A semi-analytical model for a wave energy extraction system integrating a floating-submerged dual-buoy WEC device with a Jarlan-type breakwater is proposed, and a comparison is conducted with a traditional breakwater-WEC device, highlighting the advantages of the hybrid system. The model was established using the method of separation of variables and the matched eigenfunction expansion method, and was validated through energy conservation, convergence checks, and comparison with previous results. The study determines the required restoring stiffness for the underwater buoy to prevent collisions with the floating buoy. It also analyzes the energy conversion and wave resonance within the device. The results indicate that reducing the thickness and increasing the draft of the submerged body, while decreasing the draft of the floating body, enhances the system's energy capture efficiency. Water wave resonance between the device and the coastal wall improves this efficiency. However, when the device is positioned at the nodes of standing waves formed by coastal reflection, the efficiency drops to zero. Placing a perforated wall between the floaters and the coastal wall can reduce the horizontal wave loads on the floaters by up to 60%. Meanwhile, the maximum energy capture efficiency of the system consistently remains above 0.85.

As floating offshore wind turbines (FOWTs) expand into deeper and more complex marine environments, validating mooring system performance under real-world conditions becomes critical. This study investigates whether the purposely designed offshore floating laboratory (OffLab), named ACTOR, can serve as an effective and conservative testbed for mooring line evaluation. ACTOR is a conceptual platform inspired by the floater of the UMaine VolturnUS-S 15 MW semi-submersible FOWT design. The dimension of the ACTOR is about one third of the 15 MW semi-sub floater and is intended deployment in a nearshore UK site with milder sea conditions. Using site-specific environmental data from two locations-the full-scale deployment zone in the Celtic Sea and a nearshore test location near Plymouth Sound-we perform comparative mooring analyses with OrcaFlex. Extreme load cases are defined using Direct-IFORM environmental contours, and fatigue conditions are derived from long-term wave spectral clustering. Results show that due to shallow water effects and tailored pretensioning, the ACTOR platform can replicate or exceed the mooring line tensions and fatigue damage accumulation observed in full-scale systems. The findings demonstrate the potential of ACTOR as a physically accessible, cost-effective platform for accelerated offshore component testing.

The semi-submersible aquacultural platform has attracted increasing attention in recent years. The semi-submersible aquacultural platform comprises multiple rearing tanks separated by fish nets, and the flow field characteristics within these tanks are of significant importance to fish welfare and pollutant dispersion. This study proposed a numerical model based on the mesh-free Smoothed Particle Hydrodynamics (SPH) method to investigate the flow field of the semi-submersible aquacultural platform under currents. The proposed model represents fish nets with numerous nodes through a simplified system of spheres and springs. Numerical results for both rigid and flexible nets are validated against experimental data, demonstrating that the proposed method provides a reliable and effective approach for simulating fish nets. The maximum displacement of the platform is only 0.009m, indicating that its deformation is negligible. Replacing flexible nets with rigid ones in simulations can improve computational efficiency by approximately 50%. Numerical results show that nets significantly decrease the velocity in the three rearing tanks with velocity reductions ranging from 64% in the upstream tank to 86% in the downstream tank. Velocity variations along the horizontal and vertical directions inside those tanks are discussed in detail. Drag forces on each component are evaluated, with the platform frame accounting for approximately 69% of the total fluid loads, while the nets contribute about 17% and should therefore not be neglected in structural design. The proposed SPH model serves as a powerful tool for simulating complex fluid-structure interactions in the aquacultural platform.

