Effect of spacing ratio on FIV response of multiple cylindrical oscillators supported by maglev

Abstract

Utilizing flow-induced vibrations for low-velocity ocean current energy generation is effective. Replacing metal springs with magnetic levitation systems to support the oscillators offers advantages such as easy stiffness adjustment and better underwater maintenance. This makes it significant for flow-induced ocean current energy harvesting. A multi-oscillator design can further enhance energy output capacity, but the mutual interference between oscillators results in vibration responses that differ significantly from those of a single oscillator. This paper employs the RANS method and equivalent magnetic charge methods to develop a coupled model of FIV of rigid cylindrical oscillators supported by magnetic levitation. Numerical simulations analyze the effect of spacing ratio on oscillation amplitude ratio, vibration frequency, and vortex shedding patterns. The results show that in double tandem cylindrical oscillators with identical diameters supported by magnetic levitation, the spacing ratio significantly affects the vibration response of the upstream and downstream oscillators. Under the characteristics of the magnetic spring, the interference between upstream and downstream oscillators is stronger with a small spacing ratio, leading to peak amplitude ratios even at moderate to low flow velocities. When G/D = 2 and U = 0.5 m/s, the downstream oscillator reaches a maximum amplitude ratio of A* = 1.06, 2.26 times that of a single oscillator at the same flow velocity. In three tandem cylindrical oscillators with identical diameters supported by magnetic levitation, the vibration response fluctuates more than in the two-oscillator case, exhibiting distinct three-stage branching characteristics. With G₁/D = 2 fixed, when G₂/D = 2 and U = 0.6 m/s, the downstream oscillator reaches a maximum amplitude ratio of A* = 1.2, 2.45 times that of a single oscillator at the same flow velocity. Vortex analysis indicates that under appropriate spacing ratios and flow conditions, the interference among multiple oscillators is amplified, enabling the downstream oscillators to better absorb and utilize the coherent vortices from the upstream oscillators, thus optimizing the vibration response.