Parametric Study for Lock-In Detection in Vortex-Induced Vibration of Flexible Risers

An observation that a parameter plot of a harmonically forced wake oscillator, which shows three distinct regions, in qualitative sense corresponds well with results of numerical and experimental investigations has prompted further investigations into dynamical behaviour of a flexible cylinder experiencing vortex-induced vibration. For this purpose, a reduced-order model representing a vertical pipe excited by surrounding fluid flow was built and certain aspects of its dynamics were studied. When resonance curves of a numerical and an analytical solution obtained with the method of multiple scales were compared, it became apparent that the former gives a much wider resonance region as the latter. This difference expectedly narrowed for lower values of the coupling strength parameter, indicating not only that the initial value might have been very large as defined in the method used, but also that because of this the overall dynamics were dominated by the linear part, the structure.