InfoWorks TS (transient system) simulations

Hydraulic transients (also known as water hammer or surge) are pressure fluctuations caused by a change in fluid velocity. This may be caused by starting and stopping of pumps, or opening and closing of valves for example. See the Transients advisor topic for further details.

InfoWorks TS simulations are used to analyse pressures and flows during transient operation modelled at selected locations in the network.

Transients due to change in pump station operation, valve operation or sudden change in demand at a node can be modelled. These simulations can also be used to assess the effects of surge protection devices on the system.

Transient modelling data fields

Transient modelling data is stored in the control data. When control data is added to a network object, additional transient tabs are displayed on the property sheets of the following objects:

• Nodes - a demand profile to be applied during transient simulation can be defined on the Transient - Additional Demand tab of the Node property sheet. The Transient - Surge Protection Device tab contains the parameters for modelling devices such as surge tanks and pressure relief valves.
• Pumping stations
  • a speed profile to be applied during transient simulation can be defined on the Transient tab of the Pump Station property sheet. Operation of the pumping station due to loss of power can also be modelled. Built-in four quadrant curves are available for modelling of normal and abnormal pump operation.
  • PID controller parameters can be applied as an alternative to the speed profile on the Transient tab of the Pump Station property sheet (see below).
  • transient simulation parameters for a pump station modelled as a turbine can be defined on the Transient - Turbine tab of the Pump Station property sheet. A speed profile to be applied during transient simulation can be defined. Operation of the turbine due to loss of power can also be modelled.
• Valves
  • an opening / closing profile to be applied during transient simulation can be defined on the Transient tab of the Valve property sheet.
  • flow/pressure regulating valve parameters can be applied as an alternative to the opening / closing profile on the Transient tab of the Valve property sheet. PID controller parameters may also be specified (see below).
• Reservoirs, fixed heads and wells - a pressure profile to be applied during transient simulation can be defined on the Transient - Pressure Page tab of the object property sheet.

In addition, the specification of wave celerity values is required for all links in the network.

Objects at which transient parameters have been set can be identified on the GeoPlan by a symbol next to the object.

PID control

When modelling pump stations or valves as PID controllers, the velocity form of the PID equation is used to calculate the change in regulator position from one sample time to the next.

Control input at time (t) is calculated as: where: Kc = controller (proportional) gain Ti = integral time Td = differential time Ts = sample time (specified in InfoWorks TS Options dialog) e(t) = error signal from control object

Pressure related demand and intrusion modelling

Pressure related demand and intrusion calculation parameters can be defined in the InfoWorks TS Options dialog when scheduling a transient run.

Turn pressure related demand on to allow demands to respond to pressure changes in the system; otherwise demand will remain constant during the transient simulation.

With pressure related demand turned on, intrusion calculation parameters may also be specified. The intrusion of contaminated groundwater via leaky joints or cracks in pipes can potentially be caused by extremely low or negative pressures in the network. InfoWorks TS provides two methods for estimating intrusion volume:

• Demand fraction method: calculate intrusion volume by calculating a leakage constant from a specified fraction of outgoing demand
• Leakage flow method: calculate intrusion volume using specified leakage rate for a reference pipe at 50 m pressure

The estimated intrusion volume is displayed in the Node Results Grid view.

See the InfoWorks TS Options dialog and Node Results Data Fields topics for further information.

Modelling tips

When defining a network for transient simulation, the following points are recommended:

• Keep pump and valve links short
• Avoid pipes of large diameter near surge protection devices
• Wave celerity values can be determined from curves provided by Thorley ARD, 1991 which plot wave celerity against diameter/wall thickness ratio for several pipe materials. See the Transients advisor topic for further information.

Setting up an InfoWorks TS simulation:

1. Set up the simulation as normal as described in Creating and scheduling a run.
2. Set the Run Type option to InfoWorks TS. The InfoWorks TS Options dialog is displayed automatically when this option is first selected. The dialog can also be opened later using the Options button when InfoWorks TS is the run type.
3. Set criteria on the InfoWorks TS Options dialog.
4. Run the simulation as normal.

