Experimental Study on Vortex-induced Vibration of Underwater Manipulator under Uniform Flow
To reveal the characteristics of vortex-induced vibration(VIV)responses of an underwater manipulator in a uniform flow,an experimental setup was constructed to test VIV in the uniform flow field of an underwater manipulator by utilizing the relative motion between the moving underwater manipulator and still water.Vibration displalement response at various positions on the underwater manipulator were collected at different reduced velocities.The experimental results indicate that as the reduced velocity increases,both the dominant frequency of vibration and the dimensionless amplitude exhibit an increasing trend.The dimensionless amplitude in the cross-flow direction is less than 0.04D,while the in-line direction shows significant multi-frequency characteristics and higher amplitudes,indicating that the underwater manipulator experiences more noticeable resistance in the in-line direction.The standard deviation of displacement first increases and then decreases with the increase in testing height,and the spatial distribution of the standard deviation of displacement in the cross-flow direction shows more pronounced symmetry compared to the in-line direction,with the first mode being dominant.The VIV in the cross-flow direction follows a strong regularity,generally conforming to the Strouhal pattern observed in cylinder flow.The dimensionless dominant frequency in the in-line direction is between 0.3 and 0.8,which is slightly higher than that in the cross-flow direction,with the Strouhal number being approximately 1 to 1.7 times that of the cross-flow condition.No frequency lock-in phenomenon was observed,but flow velocity and testing height have some influence on the VIV of the underwater manipulator.This study provides a theoretical basis for constructing accurate hydrodynamic models to ensure the precise positioning and control of underwater manipulator.
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