Bed Load Transport Rate in Scouring and Armoring Process of Non-uniform Sediment River Bed

Flume experiments were carried out to study bed load transport rate during rive bed scouring and ar- moring.A theoretical differential equation linking the transport rate to the probability of incipient motion of non-uniform sediment is solved.The transport rate is shown to decrease exponentially with time,according to the theory,which is in good agreement with the experiment data.

Experimental study on bed-load sediment transport under irregular wave and current combined flow

Using an irregularly oscillating tray and flume, a series of experiments are completed to evaluate bed-load sediment transport rate under irregular wave -current coexistent field. Testing conditions include three interaction angles 0', 45', 90' and two kinds of median sizes (0.38 and 1.10 mm). The results of transport rate show that the net sediment transport rate can be expressed approximately as the function of the maximum bottom shear stress of waves, mean shear stress of current and the grain size.

An Investigation of Stochastic Nature of Bed Load Motion in Chuanjiang River

Bed Load Motion and its transport rate is one of the basic issues in river dynamics.In this paper, the authors discussed the stochastic nature of bed load motion in Chuanjiang River in details.Chungjiang lies in the upstream reach of Yangtze River.Its stochastic nature is shown in the following four aspects.Firstly, even though all the conditions are the same,due to the fluctuation of the flow,the bed load discharge and the location and width of sediment transport belts are different.Secondly,during the ...

Development of All-Weather and Real-Time Bottom-Mounted Monitor of Bed Load Quantity

Quantity of bed load is an important physical parameter in sediment transport research. Aiming at the difficulties in the bed load measurement, this paper develops a bottom-mounted monitor to measure the bed load transport rate by adopting the sedimentation pit method and resolving such key problems as weighing and desilting, which can achieve long-time, all-weather and real-time telemeasurement of the bed load transport rate of plain rivers, estuaries and coasts. Both laboratory and field tests show that this monitor is reasonable in design, stable in properties and convenient in measurement, and it can be used to monitor the bed load transport rate in practical projects.

金沙江下游三堆子河段卵石推移质输沙率公式研究

金沙江上中游梯级水库运用后,进入下游的悬移质输沙量大幅减少,水沙条件显著变化;同时,卵石推移质输沙量在总输沙量中的比重明显增加,对水库淤积进程影响显著,开展变化水沙条件下金沙江下游卵石推移质输移规律研究具有重要意义。基于下游入口三堆子水文站2008—2021年卵石推移质实测资料,对经典起动流速公式和推移质输沙率公式进行了检验与修正。结果表明:与经典起动流速公式计算结果相比,通过引入以卵石粒径为变量的系数,所得到的不同粒径范围的卵石推移质起动流速修正公式,计算精度显著提高;经典推移质输沙公式的计算结果在输沙强度较低时与实测值偏差很大,通过建立输沙强度与水流强度的关系,并引入隐暴参数对公式进行修正,明显提升了其在低输沙率情况下的计算精度。修正后的起动流速公式和推移质输沙率公式能更有效地反映三堆子河段卵石推移质的输移规律。

典型非均匀推移质输沙率公式适用性比较

基于等中值粒径的“单、双峰型级配”推移质输沙试验以及“驼峰”输沙率试验数据,选择Einstein、吴伟明、Wilcock和吴保生等4种典型非均匀推移质输沙率公式计算“单、双峰型级配”推移质输沙率,将两种级配的输沙率比值及曲线形态与试验成果对比分析。结果表明:吴伟明公式在反映“单、双峰型级配”推移质输沙差异上表现最好,这4种公式均无法反映“驼峰”输沙率现象。基于多参数考虑的Patel公式较这4种公式能更好地反映上述两种现象。充分考虑床沙级配对分组沙起动切应力和输沙有效Shields数的影响,是提高非均匀推移质输沙率公式精度和适用性的关键。

Sedimentation Processes at the Navigation Channel of the Liquefied Natural Gas (LNG) Port, Nile Delta, Egypt

Liquefied Natural Gas (LNG) port is located at Abu Qir Bay on the northwestern coast of the Nile delta, Egypt. The port was constructed in 2004 to export liquefied natural gas worldwide. The offshore basins of this port including the turning and berthing areas (15-m depth) are connected to the deep water by a 15-m depth dredged channel that extends 4 km offshore. However, the navigation channel and its contiguous basins have experienced problematic shoaling that might affect the navigation activities of gas tankers. Sedimentation processes have been investigated by analyses of waves, currents, bathymetry, grain size of seabed and channel dimensions. Sedimentation rates are estimated using a developed numerical model. Sedimentation rate fluctuates between 0.048 × 106 m3/month and 0.388 × 106 m3/month, with an annual sedimentation rate of 1.977 × 106 m3/yr. The variance in the sedimentation rates between winter and summer resulted in increasing of current speed and direction flowing towards offshore. The sedimentation process is influenced by the temporal variability in the direction and intensity of the predominant waves, currents, orientation of navigation channel, basin breakwaters, seafloor morphology and sediment sources. Due to the geographic location of LNG port it lays within a sediment sink for sediments supplied from different alternating directions by several pathways, flowing towards the N-W, S-W, N-E, and S-E quadrants. Most of these currents components are substantially effective in transporting fine-grained sediment towards the navigation channel axis and contiguous basins. Together with these currents, the predominant NW and SE waves acting to agitate and stirrup sediments in the vicinity of the port, and thereby accelerating sedimentation rates.

