Two-degree-of-freedom VIV of circular cylinder with variable natural frequency ratio: experimental and numerical investigations

Narakorn Srinil, Hossein Zanganeh, Alexander Day

Research output: Contribution to journalArticlepeer-review

72 Citations (Scopus)
745 Downloads (Pure)


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.
Original languageEnglish
Pages (from-to)179-194
Number of pages16
JournalOcean Engineering
Early online date4 Sept 2013
Publication statusPublished - 2013


  • two degree of freedom
  • VIV
  • circular cylinder
  • variable natural frequency ratio
  • experimental and numerical investigations
  • experimental investigation
  • numerical prediction
  • vortex-induced vibration
  • cross-flow/in-line motion


Dive into the research topics of 'Two-degree-of-freedom VIV of circular cylinder with variable natural frequency ratio: experimental and numerical investigations'. Together they form a unique fingerprint.

Cite this