This article is selected from the journal of the Chinese Academy of Engineering, China Engineering Science, No. 2, 2024
Authors: Chen Xuguang, Kou Hailei, Niu Xiaodong, Wang Chuanrong, Zhang Linqiang, Li Huajun
Source: Research on the development of deep-sea underwater technology and equipment[J].Strategic Study of Chinese Academy of Engineering,2024,26(2):1-14.)
Editor's note
The ocean is rich in biological and mineral resources, which are crucial to the future survival and sustainable development of mankind. Deep-sea underwater technology and equipment are the key to understanding the deep sea, developing deep-sea resources and protecting marine ecology. In recent years, the mainland has continuously increased investment and made a series of breakthroughs, including the development of a number of major equipment, such as the operational manned submersible "Jiaolong", the 10,000-meter-class manned submersible "Struggler", the first set of localized underwater Christmas trees, and the "Kaifeng No. 1" deep-sea heavy-duty operation mining vehicle, which serve the sustainable development of deep-water technology and equipment and provide strong support for the independent and controllable development of deep-sea resource development equipment.
The research team of Academician Li Huajun of the Chinese Academy of Engineering published the article "Research on the Development of Deepsea Underwater Technology and Equipment" in the second issue of the journal of the Chinese Academy of Engineering, China Engineering Science, 2024. Based on the actual development of the construction of a maritime power in the mainland, this paper analyzes the system composition and development needs of deep-sea underwater technology and equipment, and sorts out the development status and trend of foreign deep-sea underwater technology and equipment from four aspects: deep-sea observation/detection and perception system, underwater construction operation equipment, deep-sea oil and gas production system, and deep-sea mineral resources development equipment. On this basis, this paper summarizes the development status of the development of underwater technology and equipment in the deep sea of the mainland, analyzes the engineering challenges faced by the development, analyzes the relevant key technology and equipment system and key physical-mechanical mechanism, summarizes the typical equipment representatives and equipment maps of the deep-sea underwater technology and equipment, and condenses the common key technologies of the deep-sea underwater technology and equipment in the mainland, covering intelligent and automation technology, precision component processing and manufacturing technology, high-precision positioning and navigation, high-speed communication technology, Calculation and analysis of mechanics of large systems and cross-scale engineering design methods and techniques. In order to realize the high-quality development of deep-sea underwater technology and equipment in mainland China, this paper suggests: strengthening the top-level design of deep-sea underwater engineering technology development and promoting the construction of a common key technology cooperation system; Enhance the industry influence of the mainland's deep-sea underwater technical specifications and standards, and vigorously explore the international market; Promote the construction of compatible and universal platforms with high quality; Focus on cultivating scientific and technological innovation talents in deep-sea underwater engineering, and provide support for accelerating the high-level development of the marine science and technology industry.
I. Preface
The ocean accounts for about 70% of the earth's surface area, contains abundant reserves of biological resources and mineral resources, and has a vast usable living space, which is crucial to the future survival and sustainable development of mankind. The depletion of terrestrial resources, the destruction of the ecological environment and the threat of climate change have prompted mankind to find a sustainable and low-carbon development path, and the protection of natural resources has become a top priority, and the development of the ocean has become an inevitable choice for the development of human society. Deep-sea development is faced with the challenges of complex and changeable environmental and underwater factors, and it is urgent to support high-level deep-sea underwater technology and equipment. Understanding the ocean is the premise of developing and protecting the ocean, which needs to rely on the development of underwater detection and perception equipment. The green development of marine resources relies on the coordination of underwater exploration, construction, oil and gas production, mineral development, detection and perception technology and equipment and industrial chain of deep-sea resources. The protection of marine ecological environment needs to rely on the coordination and cooperation between various systems of underwater technology and equipment. The mainland attaches great importance to the use and development of the ocean, regards maritime power as an important strategic goal of the country, and puts forward the strategic plan of coordinating land and sea and speeding up the construction of a maritime power. The "14th Five-Year Plan" outline points out that a number of key core technologies will be broken through in the fields of marine engineering, marine resources, and marine environment, and the innovation and development of the marine engineering technology and equipment industry will be promoted.
Deep-sea underwater technology and equipment refers to the technology and equipment used to carry out the investigation, exploration, development and utilization of deep-sea environment and resources, involving deep-sea observation/detection and perception, underwater construction operations, deep-sea oil and gas production, deep-sea mineral development and other equipment fields. In recent years, the mainland has continuously increased its investment and made breakthroughs in deep-sea observation/exploration, construction operations, offshore oil and gas exploitation, and deep-sea mineral development, and has developed a number of major equipment, such as the operational manned submersible "Jiaolong", the 10,000-meter-class manned submersible "Struggler", the first set of localized underwater Christmas trees, the "Kaifeng No. 1" deep-sea heavy-duty operation mining vehicle, and the domestically developed "dig-shop-bury" integrated underwater construction operation equipment, to serve the sustainable development of the mainland's deep-water technology and equipment. It has formed a number of R&D bases such as China National Offshore Oil Corporation (CNOOC), China Merchants Industry Group Co., Ltd., Changsha Research Institute of Mining and Metallurgy Co., Ltd., China Ship Scientific Research Center, and an industrial chain with "R&D-design-manufacturing-final assembly" of deep-sea resource development equipment as the core, providing strong support for the independent and controllable development of deep-sea resource development equipment in the mainland.
At present, the development of surface ship technology and equipment is rapid, but the development of underwater technology and equipment is relatively slow, which is manifested in: the development of technology and equipment system is relatively lagging behind, some core components supporting products and business applications rely on imports, and face the risk of foreign science and technology blockade; The development of various industries is relatively independent, some industrial links are slightly weak, the integration is not enough, and the resilience to respond to emergencies is weak. In the face of the great changes in the world unseen in a century, in the context of a new round of global marine economic development, it is urgent to improve the independent and controllable level of technology and equipment for the underwater development of deep-sea resources, and grasp the strategic initiative. Therefore, this paper focuses on the development of technology and equipment for underwater development of deep-sea resources, sorts out the development status and trend of deep-sea underwater technology and equipment at home and abroad through field investigations, questionnaire surveys, literature surveys, etc., condenses the common key problems existing in the technology and equipment for deep-sea underwater development in the mainland, and puts forward targeted suggestions for accelerating the independent and controllable development of technology and equipment in the deep-sea water, so as to provide a basic reference for promoting the rapid development of the deep-sea underwater technology and equipment in the mainland.
