Offshore Engineering Research Articles

Numerical analysis of failure mechanism and stability of reinforced embankment with DCM soft soil composite foundation

The deep cement mixing (DCM) method has been widely used in offshore geotechnical engineering. At present, the reinforcement form of pile has been researched widely, but there is a lack of understanding of the failure mode of DCM pile composite foundation reinforcement for bank slopes. In this paper, a series of unconfined compression tests was conducted to obtain necessary numerical analysis parameters. A series of study on the failure mechanism and stability control of DCM pile composite foundation reinforcement bank slope has been conducted through numerical analysis. The results of numerical analysis indicate that under different reinforcement conditions, there exists an optimal reinforcement depth, and the safety coefficient will gradually stabilize at 1.45; The bending moment of the piles under the bank slope the bending moment of the pile body under the road surface Under different overloads. The maximum bending moment of the pile body is located near one-third of the pile body, and the maximum bending moment of the pile body is located between the shoulder and foot of the slope.

Enhanced corrosion protection of rebars in alkaline solutions by ferroporphyrin and the mechanisms of electron consumption and lattice reconstruction

Abstract Reinforced concretes are the primary materials in coastal and offshore engineering. In alkaline environment of concrete, the anodic process is passivation of rebars and the conjugated cathodic process is oxygen reduction reaction (ORR). It is proposed that a novel approach to enhance the passivation films through catalyzed ORR by iron meso-tetra(4-carboxyphenyl)porphine (FeTCPP). The ORR catalyst FeTCPP promotes the formation of passivation film, as it accelerates the consumption of abundant electrons generated and accumulated by the anodic formation of passivation films. The passivation films of rebars are highly defective Fe3O4 semiconductor. The dissolution of interstitial ferrous ions and lattice iron ions produces defects of O ion vacancies, Fe ion vacancies and interstitial Fe ions, and they further cause the formation and accumulation of Fe atom vacancies on the metal surface, leading to the collapse of the passivation films. The FeTCPP adsorbs on the surface of passivation films, hindering the dissolution of lattice iron ions and interstitial ferrous ions, thereby inhibiting the generation and accumulation of Fe atom vacancies and improving the integrity and protective ability of the passivation films.

Studying development trend of coastline change in China using CiteSpace

The investigation of coastline alterations holds significant scientific and societal importance, particularly in guiding offshore engineering planning and design, as well as the economic development of coastal regions. In this study, we used CiteSpace software to examine relevant literature within the China National Knowledge Infrastructure database to explore the current status, hotspots, and frontiers of research on coastline change in China. Our findings revealed a consistent increase in the number of publications within this domain, with 1996 representing the first growth point in the number of publications on coastal changes. Since 2002, the number of publications has significantly increased owing to scientific and technological advancements and urban development. Research on coastal changes in China is primarily conducted in universities and research institutes, particularly at the Ocean University of China. However, research institutions and authors are widely dispersed, and the consistency between them is low. An apparent, balanced distribution phenomenon exists in this research field. Content related to keywords such as “coastline,” “coastal zone,” and “remote sensing” is the focus of research in this field. Remote sensing monitoring, big data analysis, and deep learning techniques are closely related to the study of coastline changes, representing the latest advancements in this field.

Experimental study on the influence of principal stress axes rotation on sand mechanical behavior and non-coaxiality effects

The soil around the foundations of offshore engineering experienced the principal stress axes rotation caused by the wave loadings. To investigate the influence of the principal stress axes rotation on the soil stress-strain relationship, a series of pure principal stress axes rotation tests under drained/undrained conditions were carried out with a hollow cylinder apparatus. The undrained test results show that the deviatoric stress, relative density, and starting point of rotation affect the mechanical properties of sand. Through the analysis of pore water pressure accumulation in the 1st cycle, it was observed that more pore pressure accumulates in Quadrants II and III, while relatively less accumulates in Quadrants I and IV. Under drained and undrained conditions, the non-coaxial behavior of the soil differs. The non-coaxiality can be significantly observed in the drained test, and the direction of strain increment tends to the stress increment direction when the cycle number increases.

