open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi!

I'm runnig a tidal simulation with V6P2 under python2.7 and with the same tidal model described in the post www.opentelemac.org/index.php?option=com...6&id=2588&Itemid=177
I've seen that you suggest to use another data base, but at least for now 4 harmonics are enough precision for my simulation in the Channel region.

Actually, I ran a simulation the 21.06.09 at 04:00 until 08:00 and I compared with the actual tide data at this day.Both were coresponding.But when I ran a simulation without changing anything except from the starting time (06:30) and the name of the result file, I found a totally different tide which do not correspond with the real data.I even launched exactly the same simulation to compare them both and make sure that they are identical.And they are.
Thus I want to know if you have to launch the simulation at a special time concerning the actual tide in order to get a correct simulation?
Regards
Hanna

Hi

Simple question, how are define the initial conditions?
If they are the same that should create some difference...

Regards

Hi,

I totally agree with Christophe.
In the English Channel, tide changes significantly during 2.5 hours. If your first initial conditions fits well for your initial time, it may not fit well 2.5 hours after and you have to wait a few hours (physical time) to go through the transient period to reach a correct solution.

What surprises me the most is that you have found that tide is well reproduced on your area, but it is only during a 4 hour duration. Do you compare results for only one location or several ones? What is the extent of your domain of computation (length and width)?
My remark for Benoît-Joseph is relevant if you try to simulate long durations, longer than a few hours.

Regards,

Chi-Tuan

Hi,

Actually,I though too that it was depending on the initial conditions.Thus I launched a simulation changing them into what I found for the real data (Initial Elevation of 2m).But this didn't really change a lot.(less than 10 différences with the first simulation when I compared the files)

My domaine has a size of 24 km * 40 km next to the raz blachard (next to Alderney Braye).
How long do you think the simulation should last in order to make sure that I quitted the transient period?
I only realise short simulation periodes for now because I just want to make sure that everthing is working correctly before simulating a longer period which takes a longer physical calculating time.I'll certainly change the tidal data base afterwards.

Regards
Hanna

Hi Hanna,

I think one tidal cycle may be enough (i.e. around 12 h physical time) with Telemac-2D, but perhaps try a little bit more.

Regards,

Chi-Tuan

Thanks a lot Chi-Tuan,

I'll try a 24h simulation then.
Regards
Hanna

Hi,

I've tried a 24h simulation starting at the same date and time as before.But nevertheless, this didn'change the problem.The tide doesn't correspond to the real data and I don't know why.I observe a tide changing every six hours as I should but not at the time I should observe the change reffering to the official french tidal predictions.This means that even after a long time the tidal model doesn't adjust correctly and it is not only a problem of initial conditions.Does anybody have an idea,why the 24h simulation doesn't correspond to the real tide data?
Regards
Hanna

Hi Hanna,

Are you sure you compare the results of your simulation with predictions (from SHOM website, predit software or something else?) with the same time zone? As I told to Benoît-Joseph, in Telemac with these databases, time is refered to UTC.

When you say "I've tried a 24h simulation starting at the same date and time as before.But nevertheless, this didn'change the problem.", do you mean that even your first 4 h results do not fit anymore whereas before they do with the same initial conditions in your first post?

If it is possible, I would like to see your harmonic constants file, your parameter file, your boundary condition file and your Fortran file if you have changed anything please.

Regards,

Chi-Tuan

Hi again,

In addition to the information I asked you, could it be possible to see some figures that show the comparisons between simulations and predictions (time series for water depth or free surface elevation and/or velocities)? Moreover, could it be possible to see on a map the location of the point where you extract your results and that also show the bathymetry. For my information, what is the reference for your bottom elevation, CD or MSL?

Regards,

Chi-Tuan

Hi Chi-Tuan,

I'm sure that I compare the predictions and the calculated data in UTC time.The official side of the SHOM permitts to choose your time and when I found out that the simulation and the real data doesn't correspond,I checked several times time and date for the real data and no mistake.This is not the problem.
No I didn't include the 4h which worked because I thoght that if 4h work,24h will work.I tried the second 4h simulation starting on the 21.6.09 06:30. And this didn't change anything in the simulation.I compared both the 4h and the first 4h of the 24h simulation.Even afterwards the tide is not correct but at least it lasts for 6h.
I'll attache the files you ask to this message except the harmonic file because I didn't change anything in the data base of the harmonic constants.
Regards
Hanna