2. System composition and demand analysis of deep-sea underwater technology and equipment
(1) Composition of deep-sea underwater technology and equipment system
1. Deep-sea observation/detection and perception systems
Deep-sea observation/detection and perception systems mainly include: physical and biochemical sensors, earthquake and other disaster monitoring and early warning sensors, geological, topographic, geomorphological detection instruments, single manned submersibles, deep-sea space stations, remotely operated vehicles (ROV), unmanned autonomous submersibles (AUVs), autonomous remotely operated vehicles, underwater gliders, anchored submersible equipment, in-situ static cone detectors (CPT), sediment sampling devices, thermohametry (CTD) water sampling equipment, submarine observation networks, etc.
2. Underwater construction equipment
Underwater construction equipment mainly includes: ultra-deepwater piling construction equipment, deep-sea engineering drilling equipment, deep-sea underwater trenching equipment, deep-sea caisson leveling equipment, deep-water dredging and dredging equipment, deep-sea pipeline and cable maintenance and overhaul operation equipment, deep-sea underwater cutting and demolition equipment, deep-sea underwater welding equipment, deep-sea underwater salvage equipment, deep-sea underwater drilling equipment, deep-sea underwater observation and sampling equipment (engineering, scientific investigation), deep-sea underwater operation manipulator, deep-sea underwater camera equipment, etc.
3. Deepwater subsea oil and gas production systems
The deep-sea subsea oil and gas production system mainly includes: underwater wellhead device, underwater Christmas tree, sealing components, umbilical cable, underwater safety valve, seismic wave exploration oil and gas reserve equipment, carbon sequestration equipment, etc.
4. Deep-sea mineral resources development equipment
Deep-sea mineral development equipment mainly includes: manganese nodule collection equipment, polymetallic sulfide mining equipment, cobalt-rich crust mining equipment, deep-sea rare earth-rich mining equipment, deep-sea ore pipeline transportation equipment, deep-sea combustible ice mining equipment, deep-sea anchor stranding equipment, ultra-deep power communication transmission cable equipment, etc.
Fig.1 Composition of deep-sea underwater technology and equipment system
The composition of the deep-sea underwater technical equipment system is shown in Figure 1.
(2) Demand analysis of deep-sea underwater technical equipment
1. Deep-sea underwater technology and cognition of the ocean
Cognitive ocean is an emerging field of research that aims to gain a deeper understanding and interpretation of the physical, chemical, and ecological processes of the ocean through ocean monitoring equipment and observation, detection, and perception systems. At present, the level of human awareness and understanding of the ocean still needs to be improved, especially the need to strengthen the understanding of important areas such as the deep sea. All kinds of manned submersibles, unmanned deep-sea submersibles, ocean observation networks and various mobile observation equipment arranged in the deep sea provide new perspectives and research methods for understanding the deep sea. The development of deep-sea monitoring instruments and observation, detection and perception systems has improved the level of human understanding of the ocean. With the continuous innovation of deep-sea underwater technology and equipment, important issues such as deep-sea physical processes, ecosystems and climate change will be solved, providing more scientific basis for marine protection and sustainable development and utilization of resources.
2. Deep-sea underwater technology and development of the ocean
To develop the deep sea, we must first use geology, topography and geomorphological detection instruments to have a comprehensive and systematic understanding of the marine environment, geology and surrounding ecology, such as the seabed optical camera system can play an important role in the exploration of marine mineral resources. Then, the submarine oil and gas resources are developed by using underwater oil and gas production equipment such as deep-sea Christmas trees, and polymetallic nodules, sulfides, cobalt-rich crusts and rare earth-rich crusts are developed by using submarine mineral resources development equipment. In addition, the rapid development of deep-sea underwater technology and equipment is closely related to the study of "gas-liquid-solid" coupling dynamics and bubble dynamics, which provides new solutions and new perspectives for solving technical and engineering problems in the process of deep-sea resource development and utilization. Deep-sea underwater technology and equipment can better develop and utilize marine resources through cross-cooperation in various fields and systems, and contribute to alleviating the imbalance between global resource supply and demand.
3. Deep-sea underwater technology and protection of the ocean
Protecting the oceans and achieving healthy ocean health is essential to promoting global biodiversity and mitigating climate change. Marine water quality and biochemical monitoring and sensing equipment provide important support for marine environmental scientific research, effective monitoring, and management decision-making, and improve the ability of human beings to monitor changes in the marine environment in real time. The systematic development of underwater construction equipment has also played a key role in marine protection. Equipment such as unmanned submersibles make marine construction and maintenance more efficient and safer, such as submarine pipeline maintenance, marine waste removal, and emergency repair of submarine oil and gas pipelines. In addition, artificial islands, artificial coral reefs and other structures based on underwater construction equipment can help restore and protect marine ecosystems and promote marine biodiversity.
Based on the above analysis, deep-sea underwater technology and equipment plays an important scientific research and engineering role in the process of ocean cognition, ocean development and ocean protection, and the rapid and stable development of underwater technology and equipment is of great significance to improve the level of marine awareness, green and efficient development of marine resources and realize marine health.
3. The development status and trend of foreign deep-sea underwater technology and equipment
(1) Deep-sea observation/detection and perception systems
The deep-sea observation/detection and perception system mainly includes deep-sea monitoring, observation and sensing equipment, deep-sea submersibles and anchored submersible observation networks. Europe, the United States, Japan, Russia, Australia and other countries and regions have developed new deep-sea pressure sensors, RDI Workhorse Navigator ADCP, Imagenex Delta-T imaging sonar, Sonardyne-Solstice 3000 multi-aperture side-scan sonar and other deep-sea observation/detection and perception sensors. Based on new sensors, underwater robots (such as ROVs and AUVs) have gradually developed into important equipment for underwater exploration and operations. In recent years, the United States, Russia, Norway, Japan and other countries have developed underwater robots with deep-sea operation capabilities, and applied them to marine science, resource development, military and other fields. In addition, Europe, the United States, Japan, Russia, Australia and other countries have built anchor system submersible observation networks. Among them, the ocean observation network of the United States and Canada is built based on the cable mode, which realizes all-round, multi-scale and cross-temporal dynamic observation of the ocean. Europe's seabed observation network covers the main seas of Europe, and is committed to the development of multidisciplinary (marine physics, marine biology, marine chemistry), multi-objective (marine environmental monitoring, marine resource development, marine disaster early warning), and multi-temporal and spatial scale (from centimeters to kilometers, from seconds to years) ocean observation capabilities to monitor the marine environment, develop marine resources, and warn of marine disasters.