Numerical analysis for the design of a central air conditioning system for center of excellence

The temperature of the towing tank floor of the Center of Excellence in Marine and Offshore Engineering, Rivers State University needs regulation due to the high level of humidity during experiments. Since vapor evaporates from the towing-tank liquid column, the need for central air conditioning is timely. With the temperature regulated, it will help enhance the comfort of the students and improve the working condition of the staff and equipment. This is achieved by conducting a cooling load analysis, consistent with ASHRAE Guidelines, on the floor plan of the Laboratory building that provided useful information on the proper selection and sizing of fit-for-purpose air-conditioning equipment. Analysis revealed a total sensible and latent heat load of 59195.74 W with system capacity of 16.91TR (tons). Duct design utilizing the Velocity Reduction method resulted in a main supply duct length of 57m and flow are of 0.72m2 incorporating four branched ducts measuring 6m each in length and flow area of 1.05m2

A comparative review of subsea navigation technologies in offshore engineering projects

Subsea navigation technologies play a critical role in enhancing precision and efficiency in offshore engineering projects. This comparative review examines the evolution and application of subsea navigation systems, with a focus on improving precision in offshore construction and surveying. The study evaluates various subsea navigation technologies, including acoustic positioning systems, inertial navigation systems, and optical imaging systems, highlighting their capabilities and limitations. The review begins by discussing the historical development of subsea navigation technologies, tracing their evolution from early acoustic systems to modern integrated solutions. It then explores the key components and operation principles of each technology, providing insights into their functionalities and suitability for different offshore applications. The study also examines the challenges and advancements in subsea navigation, including issues related to signal interference, accuracy, and real-time data processing. It discusses how these challenges have been addressed through technological innovations, such as improved sensor technologies and advanced data fusion algorithms. Furthermore, the review assesses the practical application of subsea navigation technologies in offshore engineering projects, including pipeline installation, subsea infrastructure maintenance, and underwater surveying. It analyzes case studies and industry practices to illustrate the effectiveness of these technologies in improving precision, reducing costs, and mitigating risks in offshore operations. Overall, this comparative review provides a comprehensive overview of subsea navigation technologies in offshore engineering projects. It highlights the evolution, capabilities, and applications of these technologies, emphasizing their role in enhancing precision and efficiency in offshore construction and surveying. The study concludes with recommendations for future research and development to further improve the performance and reliability of subsea navigation systems in offshore operations.

Economic Analysis of Potential Offshore Aquaculture Practice to Enhance Diversification of Blue Economy in Nigeria

The oil and gas industry has long dominated Nigeria’s blue economic growth. However, a new frontier that can play sustainable economic growth in the maritime industry and therefore national economic leverage is offshore aquaculture. Hence, this paper aims to provide relevant information on the economic analysis of the potential offshore aquaculture practice to enhance the diversification of the blue economy in Nigeria using secondary data. Sensitivity analysis considering input variations of up to 45% is also performed to take care of the unforeseen. Offshore aquaculture in this paper refers to fish production in the Open Ocean using large cages/nets. Ten (10) fish cages of 37500-fish capacity per cage were hypothetically designed with fiberglass materials and installed in Escravos offshore. A mortality of 30% was used with the current prices of other required investments. The analysis recorded a breakeven period of 2 years and NPV value of over one trillion Naira in 9 years indicating massive profitability comparable to the oil and gas industry! Sensitivity analysis identified mortality/loss of fish and falling prices of fish as events that could adversely affect the investment. It is suggested that the investment should be done with experienced professionals in fishery, offshore engineering, and cost control.

