Deep-sea mining vehicles (DSMVs) are highly prone to sinking and slippage when traveling on extremely soft seafloor sediments. In addition, DSMVs can be vulnerable to dangerous situations such as overturning due to the non-homogeneous characteristic of the seafloor sediments, the heavy loads carried by DSMVs, and the complex and varied topography of the seafloor. When the terrain is uneven, four-tracked DSMVs can show excellent traveling abilities and safety performances compared with conventional dual-tracked vehicles, thus having a broad range of applications. Consequently, modeling and simulation of a four-tracked DSMV are essential for the study of DSMV traveling performance. To enhance adaptability to uneven terrain, the tracks are designed to be rotatable. First, a multi-body dynamics model is built in the Recurdyn software based on the actual structural properties of a specially designed four-tracked DSMV prototype. Then, the model’s forces are modified to reflect the actual circumstances of seafloor travel. Applying a more accurate shear model, a user subroutine is written to modify the track–soil force. Moreover, internal resistance and water resistance are considered and applied to the model in the form of external loads. Then, based on the multi-pass effect, the track–soil force to the rear track is modified. Moreover, considering the relationship between soil forces and velocity, a velocity coefficient is summarized and added to the resistance estimation equation. Consequently, a more realistic dynamic model of the mining vehicle has been developed. On this basis, simulations of straight-line travel on flat ground are performed. In addition, to investigate the effects of rotatable tracks, a straight-line travel simulation with tracks fixed is also performed. By analyzing the simulation results, the motion features and dynamic characteristics of a four-tracked DSMV with rotatable tracks when traveling in a straight line on flat ground can be studied.

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.

The vortex-induced vibration (VIV) dynamics of commercial-scale deep-sea mining risers with complex component arrangements (pumps, buffer stations, buoyancy modules) remain insufficiently explored, especially for 6000 m systems with nonlinear tension. This study investigates VIV control strategy by adjusting tension for a nonlinear riser system using the Iwan-Blevins wake oscillator model integrated with Morison equation-based analysis. An analytical model incorporating four typical current profiles was established to quantify the dynamic response under different flow velocities, internal flow density, and structural parameters. Increased buffer station mass effectively suppressed drift distance (over 35% reduction under specific conditions) by regulating axial tension. Dynamic comparisons demonstrated distinct VIV energy distribution patterns under different current conditions. Spectral analysis revealed that the vibration follows Strouhal vortex shedding lock-in principles. Spatial modal differentiation was observed due to nonlinear variations in velocity profiles, pipe diameters, and axial tension, accompanied by multi-frequency resonance, coexistence of standing and traveling waves, and broadband resonance with amplitude surges under critical velocities (1.75 m/s in Current-B). This study proposes to control the VIV amplitude by adjusting internal flow density and buffer mass, which is proved effective for reducing vibrations in upper (0–2000 m) risers. It validates vibration amplitude and frequency control through current velocity, buffer mass and slurry density regulation in a nonlinear riser system.

The research on seafloor massive sulfide (SMS) started relatively late, and the results on its breaking process are few. However, the breaking process contains evaluation indexes of safe, efficient and low-disturbance mining, so it is necessary to study the breaking process of seafloor massive sulfide. At the same time, the finite element method is used in most existing researches, and the system will automatically delete the failure element from the system during the simulation of rock-breaking, resulting in the inability to accurately obtain the chip state in the breaking process. In addition, SPH meshless method has unique advantages in dealing with large deformations of rock-breaking, but it has the problems of difficultly in boundary processing and serious computational time. In view of this, a hybrid discretization method of finite element method and smooth particle hydrodynamics (SPH) is proposed in this paper. On this basis, numerical simulation of a single-pick cutting seafloor massive sulfide based on the FEM-SPH adaptive coupling algorithm is carried out. Through the research in this paper, the regularity of the fragmentation process of polymetallic sulfides is obtained: firstly, the breaking process of seafloor massive sulfide experiences four stages: cutting-in of the pick, evolution of the high-stress zone, formation of the dense core, and the chips’ splash. Secondly, the three-dimensional forces on the pick change in fluctuation in the cutting process. Thirdly, the stress wave propagation is unbalanced and biased in the cutting process. Fourthly, the chips’ splash mainly has three directions: jet flow towards the opposite direction of the cutter cutting, spluttering perpendicular to the cutting surface of the pick, and sliding along the cutting surface. Finally, the chip mass is positively correlated with the cutting time. In this paper, a simulation framework for rock-breaking is proposed, and its advantages have been effectively verified.