Search Results (688)

Floating Offshore Wind (FOW) enables offshore wind deployment in deeper waters not suitable for bottom-fixed turbines, unlocking new areas for renewable energy generation. Most major cost contributors to FOW have clear pathways for cost reduction however mooring systems are the exception due to the pre-existing market maturity. Solutions to lower mooring costs include Mechanical Compliance Devices (MCDs) aimed at reducing the high peak and snatch loads in mooring lines and thus driving down the capital, operations and maintenance costs. In this paper, a comparison of a physical tank testing campaign and corresponding numerical analysis, for an MCD is described and analysed. The objective of the testing campaign was to validate the component-only tank results with the modelling of an MCD, namely Dublin Offshore’s Load Reduction Device (LRD) using a multi-body dynamics (MBD) approach. The paper presents analysis of the experimental testing and numerical modelling and compares the results with the validated Load–Extension Curve (LEC). Experimental testing was carried out at 1:38.5 scale using bespoke mooring test apparatus at Lír, Ireland’s National Ocean Test Facility. The results of testing are presented for all of the MCD model scales tested and compared with the modelled LEC. The correlation between the experimental and numerical data and with the LEC, characterised by Pearson Correlation Coefficient (R) in the range of 0.952 to 0.999, demonstrates the ability to model the LRD using the MBD approach. Full article

Suction bucket foundations provide an efficient foundation solution for offshore wind turbines, but improving their uplift resistance in soft clay remains a practical challenge. Vacuum preloading has been an effective means to enhance soft clay engineering properties, yet its offshore application is constrained by the difficulty of maintaining a reliable underwater seal. This study proposes soil-plug vacuum preloading, in which the impermeable skirt and lid of an installed suction bucket serve as a natural sealed boundary for post-installation soil improvement for enhanced uplift performance. Model tests on a bucket equipped with a central prefabricated vertical drain (PVD) were conducted to examine vacuum transmission, soil consolidation, and uplift behaviour. Two vacuum-preloaded cases with prefabricated vertical drain lengths H_PVD = L and H_PVD = 2L, where H_PVD denotes the PVD length and L denotes the bucket skirt length, were compared with an untreated case. Coupled hydro-mechanical finite element analyses were performed to interpret the observed responses. The tests showed that ultimate pullout capacity increased by 197% for H_PVD = L and 288% for H_PVD = 2L. The maximum negative pore pressure beneath the lid increased by 89% and 154%, respectively, while the remaining non-suction resistance also increased markedly due to vacuum-induced consolidation. Prototype-scale numerical analyses of a double-walled bucket were further conducted to investigate the effects of the bucket length-to-diameter ratio (L/D = 0.6, 1.0, and 1.5) and the applied vacuum pressure (0 to −70 kPa) on the uplift response. Among the analysed cases, the largest increase occurred for L/D = 1.5 under an applied vacuum pressure of −70 kPa, where the predicted uplift load at a displacement of 0.20 m increased by up to 42% compared with the no-vacuum condition. These results provide proof-of-concept evidence that soil-plug vacuum preloading may offer a potentially feasible post-installation approach for improving the uplift response of suction buckets in soft clay, although further experimental and field-scale validation is required. Full article

Scour-induced degradation of soil–structure interactions (SSIs) may substantially amplify the dynamic response of monopile offshore wind turbines (OWTs) under combined environmental and seismic loads. To clarify this mechanism and provide guidance for the safety assessment of OWT foundations, this study establishes a coupled numerical model considering wind, wave, earthquake, scour, and SSI effects. Based on this model, the DTU 10 MW OWT is selected as the research object, and its dynamic responses are investigated with different scour morphologies, scour depths, earthquake inputs, and selected soil parameter sets. The results show that scour reduces the lateral stiffness of the soil–structure system, shifts the structural natural frequency toward a lower-frequency range, and amplifies the displacement, acceleration, and stress responses under seismic excitation. With the selected M8 earthquake input, the tower top displacement reaches 4.18 m in the global-2D scour case, which is more than twice that in the non-scoured case. Global scour produces stronger response amplification than local scour because it weakens the SSI constraint around the full circumference of the pile. For the selected soil parameter sets and the adopted p–y formulations, the clayey foundation model produces smaller calculated displacement and stress responses than the sandy foundation model, reflecting differences in the prescribed lateral stiffness and ultimate soil resistance. These results provide comparative insights for the seismic assessment and scour-resistant design of monopile OWT foundations. Full article