Developing rotary swaging process for improving the performance of wire-arc sprayed Al/Al2O3 composite coating

Wire-arc sprayed Al-based composite coatings attracted great attentions due to their prospective application in offshore engineering. However, the difficulty in regulating ceramic reinforcements limited the performance of these coatings. In this work, we proposed a novel rotary swaging (RS) process to improve the deposition of ceramic particles, thus the Al/Al2O3 composite coating was prepared and evaluated in comparison with the traditional coating by spraying the drawing cored wires. As expected, the RS process promotes the melt of Al2O3 particles, leading to a significant increase of their deposition fraction with the simultaneous improvement in coating compactness and the interfacial bonding of heterogeneous splats. The sufficient melt of Al2O3 particles is attributed to the enhanced cohesion strength of filled powders to bear the vibration of arc force and facilitate heat transport. The explored composite coating displays a superior corrosion resistance in 3.5 wt% NaCl aqueous solution, due to the reduced active area on electrode surface and the lower sensitivity to pitting. Benefiting from a dynamic self-reinforcing effect, the explored composite coating presents lower coefficient of friction and significantly enhanced wear resistance under dry frictional condition. The present results demonstrate a great potential of the developed Al/Al2O3 composite coating in offshore application and provide an inspiration for future works aiming to exploit the high-performance metal-matrix composite coatings synthesized by low-cost wire-arc spraying.

Experimental and numerical study on the blast performance of the corrugated double steel plate concrete composite wallboard under blast loads

The corrugated double steel plate concrete composite wallboard (CDSCW) exhibits superior axial compressive load-bearing capacity, lateral flexural stiffness, impact resistance, and seismic performance compared to the traditional reinforced concrete wallboard and plane double steel plate concrete composite wallboard (PDSCW). Therefore, it has great potential application in offshore engineering and military engineering. This study designs and fabricates two types of CDSCW specimens. Firstly, a comparative analysis is conducted to examine the damage patterns and dynamic responses of the two specimens under near-field explosion experiments. Secondly, the damage mechanisms and explosion response of CDSCW and PDSCW subjected to close-in explosions are numerically investigated by using ANSYS/LS-DYNA, and the results are then compared with experimental findings. Parameter analysis is performed to assess the influence of concrete thickness, steel plate thickness, and explosive charge on the blast resistance of CDSCWs. Furthermore, a nonlinear resistance equation and an equivalent single degree of freedom (ESDOF) theoretical model for simply supported beams is established to predict the dynamic response of CDSCWs under near-blast loads. This theoretical model considers the constitutive model of bilinear materials and the effect of plastic hinges. The reliability of the proposed theoretical model is verified by comparing the residual deflection of CDSCWs obtained from explosion tests with validated numerical simulation results. The results demonstrate that the CDSCWs, with the same concrete and component dimensions (length, width), exhibit greater flexural stiffness and superior energy dissipation capacity subjected to close-in explosion. Moreover, their blast resistance significantly surpasses that of PDSCWs. In particular, an increase in corrugation depth effectively improves the blast resistance of CDSCWs. The dynamic response equations, based on the established elastic-plastic model and primarily considering bending deformation of the components, precisely predict the dynamic response of simply supported CDSCWs under near-blast loads. consequently, these findings can provide a robust foundation for further research and the design of blast-resistant structures.

Experimental Study on Mechanical Behavior of Skirt–Pile Foundations in Saturated Clay under Horizontal Load

Skirt–pile foundations have gained widespread attention in the field of offshore engineering due to their ease of installation and high bearing capacity. In this study, the ultimate bearing capacity, pile bending moment distribution and development, cumulative deformation characteristics, and cyclic stiffness development of skirt–pile foundations were investigated using physical model tests. The experimental results indicate that the ultimate bearing capacity and deformation resistance of the foundation can effectively be improved by increasing the skirt diameter. The cumulative deformation of the skirt–piles exhibited rapid development during the initial stages of cyclic loading, eventually stabilizing. Under long-term cyclic loading, the existence of the skirt can share the bending moment, which then affects the internal force distribution of the pile foundation along the axis. The pile foundation’s cyclic stiffness reduces as the loading cycles increase and increases as the skirt diameter and length grow. Meanwhile, the horizontal cyclic stiffness decreases as the number of cycles increases, stabilizing after 3000 cycles. This study can not only deepen the understanding of the deformation laws of skirt–pile foundations in clay soil but also offers some references for the design of offshore pile foundations.

