Search Results (430)

Offshore wind turbines (OWTs) are being developed with larger capacities for deeper waters, facing complex environmental loads that challenge structural safety. In contrast to onshore turbines, OWT foundations must withstand combined hydrodynamic forces (waves and currents), leading to substantially higher construction costs. For floating offshore wind turbines (FOWTs), additional considerations include radiation hydrodynamic loads and additional hydrodynamic damping effects caused by platform motion. Dynamic analysis of these foundations remains a critical bottleneck, presenting new challenges for offshore wind power advancement. This article first introduces the main structural types of OWT foundations, with case studies predominantly from China. The remaining part of the article proceeds as follows: dynamics of fixed OWT foundations, dynamics of FOWT foundations, and conclusions. Next, it covers several important topics related to fixed offshore wind turbines, including pile–soil interaction, wave loads, and seismic analysis. It then discusses support platform motion analysis, hydroelastic analysis, and mooring system characteristics of floating offshore wind turbines. Finally, it presents some insights to improve design and optimization methods for enhancing the safety and reliability of offshore wind turbines. This research clarifies OWT foundation dynamics, helping researchers address challenges and optimize designs. Full article

Riverbank erosion in the Vietnamese Mekong Delta (VMD) poses a serious threat to agricultural lands, infrastructure, and local communities. Conventional protective measures, such as synthetic geotextiles and concrete revetments, are often costly and environmentally disruptive. This study investigates the potential of Eichhornia crassipes, a widely available invasive species, commonly known as water hyacinth (WH), to produce biodegradable geotextiles as a low-cost, nature-based solution (NbS) for small-scale riverbank protection. It is the first to test minimally processed WH mats under simulated tidal conditions in the VMD. Laboratory experiments were conducted to evaluate the geotextile’s (1) sediment retention capacity, (2) wave energy reduction, and (3) mechanical durability under wet–dry cycles. Results show that the WH geotextile effectively reduced sediment resuspension, decreasing turbidity levels from 800 FTU (unprotected scenario) to below 50 FTU. The geotextile also attenuated wave energy, reducing significant wave heights by approximately 35–40%. Mechanical testing revealed that the fish bone weaving pattern with adhesive coating achieved the highest tensile strength (8.36 kN/m after 12 wet–dry cycles), while uncoated samples demonstrated higher elongation (up to 61.67%), providing greater flexibility. These demonstrate the feasibility of WH geotextiles as a scalable nature-based solution for erosion-prone tropical deltas. Future studies should focus on field-scale validation, biodegradation rates, and performance optimization for long-term applications. Full article

This paper presents a novel submersible seaweed cultivation infrastructure designed to enhance seaweed growth through deep cycling. The system consists of a square grid of ropes for growing seaweed, supported by buoys, mooring lines, and innovative SubTractors—movable buoys that enable controlled submersion. The grid ropes are stabilized by four SubTractors, an array of small buoys, intermediate sinker weights and mooring lines anchored to the seabed. The SubTractors facilitate dynamic positioning, allowing the seaweed rope grid to be submerged below the thermocline—at depths of 100 m or more—where nutrient-rich deep water accelerates seaweed growth in offshore sites with low surface nutrient levels. Small buoys attached to the grid provide buoyancy, keeping the seaweed rope grid planar and near the surface to optimize photosynthesis when not submerged. This paper first describes the seaweed cultivation infrastructure, then develops a hydroelastic model of the proposed cultivation system, followed by a hydroelastic analysis under varying wave and current conditions. The results provide insights into the system’s dynamic behaviour, informing engineering design and structural optimization. Full article

Pure Loss of Stability is one of the five typical stability failure modes identified in the Second-Generation Intact Stability Criteria by the IMO. This study investigates the influence of hull line variations on the vulnerability of a saury fishing vessel to pure loss of stability. Hull forms were parametrically modified using the Free-Form Deformation method, and an in-house code was developed to evaluate stability performance. The numerical framework was validated against the commercial ICS-HydroSTAB software (Version 1.0), demonstrating high computational accuracy and engineering applicability. Parametric sensitivity analysis was then conducted to examine the effects of geometric characteristics under both calm-water and wave-induced conditions. The results indicate that vulnerability in calm water is primarily governed by the maximum sectional area curve and the bow portion of the DWL half-breadth curve, while in waves it is influenced by both the maximum sectional area curve and the fore and aft portions of the DWL half-breadth curve. The half angle of entrance (E = 0.08) exhibits a comparatively minor effect, but its increase reduces the initial metacentric height and significantly elevates the risk of capsizing in waves. These findings provide useful references for hull form optimization and stability design. Full article

