays but similar choppy behaviour.

Hello Shiv,

As you suspected, TOMAWAC is not as tolerant as TELEMAC in large timesteps, especially in coastal waters. I would definitely lower TOMAWAC timestep to something similar to TELEMAC. If the results are satisfactory, then you may increase it as long as the results remain acceptable.
I know that you wont't like it (runtime-wise), but if I were you, I would begin with:
Coupling period with tomawac=1
Tomawac dt=10
Number of breaking timesteps=3
Best Regards,
Costas

Thanks Costas. That did the trick. The Hsig is a lot smoother now.

Unfortunately, any changes to increase the tomawac dt (to get faster runtimes) very quickly leads to choppy Hsig, so I'll stick with 10s.

Cheers,
Shiv