地表粗糙度对坡面流水动力学参数的影响

坡面流阻力的研究对于深入认识坡面流水力特性及土壤侵蚀产沙机理具有重要意义。采用变坡试验水槽,利用定床阻力冲刷试验系统研究了坡面流Darcy-Weisbach阻力系数与粗糙度、流量、坡度和水流型态之间的关系。结果表明:阻力系数随着床面粗糙度的增加呈指数函数增大;阻力系数随着雷诺数的增加呈幂函数减小,且随粗糙度的增加;阻力系数与弗劳德数呈良好幂函数关系,且粗糙度的影响不显著,流量为主要影响因素;人工模拟粗糙度床面下,阻力系数可由粗糙度、流量和坡度的简单幂函数良好表示,并且粗糙度为主要影响因素,流量和坡度的影响相对较小。由因子分析可知,阻力系数可由粗糙度和弗劳德数良好表示,经检验该模型可用来计算不同粗糙度坡面薄层水流的阻力系数。     

The association of E. coli and soil particles in overland flow.

The removal of E. coli from overland flow under saturation-excess runoff conditions was investigated in experimental field plots that were 1 m wide and 5 m long. Variation in the attenuation of bacteria and distance transported was quantified under contrasting flow conditions. In addition, the impact of soil tillage upon microbial attenuation was examined by comparing results derived from grassed plots (intact) with those subject to tillage with the soil left bare (cultivated). For intact plots subjected to a flow of 2 L/min, 27% of the E. coli in the flow was removed after 5 m with removal following a logarithmic function with respect to distance. For the higher flow rates of 6 L/min and 20 L/min, no attenuation trend was observed over this distance. E. coli removal during flow across the cultivated plots was significantly greater compared to the intact plots. This was attributed to a greater infiltration rate in the cultivated plots (due to the tillage) which promoted a greater volume of flow to pass through the soil matrix, providing the opportunity for filtration and adsorption of microbes. Logarithmic trends with respect to distance were observed for all flow rates tested on the cultivated plots (2, 6 and 20 L/min). Total removal after 5 m at a flow rate of 2 L/min was 41% and again removal efficiency decreased as the flow rate increased. Analysis of the transported state of the E. coli revealed that the bacteria were being transported predominantly in particles less than 20 microm in diameter and were not attached to large (dense) soil particles. The limited removal (< 50%) of bacteria from overland flow under saturation-excess runoff conditions in these experiments appeared, therefore, to be primarily due to a lack of settling or deposition. Instead, most bacteria remained entrained within the overland flow down the length of the plots.     

坡面流阻力研究进展

坡面流阻力的研究对了解坡面流水流特性、汇流过程、土壤侵蚀和坡面产沙机理都非常重要。本文分5个方面总结了坡面流阻力研究的最新进展:(1)坡面流阻力系数与雷诺数的关系;(2)光滑床面上的坡面水流阻力;(3)粗糙床面上的坡面水流阻力;(4)降雨对坡面流阻力影响的研究;(5)坡面流阻力的计算模型。综合前人研究发现,阻力系数与雷诺数在不同的条件下呈正相关或负相关关系;用叠加法计算不同条件下的坡面流阻力有其合理的一面,也有不足之处;粗糙动床条件下的坡面水流阻力计算模型更接近实际情况。最后,本文指出了当前坡面流阻力研究存在的主要问题和未来需要突破的主攻方向。     

坡面流阻力研究进展

主要从坡面流流态对坡面流阻力的影响、坡面流阻力与雷诺数的关系、降雨对坡面流阻力的影响、坡面流阻力公式4个方面对前人关于坡面流阻力的研究成果进行了总结。结果表明:坡面流流态的不确定性导致了坡面流阻力变化更为复杂;坡面流阻力与雷诺数之间并无良好单一的相关关系;降雨对坡面流阻力有很大的影响作用但具体影响机理并未有明确的结论;坡面流阻力公式表征仍用明渠水流概念及表达方式,并且3个阻力系数n、f、C哪个更适合表征坡面流阻力尚无统一的结论。进而对目前存在的问题进行了分析,对今后的发展进行了展望,认为需在研究方法和实验设备及量测技术方面有所突破,才可以更好的对坡面流阻力进行全面系统的研究。     

