Offshore Systems Research Articles

Multi-condition hawser tension prediction of offshore offloading system based on long and short-term memory network and transfer learning

Real-time prediction of hawser tension of the side-by-side oil offloading system of Floating Production Storage and Offloading (FPSO) can provide early warnings for hawser breakages and ship collision risk, thus improving structural, property, and environmental security. Although offline numerical models and Long Short-Term Memory (LSTM) could offer substantial precision, they confront intensive time costs in recalibrating or retraining models. This paper proposes an integration method of LSTM networks and transfer learning for real-time tension prediction considering inputs of actual remote wave elevations. We use short-term environmental data and numerical simulation data of correlated hawser tensions during offloading operations to train a pre-trained benchmark model for transfer learning. Then, a highly generalized and efficient transferred model is constructed by using a small sample to realize short-term tension predictions in time-varying environments. The results show the occurrence time and value of extreme tensions predicted by transfer learning nearly match the reference data, and their maximum errors are 3 s and 0.11, respectively, superior to LSTM direct training. Therefore, it provides sufficient demand for real-time prediction and early collision risk prevention in dynamically changing ocean environment. The research results could provide an alternative framework for intelligent monitoring of large-scale marine structures.

Experimental and Numerical Analysis of PIP Slip Joint Subjected to Bending

Detachable circular hollow sections (CHSs) offer an innovative solution to tackle the complexities of installation, maintenance, upgrades, and repairs in offshore monopile systems, particularly in challenging environments with limited access. As an alternative to traditional tubular joints, the PIP slip joint presents advantages in terms of ease of installation, time efficiency, and reduced susceptibility to failure. This study conducts an experimental investigation on PIP (Pile-in-Pile) slip joints under pure bending conditions, accompanied by comprehensive numerical analyses to examine the relationship between section slenderness, contact properties, and structural performance. The results highlight a strong correlation between force-displacement curves and include a comparison of compressive and tensile strain values for both experimental and numerical models. The experimental and numerical models showed strong agreement across all results, demonstrating the robustness of the findings. Additionally, numerical models were utilized to investigate various D/t ratios, revealing insights into the normalized moment, rotational capacity, and the impact of local buckling and contact mechanics. Furthermore, a comparison of these findings with established code guidelines, such as Eurocode and AISC-LRFD, has been conducted and reviewed in the context of this study. From analysis, it was found that the rise in the D/t ratio prompted a transformation in the buckling mode, which substantially altered the rotational ratio. This shift indicates the importance of understanding how these variables interact in engineering applications. These findings significantly enhance the understanding of PIP slip joints and emphasize their potential as a compelling alternative for offshore wind turbine support structures.

Optimization Simulation of Mooring System of Floating Offshore Wind Turbine Platform Based on SPH Method

ABSTRACTIn this paper, the Smoothed Particle Hydrodynamics method is used to simulate the dynamic response of the floating offshore wind turbine mooring system in a complex marine environment by using its advantages of dealing with free surface flow and fluid–structure interaction. The single‐cable mooring system and the double‐cable mooring system are introduced into the numerical simulation model of fluid–solid coupling interaction. The first‐order irregular wave and the second‐order regular wave are used to simulate different wave conditions. The operating state of the platform in these two cases is analyzed, and the accurate data such as the velocity change of the geometric center of the platform and the change of six degrees of freedom are obtained. Using visual processing and data analysis, it is found that the optimized double‐cable mooring system structure improves the vibration reduction ability of the platform.

A Comprehensive Review of Remaining Useful Life Estimation Approaches for Rotating Machinery

This review paper comprehensively analyzes the prognosis of rotating machines (RMs), focusing on mechanical-flaw and remaining-useful-life (RUL) estimation in industrial and renewable energy applications. It introduces common mechanical faults in rotating machinery, their causes, and their potential impacts on RM performance and longevity, particularly in wind, wave, and tidal energy systems, where reliability is crucial. The study outlines the primary procedures for RUL estimation, including data acquisition, health indicator (HI) construction, failure threshold (FT) determination, RUL estimation approaches, and evaluation metrics, through a detailed review of published work from the past six years. A detailed investigation of HI design using mechanical-signal-based, model-based, and artificial intelligence (AI)-based techniques is presented, emphasizing their relevance to condition monitoring and fault detection in offshore and hybrid renewable energy systems. The paper thoroughly explores the use of physics-based, data-driven, and hybrid models for prognosis. Additionally, the review delves into the application of advanced methods such as transfer learning and physics-informed neural networks for RUL estimation. The advantages and disadvantages of each method are discussed in detail, providing a foundation for optimizing condition-monitoring strategies. Finally, the paper identifies open challenges in prognostics of RMs and concludes with critical suggestions for future research to enhance the reliability of these technologies.

