Search Results (64)

This study investigates the dynamic response mechanisms of discharge capacity in the Han River Estuary to hydrological process changes at the Yangtze–Han River confluence. By constructing a one-dimensional hydrodynamic model for the 265 km Xinglong–Hankou reach, we quantitatively decouple the synergistic effects of riverbed scouring (mean annual incision rate: 0.12 m) and Three Gorges Dam (TGD) operation through four orthogonal scenarios. Key findings reveal: (1) Riverbed incision dominates discharge variation (annual mean contribution >84%), enhancing flood conveyance efficiency with a peak flow increase of 21.3 m³/s during July–September; (2) TGD regulation exhibits spatiotemporal intermittency, contributing 25–36% during impoundment periods (September–October) by reducing Yangtze backwater effects; (3) Nonlinear interactions between drivers reconfigure flow paths—antagonism occurs at low confluence ratios (R < 0.15, e.g., Cd increases to 45 under TGD but decreases to 8 under incision), while synergy at high ratios (R > 0.25) reduces Hanchuan Station flow by 13.84 m³/s; (4) The 180–265 km confluence-proximal zone is identified as a sensitive area, where coupled drivers amplify water surface gradients to −1.41 × 10⁻³ m/km (2.3× upstream) and velocity increments to 0.0027 m/s. The proposed “Natural/Anthropogenic Dual-Stressor Framework” elucidates estuary discharge mechanisms under intensive human interference, providing critical insights for flood control and trans-basin water resource management in tide-free estuaries globally. Full article

This study investigates the response of laterally loaded pile foundations embedded in sloping beds under scour conditions, which is vital for the design and stability of coastal and offshore infrastructure like sea-crossing bridges, offshore wind turbines, and wharves. While previous studies have focused on scour-affected pile performance in horizontal beds, this research expands the scope by incorporating sloped beds and corresponding scour effect, which are common in coastal and offshore environments. A three-dimensional finite element model was established to evaluate the pile foundation’s lateral load-bearing capacity under different slope and scour conditions, according to preceding flume tests on the mechanism of local scour around a pile in sloping bed. The results indicate that the lateral response of the pile is significantly influenced by the seabed slope and scour depth. A negatively inclined seabed weakens the interaction between the pile and the surrounding sediment, thereby reducing the lateral bearing capacity and bending moment. As the scour depth increases, the support provided by the soil further weakens, intensifying the reduction in lateral resistance. This effect is particularly pronounced for steep negative slopes, where the combined impact of slope and scour has a more significant detrimental effect. Full article

Local scour around bridge piers poses significant challenges to the stability and safety of bridge structures. Local scour results from the combined effects of increased longitudinal flow velocity, the direct impact of the flow in front of the pier, and the suction effect of horseshoe vortices. This study utilizes a three-dimensional mathematical model to simulate the flow field around the pier, employing the SWASH (simulating waves till shore) model. Experimental observations in a bed load flume were conducted to analyze the contribution of different factors to local scour. The results indicate that the scour depth caused predominantly by the flow accounts for approximately 75–80% of the total scour depth. Analysis of the longitudinal flow velocity distribution suggests that the scour depth due to the redistribution of longitudinal flow velocity generally accounts for 15–30% of the total scour depth. These findings provide insights into the local scour mechanism and have implications for the design and maintenance of bridge foundations. Full article

Under the concept of green and low-carbon development, efficient and environmentally friendly biochar preparation methods have attracted much attention. This study assessed a novel sodium carbonate activator combined with acid modification for sludge-based biochar (SB) production and its adsorption of organics in wool scouring wastewater. Under 600 °C, the optimal carbonization temperature, the residual weight percentage of biochar carbonized material increases from 27% to 73% after Na₂CO₃ activation compared to ZnCl₂ activation. Compared to HCl-modified ZnCl₂-activated biochar (Zn-Cl-SB), HCl-H₂SO₄-modified Na₂CO₃-activated biochar (Na-Cl/S-SB) had a specific surface area of 509.3 m²/g, and the average mesopore size was 7.896 nm, with micropore volume and specific surface area increasing by 83.3% and 79.8%, respectively. Meanwhile, the C-O oxygen-containing functional groups and pyrrole nitrogen-containing functional groups were significantly increased. Na-Cl/S-SB exhibited an excellent adsorption performance for organic matter in wool scouring wastewater, with a maximum adsorption capacity of 168.3 mg/g. Furthermore, the adsorption process followed the pseudo-second-order kinetic model. Three-dimensional fluorescence spectrum analysis showed that Na-Cl/S-SB had a strong adsorption capacity for aromatic protein analogs, proteins containing benzene rings, and dissolved microbial by-products in wool scouring wastewater. This study will serve as a guideline for the green synthesis of SB while improving its ability to adsorb pollutants. Full article