Combined analytical solution of overland flow and sediment transport

With reference to the kinematic wave theory coupled with the hypothesis of constant linear velocity for the rating curve, rising limb analytical solutions have been calculated for overland flow, over an Hortonian-infiltrating surface, and sediment discharge. These analytical solutions are certainly easier to use than the numerical integration of the basic equations and they may be used to obtain an initial evaluation of the parameters of more complex models generally devised for complicated cases.Notation a exponent of the Horton law [T^–1] - b exponent of the rill erosion equation - B inter-rill erosion coefficient [ML^–m–2T ^m–1] - c sediment concentration [ML^–3] - c _o reference sediment concentration [ML^–3] - E _I inter-rill erosion [ML^–2T^–1] - E _R rill erosion [ML^–2T^–1] - f _c final infiltration rate of the soil [LT^–1] - f _o initial infiltration rate of the soil [LT^–1] - h flow depth [L] - h _o reference flow depth [L] - i infiltration rate [LT^–1] - k rill erosion coefficient [ML^–1–b T^–1] - K integration constant - L() Laplace transformation - m exponent of the inter-rill erosion equation - n Manning's coefficient [L^–1/3T] - p rainfall intensity [LT^–1] - q water discharge per unit width [L²T^–1] - q _s sediment discharge per unit width [ML^–1T^–1] - t time [T] - t _p ponding time [T] - x distance along the flow direction [L] Greek Letters coefficient of the stage-discharge equation [L^2–T^–1] - exponent of the stage-discharge equation - rill erosion coefficient [L^–1]     

坡面产流模式的神经网络模拟

坡面产流是土壤本身特性与外界影响因素相互作用的结果，它们之间具有明显的非线性输入输出关系。在分析坡面产流和神经网络模型具有某些相似的基础上，利用径流站观测资料，建立了小流域坡面产流量的三层前向网络模型(BP算法)，并显示了具有较好的模拟预测效果。     

植被覆盖下坡面流的水流特性实验研究

为研究柔性植被和刚性植被覆盖下坡面流的水流特性,用水槽模拟坡面,PVC塑料薄膜模拟植被,通过调节水槽的坡度和柔性、刚性植被覆盖度对坡面流的水流流态、流速、水流深度进行了研究。经过多组实验得出了大量植被覆盖下的坡面流水力特性数据,并通过数据分析,总结了在不同植被覆盖、不同坡度条件下坡面流流速的变化规律。最后得出,通过减小坡面流流速、增加水流水深、控制水流流态、选择刚性植被覆盖坡面,可减少对坡面土壤的水力侵蚀。实验结果对控制流域非点源污染和选择水土流失防治措施有参考作用。     

坡面流阻力规律试验研究

通过实验室人工隆雨水槽试验，初步研究了坡面浅层均匀流及由降雨形成的浅层沿程变量流的流动阻力规律，根据试验中观察到的物理现象及对实测资料的分析，进一步明确了坡面浅层水汉与一般明渠流水力特性的差别，揭示了降雨、坡度和表面粗糙度对浅层流流动特性的影响，提出了“伪层流”的概念，根据实测资料建立了不同流区的Ｄarcy-Weisbach阻力参数f的定量关系式，研究成果可用于坡面流汇流计算及土壤侵蚀、产沙模拟等生产实践。     

植被影响下坡面流阻力变化特征研究

坡面流阻力是反映坡面流水力学特性的重要特征值.利用人工模拟降雨试验,定量研究了在45、87和127mm/h降雨强度下,20°陡坡面裸地、草地和灌木地的坡面流阻力变化特征.结果表明,由于植被覆盖措施的阻滞作用,相对于裸地坡面,草地和灌木地坡面径流阻力系数明显增大.草地和灌木坡面阻力系数分别是裸地坡面的5.58 ～ 7.45倍和5.61 ～6.26倍.不同被覆条件下坡面平均阻力系数与降雨强度关系密切,随降雨强度的增大呈减小趋势.同时,坡面流阻力系数受到降雨强度和下垫面条件发育形态的共同影响.建立了不同被覆坡面的复合非线性阻力系数计算公式,变量系数表明草被覆盖度和降雨强度对坡面流阻力大小有着决定性的影响.该研究对于揭示植被调控坡面产流产沙机理,为生态修复工程建设提供科学依据具有一定的科学意义.     

不同坡长下的坡面流水力学特性研究

坡面流亦即薄层水流,指的是降雨或融雪形成的,并在重力作用下沿坡面流动的薄层水流,它是地表径流的初始阶段,提供了侵蚀的主要动力。坡度相同、降雨强度相同时,随着坡长的增加,流速逐渐增大。在相同降雨强度下．坡长对流速有一定的影响,二者呈良好的指数关系;流量随坡长的增长而逐渐增大,二者呈良好的幂函数关系。2m水槽基本能够反映出坡面流的水力学参数的变化。随着坡长的增加,相同流速下,雷诺数逐渐增大．且增长速度亦逐渐增大。     

Longitudinal variations of hydraulic characteristics of overland flow with different roughness简

