Effects of Heave Motion on the Dynamic Response of the Blocked Hydraulic Lifting System

Growing economy causes the shortage of mineral resource in the near future. The mineral resource locates at the sea bottom floor is an alternative solution. The hydraulic lifting technique is the priority option for the deep-sea mining. However, the heave motion caused by ocean wave leads to longitudinal vibration of the lifting pipe, which is also influenced by fluid structural interaction effect between the internal fluid and the pipe wall. During the longitudinal vibration, the closed end due to blockage or malfunction of the buffer will either pull or push the internal fluid that activates the pressure wave oscillation. The partitioned shell-based water hammer model is advanced to replicate the longitudinal vibration of the fluid-filled lifting pipe with one end closed. For parametric study, the frequency of the heave motion varies in the frequency range of the natural ocean wave. The masses of the lifting pump and buffer are treated as concentrated masses. Effects of concentrated masses, length of lifting pipe on the pipe dynamic response are investigated. Three resonant frequencies in the investigated range for the full scale of ocean mining lifting system are found. The first and the third resonance frequencies are identical to the frequencies of the water hammer pressure wave and the stress wave oscillation, respectively. The second resonant results from the coupling between the water hammer pressure wave and the stress wave. It also found that there is always an excited frequency a bit over the resonance frequency which depresses dynamic response of the fluid-filled lifting pipe.