Search Results (74)

In complex marine environments, monopile foundations are subjected not only to waves and currents but also to seismic loads. The long-term combined action of waves and currents induces scour around the monopile, leading to soil loss, seabed morphology changes, and an enlarged water–structure interface. When seismic load is present, scour amplifies the hydrodynamic pressure on offshore monopiles and modifies the site response, significantly influencing the seismic performance of the monopiles and their superstructures. To address the issue, this study develops three-dimensional numerical models based on the computational fluid dynamics (CFD) method and ABAQUS (2020) to systematically investigate the effects of scour on hydrodynamic pressure of offshore monopile and site dynamic response under seismic loads. First, a numerical model including scour effects is established in ANSYS Fluent (2022), and parametric analyses are performed to evaluate the impact of local scour hole geometry on hydrodynamic pressure; subsequently, comparisons are made with global scour conditions, and an added mass coefficient accounting for the distribution of scour effects along the pile is proposed. Finally, on the ABAQUS platform, a numerical model is developed to analyze the dynamic response of the free-field soil and the coupled water–soil free-field under scour conditions. Full article

Local scour around offshore wind turbine foundations is a common engineering challenge. It changes the hydrodynamic loads and affects the foundation’s load-bearing capacity. This study investigates the field scour characteristics and wave–current force characteristics under local scour effects using field data, physical modeling, and numerical simulations. The results show that the field scour hole slope is more gradual than that observed in laboratory settings, and Zhang’s scour depth equation proves more accurate for practical engineering. In addition, under wave–current conditions (Keulegan–Carpenter number, 2 < KC ≤ 15), the relative maximum post-scour wave–current force increases with the relative post-scour water depth but decreases as the KC rises. An equation is developed to predict the relative maximum post-scour wave–current force. This provides key insights for improving load assessments of offshore wind foundations on scoured seabeds. Full article

The operation and maintenance (O and M) phase of offshore wind farms is often simplified in life cycle assessments (LCA), especially with respect to scour-related activities. This study develops a refined O and M–LCA model that explicitly includes scour monitoring, repair, and protection measures, and applies it to a 202 MW offshore wind farm in China. The analysis focuses on the environmental burdens of scour-related O and M activities under predefined engineering scenarios, rather than on the prediction of structural fatigue life or reliability-based intervention timing. Two representative scour-protection strategies were compared: rock dumping (S1) and cement-stabilized soil (S2). The results show that scour protection can substantially increase the environmental burdens of the O and M phase. Relative to the baseline O and M carbon intensity of 4.36 kg CO₂-eq/MWh, S1 causes only a slight increase in global warming potential but greatly increases air pollution- and resource-related impacts because of large-scale rock extraction and transport. In contrast, S2 reduces mineral resource scarcity from 2.14 to 0.042 kg Cu-eq/MWh, corresponding to a 98% reduction compared with S1, but raises the global warming potential to 9.94 kg CO₂-eq/MWh, mainly because of cement production and offshore treatment. Sensitivity analysis shows that S1 is more affected by hydrodynamic-driven intervention frequency in air pollution-related categories, whereas S2 is more sensitive to seabed conditions and stabilization efficiency in terms of GWP. A site-specific screening framework is proposed by integrating geotechnical and hydrodynamic constraints, regional environmental concerns, and targeted mitigation options. The results provide O and M-stage environmental evidence for the site-specific screening of scour-protection strategies and for improving the environmental performance of offshore wind O and M. Full article

Seabed response and local scouring around pile groups under combined wave–current loading pose critical threats to the stability and long-term performance of offshore structures, particularly those supporting offshore renewable energy infrastructures. In this study, we present a systematic experimental investigation on the pore-water pressure and local scour around pile groups subjected to regular waves, combined regular wave–current conditions, and irregular waves generated using the JONSWAP spectrum under wave-only conditions. Pore-water pressures and seabed morphology were analyzed for different hydrodynamic conditions, pile spacings, and pile arrangements. The experimental results demonstrate that the presence and magnitude of current are the dominant factors controlling scour development. Increasing the current velocity from 0 to 0.25 m/s leads to a three (3) to five (5) times increase in maximum scour depth, whereas comparable variations in wave height and wave period produce relatively small effects. The direction of a current affects the location of maximum scour, with the wave–forward current condition promoting the development of an interconnected scour area within the pile array and wave–opposing current condition, shifting local scour toward downstream piles. Small-spaced piles ($G/D$ = 1) intensify hydrodynamic interactions and increase scour depth by approximately 30–40% compared with wider spacing. Irregular waves generate more spatially distributed but shallower scour than regular waves of comparable wave characteristics. These findings provide insights into the mechanisms governing seabed instability around pile group foundations and contribute to more sustainable design and operation of offshore infrastructure, such as offshore wind turbine foundations. Full article

