Frequency domain analysis of pipe fluid transient behaviour

Pipe transient signals are hyperbolic in nature where key features of the signal repeat periodically and are well suited to the analysis in the frequency domain. For this reason, a number of studies have been conducted on the use of frequency domain approaches for a variety of purposes, from fault detection to the prediction of the unsteady system response. Despite the number of papers on the topic over the past decades, there are no detailed review of the developments in the frequency domain analysis of pipe transient signals. This paper provides an assessment and review of the relevant research and provides a critical discussion of both the strengths and weaknesses of this approach. A method for extracting a system's frequency response function using conventional valve closure signals is proposed and the influence of various faults, friction and pipe wall viscoelasticity on this response function are compared with the corresponding impacts in the time domain. This study shows that most changes on the transient trace in time manifest as changes to the resonant responses in the frequency domain and the resonant responses encapsulate the essence of the system behaviour.