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Hi,

I want to simulate wind setup related to three measurement sites. As you can see on figure below, I get strong winds on october 9th around 12:00 which is aligned with the measurement sites.




Here are my 2 questions :

1. Until the first wind setup, i find the results satisfying...However after the wind event i get unwanted oscillations not representative of the observed data. What would explain these oscillations ? I was thinking of increasing velocity diffusivity here ??? what do you guys think ???

2. Wind setup seems to happen late by 2 hours on first two graph but seems ok but lower on last graph. what could be the cause of this offset ??? I'm using fully implicit on h and v. could that be it ???


Thanks in advance

Mathieu

Hello,

Your oscillations look like a real seiche (this can be checked if you compute the time it takes for a long wave with celerity sqrt(9.81*depth) to cross your domain). The physical phenomena that can damp this seiche can be turbulence (hence the velocity diffusivity will have an influence) but also the bottom friction (though in 2D this is not the case). Be aware that wind effects in 2D are somewhat artificial and fail to reproduce upwhellings.

Regards,

JMH

Hello,

By 2D do you mean telemac2D ??? Do you think i should consider coupling with tomawac to better represent wind setup ???

I took a look in the documentation and i see that t2d doesn't take into account fetch distance in the formula.. Is this what you mean by artificial ???

Thanks
Mathieu

Hello,

I mean that with Telemac-2D you will not get rotating flows with velocity following wind on the free surface and going back on the bottom, the phenomenon that gives upwelling or downwelling, this is a typically 3D effect. Otherwise the formula for the wind influence is empirically based and takes waves into account, although obviously it does not consider the fetch, so it is an approximation. This is not your problem as you have too large oscillations. Another way to reduce oscillations would be to reduce the coefficient of wind influence (by the way be aware that there is in this coefficient the factor RO(air)/RO(water) which is often forgotten by users, so that this coefficient is close to 1.E-6 rather than 1.E-3.

Regards,

JMH