Offshore platforms are large, complex structures designed for long-term service, and they are characterized by high risk and significant investment. Ensuring the safety and reliability of in-service offshore platforms requires intelligent operation and maintenance strategies. Digital twin technology can enable the accurate description and prediction of changes in the platform’s physical state through real-time monitoring data. This technology is expected to revolutionize the maintenance of existing offshore platform structures. A digital twin system is proposed for real-time assessment of structural health, prediction of residual life, formulation of maintenance plans, and extension of service life through predictive maintenance. The system integrates physical entities, digital models, intelligent predictive maintenance tools, a visualization platform, and interconnected modules to provide a comprehensive and efficient maintenance framework. This paper examines the current development status of core technologies in physical entity monitoring, digital model construction, and intelligent predictive maintenance. It also outlines future directions for the advancement of these technologies within the digital twin system, offering technical insights and practical references to support further research and applications of digital twin technology in offshore platform structures.

Autonomous Underwater Vehicles (AUVs) are pivotal for deep-sea exploration and resource exploitation, yet their reliability in extreme underwater environments remains a critical barrier to widespread deployment. Through systematic analysis of 150 peer-reviewed studies employing mixed-methods research, this review yields three principal advancements to the reliability analysis of AUVs. First, based on the hierarchical functional division of AUVs into six subsystems (propulsion system, navigation system, communication system, power system, environmental detection system, and emergency system), this study systematically identifies the primary failure modes and potential failure causes of each subsystem, providing theoretical support for fault diagnosis and reliability optimization. Subsequently, a comprehensive review of AUV reliability analysis methods is conducted from three perspectives: analytical methods, simulated methods, and surrogate model methods. The applicability and limitations of each method are critically analyzed to offer insights into their suitability for engineering applications. Finally, the study highlights key challenges and research hotpots in AUV reliability analysis, including reliability analysis under limited data, AI-driven reliability analysis, and human reliability analysis. Furthermore, the potential of multi-sensor data fusion, edge computing, and advanced materials in enhancing AUV environmental adaptability and reliability is explored.

This study examines the feasibility and prospects of integrating marine renewable energy (MRE) with green hydrogen production in Indonesia. As global energy demand increases and the environmental impacts of fossil fuels become more pronounced, the search for sustainable alternatives intensifies. Indonesia, with its extensive maritime resources, presents a unique opportunity to harness tidal wave and offshore wind energy for green hydrogen production from seawater. This research explores various electrolysis methods, particularly those that eliminate the need for desalination, thereby enhancing efficiency and reducing costs. The findings indicate that advanced electrolysis techniques can significantly lower energy and production costs while maintaining environmental sustainability by avoiding harmful chemicals and ensuring minimal ecological footprints. Moreover, the utilization of Indonesia’s extensive marine resources can foster energy independence, boost economic growth, and lower carbon emissions, which highlights the need for ongoing research and optimization to improve the economic and environmental feasibility of these technologies. This review article provides an in-depth analysis of the potential for MRE and green hydrogen production in Indonesia, outlining a viable path toward sustainable energy development.

Cylindrical cross sections are critical components in offshore structures, including jacket platform legs, pipelines, mooring lines, and risers. These cylindrical structures are subjected to vortex-induced vibrations (VIV) due to strong ocean currents, where vortices generated during fluid flow result in significant vibrations in crossflow and in-flow directions. Such vibrations can lead to severe damage to platforms, cables, and riser systems. Consequently, mitigating VIV caused by vortex-induced forces is important. This study investigates the hydrodynamic performance of five strake models relative to a bare cylinder at moderate Reynolds numbers. The models encompass one conventional continuous helical strake (HS) and four helical discrete strake (HDS) with varying segment spacing between the fins. The hydrodynamic performance, specifically lift and drag force coefficients, was computed using a Reynolds averaged Navier–Stokes-based CFD solver and validated with experimental measurements. The conventional HS suppresses 95% of the lift force but increases the drag force by up to a maximum of 48% in measurements. The HDS suppress the lift force by 70%–88% and increase the drag force by 15%–30%, which is less than the increase observed with the HS. Flow visualization showed that HS and HDS cylinders mitigate vortex-induced forces by altering the vortex-shedding pattern along the length of the cylinder. The HDS achieves a reduction in drag compared with the conventional continuous HS. The segment spacing is found to significantly impact the reduction in vortex-induced forces.

