The characteristics of flow field and force of a single spherical ore particle in the hydraulic collecting have been investigated. Researches of hydraulic collecting spherical particles in various collecting heights and flow velocities have been carried out with numerical method and testing method. It is verified that the vertical force prediction for single ore particle in collecting condition based on numerical simulation is feasible. The study reveals that the variation of the wake vortex is the dominant factor of force vibration. The drag coefficients of the sphere are defined as empirical equations using dimensionless quantities.
The world's growing economy demands more mineral extracted from the ocean. This demand requires the development of the deep-ocean mining technology. Polymetallic nodules are deposited over the ocean floor at water depth of 4,000~6,000 m. They are mostly spherical or ellipsoidal, with their long-axis length varying from 2 cm to 10 cm and a density of 2,100 kg/m3 (Liu et al., 2014). However, a profitable exploitation of deep-ocean mining is feasible on the premise that there is a nodule collector with maximum collecting capacity of 140 kg of wet nodules per second (Herrouin et al., 1989). As a result, effective collecting of manganese nodules out of sediment upper layer of deep seafloor is not only one of the key processes of the deep-ocean mining technology, but also the beginning of an economic and environmentally acceptable mining operation.
To pick up these nodules, a variety of collecting methods such as hydraulic methods, mechanical methods and hybrid collection methods have been developed. Commercial production must achieve high sweep efficiency (Chung, 1985). A sea test (the OMI Test, 1978) showed that hydraulic methods had a higher collecting efficiency than mechanical methods. It is also found that the hydraulic methods have better adaptability to the variation of seabed height than other methods (Zhao et al., 1995).