Scouring Effect Research Articles

The investigation of support effect from hard substrate to soft coating of PI/EP-PTFE under different coating thicknesses and frictional contacts

Engine bearings on ships can experience rapid failure under extreme conditions, such as when seawater infiltrates the engine compartment due to collisions with reefs or missile attacks. To enhance the self-lubrication and wear resistance of these bearings, a composite coating consisting of ZrO2-PI/EP-PTFE has been designed. This coating was applied using liquid spraying technology onto the surfaces of A370 aluminum alloy, CuPb22Sn2.5 copper alloy, and 15# carbon steel. Three different coating thicknesses—20 μm, 30 μm, and 40 μm—were applied to each substrate. The tribological properties of these coatings on the three substrates were investigated under both dry sliding wear and seawater corrosion conditions. The results indicated that the tribological performance of the coatings is influenced by factors such as the coating hardness, frictional contacts, and the supporting effect of the substrate. The hardness and elastic modulus of the coatings decreased as the coating thickness increased. A thicker coating results in reduced support from the substrate. The adhesive wear of these coatings under dry sliding wear conditions on the different substrates is also presented. The coefficients of friction (CoFs) of these coatings increased with coating thickness on all three substrates. In contrast, the wear rates decreased as the coating thickness increased. The hardness of the coating was influenced by the support effect of the substrate. The primary factors governing the tribological performance of the coating under dry sliding conditions are the pinch action of the hard grinding ball against the soft coating on the hard substrate and the contact pressure. Abrasive wear, spalling wear, plough grooves, and spalling pits were observed under seawater corrosion conditions. These findings suggest that increased coating thickness is associated with lower coefficients of friction (CoFs) and wear rates. The main contributing factors are seawater corrosion and the scouring effect of high-frequency reciprocating friction.

Response of soil particles around bedrock outcrops to sorting of rock surface flow derived outcrops in a rocky desertification area

Soils around bedrock outcrops, even if they are protected by vegetation to some extent after ecological restoration, are prone to being washed away by rock surface flow (RSF) derived from these outcrops in rocky desertification land. However, the extent of the scouring scale and sorting effect of RSF on the soils around outcrops remains unknown. To solve this problem, a series of soils around bedrock outcrops exposed in sloping farmland (SF, without RSF), abandoned land (AL, 1 year of RSF) and shrub–grassland (SG, 5 years of RSF) were examined by the laser diffraction method in a natural ecological restoration area of rocky desertification, where the duration of the RSF is also the time for ecological restoration. It was found that the RSF had a limited effect on the particle size distribution of the soils, only having a significant scouring effect on the soils at the rock–soil interface within a horizontal distance of 2 cm from the outcrops and an insignificant effect on the soils far away from the outcrops in terms of horizontal distance (10 cm and 20 cm). The particle size distributions of the soil around the outcrops were related to erosion caused by the RSF, but mainly benefited from ecological restoration. Compared with SF, the fine particle content in the soils around the outcrops significantly decreased in AL, but significantly increased in SG. Within a short period (1 year) after natural recovery, the RSF had a reduced effect on the fine particles of the soil around the outcrops; however, this did not occur after a long period (5 years). The results of this study further explain the influence of the RSF on soil erosion and leakage loss in karst areas.

Effects of Zr/Ti ratios on the structure and ablation characteristics of (Zr,Ti)C–SiC composites

Dense (Zr,Ti)C–SiC composites containing a dual-phase solid solution were fabricated by spark plasma sintering using homemade Mg-modified multiphase ceramic powders as raw materials. The ablation behaviour suggested that the composite with a molar ratio of Zr/Ti = 3:1 exhibited the best ablation resistance, with low mass and linear ablation rates of −2.56 ± 0.89 mg/s and 1.26 ± 0.40 μm/s, respectively, after ablation for 90 s under a plasma flame test at around 2300 °C. It is asserted that the formation of an oxide film consisting of a self-sintered ZrO2 skeleton and a high-viscosity Ti–Mg–Si–O liquid phase was responsible for the excellent ablation resistance, which has remarkable efficacy in resisting the scouring effect of ablative flames and the erosion induced by oxidizing gases on the composite matrix.

