Experimental and numerical studies are carried out to understand the behavior of ore particles in hydraulic collecting. The experiments were conducted in a water tank to measure the critical bottom clearance for the vertical incipient motion of spherical particles, which could accurately represent the collecting features. Four kinds of tests are designed to study the influence of particle size, speed of pipe and particle amount on critical bottom clearance. The characteristics of flow field and vertical force of spherical particle in the hydraulic collecting are simulated by Detached Eddy Simulation (DES) method and the six-degree-of-freedom (6-DOF) motion solver. This study will be useful for mechanism study of hydraulic collecting in the process of deep-ocean mining.
Deep-ocean mining is becoming an alternative way for human to exploit natural resources under the trend that some kind of resources on land are being exhausted. It is widely acknowledged that a vast number of resources are reserved in deep ocean, especially deep-ocean deposits. Therefore, deep-ocean mining is thought to be a key approach to the sustainable development of human beings and its applications have been proposed since 1960s (Mero, 1965; Willums and Bradley, 1974; Chung, 1999; Chung, 2005; Chung, 2009). One of the most important issues in deep-ocean mining is the hydraulic collecting near seabed. Typically, ore particles can be collected to the collector in the upward and gathering flow of water. Significant efforts have been dedicated to the hydraulic collecting system in deep-ocean mining.
A variety of collecting methods such as hydraulic methods, mechanical methods and hybrid collecting methods have been developed. Commercial production must achieve high sweep efficiency (Chung, 1985). OMI Test in 1978 showed that hydraulic methods have higher collecting efficiency than mechanical methods. It was also found that the hydraulic methods have better adaptability to the variation of bottom clearance than other methods (Zhao and Liu, 1995). The mechanism of hydraulic collecting is fairly complicated because the collecting efficiency is affected by a lot of factors such as particle size, bottom clearance, collector structure, flow rate and speed of pipe. The influence of these factors on collecting rate was studied by experiments.
