Seepage from shallow channels and irrigation furrows

Two cases of two-dimensional steady seepage from broad channels and irrigation furrows through a layer of homogeneous isotropic soil into a highly permeable pressurized aquifer in the presence of soil capillarity are examined in the hydrodynamic formulation. A uniform method of solution in which the solution of the problem of seepage from an irrigation furrow can be obtained from the solution for a broad channel is given. The special and limiting cases studied in [1–3] and elsewhere are noted. Computer calculations are used to analyze the dependence of the rate of seepage from channels and irrigation furrows and the capillary spread on the profile and width of the channel or irrigation furrow, the thickness of the layer, the head and the capillarity of the soil.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 96–102, January–February, 1989.The authors are grateful to N. N. Verigin for valuable comments.     

Measurement of liquid film thickness in a micro parallel channel with interferometer and laser focus displacement meter

In the present study, liquid film thicknesses in parallel channels with heights of H = 0.1, 0.3 and 0.5 mm are measured with two different optical methods, i.e., interferometer and laser focus displacement meter. Ethanol is used as a working fluid. Liquid film thicknesses obtained from two optical methods agree very well. At low capillary numbers, dimensionless liquid film thickness is in accordance with Taylor’s law. However, as capillary number increases, dimensionless liquid film thickness becomes larger than Taylor’s law for larger channel heights. It is attributed to the dominant inertial effect at high capillary numbers. Using channel height H for dimensionless liquid film thickness δ₀/H and hydraulic diameter D_h = 2H as the characteristic length for Reynolds and Weber numbers, liquid film thickness in a parallel channel can be predicted well by the circular tube correlation previously proposed by the authors. This is because curvature differences between bubble nose and flat film region are identical in circular tubes and parallel channels.     

Solution of two-dimensional problems of unsteady heavy-fluid seepage into unsaturated porous soil on the basis of an instantaneous saturation model

Two-dimensional problems of the unsteady seepage of a heavy fluid into a uniform unsaturated porous soil from a single channel and from an infinite periodic system of identical channels are solved. The fluid level in the channel is a known function of timet, which simulates the propagation of the fluid along a furrow normal to the plane of the problem. Seepage into the soil, which occupies the space outside (mainly below) the channel, takes place under the influence of the force of gravity and begins at the momentt=0 after it is instantaneously filled with fluid. On the interval 0 <t < t₁ the height of the fluid in the channel is constant, and whent=t ₁ it falls instantaneously to some other level, also constant. This may be the zero level, which coincides with the bottom of the channel. The problem in which the fluid level in the channel rises is also considered.Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 86–94, January–February, 1992.In conclusion the authors wish to thank V. A. Vostretsov for his assistance.     

Measurement of liquid film thickness in micro square channel

In micro channels, slug flow becomes one of the main flow regimes due to strong surface tension. In micro channel slug flow, elongated bubble flows with the thin liquid film confined between the bubble and the channel wall. Liquid film thickness is an important parameter in many applications, e.g., micro heat exchanger, micro reactor, coating process etc. In the present study, liquid film thickness in micro square channels is measured locally and instantaneously with the confocal method. Square channels with hydraulic diameter of D_h = 0.3, 0.5 and 1.0 mm are used. In order to investigate the effect of inertial force on the liquid film thickness, three working fluids, ethanol, water and FC-40 are used. At small capillary numbers, liquid film at the channel center becomes very thin and the bubble interface is not axisymmetric. However, as capillary number increases, bubble interface becomes axisymmetric. Transition from non-axisymmetric to axisymmetric flow pattern starts from lower capillary number as Reynolds number increases. An empirical correlation for predicting axisymmetric bubble radius based on capillary number and Weber number is proposed from the present experimental data.     

NUMERICAL STUDY ON THE SEDIMENTED MOTION CHARACTERISTICS OF THREE ALIGNED CIRCULAR PARTICLES IN THE INCLINED CHANNELS

主要应用浸没边界的格子玻尔兹曼方法（immersed boundary-lattice Boltzmann method, IB–LBM） 对处于不同倾斜角度通道内的三个刚体圆形颗粒在重力作用下下落的动力学特性进行了计算研究. 首先分析通道倾斜角度的影响, 结果显示当通道倾斜角处于59°90°的范围时会发生后一个颗粒超越前一个颗粒的现象. 其次, 研究了Re对颗粒沉降特性的影响, 结果表明Re 越大, 颗粒间发生聚集的时间越早. 研究还发现当3 个颗粒的直径大小不均匀时, 颗粒由大到小纵向依次排列, 或者出现中间小球直径较相邻两个小球直径大的排列情况, 均能促使颗粒加快聚集. 本文的研究结果可为环境工程及地质学中的颗粒沉降问题提供有价值的参考.     

