Steady flow calculation parameters
This tab allows you to change the parameters influencing the calculation algorithm in steady flow, especially when the iterations in case of mesh network, and/or with offtakes in flow calculation mode.
The default settings allow almost all the time to compute a solution with very good accuracy. In some cases one can help, accelerate or make possible the convergence of the algorithm.
Relaxation coefficient at diversions
This option allows you to speed up or slow down how the flow distribution is corrected at diversions during iterations of the calculation mesh. It may be necessary to decrease it when the mesh algorithm stops because of negative flow in a reach.
Max iterations meshed system
One can increase the number of iterations if the number provided by default is not sufficient to ensure the convergence of the mesh calculation.
Precision at nodes
This is the maximum permitted deviation of the water elevation at offtakes and diversions (in meters) between the assumptions made in the current iteration and real dimensions calculated considering the hydraulic conditions (elevations and flow rates) calculated in the system.
In case of difficulty to calculate in steady flow, especially in highly meshed networks where it is difficult to know the direction of flow a priori, two possibilities are offered:

Small space step
The "Small space step" mode is used to locally introduce new calculation sections (dividing the local space step by 10) if high water line slopes are detected (slope superior to 5/1000 including reverse slope). Please note that this mode is not supported in unsteady flow calculation, which is not a big problem, but this can introduce "waves" at the beginning of unsteady flow simulation.
Debug mode
You can activate the "Debug" mode that will record more intermediate variables on the log file during steady flow calculation. These informations allow to follow in more detail the computation iterations.
Allow reversing the direction of the reaches
As the name suggests, this option allows the mesh resolution algorithm to reverse the flow direction of the reaches during the calculation. Only "intermediate" reaches (ie not adjacent to a node located upstream or downstream of the system) may be reversed.
Allow calculation of supercritical
When this option is checked, FLUVIA calculates supercritical water lines and the location of hydraulic jumps. Otherwise, the supercritical flows are represented by a critical flow. To perform an unsteady flow calculation from a water line including supercritical flows, it is recommended not to check this option so that the calculation can be done with the "Simple supercritical" of SIRENE.
First time step computing only (in steady flow calculation)
This is useful for running only one time step even if the time settings specify more time steps to calculate. Indeed, the conventional use of the software to perform an unsteady flow calculation is to create a scenario specifying the simulation time, perform a calculation on the first time step in steady flow, then create a variant to perform calculation in unsteady flow with the same parameters.
This option will be unchecked only if it is desired to carry out a simulation with successive steady flow simulations.
Write in all calculation sections (to allow to initiate an unsteady flow computation
A calculation made with this option can then be selected for importing an initial condition for an unsteady flow calculation.