Last modified: 2017-07-09
Abstract
Abstract
Mineral-collecting technology is the core technology of deep-ocean mining, which has a decisive influence on the feasibility and profitability of technology application. Hydraulic collecting method is considered as one of the most promising options to collect the ores in deep-ocean mining system. Therefore, the characteristics of flow field and suction force of single spherical ore particle in the hydraulic collecting was investigated, which have a significant effect on collecting efficiency. Simulation and experimental validation of spiral flow and uniform flow are conducted respectively and compared from the aspects of the characteristics of flow field and the value of vertical force. The flow around a spherical manganese nodule placed under a collecting tube was investigated by using Detached Eddy Simulation (DES) and Large Eddy Simulation (LES) based on Shear Stress Transport (SST) model, respectively. A collecting test system was constructed in the laboratory, with which the behaviors of the flow and vortices were observed by application of flow visualization technique and the vertical force of the nodule was measured by a force transducer. It is verified that the vertical force prediction for single ore particle in collecting condition by simulation with DES/LES method based on SST model is feasible and sufficiently precise, by comparing the results of numerical simulation and tests. Also, the test system is proved to be able to catch vertical force with high precision. The study reveals that the value of vertical force of the sphere in spiral flow is greater than that in uniform flow under the same test conditions. One reason for that is the spiral flow brings about an increase of the transfer distance of negative pressure. An insight into understanding the characteristics of flow field in hydraulic collecting for deep-ocean mining was provided by comprehensive analysis on dynamic change regularity of wake vortex structures, pressure distribution and stream lines. The drag coefficients of the sphere at the two flow fields was defined as empirical equations using dimensionless quantities. The results of this study can provide reference and support for mechanism study and optimal design of the hydraulic collecting system for deep-ocean mining.
Key words: deep-ocean mining, hydraulic collecting, spiral flow, vertical force, simulation, experimental validation
Found program: the Major Research plan of the National Natural Science Foundation of China:
project for deep-sea polymetallic nodule mining tests（2016YFC0304103）
Figure 1. Schematic diagram of hydraulic collecting methods
Figure 2. Trimmer mesh model (isometric view)
Fig. 3 Overall experimental setup
Figure 4. Details of the water tank
a)
b)
Figure 5. Time-history curves and mean values of vertical force of a) numerical results and b) experimental measurements at the collecting velocity of 2m/s
Figure 6. Variation of the mean values of vertical force on the sphere under different collecting heights and collecting velocities
Figure 7. Collecting system test with the application of spiral flow collector
Figure 8. Spiral flow test with the application of flow visualization