Seepage analysis based on the unified unsaturated soil theory

The normal use of the finite element method in the analysis of earth and rock-fill dams involves troublesome modifications of the finite element mesh. In the present paper it is pointed out that in problems of steady seepage it is not necessary to determine in the iteration process the entire free surface, but only the elevation of the release point. It is shown by several examples that the proposed method can simplify the seepage analysis to a certain degree, and also give satisfactory results.     

Kv1.2钾通道闭合的靶向分子动力学模拟

钾离子通道是一种能开放或闭合孔道而控制钾离子跨膜流动的膜蛋白.Kv1.2结构是一种开式构型的钾通道结构.也是迄今获得的唯一一种来自真核细胞的钾通道结构.尽管导致Kv1.2结构内螺旋弯曲的PVP序列在KcsA等原核细胞钾通道中不存在,KcsA结构的直武内螺旋闭合构型仍常被作为Kv1.2等真核细胞钾通道的闭式模版.本文在靶向分子动力学模拟中迫使Kv1.2钾通道闭合为KcsA构型.我们发现Kv1.2无法适应KcsA的闭合构型,松弛后内螺旋恢复PVP铰链弯曲,在孔道的腔一门区域形成上下大中间小的沙漏状闭合构型.此构型使开闭构型转换效率更高,可能是钾通道从原核细胞的甘氨酸铰链进化到真核细胞的PXP铰链的原因所在.     

Two-dimensional analytical solution for compound channel flows with vegetated floodplains

This paper presents a two-dimensional analytical solution for compound channel flows with vegetated floodplains. The depth-integrated N-S equation is used for analyzing the steady uniform flow. The effects of the vegetation are considered as the drag force item. The secondary currents are also taken into account in the governing equations, and the preliminary estimation of the secondary current intensity coefficient K is discussed. The predicted results for the straight channels and the apex cross-section of meandering channels agree well with experimental data, which shows that the analytical model presented here can be applied to predict the flow in compound channels with vegetated floodplains.     

Experimental study of flow and heat transfer in rib-roughened rectangular channels

Secondary flow patterns, pressure drop and heat transfer in rib-roughened rectangular channels have been investigated. The aspect ratio of the channels is 1–8, and ribs are attached to the wide channel walls in order to set up swirling motions. The geometries tested consist of channels having cross ribs, parallel ribs, cross V-ribs, parallel V-ribs, and multiple V-ribs (Swirl Flow Tube). The flow patterns were investigated using smoke wire visualization and LDV measurements. The smoke wire experiments have been performed at Re=1100 and the LDV measurements at Re=3000 at periodic fully developed conditions. The heat transfer and pressure drop are described by j and f factors for Reynolds numbers from 500 to 15 000. The distributions of axial mean velocity and turbulent fluctuations are strongly influenced by the secondary flows. Large mean velocities and small fluctuations are found in regions where the secondary flow is directed towards a surface, while small mean velocities and large fluctuations are found in regions where the secondary flow is directed away from a surface. The Swirl Flow Tube provides a significant increase in the j factor at Reynolds numbers from 1000 to 2000, but unfortunately also an increase in the f factor. At higher Reynolds numbers, the j and f factors of the Swirl Flow Tube are of the same order of magnitude as for the other rib-roughened channels. It is found that the flow direction in a channel with parallel V-ribs has important influence on the j/f ratio. At Reynolds numbers above 4000, this channel provides the highest j/f ratio if the V-ribs are pointing upstream; while it provides the lowest j/f ratio of all rib configurations, if the V-ribs are pointing downstream.     

摆动河槽水动力稳定性特征分析

河流形态与水动力结构息息相关,形态约束水动力结构,水动力结构则通过泥沙运动进一步塑造形态,在自然界河流中形成一对辩证互馈关系.天然河流形态形式多样,大致可以分为顺直、微弯、分叉和散乱游荡几种类型,其中微弯及多个弯曲构成的河型为河流动力演化中最重要的一环.多个弯曲构成的河型可用正弦派生曲线来描述,它也是天然河流主槽与水动力结构复杂相互作用的结果.作为探讨这一过程的力学作用机理,构建摆动槽道并研究槽道摆动与其内部流动结构的互馈关系,既是流体力学研究的热点内容,也是目前河流动力过程研究的基础内容.在此重点讨论这一互馈关系前一部分,即水流对摆动边界的响应.文中建立了随体坐标系下摆动河槽与内部水流动力响应理论模型,通过给定摆动弯曲槽道的不同特征参数,研究讨论了正弦派生型摆动边界下的槽道水流动力稳定性特征,明确了弯曲槽道摆动对其内部主流及扰动水流结构的影响,确定弯曲槽道摆动波数、摆动频率对扰动流发展影响的相应参数定量关系,得到了槽道弯曲度和摆动特征对其内部水流不同尺度扰动影响的阈值选择性范围.     

