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Hi,

I use telemac2d in order to make different tidal simulations. I work with the atlas NEA and i create the harmonics constituents with the COMODO tools. I work on 20 days. When i see my results with fudaa or BK, i see that my free surface moves during one day and after , it remains constant. Normally, i should see any variations during my simulation causes by the tide.

May be, my problems are caused by my parameters in my steering file or in my conlim file.
I have 4 boundaries in my domain. The coastal which is defined like 2,2,2,2 and 3 free boundaries which are defined with 5444 in my conlim file. It's OK ?

As i work with NEA atlas, i make these parameters for the tide:
OPTION POUR LES CONDITIONS AUX LIMITES DE MAREE :1
BASE DE DONNEES DE MAREE: 3
FICHIER DES CONSTANTES HARMONIQUES : obc-fes2004.dat
DATE DE L'ORIGINE DES TEMPS: 2011 ;03;31
HEURE DE L'ORIGINE DES TEMPS : 0;0;0
COEFFICIENT DE CALAGE DU MARNAGE : 1
COEFFICIENT DE CALAGE DES VITESSES DE COURANT :999999.

Have you got an idea why my free surface doesn't vary?

Regards
Florian

Hi Florian,

The format of the HARMONIC CONSTANTS FILE (FICHIER DES CONSTANTES HARMONIQUES in French) is expected to be like the example described in Appendix 4 of the manual to model tides with version 6.2 of TELEMAC, see www.opentelemac.org/index.php/training-and-tutorials

Are you sure that it is OK (no generator of this file has been available in TELEMAC yet, so you have to be careful with the format, also described in the BORD_TIDE_LEGOS subroutine, see the READ(NFOT,*... lines if you are familiar with Fortran)? The format expected by TELEMAC is not the one written by the latest version of the COMODO tools (e.g. if you use the predictor command).

Otherwise, please send your steering file, boundary conditions file, Fortran file and harmonic constants file.

Regards,

Chi-Tuan

Hi Chi-tuan,

Thanks for your help.

I read the manual but before to give you my files, i would like to have more informations about prescribed elevations and initial elevation.
If i don't put these keywords, i have no variations during my tide simulation, why?. How can i know the values that i must make for these keywords?

Regards
Florian

Hi Florian,

The keyword PRESCRIBED ELEVATION deals with boundary conditions whereas the keyword INITIAL ELEVATION deals with initial conditions.

When modelling tides, I can see two classical options to initialise the computations (keyword INITIAL CONDITIONS): CONSTANT ELEVATION (with the value INITIAL ELEVATION) or TPXO SATELLITE ALTIMETRY as described in the TELEMAC-3D user or reference manuals for version 6.2, the dictionnaries of the codes telemac2dv6p2.dico, telemac3dv6p2.dico, or the manual to model tides with TELEMAC v6.2 in French.
After a transient period of time, if the initial condition (even constant) is not so far from the expected solution, the computation of tides should not be so sensitive to it with TELEMAC. Yet, it may depend on the extent of your model.

Do you use the standard TELEMAC-2D 6.2 version? If not, you should first try it. If you have changed anything in the code or the Fortran file, I cannot give you more advice without reading your changes. With the standard subroutines BORD_TIDE, BORD_TIDE_LEGOS and BORD_TIDE_TPXO in TPXO module for version 6.2, there are no specific treatments if you use the keyword PRESCRIBED ELEVATION or do not.

Regards,

Chi-Tuan

Chi-tuan,

I use the v6p2 version. I work with the NEA atlas. I don't change the subroutines BORD_TIDE_LEGOS.
I send you my files if you have the time to test my simulation.

When i make a simulation during 3 hours, i have good results but when i want to make a simulation during 21 or 2 days, my results are bad bacause the free surface becomes constant.

Regards
Florian

Hi Florian,

As I have suspected, your error comes from the harmonic constants file. The headline has not been written correctly. Please find enclosed an archive containing a corrected harmonic constants file and a modified steering file (some keywords have been commented because their values are default ones, others have been deleted because they are useless or tricky, and some last one have been slightly changed, e.g. when floats are expected instead of integers). Be careful with the number of columns in your steering file, in your original one, you gave me an overflow for the keyword CONDITIONS INITIALES.

For the harmonic constants file, as described in the manual to model tides, the 2 first things to fill in are the number of liquid boundaries where you want to prescribe tidal signals. It is the same description as for a liquide boundary. The numbering starts at the boundary node located the closest to the south-west and then anti-clockwise. In your case, you have 2 liquid boundaries, in the TELEMAC definition.
The limit indices are written in the new harmonic constants file (you only need to read the boundary condition file to fill in it).