This study introduces a novel adaptive Mechanical Wave Energy Converter (MWEC) designed to efficiently capture nearshore wave energy for sustainable electricity generation along the southeast surf coast of NEOM (135° longitude). The MWEC system features a polyvinyl chloride (PVC) cubic buoy integrated with a mechanical power take-off (PTO) mechanism, optimized for deployment in shallow waters for a depth of around 1 m. Three buoy volumes, V1: 6000 cm³, V2: 30,000 cm³, and V3: 72,000 cm³, were experimentally evaluated under consistent PTO and spring tension configurations. The findings reveal a direct relationship between buoy volume and force output, with larger buoys exhibiting greater energy capture potential, while smaller buoys provided faster and more stable response dynamics. The energy retention efficiency of the buoy–PTO system was measured at 20% for V1, 14% for V2, and 10% for V3, indicating a trade-off between responsiveness and total energy capture. Notably, the largest buoy (V3) generated a peak power output of 213 W at an average wave amplitude of 65 cm, confirming its suitability for high-energy conditions along NEOM’s surf coast. In contrast, the smaller buoy (V1) performed more effectively during periods of reduced wave activity. Wave climate data collected during November and December 2024 support a hybrid deployment strategy, utilizing different buoy sizes to adapt to seasonal wave variability. These results highlight the potential of modular, wave-adaptive mechanical systems for scalable, site-specific renewable energy solutions in coastal environments like NEOM. The proposed MWEC offers a promising path toward low-cost, low-maintenance wave energy harvesting in shallow waters, contributing to Saudi Arabia’s sustainable energy goals. Full article

Wave-powered desalination systems integrate reverse osmosis (RO) with renewable ocean energy, providing a sustainable and environmentally responsible approach to freshwater production. This study aims to investigate wave-powered RO desalination using supervised and deep machine learning (ML) models to predict the effects of variable feed flow on permeate recovery and salt rejection under dynamic hydrodynamic conditions. Multiple ML models, including Gaussian process regression (GPR), support vector machines (SVMs), multi-layer perceptron (MLP), linear regression (LR), and decision trees (DTs) were systematically assessed for the prediction of permeate recovery and salt rejection (%) using three distinct input configurations: limited physicochemical features (M1), flow- and salinity-related parameters (M2), and a comprehensive variable set incorporating temperature (M3). GPR achieved near-perfect predictive accuracy R² values (~1.00) with minimal errors for permeate recovery and salt rejection, attributed to its flexible kernel and probabilistic design. MLP and SVM also performed well, though they showed greater sensitivity to feature complexity. In contrast, DT models exhibited limited generalization and higher error rates, particularly when key features were excluded. Sensitivity analyses revealed that feed pressure (FP) and brine salinity (BS) were dominant positive influencers of permeate recovery and salt rejection. In contrast, brine flow (BF) and permeate salinity (PS) had negative impacts. Full article

This study focuses on the sandstone of the Kizil Grottoes as the research object. Sandstone samples reinforced with barium hydroxide nanoparticle (Ba(OH)₂) solutions at different concentrations were subjected to mass and deformation monitoring, wave velocity tests, triaxial shear tests, and conventional mercury intrusion porosimetry (MIP) to investigate the reinforcement mechanism and effectiveness of nano-Ba(OH)₂ on Kizil sandstone. The results indicate that after treatment with nano-Ba(OH)₂, the strength and wave velocity of the sandstone samples significantly increased, with the 15% concentration showing the optimal reinforcement effect. Nano-Ba(OH)₂ enhances the cementation between sandstone particles, alters pore morphology and size distribution, reduces capillary water rise height, and inhibits sulfate ion crystallization and recrystallization, thereby achieving the dual effects of strength reinforcement and deterioration prevention. Full article

The extraction of ocean wave wavelengths from optical imagery via Fast Fourier Transform (FFT) exhibits significant potential for Wave-Derived Bathymetry (WDB). However, in practical applications, this method frequently produces anomalously large wavelength estimates. To date, there has been insufficient exploration into the mechanisms underlying image spectral leakage to low wavenumbers and its suppression strategies. This study investigates three plausible mechanisms contributing to spectral leakage in optical images and proposes a subimage-based preprocessing framework: prior to executing two-dimensional FFT, the remote sensing subimages employed for wavelength inversion undergo three sequential steps: (1) truncation of distorted pixel values using a Gaussian mixture model; (2) application of a polynomial detrending surface; (3) incorporation of a two-dimensional Hann window. Subsequently, the dominant wavenumber peak is localized in the power spectrum and converted to wavelength values. Water depth is then inverted using the linear dispersion equation, combined with wave periods derived from ERA5. Taking 2 m-resolution WorldView-2 imagery of Sanya Bay, China as a case study, 1024 m subimages are utilized, with validation conducted against chart-sounding data. Results demonstrate that the proportion of subimages with anomalous wavelengths is reduced from 18.9% to 3.3% (in contrast to 14.0%, 7.8%, and 16.6% when the three preprocessing steps are applied individually). Within the 0–20 m depth range, the water depth retrieval accuracy achieves a Mean Absolute Error (MAE) of 1.79 m; for the 20–40 m range, the MAE is 6.38 m. A sensitivity analysis of subimage sizes (512/1024/2048 m) reveals that the 1024 m subimage offers an optimal balance between accuracy and coverage. However, residual anomalous wavelengths persist in near-shore subimages, and errors still increase with increasing water depth. This method is both concise and effective, rendering it suitable for application in shallow-water WDB scenarios. Full article