With the advancement of offshore wind technology, mooring design and modelling of large Floating Offshore Wind Turbines (FOWT) have become crucial for ensuring their stability and cost-effectiveness under complex design conditions. However, the applicability of conventional mooring models to these next-generation, largescale systems, particularly under harsh sea states where nonlinear effects become prominent, requires systematic investigation. This study presents a comprehensive framework for mooring system design for the IEA 15 MW large semi-submersible wind turbine, employing both a Multi-Segmented Quasi-Static (MSQS) model and a Lumped Mass (LM) dynamic model for in-depth analysis. This work not only quantifies the distinct contributions of wave kinematics and current dynamics on the mooring lines, but also further evaluates the critical interplay between mooring model fidelity and the high-order wave forces on the platform. Based on the full spectrum of IEC design load conditions, this study assessed the performance of the FOWT under normal, severe, and extreme environments. It was found that, while quasi-static models are adequate for platform motion and associated loads under normal conditions, dynamic models offer more precise predictions for platform motion, structural loads, and mooring tensions under severe and extreme conditions. A key finding is that, regardless of the design state, dynamic models consistently outperform quasi-static models in predicting mooring behaviour. Furthermore, our analysis provides an actionable guideline for designers: the effects of wave kinematics on mooring lines can often be neglected in favour of focusing on current effects. Crucially, the study reveals that, when high-order wave forces on the platform are considered, a hydrodynamic-inclusive dynamic mooring model becomes essential for accurate prediction. The selection of an appropriate mooring calculation model based on these findings not only optimizes the trade-off between computational efficiency and accuracy, but also ensures accuracy, thereby providing a more robust scientific foundation for the planning, construction, and operation of offshore wind farms.

Short-term prediction of significant wave height (SWH) has crucial impacts on operation safety of offshore structures and marine navigations. However, conventional intelligent models have limitations in predicting nonlinear situations. This paper introduces a hybrid algorithm combining chaos particle swarm optimization (CPSO) with a support vector regression (SVR) model to enhance the generalization and nonlinear handling capabilities for SWH prediction. Additionally, Principal Component Analysis (PCA) is incorporated to reduce information redundancy. To validate the proposed model's predictive performance, several alternatives are tested, including the single SVR model, PCA-SVR, and PCA-GA (Genetic Algorithm)-SVR models. Additionally, the PCA-GWO (Grey Wolf Optimizer)-SVR and PCA-CPSO-SVR models are compared to assess the effects of GWO and CPSO techniques. Significant improvements were observed when comparing CPSO-SVR with other algorithms. Prediction efficiency was evaluated using mean absolute error (MAE), root mean square error (RMSE), and the correlation coefficient (R). Across different test set lengths, the PCA-CPSO-SVR model reduced RMSE by 54.12 % to 74.88 % compared to the benchmark. These results demonstrate the hybrid PCA-CPSO-SVR model's strong generalization ability and superior predictive capacity for non-stationary waves.

This paper investigates the hydrodynamic performance of a pool-type cylindrical Floating Production Storage and Offloading (FPSO) unit equipped with a bottom damping plate designed to mitigate heave motion. Using a semi-analytical approach, we developed a three-dimensional model based on linear potential flow theory to conduct a comprehensive hydrodynamic analysis of the floating structure. The methodology integrates the eigenfunction matching method with significant nonlinear boundary conditions. We systematically evaluate the wave load and heave motion characteristics of both the entire device and the damping plate, considering various dissipation coefficients and geometric parameters of the damping plate. To validate the accuracy of the proposed semi-analytical model, we compare the results with experimental data and numerical simulations. The calculated results reveal a strong positive correlation between wave loads and different damping plate geometries, with subtle variations in specific directions within the high-frequency domain. Incorporating dissipation coefficients into the potential calculation significantly mitigates abrupt fluctuations in hydrodynamic coefficients at resonant frequencies, enhancing the stability and reliability of the computational results. Additionally, optimizing the geometric parameters of the damping plate substantially influences the hydrodynamic coefficients, particularly for the heave motion of the device. The forces acting on the damping plate under various conditions in irregular incident waves underscore the critical impact of the damping plate on structural safety. The findings identify an optimal damping plate design for a pool-type FPSO to enhance anti-heave effectiveness, providing valuable insights for engineering design.

Floating offshore wind turbines are expected to be deployed in significant numbers across the globe in the coming decades, with wet towing of these structures between ports and farms a key operation in their installation, maintenance, and decommissioning. Platforms are likely to be towed across large distances, and accurate understanding of tow dynamics will be crucial to optimising these journeys to minimise costs, timescales, emissions, and risk. This paper presents experimental and ship simulator modelling of the oceanic towing of the IEA 15 MW turbine on the UMaine VolturnUS-S platform. The work provides indicative data for floating offshore wind turbines under tow, investigates the effect of added wave resistance in head seas, and discusses some of the challenges with traditional modelling and the effectiveness of using a ship simulator to model study offshore wind turbine towing operations.

