Vortex-Induced Response of a Flexible Cylinder in a Sheared Current

In this paper we outline a method for the approximate prediction of the static and lift responses of a flexible cylinder in a unidirectional variable stream. Our prediction is based on information derived from experimental results involving rigid cylinders forced to oscillate sinusoidally orthogonally to a uniform stream. Our approach represents the multifrequency lift response of a flexible cylinder in a sheared current by predicting a number of independently determined, monochromatic, multimode dynamic solutions. For each such multimode solution, our procedure allows the simultaneous evaluation of lift response frequency, amplitude, and phase between modes. A numerical example assuming bimodal solutions is included to illustrate our method for the geometry of a single-tube marine riser.