Experimental study on dynamic characteristics of nodule particles in multi-field coupling during the Coandă-effect-based hydraulic collection

• Preparing lab-simulated sediments with similar properties to the in-situ, the mechanical and motion characteristics of semi-buried particles were revealed during the Coandă-effect-based hydraulic collection. • A novel experiment approach based on equivalent substitution was proposed to ascertain the critical incipient motion and force of particles. • Subsequent to assessing the collection performance, a criterion for particle incipient motion was proposed, and an empirical formula was established for predicting the maximum lifting force for optimizing collection mechanisms in deep-sea mining. The Coandă-effect-based hydraulic collection, celebrated for its high pick-up efficiency, has become a focus in deep-sea mining. However, prevailing research mainly focused on the performance in clear water environments, overlooking the impact of seabed sediments. This experimental study aims to examine the dynamic characteristics of nodule particles within the "fluid-solid-soil" multi-field under Coandă-effect-based hydraulic collection. The sediments were simulated in the laboratory by mixing the bentonite and water in specific proportions to replicate the physical and mechanical properties of in-situ sediments. A detailed analysis was conducted on the mechanical and motion characteristics of particles under various jet parameters and sediment shear strengths. The results illuminated that the shear strength of the sediment predominantly influenced the soil adhesion force, exhibiting an approximately linear correlation. Subsequent to assessing the collection performance, a criterion for particle incipient motion was proposed, and an empirical formula was established for predicting the maximum lifting force and experimentally confirmed to possess a maximum error below 20%. The pick-up efficiency experiments further demonstrated that when the jet parameters aligned with the critical conditions delineated by using the empirical formula, there was a significant increase to nearly 100% in pick-up efficiency, underscoring the practicality and accuracy of the predictive model. The results can offer theoretical guidance for selecting optimal jet parameters, to ensure efficient collection while minimizing potential environmental impacts due to excessive hydrodynamic forces and sediment erosion.