Tidal turbines have emerged as a promising alternative to fossil-fuel-based energy generation, with estuarine environments identified as potential sites for their deployment. However, estuaries are sensitive ecosystems, and understanding the impacts of turbine installation on local hydrodynamics and sediment transport is critical. While previous studies have shown the influence of turbines on seabed morphology under steady current conditions, the effects of combined wave–current loading remain insufficiently explored. In this study, we present a novel numerical modeling framework to predict seabed evolution in the vicinity of tidal turbines subjected to wave–current interactions. The approach integrates Blade Element Theory (BET) to represent turbine-induced forces, an Euler–Euler multiphase model for sediment transport, and the first-order wave theory to capture wave dynamics, all implemented within the OpenFOAM-based solver. Wave effects are incorporated as source terms in the momentum equations, and wave velocities are added to the current field at the velocity inlet boundary condition. Results demonstrate that wave–current loading induces oscillatory sediment transport, but net scouring remains significant in the vicinity of the turbine. The proposed framework is validated component-wise (wave forcing and rotor loading) and then demonstrated on mobile-bed simulations to quantify how oscillatory wave–current forcing modifies near-bed transport and early-stage scour development around a tidal turbine. While the present simulations focus on short morphodynamic times, the approach provides a physics-based basis for exploring wave effects on turbine-induced sediment dynamics. Full article

The radial sand-ridge field off the Jiangsu coast is a distinctive landform in a strongly tide-dominated environment, where sediment supply and geomorphic patterns have been profoundly altered by Yellow River course changes, reduced Yangtze-derived sediment, and large-scale reclamation. Focusing on a typical nearshore sector off Dongtai, this study integrates multi-source data from 1979 to 2025, including historical nautical charts, high-precision engineering bathymetry, full-tide hydro-sediment observations, and surficial sediment samples, to quantify seabed erosion–deposition over 46 years and clarify linkages among tidal currents, suspended-sediment transport, and surface grain-size patterns. Surficial sediments from Maozhusha to Jiangjiasha channel systematically fine from north to south: sand-ridge crests are dominated by sandy silt, whereas tidal channels and transition zones are characterized by silty sand and clayey silt. From 1979 to 2025, Zhugensha and its outer flank underwent multi-meter accretion and a marked accretion belt formed between Gaoni and Tiaozini, while the Jiangjiasha channel and adjacent deep troughs experienced persistent scour (local mean rates up to ~0.25 m/a), forming a striped “ridge accretion–trough erosion” pattern. Residual and potential maximum currents in the main channels enhance scour and offshore export of fines, whereas relatively strong depth-averaged flow and near-bed shear on inner sand-ridge flanks favor frequent mobilization and short-range trapping of coarser particles. Suspended-sediment concentration and median grain size are generally positively correlated, with suspension coarsening in high-energy channels but dominated by fine grains on nearshore flats and in deep troughs. These findings refine understanding of muddy-coast geomorphology under strong tides and may inform offshore wind-farm foundation design, navigation-channel maintenance, and coastal-zone management. Full article

Local scour around suction caisson foundations has emerged as a significant geotechnical hazard for offshore wind turbines as developments extend into deeper waters. This study quantitatively evaluates the scour-induced degradation of the bearing capacity of suction buckets in sand using a three-dimensional finite element model incorporating the Hardening Soil (HS) constitutive model. The HS framework enables realistic representation of stress-dependent stiffness, dilatancy, and plastic hardening, which are essential for simulating stress redistribution caused by scour. Parametric analyses covering a broad range of relative scour depths show that scour depth is the primary factor governing capacity loss. Increasing scour leads to systematic reductions in horizontal and moment capacities, evident stiffness softening, and a downward migration of plastic zones. A critical threshold is identified at S_d/L = 0.3, beyond which the rate of capacity deterioration increases significantly. The H–M failure envelopes contract progressively and exhibit increasing flattening with scour depth while maintaining nearly constant eccentricity. Empirical relationships between scour depth and key envelope parameters are further proposed to support engineering prediction. The results highlight the necessity of integrating scour effects into design and assessment procedures for suction bucket foundations to ensure the long-term performance and safety of offshore wind turbines. Full article