Analysis of flow field characteristics and factors influencing the excavation chamber in large-diameter slurry shield

The study aims to improve the flow field characteristics in the excavation chamber of the slurry shield to mitigate cutterhead clogging under cohesive strata. The Computational Fluid Dynamics (CFD) method is employed to quantitatively investigate the impact of scouring flux, cutterhead rotational speed, adding nozzles, and excavation methods on the flow field characteristics. Results show that increasing the existing scouring system flux even to 2000 m3/h couldn’t improve the slurry flowability at the cutterhead periphery. However, increasing the cutterhead rotational speed can significantly improve the slurry flowability at the cutterhead periphery and opening, resulting in a more uniform distribution of the flow field. Similarly, adding nozzles at the cutterhead periphery has positive effects. When the total scouring flux of 6 additional nozzles reached 800 m3/h, a favorable scour effect is achieved near the excavating face. Furthermore, adopting the air pressure assisted mode, the flowability of slurry at the cutterhead opening shows a significant enhancement compared to the full-chamber, and upper-half nozzles are transformed into non-submerged jets achieving a better scouring effect. Based on the analysis, it is recommended to add nozzles at the cutterhead periphery. If geological conditions permit, the “high-speed, low-penetration” or air pressure assisted excavation mode can be attempted.

A Dual-Function AgNW@COF SERS Membrane for Organic Pollutant Removal and Simultaneous Concentration Determination.

Surface enhanced Raman spectroscopy (SERS) is a highly sensitive analytical detection method commonly employed in biochemical and environmental analysis. Nevertheless, the rapid movement of analytes and interfering components in flow systems can impact the real-time, online detection capability of Raman spectroscopy. To address this issue, we developed an innovative approach utilizing covalent organic framework (COF), a robust porous material with excellent water stability, to coat the surface of Ag nanowire (AgNW) for synthesizing AgNW@COF hybrid. The regular pores of the COF serve to effectively eliminate large interfering molecules while facilitating the efficient transport of specific analytes to SERS hot spots. Additionally, the fluid flow-induced scouring effect aids in excluding interfering molecules from the surface of AgNW. By incorporating AgNW@COF into a bifunctional filter membrane with simultaneous filtration and sensing capabilities, we had achieved efficient purification of organic pollutants as well as real-time identification of pollutant species and concentration.

Local scour downstream of type-A trapezoidal stepped piano key weir in sand and gravel sediments

ABSTRACT This study examines the scouring effect downstream of a type-A trapezoidal stepped Piano key weir using experimental methods. The experiments were performed on weirs, both with and without steps at the outlet keys, while considering various discharge rates, tailwater depths, and bed material sizes. The study scrutinized three unique weir configurations, each with different dimensions and step counts at the outlet keys: the first, second, and third weirs had 5, 10, and 15 steps respectively. The findings indicate that the maximum scour depths in the Piano key weirs with 5, 10, and 15 steps were, on average, 17.5%, 31%, and 19% less than those in the non-stepped weir. It was also noted that an increase in discharge and a decrease in tailwater depth and bed material size led to an increase in the maximum scour depth. Moreover, an increase in the number of steps and a decrease in the size of the bed materials resulted in a reduction in sediment ridge height. The analysis suggests that the average scour index values in the 10-stepped weir were about 21% lower compared to the non-stepped weir. These insights contribute to the design and optimization of hydraulic structures to effectively mitigate scouring effects.

In situ cleaning of foulants by gas scouring on the membrane-electrode in an electro-membrane bioreactor

Low-maintenance membrane cleaning is essential for the stable operation of membrane bioreactors. This work proposes an in-situ electrical-cleaning method using an electro-MBR. When the applied bias was transiently increased, the membrane flux recovered rapidly because of the scouring effect from gas evolution reactions. The exfoliation of the cake layer induced by gas scouring played a major role in mitigating membrane fouling, recovering the transmembrane pressure (TMP) by 88.6 % under optimal conditions. Membrane modules did not require replacement during the operation period due to the efficacy of electrical cleaning, with the TMP varying between 37.5 % and 62.5 % of the ultimate pressure requiring change of the membrane modules. Despite the increase in power consumption of 0.66 Wh·m−3 due to the additional applied bias, there was no need for chemical additives or manual maintenance. Therefore, the electrical cleaning method enhanced the service life and reduced the maintenance costs of the electro-MBR.

