Understanding the interaction between submerged water jets and cohesive deep-sea sediment is critical for optimizing deep-sea polymetallic nodule hydraulic mining techniques. This research investigated the distinct erosion behavior of cohesive sediments through laboratory experiments and numerical simulations. Cohesive deep-sea sediments were simulated using bentonite–kaolinite mixtures. A series of laboratory experiments, including vane shear tests and viscosity tests under varying moisture content, were conducted to assess the sediments’ mechanical properties. Experimental submerged water jet erosion tests provided basic data for validating the numerical simulations. A Eulerian multi-fluid (EMF) model was implemented to capture sediment–water jet interactions under varying operational parameters, including jet velocities and nozzle heights. The erosion process was found to comprise three distinct stages, including rapid erosion, steady erosion, and stabilization. Two distinct erosion mechanisms were identified, depending on the jet intensity, which affected the depth and shape of the erosion pits. Quantitative analysis revealed that erosion depth exhibits an approximately linear relationship with jet velocity and nozzle height, whereas the erosion diameter shows nonlinear characteristics. These findings enhance the fundamental understanding of cohesive sediment responses under hydraulic disturbances, providing crucial insights for the design and optimization of efficient deep-sea mining systems.

The hydrodynamic resistance experienced by deep-sea mining vehicles (DSMV) during underwater operations and deployment/retrieval processes has a significant impact on maneuverability and operational safety. Therefore, accurate determination of the vehicle’s hydrodynamic coefficients is essential for motion control and system design. In this study, computational fluid dynamics (CFD) methods are utilized to calculate the transverse and vertical drag forces acting on the DSMV, as well as the corresponding added mass in both directions. The unsteady Reynolds-averaged Navier–Stokes equations were employed to analyze the vehicle’s dynamic behavior and the development of its wake flow structures. under uniform and accelerated motion conditions is analyzed. The time-averaging technique is applied to extract steady-state drag forces and drag coefficients, while the added mass and added mass coefficients are estimated by isolating viscous and inertial forces during acceleration. To verify the accuracy of the CFD methodology, simulations of regularly shaped bodies are performed, and the results are compared with theoretical solutions. The results show a high degree of agreement, confirming the reliability of the numerical approach used in this study.