CONTENTS
1.0 INTRODUCTION
2.0 SURGE ANALYSIS
2.1 Assumptions
3.0 SYSTEM MODELLING
3.1 WANDA Deltares System
4.0 TRANSIENT ANALYSIS
A) Engineering / Steady State
B) Transient State
C) Control Module / State
5.0 SURGE SUPPRESSION EQUIPMENT
5.1 Surge Control in Water Distribution System
6.0 CONCLUSION
1.0 INTRODUCTION
Pipeline pressure surges are occurred by a sudden increase in pressure which is produced by a change in velocity of the moving fluid in a pipeline. Usually, during pipeline design, the movement of fluid is based on steady state calculations of the static head and frictional head losses, using the maximum operating pressure plus a small safety factor. However, in any system, the flow must be started and stopped by pump or valve operations and these can generate transient pressures well in excess of the steady state pressures. The hydraulic simulation of pressure and flows in fluids caused by the transient operations of the pumps and valves are required to carryout for the pipeline surge analysis studies.
The pressure surges occur due to the events such as shutting down of a pumping station or pumping unit, unstable controls, oscillation in tank levels, the sudden closure of a valve, or any other sudden blockage of the moving fluid. These pressure surges may occur in all fluid pipeline systems and can result in pipeline fatigue and pipeline failure. The effects of surge may be catastrophic failure of the pipeline system and equipment or fatigue failure of the pipeline supports, instrumentation, equipment and compounds.
Therefore, a thorough understanding of the hydraulic behaviour in a pipeline system is essential to guarantee a low cost, safe and reliable system. However, it will need sort of experiences to get such thorough understanding of this behaviour in the system, especially the dynamic behaviour,because it is often considered a complex task.
As transient conditions can result in many situations, engineers are naturally are more concerned with those that might endanger the safety of a plant and its personnel, have the potential to cause equipment or device damage, or result in operational difficulties. Hence, the severity of transient pressure must be determined by using a system or device that can prevent hydraulic water hammer effect.
2.0 SURGE ANALYSIS
Introducing a developing water hammer software, WANDA, by Deltares , used to assist hydraulic engineers in the hydraulic analysis of pipeline systems. By using software program WANDA, we aim to simplify the complex task of assessing pipeline system throughout the entire life cycle so that user can get a thorough understanding of their pipeline system with just a few clicks.
2.1 ASSUMPTIONS
i. One dimensional flow.
ii. A common pressure at pipeline section.
iii. An average velocity at each pipe section.
iv. The pipe is full and remain full during the transient.
v. The pipe wall and fluid behave linear elastically.
vi. Pipe:
Modulus of elasticity of Steel :200 GPa
Poisson ratio : 0.27
Conduit condition :Thin wall and elastic
Friction factor : C100
vii. Fluid:
Media :Water
Bulk modulus :2.19 GPa
Density :1000 kg/m3
Operating temperature :Ambient
3.0 SYSTEM MODELLING
WANDA consists of 2 calculation modes (Engineering and Transient) and 4 modules (Liquid, Heat, Multi-species transport and Control). The modes are integrated in the core of WANDA, together with the system control functionality. The modules are connected to the core upon request of the user when the software is purchased. Each mode contains a component library specific for that domain. The user can then access the modes and modules through the user interface.
Figure 1: The architecture of WANDA 4
3.1 WANDA Deltares System
WANDA is a powerful and user-friendly program for the hydraulic design and optimization of pipeline system. Both engineers and operators use WANDA to study the steady state and dynamic behavior of liquid, heat, gas and slurry flows in arbitrarily configured pipeline networks.
The software can be easily linked to other applications, for example operator training systems or advanced real-time control. WANDA has been extensively tested, validated and designed for engineers by engineers.It can be used throughout the lifetime of the pipeline system; from initial design, component optimization, control procedure evaluation up to commissioning and operator training. In fact, detailed information of the flow can be viewed at any location in the system at any moment in time.
Special features:
• Intuitive look and feel based on iGrafx Flowcharter®
• Copy/paste of components, diagrams, graphs, tabular results and input parameters
• Different layers for text and background
• connector-tool to separate details or subsystems from the main model
• input and output properties in spreadsheet view
• Comparison of complete cases with case-compare
• Animation function to analyse wave propagation and reflection
• Several unit systems (standard SI, US, UK, user defined) are supported
4.0 TRANSIENT ANALYSIS
A) Engineering /Steady State
The Engineering mode is used for steady state analysis of the pipeline system. This mode allows user to perform common activities in the hydraulic design of the pipeline system, such as pipe sizing and capacity analysis. In this mode, the performance of the pipeline system can be quickly analyzed and optimized through continuous parameter changes and reruns.
