The investigation of the critical bed shear stress at the bed surface with negative slopes in the scour hole downstream of a submerged structure has primarily relied on experimental methods with limited theoretical exploration. This paper examined the distribution of near-bed flow velocity and turbulence intensity at the equilibrium stage based on physical model experiments of local scour downstream of a submerged weir. Additionally, the current study established equations for calculating the distribution of the near-bed mean flow velocity and relative turbulence intensity at the bed surface of the scour hole with negative slopes. Integrating mechanics, probability theory, and statistics introduced an impact force resulting from water flow on the local bed surface. Furthermore, a semi-empirical model for the dimensionless critical bed shear stress was developed applying this basis. The predicted values of the semi-empirical model were consistent with the measured values. They can be utilized to calculate the critical bed shear stress in the local scour hole downstream of the submerged weirs. The near-bed mean flow velocity and relative turbulence intensity introduced in the equation are key parameters that reflect the microscopic mechanisms on the local bed surface. Utilizing these microscopic parameters also avoids the influence of upstream structural configurations in the scour hole, thus broadening the applicability of the study's findings. This development not only deepens the understanding of velocity distribution patterns on the negative slope of the local scour hole downstream of submerged structures in rivers or the ocean but also offers a theoretical foundation for enhancing the precision of numerical models of local scour and for the application of critical standards of sediment initiation in related studies.

The hydrodynamics of the flow around piers affects the motion of ships navigating near these structures, while the motion of the ships, in turn, affects the distribution of the flow field near the piers. This study investigates the forces exerted on a ship in various ship–pier transverse distances using commercial computational fluid dynamics (CFD) software, Fluent 13.0, based on the RNG k-ε model, complemented by experiments with a physical model. The interaction between the ship’s motion and the flow field near the piers was considered. The results indicate that during the encounter between the ship and the pier, the boundary of the approaching ship affects the flow field near the pier, thereby affecting the generation and detachment of vortices behind the pier. The yaw moment of the ship demonstrates a marked “positive peak–negative peak–positive peak” pattern. Moreover, as the ship–pier transverse distance increases, the impact of the pier on the ship’s motion decreases, and it becomes negligible when the distance reaches 0.9 times the diameter of the pier (D), suggesting that the pier has a minimal impact on ship navigation if the ship–pier transverse distance exceeds this threshold.

Dispersive soil is a common problematic soil that segregates in water, resulting in instability of slopes and posing significant threats to the safety of earth structures. However, there is a limited amount of research on the hydraulic erosion of dispersive soil. Splash erosion is the initial stage of hydraulic erosion. A clear understanding of splash erosion is crucial for investigating dispersive soil hydraulic erosion. This study explored the influence of soil dispersity and rainfall intensity on the characteristics of splash erosion by conducting consecutive single-drop rainfall tests on artificially prepared non-dispersive and dispersive soil samples with varying sodium carbonate content. High-speed cameras and single-lens reflex (SLR) cameras were used to capture the variations of the splash crown, splash pan, and splash crater. Results showed that the content of sodium carbonate significantly affected splash erosion. High soil dispersity resulted in smaller masses of splashed soil material and infiltration water, but a larger mass of splashed water. It also led to a smaller volume and depth of the splash crater. The critical value of the content of sodium carbonate for soil dispersity discrimination was 0.15 %, the same as the threshold for the splash process to stop significant changes. The shape of the splash crown also helped analyze the process of splash erosion and was relevant to the splash crater shape. Increasing soil dispersity diminished the impact of rainfall intensity on splash erosion. These findings provide new comprehension of the mechanism of splash erosion of dispersive soil and lay a foundation for the systematic study of hydraulic erosion of dispersive soil in engineering slopes.

