Simulations

The behaviour of a network under particular conditions is modelled by running simulations. The simulations test the effects of a given flow of water through the network over a period of time and identify weaknesses in the system, such as nodes that are liable to flood under given conditions.

The details of particular simulations are held on the database as runs. When a run is set up, one or more time varying inputs - rainfall events, flow surveys or time series database objects - can be specified for use in calculations. The system creates one simulation for each time varying input therefore each run may contain one or more simulations. In addition, if the run includes any scenarios and/or episode collections (InfoWorks networks only), then simulations will also be created for each scenario and/or each episode for all time varying inputs included in the run.

Types of simulations for InfoWorks networks

For details of hydraulic model equations used in ICM for InfoWorks networks, see the Hydraulic Theory topic.

As well as the basic hydraulic simulation, a number of other types of simulation can be carried out:

• 2D Simulations can be used to carry out more detailed flood analysis of defined areas in the network.
• Runoff Only Simulations carry out the rainfall runoff calculations for the model. Depending on which option you choose for the runoff only simulation, no hydraulic calculations may be performed so the runoff only simulations can be extremely quick. Can be used as an aid to calibration of runoff values.
• Water Quality Simulations are used to simulate the build-up of sediment in the network and the movement of sediment and determinants through the drainage system during a rainfall event.

Types of simulations for SWMM networks

For SWMM simulations, there is a check list which allows you to indicate which processing options are to be included in a simulation. These processes include, for example, rainfall dependent infiltration/inflow (RDII), snowmelt and water quality. In addition, the method for handling surcharge conditions can also be set. See Options for further information.

In addition, 2D Simulations can be used to carry out more detailed flood analysis of defined areas in the SWMM network. A 2D simulation will be automatically performed if the network contains at least one 2D Zone.

Simulation parameters

The simulation parameters govern how the engine performs the model calculations in the hydraulic simulation. The default values have been chosen for optimum accuracy and performance, and therefore do not normally need to be amended. However, the parameters can be edited if necessary.

From the Model menu, select Model parameters | Simulation parameters to display the simulation parameters values in the Object Properties Window for the currently active InfoWorks network.

Note

If monthly RTK hydrographs are to be included in simulations for InfoWorks networks, then ensure that the Use SWMM5 RDII option is checked in the simulation parameters. This option is checked by default for any new network created using InfoWorks ICM version 8.5 onwards.

For SWMM networks, the model parameters also include options which determine how the hydraulic simulation is performed. To change any of these options, select Model parameters | Options from the Model menu to display the model parameter values for the currently active SWMM network.

Simulation diagnostics

Diagnostic checks can be set up as part of a run for InfoWorks networks. Thresholds for various parameters are set. If the simulation engine exceeds these thresholds during a simulation, the icon used for the simulation in the Explorer Window is displayed in a different colour.

If sensible threshold values are exceeded, this could mean that numerical instabilities have occurred in the simulation engine.

Note

Simulation diagnostics are not currently available for SWMM networks.

To set up run diagnostics for a run:

1. Click Diagnostics in the Schedule Hydraulic Run View. The Run Diagnostics dialog is displayed.
2. In the Run Diagnostics dialog, set threshold values for the parameters available. If a threshold of zero is set, the parameters is ignored and no checks are made.
3. Click OK to return to the Schedule Hydraulic Run View.

See Computational Instabilities for further information.

Simulation status

The colour of the simulation icon provides information on the status of the simulation after it has been run:

• Results unavailable. There are no results available either locally or on the server. This may be because the simulation was carried out by a user on a different machine, or because the results have been deleted.
• Results are not available but the local queue contains a job for this simulation that has not yet been completed. Note that it is not possible to tell if there is a job for this simulation queued on another machine.
• the simulation failed. The only results are in the log file and, optionally for InfoWorks network simulations, the prn file, which will detail the reasons for failure.
• the simulation completed successfully and full results are available.

• the simulation completed, but with warnings (for example a user threshold set in the Run Diagnostics was exceeded, or a depth exceeded the section height in a channel or river reach).
• the simulation is incomplete. This could be because the simulation ended due to failure to meet convergence criteria or, if you are using an Autodesk licence, access to it was lost. Simulation results are available up to the point of failure or to when access to an Autodesk licence is lost.

  Note: Convergence problems relate to the 1D engine. The 2D engine does not experience convergence problems as it uses an explicit solver.