open TELEMAC-MASCARET The mathematically superior suite of solvers

I have a wind of 25 m/s, say in the x direction. I want to apply on the water surface a wind shear of 1.5 N/m². Normally the starting point is a parametrization of the general form:


Hence I know that, with an air density of 1.2 kg/m³, I can set a drag coefficient C_D of 0.002.

However, I found the description of the 'wind influence' in TELEMAC unconventional and a bit wobbly -- arguments provided in another post.

What is the value of the keyword COEFFICIENT OF WIND INFLUENCE that I have to set in the *.cas file together with WIND VELOCITY ALONG X?

Is the keyword COEFFICIENT OF WIND INFLUENCE the drag coefficient in the formula above?

Thanks for helping out with this

Hello

You can find the description of the wind force in the subroutine prosou (sources/telemac2d) and more descriptions in the user manual.
The coefficient of wind influance Fair is used to compute the force of wind like:
along x: Fx=Fair * Ux* norm(U)/H
along y: Fy=Fair * Uy* norm(U)/H


I hope that this helps

with my best regards

Riadh

Thanks.

I had resorted to the forum because the explenation on the manual are not clear enough IMHO. It's no point to look into a subroutine if you don't know which physics the subroutine solves, and this should be explained in the manual anyhow. So apologies if I ask for more once again.

I assume that the 'wind force' you mention is the wind shear stress [N/m²].

Thus

with dimension of kg/m² --- is this understanding correct?

Thanks for double checking.

...or is rather the 'wind force' the whole term in the depth-averaged momentum equations where the surface shear stress is applied? In that case, the 'wind force' is a force per unit mass, units m/s². Hence:


which is dimensionless. Please confirm.

In fairness, this definition is hinted at in the manual (midway of section 6.3.1) except for the fact that it has not been not clearly stated what the baseline parametrisation of the wind shear stress is and hence whether the a_wind is the conventional wind drag coefficient (rather than some reworking of it). I would suggest that this is improved, but there's another post on this.

Watermotion.eu wrote:
The expression and value are

COEFFICIENT OF WIND INFLUENCE = rho_air / rho_water * C_d = 0.0000024

Watermotion.eu wrote:
No. See this other post for the reasoning behind a_wind = C_d