This method uses a variable time step. The time step the user enters on the Job Control dialog, Dt, is the maximum allowable time step the program should use during the simulation. The program will select the current time step based on the minimum of the smallest conduit Courant number at the beginning of each long time step Dt, and the smallest junction time step. The model determines the number of equal length small time steps required to equal Dt.
This method uses a variable time step. The time step the user enters on the Job Control dialog, Dt, is the maximum allowable time step the program should use during the simulation. The program will select the current time step based on the minimum of the smallest conduit Courant number at the beginning of each long time step Dt, and the smallest junction time step. The model determines the number of equal length small time steps required to equal Dt.
The conduit Courant number (C#) is:
Equation 28:
for enclosed conduits, and
Equation 29:
for open channels.
The junction time step (J#) is:
Equation 30:
If the smallest C# or J# equals or exceeds , the program will use only one small time step. If the smallest C# or J# is less than the program will then compute the number of small time steps required to equal . The procedure used is:
In summary, the model works between minimum [0.9·C#, J#] and Dt. The number of small time steps is always a whole number.
The sequence of flow computations in the links and head calculations at the nodes can be summarized as:
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