An investigation of the effect of the pulse width and amplitude on sand bed scouring by a vertical submerged pulsed jet

This paper investigates the effects of the pulse width and amplitude on the scouring of sand beds by vertical submerged pulsed jets using a combination of experimental and numerical calculations. The reliability of the numerical calculations is verified through a comparison between the numerical simulations with the sedimentation scour model and the experimental data at a low pulse width T2 of 0, with the result that the various errors are within 5%. The results show that the scour hole depth |hmin| grows with the relative low pulse width T3 throughout three intervals: a slowly increasing zone I, a rapidly increasing zone II, and a decreasing zone III, producing a unique extreme value of |hmin|. The optimal scouring effect equation was obtained by analytically fitting the relationship curve between the pulse amplitude V and the relatively low pulse width T3. Including the optimal T3 and optimal duty cycle ƞ. The difference in the scour hole depth |hmin| under different pulse amplitudes is reflected in the initial period F of the jet. With an increasing pulse amplitude, |hmin| goes through three intervals: an increasing zone M, decreasing zone N, and rebound zone R. It is found that the scouring effect in the pulse jet is not necessarily always stronger with a larger amplitude. The results of the research in this paper can provide guidance for optimizing low-frequency pulsed jets for related engineering practices, such as dredging and rock-breaking projects.

Scour Protection Measures for Offshore Wind Turbines: A Systematic Literature Review on Recent Developments

Offshore wind energy is considered as one of the most promising resources of clean and renewable energy to replace fossil fuels. Additionally, its cost is expected to be lower than onshore wind energy as the technology matures. Offshore wind turbines (OWTs) normally operate in harsh ocean environments, which could impact their structural integrity. Scour erosion around foundations of OWTs can substantially change the overall stiffness of these structures and shorten their lifetime. Currently, there are a limited number of studies on countermeasures and their engineering requirements for decreasing the scouring effect; this is due to their different hydraulic circumstances, such as their stability, reliability, and resistance capacity. To this end, advancements in scour protection measures in the offshore energy sector are evaluated in this paper through a thorough and critical review following the PRISMA systematic literature mapping approach. This includes 68 papers on scour protection and over 30 scour protection designs for various types of wind turbine foundations. Here, we aim to provide an overview of the latest scouring protection measures and their comprehensive assessment, as well as their prospects and future challenges. The findings of this study will provide key insights into scour protection measures for OWTs and will subsequently contribute to the future growth of the offshore renewable energy sector.

Optimizing slug bubble size for application of the ultra-thin flat sheet membranes in MBR: a comprehensive study combining CFD simulation and experiment.

Optimizing the slug bubble size specifically for ultra-thin flat sheet membranes in MBR systems can effectively enhance the scouring force and improve fouling control efficiency, thereby further advancing their targeted and widespread application. In this study, a three-dimensional model was developed based on the practical application to investigate the impact of slug bubbles on scouring performance in ultra-thin flat sheet MBR systems, encompassing their evolution, disturbance level, and shear stress. A membrane fouling probability index for quantifying the distribution of membrane fouling, along with a turbulence intensity index have been proposed. The findings revealed that the 20-mL slug bubble induced the highest disturbance level in the surrounding fluid, characterized by an instantaneous peak velocity of 0.63m/s at the local system level, conducive to bubble scouring. And exerted the greatest shear stress effect, achieving the most effective reduction in membrane contamination, with a maximum shear stress of 1.82Pa. The experimental validation conducted during the operational cycles confirmed that the scouring effect of 20-mL slug flow yielded in a maximum proportion of 48.16% within the low fouling probability region. The results provided evidence supporting the assertion that specific aeration conditions producing 20mL of bubbles resulted in minimal membrane fouling, ensuring a more pronounced scouring effect. The combination anythsis of slug bubble characteristics and behaviors, integrating theoretical and experimental approaches, implied that 20mL was the optimal bubble size in ultra-thin flat sheet MBR, which fulfilled the optimal air scouring effect.

