## 5 Conclusions  
1. A hydraulic polymetallic nodule collector with two acquisition nozzles and one transmission nozzle is described in this study. The numerical model of the hydraulic collector was established based on the solid-liquid two-phase flow method. An experimental test platform was also constructed to verify the correctness of the model. The experimental and simulated collection efficiencies were found to be in good agreement at different collection heights, with a maximum error of no more than 5%.  
2. The parameter importance analysis indicated that the collection height and slant angle of the acquisition nozzle were the two primary factors affecting the collection efficiency, and thus they should be prioritized in the design and development of hydraulic  
Figure 26: Variable Importance in the Projection (VIP) index.  
Figure 25: Collection efficiency (\(\eta\)) and power (\(P\)) vs. the transmission flow rate (\(Q_{t}\)).  
collectors. Collection efficiency decreases as the collection height increases; as such, the recommended setting is below 150 mm. Collection efficiency increases and then decreases slightly with the slant angle of the acquisition nozzle; thus, the recommended setting is 45\({}^{\circ}\)-49\({}^{\circ}\). Collection efficiency also increases and then decreases slightly with the center distance between the two acquisition confluence tubes; as such, the recommended setting is 650-730 mm.  
3. The collection efficiency increases with the acquisition flow rate, but the increase is particularly limited at \(>\)160 m\({}^{3}\)/h. At the same time, the power consumption of the collector keeps increasing with the acquisition flow rate. Therefore, it is recommended to set the acquisition flow rate between 140 and 160 m\({}^{3}\)/h to minimize the power consumption at higher collection efficiencies. A large amount of the acquisition flow was reflected into the conveying channel to ensure the smooth transportation of the polymetallic nodules. Thus, the transmission flow rate had little effect on the collection efficiency. However, the power consumption also kept increasing with the transmission flow rate. Therefore, it is recommended that the transmission flow rate be set as less than 80 m\({}^{3}\)/h to save energy.  
To further optimize the collection performance and energy utilization of the hydraulic collector, further research should be conducted in the following aspects: exploring the influence of the diameter, shape, and arrangement of the acquisition nozzle on the acquisition and transmission flow field, as well as looking to the internal channel structure of the collector. Furthermore, the lightweight design of the collector, while ensuring strength and stiffness, can also reduce the total energy consumption of the entire mining vehicle and improve driving performance.  
The paper emerged from the long-term cooperation of the authors. Data curation, P.-J.W.; Conceptualization, L.L.; Formal analysis, P.-J.W.; Funding acquisition, P.-J.W. and L.L.; Investigation, P.-J.W.; Methodology, P.-J.W. and Q.-N.W.; Project administration, J.-B.W.; Resources, J.-B.W.; Software, Q.-N.W.; Supervision, J.-B.W.; Validation, P.-J.W.; Visualization, P.-J.W.; Writing--original draft preparation, L.L.; Writing--review and editing, P.-J.W. and J.-B.W. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Hunan Provincial Science and Technology Department (Grant Nos. 2019 SK2271, 2020 GK1020).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
The authors would like to thank the editors and anonymous reviewers for their careful work and thoughtful suggestions that have helped improve this paper substantially.  
The authors declare no conflict of interest.