Photonics in offshore wind energy system development: A systematic review

Photonics in offshore wind energy system development: A systematic review

Definition of a Baseline Rotor Design for a 25MW Floating Offshore Wind Turbine

Abstract Wind turbine sizes have grown rapidly in recent years with machine ratings of 15-16 MW available from multiple manufacturers for offshore wind turbines. While the industry advances large-scale turbine designs, offshore developers have initially focused on siting in shallow waters on bottom-fixed foundations; however, eyes are also on deep-water locations where floating systems are required. The present study presents the definition for an initial baseline rotor design at 25 MW scale, designed for a floating offshore system. The purpose of this paper is to document this 25 MW blade definition for use as a reference design for future floating wind technology development by industrial and academic researchers and developers. As this is an initial reference design, some opportunities (and plans) for further mass or cost reduction are also noted. In summary, the paper documents the initial baseline rotor design including aerodynamic and structural design of the rotor blades, along with key details about the control system and floating system designs for the floating 25 MW wind turbine system.

Review of Recent Offshore Floating Photovoltaic Systems

Photovoltaic (PV) power generation is a form of clean, renewable, and distributed energy that has become a hot topic in the global energy field. Compared to terrestrial solar PV systems, floating photovoltaic (FPV) systems have gained great interest due to their advantages in conserving land resources, optimizing light utilization, and slowing water evaporation. This paper provides a comprehensive overview of recent advancements in the research and application of FPV systems. First, the main components of FPV systems and their advantages as well as disadvantages are analyzed in detail. Furthermore, the research and practical applications of offshore FPV systems, including rigid floating structures and flexible floating structures, are discussed. Finally, the challenges of offshore FPV systems are analyzed in terms of their stability and economic performance. By summarizing current research on FPV systems, this overview aims to serve as a valuable resource for the development of offshore FPV systems.

Control Structures for Combined H2/Electricity from Offshore Wind Turbines

Wind energy proves to be a highly favourable choice for electricity generation due to its clean and renewable nature, and is playing a significant role in reducing global greenhouse gas emissions. Offshore wind turbine systems have gained widespread popularity as they can capitalise on elevated and consistent wind speeds surpassing those found in onshore locations, resulting in increased energy efficiency. Furthermore, offshore wind power possesses the potential to emerge as a significant electricity source for the production of green hydrogen. As water electrolysis technology for hydrogen production continues to advance, utilizing offshore wind power for hydrogen generation is becoming more economically viable and practical. Offshore wind power with higher wind speeds in combination with efficient control structures presents an attractive option for electricity generation and hydrogen co-production. This paper aims to present and evaluate four different production structures for combined H2/energy generation from offshore wind turbines. Previous research studies in this area often overlook control structures and lack information on power converter operations. In contrast, this article studies control structures that enable proper functionality and ensure adequate interoperability, enhancing the reliability of renewable energy integration. Each structure, including both wind turbines and electrolyser, is described in detail, along with the corresponding controllers. Simulation results are presented for each structure and controller to demonstrate their effective operation.

The Method of the Natural Frequency of the Offshore Wind Turbine System Considering Pile–Soil Interaction

Accurately and efficiently evaluating the influence of pile–soil interaction on the overall natural frequency of wind turbines is one of the difficulties in current offshore wind power design. To improve the structural safety and reliability of the offshore wind turbine (OWT) systems, a new closed-form solution method of the overall natural frequency of OWTs considering pile–soil interactions with highly effective calculations is established. In this method, Hamilton’s principle and the equivalent coupled spring model (ECS model) were firstly combined. In Hamilton’s theory, the Timoshenko beam assumption and continuum element theory considering the three-dimensional displacement field of soil were used to simulate the large-diameter monopile–soil interaction under lateral load in multilayer soil. Case studies were used to validate the proposed method’s correctness and efficiency. The results show that when compared with the data of 13 offshore wind projects reported in existing research papers, the difference between the overall natural frequency calculated by the proposed method and that reported in this study is within ±10%. This calculation method achieves the goal of convenient, fast and accurate prediction of the overall natural frequency of offshore wind systems.