Monolithic CoMoB based catalyst enabling high water-sources adaptive hydrolysis of borohydrides

High water-source adaptability is meaningful to the popularization of hydrolysis of borohydrides as portable hydrogen generation technique. Herein, the key catalyst that can enable high water-sources adaptive hydrolysis of borohydrides is successfully developed for the first time. The as-prepared monolithic CoMoB based catalyst has outstanding catalytic activity with high hydrogen generation rate of the 3.0 L min−1 g−1 at 25 °C and low activation energy of 38.7 kJ mol−1 toward the hydrolysis of NaBH4 using deionized water. More importantly, the catalyst exhibits distinguished durability toward hydrolysis of borohydrides in various water, including deionized water, lake water, and even seawater benefiting from its unique structure and gas scouring effect. Furthermore, an efficient NaBH4-based H2 supply system is developed with the catalyst and this system successfully achieves full drive of 100 W fuel cell using different sources of water. This study may provide a new protocol to develop portable H2 generation system with high water source adaptability in wild environments.

Study of machining performance for electrochemical grinding of difficult-to-cut alloy U71Mn

PurposeThis study aims to apply an electrochemical grinding (ECG) technology to improve the material removal rate (MRR) under the premise of certain surface roughness in machining U71Mn alloy.Design/methodology/approachThe effects of machining parameters (electrolyte type, grinding wheel granularity, applied voltage, grinding wheel speed and machining time) on the MRR and surface roughness are investigated with experiments.FindingsThe experiment results show that an electroplated diamond grinding wheel of 46# and 15 Wt.% NaNO3 + 10 Wt.% NaCl electrolyte is more suitable to be applied in U71Mn ECG. And the MRR and surface roughness are affected by machining parameters such as applied voltage, grinding wheel speed and machining time. In addition, the maximum MRR of 0.194 g/min is obtained with the 15 Wt.% NaCl electrolyte, 17 V applied voltage, 1,500 rpm grinding wheel speed and 60 s machining time. The minimum surface roughness of Ra 0.312 µm is obtained by the 15 Wt.% NaNO3 + 10 Wt.% NaCl electrolyte, 13 V applied voltage, 2,000 rpm grinding wheel speed and 60 s machining time.Originality/valueUnder the electrolyte scouring effect, the products and the heat generated in the machining can be better discharged. ECG has the potential to improve MRR and reduce surface roughness in machining U71Mn.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2023-0341/

Effects of flow rate and wastewater concentration on the transformation of nitrogen in sediment-water system of sewage pipelines.

In this work, the transformation law of nitrogen in sediment-water system under different flow rates and wastewater concentrations were investigated in a simulated sewage pipeline system. Results showed that the different flow rates and wastewater concentrations in the pipeline caused differences in microbial community in sediments and nitrogen transformation. When the flow rate increased from 0.05 to 0.2 m/s, the scouring effect was enhanced, resulting in higher concentrations of NH4 + -N and NO3 - -N in the overlying water. At 0.2 m/s, the relative abundance of Clostridium_sensu_stricto_1 in sediments was higher, resulting in a greater conversion of amino acid nitrogen (AAN) to NH4 + -N. Meanwhile, many denitrifying bacteria (Trichococcus, Dechloromonas, norank_f__norank_o__Gaiellales, Thiobacillus) had high relative abundance in the sediments, and the denitrification process was common. When the wastewater concentration was high, the nitrification reaction was great in overlying and interstitial water. Moreover, the ammoniation process was great in the sediments, and the variation flux of AAN was large (remarkably reduced). PRACTITIONER POINTS: AAN transformed to NH4 + -N in sediment under different flow rate and concentration. Scouring was enhanced at 0.2 m/s, increasing nitrogen contents in overlying water. Difference in microbial community led to more AAN conversion to NH4 + -N at 0.2 m/s. The ammoniation process was greater in sediment at a high concentration of sewage. NH4 + -N migrated from overlying water to sediment at a high concentration of sewage.

