Particle dynamics in oscillating pipelines during hydraulic transport for deep-sea mining

Deep-sea mining involves collecting ores from the seabed and transporting them to the surface, emerging as a new frontier in marine engineering. However, safely and efficiently transporting large, high-density particles vertically over a distance of several kilometers within a pipeline using an upward flow poses a significant challenge. This study employs computational fluid dynamics and discrete element method to examine particle dynamics in an oscillating pipeline during hydraulic transport. A typical figure-eight motion is adopted to simplify the pipe oscillation under ocean currents. A sensitivity analysis is performed to evaluate the effects of pipe oscillation amplitude and frequency on hydraulic transport. Particles exhibit periodic behaviors lagging pipe oscillation, with radial distribution shifting into a symmetrical sector shape. This results in higher particle–wall collision frequency, larger contact forces, and uneven contact distributions, reducing transport efficiency and increasing structural demands. Both the pipe oscillation amplitude and frequency intensify particle collisions and elevate the hydraulic gradient, with frequency having a more prominent effect. To optimize efficiency and structural integrity, it is suggested to avoid pipe oscillation with frequencies over 0.6 Hz and amplitudes exceeding 1.2 times the pipe diameter in engineering applications.