Non-capacity transport of non-uniform bed load sediment in alluvial rivers

Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.

Solids Acceleration Length in a Cold Dense Transport Bed

The solids acceleration length was investigated in a cold dense transport bed （0.10 m-IDx17 m-height） with three kinds of Silica sand. The solids circulation rate （Gs） was up to 954 kg/（m2s）. The effects of operating conditions, particle properties, and riser structures on the solids acceleration length were investigated under high Gs conditions, with the effect of riser height non-negligible. The solids acceleration length increased with the increase of the riser height. Based on the experimental data, an empirical correlation was proposed to predict the solids acceleration length. Predictions of the correlation were in good agreement with the experimental data in this work and those from the literature over a wide range of Gs （18~954 kg/（m2s））.

Energy-saving strategy for a transport bed flash calcination process applied to magnesite

A transport bed flash calcination(TBFC)process applied to magnesite is systematically investigated through process simulation to optimize the energy-saving strategy.The high-temperature calciner flue gas is used to preheat the fed magnesite,while the sensible heat with the caustic calcined magnesia(CCM)product is cooled by air sent to the calciner.Pre-decomposition of magnesite during preheating is considered on basis of the kinetics measured using a micro fluidized bed reaction analyzer that allows the minimized effect of external diffusion on reaction.With staged fuel gas supply the TBFC process allows the equivalence ratios around 1.2 for combustion.The preferred arrangement of stages for magnesite preheating and CCM cooling are respectively 4 and 2,leading to the energy consumption of 4100 kJ/kg-CCM and the energy efficiency of 66.8%,which is almost doubly higher than the 33.9%of the conventional reverberatory furnaces(RF).The pre-decomposition occurs mainly in the 1st-stage preheater,and the maximal conversion is about 13%.Varying the stages of preheating appears more influential on the energy saving than varying the cooling stages,while residence time above 1 s in the preheaters has limited effect.

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.

Concept of Bed Roughness Boundary Layer and Its Application to Bed Load Transport in Flow with Non-Submerged Vegetation

Ecosystem conservation has become one of the purposes in river management as well as flood mitigation and water resources management, and understanding of river flow and morphology in a stream with vegetation becomes important. Recently 2D depth averaged analysis is familiar even in a stream with vegetation by taking account of form drag due to vegetation. However, the shear stress in vegetated area is not properly described because the resistance law due to bed roughness is not reasonably modified in vegetated area. In this study, we discussed the bed roughness boundary layer in flow with non-submerged vegetation to deduce a reasonable relation between U and u* in vegetated area toward improving the analysis of sediment transport. The results show that the modification of resistance law using by thickness, velocity distribution in that layer was found to bring significant improvement of accurate estimation of shear velocity and subsequently the sediment transport. The proposed modification is improved by 2D depth averaged analysis based on this concept, and its application is certificated through flume experiment.

ANALYSIS OF SALTATION CHARACTERISTICS OF BED-LOAD TRANSPORT IN FLOWING WATER

The study of bed-load transport is of great significance both in theory and in practice.This paper discusses the saltation of bed-load solid grains in flowing water.Experiments and theoretic analysis have been made by means of high-speed photographing and advanced data processing technique with a combined method based on mechanical and statistical theories.It indicates that the saltation is the main form of the bed-load transport under ordinary flowing conditions.In the meantime,taking suecessive saltation as the mod- el of bed-load transport,systematic analysis has been made with regard to the kinematic properties and mechanism of saltation.The statistical analysis shows that the probability density functions of the relative height and length of saltation are in conformity with Γ-type distribution,while the probability density func- tions of the relative velocities of saltation are in conformity with the Gaussian distribution.

Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.

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.

Research on management of coal bed methane warehousing and transportation based on GIS

At present Coal Bed Methane （CBM） has become the important part of clean energy in China. and will optimize the energy structure in China unceasingly. However, warehousing and transportation of CBM become one of the core factors that restrain its exploitation and utilization at present, due to the space-time character of natural deposit and modem utilization of CBM. In this paper, according to the character of CBM and the expanding trend of its utilization, the necessity of constructing the CBM＇s warehousing and transportation management system demonstrated. Index system that influence CBM＇s warehousing and transportation is established. And CBM＇s warehousing and transportation model is established by Voronoi diagram. In light of above research, CBM＇s warehousing and transportation management system based on Geography Information System （GIS） is designed, Using this system, CBM＇s warehousing and allocation center in one mining area is optimized. Research shows that to reinforce CBM＇s warehousing and transportation management is one of the key factors for coordinating the development of its development and utilization, thereby ensuring its sustainable development and utilization.