At present, the international deep-sea observation/detection and perception sensors are developing in the direction of higher precision, larger operating water depth, and more subdivision functions. In the field of submersibles, large-depth environment robots have become the mainstream development direction in the future, and scientists from all over the world are constantly striving to improve the intelligence level of submersibles. Deep-sea submersible equipment will focus on high autonomy, large water depth, and long endurance. In order to effectively realize ocean exploration, observation, perception and development, the seabed observation networks of various countries have developed to the goals of larger network range, cross-temporal and spatial scale, all-weather, multi-target, long-term, dynamic and real-time in-situ.
(2) Deep-sea underwater construction equipment
Deep-sea underwater construction equipment is an important support for advanced manufacturing, the integration of information technology and new materials, and marine engineering, with the characteristics of high technology, high input, high output, high added value and high risk. At present, the United States, Europe and other countries and regions are in a leading position in the field of underwater construction equipment, especially in the core design and key supporting of marine engineering equipment.
Deep-sea underwater construction equipment is mainly used for submarine trenching and buried pipes, submarine terrain leveling, dredging, repair and maintenance, etc., to protect submarine optical cables, pipelines, pile foundations and other infrastructure, and has broad application prospects. Typical representatives of deep-sea underwater construction equipment are: ultra-deepwater piling water hammer developed by IQIP in the Netherlands and Menck in Germany, which can achieve a water depth of 2000 m; Royal IHC has developed the world's first four-track submarine trencher, Hi-Traq, which can reach a depth of 1500~3000 m with deep water trenchers from Deep Ocean and IKM Subsea. Deep-sea underwater maintenance and repair equipment mainly includes: deep-sea underwater pipeline and cable maintenance and overhaul equipment, deep-sea underwater welding equipment, and deep-sea underwater salvage equipment. At present, multinational companies in the world's large-scale pipeline services, cable laying and other industries have developed a series of underwater construction robots with special functions, which are widely used in pipelines, cable laying and other construction operations in major offshore oilfields around the world. For example, the HECTOR unmanned underwater robot of the French company SIMEC can adapt to the sea state of 3000 m under the sea; The CMROV cable service robot developed by the British company ACSM can operate in extreme environmental conditions and various submarine soils around the world, with a rated water depth of 2000 m; Seatools is a submarine barracuda diamond wire saw developed by Seatools in Australia, designed for water depths of up to 3000 m.
With the rapid development of information technology, material science, energy technology and other related fields, underwater construction equipment, as the main driving force to promote the development of the marine industry to the deep sea, is accelerating its evolution in the direction of intelligence, integration and far-reaching. These equipment have the ability to operate with high efficiency and high precision, while also having stability and safety. In addition, with the deepening of deep-sea development, the functions required for underwater operations have gradually increased, and special design and manufacturing are required for different operation requirements to meet the complex and changeable characteristics of the deep-sea environment.
(3) Deep-sea underwater oil and gas production systems
The deep-sea underwater oil and gas production system is an important equipment for the development of offshore oil and gas resources, which is responsible for transporting submarine oil and gas to the terminal of the onshore platform. The underwater oil and gas production system is composed of complex modules such as wellhead, Christmas tree, underwater control system, underwater multi-functional manifold and umbilical cable, which can not only collect and transport seabed oil and gas, but also transmit hydraulic and electrical signals and production information, which is the key equipment to realize the efficient exploitation of seabed oil and gas.
In the 50s of the 20th century, the United States began to work on the research and development of underwater oil and gas production systems, and put forward the concept of "underwater wellheads" for the first time; After years of technological evolution, it has developed from the initial reliance on diver operations to the current intelligent all-electronic control system, which has established the United States' technological leadership in the field of underwater Christmas trees. The United Kingdom, Norway and other countries have also paid attention to the research and development of underwater oil and gas production systems, breaking through the key problems of deep-sea oil and gas development technology and equipment, and leading the world's offshore oil and gas exploitation. At present, more than 500 underwater oil and gas production system projects have been successfully put into operation in the world, but the key technical equipment has been monopolized by a few Europe, the United States and other countries and regions, such as ultra-deepwater (>3000 m) underwater Christmas tree products can only be provided by FMC in the United States, Baker Hughes, One Subsea and Axesin in Norway. Underwater umbilical cable is another key technical equipment for oil and gas production systems. At present, enterprises from Europe, North America, Brazil and other countries and regions are the world's leading suppliers of umbilical cables, with mature design and manufacturing capabilities, and a wide range of products to meet different application needs. At present, Norway's SINTEF Ocean and Det Norske Veritas have monopolized the testing and certification technology of umbilical cables, resulting in insufficient competition and high access conditions in the umbilical cable market. Europe, the United States and other countries and regions have accumulated rich experience in equipment design and construction in the development of underwater oil and gas, and have built a relatively complete industrial chain of technology and equipment for underwater oil and gas production systems. Taking deep-sea wellhead complete equipment construction technology as an example, the world's top five oil and gas technical service companies occupy more than 75% of the market share.
With the depletion of onshore and shallow oil and gas resources, oil and gas exploration in deepwater and ultra-deepwater areas is imminent. In the future, deep-sea oil and gas production will place greater emphasis on digital transformation, focusing on remote monitoring, smart sensors, and autonomous operations. In addition, due to the increasing concern about environmental protection and sustainability of deep-sea oil and gas production, deep-sea subsea oil and gas production systems have begun to use more advanced environmental protection technologies to reduce the impact on marine ecosystems and carry out appropriate ecological restoration work at the abandonment stage. Overall, the international deepwater subsea oil and gas production system will move in the direction of deeper water, more digital, greener and more sustainable.
(4) Equipment for the development of deep-sea mineral resources
The deep sea contains abundant reserves of strategic metal resources, including polymetallic nodules, cobalt-rich crusts and polymetallic sulfides, etc., and the reserves of rare metals such as cobalt, manganese and nickel are far greater than those on land. As early as the 70s of the 20th century, the traditional maritime powers have achieved a breakthrough in deep-sea mining technology and equipment, and successfully collected manganese nodules at the bottom of the Pacific Ocean at a depth of 5000 m. Since then, the European Union, Russia, Germany, Japan, South Korea, India and other countries and regions have set up deep-sea mining research projects, gradually breaking through the key technologies of deep-sea mining, assessing the environmental disturbance of deep-sea mining, and carrying out marine experimental research work, improving the technical equipment system, laying the foundation for the commercialization process of deep-sea mining.
