Search Results (76)

Over the past decade, significant progress has been made in the development of regional wave observational systems. In particular, the Backyard Buoys program deployed multiple wave buoys along the Alaskan Coast to collect real-time wave spectra. In parallel, the expansion of the subsea fiber optic cable network around Alaska has provided a potential new source for high-resolution Significant Wave Height (SWH) observations. In this study, we conduct Observing System Simulation Experiments (OSSEs) to quantify the potential forecasting skill of different observational configurations, including a moored buoy, a single optical cable, and a hypothetical cable network. We use the SWAN wave model configured for the regional domain along the Northern Alaskan Coast and equipped with an extension of the a4Dvar approach, which allows optimization of both the initial conditions and wind forcing. In the OSSEs, it was found that assimilation of the SWH from the network of optical cables provides the most accurate wave forecast of SWH for regular wind conditions, but assimilation of spectral wave observations from the moorings significantly outperforms the skill of a single-cable platform and provides better control of wind forcing and wave direction, especially for stronger winds. In the second part of the study, the same approach was applied to real observations from the Oliktok Point region. Experiments with real observations from the 37 km long optical cable and wave mooring agree well with the main conclusions from the OSSE results. Full article

To ensure the safety and stability of single point mooring (SPM) systems operating in shallow waters, this paper investigates the influences of shallow-water effects on mooring systems under different water depth-to-draft ratios. For the pile-founded column single point mooring system in shallow sea areas, based on the numerical calculation method verified by model tests, frequency domain and time domain calculations are carried out to study the specific impact of shallow water effects on the hydrodynamic parameters of the hull, and the critical water depth-to-draft ratios applicable to the two second-order wave load calculation methods (Newman approximation and Pinkster approximation) are analyzed. At the same time, the specific impact of shallow water effects on the dynamic response of the mooring system under three different hull loading conditions at the same and different water depth-to-draft ratios is studied, and the critical water depth conditions for bottom contact in each loading condition are summarized. The results show that the shallow water effect has a significant impact on the hydrodynamic parameters such as RAO of the hull response, especially in the low-frequency response region. There are obvious differences between the Newman approximation and the Pinkster approximation methods. In shallow water conditions, the Pinkster approximation method has a more accurate calculation effect, and when the water depth-to-draft ratio reaches a certain critical value, the calculation results of the two approximation methods are basically consistent. For the same and different water depth-to-draft ratio conditions, the amplitude of the hull motion in the full-load draft state is greater than the other two loading conditions, but the response results of the cable tension are opposite. The research results reveal the specific influences of shallow-water effects on pile-supported single-point mooring (SPM) systems, which can provide references for the safety and stability design of mooring systems and bear great engineering significance for advancing the deployment of single-point mooring systems in shallow water regions. Full article

Maintaining structural stability and reliable mooring performance remains a key challenge for offshore floating photovoltaic (FPV) systems. This study investigates the coupled hydrodynamic and mooring behavior of a novel large-scale hexagonal rigid FPV platform through 1:25-scale physical model tests. A near-zero-pre-tension slack mooring arrangement was adopted to isolate the effects of mooring type, including anchor chain (M1), steel cable (M2), and elastic cable (M3). The results show that the influence of mooring configuration is strongly degree-of-freedom dependent. Surge motion is highly sensitive to mooring type, whereas heave and pitch remain largely consistent among the three cases. In regular waves, the maximum surge-acceleration RAO of M2 is 1.82 and 2.27 times those of M1 and M3, respectively. Peak mooring tension shows a strong correlation with maximum surge acceleration in both regular and irregular waves, indicating that surge motion can serve as a useful indicator of extreme mooring loads under similar slack-mooring conditions. Among the three configurations, M1 exhibits the strongest short-term peak-load buffering. Under extreme irregular waves, its peak mooring tension is 82.4% and 24.7% lower than those of M2 and M3, respectively. These results provide experimental guidance for the mooring design of large-scale rigid FPV systems. Full article

