Frequency Response and Oscillatory Patterns of Two Tandem Cylinders in Flow-Induced Oscillations: Effect of Large Turbulence Stimulation and Adaptive Damping

Abstract The Marine Renewable Energy Laboratory at the University of Michigan has implemented nonlinear adaptive damping and passive turbulence control (PTC) on oscillating cylinders in a steady flow to study their effect on amplitude and frequency response. It is found that adaptive damping can improve the oscillation amplitude of cylinders but has little effect on frequency response. PTC can outweigh the effects of adaptive damping. Large enough PTC can reduce the oscillation frequency in VIV and modify the trend of amplitude response to be larger than usual in the VIV range. Neither damping nor PTC could affect oscillation frequency in the fully developed galloping range. Large PTC induces galloping earlier and forces the frequency of all cylinders in tandem to be the same. Further study shows that the oscillation pattern of two cylinders in tandem and its corresponding phase angle difference can be used as an indicator of each flow regime when the amplitude response is not a clear indicator. The phase angle of the upstream cylinder is always lagging the phase of downstream in VIV. On the other hand, the phase of the upstream cylinder is always leading in galloping oscillations.