To investigate the pull-out behavior of semi-embedded anchor bolts in the concrete transition sections of steel–concrete hybrid wind turbine towers, five 1:2-scale local specimens were tested under monotonic pull-out loading. The effects of reinforcement, end-plate size, number of anchor bolts, and sleeve installation on the failure mode, load–cumulative surface crack-opening displacement response, reinforcement strain, and ultimate pull-out capacity were analyzed. The results show that reinforcement significantly improved both the pull-out resistance and the apparent deformation capacity characterized by cumulative surface crack opening, changing the failure mode from brittle cracking of plain concrete to a ductile combined mechanism governed by end-plate bearing, concrete splitting, reinforcement restraint, and boundary effects. Increasing the end-plate size, changing the anchor arrangement, and installing a sleeve produced only indicative trends in this limited test series because only one specimen was tested for each configuration. Existing methods were also evaluated as benchmark approaches. The characteristic resistance predicted by EN 1992-4 was conservative, partly because of its fractile basis and partly because the tested configuration was outside the assumptions of an unconstrained concrete cone breakout model. The 45° cone method underestimated the capacity of the reinforced specimens but slightly overestimated that of the plain-concrete specimen, whereas the Nilforoush and LEFM methods overestimated the capacity. These findings provide initial experimental evidence for understanding the load-transfer and failure mechanisms of semi-embedded anchor bolts and clarify the applicability and limitations of the existing calculation methods. The development of a reliable predictive model requires a broader experimental database and systematic numerical investigations. Full article

The blades directly affect the safety and power generation efficiency of the wind turbines. With the blade size increases, the reliable modal identification becomes important for vibration-based health monitoring. Although operational modal analysis (OMA) technique has been used in condition monitoring for the wind turbine blades, most existing studies focus on investigating a specific single method or under ideal excitation conditions. To overcome this limitation, this study takes the IEA-15MW large wind turbine blade as the research object and compares three OMA methods through numerical simulations, namely covariance-driven stochastic subspace identification (SSI-COV), frequency domain decomposition (FDD), and poly-reference least squares complex frequency domain (PolyMAX). The performance of the modal parameter identification methods is evaluated with respect to different sensor layouts, blade–tower coupling conditions, and environmental excitations. The results indicate that sparse sensor deployment cannot reliably identify the damage-sensitive high-order and complex modes. A nine-channel layout concentrated near second-order deformation regions significantly improves the identification of second-order flapwise frequencies and controls the average error of the first six modes within 3%. PolyMAX shows the best identification stability under different numbers and layouts of the sensors. Blade–tower coupling changes the blade modal characteristics and increases identification difficulty. Under this condition, FDD can still identify both low-order and high-order modes with good stability. Under different real wind conditions, the increasing wind speed causes the aerodynamic load to deviate from the white noise assumption, generally leading to fluctuations in the identification errors, with relatively large local errors occurring at certain medium and high wind speeds. Overall, the three OMA methods show different advantages under different identification conditions. PolyMAX shows the best stability under different sensor layouts and performs best when wind speed increases in the coupled wind turbine model, indicating that it is the most suitable for the actual complex coupling effects and environmental conditions. This research hopefully provides a basis for the subsequent engineering application of vibration-based modal identification of large offshore blades. Full article

With the rapid expansion of offshore wind farms into deeper waters, large-scale wave-compensated transfer gangways have become critical equipment for ensuring safe personnel transfer between maintenance vessels and wind turbines. However, the increased mass and inertia of large gangways introduce significant control delays in hydraulic actuation, data acquisition, and compensation calculation processes, which severely degrade compensation accuracy and threaten operational safety. This paper proposes a predictive active wave compensation control scheme based on Back Propagation (BP) neural network to address this challenge. First, a ship vertical-plane kinematic model was established to derive the mapping relationship between ship motions (roll, pitch, heave) and gangway end-point positions. The impact of 3–5 s control delays on gangway stability was systematically analyzed, revealing that uncompensated delays can cause end-point deviations exceeding 4 m. Then, an optimized BP neural network model was constructed for short-term ship six-degree-of-freedom (6-DOF) motion prediction, with key parameters (input duration, hidden layer nodes, random seed) tuned to achieve high prediction accuracy. Finally, the proposed predictive control scheme was validated through numerical simulations. The results demonstrate that the scheme can reduce the maximum end-point deviations by more than 80% for delays up to 5 s, effectively mitigating the adverse effects of control delays. This research provides a technical solution for improving the safety and reliability of large offshore transfer gangways. Full article

