Computer analysis of transient effect on pipe system - using method of characteristics

Abstract

Transient or unsteady phenomenon in a flow system may occur as a result of closing or opening of valves, stoppage of pumps, etc. This phenomenon has to be taken into consideration during design stage. At present, the use of digital computer is so widely used for two basic reasons, achieving more accuracy and saving time. In this dissertation, the transient effects are analysed using the Method of Characteristics. Besides being able to visualise the actual physical conditions of the flow, the method also caters for all boundary conditions existing in the system. A computer program that is capable of predicting any transient phenomenon in the piping system is produced. A few case studies are identified for analysis, ie, single pipe, series pipe and simple pipe network. The scope of the investigation is limited to transients as a result of valve closure at the downstream end. Two flow parameters, ie, discharge, Q and piezometric head, H are considered. In addition, two types of closure are investigated, namely, rapid and slow closure. In general, results indicate that the transient phenomenon has performed effect around the source (valve). As the distance of propagation increases upstream, this effect slowly deminishes and is finally dissipated. Rapid closure achieves peak pressure time at or before 2L/a, whereas for slow closure, some resonance pressure arises that result in a damping at the end of the time interval.