Foundation scour is the erosion of sediments around pile foundations by wave and current in offshore wind energy. This phenomenon destabilizes foundations and poses a threat to pile safety. Therefore, scour protection becomes a crucial challenge in offshore wind projects. This paper reviews and synthesizes recent publications and patented technologies related to scour protection. Considering the primary engineering concerns, the paper proposes design principles for effective scour protection schemes to standardize evaluation criteria. These principles prioritize efficacy, independence, and cost-efficiency, enabling the analysis of scour protection scheme applicability. In addition, this paper summarizes and describes common protection schemes in the literature. The effectiveness of their protection is analyzed and summarized, and their economic and performance independence is evaluated. This paper categorizes flow-altering scour protection schemes found in the literature. Based on a comprehensive understanding of the mechanisms and engineering requirements of scour protection, the paper proposes a focus on determining the erosion reduction rate curve ($Ep-U/U_c$ curve) as a key criterion for evaluating the effectiveness of protection schemes under varying flow velocities and the erosion reduction rate of scour protection schemes under extreme conditions. The study highlights the necessity of establishing a comprehensive design evaluation methodology, which is crucial for addressing the significant challenges related to scour encountered in offshore wind power projects.

We propose a model that integrates a drift flux model with a vegetation source term and the k−ω shear stress transport with improved delayed detached eddy simulation turbulence model to simulate sediment-laden vegetated flows. The numerical model was validated using experimental data from Lu [“Experimental study on suspended sediment distribution in flow with rigid vegetation,” Ph.D. thesis (Hohai University, Nanjing, Jiangsu, China, 2008)] and Wang and Qian [“Velocity profiles of sediment-laden flow,” Int. J. Sediment Res. 7, 27–58 (1992)]. We analyzed the vertical profile characteristics and spatial distribution features of sediment-laden vegetated flows at different vegetation densities. A detailed analysis was conducted on the correlations between variables that could affect the suspended sediment distribution, including vorticity, vertical velocity, Reynolds stress, and turbulent kinetic energy (TKE) fields. It was found that the vorticity field is primarily correlated with the suspended sediment concentration (SSC) field at the vegetation canopy, while the vertical velocity field above the canopy has a positive correlation with the SSC field. Both the Reynolds stress and TKE fields above the canopy exhibit positive correlations with the sediment concentration field. However, below the canopy, both fields show negative correlations with the sediment concentration. The TKE field is closely related to the suspended sediment distribution near the bottom, whereas the Reynolds stress field influences the suspended sediment distribution near the surface. The overall correlation between Reynolds stress and TKE with sediment concentration is negative, with their correlation significantly higher than that of vorticity and vertical velocity, indicating a closer connection with the movement of suspended sediments than the other variables.

The study investigates the fluid dynamics and instability mechanisms of a three-twisted-blade pump using hydrodynamic field analysis, vortex identification, and spectral methods. High-fidelity numerical modeling was conducted with OpenFOAM, employing the Delayed Detached Eddy Simulation method and an arbitrary mesh interface on structured grids. The results identify two distinct fluid motion mechanisms: in the flow passage range of R45%–R60%, significant velocity fluctuations and vortex shedding lead to turbulent flow, while in the R80%–R90% range, the flow becomes more stable with weaker fluctuations. Vortex motion in the flow passages, driven by the twisted blade shape, resembles the Kármán vortex street. On the suction side of the blade leading edge, striped vorticity patterns extend and densify with increased flow rate and rotational speed, correlating with the vortex shedding frequency. An increased flow rate promotes the transition from single-axis to multi-axis frequency in the velocity Power Spectral Density (PSD), counteracting the volute tongue effect and eliminating single-blade frequency. Conversely, higher rotational speeds intensify turbulence near the blade tip but minimally affect the velocity PSD's peak frequency domain.

