Shape Effect of Polymetallic Nodules on Suction Forces and Flow Field During Seabed Hydraulic Collection

Abstract

Abstract Turbulent suction pipe flow around a near-wall ellipsoid nodule, as basic research of polymetallic nodule hydraulic collection, is investigated numerically and experimentally in this paper. Seven ellipsoids with axe ratios (a/b) ranging from 1 to 2 are considered as nodule models to reveal the shape effect on the characteristics of suction forces and suction flow field. Methods of particle image velocimetry (PIV) and dye tracing were used to visualize the suction flow field. The results indicate that (1) the suction force coefficient increases with a/b and its growth rate decreases with the ratio of bottom clearance to semi-thickness of the ellipsoid (h/c); (2) the weak vortex shedding in suction flow results in small-amplitude fluctuations of time-history suction forces; and (3) the detached eddy simulation (DES) method based on shear stress transport (SST) model is validated to be accurate and feasible for predicting the suction forces and suction flow field. It is expected to provide references for the design of nodule pick-up devices and to help us further understand the mechanism of hydraulic collection.