A hybrid physics-informed gated recurrent unit model for coupled motion prediction in deep-sea mining systems

As deep seabed mining technology matures and global demand for key minerals grows, new requirements are being posed to environmental governance systems. However, given the urgent need to formulate the Regulations on Exploitation of Mineral Resources in the Area, China’s existing legal provisions on environmental governance of deep-sea mining are too principled to meet the needs of practice, thus hindering the goal of marine environmental protection. In response to the above dilemma, this paper proposes improvement suggestions from three perspectives: the licensing system of deep-sea mining, the environmental regulatory system for deep-sea mining, and the financial system of deep-sea mining. These suggestions aim to enhance the adaptability and effectiveness of China’s deep-sea mining environmental governance system.

In this paper, a nonlinear integrated multi-body dynamic (MBD) model of a deep-sea mining (DSM) system was developed. A particular nonlinear interaction model between the mining vehicle and the seabed sediment was derived. The fluid resistance and the resistance torque acting on the vehicle were obtained by the computational fluid dynamics (CFD) numerical simulations. In addition, a rigid-flexible coupled discrete element method (DEM) was adopted to model an extremely long mining riser efficiently and accurately. Developed by the C# program, a user-defined subprogram was intended to establish the DEM model of the riser. A motion control system model for trajectory tracking of the vehicle was developed in which the fuzzy control algorithm and the fuzzy adaptive PID control algorithm were used to control the speed and speed ratio of the tracks, respectively. Furthermore, the collaborative simulation between the dynamic model and the control model was achieved, and a coordinated motion mode for the total mining system was proposed and simulated. Accordingly, the trajectory tracking accuracy and slip of the vehicle, the spatial state change of the riser, and the interaction forces among subsystems were analyzed. This paper can provide a valuable theoretical basis and technical reference for the integrated design, performance prediction, and operation control of the practical DSM system.

The paper deals with model tests as a means for research and development of deep sea mining vessels. Important data can also be collected for operation manuals concerned with precise specification of operations of ocean surface units. The paper reviews deep ocean mining vessels and operations and outlines the aspects which can be successfully dealt with in model tests in conventional wave basins. A range of special techniques are used to obtain the necessary information for the main set-up of the mining vessel in operation and the ore carrier in approach, attach, load, detach, and depart phases of the combined operations. It is discussed how operational conditions and survival conditions can be studied for the above objectives. The model test set-up for the purpose is complex since the many quantities and phenomena covered do not scale similarly. It is shown how servo-assisted free-model tests is the answer to the problems encountered in terms of model testing. The necessary servo units are discussed and dealt with in the appendices. Finally, the paper outlines a test programme and the ranges of test parameters and variables. INTRODUCTION Deep sea mining is a very young technology and very expensive to develop. Basic tests and pilot plants have been operated for some years to investigate possibilities and prepare the full-scale process when the law of the sea legislation and the mineral market conditions are right. The cost of an ocean mining installation for manganese nodules is about 700 million US $ and seems, under certain conditions of high nodule abundance and relatively easy recovery, to be economically feasible with a 20 years' operation in the mining sites. The nodule density of about 9 kg/m2 over a high priority area of 6,000,000 km2, will yield about 40 billion tons of dry nodules for recovery. The operation cost of such a mining system can be estimated to the order of 75 million $ per year exclusive of processing cost which might amount to 125 million per year, and exclusive of capital cost. The direct mining cost is thus 250,000 $ per day covering all operations at sea. Any attempt to improve efficiency and service operation quality or any attempt to prolong the possibility to operate in heavier weather is worth-while. Model tests are a highly qualified means of developing ocean structures, and many aspects of ocean mining can be solved in model tests. The vessels' motions and behaviour under environmental loads, steering and manoeuvring properties at the low speed of advance, carrying a 6 to 8 km long marine riser under the ship bottom, can be measured and analysed for design, development, and preparation of operation manuals. Films and video tapes can be prepared for instructions, marketing, and training purposes. Structural loads for design purposes concerned with mutual operation of the mining vessel and the ore carrier can be studied. Transfer of the recovered ore in dry or slurry form can be dealt with.

This paper describes a quantitative safety study carried out on a system which monitors the environmental conditions in an undersea mine. Of particular importance are the concentrations of methane and carbon monoxide present in the mine. Although the presence of these gases is of concern in all mines it is of particular concern in this undersea mine since up to 37 per cent of the return air of the ventilation system is recirculated. When high methane or carbon monoxide levels are detected recirculation is halted.Fault trees were constructed to represent two system failure modes for each of the trip conditions; failure to trip on demand and spurious trip. These logic diagrams were then analysed to produce the minimal cut sets and the probabilities for the system failure events. From this prediction of system performance the degree of improvement attainable by changing the system design, component repair times or test frequencies was investigated.