粗化床面发展过程中非均匀沙起动试验研究

非均匀沙在水流作用下会形成表层粒径大于底层的床面粗化现象,同时表层粗颗粒还会形成聚集结构体。已有非均匀沙起动研究仅考虑粒径差异,对多颗粒组成的粗化结构体及其影响问题考虑不足。在水槽中开展了非均匀沙床面粗化发展过程试验,分析了粗化床面条件下的起动条件及起动判别标准。结果表明,粗化床面发展可分为中粗颗粒出露、中颗粒结构体形成、粗颗粒结构体形成等3个阶段,粗化结构体对泥沙颗粒的起动和输移造成较大影响。粗化床面条件下非均匀沙起动临界希尔兹参数为0.015 5~0.023 5,小于均匀沙床面。USACE输沙率标准不适用于非均匀沙粗化床面,而Parker标准与韩其为标准均可在一定程度上反映非均匀沙粗化对泥沙起动的影响,其中韩其为标准与实测值更接近。

河床表层冻融作用下推移质输移特征研究

高纬度河流系统常会经历季节性冻结与融化。为揭示冻融作用对床面推移质运动的影响,本研究以未经历冻融过程的常规室温(20℃)推移质输沙实验结果为基准,保证实验条件不变,开展了均匀沙与非均匀沙床表层冻融后的室温(20℃)推移质输沙实验,综合比较了冻融作用影响下推移质输沙率与级配组成特征。结果表明,河床表层冻融后的推移质输沙率均高于无冻融作用的推移质输沙率,据此提出了有冻融影响与无冻融影响下的推移质输沙率比值ζ。研究显示,冻融作用下的推移质输沙率呈有规律变化:剪切力较小时ζ较大,剪切力较大时ζ减小并逐渐趋于1.0;非均匀沙中,随着泥沙粒径增大,各粒径组的ζ逐渐减小;低流量驱动时,冻融作用对非均匀输沙级配组成的影响显著,并随着流量增大而逐渐减弱。本研究剖析了冻融作用对推移质输沙率与级配组成的影响,有助于认识冰冻区河流的河床稳定性与河床演变情势。

恒定流作用下珊瑚砂输运特性试验研究

【目的】针对现有对珊瑚砂起动和输运研究的不足,基于室内水槽试验,研究了恒定流作用下珊瑚砂的起动规律和输运特性。【方法】利用电子显微镜对珊瑚砂颗粒进行观测,确定了珊瑚砂中轴长度与筛分粒径之间的关系;利用现代化测量技术测得了珊瑚砂起动流速和输沙率。【结果】与经典的石英砂起动流速及输沙率计算公式进行了比较分析,并修正了经验公式,使其适用于珊瑚砂起动流速的计算。【结论】由于珊瑚砂的形状极不规则,相比筛分粒径相同的石英砂,珊瑚砂的起动流速更小,珊瑚砂单宽推移质输沙率随水深的增加而显著减小。研究成果丰富了泥沙输运理论。

河道推移质最大输沙能力影响因素敏感性分析

河道推移质最大输沙能力受到水动力和河道边界多因素的共同影响。采用水力半径分割方法,以河岸坡角为θ的等腰梯形为过水断面,λ为河岸与河底的相对糙率,d50为床沙中值粒径,nb为河底糙率系数,Q为流量,S为比降,利用变分方法解析各因子对河道的推移质最大输沙能力和相应最优河道形态的影响程度。结果表明:河道推移质最大输沙率随着λ的增大而增大,随着θ的增大而减小,即河岸糙率的相对增大或河岸坡度的减小都会提升最大输沙能力;流量Q、比降S的增大,均可提升最大输沙能力;河底糙率系数nb减小、流量维持不变将会降低最大输沙能力,床沙中值粒径d50减小则会提升最大输沙能力;既不特别宽浅又不特别窄深的河道具有最大的推移质输沙能力。

Study on bed load transport for uniform sediment in laminar flow

Previous studies focused on the bed load transport rate for the condition of turbulent flow,while the knowledge of sediment transport in laminar flow is very limited.As an extreme case to reflect the viscous effect on sediment transport,sediment transport in laminar flow is considered in this paper.There are at least two factors affecting the transport rate of sediment under laminar flow conditions: (1) fluid forces;(2) particle to particle interactions.Together,these two factors represent the physical transport system.First,an exposure degree Probability Density Function (PDF) is developed to explore how the transport rate can be associated with characteristics of laminar flow and this factor reflects the particle to particle interactions,and the pickup probability equation in the absence of turbulence is developed based on the stochastic approach which reflects the exposure degree influence.Then,the formulas to calculate the critical shear stress of incipient motion and the bed load transport rate of fine uniform sediment are established.The derivation is made mainly based on Einstein’s bed load theory;we choose Einstein’s equation to model this system because we believe that the probabilistic approach taken is an appropriate way to account for the spatial and temporal variations in the forces causing sediment transport.These formulas have been tested against a wide range of existing laboratory data and compared with other existing empirical or semiempirical methods.The predictions by these newly proposed formulas are very good.

