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28 October 2024, Volume 11 Issue 3 Previous Issue   

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Numerical Study on Local Scour at Composite Piles with Collars in Uniform Flows WANG Hui, DU Dengxuan, LIU Haichao, YU Guoliang, ZHANG Minxi 2024, 11 (3):  1-9.  DOI: 10.12087/oeet.2095-7297.2024.03.01 Abstract ( 58 )   PDF (14824KB) ( 30 )   Local scour at piles poses a significant threat to the safety of offshore wind power and sea-crossing bridges. Addressing the issue of reducing scour depth is an urgent and pivotal challenge that requires immediate attention. The collar is a disk-like structure that reduces the scour depth by weakening the hydrodynamics around the pile. In this study, numerical experiments on the local scour at composite piles with different collars were conducted. The influence of collar layout position, thickness, width, and attack angle on local flow field, bed shear stress, and scour protection effect were discussed. The results show that the position, width, and attack angle of the collar exert a significant influence on local scour, whereas the thickness of the collar has a negligible impact on its effectiveness in scour protection. The larger the collar width and the negative value of the attack angle, the better the scour protection effect. When the collar is set at the edge of the pile cap foundation, with a width ranging from 1～1.5 times the height of the pile cap foundation and an attack angle of -45°, its scour protection effect on the composite pile is the best. The results can provide references for engineering design of pile foundation scour protection. Related Articles | Metrics

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The Research on the Selection of Anchor Cable Layout for Submerged Floating Tunnels WANG Jinduo, JI Chong, LI Xin, ZHANG Xiantao 2024, 11 (3):  10-17.  DOI: 10.12087/oeet.2095-7297.2024.03.02 Abstract ( 53 )   PDF (1894KB) ( 14 )   Submerged floating tunnels(SFTs) are a new type of transportation structure used to cross deep water. To ensure the dynamic stability of SFTs under wave and current loading, an appropriate mooring system is required. This research focuses on submerged floating tunnels with anchor cables and investigates the impact of different anchor cable layouts on the dynamic response of SFTs. Utilizing OrcaFlex software, finite element models are established to analyze the stiffness of mooring systems under both vertical and inclined layouts. The variations in tunnel displacement, acceleration, and anchor cable tension under regular waves and uniform currents are examined. The results show that the inclined anchor cable layout with an inclination angle of 45° and an installation angle of 45° can effectively suppress the vertical and lateral motion response of the tunnel, ensuring structural stability and preventing anchor cable fatigue damage. Furthermore, this layout is applicable to SFTs of different lengths. Related Articles | Metrics

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Analysis of the Characteristics of Offshore Wind Power Operation and Maintenance Technologies and Strategies YU Xichong1, LIU Chao1, LIU Xiaoyan1, LI Zhichuan2, WU Yufei1 LI Ouping1 2024, 11 (3):  18-21.  DOI: 10.12087/oeet.2095-7297.2024.03.03 Abstract ( 80 )   PDF (1382KB) ( 30 )   Based on the characteristics of offshore wind power operation and maintenance in China, this paper analyzes the current situation and development trend of offshore wind power operation and maintenance technology and equipment in China. Taking an offshore wind farm in the South China Sea as a research scenario, this paper proposes a vibration monitoring scheme for offshore wind turbine system, an offshore wind turbine boarding scheme, an offshore wind turbine maintenance and operation and maintenance scheme, and an offshore wind farm inspection scheme, which puts forward guiding significance for the operation and maintenance of offshore wind farms in China. Related Articles | Metrics

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Structural Design and Strength Check of Lunar Pool Centralizer of Ocean Drilling Vessel Under Complex Working Conditions ZHANG Tianwei1, 2, PANG Zhaoyu1, 2, ZHAO Yuhang3, DAI Shenghui3 2024, 11 (3):  22-30.  DOI: 10.12087/oeet.2095-7297.2024.03.04 Abstract ( 42 )   PDF (9407KB) ( 7 )   Shallow gas geological disasters are very easy to induce shallow drilling accidents, which seriously affect the safety of deep water drilling operations. For some shallow gas reservoirs, active blowout of shallow gas through drilling pilot holes can provide guarantee for deep water economic and efficient drilling. Based on the multiphase flow surface tracking technology and turbulence model, a finite element numerical model of deep-water shallow gas active blowout is constructed. The model considers the influence of the size of the blowout channel and the physical properties of the shallow gas reservoir on the blowout process, which can more accurately simulate the whole process of shallow gas blowout. The simulation results show that the initial gas reservoir pressure increases from 20.2MPa to 20.8MPa, and the shallow gas blowout efficiency increases from 75.4% to 84.9%. The size of the guide hole is increased from 812″ to 1214″, and the release degree of shallow gas is increased from 80.9% to 90.7%. The simulation results are in good agreement with the actual observation data, and the error of the calculated value of the maximum escape height is 2.5%. The research results provide theoretical guidance for similar shallow gas active blowout projects in deep water drilling operations in the future. Related Articles | Metrics