Increases in flood magnitude due to climate change increase the necessity of resilient river levees to prevent the breaching that can contribute to reduced flood inundation volume even when overtopping from a levee occurs. When a levee is composed of cohesive soil and the levee crest is paved, overtopping can lead to a waterfall-like nappe flow due to the erosion of the downstream slope of a levee. This flow subsequently expands the scour hole and increases the risk of levee failure. Although some models of scour hole expansion due to nappe flow were proposed, flow structures in the scour hole were not adequately taken into account. This study aimed to clarify the flow structure, including formation of vortices in the scour hole, by conducting flow visualization experiments and three-dimensional numerical analyses. After clarifying the flow structure, this study proposed a simplified model to calculate the bottom shear stress in a scour hole on the levee side. The accuracy of the estimated bottom shear stress was verified by comparing the results with a three-dimensional numerical analysis. This proposed method can predict further erosion of a scour hole. Full article

Current-induced local scour around pile groups weakens the capacity of structures. In this paper, experimental tests of local scour around an array of 5 × 5 pile groups were conducted in a steady current in a hydraulic flume. The pile-to-pile space was five times the diameter of a single pile. All the tests were in clear-water scour conditions. The effects of upstream piles on the local scour characteristics of downstream piles, as well as the outer-arranged side piles on the inner-arranged piles, were studied within flow intensities of 0.37–1.0. Both the three-dimensional topography of bed elevation changes and the maximum temporal scour depths are discussed. The results showed that the minimum threshold of flow intensity that can induce local scour around the pile groups was 0.40. The scour holes were independent of each other, though a global scouring phenomenon occurred between piles at a flow intensity of 1.0. The temporal scour depths of the downstream piles increased slowly throughout the local scour processes. During the initial scouring stage, they accelerated rapidly. At flow intensities of 0.60, 0.80, and 1.0, the scour development then progressed gradually, resembling the behavior of a single pile. The developing scouring stage can hardly be distinguished in the case of flow intensity of 0.80. The maximum scour depths in the flow intensity of 0.60 showed irregular variations with increasing row and column numbers. The equilibrium scour depths in the central-positioned piles tended to a constant value of 0.5 times the pile diameter. In larger flow intensities of 0.80 and 1.0, they decreased linearly with pile row number, with the maximum scour depths at the piles in the first row. The local scour depths of the inner-positioned piles in the parallel arrangement showed few differences at the front and rear piles. Full article

Currently, there are two primary issues with CFD simulations of local scour around bridge foundations using the RANS method. Firstly, the self-sustaining characteristics of turbulent boundary conditions at the inlet require special attention. Secondly, the simulated location of the maximum scour depth does not align with experimental observations. This paper employs the RANS method to model the hydrodynamic characteristics surrounding bridge piers. The sediment transport model and sediment-sliding model, considering any slope of the riverbed, were adopted to simulate the spatiotemporal evolution of local scour around the bridge foundation. Building on traditional methods and assuming local turbulence equilibrium, a self-sustaining model is theoretically derived. This model swiftly develops a balanced turbulent boundary layer, achieving a horizontally uniform flow field and effectively maintaining consistency between the inlet-given turbulent profile and physical reality. Additionally, by incorporating the velocity component of the downward-flow in front of the pier and the average shear stress around the pier into the excess shear stress model, the refined wall shear stress model accurately estimates the scouring contributions of the downward-flow and the horseshoe vortex system in this region. The numerical results including the maximum scour depth, location, and scour pit shape are consistent with experimental findings. The findings demonstrate that the numerical approach proposed in this study effectively addresses the issue of inadequate estimation of turbulent characteristics in scour pit at the leading edge of bridge piers using the RANS method. This method offers novel insights and approaches for addressing local scour issues in bridges and offshore wind turbines, as well as vortex-induced vibration issues in submarine pipelines. Full article

A scour hole in the pre-excavated plunge pool bed downstream of a dam can develop if the energy dissipation of the plunging jet from a spillway is underestimated. The objective of the research was to predict the equilibrium geometry of the scour hole downstream of a high-head dam to safeguard the stability of the dam foundation. A study incorporating both physical and numerical modeling was undertaken to examine the hydrodynamic and geo-mechanical aspects involved in rock scour. Experimental tests were performed to determine equilibrium scour hole profiles in an open-ended, jointed, movable rock bed under various conditions, including different flow rates, dam heights, plunge pool depths, rock sizes, and joint structure orientations. Based on the experimental findings, non-dimensional equations that describe the scour hole geometry were developed. The proposed innovative three-dimensional fluid–solid coupled numerical model is capable of realistically reproducing the equilibrium scour hole profile observed in the experimental tests. The numerical model allows detailed scour computations of fully developed rectangular jets plunging into shallow plunge pools. Full article

