open TELEMAC-MASCARET The mathematically superior suite of solvers

Hi,

I was using the Telemac-3D version 6.1, then recently I have started to use the 6.3. But the results I got are totally different. I am simulating salinity transport in an estuary. I did not change anything in the geo or the conlim files, I did not change anything in the numerical or the physical parameters. The only change I did is that I modified the key-word “DENSITY FOR STANDARD VALUE” with the new one used in version 6.3 which is 'AVERAGE WATER DENSITY'

Have anyone experienced the same thing or have explanation to that

Hello,

A well known case of differences in 2D is the implicitation coefficients which are no longer hardcoded as 1. in some options, but there are no such things in 3D. In the case of an estuary I would look at the open boundary, where the problem may be not very well posed, so that you would get another solution, among an infinity, could it be this ? (and if not what is the difference and is it at least better ?).

Regards,

JMH

it is not an infinity but a very high value for the velocity and for the inflow from the sea side. Do you think that Thompson boundary conditions could help in this case (OPTION FOR LIQUID BOUNDARIES)

Hello,

This is it, your problem could be not well posed at the open boundary when the flow gets in, and the first solution to try is indeed Thompson boundary conditions. Another solution that worked in our Berre lagoon case is to add a small head loss at the open boundary.

Regards,

JMH

Can you tell me how to introduce such head loss at the open boundary. And why the problem did not appear in the 6.1 and it appears with 6.3

Hello,

If a problem has an infinity of solutions (different patterns of entering flows are all solutions of equations if you do not specify or force them) then any difference of truncation error may cause a bifurcation to another solution.

I enclose an example of head loss added, here 0.01, which is very small and was sufficient. It is done here based on coordinate Y compared to 19000. and needless to say it must be adapted to your case.

Regards,

JMH

thank you very much