When using the theory of Time Sharing of frequencies for predicting damage and fatigue from Vortex-Induced Vibrations (VIV), the percent of time that a riser is vibrating with high amplitude VIV will significantly influence the fatigue rate of a riser. To accurately predict the fatigue of a riser using time sharing or another stochastic prediction method an accurate model is needed for the percent of time spent at these high amplitude vibrations.

Using multiple laboratory tests with both sheared and uniform flow, the percent of time that each section of a pipe vibrated at high amplitude was determined. The larger issue was determining the factors that control the percentage of time at high amplitude vibration. Energy in the system was determined to be the largest influence on the percentage of time. At both low levels and high levels of energy the system had a low percentage of high amplitude VIV. A middle set of energy is the condition that produced high amplitude VIV for the largest percentage of time.

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