Two-degree-of-freedom VIV of circular cylinder with variable natural frequency ratio : experimental and numerical investigations
Srinil, Narakorn and Zanganeh, Hossein and Day, Alexander (2013) Two-degree-of-freedom VIV of circular cylinder with variable natural frequency ratio : experimental and numerical investigations. Ocean Engineering, 73. pp. 179-194. ISSN 0029-8018 (https://doi.org/10.1016/j.oceaneng.2013.07.024)
PDF.
Filename: OE2013_NS_HZ_AD.pdf
Preprint Download (2MB) |
Abstract
Slender offshore structures possess multiple natural frequencies in different directions which can lead to different resonance conditions when undergoing vortex-induced vibration (VIV). This paper presents an experimental and numerical investigation of a two-degree-of-freedom VIV of a flexibly mounted circular cylinder with variable in-line-to-cross-flow natural frequency ratio. A mechanical spring-cylinder system, achieving a low equivalent mass ratio in both in-line and cross-flow directions, is tested in a water towing tank and subject to a uniform steady flow in a sub-critical Reynolds number range of about 2×103–5×104. A generalized numerical prediction model is based on the calibrated Duffing-van der Pol (structure-wake) oscillators which can capture the structural geometrical coupling and fluid-structure interaction effects through system cubic and quadratic nonlinearities. Experimental results for six measurement datasets are compared with numerical results in terms of response amplitudes, lock-in ranges, oscillation frequencies, time-varying trajectories and phase differences of cross-flow/in-line motions. Some good qualitative agreements are found which encourage the use of the implemented numerical model subject to calibration and the sensitivity analysis of empirical coefficients. Moreover, comparisons of the newly-obtained and published experimental results are carried out and discussed, highlighting a good correspondence in both amplitude and frequency responses. Various patterns of figure-of-eight orbital motions associated with dual two-to-one resonances are observed experimentally as well as numerically: the forms of trajectories are noticed to depend on the system mass ratio, damping ratio, reduced velocity parameter and natural frequency ratio of the two-dimensional oscillating cylinder.
ORCID iDs
Srinil, Narakorn, Zanganeh, Hossein and Day, Alexander ORCID: https://orcid.org/0000-0001-6798-3468;-
-
Item type: Article ID code: 44698 Dates: DateEvent2013Published4 September 2013Published OnlineSubjects: Naval Science > Naval architecture. Shipbuilding. Marine engineering Department: Faculty of Engineering > Naval Architecture, Ocean & Marine Engineering Depositing user: Pure Administrator Date deposited: 02 Sep 2013 13:28 Last modified: 06 Oct 2024 04:01 Related URLs: URI: https://strathprints.strath.ac.uk/id/eprint/44698