Numerical simulation on water exchange affected by tidal and runoff in Xiaohai Lagoon, Hainan province

Xiaohai Lagoon is the largest lagoon in Hainan, connected to the open sea through a narrow channel. In this study, a hydrodynamic numerical model based on the FVCOM model is established to quantitatively investigate the water exchange characteristics between Xiaohai Lagoon and the open sea under tidal and runoff conditions, utilizing concepts such as residual flow, tidal prism, and half-life time. Under the influence of runoff effect, the water exchange capacity in the lagoon has significant spatial variations, and the closer the distance to the estuary and inlet compared to the tidal drive, the faster the water exchange. The strongest areas of water exchange capacity in the Xiaohai lagoon are located in the mouth, tidal channel and estuary areas, and the weakest area is the southeastern part of the lagoon. The simulation results showed that the runoff input has a certain promotion effect on the water exchange in the lagoon, especially in the scouring effect of freshwater in the estuary area, the easier the water exchange between the sea areas.

Impact of Hydrogeological Characteristics on the Development of Underground Space Resources in Valley Cities

The development of urban underground space is a crucial aspect of current urban development. However, various factors pose challenges during the development process. In particular, in the valley cities of western China, groundwater has a significant impact on the utilization of underground space. This study focuses on understanding the influence of hydrogeological characteristics on the development of underground space in Ledu District, Haidong. Firstly, the hydrogeological characteristics of the aquifer in the study area are analyzed to determine the recharge and discharge characteristics. The dynamic changes in the groundwater table over time are then examined. Subsequently, the hydrochemical characteristics of groundwater are investigated to expound on the influence mechanism of groundwater on the development of underground space resources in Ledu District. The study reveals that the hydrodynamic effect of groundwater in the study area is substantial and has a significant physical scouring effect on underground structures. The fluctuation of groundwater levels affects the stability of buildings by increasing groundwater buoyancy. Additionally, this fluctuation also leads to engineering and environmental problems such as differential settlement and land salinization. The chemical characteristics of groundwater primarily impact the stability of building foundations through the corrosive effects of groundwater composition. This research clarifies the influence mechanism of groundwater on the development of underground space in typical valley cities of western China. The findings have practical significance for the evaluation, planning, development, and utilization of urban underground space resources in Haidong.

Hydro-mechanical analysis of water-induced pothole patch failure in asphalt pavement

Pothole repair is one of most common roadway maintenance to improve driving comfort and reduce safety risk. This study aimed to conduct hydro-mechanical analysis of water-induced pothole patch failure in asphalt pavement. Three-dimensional finite element models are used to analyze the coupled hydraulic and mechanical responses of surface patching under moving traffic loading considering different wheel path locations and asphalt patch sizes. The model results under dry and saturated conditions were validated against field measurements and simulation results from the literature, respectively. Laboratory tests were conducted to measure dynamic modulus and permeability of asphalt patch material. Analysis results show that regardless of patch size and wheel path, the maximum pore water pressure occurs either at the patch body or the interface between the patch and surrounding pavement when traffic loading approaches the pothole. The hydraulic scouring effect was observed with positive and negative pore pressure under moving loads. The maximum interface shear stress at the interface between the patch and surrounding pavement under traffic loading was found close to the bonding strength, especially for big-shallow patch. The comparison of asphalt patch responses at dry and saturated conditions indicates that water intrusion mainly accelerates edge disintegration of pothole patch.

Research on the Protective Effect of Twin-groyne Arrangement on Riverbank

A curved channel with intersecting streams can be easily scoured by incoming flow, and the concave bank is badly damaged. This research showed that the twin-groyne could effectively adjust and optimize the flow velocity distribution, change the shape of the free water surface of the bend, prevent erosion, and promote silting on the concave bank, and it could provide a scouring and silting effect on the convex bank. When the spacing of twin-groyne was increased to more than four times the body length of the single-groyne (spur dike), the protective effect on the concave bank was weakened, and the scouring and silting effect of the convex bank was reduced. Excessive spacing of the twin-groyne could cause local erosion damage to the concave bank. When the distance exceeded the theoretical optimum, it was equivalent to the effect of single-groyne. With the increase in the submergence degree, the velocity of the concave bank decreased first and then increased, while the velocity of convex bank decreased continuously. The protective effect of a non-submerged twin-groyne with a dam spacing of four times the body length of the single-groyne was better than that of other conditions, and it is recommended to be used in practice.