InfoWorks TS simulation results

The Transient System run may contain up to three simulations:

• A base hydraulic simulation will be carried out up until the start of the transient simulation.
• A second hydraulic snapshot (transient hydraulic timestep) will be run at the time of the start of the transient simulation in order to identify any serious non-convergence caused by switching to the transient hydraulic conditions. If such problems occur during this run, the Transient simulation will be aborted.
• The Transient simulation is run for the specified duration at time intervals of a few milliseconds.

It is possible to just run the hydraulic simulations by checking the Only perform hydraulic simulation option on the InfoWorks TS Options dialog.

Transient simulation results are available for valves and pumping station objects with surge modelling enabled, and for nodes with surge protection device modelling enabled. The results can be viewed in the same way as the results for a hydraulic simulation.

A Surge Animate .PRO file can be saved from a transient simulation long section and opened in the Surge Animate module.

See the Results Data Fields section for further details on transient results.

Validation

There are certain modelling restrictions that apply to network objects during a transient simulation that do not apply during a normal hydraulic simulation.

Validation of the network and control to check that these restrictions are met is carried out during run scheduling in the Schedule Hydraulic Run view. Error and warning messages are displayed in the Parameter Setup Messages section of the view.

There may be a large number of objects with the same validation message; for each message InfoWorks WS Prowill report the number of objects the message applies to and the IDs of the first ten of these objects.

The table below lists the transient simulation validation messages that may be displayed.

indicates an error - the simulation will not run until the cause of the error has been fixed

indicates a warning - for information; the simulation will run, but action may be required

Validation Message	Cause	Severity
InfoWorks TS not licensed	InfoWorks Transient System (TS) functionality is available only if the InfoWorks TS option is enabled on your licence. Contact Innovyze for information about adding this option to your existing licence.
InfoWorks TS node count = <no. of nodes>; licence allows <no. of nodes allowed>	The number of nodes in the network exceeds the number of nodes allowed according to the options enabled on your licence. Contact Innovyze for further information on licensing options.
InfoWorks TS link count = <no. of links>; licence allows <no. of links allowed>	The number of links in the network exceeds the number of links allowed according to the options enabled on your licence. Contact Innovyze for further information on licensing options.
test time is outside hydraulic start / end times	The Transient simulation start time specified on the InfoWorks TS Options dialog is before the Start or after the End time specified in the Run Parameters section of the Schedule Hydraulic Run View.
celerity not specified	Wave celerity has not been specified at one or more links
PST/valve: nodes have demand	The upstream or downstream node of a pumping station or valve has demand assigned to it
PST/Valves: nodes have multiple links	A pumping station or valve with transient modelling enabled has more than one upstream or downstream link. Objects at which transient modelling is enabled should have only a single upstream and downstream link.
>1 pump in pump station	One or more pumping stations in the network has more than one pump associated with it
pumps in flow mode	One or more pumping stations in the network has its Mode of control set to Flow.
pump curve unspecified or missing	The pump curve ID for a pump in a pump station does not exist or a pump curve ID has not been specified.
open hydrant	One or more hydrant nodes in the network is open
demand at SPD	One or more nodes at which a surge protection device is defined also has demand assigned to it
SPD must only have 2 open pipes	One or more nodes at which a surge protection device is defined has more then two open connecting links
node exceeds 10 links	One or more nodes in the network has more than 10 connecting links
inflow transfer + PRD option	Flow control has been applied to a transfer node and the Pressure related demand option on the InfoWorks TS Options dialog has been checked
no SPDS	None of the nodes in the network have a surge protection device defined
no transient demands	None of the nodes in the network have transient demand defined
no active valves	None of the valves in the network have transient modelling enabled
no PST transients	None of the pumping stations in the network have transient modelling enabled
control missing for nodes	One or more nodes in the network does not have Control data associated with it
control missing for valves	One or more valves in the network does not have Control data associated with it
control missing for pumps	One or more pumps in the network does not have Control data associated with it
plot min pressure >= plot max pressure	The value specified in the Plot minimum pressure field of the InfoWorks TS Options dialog is greater than the value specified in the Plot maximum pressure field. This will cause irregularities in the plotting of the progress graph during the transient simulation.