冰碛湖溢流溃决实验研究

冰湖溃决洪水是一种自然灾害,常常造成重大人员伤亡和财产损失。冰崩、岩崩、滑塌等斜坡运动是最常见的冰湖溃决洪水触发因素。巨大的位移波造成冰碛堤被侵蚀下切再溃决的直观想法简单明了,但这种解释还是存在许多问题。冰碛湖为浅长湖泊,物质流产生的涌浪类型只有孤立位移波。在不考虑反射损失的情况下,一次往返反射后的位移波,其振幅不到原振幅的37%,可以翻越冰碛堤的位移波,可能只有第一次传播到冰碛堤的位移波。侵蚀通常是一个相对缓慢的过程,在单个位移波通过冰碛堤的水动力过程中,其时间尺度相对较短,要完成对冰碛堤的全部侵蚀是不够的,仅一阵涌浪造成的冰碛堤侵蚀很小,不足以溃决冰碛湖。然而,恒定的水流以溢流的方式侵蚀进而溃决,要比以波浪漫过坝顶的侵蚀方式溃决容易得多。巨大的波浪必须由大体积的冰崩或滑坡进入湖泊而产生,并导致水位大幅上升,水位升高是冰碛湖溃决的主要原因。本研究对西藏6个典型冰湖展开调查,其中3个发生过溃决。在室内进行了一系列冰碛坝溢洪道溢流引发铠甲层破坏的实验研究,当铠甲层被溢流冲走后,就会发生冰碛堤溃决。当溢洪道底床坡度小于19.6°时,起动铠甲层颗粒的模式为河流输运模式。当溢洪道底床坡度大于25.2°时,起动铠甲层颗粒的模式为底床破坏模式。当溢洪道底床坡度在19.6°~25.2°范围内时,起动模式为河流输运和底床破坏两种混合模式。在河流输运模式中,冰碛堤溃决临界水深和铠甲层粒径之比与溢洪道坡度转折点上下游的坡度差成反比。对于铠甲层的底床破坏模式,冰碛堤溃决临界水深与铠甲层粒径之比为一个固定值。本文的冰碛湖溃决临界水位模型在中国西藏和加拿大不列颠哥伦比亚省的野外资料中得到了较好的验证。

海相细粒沉积成因机制与有机质富集模式研究进展

综合分析了国内外细粒沉积的特征、成因及有机质富集模式研究进展。海相细粒沉积主要由黏土矿物、石英、碳酸盐矿物和有机质组成,受风力、异轻流、重力流和底流4大搬运营力作用,发育泥纹层和粉砂纹层2类纹层,单一型、顺序型和交互型3类纹层组(层系),块状层、递变层和交互层3类层(层组)。海相细粒沉积发育浊流沉积、底流沉积及远洋-半远洋沉积3种主要沉积相类型及其过渡类型。海相细粒沉积有机质存在高生产力和强保存2种富集模式,高生产力富集模式下黑色页岩主要通过“上升洋流”、“氧含量最低值区(OMZ)”和“近岸透光带缺氧(PZE)”模式形成高有机质富集,强保存富集模式下黑色页岩主要通过“受限盆地”、“改进的受限盆地”、“不规则底形”、“水洼扩张”、“海侵化变层”和“近岸海侵(TN)”模式形成高有机质富集。目前海相细粒沉积成因机制与相模式研究存在的主要问题包括名词术语不规范、不同矿物成分成因不明确,以及细粒浊流沉积、等深流沉积和半远洋沉积难以区分,需要今后进一步研究解决。

菱镁矿输送床轻烧过程模拟与分析

利用Aspen Plus对菱镁矿输送床轻烧过程进行系统模拟.通过外接菱镁矿分解动力学方程Fortran子程序建立第一级旋风预热器内同时进行气固换热(煅烧炉出口的高温烟气与预热菱镁矿原料)与菱镁矿预分解反应模型(简称气固换热预分解模型),并与先进行气固换热、后发生固体绝热预分解反应的模型(简称固体绝热预分解模型)进行对比.结果表明气固换热预分解模型计算得到的预分解率更大、系统的能量效率更高、能耗更低.基于此模型,进一步研究轻烧温度、菱镁矿含水量对轻烧过程的影响,结果表明:随着轻烧温度和菱镁矿含水量的增加,系统能量效率逐渐降低、能耗逐渐增加,特别是菱镁矿含水量对整个轻烧系统的可操作性影响显著.

基于压差法的水平井岩屑床轴向运移规律研究

为了明确长水平段水平井旋转钻进工况下水平段岩屑床的轴向运移规律,开展了基于压差法的水平井岩屑运移试验。利用设置在井筒轴向不同位置的多个压差传感器,测量井筒的瞬时压降,用来表征岩屑床在井筒中的轴向分布,并据此计算了岩屑床运移速度,分析了流体密度、排量、转速对岩屑床运移速度和压降的影响规律。结果表明:该方法能够表征岩屑床运移特征,精细刻画了岩屑床在井筒轴向位置的分布;岩屑床运移速度与流体密度、排量和转速呈正相关关系;排量增大,可显著提高岩屑床运移速度,但压降迅速增大限制了加快清岩的最大排量;转速增大,能够提高岩屑床运移速度,且对井筒压降基本没有影响。研究结果明确了水平井岩屑床的轴向运移规律,为井下岩屑床轴向分布测量提供了理论基础,并有助于规避井筒压力复杂和卡钻等风险。

