| The flexible hose is the key section to convey minerals from the seabed to the middle compartment in the deep-sea mining system. The hose spatial configurations vary to adapt to different sea bottom terrains and meet the requirements of return path. Therefore, it’s important to optimize transporting technologies and parameters for transportation safety in deep-sea mining system. Based on the experimental results of hose hydraulic transportation, the dynamic characteristics of hose shape under different working conditions were disclosed. The transportation parameters in the hose under different working conditions and hose shapes were analyzed. The method was proposed to optimize the conveying parameters for deep-sea mining system. The main work and conclusions are as follows:(1) The influence on internal flow velocity and pressure distribution by the double pumps was analyzed. The pump installed in the front of hose provides positive pressure while it provides negative pressure when installed in the back-end of flexible hose. If double pumps are in series, the pressure in hose will be offset, the maximum negative pressure decreases to about half of a single pump, the most positive pressure drops to about 1/5 of single pump, the internal flow velocity is being strengthened, maximum flow velocity is increased about one-third than single pump.(2) The relation between hose spatial configuration and its influence factors, the moving distance of miners, the internal flow velocity, and flow characteristics, was determined. When the hose arch height is not confined by the water surface in the tank, the hose arch height and curvature increases with the growth of the miner distance and the flow velocity; When the internal flow is slurry, the transforming trend of hose shape is similar to water internal flow, but the hose arch height and curvature of slurry flow is less than water internal flow. Because the density of the slurry containing coarse soil particles is much larger than water, fluid gravity increases more significantly than the vertical component of the momentum.(3) The quantitative relation between hydraulic gradient and particle size, volume concentration, pipe inclination, was determined. The hydraulic gradient of coarse particle slurry in flexible hose increases with the increase of particle volume concentration and mixture velocity yet decreases with the increase of particle size. This change rule is same with a number of hydraulic transportation research results in inclined pipeline. In addition, when the angle in little difference, with hose curvature increases, the particle easily moves in turbulence, and the hydraulic gradient increases. Analyzed the relation of hydraulic gradient in inclined pipe and flexible hose, the hydraulic gradient computational equations of coarse particles in flexible hose was also proposed in this part.(4) The quantitative relation between critical velocity and factors was researched. The research showed that with the slurry concentration volume and particle size increases, the critical velocity increases too. But with the hose arch height and tilt angle rises, it becomes decreasing. Analyzed the relation of critical velocity in inclined pipe and flexible hose, critical velocity computational equations of coarse particles in flexible hose was also proposed in this part. In practical mining process, to avoid pipe-blocking and reduce energy consumption, transportation parameters of flexible hose should be controlled according to different mining areas.
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