Novel Use of a Bandwidth Measure for Vortex Induced Vibrations

Abstract

An innovative use of a method to detect Vortex Induced Vibration (VFV) bandwidth in the curvature data of subsea flexible risers and umbilicals is presented. The parameter epsilon gives a valuable estimate of the bandwidth of signals such as VIV as a single value which may be used to track the behavior with time and against other measures such as current speed. The method is conveniently based on a peak counting approach originally formulated by Cartwright and Longuet-Higgins. Low epsilon values close to zero indicate a narrow band process whereas values near unity indicate a broad-band process. Comparisons with the alternative kurtosis statistic are also presented. The epsilon measure is shown to have a more useful linear behavior than kurtosis, and appears to be more sensitive and resilient. Curvature data gathered for different periods in 2000 and 2001 by the monitoring system installed on Foinaven Petrojarl IV have been analyzed.