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Experimental Analysis of Dropping Motion Characteristics of Hall Anchor in Water SUN Yongqiang, LI Ruibin, WANG Wenkai, FAN Lianming 2024, 11 (3):  31-35.  DOI: 10.12087/oeet.2095-7297.2024.03.05 Abstract ( 44 )   PDF (2808KB) ( 9 )   The settlement characteristics of anchor in water, such as drag coefficient, equilibrium depth and equilibrium velocity, are of great significance to the calculation of anchorage force, the analysis of ship stability and the design of buried depth of submarine pipe and cable. In this paper, an empirical formula for calculating the drag coefficient of the Hall anchor when it falls freely in water is proposed through theoretical analysis and physical model test. The results show that it has an exponential function relationship with water depth and anchor mass. For the anchors of representative ship types corresponding to different channels, the minimum equilibrium depth is greater than the channel depth, and the actual touchdown velocity in the channel will be less than the equilibrium velocity. Related Articles | Metrics

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China‘s First DP-3 Closed Ring Power System Design of Engineer Ship XU Aijin, XU Weiping, HAN Xuyan 2024, 11 (3):  36-41.  DOI: 10.12087/oeet.2095-7297.2024.03.06 Abstract ( 40 )   PDF (4502KB) ( 13 )   In response to a leading vessel design requirement that cooperating DP-3 closed ring power system, this paper introduce an optimize design of a new deep-water diving support vessel of Shanghai Salvage Bureau from the analysis of the thruster configuration, electric load balance and single line diagram, combined with the DP capability assessment. Then, we divide the overall structure and equipment redundancy grouping of the vessel’s closed ring power station on account of “three-engine rooms, four-DP zones” design. Meanwhile, this paper discusses the design of dual feeding power supply for a special separated switchboard and the protection logic during closed ring operation. Related Articles | Metrics

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3D Enhanced Imaging Technology for Offshore Wind Power Pile Foundation HU Guofeng, DOU Qiwei 2024, 11 (3):  42-48.  DOI: 10.12087/oeet.2095-7297.2024.03.07 Abstract ( 30 )   PDF (6247KB) ( 18 )   The detection of offshore wind power pile foundation by image sonar is an important means for the healthy operation and maintenance of offshore wind farms. In response to the significant issues of coarseness and discreteness in imaging caused by the sparsity of 3D imaging sonar data, image processing techniques such as SOR filtering and Poisson surface reconstruction are applied to optimize the 3D imaging of Echo Scope sonar. The method involves detecting and removing outliers based on local area definition, statistical information calculation, and threshold selection. By dividing the spatial grid and solving the Poisson equation to extract isosurfaces, the method reconstructs surfaces from discrete data, achieving refined monitoring of underwater pile foundations. Experimental results show that this technique can enhance the density and smoothness of sonar imaging of underwater pile foundations. The integration of elevation information with enhanced display technology differentiates visual ambiguities and significantly improves imaging results. Related Articles | Metrics

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Research on the Factory Acceptance Test of Subsea Control Module in Deepwater Oil and Gas Field ZHANG Jie, LONG Xiaopin, DENG Chiyu, LI Jing, MENG Zhiwei 2024, 11 (3):  49-56.  DOI: 10.12087/oeet.2095-7297.2024.03.08 Abstract ( 35 )   PDF (854KB) ( 10 )   As a core part of subsea production system in oil and gas field, SCM (subsea control module) is complex in design, difficult and expensive for maintenance. The failure of an SCM can cause interruption of production. It‘s essential to perform the function and performance test once manufactured and prior to delivery. Currently, there is hardly any research on the SCM FAT (factory acceptance test) on the basis of literature review. The SCM FAT includes hydraulic functional test and electric-control system test ect. Researched and concluded in this paper is based on the real experience of the deepwater gas field development project. This paper can be used as a guide for SCM for deepwater oil & gas field development project in China Sea in the future. Related Articles | Metrics

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Research on Development and Adaptability of Subsea Compressor Boosting Technology MENG Yao, HOU Guangxin, LIU Weibin, LIU Yongfei 2024, 11 (3):  57-62.  DOI: 10.12087/oeet.2095-7297.2024.03.09 Abstract ( 34 )   PDF (3494KB) ( 8 )   The wellhead pressure of the subsea trees could be reduced dramatically by using subsea compressor technology, thereby increasing the production of the target gas field and achieving better economic benefits. The subsea compressor boosting technology has been increasingly valued and favored by domestic and foreign oil companies in recent years. This paper study on the development of the subsea compressor boosting technology and compare the technology roadmap of different subsea compressor to determine better solution for projects in Nanhai Sea in order to provide reference for future potential subsea compressor boosting project. Related Articles | Metrics

