Experimental and numerical studies are carried out to investigate the characteristics of flow field and forces acting on spherical particles in deep sea hydraulic collecting. For numerical simulation, Detached Eddy Simulation (DES) method is applied and is verified to be feasible for predicting the forces acting on the spherical particles. The effects of certain collecting parameters on vertical and radial force coefficients of the particles are investigated, including the angle between the collecting pipe inlet and the particle (θ), relative particle interval (l/d) and particle horizontal distribution density (nA/S). It is found that Cv begins fast fading near the point where θ=20°, and Cr always reaches its maximum somewhere between θ=35° and θ=40°. A small relative particle interval may result in a low pressure in the gap between the particles, leading to an increase in the radial force on the particles. This study is expected to be useful for understanding the mechanism of hydraulic collecting and refinements of collecting process.
The exploitation of deep-sea mineral resources is becoming an inevitable trend, facing the contradiction between increasing demand for essential metals in new-emerging industries and gradual exhaustion of terrestrial mineral resources (National Research Council, 2008). It has been discovered that enormous mineral resources are deposited on the seabed, among which manganese nodules have been attracting more and more attention for their promising economic value, huge reserves and high grade compared with land-based resources (Hein et al., 2013; Valsangkar, 2003). Therefore, deep sea mining is thought to be a key approach to the sustainable development of human beings. International consortia and enterprises have invested in the exploration of deep-sea minerals, manganese nodules in particular, and in the development of mining technology since 1960s (Mero, 1965; Willums and Bradley, 1974; Chung and Tsurusaki, 1994; Chung, 1999; Chung, 2005; Chung, 2009). So far, a variety of collecting methods (e.g. hydraulic methods, mechanical methods and hybrid collecting methods) have been developed. Results of the sea trial performed by OMI (Ocean Management Incorporated) in 1978 showed that hydraulic methods had higher collecting efficiency than mechanical methods (McFarlane et al., 2008).