Deep-sea manganese nodules are abundant in the ocean, with high exploitation potential and commercial value, and have become mineral resources that coastal countries compete to develop. The pipeline-lifting mining system is the most promising deep-sea mining system at present. A deep-sea mining vehicle is the core equipment of this system. Mining quality and efficiency rely on mining vehicles to a great extent. According to the topographic and geomorphic environmental characteristics of deep-sea manganese nodules at the bottom of the ocean, a new deep-sea mining system based on an autonomous manganese nodule mining vehicle is proposed in this paper. According to the operating environment and functional requirements of the seabed, a new mining method is proposed, and the global traverse path planning research of the autonomous manganese nodule mining vehicle based on this mining method is carried out. The arc round-trip acquisition path planning method is put forward, and the simulation verification shows that the method effectively solves the problems of low efficiency of mining vehicle traversing acquisition and obstacle avoidance.

Slurry pumps in deep-sea mining: A review of numerical and experimental studies

To ensure the safety and the production efficiency as well as the component lifetime of deep-sea mining system, a novel heave compensation system of deep-sea mining based on dynamic vibration absorber was proposed in the light of 5000m deep sea poly-metallic mining system of China in this paper. According to the work condition of heave compensation system, the response of deep-sea mining ship under random wave of sea state 4 in China’s deep sea poly-metallic mining field are numerically simulated in time domain. The proposed heave compensation system was simplified to a two-degree-of-freedom system stimulated by the displacement motion of the deep-sea mining ship and its dynamic model was built. Taking the minimum of the displacement variance of the proposed heave compensation system as the optimal object and considering the allowed displacement of the dynamic vibration absorber itself, the computation formula of the optimum parameters of dynamic vibration absorber for heave compensation system of deep-sea mining is derived. Thus the parameter of dynamic vibration absorber was determined and its effect on the performance index of the heave compensation system was simulated and compared. The dynamic vibration absorber with optimum parameters was simulated and tested on the test bench of double-storey mass-spring vibration system in the lab. The results of the example show that the performance of vibration control of the designed dynamic vibration absorber is satisfactory and the computational formulas given in the paper are effective. The results also verified that the heave compensator based on dynamic vibration absorber with the optimal parameters can have good performance of heave compensation and it is practical to isolate the lifting pipeline and its deployment platform from the vibration of the ship motion induced by the irregular wave with simplicity and less energy consumption. This work in the paper will be of great theoretical guidance in the optimum design of the dynamic vibration absorber for heave compensation system of deep-sea mining.

In a deep-sea mining system, coarse-grained minerals are transported most of the time, which puts greater demands on the hydraulic performance and wear resistance of the mining pump than the transport of other types of materials. The pump performance is affected by the parameters of its main flow passage components. The parameters of the impeller were studied in depth to propose a novel mining pump, and the wear conditions of single-stage mining pump produced by different types of solid particles and operating conditions were analyzed. After numerical simulations of 29 models were conducted, the response surface methodology (RSM) was used to develop an optimized pump model that achieves better performance than the original model. The efficiency is improved by 1.2%, head is reduced by 0.34 m, and the impeller average wear intensity is reduced by 29.5% under rated conditions.

Effects of vibration absorbers on the lifting pipe in deep‐sea mining have been attracting more and more attention in the recent three decades; however, there are very few reports about the influence of ocean current on the pipe vibration in the literature. Considering the geometrical features of the prototype, this paper establishes the physical model, mathematical model, and simulation model of the lifting subsystem. A comprehensive finite element model for the deep‐sea mining system by the OrcaFlex is developed to explore the influences of buffer mass and sailing velocity on the deflection angle and the axial load and stress of the lifting pipe. Analytical and numerical simulations have been formulated to illustrate variation rule of longitudinal vibration and axial stress at the position of pump and buffer for the lifting subsystem to determine the dynamic vibration absorber parameters. In this paper, MATLAB and Orcaflex software are used to verify the mathematical model. The simulation results show that the attaching DVAs can effectively reduce the axial stress, and longitudinal displacement at certain positions of the lifting pipe.

With the depletion of land mineral resources, people have turned their attention to the sea. As an important part of deep-sea mining systems, the technical research and development of ore collectors has always been a difficult problem in many countries. According to the characteristic that buffalo hoof is suitable for walking on soft soil, a kind of bionic grouser for a deep-sea mining vehicle is designed in this paper. Through the optimization of Rankine’s passive earth pressure theory, the formula for calculating the tractive force of the grouser is obtained. The accuracy of the analytical solution is verified by finite element simulation, and the force enhancement mechanism of the bionic grouser is revealed. The results show that the design of the bionic grouser has a significant effect on the improvement of tractive force, and the tractive force of the No. 1 bionic grouser is 17.52% higher than that of the straight grouser. On this basis, the geometric parameters of the bionic grouser profile are optimized. The results show that when L is 0 mm and R is 183 mm, the force enhancement effect reaches the maximum of 27%, which provides a design basis for optimizing the grouser and improving the mining efficiency of the collector.