After sea trial research, foreign countries have made breakthroughs in the development of deep-sea mineral resources technology and equipment, built a relatively complete technical scheme system, and mastered the key technology research and development and core equipment development capabilities, mainly including: safe walking and efficient collection of seabed ore mining equipment, overall collaborative control of ships-risers-ore collectors, deployment and recovery of deep-water heavy-duty equipment, etc. Europe, the United States, Japan, South Korea and other countries and regions have started early in the development of seabed mining, with a high degree of advanced technology and equipment, and the overall level is 8~10 years ahead of the mainland. In 2021, GSR of Belgium completed a 4500 m water depth trial at the Clarion Clipperton mine in the eastern Pacific Ocean, with a collection efficiency of 110~120 t/h. In 2022, TMC Canada completed the development of a deep-sea mining vehicle and completed a 4,300-meter-level acquisition and lifting test in the NORI-D mining area, with a collection efficiency of 86.4 t/h. The rapid development of enterprises such as TMC in Canada and GSR in Belgium will realize the commercial exploitation of seabed mine resources in recent years.
The development of deep-sea mineral resources is the largest deep-sea operation that can be manipulated by human beings, covering the industrial chain of exploration, mining, metallurgy, transportation, etc., and integrating a comprehensive platform and system equipment system such as submarine operation, underwater transportation, power transmission and distribution, central control and surface support. At present, there is no deep-sea mining system suitable for commercial development in the world, and most of the equipment is still in the development and testing stage. In the future, deep-sea mining equipment still needs to be further developed in the direction of high efficiency and low disturbance.
Fourth, the current situation of the development of underwater technology and equipment in the deep sea of the mainland
(1) Deep-sea observation/detection and perception systems
1. Engineering challenges
The construction of deep-sea observation/detection and perception system can provide technical equipment support for the smooth development of "caring for the ocean, understanding the ocean, and managing the ocean", but it also faces a series of challenges. First, deep-sea observation/detection and perception systems are facing extreme environmental challenges. The deep-sea environment has the characteristics of high pressure, low temperature, darkness and strong corrosiveness, which puts forward extremely high requirements for observation/detection and perception equipment. Second, the high absorption of water makes it difficult to communicate wirelessly in the deep sea, and wired communication is limited by the deep-sea environment, so the development of ultra-long-distance and efficient communication is an important challenge for the deep-sea observation/detection and perception system. Third, long-term observation/exploration in the deep ocean requires a reliable energy supply, and an efficient energy supply system is crucial. Therefore, the further use of ocean energy or the use of high-efficiency battery technology to provide energy for deep-sea observation/detection and perception systems is an urgent problem to be solved. In addition, deep-sea observation/detection and perception systems also need to be supported by precise positioning, durable materials, and intelligence.
2. Key technical system
In recent years, deep-sea observation/detection and perception technology has developed rapidly, providing three-dimensional, long-term, all-weather, real-time and intelligent data feedback for detecting, monitoring and perceiving the deep-sea environment, and promoting the continuous progress of ocean cognition and development. The key technologies involved in promoting the progress of deep-sea observation/detection and perception technology mainly include: intelligent perception and analysis technology for obtaining deep-sea complex environmental data, efficient and safe energy supply technology for intelligent unmanned equipment for energy transmission of deep-sea unmanned underwater vehicles, energy supply technology for deep-sea monitoring instruments and equipment, autonomous navigation and operation technology for underwater unmanned equipment, intelligent collaborative technology for underwater manned and unmanned equipment clusters to achieve collaborative work and cooperation, and underwater sealing technology for protecting equipment and structural integrity. Real-time synchronization technology, functional materials and component processing technology for real-time multi-device coordination and synchronization.
The technical system of deep-sea observation/detection and perception system involves multiple knowledge fields such as acoustics, electromagnetics, optics, fluid mechanics and materials science, which urgently needs to be interdisciplinary and integrated. Acoustics, electromagnetics, and optics are the most commonly used technical principles in the field of deep-sea observation/detection and perception, including the use of sound waves to determine seabed topography, underwater objects and marine life, the use of electromagnetic induction and electromagnetic scattering to detect metal objects, magnetic materials and geological structures, and the use of optical sensors to capture image information and achieve high-speed data transmission. The key to solving the challenges faced by deep-sea observation/detection and perception technology is to establish a high-precision and all-round multi-modal information fusion framework based on the coupling principle of acoustics, optics and electromagnetics and improve the level of intelligence. The interaction between deep-sea fluids and observation/detection and perception systems is also one of the key scientific issues in this field, and it is urgent to clarify the hydrodynamic (e.g., eddy) characteristics of deep-sea environments to guide and adjust the deployment decisions of underwater equipment attitude and path. At the same time, the mechanical response mechanism and durability of deep-sea equipment in high-pressure and corrosive environments are the basic considerations for the structural design and strength analysis of deep-sea observation/detection and perception systems to ensure that the equipment has sufficient strength and safety stability in deep-sea environments.
3. Typical equipment representatives
At present, the mainland's ocean observation/detection and perception system is in the "catch-up" stage as a whole, mainly used in shallow seas, among which there is still a certain gap between deep-sea observation sensors and developed ocean countries in terms of intelligent real-time response, lightweight design, and functional materials. From the 70s to the 90s of the 20th century, the National Ocean Technology Center, the Institute of Acoustics of the Chinese Academy of Sciences, the Institute of Ocean Instrumentation of the Shandong Academy of Sciences and other scientific research institutions have successively developed 1000 m and 3000 m self-contained CTDs through joint research, with leading performance and close to the international advanced level. Since then, the mainland CTD sensor technology has developed rapidly, and a number of new CTD sensors and instruments have been developed, which have filled the gap of domestic related technology and equipment, broken the international monopoly of related technologies, and provided strong support for the mainland's marine scientific research and marine resource development. At present, the representative deep-sea observation/detection and perception systems in mainland China are: (1) the high-temperature Raman spectroscopy probe developed by the Institute of Oceanology of the Chinese Academy of Sciences, which is the first Raman spectroscopy probe in the world that can be directly inserted into a 450 °C deep-sea hydrothermal vent; (2) The State Key Laboratory of Sensing Technology and the Institute of Deep-Sea Science and Engineering, Chinese Academy of Sciences, have successfully developed the first set of microelectromechanical system (MEMS) gas chromatograph applied to the deep sea in mainland China, which can obtain in-situ quantitative test data of carbon dioxide in the deep-sea background area and carbon dioxide and methane in the cold seep area; (3) The Institute of Geology and Geophysics of the Chinese Academy of Sciences has made a series of major breakthroughs in the field of submarine seismographs, and has achieved leapfrog development from scratch, from "following" to "running and leading"; (4) Shandong University has studied a new seabed static cone penetration and sampling system, which has realized multi-parameter in-situ testing and low-disturbance sampling of 3000-meter-level deep-sea seabed sediments. Figure 2 shows the representative sensor and instrument maps of the continental observation/detection and perception system.