Jack-up offshore platforms, supported by truss legs, are integral to the development of marine energy resources, including oil, gas, and offshore wind. Due to the structural complexity of truss legs, accurately quantifying wave loads is crucial for ensuring the safety and efficiency of energy extraction operations. In this work, a numerical wave tank approach combined with theoretical analysis is employed comprehensively to investigate wave loads on truss legs, with a particular emphasis on the effects of component forces and inflow angle. The results demonstrate that wave loads are not solely dependent on member dimensions. The influencing factors affecting component forces include water depth and phase differences between structural units, which amplify the contribution of the component forces of members near the free surface and without phase difference to the total force. Furthermore, the total force varies periodically with the inflow angle in cycles of 60°. Notably, the influence of inflow angle on the total force becomes negligible when the wavelength substantially exceeds the pile spacing. This framework fundamentally provides a theoretical basis for the structural optimization of Jack-up offshore platform support systems, thereby enhancing the safety and reliability of energy infrastructure. Full article

The study focuses on the detection of breaking wave crests in the highly dynamic waters of an Antarctic coastal polynya using high-resolution panchromatic satellite imagery. Accurate assessment of whitecap coverage is crucial for improving our understanding of the interactions between wave generation, air–sea heat exchange, and sea ice formation in these complex environments. As open-ocean whitecap detection methods are inadequate in coastal polynyas partially covered with frazil ice, we discuss an approach that exploits specific lighting conditions: the alignment of sunlight with the dominant wind direction and low solar elevation. Under such conditions, steep breaking waves cast pronounced shadows, which are used as the primary indicator of wave crests, particularly in frazil streak zones. The algorithm is optimized to exploit these conditions and minimize false positives along frazil streak boundaries. We applied the algorithm to a WorldView-2 image covering different parts of Terra Nova Bay Polynya (Ross Sea), a dynamic polar coastal zone. This case study demonstrates that the spatial distribution of detected breaking waves is consistent with ice conditions and wind forcing patterns, while also revealing deviations that point to complex wind–wave–ice interactions. Although quantitative validation of satellite-derived whitecaps coverage was not possible due to the lack of in situ data, the method performs reliably under a range of conditions. Limitations of the proposed approach are pointed out and discussed. Finally, the study highlights the risk of misinterpretation of lower-resolution reflectance data in areas where whitecaps and sea ice coexist at subpixel scales. Full article

In the present study, a novel air-floating tripod bucket foundation (AFTBF) with taut mooring is proposed. The mechanical and motion response characteristics of this foundation were investigated through model tests. Furthermore, a parametric study was performed on the factors influencing the RAOs of mooring tension, air cushion pressure, as well as motion in the surge, heave, and pitch directions. The conclusion of this research is as follows: mooring tension, air cushion pressure, and pitch angle exhibit wave-frequency responses in small periods and low-frequency responses in large periods. Surge response is characterized by dual-peak features, while heave response predominantly demonstrates wave-frequency characteristics. As draft increases, the air cushion pressure inside the buckets exhibits a decreasing trend. Changes in water depth have more pronounced impacts on mooring tension and motion responses than on air cushion pressure. The impacts of changes in mooring distance and water depth on mechanical and motion responses are significantly more pronounced than those induced by changes in draft. These findings provide a critical foundation for the optimal design of this foundation in water depths of 30–50 m. Full article

