open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello everyone,
I have some questions about Tomawac.

1. What's the difference between Spectral Significant wave height and significant wave height ?
2. What does exactly represent DMOY, the mean wave direction? Is it the current diretion? Because there are 2 variables for that (UX, and UY)


3. I'm trying to modelize a really simple wave propagation. So, I create a boundary condition on significant wave height, but during the simulation (an animation created with Fudaa Prepro), the wave height on the boundary doesn't decrease. Can you help me please?

PS: I joined my steering file

Hello,

Regarding your questions :

1) The significant wave height is, by definition, the average of the 1/3 highest individual wave heights in a sea state, obtained from a statistical (or wave-by-wave) analysis from a time series of free surface elevation. It is usually denoted as H1/3. The spectral significant wave height, denoted by Hmo, is computed from the variance spectrum as Hmo = 4 sqrt(mo), where mo is the variance of the sea-state, computed as the integral of the variance spectrum. This spectral significant wave height is obtained from a spectral analysis. In deep and intermediate water depths H1/3 and Hmo can be considered as being (nearly) identical, but this is not true in shallow water and coastal areas ; that is why it is important to mark the difference between these two wave heights. Additional details can be found in textbooks on waves.
=> Note that TOMAWAC, being a spectral model, it can only predict and output the spectral significant wave height Hmo.

2) DMOY is the mean direction of the sea state, i.e. of the waves. It is the average direction (measured clockwise from the North), towards which waves propagate. The definition is given in Appendix 7 of the Tomawac manual, available online.
It has nothing to do with the current direction (if there is an ambiant current field).

3)I am not sure to understand your point. If you create a boundary condition on the significant wave height in the steering file, this boundary condition will be steady during the whole simulation with Tomawac. So it is fully normal that the wave height on the boundary doesn't decrease during the simulation !
If you want that the spectral significant wave height varies in time at the boundary, you have to modify the LIMWAC subroutine and code your desired law for evolution in time of Hmo at the boundary.
I am however not certain that this is what you meant, so do not hesitate to provide additional details regarding this point if I did not answer properly.

Regards,

Michel Benoit

2) I tried to show the direction of the wave by vectors. I followed instructions from this post with ux=cos(D_MOY).
But I dont think that I have something good, as you can see on this picture

I created a simple and constant wave with a North direction(0°).

3) So, what's the difference between the groups of keywords "INITIALISATION DU SPECTRE" and "CONDITIONS AUX LIMITES"?
I thought that if I change the only the group "INITIALISATION DU SPECTRE", I would have a (simple) propagation like a LIMWAC modified.

Thank you very much for your help.

hello

for the directionnal vectors, you must create new variables and one vector.firstly you have to convert DMOY in radian. d=DMOY*2pi/360
next you can create 2 variables ux and uy
ux=cos(d-pi/2)
uy=-sin(d-pi/2)
It should work now

regards

Hello Liot,

Regarding question 1, I agree with the reply in the post by tannycke. If you wish to plot vectors showing wave propagation direction, you should first create a vector whose components are :
dir_X=sin(DMOY*PI/180)
dir_Y=cos(DMOY*PI/180)
DMOY is indeed given in the result file in degrees with origin being the North (vertical Y axis), and increasing clockwise.

Regarding your second point, the group of keywords "INITIALISATION DU SPECTRE" refers to initial conditions (at t = 0 only) over the whole computational domain. They permit to initialize the wave spectrum over the whole domain : same spectrum is used at all points at the start of the run. The group of keywords "CONDITIONS AUX LIMITES" refers to boundary conditions for the whole duration of the simulation. The parameters you specify there apply to all boundary points where incident wave conditions have to be imposed.
If you want to propagate steady conditions from the boundaries, you have to specify the wave parameters of the incident spectrum at the boundary in the "CONDITIONS AUX LIMITES" group of keywords (initial conditions do not really matter in this case).

Regards,

Michel Benoit

If you want to .

Hello,

For the vectors, it's ok now. I didn't notice that I had to use radian.

Regarding the second point, I understand now what's the difference.
"INITIALISATION DU SPECTRE" is used to initialize over the whole domain.
I will try with a LIMWAC modified.

Thank you very much for you help, both of you.

Regards,
Liot.

Hello,

I'm trying to configure a LIMWAC fonction, by using the one from whirl_current (test case), but I dont understand how to create a boundary limit depending on the time.
I mean, for example :

at t=0 seconde, BOUNDARY SIGNIFICANT WAVE HEIGHT = 2

between 0<t<2, BOUNDARY SIGNIFICANT WAVE HEIGHT = 1

at t>2, BOUNDARY SIGNIFICANT WAVE HEIGHT = 0


I don't know which part of the code should I modify.

Bonjour,
Je me demandais si vous êtes l'auteur de l'article:
"TOMAWAC : un modèle de prédiction des houles de tempêtes en eau profonde et en zone côtière"

Si oui, je voudrais savoir comment obtenir cet article?

Cordialement