Modelling exceptional demand

You can represent exceptional demands at a  node, such as those from bursts or firefighting for example, by setting a time-varying Exceptional Flow profile for the node using a series of date-time / flow value pairs. Exceptional demand can be applied to basic nodes, reservoir nodes and hydrant nodes.

To model exceptional demand:

1. Open the property sheet for the appropriate node and choose the Exceptional Flow Profile page. If the Exceptional Flow Profile page is not visible, click the Add Control button to add control parameters for the node.
2. Enter the time varying profile for the exceptional demand using the Exceptional Flow grid. Enter a series of dates and times in the Date Time column, and for each time set the demand flow value in the Flow column.
3. Check the Linear Profile box for linear interpolation to be used between data points. If this box is unchecked each exceptional flow entered is maintained until the next date / time entry, or until the end of the simulation.
4. Select an option for extending the profile before the first time defined in the grid:
• Extend Back - The first value in the grid is extended back to the start of the simulation
• Extrapolate Back - Applies to Linear Profiles only: the first two values in the grid are used to extrapolate back to the start of the simulation.


Please Note

(If Extrapolate Back is selected for a non linear profile, the profile will be extended back.)

• Zero/Unchanged - A value of zero or "off" is applied from the start of the simulation until the date / time of the first value in the grid
5. Select an option for extending the profile after the last time defined in the grid:
• Extend Forward - The last value in the grid is extended to the end of the simulation
• Extrapolate Forward - Applies to Linear Profiles only: the last two values in the grid are used to extrapolate forward to the end of the simulation.


Please Note

(If Extrapolate Forward is selected for a non linear profile, the profile will be extended forward.)

6. Check the Repeat Profiles box to repeat the first 24 hours of the defined profile for the duration of the simulation

5. Decide whether local demand is to be applied to the node during simulation by setting the Keep Local Demand check box on the Node Control Page. The two options are:
• checked - any demand assigned to the node on the Node Demand Page (eg customer point demand), will be applied in addition to the Exceptional Demand
• unchecked - demand that will be applied to the node will be the Exceptional Demand defined on the Exceptional Flow Profile Page and demand due to hydrant operation defined on the Hydrant Flow Profile Page. (If exceptional demand is zero and hydrant is closed, local demand will be applied).