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。

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。

基于颗粒级配的尾砂料浆管输模式判据与输砂效率计算模型研究

目的:以云南某锡矿选矿厂排放的尾砂为对象,通过试验研究与数值模拟分析尾砂料浆管输模式与输砂效率的影响因素。方法:通过水筛试验测得尾砂级配分布规律,以及料浆流变试验测得料浆流变特性,并结合ANSYS-FLUENT对料浆管输模型模拟计算。结论:对比分析Wasp等判据不足,提出了基于颗粒级配的管输模式新判据,并结合级配模型与流变参数计算了输砂效率,结果与实测值的误差绝对值在5%以内,表明了新判据合理,同时构建了输砂效率计算新模型。意义:研究内容为尾砂料浆管输模式提供了新判据,可为相似情况的矿山尾砂料浆管输应用提供一定的参考价值。

七一冰川融水径流中悬移质与推移质动态输沙特征

[目的]冰川融水输沙不仅可以反映冰川侵蚀速率,而且是下游河流泥沙的重要来源之一,因此,认识青藏高原地区冰川融水径流中悬移质和推移质动态输沙特征对于冰川地貌演化预测和下游防灾减灾工作具有十分重要的意义。[方法]基于2023年8月11-24日七一冰川下游河道的水文泥沙实测数据,分别构建流量-水位、悬移质含沙量-流量和单宽推移质输沙率-水流剪切应力之间的相关关系,进而重建整个研究时段的流量、悬移质和推移质动态输沙过程。[结果]七一冰川融水径流中悬移质含沙量和推移质输沙率受径流变化控制,日变化十分剧烈。悬移质含沙量每日最小值一般出现在10:00,最大值出现在16:00,中值粒径约为0.3 mm。推移质输沙过程与悬移质含沙量的日变化趋势基本相同,但推移质中值粒径远大于悬移质,约12 mm,而且在每日05:00-09:00时段,由于水流搬运能力的限制,没有推移质输沙。就输沙量而言,七一冰川融水输沙以悬移质泥沙为主,推移质日输沙量远小于悬移质日输沙量,约占悬移质日输沙量的1.73%~2.81%。冰面气温是影响冰川融水径流量、悬移质含沙量和推移质输沙率的关键因素,随着冰面气温的增加,径流量和悬移质含沙量均呈线性增加趋势而推移质输沙率呈指数函数增加趋势。[结论]在未来气候变化情景下冰川融水径流增加时,七一冰川融水径流中悬移质和推移质输沙均将变得更加显著,值得更加重视。

三维球床几何稀疏条数长特征线加速方法

特征线法具有非常强的几何适应性,可用于三维球床高温气冷堆全堆芯求解,但存在迭代次数多、计算速度慢的缺点。本文将长特征线加速方法应用于三维球床高温气冷堆以解决非规则几何数值加速的问题,基于三维模型特征线布置较二维模型稠密的分析,提出了稀疏条数长特征线加速方法,极大地减少了加速方程的计算量,在不降低角度离散精度的前提下,获得了非常好的加速效果。通过基准题对加速参数的选取方式进行了研究,条数稀疏度取3~5、长特征线长度取2.0 cm左右、加速迭代步取20~60步可获得良好的加速效果。小型轻水堆三维基准题和球床堆芯简化模型的计算结果表明,采用稀疏条数长特征线加速可获得7倍左右的时间加速比,此时对应的迭代步加速比为20倍左右。

无缝线路施工期间道床刚度对速度的影响分析

为了解决因施工线路道床密实度不足导致的列车提速受限问题,依托国外某工程轨排成组铺设焊连无缝线路施工方案,建立了车辆-轨道耦合动力学模型。以轮轨动态作用指标及行车安全评价指标为评价依据,研究道床刚度和列车速度对钢轨接头动力响应的影响,确定施工线路合理的道床刚度及其速度阈值。结果表明:钢轨接头区的轮轨垂向力、钢轨和轨枕垂向加速度及行车安全评价指标受列车行车速度的影响较大,钢轨和轨枕的垂向位移受道床刚度影响较大;依据各指标的容许限值,应将施工期间的道床刚度控制在35~65 kN/mm;平车满载时的速度阈值显著高于空载时的速度阈值,合理道床刚度下平车满载及空载情况下速度最小值分别为53 km/h和23 km/h。研究结果对提高无缝线路施工效率,确保工程列车行车安全具有重要意义。

基于Visual MODFLOW的红层地区某钛白粉厂地下水污染物运移模拟研究

数值模拟技术是保护地下水环境的有效方法,但实际中获取准确的水文地质参数难度较大,如何准确获取参数成为数值模拟技术应用成败的关键。基于该关键问题,本文以广西某钛白粉厂为例,在查明水文地质特征基础上,应用Visual MODFLOW软件建立地下水流数学模型和溶质运移模型。选取钛白粉厂主要污染物COD、氨氮和氟化物作为预测因子,预测其在地下水中运移情况。结果反映钛白粉厂污水处理车间和污水调节池发生渗漏未对下游地谷岭造成影响。本次模拟的预测结果对该区地下水的保护有着重要意义。