Swimming behavior of crucian carp in an open channel with sudden expansion

The sudden‐expansion effect created by natural and man‐made structures such as unsubmerged boulders, spur dikes, and culvert structures is common in open channels. Migratory fishes may use the heterogeneous flow generated by sudden expansion to their benefit, to select habitats for balancing energy expenditure or for maximizing predation opportunities. This study explores the swimming behavior of three size classes of crucian carp in response to hydrodynamic characteristics in an experimental open channel with sudden expansion. The flow field was characterized using particle image velocimetry (PIV) measurements and featured a recirculation zone in the vicinity of the expansion. Based on the classification of the swimming trajectory, four specific swimming behaviours (SSBs) were utilized by crucian carp during migration. With increasing flow velocity, fish spent more time in the recirculation zone. Residence time in the recirculation zone was inversely correlated with fish body length. Due to the advantage in providing shelter from challenging heterogeneous hydraulic conditions, the recirculation zone was preferred by crucian carp, especially the smaller ones, indicating the importance of energy conservation in habitat occupation. These findings confirm that the recirculation zone generated by sudden expansion may be beneficial to the upstream passage of fish and in habitat restoration.     

泥沙吸附磷前后Zeta电位变化试验

选取长江南京段、淮河蚌埠段以及甬江口3种来源不同的细颗粒泥沙,通过泥沙对磷的等温平衡吸附试验,研究细颗粒泥沙吸附磷前后Zeta电位的变化。结果表明:泥沙的Zeta电位绝对值随着单位质量泥沙对固相磷的平衡吸附量的增大而增大,泥沙稳定性增强,不易絮凝;泥沙的Zeta电位绝对值变化量与单位质量泥沙对固相磷的平衡吸附量呈正比关系,对于不同来源的泥沙,单位质量泥沙对固相磷的平衡吸附量增量相同时,Zeta电位绝对值的增幅不同,甬江泥沙增幅最大,淮河泥沙次之,长江泥沙最小;Zeta电位绝对值相对变化量与固相磷相对吸附量呈正比,甬江泥沙Zeta电位绝对值相对变化量对固相磷相对吸附量变化的敏感度更高,长江与淮河泥沙的敏感度相近。     

突扩通道内横掠圆管对流换热的数值模拟

采用非稳态数学模型对突扩通道内横掠圆管流动与换热进行了数值模拟。分别对不同雷诺数Re以及不同通道突扩比Er情况进行数值模拟。结果表明:随着Re的变化,数值解有稳态,周期振荡和混沌。同时随着雷诺数的增加,圆管附近的换热不断增强。对于不同突扩比,当10≤Re≤100和250≤Re≤300时,圆管的换热随着通道突扩比的增加而变弱;当100Re≤200时,圆管换热并不单调减弱。     

Characteristics of phosphorus adsorption by sediment mineral matrices with different particle sizes

The particle size of sediment is one of the main factors that influence the phosphorus physical adsorption on sediment. In order to eliminate the effect of other components of sediment on the phosphorus physical adsorption the sediment mineral matrices were obtained by removing inorganic matter metal oxides, and organic matter from natural sediments, which were collected from the Nantong reach of the Yangtze River. The results show that an exponential relationship exists between the median particle size (D₅₀) and specific surface area (S_g) of the sediment mineral matrices, and the fine sediment mineral matrix sample has a larger specific surface area and pore volume than the coarse sediment particles. The kinetic equations were used to describe the phosphorus adsorption process of the sediment mineral matrices, including the Elovich equation, quasi-first-order adsorption kinetic equation, and quasi-second-order adsorption kinetic equation. The results show that the quasi-second-order adsorption kinetic equation has the best fitting effect. Using the mass conservation and Langmuir adsorption kinetic equations, a formula was deduced to calculate the equilibrium adsorption capacity of the sediment mineral matrices. The results of this study show that the phosphorus adsorption capacity decreases with the increase of D₅₀, indicating that the specific surface area and pore volume are the main factors in determining the phosphorus adsorption capacity of the sediment mineral matrices. This study will help understand the important role of sediment in the transformation of phosphorus in aquatic environments.     

底泥疏浚对湖泊内源磷释放的短期效应研究

对大纵湖底泥疏浚的短期效应进行模拟实验,分析了上覆水体的Eh、pH和磷质量浓度随时间的变化规律,以及沉积物中总磷、无机磷、有机磷、铁/铝磷、钙磷等5种形态磷质量比的垂向变化规律。结果表明:底泥疏浚30 cm对上覆水体Eh、pH以及磷浓度控制效果不显著,且沉积物磷形态不是影响沉积物释磷的主要因素。     