Existing methods for estimating critical bed shear stress are limited and usually do not consider local scour processes; therefore, the accuracy of numerical modeling is usually compromised. This paper presents the results of physical experiments on scour downstream of low-head weirs and proposes new equations for estimating the critical bed shear stress in scour holes. The experiments were done using a camel hump weir and coarse-bed materials which are applicable to steep streams with coarse-bed materials (gravel, rocks, etc.). The critical shear stress was regarded as the bed shear stress within the scour holes, which was determined using the three-dimensional (3D) flow field and bed morphology measured at the equilibrium scour state. The influence of the sediment size also was investigated. The experimental results showed that a scour hole can be divided into three zones: Zone-I for the upstream scour slope, Zone-II for the downstream scour slope, and Zone-III for the downstream slope of the sediment deposit downstream of the hole. The relation between the critical shear stress of the bed surface in Zone-I, the flow rate, and bed position was established, and the new equations yielded better accuracy than existing methods. In addition, the relation between the critical shear stress and the slope of the bed and the ratio of the local water depth to the particle size in Zone-II and Zone-III were established. After verification, the calculation results of the newly proposed equations were in good agreement with the standard values of the dimensionless critical Shields parameter obtained through processing the experimental results in the current study. Further discussion is provided regarding the integration of the parameters calculated applying the new parameters in the numerical models. (c) 2024 International Research and Training Centre on Erosion and Sedimentation. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BYNC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

A modified piano key weir with a rounded nose and a parapet wall (MPKW) can improve the discharge capacity significantly compared to a standard piano key weir. However, the optimum of the inlet/outlet width ratio (Wi/Wo) on the discharge efficiency of MPKW is still not investigated numerically. The present work utilized the numerical modeling to investigate and analyze the effects of the inlet/outlet key width ratios on the hydraulic characteristics and discharge capacity of the MPKW. To validate the numerical model with the experimental data, the results indicate that the average relative error is 2.96%, which confirms that the numerical model is fairly well to predictthe specifications of flow over on the MPKW. Numerical simulation results indicated that the discharge capacity of the MPKW can be improved up to 8.5% by optimizing the Wi/Wo ratio ranging from 1.53 to 1.67 even if the other parameters of the MPKW keep unchanged. A big Wi/Wo ratio generally leads to an increase in discharge capacity at low heads and a little effect on the discharge efficiency at high heads. The discharge efficiency of the inlet and outlet crests increases up to 9.6% for high heads, while discharge efficiency of the lateral crest decreases up to 23.5% compared with the reference model. The findings of the study revealed that the intrinsic influencing mechanism of the Wi/Wo ratio on the discharge performance of MPKWs.

挑流消能为高水头水利枢纽主要泄洪方式,耗散能量的同时会对下游产生剧烈冲刷.为分析冲刷坑形成原因,探究鼻坎型式对于冲刷的影响,针对某一具体工程,采用自编程序以临界起动切应力作为泥沙起动条件进行数值模拟,结果表明:差动式鼻坎挑流水舌集中,单宽流量大,冲刷深度深,河床冲刷严重;舌型鼻坎挑流水舌横向扩散较大,单宽流量小,冲刷深度较浅.将计算结果与物理模型试验结果对照,两者基本吻合.证明通过用户自定义编程方法进行数值模拟能够较为准确的预测冲刷坑范围与深度,合理的鼻坎型式对于削弱下游冲刷效果显著.

针对长距离输水隧洞小比尺物理模型难以满足阻力相似的问题,依托陕西省某县城分洪隧洞工程,通过对进口闸室段过流能力及隧洞段输水能力进行分别验证,实现了在小比尺物理模型上进行隧洞过流能力的试验研究.基于隧洞段内可以形成均匀流的特点,采用明渠均匀流计算方法对模型实测结果进行了计算验证.结果表明:计算流量与模型实测流量的最小差值为11.71 m3/s,最小相对误差为1.93％;基于进口闸室段距离短、局部水头损失远大于沿程水头损失的特点,控制隧洞桩号0+099.25 m处水深为隧洞正常水深,可直接验证其过流能力,进口闸室段过流量与实测过流量最大误差不超过1.78％;在30年一遇洪水时,推荐方案闸室和隧洞的过流能力相匹配且与模型实测值基本一致,隧洞的分洪流量达到863 m3/s,较设计分洪流量800 m3/s超泄了63 m3/s,超泄流量占设计过流量的7.88％,完全满足设计要求.

