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Two Degrees of Freedom Vortex-Induced Vibrations of a Rigid Circular Cylinder With Varying Natural Frequencies in the X and Y Directions

[+] Author Affiliations
Arnaud Sanchis

University of Oslo, Oslo, Norway

Paper No. OMAE2009-80252, pp. 889-894; 6 pages
doi:10.1115/OMAE2009-80252
From:
  • ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering
  • Volume 5: Polar and Arctic Sciences and Technology; CFD and VIV
  • Honolulu, Hawaii, USA, May 31–June 5, 2009
  • Conference Sponsors: Ocean, Offshore and Arctic Engineering Division
  • ISBN: 978-0-7918-4345-1 | eISBN: 978-0-7918-3844-0
  • Copyright © 2009 by ASME

abstract

VIV experiments in two degrees of freedom are performed with a new apparatus designed to achieve a very low mass ratio and structural damping (ζ = 0.01 ). We investigated the influence of the ratio between the natural frequencies in the horizontal (fx ) and vertical (fy ) directions on the system response. Experiments were conducted at fx /fy = 0.42 , 0.87, 1.16, 1.36 and 1.44 with mx* = 2.87 and my* = 1.65 . For fx /fy < 1 , the amplitude and frequency response were found to be similar to the classical case where fx /fy = 1 , except in the transition zone between the upper and lower branches. For fx /fy > 1 however, radical changes were observed in the system response in amplitude, frequency and phase θ between the horizontal and vertical displacements. The most obvious is the appearance of a local maximum of Ay* in the middle of the upper branch. Secondly, the nature of the transition between the upper and lower branches changes from intermittent switching to a hysteretic one. The shape of the figure-of-eights describing the cylinder trajectory is also affected so that the cylinder is moving upstream at the top of its trajectory instead of downstream, indicating a profound modification of the interaction between the two degrees of freedom. Lastly, the range of reduced velocities over which stable, two-degrees-of-freedom oscillations were recorded is greatly increased up to 3.8 < U* < 8.4 .

Copyright © 2009 by ASME

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