I have a few questions/suggestions to give you when reading your steering file. Why do not you use DIFFUSION OF VELOCITY? Perhaps with YES and VELOCITY DIFFUSIVITY = 0., it may be better.
In other posts, with such flows, it is recommended to use TREATMENT OF THE LINEAR SYSTEM = 2 with SOLVER = 1 (wave equation + conjugate gradient) that reduces time computation. Do you have a reason why you do not use these options?
As you only prescribe the elevation of tide without any velocity, you can try to use the classical boundary conditions rather than the Thompson conditions (OPTION FOR LIQUID BOUNDARIES =1).
At last, do not forget to take into account the Coriolis force (CORIOLIS = YES and COEFFICIENT COEFFICIENT to calculate depending on the latitude, please read the help in the telemac2dv6p2.dico or the TELEMAC user manuals).

With your harmonic constants file, I wonder how you could have had "good results". Perhaps because of a transient period?

Hope this helps,

Chi-Tuan

Hi Chi Tuan,

Thank you very much for your help

I read the manual to model tides before to begin my simulation. I didn't understood how i made the header.

I didn't test Diffusion of velocity because to start with this tidal model, i use the test "ondem2" where this keyword was define by "NON".

I try to make a run in using TREATMENT OF THE LINEAR SYSTEM = 2 with SOLVER = 1 but the simulation didn't run:





I make a run in changing the keyword OPTION FOR LIQUID BOUNDARIES. But during the simulation, i have this error message:
================================================================================
ITERATION 180 TEMPS : 30 MN 0.0000 S ( 1800.0000 S)
PROBLEME MAL POSE, VITESSE LIBRE ENTRANTE
PAR EXEMPLE AU POINT DE BORD NUMERO 116

---

I forgot the Coriolis force. My domain is in Cartesian coordinates. I can't define the Coriolis coefficient in function of the latitude. In the manual, it is said that if the domain is in Cartesian coordinates the Coriolis coefficient is constant.

With my harmonic constants file, i told about "good results" because i had some variations but it was stupid.

i saw that the SHOM institute works with telemac in order to make a tidal prediction. How can i make if i want to make a prediction?
Where can i find a manual or the methods to make these predictions?

Can i use with the NEA ATLAS the Fourier Analysis?

Regards
Florian

Hi Florian,

You should use the parameters coming from the test case 123_tide rather than 027_m2wave.
If you read your error message, you can see that when solving a linear system with the conjugate gradient method, the relative accuracy is around 10^15 that is very huge. There may be a problem with your initial conditions or some combo of parameters.

Without the Thompson conditions, when only prescribing water depth, when the wave enters the domain, it should be better to prescribe velocities rather than let free velocities, that is why you got this warning message. But your solution farther from the liquid boundary should be OK.

For the Coriolis coefficient, you are advised to calculate it at the center of your domain, with the equivalent latitude. Then, it will be constant for all your domain. Otherwise, you will have to use the SPHERICAL COORDINATES option.

What do you mean with "to make a tidal prediction", do you mean to know the field of water depth, free surface elevation or velocities over an area or those values at a specific location?

Yes, you can use the Fourier Analysis with the NEA ATLAS .
Are you sure of the name of this atlas? Is your study located around Congo? If yes, the real NEA atlas only covers the North-East Atlantic ocean, from Mauritania to Norway. Do you use another regional atlas or FES2004 global atlas?

Regards,

Chi-Tuan

Chi-Tuan,

Thank you very much for yours indications.
I don't see the test case 123_tide in the telemac2d.tar v6p0. Where is it? I download it but i have not this test case.

I modify the type of boundary in putting prescribe velocities.I will see the results of this modification.

I will precise the latitude of a central point in my domain for the Coriolis force.

When i say "how can i make a tidal prediction", i mean that i want to predict the free surface elevation or velocities over an area during one month or each month during one year by example.
I put in my boundary the harmonic constants and i would like to have the height water, or free surface elevation on a time period.

I use the Atlas fes2004 and fes2012 and they are developed like the NEA atlas. Also i parameter the fes atlas in using the NEA atlas in the keyword BASE DE DONNEES DE MAREE:3 in my steering file.
But i use the harmonics constants of fes2004 or fes2012 and the U or V velocities of fes2004 and fes2012.

Regards

Florian

Hi Florian,

As already told in other posts, you should download the test cases corresponding to the latest version of TELEMAC (6.2). They are available via SVN in the Download section, then Sources: SVN menu on the right and read the section "The details of the TELEMAC SVN repository"? As the code has changed since version 6.0, if you use a 6.2 version, you will not be able to run every test case correctly for sure!
123_tide has existed since version 6.1, but as there were many changes to model tides between version 6.1 and 6.2 of TELEMAC, I strongly recommend you to use the 6.2 version.

To predict free surface elevation or velocities, you only have to change the origin of date (and time), and perhaps the time step and the number of time steps, and then you can propagate tides on your domain.

I asked you about NEA or FES, because it would surprise me that NEA atlas covers an area in the south of Mauritania.

Regards,

Chi-Tuan