![pipesim water hammer pipesim water hammer](http://www.fluidmechanics.co.uk/wp-content/uploads/2015/08/Figure_5_second_wave_reflection.jpg)
Then an event or events occurs which cause a flow transient. Usually in a surge analysis you start at some predefined steady state condition. Then by stepping forward in small time increments it is possible to predict what happens over an extended period throughout the whole system. These days surge problems are often solved using computer programs which split the pipeline or network into a number of small sections and then analyse what happens in each section over a small increment of time. Predicting how the surge waves progress over time can become very complex. Methods used for Surge Analysis.īecause of the various phenomena that can occur in a pipeline or pipe network following a transient flow event.
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These air bubbles reduce the bulk modulus of the fluid which then reduces the sonic speed. Also any gas that is released in a negative pressure transient is not instantaneously re-absorbed into the fluid, but can remain as very small air bubbles dispersed in the fluid. Surge can induce sub atmospheric or negative pressure transients which cause cavitation and out gassing of air from the fluid which complicates the situation further because when the negative pressure transient has passed, a cavitation collapse occurs which induces additional surge waves. These surge wave reflections can induce very complex surge flows and pressures in the pipeline. Surge waves are reflected and modified where there are changes in the pipe such as at the ends, changes in pipe diameter, branch connections, valves and other connected equipment such as accumulators which may have been added to control the surge. The movement of these pressure and velocity waves along a pipeline can lead to very high and low pressure transients which is why it is called surge. Alongside this velocity wave there is also a pressure wave which forces the fluid velocity (momentum) to change. A velocity change propagates along the pipeline as a wave at the sonic speed. This compressibility means it takes a finite amount of time for a velocity change in one part of the pipe to propagate along it.
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In a pipeline this external force is provided by a change in pressure or a pressure transient.įor steady state flow calculations it is usual to assume the fluid is incompressible however for unsteady flow this assumption is not so valid, particularly if the change in fluid velocity is very rapid. In accordance with Newton’s second law if there is a change in fluid momentum the fluid must be subject to an external force. When the velocity of a fluid in a pipe changes, such as when a pumps stops or starts there is a change in the fluid momentum. We can help our clients find safe and cost effective solutions to any surge issues they may have. From preliminary review and concept design to finial design and safety case studies. We have many years’ experience of doing pipeline surge analysis for clients in the water, wastewater, fuel systems, oil and gas and renewable sectors. Surge analysis is one of our core competences.