Scour Process Research Articles

Underwater in-situ plasma treatment of coarse wool fibers for scouring and bleaching

Wool, in its natural state, is laden with impurities such as grease, suint, dust, and vegetable matter on its surface, necessitating their removal for the wool to be suitable for various products. Traditional scouring methods involve the extensive use of water, detergents, and chemicals, leading to the generation of hazardous wastewater. Moreover, coarse fibers often require bleaching due to the retention of natural pigments during the scouring process. This study introduces an innovative and environmentally friendly plasma treatment for scouring and bleaching of the coarse wool fibers, referred here after as underwater in-situ plasma treatment (UIPT), which is entirely free from chemicals and detergents. Research includes a comparative analysis of UIPT, plasma-activated water (PAW), normal water (NW) and conventional wet-chemical process (CWP) for wool fiber scouring and bleaching. Surface morphology and surface chemistry analyses underscore the efficacy of UIPT in cleaning the coarse wool. The residual grease analysis demonstrated a substantial reduction in grease content of raw wool from 20% to 2% after plasma treatment, while the whiteness index of wool fibers increased from 48% to 70%.

Effects of finishing processes on physical properties of knitted fabrics produced by recycled cotton fibers

This study examines conventional wet-finishing processes applicable to fabrics containing recycled cotton fibers. The knitted fabrics were produced using open-end and compact yarns, with up to 80% of the cotton fibers being obtained from mechanical recycling of pre-consumer textile wastes. The study evaluated the effects of these finishing processes on the physical properties of the fabrics based on the recycled fiber ratio, yarn type, and yarn count. After determining the parameters for enzymatic bio-polishing, scouring, and color removal processes, two sequential finishing routes were designed: using the fabrics as mélange without a dyeing process (F1) or coloring them with color stripping and subsequent dyeing (F2). The resulting fabrics were tested for bursting strength, pilling resistance, weight, thickness, air permeability, and abrasion resistance, and the results were evaluated statistically. The study demonstrated that compact yarns provide superior strength, particularly when the F2 process was employed. The F2 process resulted in high pilling resistance and increased breathability of recycled knitted fabrics. The study concluded that the quality of fabrics containing recycled cotton fibers could be optimized by the selection of the appropriate finishing processes.

A quasi-three-phase flow simulation of the interactions between solitary waves and a vertical seawall installed on a sandy beach

Local scour and wave loading are two key factors that affect the safety of seawalls under tsunami attacks. In this study, the scouring process at the toe of and wave impact force on a vertical seawall under consecutive solitary wave attacks are simulated using a quasi-three-phase (air, water, and sediment) flow model, which models the air and water as a fluid mixture phase and sediment as a solid phase. The air and water interface is modeled by a VOF method and the sediment–fluid interaction is modeled using the Eulerian two-phase flow method. A comparison between the beach profiles with and without the seawall shows that, with a seawall, a deeper scour hole is generated at the toe of the seawall. Besides, the presence of the seawall causes the eroded sediment to be deposited further offshore. The numerical results are then analyzed in detail regarding the flow field and sediment transport process to reveal the mechanisms of the above eroding/depositing patterns. The wave impact force on the seawall is also analyzed to understand the effect of scouring on the wave loading. It is shown that the wave impact force, despite being stochastic for a specific wave, increases in general with the deepening of the scour hole because the latter increases the exposure of the seawall to wave slamming.

Experimental investigation of scour reduction around side-by-side piers by a downstream bed sill and continuous footing

ABSTRACT Understanding the scour process around bridge piers and investigating approaches to reduce these phenomena is an important issue for engineers. Side-by-side piers cause lower scour depth compared to a single pier with the same diameter. In this study, the application of downstream bed sill and continuous footing to control the scour depth around single piers and two side-by-side piers is investigated experimentally. The results show that by using a continuous footing with a thickness equal to the pier diameter, the scour depth in front of the pier is reduced by 50% and 55% for single pier and side-by-side piers, respectively. Moreover, when the continuous footing thickness is doubled, no scour depth is observed in front of the pier. Additionally, incorporating a downstream bed sill adjusted to the pier results in a reduction of approximately 30% in scour depth in front of the piers.