How to optimize the spatial distribution of terraces in the watershed is an important scientific problem. It was researched through a watershed solid-scale physical model based on the 3D reappearance of a scene under the Cartesian coordinate system, with the lowest point of the watershed as the origin. The results showed that the change of the spatial pattern of terraced fields in the basin had an important impact on the production of runoff and sediment. There was an approximate quadratic-function relationship between the spatial location and the parameters of runoff and confluence. If Rt was terrace-erosion-reduction benefit, it could be defined as the reduction in the watershed-erosion modulus per unit of terrace area. The longitudinal distribution of Rt was upper and middle > lower parts, and the vertical distribution of Rt was high > low place. The erosion reduction was 77.67% of the terraces of the middle and upper, occupying 33% of the watershed area. The change of the Rt was logarithmically related to the relative distance (r) from the center of the terrace. When r was around 0.35, there was an inflection point in Rt growth. The results of this study have important practical significance for the planning and construction of terraces in the watershed.

基于Melville桥墩局部冲刷试验模型,采用FLOW-3D软件,利用大涡模拟方法模拟了桥墩绕流局部冲刷过程,通过分析冲刷坑形态、深度的变化过程,评价了 Meyer-Peter和Van Rijn推移质输沙率公式在桥墩绕流局部冲刷模拟中的适用性,并结合两输沙率公式结构分析了模拟结果存在差异的原因.结果表明:大涡模拟方法能够有效模拟桥墩绕流的复杂流态,采用Meyer-Peter推移质输沙率公式的局部冲刷模拟结果较好,预测的冲刷坑形态更接近试验观测结果;当时间为30 min时,最大冲刷深度与试验观测结果相对误差为2.3％.采用Van Rijn推移质输沙率公式的预测结果相对较差,最大冲刷深度与试验观测结果相对误差为15.5％.

Despite its wide application across arid land types, furrow irrigation is often associated with numerous environmental problems related to deep percolation, runoff, and soil erosion. In this study, a straightforward approach was proposed to achieve higher uniformity and reduce erosion. Here, the impacts that a moveable “plug” has on the behavior of irrigation water in the furrow were simulated using FLOW-3D and HYDRUS-2D, where three plug heights and two flow rates were set. The effect of inflow rate and plug height on the water advance, water level, cumulative infiltration in the furrow, and uniformity coefficient was determined. Results indicate that the plug was able to slow water velocity by approximately 60% in the furrow and increase the furrow advance time by 3–4 times; the water level was increased by nearly 10 cm compared with no plug. Moreover, an irrigation uniformity range of 90.18–99.22% was associated with this plugging. The addition of a plug in the furrow irrigation practices for smallholder farmers in developing countries demonstrates great potential in reducing the probability of erosion under large slopes and can effectively improve irrigation uniformity.

Ships sailing in the area of a bridge are vulnerable to the influence of complex water flow, due to the complex flow pattern around the bridge pier. Ships often crash into bridge piers, leading to serious economic losses and threating personal safety. Based on the common forms of piers of skew bridges, the hydrodynamic problems encountered during ship–bridge interactions in the area of a skew bridge were studied using particle image velocimetry-based flume testing, physical model testing, and numerical simulation. The influence of the flow angle of attack of a round-ended pier on the force and center of gravity of a ship moving on both sides of a pier is discussed under various ship–bridge transverse spacings. The results show that as a ship passes through the bridge area, the bow roll moment exhibits three peak values: ‘positive’, ‘negative’, and ‘positive’, and the curve of the center of gravity position forms the shape of a ‘straw hat’. With an increase in the flow angle of attack of the pier, the negative peak value and the second positive peak value of the bow roll moment of the ship passing through the back flow side of the pier become greater than those on the upstream side. Moreover, the ship’s navigation attitude is more unstable compared to that upstream, and the ship is at risk of colliding with the pier and sweeping. The width of the restricted water area, determined by the hydrodynamic action between the ship and bridge in the skew bridge area, is the same as that determined by the critical lateral velocity. For the ship class referred to in this study, the current code can also be used in channel design, to safeguard ship and personal safety with piers with a large flow angle of attack.