A localization algorithm based on pose graph using Forward-looking sonar for deep-sea mining vehicle

During deep-sea mining operations, the unpredictable marine environment and the complexity of simulating the interactions between the riser and the mining vessel the riser cause significant challenges in the coupled dynamic behavior prediction of the mining system. Based on FEA method, this paper develops coupled models of the mining vessel and risers of varying lengths. Considering ocean current and surface wave, the coupling dynamic behavior of the riser and mining vessel, including the heave, pitch, and roll movements of the vessel as well as the stress on the riser, is calculated and analyzed. The results of the simulation indicate that the interaction between the riser and the mining vessel influences the dynamic behavior of both the vessel and the riser, leading to a significant increase in the riser's stress. The mining vessel experiences an increase in heave motion, while its pitch and roll motions are restricted.

Offshore mining for minerals such as barite, coal, calcium carbonate, gold, and tin is a well-established industry in many countries. Although there have been several attempts to develop mining systems to recover manganese nodules in water depths of 4,000 m, commercial mining is at present confined to shallow coastal waters. Undersea mining for sub-surface deposits dates from at least the early 1600s and accounts for a significant proportion of the total mineral production in some countries. More than 100 undersea mines have been constructed worldwide; with few exceptions they began as onland mines that moved offshore after the onland sources were depleted (Austin, 1967). In 1977, the last year for which comprehensive global production statistics are available, offshore non-fuel mineral production was worth about $460 million, with most of that coming from sand and gravel, tin, and calcium carbonate (Glasby, 1979). This valuation is conservative because numerous small operations go unreported and the Soviet Union does not make public its production statistics. The Soviet Union has, for several years, dredged cassiterite for tin in the Arctic Ocean, but we have no information regarding the level of production. Most marine mining activity to date has taken place in temperate or tropical regions, yet the Arctic may host equally exciting mineral deposits, and both tin and sand and gravel are already mined there. The problems of mining in a region covered by ice for much of the year should not, however, be underestimated. New technologies will be required for exploration and mining

Deep-sea lifting pump is a key equipment of deep-sea mining system. The internal unsteady fluid radial force may cause vibration of the pump and even bring harm to the entire mining system. The paper takes the six-stage deep-sea lifting pump being developed in China as the research object and the internal flow law and fluid radial force of the pump are studied based on numerical simulation. Firstly, the accuracy of the numerical simulation method adopted in this paper is verified by taking the domestic two-stage deep-sea lifting pump as the test object. Then, the numerical calculation of the six-stage deep-sea lifting pump is carried out, and the pressure distribution cloud map in the six-stage deep-sea lifting pump and the fluid radial force in each stage pump are obtained. The analysis results show that the rotor-stator interaction between the impeller and the guide vanes is an important reason for the fluid radial force in the pump; the fluid radial force in each stage pump changes periodically, and it is more regular in the final stage. The variation period of the fluid radial force in each stage pump is related to the number of blades of the impeller. The research results provide a theoretical basis for revealing the flow law and fluid radial force characteristics in the deep-sea lifting pump.

In the concept of subsea mining field development, a subsea crawler generally has a big drill and scrapes the mineral deposit horizontally. In this "Horizontal Mining System (HMS)", ores vary in size and large chunks should be crushed into transportable particles. So the Subsea Crushing and Feeding Unit (SCFU) must be required for efficient slurry transportation to use the traditional riser system. In this paper, we introduce and discuss our "Vertical Mining System (VMS)" concept, which consists of a Down-The-Hole Drill (DTH) unit mounted on a jack up platform. This vertical mining system can be used for both exploration and production of the subsea mineral deposit. The DTH unit makes the mineral deposit into powder-like particles while it digs into the hole. We executed drilling experiments on land with a granite rock using a DTH unit. The result showed the drilled particle size were less than 1mm, which indicates that this method allows us to transport the ore slurry directly through the traditional riser/pump system. Because the ore particle is even and small enough, the Subsea Crushing Unit (SCU) can be eliminated. So we believe the total project cost and period can be reduced compared to the HMS concept. The maximum drill length can be from 30 to 50 m. The mining speed per a DTH is determined by the drill diameter and the drilling speed depending on the rock strength. At present, in our granite experiments, the DTH drilling speed was around 3.0 cm/sec. The desired production amount is achieved by installing plural drilling units. We deploy the jack up platform instead of a crawler considering several reasons. The priority is we need to keep the xy coordinate of the drilling unit precisely controlled for efficient field layout. The second reason is we should keep the drill stem vertically even though the seabed has a slope or it is uneven. It is a gravity type jack up with 4 legs and has a set of xy horizontally sliding actuators which enables us to position the drill units automatically on the seabed. The horizontal size of the jack up is around 15 m times 15 m. The position of the platform will be changed continuously by suspending it with the support vessel's crane after it digs the 10 meters square seabed area. A subsea ore separator will be settled near the platform to select high-grade ore from low-grade ore on the seabed, which reduces not only the transportation cost/time but also the amount of marine disposal from the surface facility.