Development and prediction of scour around offshore wind turbine monopile foundations in ebb and flow tides

Monopile foundations are commonly used to support offshore wind turbines (OWTs) in nearshore shallow waters, where the periodic ebb and flow of tides can cause severe seabed erosion around these foundations. Accurately predicting the progression of scour depth under these tidal conditions is crucial for the safety of OWTs. While a few empirical formulas for equilibrium scour depth in periodic tides have been proposed, they often overlook the backfilling effects during their derivation. Consequently, these methods fail to predict the progression of scour depth characterized by recurring scouring and backfilling processes. In this study, the scour progression under different tidal patterns, including square tides, symmetrical sinusoidal tides, and asymmetrical sinusoidal tides with various periods, is investigated using numerical methods. It is indicated by the results that deeper scour depths are produced by symmetrical tides compared to asymmetrical tides, while the highest scour depth is observed under square tides, potentially slightly exceeding that under unidirectional currents. Additionally, asymmetric scour depths at the front and back sides of the pile can result from the asymmetry of tides. Although scour progression is affected by tide periods, their impact on the equilibrium scour depth is limited. Furthermore, a new concept called normalized cumulative effective flow intensity is introduced, which plays a primary role in governing equilibrium scour depth. Based on this concept, prediction methods for both equilibrium scour depth and scour progression under sinusoidal tides, which closely resemble natural tidal patterns, are proposed. The accuracy of these methods is validated by experimental data from previous studies. These findings not only provide a method to optimize the design of monopile burial depth but also aid in the development of appropriate maintenance measures to prevent scour-induced damage to OWT foundations over their long lifespans.

Riverbank fascines mostly fail due to scouring: Consistent evidence from field and flume observations

AbstractThe willow fascine soil bioengineering technique is commonly used worldwide in river restoration projects to stabilize riverbanks, thanks to high theoretical shear stress resistance and adaptable configuration. Fascines are composed of bundles of living branches fixed between stakes. When positioned in meanders at bank toe, they are subjected to strong hydraulic constraints. Here, we present the field back‐analysis of 470 willow fascines alongside experiments in a small‐scale model (scale 1:25). We describe the dynamics of failure in various situations. The field analysis revealed that 78% of fascines present no signs of bank instability. No fascines were pulled out, and they rarely showed signs of destruction once vegetation had established. Flume experiments confirmed that the main mechanical process of failure is erosion at fascine toe and extremities (9% and 3% of occurrence in the field, respectively). The dynamics of failure occur through: (i) erosion at the fascine toe, removing materials under the bundle; (ii) bank sediments, sliding underneath the fascine; (iii) scouring, leaving stakes exposed to falling into the river. Based on these observations, the fascine toe should be protected sufficiently deeply against undermining to keep sediments in place while vegetation is established. Bank slopes should be reduced as far as possible to decrease scouring. Finally, the mean shear stress values used as reference when designing bioengineering techniques do not capture the local and continuous scouring processes leading to failure. Thus, bend curvature, degradation, grain sizes, and level of fascine implementation should be considered when adapting design.

Spatiotemporal distribution patterns of iron, manganese, and arsenic within the river infiltration zone and the potential geochemical activity at key interfaces

