Chaos in VIV

In this study the existence of chaotic oscillations in signals from vortex induced vibrations is investigated using some experimental data of flexible risers. VIV is traditionally known as a periodic phenomenon for which the oscillations are mainly at a fundamental frequency of oscillations. As observed recently, in many VIV signals, there is a second peak at three times the fundamental frequency, which represents the existence of a third harmonic oscillation. This view is based on analyzing a statistically stationary region of experimental VIV signals. The original non-filtered signals, however, do not show a statistically stationary behavior in the entire period of oscillations. Practically, the major part of the signal illustrates non-stationary behavior. Here, we do not limit our analysis to the statistically stationary regions; instead, we use the entire experimental signal. The time histories, PSD and phase plane plots, and Poincar\'{e} maps of analyzed signals show cases where the signal is (i) mainly periodic/quasiperiodic or (ii) periodic/quasiperiodic with bursts of chaos or (iii) entirely chaotic.