Study on resistance coefficient in compound channels

This paper presents a further study of the Manning and Darcy-Weisbach resistance coefficients, as they play a significant role in assessing the cross-sectional mean velocity, conveyance capacity and determining the lateral distribution of depth mean velocity and local boundary shear stress in compound channels. The relationships between the local, zonal and overall resistance coefficients, and a wide range of geometries and different roughness between the main channel and the flood plain are established by analyzing a vast amount of experimental data from a British Science and Engineering Research Council Flood Channel Facility (SERC-FCF). And the experimental results also show that the overall Darcy-Weisbach resistance coefficient for a compound channel is the function of Reynolds number, but the function relationship is different from that for a single channel. By comparing and analyzing the conventional methods with the experimental data to predict composite roughness in compound channels, it is found that these methods are not suitable for compound channels. Moreover, the reason why the conventional methods can not assess correctly the conveyance capacity of compound channels is also analyzed in this paper.The project supported by the National Natural Science Foundation of China (50279024), the National Key Basic Research and Development Program of China (973 Program) (2003CB415202) and the Specialized Research Fund for the Doctoral Program of Higher Education (20030610039)The English text was polished by Ron Marshall     

RULE OF TRANSIENT PHREATIC FLOW SUBJECTED TO VERTICAL AND HORIZONTAL SEEPAGE

In a semi-infinite aquifer bounded by a channel,a transient flow model is constructed for phreatic water subjected to vertical and horizontal seepage.Based on the first linearized Boussinesq equation,the analytical solution of the model is obtained by Laplace transform.Having proven the transformation between the analytical solution and some relevant classic formulas,suitable condition for each of these formulas is demon- strated.On the base of the solution,the variation of transient flow process caused by the variables,such as vertical infiltration intensity,fluctuation range of river stage,aquifer parameters such as transmissivity and specific yield,and the distance from calculating point to channel boundary,are analyzed quantitatively one by one.Lagging effect will happen to the time,when phreatic water gets its maximum fluctuation velocity,response to the varying of the variables stated above.The condition for some variables to form equivalent lagging effect is demonstrated.Corresponding to the mathematical charac- teristics of the analytical solution,the physical implication and the fluctuation rule of groundwater level are discussed.     

Seepage-limitation optimization of the shape of an irrigation channel by the inverse boundary-value problem method

A study is made of the problem of finding the optimal shape of the section of an irrigation channel from the point of view of minimizing the seepage loss; the inverse boundary-value problem method [1] is used.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 74–80, May–June, 1984.     

微重力下薄燃料表面火焰传播的地面窄通道模拟

对微重力下薄燃料表面逆风火焰传播的地面窄通道模拟，进行了量纲分析，并通过火焰传播 图像记录进行了实验验证. 结果表明，减小实验段特征尺寸可以实现微重力燃烧的地面模拟. 在各种氧气浓度条件下，竖直和水平窄通道内的火焰传播速度随气流速度的变化趋势完全不 同，而且，水平窄通道可以有效限制自然对流，而竖直窄通道较难. 当通道高度增大时，竖 直和水平窄通道中，火焰传播速度和吹熄极限速度都不同程度地增大，这是热损失减小、火 焰面遇见的气流速度减小以及自然对流速度增大3个因素的综合结果. 对于水平窄通道， 1cm是一个可以定性模拟微重力下自然对流的尺寸. 对于竖直窄通道，则需要高度更小的窄通 道来限制自然对流.     