湖泊底泥中磷的形态分布分析

目前自然水体富营养化程度越来越严重,其底泥中磷的含量也与日俱增。不同形态分布的磷在自然情况变化时表现出不同的特性,底泥中磷的形态分布对于控制水体中磷的浓度有着重要影响。本研究以五步化学分级提取法测定了12个湖泊底泥中磷的形态分布。结果表明：在底泥中与钙结合的磷较多,平均占总量的60％左右。射线衍射结果也表明12个样品中均含有较高比例的晶体钙矿物,平均含量约为49％。除了与钙结合的磷之外,其余的磷多数与铁、锰化合物相结合,其含量平均占总数的18％。黏土矿物及铝氧化物中结合的磷占总量的8％,与残余磷9％相当。松散吸附结合态的磷含量最低约占6％。研究磷的形态分布分析方法对于了解底泥中磷的形态分布以及磷在水体一底泥中的迁移转化规律有着重要意义。     

管路突然扩大时局部水头损失的数值模拟

选取了Spalart-Allmaras湍流模型,对Re＜5500时管路中突然扩大的局部水头损失进行了数值模拟.计算结果表明:模拟得到的测压管水头与试验值吻合较好,用断面平均速度计算速度水头时,若取动能修正系数为1.0,则会使局部水头损失的计算值较实际值偏小,速度水头计算方法的影响远大于突然扩大管路的沿程损失对局部水头损失系数的影响.     

洱海沉积物磷的化学赋存形态研究

本文对洱海沉积物磷的含量、空间分布以及沉积剖面上沉积磷的化学赋存形态进行了研究。结果发现，洱海表层（5cm）沉积物中总磷的含量范围为736．40～1602．50mg／kg，平均为964．60mg／kg；北部湖区高于南部，弥苴河是湖泊的主要磷来源；洱海沉积物中各形态磷的含量高低顺序为：钙结合态磷，碎屑态磷，有机态磷，铁结合态磷，吸附态磷，磷形态的剖面变化反映了埋藏作用对沉积磷的强烈改造作用。     

河流泥沙与磷作用情景模拟及分析

泥沙是河流水环境系统的重要组成部分,泥沙运动过程和泥沙吸附解吸作用对河流水质具有显著的影响。天然河流中泥沙运动状态存在一定的变化,尤其是河流上修建大坝蓄水后,库区泥沙运动过程的变化更加明显,相应也会引起水环境条件的改变。本文采用挟沙水流水质一维数学模型,以磷为代表污染物,在一定的水流、泥沙和水质的计算条件下,对泥沙稳定吸附、泥沙淤积、床沙冲刷和不同冲刷位置等4种情景对水环境的影响进行了模拟和分析。通过模拟说明了特定条件下泥沙运动状态和吸附特性变化对水环境的影响,从而为进一步认识天然河流中泥沙对水环境的影响提供支持。     

水体沉积物磷释放及控制

分类介绍了影响水体沉积物磷释放的各种因素,其中主要分析了温度、pH值、溶解氧、沉积物磷形态、水体扰动的影响,认为影响释放的主导因素因地而异。评述了目前较多采用的控制磷释放的措施,包括自然净化、原位固定、底泥疏浚、生态修复、稀释冲刷等,着重分析了前四者的优缺点,认为目前综合利用这些控制技术会取得较好效果,提出最终要以生态学方法来控制磷释放和解决富营养化问题。     

湍流中泥沙垂线分布的力学解释

作者从泥沙垂向动量交换出发，分析了泥沙在紊流中由于湍流脉动产生的升力效应，并综合考察了非湍流脉动原因存在的升力以及在不同浓度下含沙水流中泥沙受到的有效重力，得到了基于力学角度的泥沙浓度垂线分布的关系式。在此基础上，通过对床面粗糙度、泥沙粒径和含沙量等影响泥沙浓度垂线分布有关因素的分析，探讨了挟沙水流中两种不同浓度分布类型产生以及转化的原因，并结合具体的试验资料对泥沙浓度垂线分布形态时行了计算和验证，取得了较好的结果。     

湖泊底泥中磷释放的随机动力学模型

本文从随机过程的观点出发，推导出湖泊底泥磷相对释放量概率密度函数的随机微分方程，并给出了相应的定解条件。利用隐式差分法进行求解，分析了磷释放的均方差系数(D)、吸附系数(K1)、解吸系数(K2)及其对磷相对释放量概率函数分布的影响情况。所建立的磷释放随机动力学模型计算结果与实验数据吻合良好。     

Numerical research for contaminant release from un-suspended bottom sediment under different hydrodynamic conditions

Contaminant release from bottom sediments in rivers is one of the main problems to study the environmental hydrodynamics. Contaminant will release into the overlying water column under different hydrodynamic conditions through pore-water in sediment, the release mechanism can be roughly divided into convection diffusion, molecular diffusion and adsorption/desorption. In this article, phosphorus was as a typical contaminant with sorption. Through theoretical analysis of the contaminant release, according to different particle-sized and hydraulic conditions, the mathematics model of contaminant release can be established by the coupled Navier-Stokes equation, Darcy equation, solute transport equation and adsorption/desorption equation. Then that model was verified by flume experiment. Numerical studies show that, under different velocity, the instantaneous concentration of convection diffusion is about 6 times to 50 times larger than that of molecular diffusion during initial stages. The concentration of molecular diffusion is about 1 times to 4 times larger than to that of convection diffusion during late stages. Through analysis, the diffusive boundary layer near the interface can be obtained. In addition, the release will increase with particle size decreasing, and the release will be influenced much more by the size change when the particle size is relatively big under different velocity.     

