open TELEMAC-MASCARET The mathematically superior suite of solvers

Hello,

I am modelling a river of around 10.5 km with a mesh resolution of 2 m. It has an inlet and outlet (Figure 1, conceptual sketch) and I am using variable time-step (See setup.cas file).

In order to initialize the river under dry conditions and get a steady-state, I put water depth values at the inlet nodes in BlueKenue. The Boundary conditions are as follows:

Upstream (inlet - Boundary 2) : 455 (Prescribed Q )
Downsteam (outlet - Boundary 1) : 555 (Prescribed Q and H)

In the steering file:

PRESCRIBED FLOWRATES : 28.32;28.32
PRESCRIBED ELEVATIONS : 38.00; 0.

1- After three days of simulation, the inflow equals the prescribed flow of 28.32 m3/s and the outflow fluctuates between 28.30 and 28.32 m3/s. However, when the simulation ends, the outflow value decreases to 27.66 m3/s (See Figure 2). May I just need more time of simulation to make both, inflow and outflow equal?

2 - When I tried to run the simulation with a downstream boundary condition of 544 (Prescribed H). I got Ill-posed problems (free velocities) at the outlet, which is very closed to an island like in Figure 3, where back water occurs in the red circle. This island may be the reason of the ill-posed problems and also of outflow fluctations. What is your opinion?

3 - I noticed that control sections do not work with a boundary condition of 555. In other words, the outflow values are not written in the Sections output file. For example, if I prescribed a Q= 28.32 m3/s and H = 38 masl, the section output file will only contain 28.32 during the whole simulation time.

Thank you in advance for your comments.
Kind regards,
Diego