The position deviation of the underwater manipulator generated by vortex-induced vibration (VIV) in the shear flow increases relative to that in the uniform flow. Thus, this study established an experimental platform to investigate the vibration characteristics of the underwater manipulator under shear flow. The vibration response along the manipulator was obtained and compared with that in the uniform flow. Results indicated that the velocity, test height, and flow field were the main factors affecting the VIV of the underwater manipulator. With the increase in the reduced velocity (U_r), the dimensionless amplitudes increased rapidly in the in-line (IL) direction with a maximum of 0.13D. The vibration responses in the cross-flow (CF) and IL directions were concentrated at positions 2, 3 and positions 1, 2, with peak values of 0.46 and 0.54 mm under U_r = 1.54, respectively. In addition, the vibration frequency increased with the reduction of velocity. The dimensionless dominant frequency in the CF and IL directions varied from 0.39–0.80 and 0.35–0.64, respectively. Moreover, the ratio of the CF and IL directions was close to 1 at a lower U_r. The standard deviation of displacement initially increased and then decreased as the height of the test location increased. The single peak value of the standard deviation showed that VIV presented a single mode. Compared with the uniform flow, the maximum and average values of VIV displacement increased by 104% and 110% under the shear flow, respectively.

This study investigates the effects of radiation force due to the rotational pitch motion of a wave energy device, which comprises a coaxial bottom-mounted cylindrical caisson in a two-layer fluid, along with a submerged cylindrical buoy. The system is modeled as a two-layer fluid with infinite horizontal extent and finite depth. The radiation problem is analyzed in the context of linear water waves. The fluid domain is divided into outer and inner zones, and mathematical solutions for the pitch radiating potential are derived for the corresponding boundary valve problem in these zones using the separation of variables approach. Using the matching eigenfunction expansion method, the unknown coefficients in the analytical expression of the radiation potentials are evaluated. The resulting radiation potential is then used to compute the added mass and damping coefficients. Several numerical results for the added mass and damping coefficients are investigated for numerous parameters, particularly the effects of the cylinder radius, the draft of the submerged cylinder, and the density proportion between the two fluid layers across different frequency ranges. The major findings are presented and discussed.

This study evaluates the physical mechanisms of incident waves as they interact with a porous wavy barrier of finite thickness. A wave-trapping chamber is formed between the thick wavy barrier (TWB) and partially reflecting seawall (PRS). The effect of seabed undulations is incorporated into the wave-trapping analysis of the TWB. The boundary value problem proposed in this study is solved using a multidomain boundary element method within the context of linear potential flow theory. Coefficients such as reflection, runup, horizontal force on PRS, and vertical force on TWB are examined for various structural configurations. The position of seabed undulations is analyzed for four scenarios: ⅰ) seabed undulations upwave of the wavy barrier with a trapping chamber, ⅱ) seabed undulations upwave of the wavy barrier without a trapping chamber, ⅲ) seabed undulations underneath the wavy barrier with a trapping chamber, and iv) seabed undulations beneath the wavy barrier without a trapping chamber. The study results are compared with known results to verify their accuracy. The effects of PRS, TWB porosity, trapping chamber, plate thickness, seabed type, and submergence depth on hydrodynamic coefficients are analyzed against relative water depth. The study reveals that the introduction of a porous TWB with a trapping chamber results in minimal hydrodynamic coefficients (reduced reflection and force on a wall) compared to a rigid TWB without a trapping chamber. A comparison of various seabeds is reported for all combinations of TWB with a chamber. The sloping seabed upwave of the barrier with a trapping chamber, 20% plate porosity, and 50% wall reflection at an appropriate submergence depth could replace gravity-type breakwaters in deeper waters. This study holds great potential for analyzing wave trapping coefficients by TWB to provide an effective coastal protection system.