The river infiltration zone is a mixed area of surface water and groundwater under the riverbed and along the riverbank, which is greatly affected by river infiltration. Currently, there is a lack of understanding regarding the migration and transformation processes of Fe, Mn, and As, along with their correlation with organic carbon in the river infiltration zone affected by riverbed scouring and siltation processes. In this study, based on techniques such as pore water sampling and the Tessier sequential extraction, the spatiotemporal variations in Fe, Mn, and As concentrations and possible geochemical processes at the riverbed sediment–water interface and along the river infiltration flow path were revealed. The results indicated that the potential geochemical activity of Fe, Mn, and As and the distribution of organic carbon in the riverbed sediment responded to riverbed scouring–siltation processes. Compared to the high water level period, the potential geochemical activity of Fe, Mn, As, and organic carbon in the riverbed sediment generally exhibited an upward trend during the low water level period, indicating more intense Fe and Mn biogeochemical reactions. During river infiltration, the labile organic carbon (LOC) was preferentially utilized, and with increasing depth, the sedimentary organic carbon (SOC) continuously transformed into LOC and dissolved organic carbon (DOC). Affected by riverbed scouring processes, the transition time from oxidizing to reducing conditions in the pore water increased, and the Fe, Mn, and As reduction zones moved deeper and farther from the riverbank, resulting in a significant expansion of the groundwater pollution area. The reductive dissolution of iron and manganese oxides/hydroxides and the oxidation of organic matter–bound Fe, Mn, and As were the main biogeochemical processes contributing to the release of Fe, Mn, and As in the river infiltration zone. These research results have crucial theoretical significance and practical application value for the sustainable utilization of groundwater resources and the remediation of groundwater pollution.

Computational Simulation of Monopile Scour under Tidal Flow Considering Suspended Energy Dissipation

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.

Yardangs sculpted by erosion of heterogeneous material

The recognizable shapes of landforms arise from processes such as erosion by wind or water currents. However, explaining the physical origin of natural structures is challenging due to the coupled evolution of complex flow fields and three-dimensional (3D) topographies. We investigate these issues in a laboratory setting inspired by yardangs, which are raised, elongate formations whose characteristic shape suggests erosion of heterogeneous material by directional flows. We combine experiments and simulations to test an origin hypothesis involving a harder or less erodible inclusion embedded in an outcropping of softer material. Optical scans of clay objects fixed within flowing water reveal a transformation from a featureless mound to a yardang-like form resembling a lion in repose. Phase-field simulations reproduce similar shape dynamics and show their dependence on the erodibility contrast and flow strength. Through visualizations of the flow fields and analysis of the local erosion rate, we identify effects associated with flow funneling and the turbulent wake that are responsible for carving the unique geometrical features. This highly 3D scouring process produces complex shapes from simple and commonplace starting conditions and is thus a candidate explanation for natural yardangs. The methods introduced here should be generally useful for geomorphological problems and especially those for which material heterogeneity is a primary factor.

Numerical investigation of the scour around a diamond- and square-shaped pile in a narrow channel

In this paper, a numerical investigation is conducted to study the scour dynamics around vertical square- and diamond-shaped piles in clear-water and live-bed conditions. The focus is particularly on cases involving narrow channels, aiming to examine the differences compared to more extensively studied scenarios, such as wide channels with circular piles. This work employs a Large Eddy Simulation (LES) model to simulate the turbulent flows around the structures. The hydrodynamic model is based on the Navier–Stokes equations in σ-coordinate, and the bed evolution is simulated by solving the Exner-Polya equation. The governing equations are solved using a second-order unstructured finite-volume method. The model is initially validated through a comparison with experimental data and numerical results found in the literature. Subsequently, it is applied to conduct a comprehensive study, enhancing our understanding of the various conditions influencing the scour process. The results indicate that the shape of the piles has different effects on the scour depth under clear-water and live-bed conditions. In live-bed conditions, the simulations reveal a deeper scour around the square-shaped pile compared to the diamond-shaped pile at the equilibrium stage. Conversely, an opposite behavior is observed in clear-water conditions, with a deeper scour around the diamond pile. Moreover, this behavior is consistent across both narrow and wide channels. It is discovered that, in clear-water conditions, the evolution of the scour in a narrow channel reaches equilibrium faster than in a wide channel, leading to a deeper equilibrium scour hole in the wide channel scenario.

