This tab is used to define the simulation time parameters and result writing time parameters for a scenario and its variants.

Simulation time parameters

• Beginning time (Day: 0 Time: 00:00:00 by default)
• End time (Day: 0 Time: 00:00:00 by default)
• Calculation step (10 minutes by default)

Simulation time parameters for result writing

These parameters are used to reduce the size of written results during simulation. This allows to get simulations and operations on results faster but also to solve memory overflow problems that may occur with very long simulations on large systems.

• Start time for writing (day: 0 Time: 0:00:00 by default): useful if one is interested in a phenomenon having place only after a certain time step.
• Write results frequency (1 time step by default): useful if the results are not essential at each calculation time.

Steady flow simulation

By default, for a steady flow simulation (FLUVIA), only the first time step is executed. To run several successive steady flow regimes over time, the option "First time step computing only" in the "Steady calculation" tab should be unselected.

Unsteady flow simulation

The default value of the calculation time step is set at 10 minutes. One must be careful when changing this value since it has an influence on the numerical scheme and consequently the accuracy of the calculation. However, it has no influence on the stability of the numerical scheme since the scheme used is the implicit scheme Preissmann which is unconditionally stable (see Theoretical documentation).

We can choose local spaces step and the time step as desired according to the study carried out. What is known (cf. Cunge 1983, Malaterre 1994) when the Courant–Friedrichs–Lewy condition is very small (eg. <0.1) or very large (eg.> 10) then the scheme introduce numerical diffusion and phase difference. It is therefore desirable to keep the Courant–Friedrichs–Lewy condition in the range [0.5, 10].