Features of Vortex-Induced Vibration in Oscillatory Flow

Abstract

Vortex-induced vibration (VIV) in oscillatory flow is experimentally investigated in the ocean basin. The test flexible cylinder was forced to harmonically oscillate in various combinations of amplitude and period with Keulegan-Carpenter (KC) number between 26 and 178 in three different maximum reduced velocities, URmax=4, URmax=6.5, and URmax=7.9 separately. VIV responses at cross-flow (CF) direction are investigated using modal decomposition and wavelet transformation. The results show that VIV in oscillatory flow is quite different from that in steady flow; features, such as intermittent VIV, hysteresis, amplitude modulation, and mode transition (time sharing) are observed. Moreover, a VIV developing process including “building-up,” “lock-in,” and “dying-out” in oscillatory flow, is further proposed and analyzed.

Time domain simulation of vortex-induced vibrations in stationary and oscillating flows

“…An experimental investigation of VIV in oscillating flow was performed by Fu et al (2014). These experiments were conducted in the ocean basin at Shanghai Jiao Tong University (SJTU), and consisted of a flexible cylinder being towed horizontally with a prescribed oscillating motion.…”

“…The relative flow velocity caused by the riser moving back and forth in the water may cause vortex shedding and VIV if the motion amplitude is sufficiently large. VIV of an elastic cylinder in oscillating flow was studied experimentally by Fu et al (2014). They found that the structure vibrated significantly due to vortex shedding, and noted some important differences compared to stationary flow VIV.…”

“…Secondly, the improved model is used to simulate a flexible cylinder in oscillating flow. The experiment by Fu et al (2014) is used for comparison, allowing for direct assessment of the prediction accuracy. Finally, the model is used to explore the effect of changing certain key parameters.…”

Experimental analysis of fluid-structure interaction phenomena on a vertical flexible cylinder: modal coeficients and parametric resonance.

“…Besides, numerical models could lead to a full characterization of hydrodynamics coefficients in a wide range of Reynolds number and Keulegan-Carpenter number. Fu et al (2014) and Thorsen et al (2016) present interesting results of hydrodynamic forces on a flexible cylinder. Further experiments in order to assess the inertia coefficient would assist towards a deeper understanding of added mass results obtained in the present work.…”

“…Nevertheless, Pesce and Fujarra (2000) have also found an added mass value for a flexible cantilever greater than the unity (C a,1 = 1.17). Thorsen et al (2016), analyzing experimental data of a flexible cylinder subjected to an oscillatory flow presented by Fu et al (2014), also found added mass coefficient value greater than the unity (C a = 1.53). It should be recalled that the Sarpkaya charts were obtained for rigid cylinders under oscillatory flow, not for flexible cylinders.…”