Probabilistic failure envelopes of tripod bucket-supported offshore wind turbines in spatially variable clay based on a novel continuous method

Marine geologic conditions play key roles in offshore geotechnical preliminary design and construction decisions. Tripod bucket foundations are considered promising geotechnical foundations for offshore engineering. Their bearing characteristics are often determined based on tripod foundation system failure modes in uniform clay without considering spatially variable soil properties. Therefore, this study investigates the combined bearing capacity of tripod bucket foundations in spatially variable clay based on comprehensive finite element analysis with Monte Carlo simulation (MCS) using a novel simplified modified swipe (SMS) method considering the effects of bucket spacing and foundation skirt length. The SMS method can directly represent the ultimate combined bearing capacity of the whole space efficiently and accurately. The results show that a reduced bucket spacing or increased skirt length changes the failure mode of the foundation from independent caisson failure to global failure. Moreover, the spatial variation in soil leads to an asymmetric failure mode, which is more remarkable for foundations with small bucket group effects. An independent safety factor design approach is adopted to represent failure envelopes with different recurrence probabilities, which should be cost-effective, especially for foundations sensitive to soil variability. Finally, an application based on a convex polynomial optimization strategy for representing failure envelopes is demonstrated.

FOSTERING CROSS-DISCIPLINARY COLLABORATION IN OFFSHORE PROJECTS: STRATEGIES AND BEST PRACTICES

In the realm of offshore engineering projects, the integration of diverse professional expertise is essential for successful planning and execution. This paper explores strategies and best practices for fostering cross-disciplinary collaboration in offshore projects, aiming to enhance project outcomes and mitigate risks. The abstract begins by highlighting the significance of cross-disciplinary collaboration in addressing the complex challenges inherent in offshore endeavors. It delineates the various strategies proposed for effective collaboration, including establishing clear project objectives, creating a collaborative culture, implementing robust communication channels, promoting mutual understanding, and encouraging interdisciplinary training. Furthermore, it outlines best practices such as forming cross-functional teams, utilizing integrated project management tools, holding regular interdisciplinary meetings, and embracing diversity. Through the analysis of case studies and examples, this paper illustrates the application of these strategies and best practices in real-world offshore projects, emphasizing successful outcomes and key lessons learned. The abstract concludes by emphasizing the importance of fostering cross-disciplinary collaboration in offshore engineering projects and suggests avenues for future research to further enhance collaboration methods and outcomes in this critical field.
 Keywords: Cross-Disciplinary Collaboration, Offshore Projects, Integrating Diverse Professional Expertise, Planning, Execution, Offshore Engineering Projects.

The effect of shear rate and overconsolidation ratios on undrained clay–suction caisson interface behaviors

The interface resistance during installation is crucial for the stability and safety of suction caisson in offshore geotechnical engineering, which is strongly affected by the penetration rate and soil–structure interface mechanical properties. This research conducts a series of clay–structure interface shear tests using modified direct simple shear device to fully study the mechanical behavior of clay–suction caisson interface. The effect of shear rate, over consolidation ratios (OCRs), interface boundary conditions, stress levels, and interface roughness were considered. Results show that as the OCR increases, the strength of both the clay and interface increase but show distinct patterns under constant volume (CV) and constant normal load (CNL) boundary condition. It was found that the interface strength is positively related to interface roughness and shear rate impact both the clay and corresponding interface strength. Under CNL conditions, the strength of normally consolidated (NC) clay decreases with rising shear rate, while the over consolidated (OC) clay demonstrate a opposite trend. In contrast, the effect of shear rate on interface behavior gets complicated owing to the combination of roughness, stress levels, and OCRs. Under CV conditions, the shear strength of clay and interface exhibits a logarithmic growth relationship with shear rates. The result of this work can provide a basis for interface resistance evaluation for suction caisson installation in clay.

