In order to improve the life cycle and cutting ability of a suspension abrasive water jet nozzle at the same time, hydrodynamics technology, an enumeration method and multiparameter orthogonal optimization are used to optimize the nozzle section geometry, taking the inlet diameter coefficient of the nozzle, the axial length coefficient of the contraction section and the contraction section curve as optimization variables, and selecting the peak velocity and the unit flow erosion rate as the indicators, it is concluded that the optimal contraction section curve is a Widosinski curve, the optimal inlet diameter coefficient of the nozzle is 0.333 and the optimal axial length coefficient of the contraction section is 2.857. Compared with the commercial product single cone nozzle, the performance of the optimal section nozzle improves by 5.64% and the life cycle increases by 43.2%. On this basis, the effects of operating parameters, including inlet pressure, abrasive particle flow rate and abrasive particle size, are further studied. It is determined that the optimal section nozzle has the best performance under the above operating parameters. It is demonstrated that by optimizing the nozzle section geometry, the cutting capacity and life cycle of the nozzle are improved, the performance of the nozzle can be significantly improved and the optimization of the performance of the nozzle is realized.

This paper proposed a compact design of the subsea cobalt-rich crust mining vehicle with a general purpose support vessel for subsea resource exploration, sample collection, and research. The necessary functions were considered in the concept design, including walk, crushing/mining, sample collection, cutter head adaptation, vehicle orientation, crust texture measurement, awareness, positioning, and navigation. The prototype was tested in both tank and subsea environment. The sea trials were carried out with the support of a general purpose support vessel. The track design worked well in both the tank and subsea environment and the mining vehicle walked smoothly in the sea trial. The crust was crushed to the size of 2 mm and 10 mm with different cutting parameters and successfully collected by the jet pump, 6 kg in total. The crust texture was measured by the onboard sonar successfully and can be used for cutting parameter selection. The cameras captured the images of the subsea environment, but the actions of crushing and sample collection produced plumes, which blocked the camera vision. In the situation, the front image sonar can be used to keep the vehicle away from big rocks. The mining vehicle is not limited to the mining and sampling of subsea cobalt-rich crust. Most of the subsea solid resources on the seabed can be considered to use the compact mining vehicle for sampling and related research. The only issues to be considered are the crushing ability and sample size required.

To mine the cobalt-rich crust deposits at the substrate of the slope of the seamount, the mining vehicle needs to walk on the slope and strip the cobalt-rich crust from the substrate. To achieve safety and control, the vehicle needs to stably walk on the slope. In this paper, we propose a modeling method for mining vehicle performance based on slope stability and antislip and antiskid conditions. The specific energy of three types of mining vehicles is compared based on dimensionless parameters. The dual-drum type is determined to be the best choice in terms of energy costs, followed by the down-milling type. The performance of the compact mining vehicle based on different slope angles and two sea trial results in the South China Sea indicate that the slope angle, substrate, and crust have significant effects on the stability. The modeling method proposed in this paper can help designers estimate the structure and power of mining vehicles based on mining stability.

This paper proposed a concept prototype of the arm-claw-type manipulator with a general purpose support vessel for the rapid salvage of deep submergence vehicles, aircraft, satellites, etc. The key functions were realized, including object clamping, claw butting and locking, position and posture adjustment, awareness, positioning, and navigation. The prototype was successfully tested in a lake environment on a hollow and cylindrical object. The arm-claw-type manipulator is suitable for the rapid salvage of cylindrical objects in an underwater environment to minimize the clamping force and possible clamping damage on the object being salvaged. Four propeller thrusters with a symmetrical arrangement can be used for the adjustment of position and posture in underwater environments, to match the orientation of the object. Cameras capture the profile images of the underwater salvage object and can be used for posture adjustment, but in dark, deep-water environments, sonar can be used in the place of underwater cameras.

As a key piece of equipment in underwater production system, a reliability study of deep-sea connectors has important theoretical significance and engineering value for increasing fault-free operation time, improving engineering safety, and reducing maintenance costs. However, the diverse failure modes of connectors and the lack of high-quality and credible reliability data can lead to biased analysis outcomes. To tackle this problem, this study aims to establish a reliability model for deep-sea horizontal clamp connectors. Based on the actual engineering background, a fault tree model for deep-sea horizontal clamp connectors is developed, and the distribution types of bottom events are analyzed concerning the failure mechanism. To enhance the model’s credibility, a multi-source information approach is employed, combining prior product information, expert experience, and design information to quantitatively solve the reliability probability of the connector. The expert experience is quantified using the fuzzy quantitative analysis method, while the design information is estimated by developing a corrosion prediction model combined with grey theory. Thus, the reliability assessment of deep-sea horizontal clamp connectors is completed. Factory Acceptance Test (FAT) is performed on the improved connectors, and the closed-loop work of reliability analysis is completed.

Radial seals are sensitive to axial overload failure and may cause leaks. This paper presents two semi-analytical methods for the joint strength and sealing performance of the subsea pipeline compression connector under axial overload failure. The method for the joint strength consists of two parts: One is the analytical model for the joint strength of the connection and seal under axial tension and compression conditions. The models are based on membrane theory, considering the hardening and bending effects. The other is a two-dimensional, axisymmetric finite element model for the joint strength of the radial metal seal. The semi-analytical method for the overload sealing performance is derived using a finite element model and the Reynolds equation of the laminar flow. The effects of critical parameters on the joint strength and the overload sealing performance are analyzed. The experiments are carried out with specimens and prototypes to evaluate the evolution of the sealing interface and the joint strength. The results show that both the internally turned sealing surface and the deflection of the pipe can improve the joint strength. In addition, the compression-type connector can remain sealed under the maximum axial overload. The proposed methods allow the prediction and identification of the overload joint strength and the sealing condition of the compression-type connector and provide a better understanding of the radial metal seal under the axial overload condition.