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The Design and Application of Step-by-step Retractable Beam System in Monopile Installation GUO Xiaoliang1, ZHANG Xiaodong2, ZHANG Mingming2, TANG Yong2, CUI Wentao1, CHEN Chong1 2024, 11 (3):  63-68.  DOI: 10.12087/oeet.2095-7297.2024.03.10 Abstract ( 28 )   PDF (5101KB) ( 6 )   In this paper, starting from the existing problems in the pile holding system of monopile holding equipment, the small stroke problem of the thrust cylinder is successfully solved through the design of the first generation step-by-step retractable beam system. Through the design of the second generation step-by-step retractable beam system, the composition of the first generation system is simplified, and the problem of thrust cylinder direct contact with the monopile is solved, which fundamentally solves the problem of possible damage of the thrust cylinder, and greatly improves the reliability of the system. Finally, the successful application of the step-by-step retractable beam system in practical engineering further verifies the reliability of the design. Related Articles | Metrics

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Overview of the Development of Flexible Ocean CTD Sensors LI Jihao1, LIN Guanying2, WANG Nuansheng3, LI Yang3, LI Junyang1 2024, 11 (3):  69-77.  DOI: 10.12087/oeet.2095-7297.2024.03.11 Abstract ( 141 )   PDF (5779KB) ( 17 )   Marine hydrological information plays a significant role in development and exploration of marine resources. Temperature, salinity and depth are fundamental elements of marine hydrology. Monitoring of marine temperature, salinity and depth data plays an important role in the development and utilization of marine resources. The conductivity temperature depth profiler (CTD) is the main instrument for observing seawater temperature and salinity profiles. By using CTD sensors, parameters such as temperature and conductivity of seawater at different depths can be measured. In recent years, flexible electronic sensors have demonstrated great potential for application due to their excellent stretchability and easy attachment, which not only achieve the sensing performance of traditional rigid sensors to a certain extent, but also compensate for the shortcomings of traditional sensors such as large volume and weight. This review introduces the research progress of flexible ocean CTD sensors in recent years, mainly including the working mechanism and classification, common materials, manufacturing processes of flexible sensors, and analyzes the structure, performance, and application platform of existing flexible ocean CTD sensors. Finally, the development of flexible ocean CTD sensors is prospected. Related Articles | Metrics

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Rheological Properties of Epoxy Resin Sealant and Experimental Study of Underwater Sealing LIU Yang, SUN Shiyu, HE Zhenlin, MA Rongtai 2024, 11 (3):  78-83.  DOI: 10.12087/oeet.2095-7297.2024.03.12 Abstract ( 42 )   PDF (5087KB) ( 8 )   In this work, the properties and sealing properties of epoxy resin sealants are studied by means of rheology and laboratory simulation experiments. The result shows that the epoxy resin sealant and its components are pseudoplastic fluids with obvious shear thinning properties. The temperature has a significant effect on its properties. The sealant formed by the ratio of material components in 3∶1 presents a high viscosity at 4℃. In addition, Exponential relationship model between viscosity and temperature is proposed by using Arrhenius relationship and experimental data. The result of underwater simulation experiments confirmed that the sealant has good bonding performance and compressive strength, and can be used as a raw material for injection of shallow water sealing structures. Related Articles | Metrics

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Study on Wind and Wave Influence Characteristics of Cylindrical FPSO ORGREEN Sulfur Recovery System Based on CFD Simulation Chen Jinfu1, Song Chengju2 2024, 11 (3):  84-88.  DOI: 10.12087/oeet.2095-7297.2024.03.13 Abstract ( 34 )   PDF (3298KB) ( 5 )   With the in-depth development of deep-sea oil and gas fields in recent years, there are more and more H2S-containing oil and gas. Considering the requirements of health of production personnel, environmental protection and corrosion protection of facilities, it is imperative to deal with H2S. The relevant system and process have not been used in domestic offshore facilities before, and the reliability and adaptability need to be verified, especially in cylindrical FPSO with random shaking direction.  The OR-GREEN sulfur recovery system was used for the first time in a cylindrical FPSO. In the case of strong wind and waves at sea and severe swaying of FPSO, the oil-gas treatment reactor of OR-GREEN sulfur recovery system will also sway, which may cause the gas-liquid two-phase flow bias in the reactor, affect the reaction and mass transfer time, and further affect the effect of natural gas desulfurization treatment. In this paper, the gas-liquid two-phase flow in a reactor under wind and wave conditions is simulated by Ansys Fluent software. Through simulation, it is verified that the designed structure will not affect the normal operation of the system under the once-a-year wind and wave conditions, and the designed OR-GREEN system can resist the once-a-year wind and wave conditions. Related Articles | Metrics