Demand calculation with Continuous vs Stepwise patterns

Applies To
Product(s): WaterCAD, WaterGEMS
Version(s): 08.11.XX.XX, 10.XX.XX.XX
Area: Output and Reporting
Original Author: Mark Pachlhofer, Bentley Technical Support Group

 

Problem Description

What is the difference between a continuous pattern vs. a stepwise pattern?

Why doesn't the demand at a particular timestep in an EPS appear to be calculated based on the multiplier on its pattern?

Solution

Stepwise—The multiplier values are considered to be the average value for the interval between the specified time and the next time. Patterns using this format will have a staircase appearance. Multipliers are set at the specified time and held constant until the next point in the pattern.

Continuous—The multipliers are considered to be the instantaneous values at a particular time. Patterns using this format will have a curvilinear appearance. Multipliers are set at the specified time, and are linearly increased or decreased to the next point in the pattern.

With a continuous pattern the calculated demand at a particular timestep is equal to the average of the calculated demand for that timestep and the next one (for a "smoothing" effect). For example, assume the base demand on a given junction is 500gpm, the hydraulic time timestep in the calculation options is set to 1 hour, the pattern multiplier for timestep 8 is 1.0 and for time step 9 is 1.945, and the Start Time field would be 8 am (assuming the simulation was started at 12 am). The total calculated demand at the junction shown for timestep 8 will be (500 * 1) + (500 * 1.945) / 2 = 736.25.

For the continuous pattern, if you want to achieve a demand that is very close to the one specified in the pattern you can try a smaller Hydraulic Time Step.

See Also

EPS Snapshot calculations for demands with patterns

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