A review on the interactions between engineering and marine life: key information for engineering professionals

AbstractMarine life both affects and is affected by coastal, marine and offshore engineering. As engineering projects have become larger, more frequent and more complex, hence has the number and type of interactions with marine life. Engineers are looking for more information about these interactions so they can better mitigate against any harmful effects to marine life and enhance any positive impacts. This review aims to fill this purpose, giving professional engineers a broad understanding of the impacts that marine engineering projects can cause to marine life and to suggesting some “best practice” mitigation strategies. The review considers the interactions between engineering projects and marine life from three perspectives with a specific example given in each case. First, potential mitigation measures are discussed in the context of offshore windfarms. Secondly, the issue of engineering noise affecting marine species in different ways. Lastly, the engineering solutions employed in the “Great Barrier Reef (GBR) Restoration Project” is exampled. Environmental Impact Assessments used by managers must reference up-to-date and detailed data from biological surveys so that local species that are vulnerable to the specific engineering activities can be identified. The mitigation activities must include acoustic mitigation, be scalable and affordable. This review highlights the need for engineers to liaise closely with marine scientists and biologists to ensure that solutions are appropriate and do not have unexpected or indirect consequences to marine life.

Characterizing vibrations and associated wake structures of tandem square cylinders at different angles of incidence

Finite element computations were conducted to investigate the transverse vibrations of three identical tandem square cylinders and the associated wake patterns at a Reynolds number Re = 150. The reduced velocities ranged from U*=3 to 20, and the angles of incidence were set at α=0°, 22.5°, and 45°. The streamwise gaps for these three α were Lx=5H, 3.8H, and 3.5H, respectively, where H represents the projected dimension of the cylinder normal to the freestream. The mass ratio of the cylinders was fixed at m*=2, and damping was neglected to allow the cylinders to attain maximum amplitudes. In the presence of primary vortices being shed from all three cylinders, the upstream cylinder at α=22.5° and 45° exhibits three distinct vibration regimes: initial excitation and upper and lower response regions. On the other hand, due to interaction with the upstream vortices, the two downstream cylinders display four response regions. In the case of α=0°, the dynamic response of the upstream cylinder appears in only two regimes, but with a higher peak amplitude compared to α=22.5° and 45°. Vibration and shedding frequencies closely synchronize with the natural frequency of the spring-mass system in the second regime, leading to high amplitude oscillations for the most upstream cylinder with α=22.5° and 45°. The third response regime for the two downstream cylinders is associated with the lock-in phenomenon. In α=0° and 22.5° configurations, the shedding mode is 2S in all response regimes, while at α=45°, the shedding mode shifts to P + S during the second regime. Up to the second regime, lift and vortex forces are in-phase with the cylinder's oscillation for α=0° and 22.5°, but they go out of phase beyond that. In the case of α=45°, although lift remains in-phase with the displacement in the second regime, the vortex force is found to be out of phase. This study is expected to enhance the understanding of fluid–structure interaction phenomena involved in multiple structures and can aid in the design of stable structures in civil engineering, offshore engineering, and development of energy harvesting devices.

The Adoption of AISC 360 for Offshore Structural Design Practices

The offshore design standards for U.S. practices refer to AISC specifications when designing structural components with nontubular shapes. The widely used API RP-2A WSD standard (API, 2014) asks designers to use the 1989 AISC Specification. The newly published API RP-2A LRFD and RP-2TOP ask designers to use the 2010 AISC Specification. Although the 2010 AISC Specification has been partially adopted by API, the current offshore practice is still primarily dominated by the 1989 AISC Specification. The key issue hampering the offshore community’s full adoption of the 2010 AISC Specification is the relative ease of accounting for second-order effects in the 1989 AISC Specification. In 2019, API formed a Task Group dedicated to studying this issue, with the main findings summarized in this paper. By illustrating the key code check process in two examples with an easy-to-understand format, this paper aims to assist offshore structural engineers to better understand the latest AISC specification. The authors also hope that this paper will serve as a communication path between the offshore structural community and AISC for current and future standards’ adoption and harmonization.

