Smart hybrid VIV control of a linearly sprung cylinder using an internal semi-active NES-based vibration absorber coupled with two active rotating wake-control rods

Abstract

Extensive two dimensional CFD simulations were carried out to investigate the hybrid active/semi-active cross-flow vortex induced vibration (VIV) suppression of a flexibly-mounted circular cylinder. The cylinder is equipped with two smart actively rotating control rods that are symmetrically oriented 120° apart in the near-wake region in real-time collaboration with an internally-fitted semi-active NES-based vibration absorber in the low Reynolds number flow regime (Re=100) over a typical range of lock-in reduced flow velocities (3≤U∗≤10). The control rods function as flow control actuators by enforcing the desired momentum injection into the near-wake region, while the semi-active structural control is realized by switching the nonlinear absorber force between some minimum and maximum values consistent with certain control logics. Selected multi-input-multi-output (MIMO) feedback control laws are introduced into the coupled transient dynamic simulation framework through a manually hooked user defined function (UDF) subroutine. The modified active rotating rod control system equipped with passive NES is found to be fairly successful in overall mitigation of the time response amplitudes (i.e., up to 56% reduction in the cylinder displacements, 78% reduction in the lift amplitudes, and 8% reduction in the drag coefficients as compared to the hybrid passive system). Similarly, notable reductions are obtained when a modified continuous feedback control strategy is directly applied in the NES-based semi-active vibration absorber (i.e., up to 55% in the displacements, and up to 11% in the drag coefficients). Moreover, the superior performance of proposed smart hybrid active/semi-active VIV control system in comparison to the hybrid passive system is demonstrated (i.e., up to 68% reduction in the displacements, 61% in the lift amplitudes, and 12% in the drag coefficient). Lastly, the key novelties, advantages, practical limitations, and trade-offs of the proposed numerical model are briefly pointed out in regard to the real-world marine/offshore applications and forthcoming investigations.