This mode assists you with:
• Head loss calculations
• Pipe, pump & valve sizing
• Flow capacity analysis
• Hydraulic gradient & pressure analysis
• Pump & System characteristic plotting
• Optimization of multi-pump operation
• Impact analysis of system changes
Figure 2: Hydraulic Design for a Pipeline System
B) Transient Mode
The Transient mode is used for unsteady (transient) analysis of the pipeline system. This mode allows user to analyse incidents such as pump trips and valve closures, and the consequential reaction of surge towers, relief valves and control systems. In this mode, the pipeline system can be designed to withstand these incidents and ensure a safe & reliable operation.
|
Incidents |
Protection |
Phenomenon |
• Valve closure/opening
• Pump trip or start-ups |
• Surge towers
• Air vessels
• Pressure relief valves
• Air vents
• Control systems |
• Pressure & discharge change
• Pressure wave propagation
• Water hammer
• Wave reflection
• Line packing
• Cavitation |
Figure 3: Analysis of pressure wave propagation through a pipeline
C) Control Module/ State
The Control module allows user to link a control system to a hydraulic system. This enables us to evaluate the effectiveness of different control philosophies on the hydraulic system and to optimize the control properties. The Control module can be combined with the Liquid, Heat and MST module.
l Liquid Module
User can model and analyse a pipeline system for liquid transport. This module contains a wide variety of hydraulic components, including special components such as, surge protection equipment and free surface flow pipes. With this module, user can also access the special system characteristic plotting and pump operation optimization features to improve the performance of their pumping station.
l Heat Module
User can model and analyse a pipeline system for heat transport via liquid flow. This module allows us to model district heating networks and process industry piping, for which temperature and heat loss play an important role in the design of a pipeline system.
l MST Module
With the Multi-Species Transport (MST) module, user can model and analyse transport of separate batches of fluids through a pipeline system. This module can be used in mining and dredging industry, where multiple fluids are transported in batches.
5.0 SURGE PROTECTION EQUIPMENT
As emphasized in the previous section, a number of techniques can be used for controlling transients in water distribution systems. Some strategies involve design and operational considerations alone, and some also use the addition of dedicated surge protection devices. The general principles of surge control devices are to store water or otherwise delay the change in flow rate, or to discharge water from line.
Devices such as pressure-relief valves, surge anticipation valves, surge vessels, surge tanks, pump-bypass lines, or any combination of these, are commonly used to control maximum pressures. Minimum pressures can be controlled by increasing pump inertia or by adding surge vessels, surge tanks, air-release/vacuum valves, pump-bypass lines, or any combination of that group. The overriding objective is to reduce the rate at which flow changes occur.
Specific devices are usually installed at or near the point in which the disturbance is initiated, such as at the pump discharge or by the closing valve ( with the exception of air-relief/ vacuum breaking valves and feed tanks. Figure 4 illustrates typical locations for the various surge protection devices in a water distribution system.
Figure 4: Typical Locations for Various Surge Protection Device
5.1 Surge Control in Water Distribution System
Any surge protection devices and/or operating strategies must be chosen accordingly. The final choice will be based on the initial cause and location of transient disturbances, the system it self, the consequences if remedial action is not taken, and the cost of protection measures. A combination of devices may prove to be the most effective and the most economical.
The strategies by which surge control is achieved may be classified as either direct action, or diversionary tactics. Direct actions strategies attempt to influence the behaviour of the primary causes of the flow changes, such as valve or pump operations. Diversionary tactics attempt to control the transient once it has been created,by which fluid is drawn into or expelled from the piping system.
6.0 CONCLUSION
Hydraulic transient, also called pressure surge or water hammer is the means by which a change in a steady state flow and pressure is achieved. When condition in water distribution network are changes, such as by closing a pump or a valve or starting a pump, a series of pressure waves are generated.
Problems such as selecting the pipe layout and profile, locating control elements within the system, formulating operating rule, as well as the ongoing the challenges of system management are all influenced by the details of the control system. A detailed transient analysis will offers a comprehensive guide to the selection of surge control and suppression in water distribution system.
Using a surge analysis computer model, such as WANDA software by Deltares System, will greatly enhanced engineers ability to better understand and estimate the effects of hydraulic transient, to conceive and evaluate efficient and reliable water supply management as it can be applied in a vast number of industries. WANDA is definitely a favourite program for surge analysis.
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