Todos Santos Bay, Mexico, features several wave-focusing areas driven by its complex bathymetry, making it an ideal real-world test case for wave energy converter (WEC) park optimization. This study quantifies the influence of submarine cable costs and bathymetry-dependent mooring costs on the proposed park layout (hereafter the star-layout) and the levelized cost of energy (LCOE) of a 10-device WEC park, using a multi-state operational wave climatology of $N=179$ representative sea states from a 2008–2018 SNL-SWAN hindcast (covering 97.20% of the annual time). A binary genetic algorithm combined with K-means clustering analysis was used to minimize LCOE under three cost scenarios: baseline, cable-only, and cable plus bathymetry-dependent mooring. Both infrastructure cost components contribute substantially: cable costs add 52.2% to the baseline LCOE, and bathymetry-dependent mooring costs add a further 16.0% at this site, with cable approximately three times more impactful. These quantitative magnitudes are conditioned on the moderate depth-gradient setting of Todos Santos Bay; the qualitative cost-component hierarchy is expected to generalize, but the relative weights will depend on the bathymetric and wave-climate characteristics of each candidate site. The mooring contribution is nontrivial both economically and spatially (the centroid of the park shifts by approximately 151 m between the cable-only and cable-plus-depth scenarios). K-means clustering identified 2–4 layout families per scenario (K $=4\to 3\to 2$ as cost components are added), indicating that infrastructure constraints reduce the viable solution space. These results support the central hypothesis of this work: WEC park optimization studies that adopt flat-bathymetry simplifications, the prevailing assumption in much of the prior literature, risk substantial underestimation of LCOE at sites with nontrivial depth variation. We recommend that bathymetry-dependent mooring costs be included alongside cable costs in any early-stage techno-economic assessment of WEC parks at sites with complex bathymetry. Full article

Over the past few decades, with the continuous expansion of offshore oil and gas resource development into deepwater and ultra-deepwater environments, slender structures such as flexible risers, subsea pipelines, mooring cables, and underwater cables have served as core links connecting offshore platforms, subsea production systems, and onshore terminals [...] Full article

Safe exploitation of the marine natural gas hydrate (NGH) resource is essential to meet the demand of the future energy requirement. To enable real-time monitoring of methane leakage during the production test of NGH, an ocean stereoscopic monitoring system based on underwater single-point mooring structure is developed, which supports in situ monitoring of marine environment at the sea-air interface, the euphotic zone, and the seabed boundary layer. Numerical simulations were conducted to evaluate the effect of mooring configuration, cable lengths, and buoyancy settings on the mooring stability of the system against the current and waves. Based on the simulation result, an optimized segmented inverse-catenary mooring configuration is developed to achieve a balance between the performance and cost. The designed submersible relay buoy isolates the upper dynamic S-shaped cable from the lower static straight electro-optical-mechanical (EOM) cable, thereby improving system stability. The monitoring system based on the optimized mooring structure is successfully deployed at the NGH zone in the northern South China Sea at the water depth of 1330 m confirming its working stability in harsh sea conditions. Full article

To address the issues of insulation layer damage and conductor exposure in offshore floating photovoltaic systems occurring in shallow marine regions characterized by significant tidal ranges under multi-field coupling effects, an overhead cable laying scheme based on the hybrid pile–floater structure is proposed, while its mechanical response is investigated in this paper. The motion response model of the floating platform, considering wind load, wave load, current load, and mooring load, as well as the equivalent density and mathematical model of the overhead cable are established. The mechanical response characteristics of the overhead cable are analyzed through finite element analysis software. The results indicate that the overhead cable’s mechanical response is influenced by the span length and coupled wind–ice loads. Specifically, the tension exhibits a nonlinear increasing trend, while the deflection shows differential variations driven by the antagonistic interaction between wind and ice loads. The influence of ice loads on the configuration of overhead cables is significantly weaker than that of wind loads. This study provides crucial theoretical support for enhancing the lifespan of the overhead cable. Full article

Floating offshore production systems play a critical role in offshore resource development, where the structural integrity and operational safety of risers, umbilical cables, and mooring cables are of paramount importance. Focusing on the failure risks of these key components under harsh marine environments, this paper systematically reviews the coupled mechanisms of wave-induced loading, electrochemical corrosion, and material fatigue. Unlike traditional reviews on offshore pipelines and cables, this study not only examines the mechanical performance of deepwater pipelines and cables along with representative research cases but also discusses corrosion mechanisms in marine environments and corresponding repair and mitigation strategies. In addition, recent advances in machine learning-based digital twin frameworks and real-time monitoring technologies are reviewed, with an analysis of representative application cases. The findings indicate that interdisciplinary material innovations combined with data-driven predictive models are essential for addressing maintenance challenges under extreme ocean conditions. Furthermore, this review identifies existing research gaps in data fusion for monitoring technologies and outlines clear directions for the intelligent operation and maintenance of future deep-sea infrastructure. Full article

