Hydraulic Transient in a Pipeline (Using Computer Model to Calculate and Simulate Transient)

University essay from Lunds universitet/Avdelningen för Teknisk vattenresurslära

Abstract: A hydraulic transient, which is a flow condition where the velocity and pressure change rapidly with time, can collapse a water distribution system if that system is not equipped with adequate transient protection device(s). The occurrence of transients can introduce large pressure forces and rapid fluid accelerations into a water distribution system and if the system is not well protected, it can fail. A hydraulic transient normally occurs when a flow control component changes status (for example, a valve closing or pump stop), and this change flows through the system as a pressure wave. A valve can be closed in two ways; linear or stepwise (fast initial closure and slow subsequent closure). Pump stop could be due to planned stop, power failure or mechanical problem with the pump. There are many transient analysis methods, but this thesis work employed only the graphical method and the method of characteristics to construct models (using the FORTRAN language) to calculate and simulate transients in a pipeline. Many scenarios and different valve closure operations were applied to the models (with a pump and without a pump in the pipeline) to study the transients. The pump model was also used to simulate real cases. The model solutions were compared with the graphical solutions for the two transient flows. It was found that the stepwise valve closure can reduce transients significantly than the linear valve closure operation. A pump with a high inertia can also reduce transients significantly, and this inertia can be achieved by using the softstop program. The water velocity and the frictional coefficient were seen to be important factors which affect the hydraulic transient, even though both relate to each other. A high frictional coefficient reduces the velocity and as a results reduces the transients, and vice versa. Also low frictional coefficients lead to increase in water velocities and as a result increase in hydraulic transients, and vice versa. The graphical solution was found to agree well with the computer solution.

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