This study investigated twin-propeller-induced scour on sandy seabeds with varying grain sizes (d₅₀ = 0.11, 0.5, and 0.95 mm) through a series of laboratory experiments. The effects of propeller rotation speed (rpm), offset height (y₀), propeller diameter (D_p), and sediment grain size (d₅₀) on scour development were examined. Results indicated that sediment grain size significantly influences scour patterns. A key objective was to develop predictive expressions for primary scour characteristics at equilibrium: maximum scour depth (S_max), scour hole length (L_max), and maximum scour width (B_max). Using a nonlinear regression approach, the proposed expressions demonstrated strong predictive performance. Findings show that equilibrium scour depth increases with higher Froude numbers (F₀) but decreases with larger sediment size (d₅₀) and higher propeller offset (y₀). Additionally, empirical equations were formulated to predict the temporal evolution of scour depth, achieving high correlations with experimental data (R² > 0.97). These results enhance understanding of scour induced by unconfined twin-propeller jets in harbors or navigation channels and provide valuable data for the design and protection of harbor basins. Full article

The global transition towards sustainable energy has accelerated the development and deployment of offshore wind turbines. Jacket foundations, commonly installed in intermediate to deep water depths to access available space and higher load capacities, are built to withstand intensified hydrodynamic loads. Due to their structural complexity near the seabed, however, they are prone to local and global scour, which can compromise stability and increase maintenance costs. While extensive research has addressed scour protections around monopiles, limited attention has been given to complex foundation geometries or even hybrid configurations that combine energy-harvesting devices with structural support. These hybrid systems introduce highly unsteady flow fields and amplified turbulence effects that current design frameworks appear to be unable to capture. This study provides an experimental characterisation of scour damage in riprap-protected jackets as well as additional tests for a hybrid jacket foundation. A novel adaptation of a high-resolution overlapping sub-area methodology was employed. For the first time, it was successfully applied to quantify the damage to riprap protections for a complex offshore foundation. Results revealed that, although hybrid jackets showed the capacity to attenuate incident waves, the scour protection experienced damage numbers (S_3D) two to six times higher than conventional jackets due to flow amplifications. The findings highlight the need for revised design guidelines that can account for the complex hydrodynamic-structural interactions of next-generation marine harvesting technologies integrated into complex foundations. Full article

Local scour around support structures has remained a critical barrier to tidal stream turbine deployment in energetic marine channels since loss of embedment and bearing capacity has undermined stability and delayed commercialization. This review identifies key mechanisms, practical implications, and forward-looking strategies related to local scour. It highlights that rotor operation, small tip clearance, and helical wakes can significantly intensify near-bed shear stress and erosion relative to monopile foundations without turbine rotation. Scour behavior is compared across monopile, tripod, jacket, and gravity-based foundations under steady flow, reversing tides, and combined wave and current conditions, revealing their influence on depth and morphology. The review further assesses coupled interactions among waves, oscillatory currents, turbine-induced flow, and seabed response, including sediment transport, transient pore pressure, and liquefaction risk. Advances in prediction methods spanning laboratory experiments, high-fidelity simulations, semi-empirical models, and data-driven techniques are synthesized, and mitigation strategies are evaluated across passive, active, and eco-integrated approaches. Remaining challenges and specific research needs are outlined, including array-scale effects, monitoring standards, and integration of design frameworks. The review concludes with future directions to support safe, efficient, and sustainable turbine deployment. Full article

Using the geologically complex Wanning (Hainan) site as context, this study applies finite-element analyses to quantify how three construction-induced conditions—foundation out-of-level, directional misalignment, and seabed scour—affect the bearing performance of deep-water pile-anchor foundations for floating offshore wind. For the Wanning case, typical installation and loading deviations reduce the characteristic resistance by a clearly measurable amount: changing the loading inclination from 30° to 45° and superimposing a 5° out-of-level installation leads to reductions in R_c of approximately 7–10%. A 3 m scour pit around the pile has a more severe impact, decreasing R_c by about 18% for 30° loading and up to 28% for 45° loading. Under accidental-limit-state loading, the maximum pile-head displacement increases from about 0.247 m (ULS) to 0.396 m (ALS), i.e., by roughly 60%. These quantitative results demonstrate that construction-induced deviations and scour can significantly erode safety margins, highlighting the need to control installation accuracy and to explicitly incorporate scour allowances and protection in design. Full article

