This paper presents results from two field experiments using long flexible cylinders, suspended vertically from surface vessels. The experiments were designed to investigate vortex-induced vibration (VIV) at higher than tenth mode in uniform and sheared flows. The results of both experiments revealed significant vibration energy at the expected Strouhal frequency (referred to in this paper as the fundamental frequency) and also at two and three times the Strouhal frequency. Although higher harmonics have been reported before, this was the first time that the contribution to fatigue damage, resulting from the third harmonic, could be estimated with some certainty. This was enabled by the direct measurement of closely spaced strain gauges in one of the experiments. In some circumstances the largest RMS stress and fatigue damage due to VIV are caused by these higher harmonics. The total fatigue damage rate including the third harmonic is shown to be up to forty times greater than the damage rate due to the vibration at the fundamental vortex-shedding frequency alone. This dramatic increase in damage rate due to the third harmonic appears to be associated with a narrow range of reduced velocities in regions of the pipe associated with significant flow-induced excitation.
- Ocean, Offshore, and Arctic Engineering Division
Fatigue Damage From High Mode Number Vortex-Induced Vibration
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Vandiver, JK, Swithenbank, SB, Jaiswal, V, & Jhingran, V. "Fatigue Damage From High Mode Number Vortex-Induced Vibration." Proceedings of the 25th International Conference on Offshore Mechanics and Arctic Engineering. Volume 4: Terry Jones Pipeline Technology; Ocean Space Utilization; CFD and VIV Symposium. Hamburg, Germany. June 4–9, 2006. pp. 803-811. ASME. https://doi.org/10.1115/OMAE2006-92409
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