Numerical evaluations on enhanced steam–air condensation outside S-type tubes under natural convection conditions

Steam-air condensation is extensively utilized in various industrial fields. In pursuit of better efficiency in applications, this study promoted a novel structure of heat transfer enhancing tube named S-type tube. It combines the superior heat transfer performance of short tubes and inclined tubes, demonstrating a high potential for enhanced condensate heat transfer. To evaluate the heat transfer property and obtain the optimized S-type tube structure, three-dimensional CFD methods were used, coupled with the liquid film model in STAR-CCM + software. The effcts of wall sub-cooling, pressure, air mass fraction and downward forced velocity, bend radius, horizontal section length on the steam–air condensation heat transfer characteristics outside S-type tubes were investigated. It was identified that S-type tubes can enhance the steam–air condensation heat transfer capability, and the enhanced heat transfer ability increases with the increase of pressure and the decrease of air mass fraction, and remains basically unchanged with changes in sub-cooling. The condensation heat transfer coefficients outside S-type tubes are 0.9 ∼ 1.71 times that of vertical tube range 0.2 MPa to 0.8 MPa. The main mechanisms affecting the condensation heat transfer are summarized: the scouring effect between tube segments to enhance heat transfer and the air layer pileup effect to inhibit heat transfer. The heat transfer enhancement capacity for the S-type tube is determined by the relative magnitude between the scouring effect and the pileup effect. Both effects increase as bend radius decreases; therefore, selecting an appropriate bend radius is crucial.

The dominant factor of C/SiC composites in ablation environment with heat and particle flow

As thermal structure components in scramjet engines, carbon-reinforced silicon carbide (C/SiC) composites are often subject to an ablation coupled with heat and particle flows. This study simulates the working environment of the scramjet engine's thermal structure component by coupling an Al2O3 particle flow with a plasma flow. The ablation behaviour of C/SiC composites in the presence and absence of particle impact have been comprehensively analysed. The results show that the factor dominating the ablation behaviour varies with temperature. At relatively low temperatures, the particles have difficulty breaking down the dense SiO2 layer formed from the oxidation of SiC in the presence of heat flow which is the dominant factor. As the temperature rises, the SiC begins to shift towards active oxidation. A few defects appear in the oxide layer, leading to a significant particle mechanical flaking effect. Particle flow is the dominant factor. However, a higher temperature led to the substantial active oxidation of SiC, and the oxide layer dissipated, exposing more defects. The heat flow causes a strong oxidation reaction, and the scouring effect of the particles is significant as well, both of which play a dominant role in the ablation process.

Analyzing the response distribution of DO concentration and its environmental factors under the influence of typhoon rain events with remote sensing

Typhoon rain events are important factors that trigger changes in dissolved oxygen concentrations in watersheds. The direction of the typhoon driving force is clear, but the mode of action and mechanism are complex. Moreover, quantifying the relationship between these actions and dissolved oxygen is challenging. This study collected measured data from water quality monitoring and remote sensing during the 2022 typhoon rain events. By analyzing the changes in typhoon driving factors and dissolved oxygen (DO) concentrations in water under various typhoon storms, extended MOORA plus the full multiplicative form (MULTIMOORA), Multiscale Geographic Weighted Regression (MGWR), and spatial autocorrelation analysis were used to evaluate the response of DO concentration. Furthermore, the effects of the atmospheric environment under the influence of human activities on the response distribution of the urban water environment were analyzed. The results of the study showed that under the effect of a typhoon with higher rainfall intensity, the response of DO concentration in the water body of the river in the center of the city was better. However, the response of DO concentration in the water body at the mouth of the sea had a tendency to become worse. Under the influence of typhoon rain events with smaller intensity, the scouring effect of rainwater dominated, and the DO concentration response in the water body had a tendency to become worse. The analysis of spatial heterogeneity under the influence of human activities showed that the ranking values of DO concentration response in rivers in the city area of Zhongshan, under the influence of typhoon rain events, were positively correlated with the distribution of ozone (O3) concentration and sulfur dioxide (SO2) concentration in the eastern, central, and western parts of Zhongshan. Conversely, it was negatively correlated with the distribution of O3 concentration and SO2 concentration in the northern and southern parts of Zhongshan. Based on the research results, we constructed a technique to evaluate the response of dissolved oxygen concentration during the typhoon transit period, which can provide an indicator reference for urban managers in water environment management.