挟沙水流紊动结构

挟沙水流的紊动结构是十分复杂的研究课题。本文中首先综述了有关清水水流的紊动结构中有代表性的几种研究途径及其存在的问题，进而对挟沙水流的紊动结构进行了综合评述。     

沉沙池中调流板对水流调节作用的试验研究

沉沙池是一种重要的泥沙处理工程设施，其作用是沉降含沙水流中有害粒径的泥沙。泥沙在沉沙池中沉降效果的好坏，与池内水流流场分布直接有关。为使沉沙池内水流流场分布更利于泥沙的沉降，对传统沉沙池进行了改进，在沉沙池工作段首部加设调流板来对人池水流进行调节，并用室内模型试验检验调节效果。对试验结果进行分析，表明经过调流板调节后的水流流场分布更利于泥沙在沉沙池内的沉降，可为工程设计提供参考。     

泾河水沙基本特性分析

通过分析泾河张家山站实测水文资料,得出泾河水、沙年内的分配关系,洪峰传播时间,最大流量、最大含沙量出现时间及洪水过程的水沙关系等.     

Forms of particulate phosphorus in suspension and in bottom sediment in the Danube Delta

In the summer of 1995, samples of suspended solids and bottom sediments were collected from the lower course of the Danube, downstream from potential pollution sources such as tributaries draining industrialised and densely populated watersheds (the Jiu, Olt, Arges and Ialomita rivers) or big cities on the border of the river (Tulcea, Galati, Braila), and from the Danube Delta. Chemical and toxicological analyses were carried out on these samples. In the present paper, the results of the measurements of the forms of particulate phosphorus are discussed. Phosphorus occurring in the bottom sediments and the suspended solids has various origins and chemical forms. These forms may be operationally defined as: organic phosphorus (OP ) , apatite inorganic phosphorus (AP) and non‐apatite inorganic phosphorus (NAIP). The AP shows low variability, ranging from 350 to 400 p.p.m. for suspended solids and from 425 to 500 p.p.m. for bottom sediments. This is essentially due to the detrital origin of this form. These values are typical for freshwater sediments in European rivers. The NAIP, which originates both from natural sources and from human pollution, shows a high variability. This indicates that the nutrient pollution is derived from both point and non‐point sources in the watershed. The NAIP concentrations of 800 p.p.m. (Vadul Oii) and 850 p.p.m. (Oltenita) are very high (fourfold the average for European rivers), indicating that strong anthropogenic sources of phosphorus are present in the lower Danube watershed. As the NAIP is potentially bioavailable, its high concentration may contribute to eutrophication in the lower Danube and the Danube Delta.     

紫色土区小流域泥沙输出过程对雨型和空间尺度的响应

以紫色土区3个具有不同集水面积、物理特征和土地利用方式的小流域为研究对象,在1999～2000年间对流域野外自然降雨下泥沙输出过程进行了监测,旨在从小流域尺度阐明径流含沙量过程特征及其空间约束效应。结果表明：天然降雨侵蚀过程中流域径流含沙量时间曲线表现为波浪起伏形、幂函数递减形和抛物线复合形3种类型;峰值径流流量后,含沙量降低,表现为变化幅度小的低含沙量特征。泥沙输出过程对流域空间尺度的响应受降雨型式的强烈影响。均匀型降雨侵蚀下,径流含沙量时间曲线表现为低含沙量的波浪起伏形,并且,随流域面积的增加,次降雨平均含沙量增加;间歇型降雨侵蚀下,随流域面积的增加,径流含沙量曲线从抛物线复合形向幂函数递减形过渡;中大型降雨侵蚀下,径流含沙量时间曲线表现为幂函数递减形,泥沙输出过程对流域空间尺度的响应不敏感。     

波流耦合作用下紊流边界层水沙数学模型

在河口地区,波流相互作用下紊流边界层的泥沙起动输移规律非常复杂,深入探讨其泥沙运动规律很有必要。该文基于波浪边界层的控制方程,引入了时均水流压力,通过波流相互作用下的摩阻流速反映波浪与水流的夹角,用标准k-ε模型封闭方程,建立了波流叠加的紊流边界层内的弱耦合水流模型,分别讨论了波浪速度振幅、时均流速等的分布情况,与实测数据对比得到了较好的模拟结果。其次,基于水流模型建立了泥沙模型,采用对称振荡流和波流相互作用两种情况下的泥沙实测数据验证了泥沙模型的正确性,讨论了不同分布规律的涡黏系数对于模型的影响,为实际工程提供理论参考,结果具有一定的指导意义。     

圆管螺旋流输沙特性试验研究

螺旋流的流速分布有着与普通平直流不同的特点 ;运用圆管螺旋流的特性可以在管道中实现高浓度 ,远距离的泥沙输送。本文在试验的基础上对螺旋管流中的流速分布、泥沙的起动、起旋以及输沙等特性进行了研究 ,同时进行了理论分析 ,探讨了螺旋流高浓度输沙的可能性。