Experimental analysis of scour around an offshore wind gravity base foundation

Scour processes and corresponding scour protection measures have been extensively studied for vertical cylinders. Several formulations for estimating scour and determining the optimum size of rocks for scour protection are widely available in the literature. However, when studying other types of structures, the geometric variability of the structures, limits the application of available semiempirical formulations. Scour phenomena around complex structures have been investigated experimentally in reduced-scale wave-current basins. However, the number of tests focused on support typologies different from monopile structures is still limited, restricting the availability of semiempirical formulations focused on conceptual design of scour protection solutions or in the estimation of the free scour development.In this work, a better understanding of the scour processes around gravity-based foundations (GBFs) and the performance of different scour protection solutions is gained via experimental results obtained from a large-scale test programme (1:35 test scale), including combined wave and current tests. The experimental tests were divided into two main types: (1) free scour and (2) scour protection tests. The main conclusion was that the triggering of a horseshoe vortex is the main driver of scour processes together with the contraction of flow lines at the foundation contours. Since monopile semiempirical formulations are not suitable for scour prediction, a new semiempirical approach was obtained from the test results. Moreover, two distinct scour mitigation methods were analysed (rock protection and concrete mattresses). Based on the undisturbed mobility parameter, statistical and dynamic limits were defined considering the rock grading tested. Finally, for concrete mattresses, the design driver was identified, and the adaptability of these types of solutions to seabed changes was verified.

Geomorphological processes following the construction of an offshore artificial island in the radial sand ridges of the South Yellow Sea

Offshore artificial islands represent a novel way to develop and utilize marine space resources. Previous research has focused on predicting erosion and deposition distributions following the islands construction, utilizing laboratory experiments and numerical simulations. However, the absence of long-term continuous monitoring has hindered systematic studies on the geomorphological processes of these islands. A 20-years of underwater terrain monitoring scheme was conducted before and after construction of the Rudong Artificial Island in Jiangsu Province, China. The results were combined with on-site observations of tidal currents, suspended sediment concentrations, and surficial sediment to investigate the evolution of the water channel–sand ridge system and the development process of local scour around the artificial island. The results indicated that after the construction of the artificial island, its surrounding water channels showed an overall evolution trend of the north channel shifting towards the north, the middle channel widening and moving south, and the south channel extending westward and southward. Scour has been observed at the four corners of the artificial island, with the peak depths of 7.3 m, 5.6 m, 13.7 m, and 12.2 m at the southwest, northwest, northeast, and southeast corners respectively. The scour in the southwest and northwest corners reached an equilibrium within five years. However, in the southeast corner, continuous erosion of the shoal on the southeast side of the artificial island enhanced the local hydrodynamic force, leading to further scour development. The large-scale scour in the northeast corner was mainly caused by changes in the local flow field following the construction of water intake pipelines and their protection projects. These geomorphological changes are the joint results of the natural evolution of the radial sand ridges and local erosion and deposition from engineering construction. Currently, the sandbanks surrounding the island are still undergoing dynamic evolution following engineering construction, and local scour around the island has not yet reached equilibrium.

Incompressible Smoothed Particle Hydrodynamics Simulation of Sediment Erosion around Submarine Pipelines

Sediment erosion around submarine pipelines is a popular topic, widely investigated in both ocean and submarine-pipeline engineering. In this paper, the incompressible smoothed-particle hydrodynamics (ISPH) method is modified for simulation of local scouring process around the submarine pipeline under the action of unidirectional flow. The erosion model is based on the Clear Water Particle–Turbid Water Particle–Critical Shear Stress (CWP-TWP-CSS) concept, and a sand–water two-phase model is proposed to deal with the sediment-entrained flow. The results of the numerical simulation are compared with the experimental data to verify the accuracy and applicability of the numerical model. The scouring process around the pipeline is investigated under different conditions, i.e., pipeline diameters, gap ratios, and flow velocities. The ISPH model is further used to study the flow characteristics of the scour pits around the submarine pipeline and the influence of the vortices on the maximum scour depth, to provide a theoretical basis for the stability design of submarine pipelines.