This study proposes a numerically efficient technique for computing the far-field scattered by a spherical target placed near the seabed. The bottom is supposed to be a homogeneous liquid attenuating half-space. The transmitter and receiver are situated at different points of a homogeneous water half-space. The distances between the transmitter, receiver, and object of interest are assumed to be much larger than the acoustic wavelength in water. The scattered far-field is ascertained using Hackman and Sammelmann’s general approach. The arising scattering coefficients of a sphere are assessed using the steepest descent approach. The branch cut contribution is also considered. The obtained formulas for the form-function can be used for acoustically rigid or soft scatterers, as well as elastic targets or spherical elastic shells. Numerical simulations are conducted for an acoustically rigid sphere. Asymptotic expressions for the scattering coefficients allow a decrease in the number of summands in the formula for the target strength and a significant reduction in computational time.

The BZ oilfield in the Bohai Sea is a rare, highly volatile reservoir with fractures in the metamorphic rocks of buried hills. Clarifying the mechanism of gas injection for improving oil recovery and determining the optimal way to deploy injection-production well networks are critical issues that must be urgently addressed for efficient oilfield development. Experimental research on the mixed-phase displacement mechanism through gas injection into indoor formation fluids was conducted to guide the efficient development of gas injection in oil fields. We established a model of dual-medium reservoir composition and researched the deployment strategy for a three-dimensional well network for gas injection development. The coupling relationship between key influencing factors of the well network and fracture development was also quantitatively analyzed. The results show that the solubility of the associated gas and strong volatile oil system injected into the BZ oilfield is high. This high solubility demonstrates a mixed-phase displacement mechanism involving intermediate hydrocarbons, dissolution and condensation of medium components, and coexistence of extraction processes. Injecting gas and crude oil can achieve a favorable mixing effect when the local formation pressure is greater than 35.79 MPa. Associated gas reinjection is recommended to supplement energy for developing the highly volatile oil reservoirs in the fractured buried hills of the BZ oilfield. This recommendation involves fully utilizing the structural position and gravity-assisted oil displacement mechanism to deploy an injection-production well network. Gas injection points should be constructed at the top of high areas, and oil production points should be placed at the middle and lower parts of low areas. This approach forms a spatial three-dimensional well network. By adopting high inclination well development, the oil production well forms a 45° angle with the fracture direction, which increases the drainage area and enhances single-well production capacity. The optimal injection-production well spacing along the fracture direction is approximately 1 000 m, while the reasonable well spacing in the vertical fracture direction is approximately 800 m. The research results were applied to the development practice of the buried hills in the BZ oilfield, which achieved favorable development results. These outcomes provide a valuable reference for the formulation of development plans and efficient gas injection development in similar oil and gas fields in buried hills.

Centrifugal pumps are extensively employed in ocean engineering, such as ship power systems, water transportation, and mineral exploitation. Pressure fluctuation suppression is essential for the operation stability and service life of the centrifugal pump. In this paper, a new method of bionic structure is proposed for the blade surface of a centrifugal pump, which is inspired by the fish scale and comprises a leading edge, a trailing edge, and two symmetrical side edges. This fish scale structure is applied to the blade pressure and suction surfaces, and an impeller with a fish scale structure is constructed. A test rig for a centrifugal pump is developed to determine the pressure fluctuation in the pump with a prototype impeller and fish scale structure impeller. Results reveal that the dominant frequency of pressure fluctuation in volute is the blade passing frequency (f_bpf) of 193.33 Hz, which is triggered by the interaction between the tongue and the impeller. The bionic structure of the fish scale effectively suppresses the pressure fluctuation amplitude at f_bpf. From flow rates of 0.6 Q_d to 1.2 Q_d, the average suppressions in pressure fluctuation amplitudes at f_bpf are 20.98%, 5.85%, 19.20%, and 25.77%.

