[quote]... the “Filtration period” and “Backwash Period” cannot alternate automatically between each other ... I find the parameter “Backwash” where I must decide to input a “1” or a “0” ...[/quote]
Correct.
"Backwash" is a [i]manipulated[/i] interface variable that should be linked to an input provider, e.g. input file or timer for scheduling, control model, ...
The 1 state corresponds to backwash ON; 0 to backwash OFF.
[quote]About the “Q_Backwash”, ...[/quote]
"Q_Backwash" is a state variable of the model, i.e. computed: you can retrieve its value but not impose it.
To impose a certain backwash intensity at a certain time, you are to set both interface variables "Backwash" (on/off) and "Inflow_Backwash". The latter carries the state vector (water + components).
For instance, you could derive the backwash inflow from a buffer tank, at a given point in time and at the desired flow rate.
The [b]actual hydraulics[/b] (simplified) of the model is as follows:
[list]
[li]Q_Filtered: 0 during backwash; Q_Backwash + Q_Out* during filtering[/li]
[li]Q_Unfiltered: Q_In + Q_Backwash during backwash; Q_In - Q_Out* during filtering[/li]
[/list]
which, if you properly set the backwash inputs (i.e. make sure that Inflow_Backwash is 0 when Backwash is 0), guarantees that you don't have unfiltered flow during filtering.
[quote]... how I could build a sand filter model of at least 2 lines working in parallel ...[/quote]
You could:
[list]
[li]have the backwash from e.g. a buffer tank directed to one line (A) for a period - and set Backwash(A)=1 and Backwash(B)=0[/li]
[li]simultaneously, divert the flow to be treated to line B[/li]
[li]do the opposite for the second period[/li]
[/list]
Only be aware that such hard switches (0/1) may result in (local) numerical instability.
