The design of deep-sea free-hanging water intake riser(WIR)tends towards large diameter and high internal flow velocity.The influence of internal flow on the vibration characteristics of WIR cannot be ignored.Analyzing the dynamic instability behavior caused by internal flow and evaluating the critical flow velocity for instability is of great engineering significance.Based on small-scale model experiments of WIR are performed to investigate,the impact of internal flow on the vibration characteristics of deep-sea free-hanging water intake riser is studied.The results show that as the internal flow velocity increases,WIR model undergoes dynamic instability behavior,manifested as intermittent nearly periodic motion,mainly induced by the instability of the first bending mode of the pipe.The material of the pipe,the top connection method,and the bottom counterweight block all affect its dynamic stability.Pipes with lower mass ratios are more prone to dynamic instability when fixedly connected at the top.When the top is changed to a pinned connection,the critical flow velocity for instability decreases for pipes with higher mass ratios and increases for pipes with lower mass ratios.Compared to the top boundary condition,the bottom counterweight block has a less significant effect on the critical flow velocity for pipe instability but can reduce its vibration amplitude.
free-hanging water intake riserdynamic instabilitycritical flow velocity assessmentexperimental research
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