Coasts are subject to multiple natural hazards, which are increasing nowadays. Coastal flooding and erosion are some of the most common hazards affecting coastlines. Being aware of the vulnerability of coasts is important to achieve integrated coastal management. The coastal vulnerability index (CVI) is a common index used to assess coastal vulnerability because it is easily calculated. However, given that its calculation includes numerous manual steps, it requires considerable time, which is often unavailable, to produce accurate and utilizable results. In this work, we developed a ModelBuilder model by using the tools provided by ArcGIS Pro (ESRI). Through this model, we automatized most of the steps involved in CVI calculation. We applied the ModelBuilder model in the northern Peloponnese, for which the CVI has already been calculated in three other works. We were thus able to assess the effectiveness of our ModelBuilder model. Our results demonstrated that through the ModelBuilder, most of the processes could effectively be automatized without problems, and our results are consistent with the findings of previous works in our study area.

Captive model tests are one of the most common methods to calculate the maneuvering hydrodynamic coefficients and characteristics of surface and underwater vehicles. Considerable attention must be paid to selecting and designing the most suitable laboratory equipment for towing tanks. A computational fluid dynamics (CFD) -based method is implemented to determine the loads acting on the towing facility of the submarine model. A reversed topology is also used to ensure the appropriateness of the load cells in the developed method. In this study, the numerical simulations were evaluated using the experimental results of the SUBOFF benchmark submarine model of the Defence Advanced Research Projects Agency. The maximum and minimum loads acting on the 2.5-meter submarine model were measured by determining the body’s lightest and heaviest maneuvering test scenarios. In addition to having sufficient endurance against high loads, the precision in measuring the light load was also investigated. The horizontal planar motion mechanism (HPMM) facilities in the National Iranian Marine Laboratory were developed by locating the load cells inside the submarine model. The results were presented as a case study. A numerical-based method was developed to obtain the appropriate load measurement facilities. Load cells of HPMM test basins can be selected by following the two-way procedure presented in this study.

This study focuses on wave energy harvesting by leveraging the impact-induced frequency of sea waves. It introduces a novel double-buoyed model based on the existing single-buoyed system to address the shortcomings of previous systems. Notably, the traditional single-buoyed system, which is characterized by a long beam extending to the sea floor, proves impractical in deep-sea environments, especially in distant offshore regions. The proposed double-buoyed model replaces the long beam with a second buoy to increase energy harvesting efficiency. A parametric analysis that included the density and height of the first buoy and wave period was conducted to enhance the proposed model further. Results indicated that with the selection of optimal parameters, the power output of the double-buoyed system increased by approximately 13-fold, thereby enhancing the viability and efficiency of wave energy harvesting.

Misfire is a common fault in compression ignition engines, characterized by the absence or flame loss due to insufficient fuel in the cylinders. This fault is difficult to diagnose and resolve due to its multiple potential causes. This study focuses on identifying misfires in a 12-cylinder Ⅴ-type marine diesel engine by analyzing vibration data collected from 15 accelerometers mounted on the engine block. Three machine learning algorithms—K-Nearest Neighbors (K-NNs), support vector machines (SVMs), and random forests (RFs)—were employed to classify engine conditions using 18 time-domain features. Results showed that the K-NN, SVM and RF algorithms achieved F1 scores of 99.87%, 100%, and 99.87%, respectively, when using 18 time-domain features and all 15 accelerometers mounted on the engine block. Additionally, the study evaluated classification performance while reducing the number of accelerometers and features using two methods: Relief-F and general combinatory analysis (GCA). Although the GCA method yields better results when using only two accelerometers and nine features for misfire classification, its overall process required substantially more computational time compared to Relief-F. The best result obtained with Relief-F was achieved using 3 accelerometers and 18 features. Therefore, Relief-F proved to be more practical and take less overall computational time within the proposed framework.