Vegetation plays a key role in trapping sediments and further controlling pollutants. However, few studies were conducted to clarify the erosion and deposition laws of sediments and the influence factors caused by vegetation patch properties, which is not conducive to the revelation of riverbank protection and erosion prevention. Therefore, this study investigated the change in scouring and deposition characteristics around submerged vegetation patches of nine kinds of typical configurations and their influencing factors. Vegetation patches were assembled from three vegetation densities (G/d = 0.83, 1.3, and 1.77, representing dense, medium, and sparse, respectively), and three vegetation patch thicknesses (dn = 170, 400, and 630, representing narrow, usual, and wide, respectively), to measure vegetation patch property influences. Flow velocity, scouring, and deposition characteristics under nine patches were determined by a hydraulic flume experiment, three-dimensional acoustic Doppler velocimetry (ADV), and three-dimensional laser scanner, and then ten geometry and morphology indices were measured and calculated based on the results of laser scanning. Results showed that both vegetation patch density and thickness were positively related to the turbulence kinetic energy (TKE) above the vegetation canopy, and only vegetation patch density was negatively related to the flow velocity above the vegetation canopy. The relation between the product of density and vegetation patch thickness and erosion area in planform (EA) showed a power function (R² = 0.644). Both density and vegetation patch thickness determined the scouring degree, but deposition location and amount did not rely on each one simply. On average, medium density showed the smallest maximum erosion length (MEL), EA, deposition area in planform (DA), and average deposition length (ADL) and a minimum of the above parameters also occurred at narrow vegetation patch thickness. The shape factor of the erosion volume (SFEV), the shape factor of the deposition volume (SFDV), ADL, and MEL of medium density and narrow thickness vegetation patch (G/d = 1.3, dn = 170) were significantly smaller than that of other types of patches. DA and equivalent prismatic erosion depth on the erosion area (EPED) were significantly linearly related (R² = 0.766). Consequently, most sediment was deposited close to the vegetation patch edge. It is suggested that vegetation patch thickness and density should be given to control sediment transport. In particular, natural vegetation growth changes vegetation patch density and then alters vegetation patch thickness. Management and repair need to be first considered. The results of this study shed light on riparian zone recovery and vegetation filter strip mechanism. Full article

Local scour around bridge foundations significantly impacts the stability and safety of marine structures. The development of scour holes adjacent to the pile foundations of sea-crossing bridges, influenced by tidal currents, involves multidimensional physical fields, multiscale coupling, and complex variations in marine loads. However, experimental models alone are inadequate for investigating the underlying mechanisms. Numerical simulation, a critical tool for studying local scour processes, faces the challenge of accurately modeling sediment transport, particularly under tidal flow conditions near pile foundations. To solve this challenge, this research considers the effect of reciprocating flow on sediment shear as well as its characteristic dissipation based on the immersed boundary method, introduces a reciprocating flow dissipation mechanism, and adds a momentum exchange term between the fluid and the sediment to derive a new controlling equation; a new tidal flow localized scour solver is ultimately constructed, termed TidalflowFOAM. The solver effectively simulates complex flow conditions under tidal currents, extending the modeling capabilities to more realistic three-dimensional bridge scour scenarios under combined wave and current conditions. Validation through cases reported in the literature and a series of controlled experiments, encompassing varying depths, flow velocities, and pile diameters, demonstrates the solver’s proficiency in capturing post-vortex data and accurately reflecting the influence of key factors on scour depth. However, the fidelity of the simulated scour hole morphology under tidal flow conditions behind the piles requires enhancement. The proposed numerical model for tidal flow conditions has high solution accuracy and can guide practical engineering applications. Full article

Numerous offshore wind turbines (OWTs) with bucket foundations have been installed in seismic regions. Compared to the relative development of monopiles (widely installed), seismic design guidelines for bucket-supported OWTs still need to be developed. Moreover, scour around bucket foundations induced by water–current actions also creates more challenges for the seismic design of OWTs. In this study, a simplified seismic analysis method is proposed that incorporates the soil–structure interaction (SSI) for the preliminary design of scoured bucket-supported OWTs, aiming to balance accuracy and efficiency. The dynamic SSI effects are represented using lumped parameter models (LPMs), which are developed by fitting impedance functions of the soil–bucket foundation obtained from the four-spring Winkler model. The water–structure interaction is also considered by the added mass in seismic analysis. Based on the OpenSees 3.3.0 platform, an integral model is established and validated using the three-dimensional finite element method. The results indicate that the bucket-supported OWT demonstrates greater dynamic impedance and first-order natural frequency compared to the monopile-supported OWT, which has an increased seismic response. Seismic spectral characteristics and intensities also play an important role in the responses. Additionally, scour can change the bucket impedance functions and the frequency characteristics of the OWT system, leading to a significant alteration in the seismic response. Scour effects may be advantageous or disadvantageous, depending on the spectral characteristics of seismic excitations. These findings provide insights into the seismic response of bucket-supported OWTs under scoured conditions. Full article