Optimized hybrid osprey with PSO control for improved VSC-HVDC-wind power integration

Innovative power systems include offshore wind farms (OWFs) to generate electricity from renewable sources. So, reliable control systems are also necessary to make sure these power systems run smoothly. The purpose of this study is to combine the Osprey Optimization with Particle Swarm Optimization (OOPSO) to fine-tune the gains of Proportional-Integral (PI) controllers within the investigated wind energy conversion system (WECS) to enhance its performance. The study confirms the effectiveness of using the Hybrid OOPSO algorithm to optimize PI controllers in a WECS. The WECS includes two voltage source converter (VSC) stations at each end of a high voltage direct current (HVDC) transmission system. The transmission system links OWFs to the grid. The research demonstrates that the Hybrid OOPSO algorithm is superior to the genetic algorithm (GA) and PSO by enhancing setup stability and allowing fast voltage regaining following different fault cases. The introduced method performs more remarkably than traditional methods such as GA and PSO. The results of this study have shown that the proposed OOPSO enhances the overshoot in onshore voltage transient response under a symmetrical fault condition by 26% over PSO, 24% over GA, and 16% over OOA. The study is conducted using MATLAB/Simulink. The study underscores the importance of advanced optimization methods to guarantee offshore wind energy systems' efficient and dependable functioning.

In Search of Suitable Methods for Cost-Benefit Analysis of Cyber Risk Mitigation in Offshore Wind: A Survey

In recent years, notable incidents have highlighted the vulnerability of wind energy infrastructure, making cybersecurity crucial for the offshore wind industry. However, justifying the costs of cybersecurity measures is essential. A cost benefit analysis (CBA) is commonly utilised to support decision-making for risk mitigation. With a cost benefit analysis, risk mitigation strategies that strike an optimal balance between the costs of mitigation measures and the resulting risk reduction can be identified. This survey of literature was carried out to identify the existing proposed solutions for cost benefit analysis on cyber risk mitigation measures for offshore wind cyber physical systems. After narrowing the area scope, a systematic search across Scopus and Web of Science, yielded 18 articles, of which six met the selection criteria. It was found that the there was a lack of cost benefit analysis of cybersecurity solutions for, or set in, the area of offshore wind directly. From the analysis of the surveyed works, suggestions on future directions were given. The existing literature found lacks detailed cost modelling for offshore wind, beyond general breakdowns encompassing capital, maintenance, and labour/installation expenses, risk and scenario loss. Some of the literature used contextual factors such as compatibility and effectiveness of mitigation measures, effects on OT performance, geographical location, geopolitical context, and installed rated power which could be adapted to suit offshore wind. Since offshore operations contribute significantly to costs, cost modelling and consideration of other relevant factors pertaining to this area would be beneficial if explored. As an emerging area, in the future we expect this research to be a basis and a methodology that can be expanded with a larger data set from other publications in the field. Thus, it represents an opportunity to advance knowledge in offshore wind cyber-physical systems.

Optimization of offshore wind farm cluster transmission system topology based on Stackelberg game

Offshore wind energy is pivotal in the global energy transition, with a global installed capacity reaching 64.3 GW by 2022 and an expected annual increase of 60.2 GW over the next decade. This study aims to optimize the topology of transmission systems (TS) for offshore wind farm (OWF) clusters using Stackelberg game theory. The OWF investor (OWFI) acts as the leader, optimizing investment returns while considering wake effects, and the offshore TS operator (OTSO) follows by adjusting transmission strategies to reduce costs. The analysis includes the wake effects within OWF clusters and their impact on power generation efficiency. Simulation results demonstrate that the proposed model can balance stakeholder interests and enhance the economic viability of OWF clusters, showing a potential increase in net present value (NPV) by up to 30 %. This study validates the practical application of the Stackelberg game model in optimizing OWF cluster TS topology, contributing to more efficient and cost-effective renewable energy integration.

