Abstract
Effects of vibration absorbers on the lifting pipe in deep-sea mining have been attracting more and more attention in the recent three decades; however, there are very few reports about the influence of ocean current on the pipe vibration in the literature. Considering the geometrical features of the prototype, this paper establishes the physical model, mathematical model, and simulation model of the lifting subsystem. A comprehensive finite element model for the deep-sea mining system by the OrcaFlex is developed to explore the influences of buffer mass and sailing velocity on the deflection angle and the axial load and stress of the lifting pipe. Analytical and numerical simulations have been formulated to illustrate variation rule of longitudinal vibration and axial stress at the position of pump and buffer for the lifting subsystem to determine the dynamic vibration absorber parameters. In this paper, MATLAB and Orcaflex software are used to verify the mathematical model. The simulation results show that the attaching DVAs can effectively reduce the axial stress, and longitudinal displacement at certain positions of the lifting pipe.
Highlights
E solid mineral resources from the deep-sea bottom, such as ferromanganese nodules and cobalt-manganese crusts, most common ferromanganese nodules, are found typically at water depths of 4000–7000 m, and in the coastal areas of the shelf [5]. e deep-sea mining system consists of an ore collection system, a mother station, and a transportation system between the miner and mother station [6]
The movement of the mining vessel will produce a motion excitation to the lifting pipe, which affects the reliability of the transportation system and the sea miner; especially the heave direction motion caused by ocean wave
In order to reduce the longitudinal vibration of the lifting pipe, Aso et al [8, 9] proposed a vibration absorber composed of a mass, springs, and dampers to the pump module as well as the buffer, and gave an active control system to control the longitudinal vibration of the pipe string [10]; the resonance amplitude at the top of the lifting pipe is greatly reduced
Summary
In order to solve the geometric nonlinear problem of current velocity, a linear approximate solution of current velocity in deep-sea mining is proposed in this paper. In this linear approximation model, the lifting pipe string is regarded as a rigid body. When the string is placed in still water, the twodimensional coordinate system W-O-V is established, and the O-W axis is vertical downward, and the positive direction of O-V axis is consistent with the wave propagation direction When it is placed in ocean current, the string will shift angle θ, and its coordinate system is X-O-Y. e stability analysis of deep-sea mining lifting pipe involves ocean current, resistance coefficient, Reynolds number (Re), and other factors [26]. According to the moment balance condition at the origin, the equation of moment balance can be deduced as (5b)
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