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.
Acknowledgement: The InfoWorks TS module utilises the KYPipe Surge engine copyright © Dr. Don J. Wood, Dr. Srini Lingireddy, Lexington, KY. USA. All rights reserved. See the KYPipe Web Page for further information.
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:
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.
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.
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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 |
PID control setup for control valves requires specialist knowledge and information about the valve in question ( Ku, "critical gain" and Tu "oscillation period at stability limit "). The two cited papers give more information:
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:
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.
When defining a network for transient simulation, the following points are recommended:
The Transient System run may contain up to three simulations:
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.
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 |
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InfoWorks TS not licensed | InfoWorks Transient System (TS) functionality is available only if the InfoWorks TS option is enabled on your licence. Contact Autodesk for information about adding this option to your existing licence. |
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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 Autodesk for further information on licensing options. |
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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 Autodesk for further information on licensing options. |
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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. |
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celerity not specified | Wave celerity has not been specified at one or more links |
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PST/valve: nodes have demand |
The upstream or downstream node of a pumping station or valve has demand assigned to it |
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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. |
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>1 pump in pump station | One or more pumping stations in the network has more than one pump associated with it |
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pumps in flow mode | One or more pumping stations in the network has its Mode of control set to Flow. |
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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. |
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open hydrant | One or more hydrant nodes in the network is open |
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demand at SPD | One or more nodes at which a surge protection device is defined also has demand assigned to it |
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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 |
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node exceeds 10 links | One or more nodes in the network has more than 10 connecting links |
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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 |
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no SPDS | None of the nodes in the network have a surge protection device defined |
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no transient demands | None of the nodes in the network have transient demand defined |
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no active valves | None of the valves in the network have transient modelling enabled |
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no PST transients | None of the pumping stations in the network have transient modelling enabled |
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control missing for nodes | One or more nodes in the network does not have Control data associated with it |
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control missing for valves | One or more valves in the network does not have Control data associated with it |
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control missing for pumps | One or more pumps in the network does not have Control data associated with it |
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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. |
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