Experimental Study on Vortex-Induced Vibration of Underwater Manipulator Under Shear Flow

The position deviation of the underwater manipulator generated by vortex-induced vibration (VIV) in the shear flow increases relative to that in the uniform flow. Thus, this study established an experimental platform to investigate the vibration characteristics of the underwater manipulator under shear flow. The vibration response along the manipulator was obtained and compared with that in the uniform flow. Results indicated that the velocity, test height, and flow field were the main factors affecting the VIV of the underwater manipulator. With the increase in the reduced velocity (Ur), the dimensionless amplitudes increased rapidly in the in-line (IL) direction with a maximum of 0.13D. The vibration responses in the cross-flow (CF) and IL directions were concentrated at positions 2, 3 and positions 1, 2, with peak values of 0.46 and 0.54 mm under Ur = 1.54, respectively. In addition, the vibration frequency increased with the reduction of velocity. The dimensionless dominant frequency in the CF and IL directions varied from 0.39-0.80 and 0.35-0.64, respectively. Moreover, the ratio of the CF and IL directions was close to 1 at a lower Ur. The standard deviation of displacement initially increased and then decreased as the height of the test location increased. The single peak value of the standard deviation showed that VIV presented a single mode. Compared with the uniform flow, the maximum and average values of VIV displacement increased by 104% and 110% under the shear flow, respectively.