Parametric tropical cyclone models are widely used to generate large wind field ensembles for assessing extreme storm tides and wave heights. The radius of maximum wind (RMW) is a key model parameter and is commonly estimated using empirical formulas. This study shows that uncertainty introduced by the choice of RMW formulas has been largely overlooked in tropical cyclone risk assessments. Using the Pearl River Estuary as a case study, historical wind fields (1981–2024) were generated with a parametric tropical cyclone model combined with eight empirical RMW formulas. Storm tides and wave heights during tropical cyclone events were simulated using a coupled wave–current model (ROMS–SWAN) and analyzed with extreme value theory. The results indicate that, for estuarine nearshore zones, the 100-year return period of water level and significant wave height vary by up to 1.26 m and 1.54 m, respectively, across all the selected RMW formulas. Joint probability analysis further shows that RMW uncertainty can shift the joint return period of the same compound storm tide and wave event from 100 years to 10 years. For an individual extreme event, differences in the RMW formula alone can produce deviations up to 2.11 m in peak storm tide levels and 3.8 m in significant wave heights. Such differences can also change the duration of extreme sea states by 13 h. These results highlight that RMW formula selection is a critical uncertainty factor, and related uncertainty should be considered in large-sample tropical cyclone hazard assessment and engineering design.

In this study, laboratory experiments were conducted to investigate the influence of changes in storm wave height and water level on beach response in a medium-scale wave flume. A schematic storm was simulated (rising, apex, and waning phases). A non-intrusive photogrammetric method was used to collect high-resolution and synchronous data regarding the free surface water elevation and bed level, from which shoreline location, sandbar position, cross-shore sediment transport rates, and nonlinear wave parameters were derived. The cross-shore sediment transport was in agreement with previous laboratory measurements, including the monotonous exchange from foreshore erosion to shoaling zone accretion in most stages of the storm simulation. The surf zone was the main region supplying sediment for beach morphology modification and sandbar generation. The degree of storm erosion was not completely determined by the largest wave height and water level or the cumulative wave power of the apex phase. The largest gradients of the wave parameter sequence change occurred in the rising phase, and this was the main factor generating efficient beachface erosion. It induced an increase in sandbar size, accompanied by the cross-shore motion of maximum velocity amplitude, more violent disturbances of wave nonlinearity, and increased surf zone erosion, with these factors increasing beach instability and leading to more severe storm erosion. The large wave height and water level resulted in shoreline retreat, with a more significant swash zone erosion under a higher runup. The offshore sediment transport turned toward the onshore direction as the original large sandbar deteriorated under the decreasing wave parameter sequence in the waning phase.

A series of laboratory experiments were undertaken to qualitatively investigate the evolution of wave nonlinearity over a movable bed of sediment with five different beach slopes under regular waves in a medium-scale wave flume. An innovative non-intrusive data collecting system, which mainly consists of three side-looking high-speed cameras, was developed to collect high-resolution and synchronous data on free-surface water elevation of waves and bed level changes without causing any disturbances to wave motions and the movable bed of sediment. On analyzing the collected experimental data, it is found that regular waves become nonlinear when they propagate to the shoaling zone and start breaking, and linear wave theory is quite accurate for calculating wave parameters such as orbital velocity with the correlation coefficient r2 = 0.8–0.95 before the waves break, but becomes less accurate after the waves break or are in the breaking zone with the smaller correlation coefficient r2 = 0.4–0.6. Four parameters, wave skewness Skη, asymmetry Ayη, Ursell number Ur, and Rocha number NP0, are introduced to describe the wave nonlinearity, of which Skη and Ayη are found to be of largest amplitudes at the wave breaking point and then start to decrease in the breaking zone and are almost unchanged for different beach slopes, while Ur further increases in the breaking zone and exceed the first larger value as waves approach to shoreline, but NP0 is almost linearly proportional to wave orbital velocity amplitude and quite sensitive to beach slope. The location of sandbar is found close to the wave breaking point in the wave flume and may be also considered as the point where wave nonlinearity becomes important for sediment transport in the surf zone, and the linear wave theory becomes less accurate.