open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi,
I have a question regarding coupling of Telemac3D and Tomawac. I have conducted 3 simulations:
1) with Telemac3D only
2) with Telemac3D coupled with Tomawac and with wind-driven currents = 1
3) with Telemac3D coupled with Tomawac and with wind-driven currents = 0

The surface current results are shown in the pictures attached (black for case 1, red for case 2 and blue for case 3).

I found that there is negligible difference in surface currents between Case 1 and Case 2 even when the area experienced wave height of 0.5 m. Case 3 in theory should produce the same result as Case 1 since FX and FY are never added to the source terms in trisou.f. However, the model actually predicted stronger current than Cases 1 and 2. Is there any suggestion on what I may possible have done wrong?

Also how does the coupling work between Tomawac and Telemac work when the time step in Tomawac is 10 times greater than Telemac? Does Telemac3D retain the same FX and FY and add the same values to the source terms in trisou.f every time step until these values are updated in wac.f?

Thanks.

Edwin

Hello,

Apart from the fact that the keyword is WAVE DRIVEN CURRENTS and is a logical value, this is strange.

Comparison between cases 1 and 2 may require looking more precisely, but cases 1 and 3 should give the same result. As it is a matter of adding a value FXWAVE and FYWAVE or not, depending on WAVE DRIVEN CURRENTS, there is little room for errors, but this test has perhaps never been done and we will check (we always assume that the keyword is true when coupling so maybe this must be controlled).

Note also that for the time being, only the 2D component of the forcing terms is added in 3D, the 3D forcing varying on the vertical has not been programmed yet (suggestions of good references on this topic welcome).

With best regards,

Jean-Michel Hervouet

Hi,

I haven't looked at the codes on why Cases 1 and 3 have different results yet. Instead, I spent the day looking at the results from Cases 1 and 2. The LOGICAL statement in TRISOU.f for WAVE DRIVEN CURRENTS works fine. However, I noted that my model predicts really small values for the radiation force due to wave.

Attached figure shows a snapshot from the model during a storm event. The colour contour shows the wave height. The line contour shows the water depth and the vector shows the radiation force (the magnitude can be estimated from the reference vector on the right).

As shown in the shallow region (2 m water depth and with wave height of 0.5 m), the radiation force is in the order of 1e-5 m/s2. Hence, the surface current speed in the coupled model is only about 2 cm/s greater than the surface current speed from Telemac model under this particular wave climate. Any thought on why FX and FY are so small?

Edwin

Hi, I don't know where you are at concerning 3D wave radiation stress, the formula used in Tomawac (radiat.f) gives the depth-integrated radiation stress and maybe you should check this out :
Vertical variation in radiation stress and wave-induced current Huayong Xia , Zongwan Xia , Liangsheng Zhu
Formulas (15) to (19) (and (20) to (23)) give expressions for radiation stress components (Sxx,Sxy,Syy,Syx) which depend on depth.
I don't know if this a good reference, but I saw you were looking for suggestions...

Many thanks, this is actually something that we should do for the next release. We try to organise it and find the manpower...

Regards,

Jean-Michel Hervouet

Looking into radiat.f, I have a couple questions on the radiation stress calculations.

1) Don't we need to have multiply by density when calculating SXX, SXY and SYY?

2) For SXX, SXX(IP)=SXX(IP)+(CGSUC1(IP,JF)*(1.D0+SISI)-0.5D0)*FS(IP,JP,JF)*COEF

should it be (1.DO+COCO) instead of (1.DO+SISI)?

similarly, for SYY, SYY(IP)=SYY(IP)+(CGSUC1(IP,JF)*(1.D0+COCO)-0.5D0)*FS(IP,JP,JF)*COEF

should it be (1.DO+SISI) instead of (1.D0+COCO)?

Edwin

Hi all,

By going through the units for SXX, SXY and SYY, I believe that we don't need to multiply density in the calculation as I have previously questioned - my bad.

Edwin

Hello,

Yes, and we are now looking at the second question...

REgards,

JMH

Hello Edwin,

sorry for the late reply. I don't think there is an error in the formulation of SXX and SYY. It is (1.DO+SISI) in the SXX formula and (1.DO+COCO) in the SYY formula because the TETA direction in Tomawac is expressed with respect to the North.

Best regards,

Elodie

Thanks Elodie. I will check my notes to see where I got mixed up.

Edwin