open TELEMAC-MASCARET The mathematically superior suite of solvers

hi everybody,

I have some question about DIRECTIONAL SPREADING :

1- I don't have a clear understanding of this phenomenon. I saw a definition of the directional spread in Zhaoxian Lin et al 2021 in the introduction of "Estimating ocean wave directional spreading using wave following buoys: a comparison of experimental buoy and gauge data"
which is : " Directional spreading is a measure of how wave energy for a given sea state is spread as a function of direction of propagation."

But the dynamic of the word "spread" is very close to the dynamic of the mean direction in my first understanding. Or in my second understanding I see "spread" like a dispersion or a rate of dispersion, how a wave once generated by a certain wind in a certain direction, is dispersed or deviated from this direction.

2- Directional spread is a measure but there is also formulas. I don't have this measure in my database, and I didn't found range of values of this variable in my internet research, can it be computed/calculated ? how?

thx for your help

Josias

hi everyone,

In case sensitivity tests, I included SPD the directional spread calculating by the model value in VARIABLES FOR 2D GRAPHIC PRINTOUTS, to find this value "experimentally" (if I can say that).

I used a bimodal spectra, (in fact I test Bi and Unimodal), Fixing the directional spread to 1 first, I made varied the Boundary and Initial directional spectrum first.
finding that the Initial and boundary directional spectrum 4 was suited for my modal, (the variable of comparison was the wave height and the mean direction ) ... , I made varied the directional spread using the value 1, 10, 100 and 200. 200 and 100 made excessive wave height but 10 and 1 was the values that seems suited for the modal, with the value 10 as the most relevant.
This value of 10 is the one recommended as Smax for wind wave when using the INITIAL/BOUNDARY ANGULAR DISTRIBUTION FUNCTION = 4 , Mitsuyasu with coefficient proposed by Goda et al.
In fact I didn't use 4 as ANGULAR DISTRIBUTION FUNCTION but 1 and 2. the value 4 leading to excessive heights.
So for now I use
ANGULAR DISTRIBUTION FUNCTION = 2
DIRECTIONAL SPREAD 1/2 = 10
DIRECTIONAL SPECTRUM =4

thx
Josias