This paper investigates collaborative trajectory planning and tracking control for semi-trailer-mounted lifting vehicles used in wind turbine blade transport on complex mountainous roads. The proposed approach addresses the challenging problem of coordinating the articulated chassis with a three-degree-of-freedom upper operating device during ultra-long blade transport. First, a unified kinematic model of the articulated chassis and the three-degree-of-freedom upper operating device is established for collaborative trajectory planning and tracking control under low-speed transport conditions. In addition, a dynamic formulation is provided to describe the inertial coupling characteristics of the vehicle-blade system. Second, a continuous trajectory planning method driven by task gradients is proposed to generate collision-free trajectories satisfying multiple constraints, including kinematic feasibility, obstacle avoidance, and actuator limits. A damping injection strategy is introduced to improve numerical conditioning during the iterative optimization process. Third, a linear time-varying model predictive controller is designed based on local linearization along the reference trajectory, which handles system constraints explicitly and achieves high-precision trajectory tracking. Simulation and hardware-in-the-loop experiments show that the proposed method generates smooth and feasible trajectories, while the tracking controller achieves engineering-level position accuracy and joint-angle tracking errors below 3 degrees, satisfying practical requirements for wind turbine blade transport on mountainous roads. Full article

The wake evolution of vertical-axis wind turbines (VAWTs) plays a critical role in turbine-array performance, yet the wake variations associated with rotor geometry, operating condition, and Reynolds-number-related factors remain insufficiently understood. In this study, the wake characteristics of H-type VAWTs were systematically investigated under varying rotor diameters (D = 2, 3, 4 m), chord lengths (c = 0.1–0.4 m), and incoming wind speeds ($v_{\infty }$ = 6–10 m/s) using a two-dimensional mid-span CFD approach based on Improved Delayed Detached Eddy Simulation (IDDES) built on the SST k-ω model. The simulations are intended to examine mid-span wake mechanisms rather than to directly predict full three-dimensional far-wake recovery, turbine-array interaction, or engineering layout performance involving tip vortices, spanwise momentum transport, and three-dimensional breakdown of coherent structures. The results show that, for the selected reference geometry and within the tested inflow-speed range, the lateral mean-velocity profiles at the same downstream location collapse reasonably well after normalization by $v_{\infty }$ and D, indicating weak sensitivity to incoming wind speed under these conditions rather than general Reynolds-number independence of VAWT wakes. For cases with different solidities, the observed wake differences should be interpreted as the combined effects of rotor solidity and the corresponding near-optimal operating condition. Overall, this study provides a mechanism-oriented numerical assessment of wake behavior in H-type VAWTs. Full article

Vertical-axis wind turbines (VAWTs) are recognized as a viable option for wind energy farms due to their compact design and suitability for different wind settings, such as urban and offshore environments. VAWT wind farms have been studied with respect to various turbine spacing and configurations that demonstrate that the VAWT wind farm is well-suited for improving efficiency while requiring less land, compared to horizontal-axis wind turbines (HAWTs). Moreover, the use of combined dual-rotor configurations has recently given attention as a passive strategy to enhance the aerodynamic performance of VAWTs. Despite these advances, the optimal arrangement of VAWT farms, including inter-turbine distances, clustering configurations, and land-use efficiency of such dual rotors, has yet to be explored. This study investigates different clustering scenarios, including vertically aligned pairs and staggered clusters of three turbines, to evaluate their impact on power capture and land usage for a dual-rotor straight-blade vertical-axis wind turbine (DR-SBVAWT). The 2D-dimensional transient (URANS) numerical simulations are conducted using the k-$\omega$ SST turbulence model. Performance indices, namely, total power coefficient and improvement relative to standalone turbines, are analyzed. Wake effects are investigated through detailed velocity contour plots of the wind field. Results reveal that a DR-SBVAWT turbine arrangement can enhance wind farm performance by approximately 25% for two turbines and about 20% for three staggered turbines, with required spacing of 1.5 D and 2.5–3 D, respectively (Here, D is the outer diameter of the DR-SBVAWT). The study overall provides insights into the optimal placement and configuration of DR-SBVAWTs for maximizing energy output while minimizing land usage, offering guidance for the design of more efficient VAWT farms. Full article