Lighter-than-air parakites deployed at sea in the close proximity of wind turbines may offer the possibility of mitigating wake losses encountered in large offshore wind farms. Such devices, having an order of magnitude similar to wind turbine rotors, can divert the stronger winds available at high altitudes to the lower level within the atmospheric boundary layer to enhance the wind flow between turbines. Mooring the parakites directly to the offshore wind turbine support structures would avoid the need for additional offshore structures. This paper investigates a novel and simple approach for mooring a parakite to an offshore wind turbine. The proposed approach exploits the lift forces of the inflatable parakite to reduce the tower bending moment at the base of the turbine induced by the rotor thrust. An iterative numerical model coupling the parakite loads to a catenary cable piecewise model is developed in Python 3.12.7 to quantify the bending moment reduction and shear load variations at the wind turbine tower base induced by the different kite geometries, windspeeds, and mooring cable lengths. The numerical model revealed that the proposed approach for mooring parakites can substantially reduce the tower bending loads experienced during rotor operation without considerably increasing the shearing forces. It was estimated that the tower bending moment decreased by 7.7% at the rated wind speed, where the rotor thrust is at its maximum, while the corresponding shear force increased by 0.6%. At higher wind speeds, where the magnitude of the rotor thrust decreases, the percentage reduction in bending moment gradually increases to 51.7% at a wind speed of 24 m/s, with the corresponding shear force increasing by only around 4.6%. Furthermore, while upscaling the parakite augments the tower bending moment reduction, changes in cable length had little effect on bending moment reduction and shear increase. Full article

Offshore floating photovoltaic (FPV) platforms are usually deployed in shallow waters with large tidal variations, where the modules of FPV are connected with each other via the connectors to form an array and mounted to the seabed via the mooring system. Therefore, the mooring system and module connectors have significant influence on the dynamic response characteristics of FPV. In targeting such shallow waters with large tidal ranges, this paper proposes four integrated mooring-connection schemes based on configuration and parameter customization guided by adaptability optimization, including two kinds of mooring systems, named as horizontal mooring system and catenary mooring system with clumps, and two kinds of connection schemes, named as cross-cable connection and hybrid connection, are proposed. The feasibility of the mooring systems to adhere to the tidal range and the influence of the connection schemes on the dynamic response of the FPV are numerically investigated in detail. Results indicate the two mooring systems have comparable positioning performance; horizontal mooring offers slightly better tidal adaptability but much higher mooring tension, compromising system safety. Hybrid connection yields smaller surge amplitudes than cross-cable connection but generates excessively large connection forces, also posing safety risks. Comprehensive comparison indicates that catenary mooring with clumps combined with cross-cable connection imposes lower requirements on platform structural safety factors, while horizontal mooring with cross-cable connection exhibits stronger adaptability to water level and environmental load direction changes in shallow waters. Full article

To address the current lack of specialized equipment for offshore wind platform installation and the unresolved challenges in deploying large offshore converter stations, this paper proposes a novel T–U-shaped barge for large offshore wind structures. First, a hydrodynamic model of the T–U-shaped barge is constructed and analyzed in ANSYS-AQWA. The influence of resonance occurring in the gap at the U-shaped stern on the frequency-domain model of the T–U-shaped barge is investigated. Subsequently, two installation configurations are examined: loading at the bow and loading at the stern of the T–U-shaped barge. This study comprehensively considers key components of the float-over installation system, including leg mating units (LMUs), deck support units (DSUs), fenders, and mooring cables. The results show that, for both installation schemes, the dynamic load distribution on each LMU evolves as the load-transfer stage progresses, and the sensitivity to wave period varies across different load-transfer stages, even under the same operating condition. This study evaluates the performance of the proposed T–U-shaped barge in the float-over installation of large offshore converter stations, demonstrating that its distinctive configuration endows it with strong functionality and provides valuable references for optimizing offshore wind-structure installation methods, as well as for the design and manufacturing of installation equipment. Full article