During the sudden closure of gates in long-distance gravity flow water supply projects, intense water hammer waves are generated. These waves can cause severe damage to the water supply tunnel structure, posing a significant threat to project safety. To develop an economical and effective hydraulic safety control strategy, this study uses the example of a specific gravity flow water supply project with long-distance and multi-fluctuation pressure tunnels in Zhejiang Province. A novel combined protection strategy was investigated, involving the conversion of construction branch tunnels into branch tunnel surge tanks combined with an overflow surge tank. Numerical simulations of gate closure-induced water hammer pressures were conducted using the method of characteristics. Additionally, the effectiveness of the overflow surge tank on controlling the surge water level in the branch tunnels was analyzed with respect to variations in its height, diameter, and impedance hole diameter. The results indicate that a 300 s linear gate closure without any protective measures induces severe water hammer pressure. Extending the closure time to 1200 s still results in pressures far exceeding the safety threshold. Converting construction branch tunnels into surge tanks effectively controlled the water hammer pressure; however, overflow issues emerged in some branch tunnels. The subsequent addition of an overflow surge tank at the end of the water supply system successfully eliminated the risk of overflow in the branch tunnels. Building upon this, multi-parameter optimization analysis was used to determine the optimal configuration for the overflow surge tank. This solution ensures hydraulic safety while maintaining cost-effectiveness. Both the maximum pressure and the minimum pressure along the water supply tunnel, as well as the surge water levels in all branch tunnels, meet the code requirements. Furthermore, the reduced size of the surge tank significantly lowered construction costs. The findings of this research provide theoretical foundations and technical support for similar long-distance gravity flow water supply projects. Full article

Land availability constraints limit the installation of conventional ground-mounted solar installations. As a result, Floating Photovoltaic (FPV) systems are gaining popularity as an alternative to renewable energy generation. FPV consist of individual solar panels that are commonly symmetrical and modular. However, the hydrodynamic behaviour of FPVs in water surface waves is understudied to ensure their stability and optimal performance under varying environmental conditions. This literature review examines various modelling techniques applied in studying FPV hydrodynamics. Specifically, the application of Computational Fluid Dynamics (CFD) solvers and potential flow theory solvers is investigated for their effectiveness in capturing the behaviour of FPVs and mooring dynamics under the impact of wind and waves. The review highlights the advantages and limitations of each approach. Findings suggest that a combined CFD-potential flow approach offers a perfect balance between accuracy and computational efficiency, offering valuable insights into the performance of FPVs. However, extensive research is notably absent in hydrodynamic modelling for large-scale FPVs. This lack of research represents a significant gap in our current study on multiscale FPV systems. Full article

To enhance the spectral efficiency of hybrid beamforming in millimeter-wave massive MIMO systems, the problem is formulated as a high-dimensional non-convex optimization under constant modulus constraints. A novel algorithm based on fourth-order tensor Tucker decomposition is proposed. Specifically, the frequency-domain channel matrices are structured into a fourth-order tensor to explicitly capture the couplings across the spatial, frequency, and user domains. To tackle the non-convexity induced by constant modulus constraints, the analog precoder and combiner are derived by solving a truncated-rank Tucker decomposition problem through the Alternating Direction Method of Multipliers and Alternating Least Squares schemes. Subsequently, in the digital domain, the Regularized Block Diagonalization algorithm is integrated with the subcarrier and user factor matrices—obtained from the tensor decomposition—along with the water-filling strategy to design the digital precoder and combiner, thereby achieving a balance between multi-user interference suppression and noise enhancement. The proposed tensor-based algorithm is demonstrated through simulations to outperform existing state-of-the-art schemes. This work provides an efficient and mathematically sound solution for hybrid beamforming in dense multi-user scenarios envisioned for sixth-generation mobile communications. Full article

Background: This study investigated the biomechanical and physiological demands of the hiking position in Laser sailing, a posture requiring sailors to extend their upper bodies outside the boat to counter wind-induced heeling. This study utilized a mixed-methods approach. Methods: Twenty-two experienced Laser sailors participated in both on-land and offshore assessments. The study combined subjective discomfort ratings, biomechanical measurements, digital human modeling, and muscle activation analysis to evaluate the effects of hiking during and after exertion. Results: A two-way ANOVA showed significant effects by body region and time. The quadriceps, abdominals, and lower back reported the highest discomfort. Key postural angles were identified, including knee and hip flexion, trunk inclination, and ankle dorsiflexion. Muscle activation analysis revealed the highest engagement in the rectus abdominis (46.1% MVC), brachialis (~45%), and psoas major (~41%), with notable bilateral asymmetries. The trunk region had the highest overall activation (28.7% MVC), followed by the upper limbs (~18.7%), while the lower limbs were minimally engaged during static hiking. Conclusions: On-water conditions resulted in greater variability in joint angles, likely reflecting wind fluctuations and wave-induced boat motion. Findings highlight the quadriceps, abdominals, and lower back as primary contributors to sustained hiking, while also emphasizing the importance of targeted endurance training and ergonomic equipment design. These insights can guide training, recovery, and ergonomic strategies to optimize performance and reduce injury risk in Laser sailors. Full article