Experimental investigation of online solving for critical valve opening for eliminating severe slugging in pipeline-riser systems

In an offshore pipeline-riser system, the critical opening of choke valve, i.e., the maximum permanent opening to eradicate severe slugging, plays an important role in both pipeline design and offshore oil and gas production processes. However, solving critical opening online in an offshore oil field is very difficult because only topside measurements are available and system information such as inlet gas–liquid flow rates and transfer functions are unavailable or far from precise. In order to cope with this problem, manually traversal experiments were first conducted in a large-scale experimental system consists of a 114-m horizontal pipeline, an 18.7-m downward-inclined pipeline with an inclination angle of −5˚ and a 16.3-m riser. Based on the results, a new process variable characterizing cut-off ratio of outflow and a new valve parameter describing the influence of valve on flow were derived. An approximate linear relation between these two parameters was found, with which critical openings can be calculated by processing real-time data. Finally, a control scheme was designed to overcome the calculation errors and solve for critical openings on line. The performance was validated by automatic control experiments.

Opportunities and challenges in new production systems for salmon farming in Norway—Industry perspective

The Norwegian salmon farming industry is characterized by an increasing technological diversity with new production systems emerging. The objective of this paper is to provide knowledge about challenges and opportunities with new production systems as perceived by industry representatives with hands-on experience. Interviews and workshops with fish farmers and suppliers illustrate that even though environmental issues concerning salmon lice, escapes, and diseases can be reduced, and in some cases solved, new challenges might arise. Semi-closed containment and land-based system concerns pertained to water quality and fish welfare, while exposed and offshore systems were more concerned about harsh conditions and their effects on fish, structures, and work operations. However, possibilities for beneficial new production strategies, the potential for a more stable production environment, and increased biosecurity are seen as important advantages. These findings provide valuable perspectives for industry, technology suppliers, and regulators moving forward.

Numerical investigation of punch-through mitigation in stiff-over-soft clays using skirted spudcan

Punch-through failure, a critical issue in offshore engineering, occurs when a foundation penetrates through strong-over-weak soil layers. This paper presents a study on the effectiveness of skirt addition to spudcans in addressing punch-through failure through numerical simulations using the axisymmetric Particle Finite Element Method (PFEM). The validity of the PFEM is verified by simulating a spudcan penetration centrifuge test. Subsequently, PFEM simulations are conducted to analyse the penetration behaviour of both generic and skirted spudcans in stiff-over-soft clays. Results from the simulations reveal the bearing responses of spudcans as they penetrate into clays, elucidate associated failure mechanisms, and underscore the significant of considering the spudcan-driving process in estimating punch-through failure mitigation. Findings indicate that, the skirt effectively mitigates punch-through failure by increasing plug height in the lower soft layer, thus reducing the rate of bearing capacity reduction. Furthermore, critical factors such as skirt length, upper layer thickness, lower layer strength gradient, and the strength ratio between lower and upper layers are assessed through comprehensive parametric studies to evaluate the efficacy of skirted spudcans in mitigating punch-through failure, with eventual goal to provide essential guidance for practical design considerations in offshore foundation systems.

A New Zero Waste Design for a Manufacturing Approach for Direct-Drive Wind Turbine Electrical Generator Structural Components

An integrated structural optimization strategy was produced in this study for direct-drive electrical generator structures of offshore wind turbines, implementing a design for an additive manufacturing approach, and using generative design techniques. Direct-drive configurations are widely implemented on offshore wind energy systems due to their high efficiency, reliability, and structural simplicity. However, the greatest challenge associated with these types of machines is the structural optimization of the electrical generator due to the demanding operating conditions. An integrated structural optimization strategy was developed to assess a 100-kW permanent magnet direct-drive generator structure. Generated topologies were evaluated by performing finite element analyses and a metal additive manufacturing process simulation. This novel approach assembles a vast amount of structural information to produce a fit-for-purpose, adaptative, optimization strategy, combining data from static structural analyses, modal analyses, and manufacturing analyses to automatically generate an efficient model through a generative iterative process. The results obtained in this study demonstrate the importance of developing an integrated structural optimization strategy at an early phase of a large-scale project. By considering the typical working condition loads and the machine’s dynamic behavior through the structure’s natural frequencies during the optimization process coupled with a design for an additive manufacturing approach, the operational range of the wind turbine was maximized, the overall costs were reduced, and production times were significantly diminished. Integrating the constraints associated with the additive manufacturing process into the design stage produced high-efficiency results with over 23% in weight reduction when compared with conventional structural optimization techniques.