A novel fully nonlinear circular numerical wave basin is developed based on potential flow theory and high-order boundary element methods (HOBEM). By controlling the vector input of wave velocity from wave-making sources uniformly distributed on the three-dimensional cylindrical surface, the wave basin is capable of generating waves in all directions. The wave basin is used to simulate nonlinear waves, including uni-directional, multi-directional, and even omni-directional focused waves. These waves as typical cases demonstrate the advantages of the wave basin generating multi-directional, multi-frequency waves and localized distorted waves. The results show that the fully nonlinear free-surface boundary conditions allow the wave basin to capture higher-order wave components during the propagation and deformation of stronger nonlinear waves. The annular artificial damping layer effectively absorbs wave energy from all directions, ensuring the stability of the simulation by mitigating spurious reflections. This fully nonlinear numerical wave basin overcomes the limitations of traditional wave tanks regarding wave direction angles.

As the importance of marine energy development increases, deep-sea aquaculture net cages, critical for improving energy efficiency and modernizing fisheries, face challenges such as high power supply costs, maintenance difficulties, and environmental impact. This paper proposes a Two-wing Pendulum Wave Energy Converter (TPWEC) suitable for offshore deep-sea regions. The device captures wave energy through a pendulum wing system, converting it into electricity to support deep-sea aquaculture, while efficiently utilizing marine resources. A three-dimensional numerical wave tank is developed based on viscous flow theory, and convergence analysis is performed using the k-ε turbulence model. The hydrodynamic and energy conversion characteristics of the TPWEC under various sea conditions are analyzed. The results show that the shape of the pendulum wings significantly impacts energy capture. Within a reasonable range, increasing the wing width enhances the wave moment and captured energy, but the rate of increase becomes slower as the width grows. Regarding the PTO damping constant, the system's average power output increases with linear damping up to an optimal point, then decreases. The optimal damping constants vary between 2.5 and 7.5 N·m·s/rad depending on the wave period. Additionally, the spacing between the TPWEC and the aquaculture float structure significantly affects its hydrodynamic response. The motion response is largest when the spacing ratio (D/a) is 1.5. The energy capture efficiency is also influenced by the number and relative positioning of the devices. Maximum energy capture is achieved when six devices are placed symmetrically on both sides of the net cage. Simulation results from Comsol software further confirm the energy output characteristics of the TPWEC. This study concludes that the TPWEC offers high energy efficiency and environmental adaptability, providing a viable solution for integrating renewable energy generation with deep-sea aquaculture systems.

The present paper proposes a hybrid raft-type system which can act as wave energy converter (WEC) and breakwater. The device, anchored to the seabed with mooring lines, comprises multiple plate-like rafts equipped with power take-off (PTO) systems at their joints. Based on the Smoothed Particle Hydrodynamics (SPH) method, a two-dimensional wave tank is established to study wave interactions with this hybrid multi-raft system. To validate the proposed SPH model, a laboratory experiment is conducted to assess the hydrodynamic performance of a triple-raft structure. The SPH model is then applied to compare hydrodynamic performance between double and triple raft configurations. This study reveals the interaction and interference effects between waves and the rafts. The results indicate that, compared to the double-raft structure, the addition of a third raft significantly enhances the pitching motion of the original two rafts. The effects of the raft width, the resonance mode, and the mooring system are analyzed. The findings demonstrate that resonance dominates the wave energy extraction performance at specific frequencies. The double-point mooring mode facilitates the device's absorption of multiperiod waves, while its mooring forces are significantly higher than that of the single-point mooring system. These results offer valuable insights on the design of hybrid floating WEC-breakwater system.

A study was conducted on an integrated wave energy extraction (IWEE) system, which includes a heaving wave energy converter (WEC) and a Jarlan-type breakwater, using the linear potential flow theory for analysis. The methods of variable separation and eigenfunction expansion matching were utilized to calculate the velocity potentials in space. Following theoretical and numerical validation, the IWEE system model was compared with existing models, and parametric studies of its hydrodynamic performance and energy capture capabilities were conducted. Subsequently, the wave loads on the system were calculated for safety and reliability design. Results indicate that integrating a Jarlan-type breakwater downstream of the buoy significantly enhances the device's energy capture efficiency and wave dissipation performance compared to an isolated WEC. The presence of a perforated plate can effectively suppress the considerable wave force caused by the wall reflections. The wave attenuation performance and energy capture capability could be improved by correctly adjusting the geometrical parameters. Additionally, the comparison results of the wave forces indicate that the IWEE system is benefited of larger wave forces which can perform better wave dissipation and wave power extraction, thus a compromise analysis between power conversion performance and reliability of the hybrid system is needed for appliance.