The scouring effect is widely acknowledged as a primary contributor to the weakening in the bearing performance of offshore piles; it often results in asymmetric scour patterns around the pile. To meticulously examine the impact of three-dimensional asymmetric local scour on the lateral bearing performance of a single pile, the Boussinesq solution is employed to determine the effective stress within the soil encompassing the pile, considering the presence of a three-dimensional asymmetric local scour hole. Utilizing the strain wedge model, the calculation method for the lateral bearing performance of a single pile under the condition of three-dimensional asymmetric local scour is established. The validity of this approach is established, and parameter analysis unveils the effect of varying sizes of three-dimensional asymmetric scour holes on the mechanical properties and displacement performance of a single pile. The analysis reveals that, as scouring dimensions around the pile escalate, the impact of scouring on single-pile lateral displacement and internal forces intensifies, leading to a decrease in the lateral bearing performance of a single pile. At a constant scour depth, the bottom area of the upstream scour hole significantly influences the displacement performance of a single pile. When the bottom length S_wb1 of the upstream scour hole grows by 1 time, 4 times, and 8 times, the lateral displacement of a single pile at a buried depth of 6 m is augmented by approximately 0.41%, 1.65%, and 2.06%, respectively. The simplified model obtained via the modified strain wedge model and Boussinesq solution can provide a theoretical basis for the preliminary design of a single pile under asymmetric scour hole conditions. Full article

In response to the deficiencies in existing bridge pier scour protection technologies, this paper introduces a novel protective device, namely a normal distribution-shaped surface (BND) protection devices formed by rotating a concave normal curve. A three-dimensional turbulent SST $k-\omega$ model is constructed, and physical model experiments of conical surfaces are conducted to validate the mathematical model. The simulation analyzes longitudinal water flow, downflow, vorticity intensity, and shear stress within normal and conical surfaces. The results show that the downflow distribution in front of the pier spans a relative water depth of (−0.45, 0.67), with a peak velocity approximately 70% of the longitudinal flow velocity. Circulation forms within the surfaces, with the main vortex flux inside the BND being 33% lower than that inside the conical surface. The maximum shear stress coefficient inside the BND can reach 9, and the protective surface isolates the bed from the flow to prevent scouring by high shear stress. The velocity gradient at the edge of the surface is small, and the edge shear stress of the 3D normal distribution-shaped surface (BND) protection device is only one-third of that of the conical surface, preventing edge scouring. The large shear stress and its distribution area decrease monotonically with the increase in surface width. When the surface width is four times the diameter, the distribution range of the shear stress coefficient greater than 1 is very small. The study of three-Dimensional turbulence within the BND provides a numerical basis for an anti-scour design. Full article

This study proposes the new condition monitoring concept of using features in the measured rotation, or ‘pitch’ signal, of a crossing vehicle as an indicator of the presence of foundation scour in a bridge. The concept is explored through two-dimensional vehicle–bridge interaction modelling, with a reduction in stiffness under a pier used to represent the effects of scour. A train consisting of three 10-degree-of-freedom carriages cross the model on a profiled train track, each train varying slightly in terms of mass and velocity. An analysis of the pitch of the train carriages can clearly identify when scour is present. The concept is further tested in a scaled laboratory experiment consisting of a tractor–trailer crossing a four-span simply supported bridge on piers. The foundation support is represented by four springs under each pier, which can be replaced with springs of a reduced stiffness to mimic the effect of scour. The laboratory model also consistently shows a divergence in vehicle pitch between healthy and scoured bridge states. Full article

A three-dimensional large eddy simulation model is used to simulate the turbulent flow dynamics around a circular pier in live-bed and clear-water scour conditions. The Navier–Stokes equations are transformed into a $\sigma$-coordinate system and solved using a second-order unstructured triangular finite-volume method. We simulate the bed evolution by solving the Exner-Polya equation assisted by a sand-slide model as a correction method. The bedload transport rate is based on the model of Engelund and Fredsœ. The model was validated for live-bed conditions in a wide channel and clear-water conditions in a narrow channel against the experimental data found in the literature. The in-house model NSMP3D can successfully produce both the live-bed and clear-water scouring throughout a stable long-term simulation. The flow model was used to study the effects of the blockage ratio in the flow near the pier in clear-water conditions, particularly the contraction effect at the zone where the scour hole starts to form. The scour depth in the clear water simulations is generally deeper than the live-bed simulations. In clear-water, the results show that the present model is able to qualitatively and quantitatively capture the hydrodynamic and morphodynamic processes near the bed. In comparison to the wide channel situation, the simulations indicate that the scour rate is faster in the narrow channel case. Full article