To address the issues of traditional mooring lines, such as high self-weight, low strength, and poor durability, Carbon-Fiber-Reinforced Polymer (CFRP) was investigated as a material for mooring lines of offshore floating wind turbines, aiming to achieve high performance, lightweight design, and long service life for mooring systems. Based on a “chain–cable–chain” configuration, a CFRP mooring line design is proposed in this study. Taking a 5 MW offshore floating wind turbine as the research object, the dynamic performance of offshore floating wind turbines with steel chains, steel cables, polyester ropes, and CFRP mooring lines under combined wind, wave, and current loads was compared and analyzed to demonstrate the feasibility of applying CFRP mooring lines by combining the potential flow theory and the rigid–flexible coupling multi-body model. The research results indicate that, compared to traditional mooring systems such as steel chains, steel cables, and polyester ropes, (1) under static water, the CFRP mooring system exhibits a larger static water free decay response and longer free decay duration; (2) under operating sea conditions, the motion response and mooring tension of the offshore floating wind turbine with CFRP mooring lines are smaller than those with steel cables and steel chains but greater than those with polyester ropes; and (3) under extreme sea conditions, the motion responses of the offshore floating wind turbine with CFRP mooring lines are smaller than those with steel wire ropes and steel chains but close to the displacement responses of the polyester rope system, while the increase in mooring tension is relatively moderate and the safety factor is the highest. Full article

To address the issues of large fatigue loads on key components and poor platform motion stability under the coupling effect of wind, waves, and internal excitations in semi-submersible wind turbines, this paper proposes a data-driven load suppression and platform motion optimization method. First, the NREL 5 MW OC4 semi-submersible wind turbine is used as the research object. Wind-wave environment and aeroelastic simulation models are constructed based on TurbSim and OpenFAST. The rainflow counting method and Palmgren–Miner rule are applied to calculate the damage equivalent load (DEL) of key components, and the platform’s maximum horizontal displacement (Smax) is defined to represent the motion range. Secondly, a systematic analysis is conducted to examine the effects of servo control variables such as generator speed, yaw angle, and active power on the DELs of the blade root, tower base, drivetrain, mooring cables, and platform Smax. It is found that the generator speed and the yaw angle have significant impacts, with the DELs of the blade root and drivetrain showing a strong positive correlation with Smax. On this basis, a fatigue load model based on random forests is established. A multi-objective optimization framework is built using the NSGA-II algorithm, with the objectives of minimizing the total DEL of key components and Smax, thereby optimizing the servo control parameters. Case studies based on actual marine environmental data from the East China Sea show that, compared to the baseline configuration (a typical unoptimized control strategy), the optimization results lead to a maximum reduction of 14.1% in the total DEL of key components and a maximum reduction of 16.95% in Smax. The study verifies the effectiveness of data-driven modeling and multi-objective optimization for coordinated control, providing technical support for improving the structural safety and operational stability of semi-submersible wind turbines. Full article

Directly measuring the mooring cable load while a ship is moored at a wharf poses significant practical challenges. This paper proposes an indirect load measurement method to identify mooring cable static loads based on the Influence Coefficient Matrix (ICM) method. First, a finite element analysis of the bollard is conducted to obtain the full-field strains under each unit load. A solution procedure based on the genetic algorithm (GA) is then implemented to determine the optimal placement and orientation of strain gauges, aiming to improve load identification accuracy. An optimal load coefficient matrix is derived to establish the correlation between cable loads and bollard strains. Subsequently, following the established measured point placement scheme, strain gauges are installed on the bollard surface to capture the strains, enabling inverse identification of mooring cable loads through the measured strains and the pre-established load–strain relationship. A numerical case study validated the feasibility of this method, demonstrating high identification accuracy. Furthermore, experimental verification was conducted to assess its reliability under different conditions. Results confirmed the effectiveness of this indirect approach for mooring cable static loads measurement. The research findings provide a technical framework for real-time monitoring of mooring cable loads. Full article

In this paper, a new solution is proposed for the problem of mooring safety of large ships in complex sea conditions. Firstly, a dual-mode mooring system is designed to adaptively switch between active control and passive energy storage, adjusting the mooring strategy based on real-time sea conditions. Second, a collaborative analysis platform based on AQWA-Python-MATLAB/Simulink was researched and developed. Thirdly, based on the above simulation platform, the performance of the mooring system and the effects of different configurations on the stability of ship motion and dynamic tension of the cable are emphasized. Finally, by comparing the different mooring positions under various sea conditions with the traditional mooring system, the results show that the constant tension mooring system significantly improves the stability and safety of the ship under both conventional and extreme sea conditions, effectively reducing the fluctuation of cable tension. Through the optimization analysis, it is determined that the configuration of bow and stern cables is the optimal solution, which ensures safety while also improving economic benefits. Full article