About simulations

In most cases, you will select Normal as the run type when scheduling the run. However, several types of special run are available:

• Calibration runs allow you to automatically adjust roughness values in the network to match predicted and actual flows as closely as possible at a specific important timestep, such as the time of peak demand. For more details, see the Calibration Simulations section.
• Water Quality runs allow you to model the concentration of a single pollutant or other substance over time at any point in the network. See Water Quality Simulations for more details.
• WatSed runs simulate sedimentation transport within a water supply network. See WatSed Pipe Sedimentation Model for more details.
• Fire Flow runs. There are three types of fire flow run:
• Fire Flow Availability runs allow you to check the availability of a specified fire flow and view the effects on head at the node of trying to maintain that flow, or to see the effect on available fire flow of maintaining a minimum head at the node. See Fire Flow Availability for more information.
• Hydrant Testing runs allow automated testing of a selection of nodes in turn against user defined constraints such as minimum allowable network pressure. See Fire Flow - Hydrant Testing for more details.
• Forced Fire Flow runs allow automated testing of a selection of flows at a single fire flow target point. Each flow is tested in turn against user defined constraints such as minimum allowable network pressure. See Forced Fire Flow Simulations for more details.
• Flushing runs allow modelling of the effects of a sequence of actions carried out on the network for the purpose of cleaning the network by flushing the pipes with water. See Flushing Simulations for more details.
• Critical Link Analysis runs allow automated testing and reporting of the effects of failure of a selection of links. Each link in the selection is tested in turn against user defined analysis criteria. See Critical Link Analysis for more details.
• Shutdown runs allow assessment of the impact of watermain breaks and shutdowns on the system without the need to make changes to the Network or Control Data. See Shutdown Simulations for more details.
• Leakage Locator runs can be used to help identify the location of a suspected leak. See Leakage Locator Simulations for more details.
• InfoWorks TS runs allow analysis of pressures and flows during transient operation at selected locations in the network. Transients due to changes in pump station operation, valve operation or change in node demand can be modelled. These simulations can also be used to assess the effects of surge protection devices on the system. See InfoWorks TS (Transient System) Simulations for more details.
• BalanceNet runs allow automated optimisation of a selection of pumping stations. Pump schedules are optimised to minimise electricity costs whilst maintaining reservoir volume and meter and pipe flow constraints. See BalanceNet Simulations for more details.

Transients advisor

In addition to the run types listed above, further results can be calculated which will indicate potential locations of large transient pressures.

To produce these additional transient advisor results as part of the run, select the Advise on Hydraulic Transients option from the Simulation Options dialog.

See the Transients Advisor topic for further details.

Price of water

Calculations on the cost of water can be included in a run. Simply add data for the cost of water to the pipe control properties (on the Pipe Control Page). This option is available with any run type. See Price of Water for more information.

Pressure related demand

InfoWorks WS Pro normally calculates demand without reference to the actual pressure at a node. A pressure related demand run allows demand to vary with changing pressure at nodes. See Pressure Related Demand for more details. This option should be used with care.

Disconnected system

It is possible to carry out a run using disconnected networks - a model that contains more than one network segment that are not linked - as long as all the segments contain a means of calculating head. This means that each segment must contain a reservoir or fixed head node. See Modelling a Disconnected System.

Network subset run

It is possible to carry out a run for a selected subset of the network only, by including a selection list when scheduling the run. Only objects in the selection list will be included in the simulation. See Modelling a Subset of the Network.

Cost management

Optimisation of pumping stations can be carried out for a Normal run type. An optimisation run can be used to determine optimal pumping schedules to reduce electricity costs for a selection of pumping stations. See Cost Management Simulations for further details.

Sustainability

Calculations to express energy losses in the network and energy used at pumping stations as a CO2 equivalent, can be included in a run. This option is available with any run type. See Sustainability Analysis for more information.

Generalised multi run

A generalised multi run lets you set up a simulation that runs multiple test cases. See Generalised Multi Run Options dialog and Generalised Multi Run Configuration dialog.

Initial state

The state of a network at times during a simulation can be saved for use as the initial state of a subsequent simulation.

To save the state of a simulation, check the Save state of this simulation option on the Simulation State dialog.

To use the saved state of a previous simulation to provide initial conditions for the current simulation, select an initial state simulation and saved state time in the Schedule Hydraulic Run view.

InfoWorks WS Pro simulates the behaviour of a water supply system by solving several consecutive steady states (timesteps) taking into account all the changes of boundary conditions over time, for example variations of water consumption and water levels in reservoirs and water towers, the on/off state of pumps, valve operation, changes in demands.

Validity checks

The next operation is to check that the model data makes sense. The InfoWorks WS Pro engine checks the data before any computation takes place. Errors may still exist in the model data that have not been trapped by the validation procedures. These procedures do not cover live data, or the relationship between the different types of data that comprise the run.

See Runtime Messages for further information on warning and error messages that might be displayed during runtime validation checks.

Initial state

After carrying out checks on the validity of the data, InfoWorks WS Pro defines the initial state of the system.

If an initial state simulation has been selected in the Schedule Hydraulic Run view, the initial state of the system will be set from the selected simulation.

If an initial state simulation has not been selected, the initial state of the system will be set from the control data. Any controls for which control data has not been defined will be given defaults:

• reservoirs are treated as empty, with water level at bottom elevation
• pumping stations are not active. All pumps are off
• control valves are closed

InfoWorks WS Pro displays these settings in the output window and in the log results. Simulation starts with computation of demand for the start date and time.

Solution of a steady-state

InfoWorks WS Prosolves each steady state in the water supply system by applying the improved node-oriented method, perfected and streamlined through long experience.

Each link has an equation relating flow to headloss. The node-oriented method is an iterative scheme that tries to solve these equations for flows into and out of each node, with a flow balance within the tolerance set in the Computational Accuracy field in the Schedule Hydraulic Run view. It is recommended that the tolerance be set to approximately 1% of the average model inflow.

During the process, InfoWorks WS Pro displays output messages . These are also listed in the log results for the simulation. These messages will describe:

• changes in the state of controls in the system
• current run status
• progress of the auto-calibration process in calibration runs

Errors in computation

It is possible that the engine may fail to converge on a solution. InfoWorks WS Pro stops computation after the maximum number of iterations set in the Schedule Hydraulic Run view. The default value is 99 iterations. If a solution is not reached, InfoWorks WS Pro displays a warning and by default proceeds with the run (the option to stop the run after a failed snapshot can be set in the Simulation Options dialog). This warning is also listed in the log results for the simulation.

The integration scheme

InfoWorks WS Pro assumes that the system remains in a steady state throughout the timestep. At the end of each timestep InfoWorks WS Pro does the following:

• computes changes of water level in all reservoirs and water towers
• computes the water demand for this instant
• checks whether the status of any pumps or the opening of any control valves should be changed according to their time schedule or because of changes within the system
• saves results

InfoWorks WS Pro keeps the timestep constant throughout a simulation. The user can decrease the timestep to reduce any inaccuracies that may arise. The advantage of a fixed timestep when dealing with large and complex systems is that it keeps the simulation within reasonable computation time and size limits.

You can carry out simulations using checked out networks if you want to test out modelling scenarios before committing network changes to the master database.