基于随机森林算法的推移质输沙率计算研究

为探寻随机森林算法在预测推移质输沙率方面的效果,本文筛选了3060组天然河道输沙数据,将其划分为三种方案,得到了算法在单一流域、综合流域情况下的预测数据,并利用沙莫夫公式的计算结果作为对比。结果表明:水力参数与输沙率之间的相关性和参数在算法中的重要性并不完全一致;同一参数以不同形式出现在算法运算中时,会呈现不同的重要性;在足够的数据量支持下,随机森林算法相比于传统公式明显有更好的预测效果。

THE NONLINEAR CUSP-CATASTROPHE MODEL OF THE SEDIMENT TRANSPORT RATE

In the catastrophe theory of nonlinear science, the intensity of water flow Θ and the coefficient of non uniform sediment m are regarded as two bound variables, and the intensity of bed load transport Φ as the state variable in the motion of non uniform sediment in cusp catastrophe model. Based on the standard equation of the cusp catastrophe theory, the relation equation between the intensity of bed load transport Φ and the intensity of water flow Θ has been derived by used coordinate transform and topology transform. The equation of bed load transport rate was built on the cusp catastrophe theory of nonlinear science. The others are applied to verify this equation, that the results calculated by the cusp catastrophe equation agree well with the other equations. This indicates that the cusp catastrophe equation is reasonable, and the results fully reflect the characteristics of threshold motion and transport of non uniform sediment. The purpose of this paper is to explore the incipient motion and transport laws of non uniform sediment from the viewpoint of nonlinear science.

渗流边界上推移质输沙率

天然河道边界上常由于地下水和地表水的水位不同而产生渗流,引起水流的非静水压力分布,进而影响推移质输移规律,也使得常用的推移质输沙率公式不再适用。利用水槽试验测定沙波的尺寸及运动速度与床面渗流水力梯度的关系,结果表明沙波的高度及运动速度随着向下渗流强度的加大而增加,随着向上渗流强度的加大而减少;进而结合理论分析,利用沙波运动特点估算推移质输沙率,并推导出推移质输沙率随床面渗流的引入而变化的计算公式,分析渗流引起非静水压力分布下推移质输沙率的变化。

泥沙颗粒跃移运动机理

水流中泥沙颗粒的跳跃运动是推移质运动的重要形式,根据泥沙颗粒运动过程的受力分析,建立了忽略颗粒旋转和紊动影响的泥沙颗粒跃移运动模型,并采用数值计算方法,求解了跃移运动方程,得到了跃移运动参数(跃移长度、跃移高度、跃移速度)的统计特性,所得结论与实验资料吻合较好;通过对数值计算结果回归分析,得到了跃移运动参数以及输沙率的数学表达式,对于了解推移质运动机理有重要的意义.

卵石河床清水冲刷粗化层破坏临界条件试验研究

针对山区卵石河道普遍存在的床面粗化层现象,进行了水流强度连续小幅增大的清水冲刷粗化层破坏试验研究,旨在探讨粗化层破坏与水流强度之间的临界关系。试验结果表明,水流强度的增大并不一定能破坏床面粗化层,只有当水流强度增大到一定程度时,粗化层才会破坏。对于本系列试验所用泥沙,只有床面切应力大于初始粗化床面切应力的1.2倍,粗化层才会破坏。粗化层床面结构对粗化床面切应力有着重要的影响。

清水冲刷推移质输沙率变化规律

分析恒定清水冲刷水槽试验资料发现,推移质输沙率变化可分为两个阶段,即时均稳定阶段和衰减阶段。通过机理分析,建立了该两个阶段的计算公式,计算结果与试验资料吻合良好。该式可用来估算任一河段及任一时刻推移质输沙量及冲刷剖面。

沙波运动与推移质输沙率

基于沙波运动,通过理论分析水沙运动的动力学因素,合理概化水沙运动模式,综合分析水流运动过程中所受到的力,利用沙波迎流面水体的动量方程,从理论上研究沙波波高随水流运动变化的数学表达,并将其与推移质输沙率联系起来,建立一个推移质输沙率与相对水流强度的数学关系式.计算分析表明,公式所能描述的规律与室内外资料相符,能较好地反映推移质输沙率与相对水流强度间的正向变化的全过程,具有理论和实用价值.

细颗粒对粗颗粒床沙质输沙率影响的初步研究

考虑高含沙紊流涡团中细颗粒絮凝形成网络结构对粗颗粒运动影响后 ,建立了粗颗粒悬移质泥沙的输沙率计算方法。该方法中包含的细颗粒影响项反映了流域因素对粗颗粒泥沙输沙的影响 ,证明细颗粒的影响是引起多沙河流中“多来多排”现象的一个重要因素。与黄河实测资料的对比表明 ,该计算方法能够反映高含沙紊流输沙时随流域细颗粒增多粗颗粒悬移质输沙率相对增大的现象 。