This research presents a comprehensive analysis of the mooring system design for the 1 MW OE35 wave energy converter, which is being developed by the WEDUSEA project. The study centres on the dynamic analysis of mooring configurations using Orcaflex software to simulate the environmental and operational conditions expected at the deployment site. The analysis involved an iterative design and validation process, refined through both numerical modelling and basin testing. These tank tests were crucial for validating the Orcaflex model outcomes by providing a controlled environment to observe the physical behaviours of the proposed mooring configurations under simulated sea conditions. The finalized mooring system design employs a three-point catenary setup, optimized through extensive simulation to withstand varied environmental loads while maintaining system integrity and device stability. This paper outlines the progression from initial mooring concepts to a thoroughly validated design, demonstrating improvements in mooring strategies that enhance the reliability and performance of wave energy converters in real sea conditions. The findings from this analysis contribute significantly to the ongoing efforts to scale wave energy technologies, aligning with broader industry targets for cost reduction and sustainability in renewable energy deployments.

Accurate forecasting of motion and mooring loads in fish cages is vital for efficient field monitoring and numerical simulations. This research introduces an innovative hybrid model that leverages Bidirectional Stateful Long Short-Term Memory (Bi-SLSTM) neural networks to predict the dynamic behavior of fish cages. By incorporating bidirectional data flow and state-preserving mechanisms, the model enhances the accuracy of multi-step predictions. Performance is assessed through the Root Mean Square Error (RMSE) and the Trapezoidal-based Integral Similarity Index (Rtrapz). Results show that Bi-SLSTM outperforms Long Short-Term Memory (LSTM), Gated Recurrent Unit (GRU), and Bidirectional Long Short-Term Memory (BiLSTM) models, achieving Rtrapz values above 0.85 in large multi-step predictions. Further analysis reveals that combining wave and motion data as inputs improves prediction accuracy, with surge and heave predictions reaching 91 % and 98 %, respectively. The hybrid strategy combining motion response and load data provides the best performance for mooring load prediction, with Rtrapz values exceeding 0.85 across different output steps. The Bi-SLSTM model demonstrates strong prediction capability and robustness in forecasting cage dynamics.

The hybrid system consisting of an Oscillating Buoy and a floating dock provides a promising solution for wave energy conversion and power supply of marine vehicles. In this paper, a floating dock station (FDS) combined with a cantilevering oscillating buoy (COB) was proposed. The COB is hinged to the floating dock and helps to generate the electric power by relative movement between the COB and FDS. Based on the potential flow theory, a three-dimensional model was set up in the AQWA software to investigate the hydrodynamic characteristics of this proposed hybrid system. In this paper, the effects of wave conditions and geometric properties of the FDS-COB device were studied and optimized to improve the power capture performance of the hybrid system. The results show that the device achieves a high wave energy conversion efficiency of 44.3

The transition to sustainable energy is crucial for mitigating climate change impacts. This study addresses this imperative by simulating a green hydrogen supply chain tailored for residential cooking in Oman. The supply chain encompasses solar energy production, underground storage, pipeline transportation, and residential application, aiming to curtail greenhouse gas emissions and reduce the levelized cost of hydrogen (LCOH). The simulation results suggest leveraging a robust 7 GW solar plant. Oman achieves an impressive annual production of 9.78 TWh of green hydrogen, equivalent to 147,808 tonnes of H 2 , perfectly aligning with the ambitious goals of Oman Vision 2040. The overall LCOH for the green hydrogen supply chain is estimated at a highly competitive 6.826 USD/kg, demonstrating cost competitiveness when benchmarked against analogous studies. A sensitivity analysis highlights Oman’s potential for cost-effective investments in green hydrogen infrastructure, propelling the nation towards a sustainable energy future. This study not only addresses the pressing issue of reducing carbon emissions in the residential sector but also serves as a model for other regions pursuing sustainable energy transitions. The developed simulation models are publicly accessible at https://hychain.co.uk , providing a valuable resource for further research and development in the field of green hydrogen supply chains.