Local scour downstream of the release structure is a critical problem to the safe and stable operation of water resources and hydropower engineering. In order to investigate the shape and depth of the scour hole under the equilibrium state of erosion and deposition downstream of an apron, a group of 16 experiments from the hydraulic similarity model test of Dangka Hydropower Station was conducted with the non-cohesive sediment of different median particle sizes under different flow rates in this study. The control variable method was to study the influence of the flow rate and sediment size on the shape of the scour hole to define the number of experiment times of each test group. The results showed that the plane shape of the scour hole was irregular ellipse or semi-ellipse. The depth and size of the scour hole increased with the increase of the flow rate, and decreased with the increase of the sediment size; the downstream longitudinal slope ratio of the scour hole increased with the increase of the sediment size. The coefficients of the upstream and downstream slope ratio of the local scour hole were 1/2 to 1/6 and about 1/10, respectively.

为了研究弯曲河段的船舶安全航行条件,考虑引航道布置在凸(凹)岸、上(下)游引航道水流条件及船舶航行的特点,建立了弯道概化模型.通过水流条件试验和船舶模型航行试验,完善了弯曲河段船闸口门区船舶安全通航的判别公式,提出口门区船舶安全通航的2种判别方法.通过试验,验证了该方法的合理性.

串列双圆柱桥墩周围流场与两桥墩间距密切相关,采用黏性流求解方法,使用商业CFD软件中的FLUENT软件,并基于RNG k-ε湍流模型对单圆柱及串列双圆柱桥墩绕流非稳态瞬时流场进行了数值模拟.研究结果表明:桥墩间距影响着两桥墩墩后尾涡的生成与脱落;桥墩墩后横向流速呈正负交替变化;以碍航紊流宽度为标准,航道边线与串列双圆柱桥墩边壁之间的横向安全距离至少应为1.5倍桥墩直径.

考虑桥墩绕流与船舶的耦合作用,以物理模型试验为基础,采用FLUENT软件,并基于RNG k-ε模型,研究不同桥墩间距下船舶驶经串列桥墩时的船体受力特性.研究结果表明:在船、桥交汇过程中,船舶边界的贴近挤压着桥墩周围的流场,干扰墩后涡体的生成和脱落,船舶艏摇力矩以明显的正、负峰值交替的规律演进.两桥墩间距达9.0D时,下游桥墩对上游桥墩的水动力干扰消失.在两桥墩间距大于13.0 D后,船舶驶经上、下游桥墩时,船舶艏摇力矩相当于连续经过2个孤立的单桥墩.

航行船舶与桥墩间的水动力作用随航行速度不同而变化,致使船舶在航行过程中受力及航行姿态发生变化.采用物理模型试验验证和数学模型计算相结合的方法,以船舶航速为变量,分析了船舶沿程受力、艏摇力矩及重心位移受航速影响的变化规律.研究表明:随着航速的增加,船舶受到的横荡力、艏摇力矩正负峰值相应增加;船舶航速越高,船艏驶至桥墩尾涡负压区时,船舶越容易横向靠近桥墩;船尾驶至桥墩尾涡负压区时,航速越高,船尾越容易横扫桥墩,且后续航行过程中船舶横向远离桥墩偏航越大.研究成果可为后续研究船舶运行安全性和工程中确定安全的船桥间距提供参考.