Extended Period Simulation

When the variation of the system attributes over time is important, an extended period simulation is appropriate. This type of analysis allows you to model wet wells filling and draining, regulating valves opening and closing, and pressures and flow rates changing throughout the system in response to varying load conditions and automatic control strategies formulated by the software.

While a steady-state model may tell whether the system has the capability to route calculated loads, an extended period simulation indicates whether the system has the ability to provide acceptable levels of service over a period of minutes, hours, or days.

Data requirements for extended period simulations are greater than for steady-state runs. In addition to the information required by a steady-state model, you also need to determine load patterns and operational rules for pumps and valves.

The following additional information is required only when performing Extended Period Simulation, and therefore is not enabled when Steady-State Analysis has been specified.

Start Time—Select the clock time at which the simulation begins.
Duration—Specify the total duration of an extended period simulation.
Hydraulic Time Step—Select the length of the calculation time step.
Override Reporting Time Step?—Set to true if you want the Reporting Time Step to differ from the Hydraulic Time Step.
Reporting Time Step—Data will be presented at every reporting time step. The reporting time step should be a multiple of the hydraulic time step.

Note: If you run an Extended Period Simulation, you can generate graphs of the domain elements in the results by right-clicking an element and selecting Graph.

Note: Each of the parameters needed for an extended period analysis has a default value. You will most likely want to change the values to suit your particular analysis.

Occasionally the numerical engine will not converge during an extended period analysis. This is usually due to controls (typically based on tank elevations) or control valves (typically pressure regulating valves) toggling between two operational modes (on/off for pump controls, open/closed for pipe controls, active/closed for valves). When this occurs, try adjusting the hydraulic time step to a smaller value. This will minimize the differences in boundary conditions between time steps, and may allow for convergence.