In recent years, driven by the strategy of maritime power, the continental marine technology and equipment have achieved rapid development, and the observation/detection and perception system has gradually escaped the technological blockade of the developed maritime countries. Since the "Twelfth Five-Year Plan" period, the mainland has strengthened its investment and support for key deep-sea technologies and equipment, and has made a series of breakthroughs in the field of deep-sea science and technology, such as the "Jiaolong" manned submersible, the "Deep Sea Warrior" manned submersible, the "Struggler" manned submersible, the "Haiyi" underwater glider, and the "Haidou-1" all-sea deep-sea unmanned submersible. The localization process of deep-sea observation/detection and perception system shows that the mainland's deep-sea resource development strength is steadily increasing, and key core technologies and equipment continue to make breakthroughs.
Fig.2 Map of representative technical equipment for deep-sea observation/detection and perception systems
(2) Equipment for underwater construction operations
1. Engineering challenges
With the increasing attention to marine resources and deep-sea development, there is a growing international demand for deep-water, diversified, refined and intelligent technologies for safe construction operations in deep-sea waters. In this context, underwater construction equipment is facing severe challenges in terms of accurate navigation and positioning, equipment sealing and compression resistance, and efficient power system. Further ensuring the stable performance of underwater construction equipment, reducing the failure rate, and strengthening the effective maintenance and maintenance of equipment have become the key issues to maintain the reliability and high efficiency of underwater equipment; At the same time, there is an urgent need to develop more advanced communication equipment and control systems to ensure the effectiveness of real-time monitoring and control. In addition, while underwater construction, it is necessary to pay attention to the protection of the deep-sea environment, such as reducing noise and light pollution, reducing the disturbance of seabed sediments, etc., so as to avoid harm to organisms and reduce the damage to the seabed ecology, which has become an important problem faced by the current deep-sea underwater construction operations.
2. Key technical system
Underwater construction equipment is an important support for marine engineering, and plays an important role in offshore oil exploitation, submarine pipeline laying, and underwater facility construction. The key technologies mainly include: special material manufacturing and processing technology for deep-water equipment manufacturing, underwater hydraulic technology for control and power transmission of deep-water equipment, intelligent electrification technology for efficient, safe and reliable operation of deep-water equipment, adaptive adjustment and control technology for stability and performance optimization of marine equipment, lightweight design technology, and deep-sea power supply technology. Sealing and pressure-resistant technology to maintain effective sealing and resist high pressure, integrated intelligent control technology to realize automated, intelligent and collaborative operation of equipment.
The key physical and mechanical principles include: deep-water corrosion-fatigue coupling mechanism and low-temperature embrittlement mechanism in complex environment, high-pressure liquid dynamic transmission mechanism, electromagnetic compatibility and electromagnetic interference coupling mechanism, hydrodynamic effect and structural dynamics theory, structural mechanics and topology optimization theory, Internet of Things and intelligent control algorithms, etc. In short, underwater construction equipment is a complex system engineering, which needs to comprehensively consider factors such as underwater operation environment, platform design, perception control, human-computer interaction, energy communication, safety and reliability, so as to realize the intelligent, automated and safe development of underwater construction operations.
3. Typical equipment representatives
The underwater operation environment is harsh and requires the use of customized equipment for operation, and underwater construction equipment has become an important part of the field of marine engineering. In 2023, the mainland independently developed the first 2,500-meter-class ultra-deepwater piling hammer and successfully completed sea trials, filling the technical gap of the core equipment of ultra-deepwater piling in China. China National Offshore Oil Corporation (CNOOC) pioneered domestic deepwater surface synthetic diamond (PDC) jet drilling technology in the eastern South China Sea oilfield, setting a new record for the domestic deepwater surface mechanical penetration rate. At present, the mainland's offshore drilling technology and operational capacity have entered the "ultra-deepwater era", and the level of deepwater drilling technology is gradually in line with international standards.
Continental started late in the research and development of deep-sea underwater trencher equipment. In 2018, China National Offshore Oil Corporation (CNOOC) introduced the first large-scale trencher VMP500 deep-water submarine pipeline plow-type trencher in mainland China, and led the implementation of the first deep-water plough trencher sea trial operation, filling the technical gap in related fields in mainland China. In addition, in 2018, CRRC Aisendi Marine Equipment Co., Ltd. successively released 6,000-meter-level deep-sea exploration and production robots, 3,000-meter-level deep-sea pipe and cable trenchers, 2,000-meter-level cable laying plows and other complete equipment.
In recent years, the mainland underwater caisson has developed rapidly. CCCC First Harbor Engineering Bureau Co., Ltd. built a sand-filled semi-circular caisson hybrid embankment with a length of 10.88 km and prefabricated and installed 544 semi-circular caissons in the deep-water channel treatment project of the Yangtze River Estuary. Jointly developed by CCCC First Harbor Engineering Bureau Co., Ltd. and Shanghai Zhenhua Heavy Industry Co., Ltd., the "Yihang Jinping 2" is the world's largest and most advanced self-elevating gravel laying leveling ship, consolidating the world's leading position in the field of undersea tunnel foundation construction. The Third Engineering Company of CCCC Fourth Harbor Bureau has independently developed a lightweight hydraulic underwater stone paving and leveling machine, which has become a representative of lightweight leveling machine. The mainland has also been working hard to develop deep-water dredging and dredging equipment, such as CCCC Guangzhou Waterway Bureau Co., Ltd., which independently transformed and built the first special dredging vessel "Jielong" in China, which solved the technical problem of high dredging intensity of the Shenzhen-Zhongshan Corridor project. Figure 3 shows the map of representative technical equipment for underwater construction operations in China.
