On fatigue damage of long flexible cylinders due to the higher harmonic force components and chaotic vortex-induced vibrations

Recent experimental data have revealed that vortex-induced vibrations of long flexible cylinders are characterized by time intervals of chaotic response, followed or preceded by periods of statistically stationary response. A chaotic response is characterized by a broad-band PSD, while the steady response can have large higher harmonic stress components. Regions of chaotic response and the steady regions with large higher harmonic stress components contain distinctly different response features and have significant implications on the fatigue analysis. To quantify the effect of the higher harmonic force components and chaotic oscillations on fatigue damage of long flexible structures, we generate stress time series such that we can include or remove the higher harmonics, and also use either a narrow-band or broad-band PSD. This approach enables us to conduct a systematic study on the influence of each of these phenomena on the resulting fatigue damage. We show a dramatic increase in fatigue damage for signals containing higher harmonics. On the other hand, for chaotic stress signals, the fatigue damage is increased moderately, relative to a stress signal with a narrow-band PSD with the same total power. (c) 2014 Elsevier Ltd. All rights reserved.