Spatiotemporal Scouring Processes around a Square Column on a Sloped Beach Induced by Tsunami Bores

Spatiotemporal Scouring Processes around a Square Column on a Sloped Beach Induced by Tsunami Bores

Experimental study on Local Scour around Bridge Pier Models generated by Flash Floods carrying Debris

The analysis of local scouring around bridge piers currently is based on typical river flood discharges. However, extreme events like flash floods with high velocity and discharge, carry wooden debris that accumulates upstream of the bridge pier. This results in additional forces due to flow diversion and reduction in flow area, so impacting hydraulic structures and exacerbating the scouring process. The study objective was to examine the impact of debris transported by flash floods on the depth and distribution patterns of scouring around bridge piers. This research was conducted in a 15.5-m-length, 0.5-m-width, and 1.0-m-height glass flume, layered by 25 cm thick of sand which is d50=0.52 mm and σg=2.327. Flash flood simulations were conducted by flowing the water mixed with debris content of 0, 5, 10, and 15% to hit a sharp nose pier model which is installed in the channel. Scour depth was measured using point gauges at 50 points around the pier. The findings indicated that an irregular distribution pattern of scour is formed around the pier, and scour depth decrease when increasing debris content. It is necessary to corrected in the range of 0.65-1.43 for 0-15% debris content carried by the flash flood compared to normal flood.

Experimental investigation on local scour downstream of stepped chutes with a flip bucket

Stepped chutes and flip buckets are the most prevalent energy dissipators in emergency spillways at dams. Given the impact that scour depth has on the stability and safety of these structures, the effects of stepped and smooth chutes on the local scour process downstream of a flip bucket for various hydraulic and geometric conditions were experimentally investigated in the present study. Experiments were conducted for 1:1 and 1:2 chute slopes (V: H), bucket exit angles of 15° and 30°, and a ratio of critical flow depth to step height (yc/h) between 0.53 and 0.97. The comparison of results revealed that installing steps over the chute profile reduced the maximum scour depth downstream in range of 15–51 percent, compared to smooth chute. By changing chute slope from 1:1 to 1:2, the maximum scour depth was reduced by an average of 16 and 25 percent for smooth and stepped chutes, respectively.

Tidal currents-induced scour development around pile foundations: Effects of flow velocity hydrograph

There is a lack of research in the existing literature regarding the scour around foundations for offshore wind turbines under tidal currents, which primarily relies on laboratory experiments with simplified flow velocity hydrographs like square tidal currents. To improve the prediction accuracy of scour development under tidal currents, a series of experiments were conducted to investigate the local scour process around a pile foundation under two typical tidal velocity hydrographs (sinusoidal and square tidal currents) in a specially designed fluid-structure-soil coupling flume. The results demonstrate that reciprocating tidal currents lead to a continuously evolving process of sediment erosion and backfilling around the pile. Although the shapes of the scour holes are similar between sinusoidal and square tidal currents, there are significant differences in the evolving process of the scour depth, presenting a short-platform shape and serrated shape, respectively. A consistent relationship is found between the dimensionless scour depth and the dimensionless effective flow work (DFW) under both tidal and unidirectional currents. An equivalent velocity expression for sinusoidal and square tidal currents is proposed and verified using existing experimental data. Furthermore, an empirical expression for the scour depth reduction coefficient between square tidal currents and unidirectional currents is proposed. These outcomes not only establish a theoretical approach for simplifying tidal currents hydrographs in laboratory experiments, but also provide practical guidance for assessing the tidal currents-induced scour development around pile foundations for in-situ offshore wind turbines.

