Study on sediment erosion generated by a deep-sea polymetallic-nodule collector based on double-row jet

Abstract

The hydraulic double-row jet collector is widely used due to its high collection efficiency. Deep-sea sediments are usually characterized by high water content and semi-fluid dynamics, and there are few studies on the erosion properties of such sediments under jets. Resulting in the failure to accurately assess the efficiency and disturbance of a two-row jet collector. In this paper, the flow field characteristics are simulated for different double-row jet parameters (jet outlet pressure, nozzle-to-seabed height, target distance and number of nozzles). The erosion of a high water content, semi-fluid dynamic sediment layer (similar to the deep sea) under a double-row jet is experimentally investigated. According to the results from study, the jet flow field had a powerful central flow field, and decayed to both sides gradually. The formulas of flow field attenuation distribution in the upper jet zone and the maximum axial pressure are proposed. Moreover, the experiments showed that the erosion holes on the surface layer was mainly a "bowl" shape with a flat bottom and concave side, which had self-similarity. The erosion depth grew with the increase of jet outlet pressure, decreased with the increase of the nozzle height to the seabed. With the increase of target distance, the erosion depth first increased and then decreased. A new model of the erosion depth-time and erosion depth prediction are proposed. These results can provide theoretical reference for flow field calculation in nodule mining operation with double-row jet collector. It may have potential benefits on melioration of the collection efficiency and reduction of the jet disturbance.