To address the coupling among bidding decisions, resource allocation, and coordinated utilization of environmental rights for distributed resource aggregators in multiple markets, including the energy market, peak regulation ancillary service market, carbon trading market, and tradable green certificate market, this paper proposes a bi-level optimization model for multi-market joint trading considering a limited carbon–green certificate linkage mechanism. First, a quantitative mapping relationship between the emission reduction attribute of surplus green certificates and carbon emission reduction is established, and an upper limit constraint on the offset ratio is introduced to describe the limited conversion of green certificate environmental attributes into carbon emission reduction value. Second, an upper-level bidding model for the distributed resource aggregator is constructed, aiming at profit maximization while considering revenues from the energy, peak regulation ancillary service, carbon trading, and green certificate markets, as well as the operational constraints of gas turbines, energy storage, and flexible loads. This model characterizes the aggregator’s joint bidding strategy and internal resource coordination. Then, a lower-level unified market clearing model is developed to minimize system operating cost and simulate the segmented bidding and unified clearing process of the aggregator, wind power, and thermal power units in the energy and peak regulation ancillary service markets. Finally, the bi-level model is transformed into a solvable single-level model using the Karush-Kuhn-Tucker (KKT) conditions and the Big-M method, and case studies are conducted to verify its effectiveness. The numerical results show that under the complete multi-market mechanism, the distributed resource aggregator (DRA) obtains a net profit of 2245.03 yuan, which is higher than 1450.33 yuan in the scenario without the carbon–green certificate mechanism and 773.48 yuan in the energy-only scenario. The wind curtailment rate decreases from 8.53% in the energy-only scenario to 2.71%, and the carbon emissions accounted for within the DRA boundary are reduced to 2865.40 kg. Although the price-taker scenario obtains a slightly higher net profit of 2300.20 yuan, its average regulation price reaches 455.20 yuan/MWh, compared with 412.50 yuan/MWh under the proposed model, indicating that the proposed strategy achieves a better balance between aggregator revenue and system-side regulation cost. Full article

Wind turbine gearbox degradation driven by lubricating oil contamination represents one of the most environmentally and economically consequential challenges facing modern wind energy operations. This study proposes a dual-reservoir imperfect preventive maintenance strategy designed to extend gear train service life, reduce the carbon footprint of maintenance operations, and recover renewable energy production losses inherent to conventional intervention practices. The proposed architecture employs two alternating oil reservoirs. While one supplies the active lubrication circuit at full turbine output, the second undergoes filtration, completely decoupling the filtration operation from production continuity. When the concentration of metallic particles resulting from gear wear exceeds a predefined contamination threshold in the lubricating oil, imperfect preventive maintenance (IPM), performed in parallel with an oil change operation, is initiated; this action partially restores the gear train failure rate to an intermediate value between the degraded and as-new states. A mathematical model is derived to jointly optimize the filtration interval TF and the preventive maintenance interval TM, minimizing the average total cost per unit time over a finite operational horizon while explicitly incorporating environmental costs attributable to each filtration cycle. Numerical optimization yields the optimal filtration interval TF and preventive maintenance interval TM that minimize the total average cost per unit time over the operational horizon H. A dedicated environmental performance assessment demonstrates that the proposed strategy substantially recovers lost wind power generation, significantly reduces hazardous lubricating oil waste and lowers total CO₂-equivalent emissions. This confirms the strategy’s meaningful contribution to sustainable wind energy operations. Sensitivity analyses confirm the robustness of the optimal solution across varying operational and economic conditions, providing wind farm operators with an adaptable and environmentally responsible decision-making framework. Full article

Seabed scour-induced degradation of the pile–soil system, together with the coupled action of seismic, wind and wave loads, poses great challenges to the long-term service safety of jacket-type offshore wind turbines. In this study, an integrated structural numerical model is established with consideration of nonlinear pile–soil interaction. By coupling OpenFAST (Version 3.5.0) and OpenSees (Version 3.7.0), accurate wind and wave load generation and refined calculation of structural dynamic responses are achieved. Then, the dynamic performance of jacket-type offshore wind turbines under combined wind–wave–seismic loads is analyzed at different scour depths (0D, 1D, 2D and 3D, where D is the pile diameter). Structural response characteristics before and after seismic excitation are emphatically compared under two typical sea states: collinear wind–wave condition (COD-2.2) and non-collinear wind–wave condition (MIS-2.4). The results show that seismic excitation substantially amplifies structural dynamic responses. Meanwhile, strong seismic interference weakens the influence of wind–wave directionality to a certain degree, lowering the response difference between the COD-2.2 and MIS-2.4 cases. It is further found that scour depth remains the dominant factor controlling pile internal forces and foundation lateral deformation even when seismic effects are incorporated. Moreover, under the selected Chi-Chi ground motion, scour aggravation markedly increases the seismic response amplification and internal force concentration of the structure. This research provides a theoretical reference for the multi-hazard resilience design and assessment of wind turbine foundations under complex marine environments. Full article