Bayesian network analysis enhancing alternative design schemes of large-scale offshore systems

Bayesian network analysis enhancing alternative design schemes of large-scale offshore systems

A field study to optimize protein and lipid levels in diet for cage-cultured subadult rockfish Sebastes schlegelii

A feeding trial was conducted to evaluate growth, body composition, serum biochemistry, digestion and metabolism, and oxidation resistence of S. schlegelii fed 9 diets in a 3×3 factorial design (protein levels: 44 %, 48 %, 52 %; lipid levels: 6 %, 10 %, 14 %), to optimize protein and lipid levels for practical feed formula. Rockfish (114.25 g) were stocked into 27 cages in an offshore system and fed test diets to satiation twice daily for 8 weeks. Growth increased but feed conversion rate decreased with dietary protein increasing. Increasing dietary protein to >48 % led to reduced feeding intake but increased protein efficiency ratio. Lipid efficiency ratio increased with dietary protein increasing but decreased with dietary lipid increasing. Hepatosomatic index decreased coupling with the increases in condition factor and liver lipid content as dietary lipid increased to 14 %. Intraperitoneal fat ratio increased with dietary lipid increasing. Increasing dietary protein to > 48 % significantly elevated serum total protein and glucose concentrations, hepatic glycogen synthase activity. High-protein (52 %) diets elevated serum albumin and urea nitrogen concentrations, hepatic pyruvate kinase and alanine aminotransferase (ALT) activities but downregulated hepatic growth-hormone (GH) receptor. Activities of trypsin, lipase, serum superoxide dismutase and total antioxidant capacity decreased with the dietary lipid increasing. Increasing dietary lipid to > 10 % reduced serum GH concentration, and high-lipid (14 %) diets significantly enhanced serum triglyceride concentration and hepatic transaminases activities, and resulted in a visual increase of adipocytes in liver. Serum cholesterol and low-density lipoprotein decreased as dietary protein increased to 48–52 % or dietary lipid >10 %. Hepatic succinate dehydrogenase activity and serum IGF-1 significantly increased while hepatic fatty acid synthetase decreased as dietary protein increased to >48 % or dietary lipid >10 %. High-protein (52 %) diet or high-lipid (14 %) diet elevated serum malonaldehyde concentration. These findings suggested 48 % protein and 10 % lipid were the optimal in diet for subadult S. schlegelii.

Dynamics of an offshore drilling tube system based on a riser–drill string–drilling fluid coupling model

ABSTRACT Accurate prediction of dynamic characteristics of an offshore drilling tube system under marine environmental loads is significant to secure the safety of offshore drilling operations. Based on previous works for coupling riser with drill string to form a pipe-in-pipe structure, in this present work, the influence of drilling fluid is taken into consideration to develop a riser–drill string–drilling fluid coupling model; and the corresponding verifications are conducted via comparison with the experimental results. The collisions between riser and drill string are demonstrated to restrict the lateral drifting of the riser, which, however, can be intensified by the upward flow of drilling fluid. In addition, as increasing the offset of the drilling platform, the lateral drifting of the riser also increases; moreover, the position for the maximal drifting moves upwards to the sea surface. When the part of the drill string below the mudline is taken into consideration, the increasing angle of well inclination is illustrated to restrict the lateral drifting of the riser above the mudline.

Individual-based numerical experiment to describe the distribution of floating kelp within the Southern Benguela Upwelling System

Abstract Kelps are resilient organisms, capable of thriving in high-energy wave environments. However, when hydrodynamic drag forces exerted by the wave environment exceed the kelps’ structural limits, individuals become dislodged. Floating kelps generally follow ocean currents, traveling long distances until air-filled structures fail or the epibiont load becomes too great, causing them to sink to the seafloor. The ability of kelp to disperse over vast offshore and nearshore systems makes them important for organic subsidy and as a dispersal vector for marine organisms. Previous research on dislodged macroalgae focused on context-specific rafts, limiting insights into the broader ecological role of floating kelp. This study employed a site-specific Lagrangian trajectory model to describe the spatial distribution of floating Ecklonia maxima along the South African coastline. The model incorporated buoyancy and sinking using site-specific morphological data. Findings revealed that the distribution of floating E. maxima is influenced by oceanographic conditions, and seasonal patterns were also evident. Mesoscale features played a vital role in kelp accumulation on the surface and seafloor and acted as barriers to dispersal. This study offers essential insights into kelp’s role as an organic subsidy and provides numerical evidence for kelp’s potential as a carbon sink, contributing to a better understanding of kelp ecosystems and their ecological functions.