Robust, all-state superhydrophobic-superoleophilic coating for ultrafast selective dye adsorption and oily wastewater purification

Superwettable surfaces have high application potential in liquid separation and dye adsorption, but considerable challenges remain in separately and quickly removing different contaminants in industrial wastewaters such as effluents from textile dying and wool scouring processes. Herein, a robust, all-state superhydrophobic-superoleophilic (SHP-SOI) composite coating was fabricated, using cobalt 2-methylimidazole nanoparticles (ZIF-67 NPs), polydimethylsiloxane (PDMS) and octadecylamine (ODA), and applied to various substrates via a facile two-step dip-coating method. The ZIF-67/PDMS-ODA coated fabrics turned superhydrophobic with a water contact angle (WCA) of over 150°, and oils could easily spread into the fabric with an oil contact angle (OCA) of 0° either in air or water. Owing to the synergistic effect of the coating components, the coating showed ultrafast and repeatable adsorption to anionic dyes (e.g. methyl orange, MO) with the maximum equilibrium adsorption capacity of 205.7 mg/g (MO concentration 100 mg/L, pH = 3). More importantly, 97.9 % of MO was adsorbed in only 5 min and the adsorption reached equilibrium in 30 min. In addition, owing to the coating’s strong affinity toward different oils, the treated fabrics could efficiently separate/adsorb oils from oil contaminated dye solutions. This all-state SHP-SOI coating was robust and could withstand various severe treatments without losing its original wettability and dye/oil adsorption/separation capability; it also exhibited heat induced self-healable property.

Numerical modeling of local scour around a subsea pipeline on cohesive seabed under steady currents

The present study introduces a numerical model for simulating local scour around a subsea pipeline on a cohesive seabed, representing a pioneering endeavor in the development of such a numerical model. The flow dynamics around the pipeline are solved using Reynolds-Averaged Navier–Stokes (RANS) equations with the SST k–ω turbulent model. Sediment movement on cohesive seabed is assessed through erosion rates, determined by an empirical formula derived from experimental data, rather than sediment transport rates typically used for non-cohesive sediment. Three different erosion rate formulas—linear, power law, and stochastic—are investigated in the simulation of the scour process. The numerical simulations are validated using laboratory data with artificial and marine sediments, demonstrating a satisfactory level of agreement in predicting scour bed profiles. Nevertheless, it is recommended to utilize the erosion rate formula that is calibrated to the specific sediment type based on experimental data for precise numerical prediction of scour process. The study reveals that the equilibrium scour depth is approximately a linear function of the bed shear stress, and the nondimensional time scale is inversely proportional to the bed shear stress within the specified range. Subsequently, an examination of the scale effect on the scour process with cohesive sediment around a pipeline is conducted. The results indicate that the nondimensional equilibrium scour depth marginally increases with larger pipeline diameter on cohesive seabed, contrary to the observed trend for non-cohesive sediments.

Hydrodynamic Modeling and Comprehensive Assessment of Pier Scour Depth and Rate Induced by Wood Debris Accumulation

This study mainly investigates the impact of debris accumulation on scour depth and scour hole characteristics around bridge piers. Through controlled experiments with uniform sand bed material, the influence of various debris shapes (high wedge, low wedge, triangle yield, rectangular, triangle bow, and half-cylinder), upstream debris length, downstream debris extension, and debris thickness on scour depth and scour hole area and volume around the cylindrical pier were analyzed. The findings revealed that the shape and location of debris in the water column upstream of piers are key factors that determine the depth of scour, with high wedge shapes inducing the deepest scour and potentially the largest scour hole, particularly when positioned close to the pier and fully submerged. Scenarios in which triangle bow debris was submerged at full depth upstream of the pier closely resembled situations devoid of debris. Conversely, debris extension downstream of the pier was found to reduce local scour depth while concurrently enlarging the dimensions of the scour hole. The existing scour prediction equations tend to overestimate scour depth in scenarios involving debris, particularly when applying effective and equivalent pier width. This discrepancy arises because these equations were originally developed to predict scour depth around piers in the absence of debris. In response, a refined model for predicting scour induced by debris was proposed, integrating factors such as upstream debris length, downstream extension, obstruction percentage, and debris shape factor. This model demonstrated strong agreement with experimental data within the scope of this study and underwent further validation using additional experimental datasets from other research endeavors. In conclusion, this experimental study advances the comprehension of scour processes around cylindrical bridge piers, providing valuable insights into the role of debris characteristics and positioning.