Offshore pipelines are commonly used for the transportation of oil and gas from offshore to near-shore facilities in the oil and gas industry. In ocean environments, the wave- and current- induced pore-water pressure within the seabed, and the associated seabed liquefaction and local scour around pipelines, are widely recognised as among the key factors in the design of offshore pipelines. In this paper, a series of wave flume experiments were carried out on the three-dimensional (3D) scouring around a pipeline. In the experiment, in addition to the measurement of hydrodynamic characteristics and local scour, the pore-water pressure within a sandy seabed was measured. Both waves and currents were considered with different incident angles to the pipeline. This study focuses on the relationship between the variation in pore-water pressure and the development of the scouring process around the pipeline, as well as the evolution of the 3D scouring morphology near the pipeline. The experimental results show that the pore-water pressure exhibits significant changes (up to 12.5% of $P_0$) in the beginning stage of the scouring process, especially in the area below the pipeline, where the influence of scouring on pore-water pressure is most obvious. Full article

This study presents numerical results on 2D local scour around subsea pipelines positioned on sand wave seabeds under steady flow conditions, utilizing Flow-3D (v11.2) software. In the computational model, the flow dynamics surrounding the pipeline are resolved using the time-averaged 2D Navier–Stokes equations in conjunction with the Renormalization Group (RNG) k-ε turbulence model. The bed morphology is governed by the bedload transport rate, suspended load transport rate, and sediment mass balance equation. The research explores the influence of pipeline diameter and water depth on scour patterns over flat beds and investigates how the pipeline’s relative position to symmetrical sand waves affects the severity and morphology of scour. It is demonstrated that the non-dimensional scour depth decreases with an increase in pipeline diameter, whereas in shallower waters, the intensity of scour is greater for a given diameter. In the study of sand wave bed conditions, it was determined that the scour strength exhibits a hierarchical order from strongest to weakest as follows: pipeline located at the crest, downstream slope of the sand waves, pipeline situated on the upstream slope, and at the trough. It is noteworthy that the scour effect is marginally more pronounced at the crest compared to a flat seabed. Conversely, scour intensity diminishes at the other positions, particularly at the trough, where it often results in backfilling and the self-burial of the pipeline. Finally, the distributions of velocity and bed shear stress around the pipeline and seabed are presented to elucidate the flow mechanisms underlying the scour process. Full article

Riprap protection is widely used in offshore wind power foundations. The boundary of riprap will change and affect the hydrodynamics around the foundation during scour. In this study, the experiment was conducted to obtain the topographic data of the riprap failure process. Then, a numerical model of current-pile-riprap-seabed interaction was set using the data to explore the hydrodynamic characteristics around the monopile during the process of stone moving under the action of current. The numerical model is verified through theory and test data. The results show that compared with an unprotected foundation, the maximum flow velocity and range of horseshoe vortex around the monopile with intact riprap will increase, while pressure around the monopile will decrease. During the process of scour, the riprap will sink and be scoured, resulting in increased water cross-section and a velocity decrease of 9.32% to 17.05%. In the process of riprap damage, the height of the diving flow increases, and the horseshoe vortex continuously decreases. The wake vortex near the surface remains stable during the process, while the wake vortex near bed gradually shrinks and disappears. Meanwhile, the pressure around the monopile increases, with maximum pressure increasing by 3.38 times. Full article

This study presents an experimental investigation of seabed scour in front of a quay wall due to the interaction between propeller jet flow and the wall effect. For this purpose, two propellers (D_p = 6 and 9 cm in diameter) were used, and four different wall clearances (X_w = 2, 4, 6 and 8D_p) were selected. The experiments were carried out for propeller rotational speeds ranging from 300 rpm to 1000 rpm. The effect of clay content was also investigated using three different clay contents of 0, 5 and 10% by weight (i.e., p = 0, 0.05 and 0.1). The results of the study reveal that at low propeller rotational speeds, scour in the cohesive seabed is decreased compared to that in the cohesionless bed. The scour profiles obtained at high propeller rotational speeds for the seabed with a clay content of 5% were found to have the same characteristics as those obtained for the cohesionless seabed. However, as the clay content increases to 10%, significant changes occur in the scour profiles, and the cohesion effect begins to dominate. Full article