Fig.3 Map of representative technical equipment for underwater construction operations in mainland China
(3) Deep-sea underwater oil and gas production systems
1. Engineering challenges
Deep-sea oil and gas extraction refers to the exploitation of oil and gas in waters with water depths of more than 500 m. In recent years, due to the depletion of onshore oil and gas resources, deep-sea oil and gas exploration has become an important energy strategy. Deep-sea underwater oil and gas exploitation faces many problems and engineering challenges, such as "entering the ground and going to the sea", which are mainly reflected in the safe operation of deep-sea oil and gas exploitation technology and equipment, and environmental protection. At the technical level, deepwater drilling differs from onshore and shallow sea drilling in that it requires floating work platforms, subsea wellheads, and self-matching production and manifold systems. This not only increases the potential risks of deepwater oil and gas extraction operations, but also increases the complexity of the technical system and the cost of engineering construction. At the level of safe operation, extreme environmental conditions such as high pressure and low temperature in the deep sea have put forward extremely high requirements for the underwater oil and gas production system, which requires material research and development, equipment design and construction, overhaul and maintenance to adapt to the deep-sea environment. The safety management of the production system and the ability to respond to sudden accidents are also top priorities. At the level of environmental protection, deep-sea oil and gas exploitation has a certain impact on the marine ecosystem, including destroying benthic habitats, reducing biodiversity, and hindering biological migration pathways. At the same time, there is a risk of crude oil leakage in deep-sea oil and gas extraction, and once a leak occurs, it will pose a serious threat to the marine ecosystem.
2. Key technical system
In view of the particularity of the deep-sea environment, the future development of subsea oil and gas production system development technology will pay more attention to the breakthrough of deep-sea engineering technology, including more advanced deep-sea equipment and tools, and more effective seabed infrastructure construction. Among them, the rapid development of digital transformation and intelligent technology will continue to promote the development of deepwater subsea oil and gas production systems in terms of intelligence, efficiency and safe production. The key technologies of the deep-sea oil and gas production system mainly include: deep-water and ultra-deepwater underwater oil production technology for kilometer-level deep-sea oil and gas production, intelligent technology of the underwater production system for real-time monitoring and diagnosis of underwater control system, underwater manifold, underwater connector failure, and timely fault alarm, underwater sensing technology for monitoring a series of important parameters such as pressure, temperature, and flow rate in oil and gas field production operations, underwater oil and gas pressurization system for maintaining high transmission pressure and flow rate and realizing long-distance transportation, and underwater oil and gas pressurization system for high-precision, Precision component processing and manufacturing technology for high-quality and high-efficiency parts processing, acquisition and docking control technology for accurate acquisition and connection between two objects in the marine field, hot oil pipeline flow guarantee technology used to solve the flow blockage in deep-sea oil and gas fields during exploitation, and underwater oil and gas treatment technology for obtaining longer drilling range and better drilling effect in oil and gas exploration and production. The maturity and development of oil and gas production technology is closely related to the development of multiphase flow motion theory, long-distance signal transmission and processing theory, underwater robot control mechanics, anti-corrosion material chemistry, multiphysics coupling theory, bubble dynamics, gas-liquid-solid interaction dynamics, etc. A deep understanding and application of these physical and mechanical mechanisms can improve the efficiency of exploration, development, and production of deepwater subsea oil and gas production, while reducing production risks.
3. Typical equipment representatives
The mainland's research in the field of deep-sea underwater oil and gas production systems started relatively late. The relevant preliminary research focuses on the shallow sea within 300 m, which leads to a large gap between the deep-sea oil and gas production technology in the mainland and the international level. In 2021, the first set of underwater Christmas tree system independently developed by the mainland was successfully installed and tested on the seabed of the Bohai Oilfield, marking the leapfrog development of the localization of underwater oil and gas production equipment. In 2022, the subsea oil and gas production system independently developed by the mainland was put into use in the Ledong block in the southeast area of the Dongfang 1-1 gas field in the South China Sea, further improving the localization level of subsea oil and gas production equipment. In 2023, CNOOC's Enping 15-1 platform, located in the Pearl River Estuary Basin of the South China Sea, was equipped with the mainland's first offshore carbon dioxide storage device and officially started the drilling operation of carbon dioxide reinjection wells. The core components of the equipment include carbon dioxide compressor skids, molecular sieves, coolers, etc.
Underwater umbilical cable is a key component in the offshore oil and gas development equipment system. The mainland has actively carried out core technology research on underwater umbilical cables, strengthened independent research and development, alleviated the situation of being controlled by others, and ensured the strategic security of offshore oil and gas development. In 2010, CNOOC Research Institute Co., Ltd. successfully prepared a first sample of umbilical cable, marking a breakthrough in the field of umbilical cable manufacturing in China. Qingdao Dimar Offshore Engineering Co., Ltd. and Qingdao Han Cable Co., Ltd. have successfully developed a dynamic umbilical cable, which can withstand a water depth of 3000 m and a pressure of 69 MPa. In 2018, Shanghai Hengtong Marine Equipment Co., Ltd. produced the world's first 18.15 km long, unjointed 500 kV ultra-high voltage submarine cable, which is the longest single unjointed ultra-high voltage submarine cable in mainland China. Zhongtian Technology Submarine Cable Co., Ltd. has developed a steel tubular photoelectro-hydraulic composite umbilical cable for underwater production system, and the whole process of sample trial production and testing has passed the certification of Det Norske Veritas.
The research and development of functional high-end products such as underwater multiphase flowmeters, underwater nozzle connectors, underwater insulation materials, underwater multi-functional hydraulic quick connectors, ultra-deep underwater equipment seals, and anti-corrosion materials for shallow cement surface systems of the underwater oil and gas production system in mainland China are still weak. In recent years, the mainland underwater oil and gas production system has made great progress, but the level of autonomy of some equipment needs to be improved urgently, and there are still some challenges: it has not yet fully owned the independent intellectual property rights of key technologies and equipment of the underwater oil and gas production system, and some technologies are highly dependent on foreign countries (such as oil and gas system installation, maintenance, deepwater positioning, etc.). Figure 4 shows the map of some key technologies and equipment of the continental underwater oil and gas production system.