Simultaneous convection and radiation in flow between two parallel plates

A numerical solution is described for simultaneous forced convection and radiation in flow between two parallel plates forming ahannel. The front plate is transparent to thermal radiation while the back one is thermally insulated. Analyses for both flow and heat are presented for the case of a non-emitting ‘blackened’ fluid. The governing equations of the stream function and the temperature together with their boundary conditions are presented in non-dimensional expressions. The solution is found to depend on eight dimensionless parameters, namely the ratio of the height of the channel to the distance between the plates, the initial dimensionless temperature, the optical thickness, the absorptivities of both plates, the Reynolds number, the Prandtl number and the heat transfer coefficient from the front plate to the surroundings. The numerical solution is obtained using a finite-difference technique. A study has been made of the effect of the initial temperature of the flow at the channel inlet, the dimensionless loss coefficient from the front plate, the absorptivity of the back plate and the optical thickness, on the temperature distribution in the channel, the heat collection efficiency and the average temperature rise in the channel. Results showed that increasing the optical thickness increases the temperature of the front plate and decreases the temperature of the back plate. Also, increasing the optical thickness increases the efficiency of heat collection, which reaches its maximum asymptotic value at an optical thickness of about 1.5. Moreover, the location of the maximum temperature is found to depend on both the optical thickness and the dimensionless heat loss coefficient from the front plate.     

裂隙岩体渗流模型研究现状与展望

裂隙岩体渗流对于边坡、地下工程及基础岩土体的承载能力有显著的制约作用。本文简要地介绍了多种裂隙岩体渗流模型研究现状,评述了几类比较有代表性的渗流模型特点以及存在的不足,为选取合理的数学模型用于求解具体的裂隙岩体渗流问题提供了参考依据,并在上述基础上提出了一些需要进一步研究的问题。指出就目前应用最为广泛的等效连续介质模型而言,裂隙岩体几何参数、有效孔隙度以及等效渗透张量的确定仍有待于更深入的研究,而从细观力学结构入手研究渗流耦合模型将具有重大的理论意义和实用价值。     

Analysis of nano channel formation in quartz cubes by laser-induced process

A novel laser processing technique was developed for making channels in the nano regime in this paper. A Nd:YAG laser was used to dry fabricate micro channels (25μm～100μm di ameter) in a 1 cm^3 fused silica substrate by thermal-induced processing. By controlling the locations of these initiating micro channels on a silica cube, 1D-controllable self-connecting nano fractures can be formed as rectangular channels. These nano channels are smooth and with extremely high aspect ratio (～10^4 depth to width ratio). A possible mechanism is proposed to explain the formation of the nano channels. This laser-based nano channel fabrication technique is fast and inexpensive, and with potential applications in capillary electrophoresis and electro-osmosis driven nano-filtration.     

纳米尺度通道内的界面流体粘性研究

含液微纳米孔隙在自然界中普遍存在,在发展 日趋精密化、微型化的工业中也有着广泛的应用,深刻理解流体在微纳米通道内的物性变化对于相关自然现象以及工业应用具有重要的指导意义.本文基于分子动力学方法,建立了由金属铂板构成的二维纳米尺度通道分子模型,分别考察了受限Lennard-Jones流体和水的物性变化.根据密度、剪切应力和粘性在通道高度方向的分布情况,确定了两种流体的边界层厚度约为4.8 ?和4.6 ?.针对边界层内的流体,发现界面流体的粘性相比宏观尺度体态流体粘性明显提高,且随着固-液相互作用强度的增加而增加,但随着通道壁面晶格常数的增加而减少.基于计算结果,给出了由接触角表征的具有一定普适性的流体界面粘性计算公式.研究工作为微纳米尺度通道输运性能及其调控提供了有价值的参考和指导.     

Effects of information transmission delay and channel blocking on synchronization in scale-free Hodgkin-Huxley neuronal networks

In this paper,we investigate the evolution of spatiotemporal patterns and synchronization transitions in dependence on the information transmission delay and ion channel blocking in scale-free neuronal networks.As the underlying model of neuronal dynamics,we use the Hodgkin-Huxley equations incorporating channel blocking and intrinsic noise.It is shown that delays play a significant yet subtle role in shaping the dynamics of neuronal networks.In particular,regions of irregular and regular propagating excitatory fronts related to the synchronization transitions appear intermittently as the delay increases.Moreover,the fraction of working sodium and potassium ion channels can also have a significant impact on the spatiotemporal dynamics of neuronal networks.As the fraction of blocked sodium channels increases,the frequency of excitatory events decreases,which in turn manifests as an increase in the neuronal synchrony that,however,is dysfunctional due to the virtual absence of large-amplitude excitations.Expectedly,we also show that larger coupling strengths improve synchronization irrespective of the information transmission delay and channel blocking.The presented results are also robust against the variation of the network size,thus providing insights that could facilitate understanding of the joint impact of ion channel blocking and information transmission delay on the spatiotemporal dynamics of neuronal networks.