Analysis of Chinese Patents on Cathodic Protection by Applied Current Method in Marine Sector

The resource problem is the top priority of China's current development, while the ocean is an inexhaustible treasure. The development and utilization of marine resources has always been the key direction of development. The characteristics of offshore engineering operation equipment are: first, the scale of the platform is particularly large, and second, it is long-term in the harsh environment such as moisture and salinity [1]. Therefore, the anti-corrosion of offshore platforms is the research hotspot of relevant technicians, this paper systematically summarizes the patent application of external current in cathodic protection of anti-corrosion technology. It analyzes the patent type, affiliated institution, important applicant, application field and other related contents. The results show that enterprises prefer to actually invent devices, while scientific research institutions, universities and colleges are more about the creation of technical methods.

A review of scour impacting monopiles for offshore wind

Monopiles are important structures in offshore wind engineering, primarily serving as foundations for wind turbines. When installed on a sandy seabed, local scour around monopiles can reduce their capacity, and is a significant hazard to be addressed in the design process. This paper provides a review of research related to local scour around monopiles, focusing on the following aspects: (1) identifying flow structures related to local scour, (2) synthesizing existing data on equilibrium scour depth and scour time-scale, (3) summarizing technology for observing local scour through laboratory experiments, numerical simulations and field observations, and (4) outlining the existing challenges and research opportunities.

Barrier Lyapunov function-based adaptive optimized control for full-state and input-constrained dynamic positioning of marine vessels with simulation and model-scale tests

For practical marine engineering, ensuring system performance and avoiding violations of safety-related system constraints in various scenarios remains a challenging problem. To tackle this problem, this paper addresses adaptive neural network (NN) optimized control for dynamic positioning (DP) of marine vessels suffering from unknown model uncertainties and control gains, ocean disturbances, and full-state/input constraints. To realize model-free optimized control, the reinforcement learning (RL) with a critic–actor–identifier architecture is constructed on the basis of NN approximation, in which the actor, critic, and identifier NNs are designed to perform control actions, evaluate control performance, and estimate unknown dynamics, respectively. To effectively guarantee the system safety, the critics and actors in the corresponding subsystems are decomposed into a guaranteed safety-related constraint term with respect to the barrier Lyapunov function (BLF) and an unknown dynamic term to be learned. Such a control strategy can ensure that all the state variables are restricted to a predefined safety region, even in the learning control process. From the above logical ideas, the adaptive optimized kinematic and kinetic control laws are presented to guarantee that the whole vessel system is optimized. Moreover, the motion control responses of vessels in various scenarios are realistically simulated through convincing simulations and model-scale tests. The validation results prove the applicability and feasibility of the proposed DP control strategy for practical offshore engineering.

Real-time prediction of mooring tension for semi-submersible platforms

The harsh operating environment of deepwater semi-submersible production platforms poses severe challenges to the safe operation and maintenance of their production processes. Using artificial intelligence technology to improve the operation and maintenance level of large-scale offshore engineering equipment has become an inevitable trend. Accurate mooring tension prediction for semi-submersible production platforms can effectively identify potential damage and ensure the platform's safe and efficient production operation. Compared with traditional cyclic neural networks, transformer neural networks have faster calculation speeds, better generalization abilities and scalability, and better abilities to capture long-distance dependencies. In this study, the first deepwater semi-submersible production platform in the South China Sea, “DeepSea One,” was selected as the research object, and an improved novel transformer neural network architecture was proposed for the mooring tension prediction of semi-submersible production platforms using actual long-term mooring tension data obtained during the platform's production process. The proposed method was compared with the commonly used long short-term memory neural network model, and the comparison proved the effectiveness of the proposed method in predicting the dynamic tension of semi-submersible production platform mooring. In addition, the proposed method is also applicable for the prediction of other time series data in the field of shipbuilding and offshore engineering, which is of certain value for generalization.