Abstract
Vortex-induced vibrations (VIV) establish key design parameters for offshore and subsea structures subject to current flows. Understanding and predicting VIV phenomena have been improved in recent years. Further, there is a need to determine how to effectively and economically mitigate VIV effects. In this study, linear and nonlinear velocity feedback controllers are applied to actively suppress the combined cross-flow and in-line VIV of an elastically-mounted rigid circular cylinder. The strongly coupled fluid-structure interactions are numerically modelled and investigated using a calibrated reduced-order wake oscillator derived from the vortex strength concept. The importance of structural geometrical nonlinearities is studied which highlights the model ability in matching experimental results. The effectiveness of linear vs nonlinear controllers are analysed with regard to the control direction, gain and power. Parametric studies are carried out which allow us to choose the linear vs nonlinear control, depending on the target controlled amplitudes and associated power requirements.
Highlights
Controlling or supressing Vortex-induced vibrations (VIV) has drawn a considerable attention over years for economical and technical interests in enhancing safety, efficient operation and life time of the offshore structures
In this paper, we focus on the control strategies for 2-DOF VIV of a circular cylinder in sub-critical flow regime with a relatively low mass ratio, which is practical for offshore applications
Based on the above comparison, the linear controller is relocated from y to x direction with the same gain ( ∗ 0 and ∗ 0) and it is found that differences between non-controlled amplitudes and controlled amplitudes are extremely minor even in the lock-in region. This suggests that the in-line controller is not as effective as the cross-flow controller in suppressing VIV responses over the synchronization regime
Summary
Controlling or supressing VIV has drawn a considerable attention over years for economical and technical interests in enhancing safety, efficient operation and life time of the offshore structures. A velocity feedback control for a high mass ratio fluid-structure system was studied by Mehmood and Abdelkefi [9], where linear and nonlinear active feedback controllers for transverse VIV oscillations were investigated numerically though CFD. A linear analysis was conducted regarding the effects from various control gains and time-delayed terms on the coupled damping and frequency by ignoring fluid forces and associated nonlinear terms.
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