Offshore wind can diversify the Brazilian electricity matrix, but foundation design on the Ceará continental shelf must account for carbonate sands whose stiffness, crushability and stress-dependent response differ from those of quartz sands. This study contribution is the use of carbonate-sand parameters calibrated from consolidated-drained triaxial tests on Ceará-shelf sediments and the direct comparison of two sands with contrasting carbonate contents. The measured responses calibrated the Hardening Soil model in PLAXIS 2D, and the resulting parameters drove PLAXIS 3D simulations of monopiles with different diameters, embedment lengths and tower heights under monotonic lateral loading. The more calcareous sand showed higher frictional strength but lower stiffness—as a result, it mobilised larger mudline displacements, making the Serviceability Limit State more restrictive than the Ultimate Limit State. Pile diameter controlled lateral capacity, whereas reduced L/D lowered system stiffness and serviceability performance. Within the monotonic, homogeneous-profile scope adopted here, M3 (D = 9 m, L = 36 m, L/D = 4) gave the most favourable response for the medium-rated turbine class. The results provide screening-level comparative evidence, not a design-ready proof of feasibility. Full article

This paper presents a comprehensive three-dimensional numerical investigation of a novel vertical-axis wind turbine (VAWT) characterised by a unique aerodynamic profile and a passive blade-pitch control mechanism. Unlike conventional fixed-geometry designs, the proposed turbine utilizes rectangular blades mounted on horizontal axes via articulated bearings, allowing them to rotate freely up to 90 degrees, constrained by a vertical pin-and-belt system. This configuration ensures that blades on the power-stroke side hit the vertical stopper to capture maximum wind energy, while blades on the return-stroke side open up to 90 degrees to significantly reduce aerodynamic drag. This dynamic adjustment enables the turbine to operate efficiently in low-wind conditions (3–5 m/s) while maintaining enhanced torque stability. To ensure numerical reliability, a rigorous grid independence study was performed, and the computational domain was configured to eliminate wall interference effects. The aerodynamic performance was analyzed using COMSOL Multiphysics v6.2 by solving the Reynolds-averaged Navier–Stokes (RANS) equations. Four turbulence models—SST, k–ε, k–ω, and RNG—were evaluated, with the SST model demonstrating the highest fidelity in capturing flow separation and wake structures under adverse pressure gradients. This study establishes the turbine’s performance benchmarks, including the power coefficient (C_p) versus tip speed ratio (TSR) curves. The numerical results were validated against laboratory experimental data, with excellent agreement (relative error < 5%). The findings identify the optimal geometric parameters and tangential velocity distributions that distinguish this configuration (Patent FAP 20240465) from traditional VAWTs. Finally, the successful implementation of a 2 kW prototype confirms the model’s accuracy and highlights the turbine’s potential as a stable and efficient solution for sustainable urban energy harvesting. Full article

The integration of wave energy converters with offshore wind foundations offers a potential route to improving the utilization of offshore renewable energy infrastructure. This study numerically investigates the power-load characteristics of fixed oscillating water column (OWC) chambers intended for potential installation near offshore wind jacket foundations. A preliminary jacket comparison is first used to delimit the scope, after which the main parametric study is performed on isolated OWC chambers so that pneumatic response and local chamber loads can be compared consistently. The simulations are conducted under regular waves with a wave height of H = 0.05 m, a water depth of h = 1.6 m, and wave periods of T = 0.9–1.7 s. Three baseline geometries, namely cylindrical, sandglass-shaped, and bottle-shaped OWCs, are first screened in order to identify the most suitable reference chamber family. The cylindrical chamber is then retained as the reference configuration for subsequent local parameter studies of the frustum-contraction parameter D₂ and the front-wall draft d₂. The results indicate that the geometric effect is strongly dependent on the incident-wave period. The sandglass-shaped and bottle-shaped chambers can enhance short-period pneumatic power or reduce loads at longer periods, whereas the cylindrical chamber provides a more consistent reference response over the tested range. Under the wave conditions adopted in this study, further analysis reveals that D₂ exerts a non-monotonic tuning effect varying with wave period. For the selected frustum-shaped configuration, increasing d₂ reduces hydrodynamic loads yet simultaneously weakens pneumatic power output and CWR. Because the air phase is treated as incompressible and the orifice represents an orifice-only damping condition rather than a turbine-controlled PTO system, the reported P_e should be interpreted as a pneumatic/hydrodynamic comparison metric and not as wave-to-wire electrical power. The conclusions are therefore positioned as regular-wave geometry-tuning trends for the present model scale rather than as full coupled jacket-OWC design rules. Full article