Fig.4 Map of key technologies and equipment for underwater oil and gas production in mainland China
(4) Equipment for the development of deep-sea mineral resources
1. Engineering challenges
The deep sea contains abundant mineral resources, and its precise exploration and rational development will drive the development of related industries and create new economic growth points. Deep-sea mineral resources are located in a special location, and there are many challenges in resource exploration, development and utilization, such as polymetallic nodules distributed on the ocean floor surface of 4000~6000 m. (1) The high-pressure, low-temperature, dark and corrosive environment at the bottom of the deep sea poses a severe test to the exploration and exploitation of deep-sea mineral resources, as well as the design of materials and structures. Taking deep-sea resource exploration as an example, the current acoustic positioning accuracy and transmission rate are difficult to meet the exploration needs of massive data fusion analysis and real-time collaboration of large clusters. (2) Different mineral resources require different mining methods, such as hydraulic mining for polymetallic nodules, and mechanical mining for cobalt-rich crusts; One of the challenges of commercial deep-sea mining is to further develop an efficient ore collection system, optimize the mining process, and improve the collection efficiency of different minerals while ensuring operating costs. (3) To a certain extent, deep-sea mining activities will disturb seabed sediments, damage seabed topography, affect the habitat environment of benthic organisms, increase seawater turbidity, release seabed heavy metals, and produce noise pollution. The environmental impact of deep-sea mining is the focus of international attention, and the key to the exploitation of seabed mineral resources is to deal with the relationship between seabed environmental protection and seabed mineral resource exploitation.
2. Key technical system
For the commercial exploitation of deep-sea mineral resources, the current requirements for equipment stability, reliability, monitoring and early warning, and emergency treatment need to be further improved, and in-depth research and verification are still needed in many aspects such as technical scheme formulation, key equipment research and development, system reliability testing, environmental impact and restoration research. The key technologies for the development of deep-sea mineral resources mainly include: intelligent multi-mining vehicle distributed cooperative operation control technology for cooperative operation control of multiple mining vehicles in deep-sea environment, mining truck operation extreme working condition forecasting and monitoring technology for predicting and monitoring the operation of mining trucks under extreme working conditions, underwater positioning and navigation technology for determining location and navigation in the underwater environment, and intelligent, safe, stable and autonomous walking technology for mining vehicles to realize intelligent walking, safe operation and stable control of vehicles in deep-sea environment. The automatic control technology of the underwater motion attitude of the mining vehicle is used to realize the stable movement and precise control of the vehicle, the low-disturbance acquisition technology of polymetallic nodules used to reduce the disturbance to the marine environment and improve the efficiency of ore collection, the deep-water high-power hydraulic control technology used to provide high-power hydraulic pressure in the deep-water environment, the deep-water high-voltage power energy supply technology used to provide high-voltage power in the deep-water environment, the automatic control technology used to recover the attitude of underwater equipment deployment, and the in-situ high-fidelity survey and sampling technology used for deep-sea resource exploration. The deep-sea mining technology system involves a variety of physical theories and mechanical mechanisms, including multi-body dynamics and cooperative control theory, surface driving mechanics and predictive control theory, multi-sensor information integration processing mechanism, vehicle system control theory, jet-thin soft soil coupling mechanism, hydraulic mechanics and hydraulic circuit energy conversion mechanism, multi-system cross-scale coupling dynamics and system control, etc. The understanding and application of these theories and mechanisms can help to optimize the design and implementation of deep-sea mining activities and enhance the protection of the marine environment.
3. Typical equipment representatives
The development equipment of deep-sea mineral resources (such as polymetallic nodules, cobalt-rich crusts, and polymetallic sulfides) is the largest equipment system in marine engineering. After years of development, in 2017, Continental developed a 400-meter-class cobalt-rich ore mining test vehicle, which can monitor the occurrence of cobalt-rich ore online in real time, obtain the thickness of the prospecting layer and adjust the cutting and crushing amount of the mining head. In 2018, the Kunlong submarine mining vehicle, led by the Changsha Institute of Mining and Metallurgy of China Minmetals, successfully completed a 500-meter-level sea trial, with an underwater positioning accuracy of 0.72 m, achieving a milestone breakthrough in the field of deep-sea mining in mainland China. In 2021, the team of Shanghai Jiao Tong University successfully developed the prototype of deep-sea heavy-duty mining equipment "Kintor No. 1", which has the capabilities of seabed operation environment perception, intelligent autonomous control, and efficient hydraulic ore collection. The successful sea trial of the prototype of the "Kin Kai Kai No. 1" deep-sea heavy-duty mining equipment marks an important step in the research and development of deep-sea heavy-duty mining vehicles towards engineering and intelligence, and is gradually approaching the world's advanced level. In 2022, Beijing Pioneer High-tech Development Co., Ltd., together with Shanghai Jiao Tong University and other units, developed a new concept of deep-sea polymetallic nodule in-situ ore gathering technology verification platform "Manta", which adopted the original floating marching ore gathering technology scheme. In 2023, China State Shipbuilding Corporation (CSSC) has developed a prototype of a heavy-duty four-track independent suspension walking system suitable for deep-sea sulfide mining, which significantly improves the walking speed of ore collection trucks in complex deep-water terrain. Figure 5 shows the representative technical equipment map of deep-sea mineral resource development.
Fig.5 Map of representative technologies and equipment for the development of deep-sea mineral resources in mainland China
(5) Common key technologies in deep sea water
Deep-sea underwater generic technologies refer to general technologies in the deep-sea underwater environment, covering engineering, scientific research, resource development and other fields. Due to the complexity of the deep-sea underwater technology system and the interdependence of various technologies, this paper condenses the common technology system of deep-sea water, and summarizes the common key technologies that hinder the development of deep-sea equipment and need to be prioritized, including: intelligent and automation technology, multi-mechanism underwater high-precision positioning and high-speed communication technology, lightweight design technology, underwater positioning and navigation technology, deep-sea power supply technology, underwater hydraulic technology, underwater sealing technology, precision component processing and manufacturing technology, corrosion control technology, Underwater target detection and positioning technology, marine monitoring and control technology, human-computer interaction technology, large system mechanical calculation and analysis technology, cross-scale engineering design methods and technologies, etc.
