Test Device Design And Experimental Study Of Vortex-induced Vibration For Underwater Manipulator

Compared with the terrestrial environment,the underwater manipulator with large aspect ratio is full of challenges during operation in the Marine environment.In the ocean,the underwater manipulator will not only be affected by current disturbance and unbalance force,but also generate vortex-induced vibration due to vortex shedding,thus reducing the stability and accuracy of operation.The form of water flow in the actual marine environment is intricate.In order to realize the vortex-induced vibration test of underwater manipulator and reveal the influence of flow field form,velocity size,test height and other factors on vortex-induced vibration,the innovative design of test equipment and vortex-induced vibration test of different flow fields(uniform flow and shear flow)were carried out respectively.The results showed that:(1)The existing problem of the traditional test device include the limitation of flow generating mode,the lack of speed regulating structure,the single form of flow field and the complex test device.The vortex-induced vibration test device of the underwater manipulator designed by means of invention principles 20,26,24 and 17 can improve the deficiencies and achieve accurate test.(2)With the increase of flow velocity,the vibration frequency and displacement values of the end of the underwater manipulator at the cross-flow and in-line were increasing.In the uniform flow field,the vibration displacement amplitude of the in-line was higher than that of the cross-flow.The multi-frequency phenomenon was obvious in the spectrum diagram.At the same time,the shear flow excited the high frequency vibration and larger vibration displacement at the end of the underwater manipulator.(3)Under uniform flow,the dimensionless amplitude of the underwater manipulator increased with the increase of reduced velocity.The variation range of dimensionless amplitude in the cross-flow was small.Due to the greater resistance in the underwater manipulator at the cross-flow,it showed a more obvious trend of growth and vibration response.The standard deviation of the displacement of the underwater manipulator first increased and then decreased with the increase of the height of the test position.The spatial distribution was basically symmetrical,the peak value was single and concentrated in the middle position of the manipulator,and the dominant mode was order 1.Under the action of shear flow,the dimensionless amplitude had a larger change range and an upward trend,and the symmetry of the spatial distribution of displacement standard deviation decreased.(4)In this test,dimensionless dominant frequency was less than the natural frequency of the underwater manipulator.The dimensionless dominant frequency increased with the increase of reduced velocity.So frequency lock-in and resonance phenomenon did not occur.In the uniform flow field,the St of the cross-flow basically conformed to the St rule when the cylinder flows around.In the in-line,the dimensionless dominant frequency was slightly larger than the cross-flow,and the Strouhal Number was 1-1.7 times that of the cross-flow.In the shear flow field,the dimensionless frequency of the cross-flow was close to 0.8,while the Strouhal Number was maintained at about 0.3.In the in-line,the dimensionless dominant frequency was concentrated in the range of 0.4-0.6.Under the influence of shear flow field,the Strouhal Number decreased and the variation regularity was poor.