open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi,

If I got it right, according to the formula in spejon.f for the Jonswap spectrum, for limspe=6, we should have:
E(fpeak) = [al*g^2*gamma*exp(-5/4)] / [fpeak^5*(2*pi)^4]

which should be the maximum value of the spectrum,

and where al = (2*pi*fpeak)^4*hm0^2/g^2 * 0.0624/(0.230+0.0336*gamma-0.185/(1.9+gamma))

in my steering file I define
TYPE OF BOUNDARY DIRECTIONAL SPECTRUM = 6
BOUNDARY PEAK FACTOR = 3.3
BOUNDARY SIGNIFICANT WAVE HEIGHT = 4.0
BOUNDARY PEAK FREQUENCY = 0.098039

I should then obtain al = 0.0049
and E(fpeak) = 31.5370 m2/s

But when I run a case with no source terms (geometry: 1000m long square, 40m depth, 3 solid borders and one liquid), the maximum that I get is 397,7219 m2/s
In fact the Jonswap spectrum are the same with a ratio of 3.43 (=397.7219/31.5370)

I guess there is something that I'm missing in the definition of the Jonswap spectrum for limspe=6, but what?

I hope you have everything you need to understand my question, otherwise let me know.

Thank you,
Pauline.

Hello,

the output of TOMAWAC is the directional spectrum S(f,theta)=E(f).D(f,theta), where E(f) is the omni-directional frequency spectrum (e.g. JONSWAP spectrum) and D(f,theta) is the directional spreading function.
If you make a cross-section of the spectrum along the mean propagation direction theta0, you do not visualize E(f), but E(f).D(f,theta0)
Thus, the maximum value of this cross section is not E(f).

If you want to visualize E(f), you must integrate the directional spectrum over the directions, at each frequency :

E(f_i)=Sum[S(f_i,theta_j)*DTETAR] for j=1,NPLAN
NPLAN is the number of discretized direction and DTETAR=2.PI/NPLAN.

Kind regards,

Michel Benoit