5. Problems and development suggestions for underwater technology and equipment in the deep sea of the mainland
(1) Problems faced
1. Insufficient core technology limitations and innovation capabilities
First, some of the key equipment and core technologies in the mainland's deep-sea underwater technology and equipment are subject to the problem of being controlled by others and being blocked by the international community. Mainland underwater equipment manufacturing enterprises are facing the problem of "stuck neck" of core components, such as the R&D and manufacturing technology of high-performance control systems for submarine operation equipment; The blockade of core technologies has further hindered the research and development of peripheral supporting and downstream connection technologies and product manufacturing, such as deep-water navigation and positioning and integrated control systems. Second, there is a certain gap between the product accuracy and reliability of domestic deep-sea underwater technology and equipment and the international advanced level. Due to the relative weakness of basic research and the limitation of general technical level, the application effect or durability of mainland underwater equipment materials and parts are not good. Among them, there is a large gap between the main performance indicators of kilometer-level watertight connectors produced in mainland China and foreign products, such as the design service life of domestic deep-sea equipment coatings is 5~6 years, and the international high-end products of the same kind can reach 8 years.
2. The misalignment of narrow market space and huge demand potential coexists
First, the existing market space for deep-sea underwater technology and equipment in the mainland is relatively narrow. At present, the operation capacity, high-end manufacturing capacity and intelligent level of deep-water equipment in the mainland are gradually improving, but foreign related equipment manufacturers occupy the deep-sea underwater technology and equipment market in the mainland by virtue of their strong technical strength and market influence, such as deep-sea underwater wellhead system, underwater Christmas tree, etc. Second, the demand for deep-sea underwater technology and equipment has huge potential. In recent years, the Nord Stream submarine pipeline incident, Japan's nuclear wastewater discharge incident, and the South China Sea rights and interests dispute have highlighted the importance of the development of deep-sea underwater technology and equipment industry. Deep diving exploration, deep-sea archaeology, sightseeing and tourism provide new development space for the underwater development technology and equipment market; To further promote the construction of the "Belt and Road", the support of large-scale and high-quality underwater engineering technology and equipment is urgently needed.
3. Lack of high-end platforms and lack of professional talents
The field of deep-sea equipment in mainland China involves a number of key platforms, such as the State Key Laboratory of Deep-sea Manned Equipment, the State Key Laboratory of Efficient Offshore Oil Development, and the State Key Laboratory of Deep-sea Mineral Resources Development and Utilization Technology. However, these platforms belong to different industries, lack of closer collaborative division of labor, especially the lack of national high-end professional platforms, resulting in product development to be customized, production enterprises are small and scattered, and it is difficult to form an industrial scale and achieve market-oriented production. At the same time, there is a shortage of professionals in the field of deep-sea underwater technology and equipment in the mainland, although there are a certain number of professionals in related fields, but due to the lack of collaboration between platforms, the exchange and cooperation of talents are restricted, which further restricts the development of the industry.
(2) Development suggestions
1. Strengthen the top-level design of the development of deep-sea underwater engineering technology, and promote the construction of a common key technology cooperation system
Focus on the key areas and main directions of the development of the deep-sea underwater engineering technology and equipment industry in the future, adhere to the deep-sea-deep space integration model of underwater engineering technology and equipment, form a deep-sea underwater engineering technology and equipment innovation alliance supported by the state, and organize and build a cross-border, cross-field and interdisciplinary innovation cooperation model; With innovation as the core and Chinese characteristics as the main line, we will work together to compile a map of deep-sea underwater engineering technology and equipment; Aiming at the strategic goal of becoming a national maritime power, we will promote the construction of major marine projects, and actively lay out the construction of common technology platforms in high-precision and cutting-edge fields of the deep-sea underwater engineering industry; Accelerate the convergence of high-end innovation elements, continuously connect the chain of "production, education, research and application", and promote the construction of a multi-level, wide-field, functional, and open new common technology collaboration support system.
2. Enhance the industry influence of the mainland's deep-sea underwater technical specifications and standards, and vigorously explore the international market
It is recommended to organize domestic scientific research institutes and institutions of higher learning in the field of marine science to speed up the construction of deep-sea underwater engineering technology systems and standards. Focus on building innovative R&D bases and demonstration projects, enhance the influence of the mainland in the field of deep-sea underwater engineering, achieve breakthroughs in the formulation of international standards and specifications for underwater engineering instruments and equipment, and enhance the mainland's international voice in the field of underwater technology. Plan and promote the "going out" of the mainland's deep-sea underwater engineering technology and equipment industry, and encourage relevant equipment, software, standards and solutions to actively solve international engineering problems. Relying on the policy of opening up to the outside world, strengthen international cooperation and exchanges, broaden the field of cooperation, expand and strengthen the industrial system and industrial cluster of deep-sea underwater engineering technology and equipment, and enhance the international market competitiveness of deep-sea underwater engineering technology and equipment in the mainland.
3. Promote the construction of a compatible and universal platform with high quality
Aiming at the actual needs of the mainland's deep-sea technology and equipment innovation and development, we will build a compatible and universal deep-sea underwater engineering equipment construction platform. It is suggested that the competent departments of the industry should actively promote and carry out special docking activities between schools and enterprises, break through barriers to technology transformation, and establish an efficient channel for school-enterprise cooperation. Regularly conduct a thorough investigation of the "stuck neck" technology encountered in the research and development process of equipment in various fields of deep-sea underwater engineering, deeply learn the physical principles and mechanical mechanisms behind the "stuck neck" technology, break through the key common technical bottlenecks restricting the development of deep-sea underwater engineering equipment, and promote the continuous update of technical equipment.
4. Pay attention to cultivating scientific and technological innovation talents in deep-sea underwater engineering
Focusing on the multidisciplinary characteristics of the field of deep-sea underwater engineering technology and equipment, combined with the curriculum system of civil, mechanical, automation, information, materials and other disciplines, establish and improve the innovative compound talent training system of deep-sea underwater engineering technology and equipment. Strengthen the in-depth cooperation between universities and enterprises, innovate the talent training model, and solve the problem of disconnection between knowledge and practice in the traditional school-enterprise connection mode. Strengthen the efforts of enterprises to provide practical cases, technical support and practical opportunities for the talent training process, realize the seamless connection between universities and enterprises in talent training, cultivate talents with interdisciplinary knowledge, vision and professional skills, and continuously meet the demand for engineering science and technology innovation talents in the field of deep-sea underwater engineering.
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About the Author
Li Huajun
He is an expert in marine engineering safety and an academician of the Chinese Academy of Engineering.
He is mainly engaged in the research of marine engineering safety analysis and design, construction and operation and maintenance technology.
Note: The paper reflects the progress of research results and does not represent the views of Chinese Journal of Engineering Science.