Introduction to Pressure Related Demand in InfoWorks WS Pro

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In the InfoWorks WS Pro simulation engine, the flow through pipes is driven by a fixed pre-determined demand.

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This is because, by default, WS Pro calculates demand without reference to the actual pressure at a demand node.

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In most cases, you can consider this to be a reasonable assumption,

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but, sometimes this does not reflect reality,

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as local service pressures have an influence on how customers use water

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and the losses associated with the network.

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For example, if a user consumes a fixed volume of water, such as a load of washing or a dishwasher cycle,

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then it is easier to reflect that situation in the model.

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However, if the user consumes water based on a task, such as a shower, that task may take a variable amount of time.

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In that case, the pressure in the system would have an influence on the volume removed,

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such that the greater the pressure, the greater the removed volume.

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The pressure related demand option is recommended for use in simulations where the hydraulic conditions

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will make a significant difference to the heads observed in the network, as compared with the calibration model.

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This is likely to include any kind of incident or design scenario modelling

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that affects a demand-driven area.

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A model calibrated against measured demands indirectly takes into account the effects of pressures in the network.

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When simulation conditions are similar to calibration conditions,

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the use of the model without using the Pressure Related Demand option is still valid.

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Experiment carefully with this option since it is dependent on accurate ground levels and working pressures.

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Bear in mind that with the Pressure Related Demand option activated,

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total demand depends on the results of the simulation and cannot be predicted accurately.

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InfoWorks WS Pro has eight built-in pressure-related demand curves.

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To make use of the pressure related demand functionality to estimate the hydraulic conditions during an incident,

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open the PRD Network and Control, by double-clicking on the PRD Network.

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Then, from the Windows toolbar, click Grid Windows > New Nodes Window.

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In the Nodes grid view, click the PRD Curve tab to review the PRD curves.

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To open the properties of one of these curves, right-click it and select Properties.

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Be aware that you can overlay another curve for comparison.

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Also, you can create custom curves.

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Close the Grid Window.

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Before running a pressure related demand simulation, the nominal pressures must be updated.

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The nominal pressure can be described as the average baseline pressure for the period of a simulation.

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This can be done manually by entering a value for nominal pressure at each node,

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or by updating nominal pressures in the Network from a base simulation.

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In this example, you will update the nominal pressures from a simulation.

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To update the nominal pressure, first ensure the PRD Network is open in the GeoPlan.

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Expand the Network menu and select Update nominal pressures… from the flyout.

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In the Database item selection dialog, choose the BridgeTown Base BridgeCon simulation results

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from which the Nominal Pressure data field is to be populated.

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If the simulation icon on the left side of the BridgeTown Base > BridgeCon simulation is grey,

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then right-click the BridgeTown Base simulation and from the flyout select Re-run.

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Then, Commit the changes to the PRD Network.

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To begin running a PRD simulation, open the BridgeTown PRD demand diagram by double-clicking it.

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In the Demand Diagram dialog box, to set the demand in DMA 0404 to be 100% pressure related,

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expand the Demand Category drop-down and select DOM-0404.

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Check the Leakage checkbox to enable leakage in the demand profile.

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Then, set the Pressure-related (%) to 100.

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Click Save.

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Next, you need to set up the Pressure Related Demand simulation.

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From the Model Group, right-click Run Group, and select New.

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In the Schedule Hydraulic Run dialog, name the run “BridgeTown - Incident with PRD”.

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Click Experimental to enable it.

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Then, drag and drop the PRD Network into the Network panel.

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The Control and Demand Diagram group box populate as well.

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In the demand diagram box, remove the demand diagram by clicking on the “X”

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and replace it with the BridgeTown PRD demand diagram.

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In the scenario tab, deselect the Base scenario and select the incident scenario.

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In the Run Type group box, leave the Run Type as Normal,

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but check the Pressure Related Demand option.

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The Pressure Related Demand Options dialog appears.

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In the Pressure Related Consumption Curves group box, expand the Demand Curve drop-down and select Default Demand.

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Then, expand the Leakage Curve drop-down and select Power Law.

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In the Nominal Pressures from Pressure Profile group box,

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drag and drop the PRD Control from the Baseline simulation into the Sim panel.

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In the Options group box, deselect the Increase Pressure Related Demand on increased pressure option

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and set the Pressure Related Demand to 100 percent.

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Click OK.

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Save and then run the simulation.

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Once the simulation is complete, open the BridgeTown- Incident with PRD simulation into the Workspace.

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Then, right-click on BridgeTown without PRD simulation and select Open As… > Alternative Results for Comparison.

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Using the graphing tool, select objects in the east of the model

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to observe how the results differ when utilizing the PRD functionality.