The evolution of the overland flow velocity along the distance downslope on smooth and granular beds in different cases is investigated by means of the electrolyte tracer via flume experiments.The results demonstrate that a non-uniform flow regime and a uniform flow regime exist in the development process of the overland flow.Owing to the different attributes of beds’roughness,the position of those zones with different flow regimes varies correspondingly:(1)the overland flow on granular beds enters into the uniform regime much sooner,additionally,the roll waves tend to appear because of the presence of the proper flow resistance imparted by the roughness(coarse sands),and large slopes(20o and 25o)which makes the flow velocities and depths to undulate spatially.Furthermore,the flow resistance of the overland flows with different roughness elements,that is the non-sands,the fine sands and the coarse sands,is calculated.A quadratic interpolation method of the third order accuracy is employed in the calculation of the longitudinal flow resistance.The results show that it is rational to use the bed slope to approximate the hydraulic energy slope over a relative small roughness(the present roughness),however on the other hand,if the mean flow velocities and depths rather than the local parameters are used to calculate the flow resistance,a considerable error will be induced within the non-uniform regime of the overland flows,including the acceleration zone and the roll-wave zone.     

冻土区地下水流过程及其与地表水转化关系研究进展

针对地下水流过程及其与地表水转化关系研究中,冻土分布特征及融冻过程对地下水系统的影响机制相关研究较少的问题,通过分析国内外冻土区地下水对河道径流的贡献、地下水流动路径和地下水-热耦合模型的相关文献,对地下水流过程及其与地表水转化研究进行综述,认为:①受土壤中冻土空间异质性的影响,不同冻土区地下水对径流的贡献比例不一致;②利用水化学和同位素示踪剂研究地下水流动路径,有助于冻土区地下水流动系统概念模型的构建,但只能获得定性或半定量的结果;③地下多相流系统的水-热耦合模型可将冻土的变化与其相应的水文响应过程耦合在一起,实现了地下水流过程及其与地表水转化关系的定量刻画,但在实用性方面仍需进一步完善,是未来的主要研究方向。     

坡面径流阻力计算模式对比研究

坡面流是污染物迁移、土壤侵蚀、泥沙输移的主要动力因素,阻力系数是影响坡面流模拟的重要参数。为比较三种阻力计算模式(阻力系数为常数、以淹没度为变量的Lawrence模型和阻力分割模型)在裸坡、砾石覆盖坡面、植被覆盖坡面三种常见坡面上的适用程度,本文建立了坡面降雨径流模型,对不同类型坡面的产流进行了模拟。坡面径流模型采用扩散波模型,坡面降雨入渗模型采用考虑坡度影响的Green-Ampt模型,当存在植被时,考虑冠层降雨截留损失。结果表明:在裸坡上,三种阻力计算模式均适用;而在有砾石覆盖和植被覆盖的坡面上,考虑阻力系数时空变化的阻力分割模型模拟精度最高。阻力系数对坡面径流流量的影响在坡面汇流的涨水与退水阶段较大,而在稳定阶段很小。对有植被覆盖坡面,降雨强度存在阈值,大于阈值时,不同阻力模式对坡面流模拟结果影响甚微;反之,需选择合适的阻力计算模式,且坡长越长,坡度越缓,降雨强度阈值越大。     

植被排列方式及坡度对坡面流Fr影响的试验研究

为探究植被的排列方式及坡度大小对坡面流弗劳德数Fr的影响,以期揭示坡面流弗劳德数Fr的内在规律。利用人工模拟试验,系统研究了6个坡度、3种植物排列方向与水流方向呈不同走向角的条件下Fr与单位底面积的空间摩阻表面积K值的特征关系。表明在非淹没状态下,Fr与K值的关系为随K值的增大Fr呈现先减小后趋于平稳的趋势;Fr的取值随坡度的增大而增大;在一定的坡度范围内,同一坡度下,当Fr1时,同一K值下,走向角越大对应的Fr值越小,当Fr1时则相反;同一走向角下,在同一K值下,坡度越大对应的Fr就越大。得出在坡度一定的条件下,坡面植被的排列方式不同,弗劳德数Fr的取值也不相同;坡度是影响Fr取值范围的重要因素之一。     

The experiment and analysis of transitional flow in pipe

The transitional flow in a pipe is important for delivery, but its characteristics remain to be explored. In this paper, the two-dimensional laser Doppler velocimetry(LDV) is used for the study, focusing on the attenuation characteristics of the axial velocity, the variation of the velocity gradient, the effect of the angle between the axis and the resultant velocity vector, and the relationship between the energy coefficient and the flow state. The attenuation characteristics of the axial velocity along the radial direction are obtained. It is shown that with the increase of the Reynolds number, the change rate of the velocity gradient slows down with a similar distribution, and a rapid decrease is seen in the near wall region. The amplitude and the frequency of the angular variation are obviously improved with the increase of the Reynolds number. The instability of the velocity field is enhanced with the increase of the energy coefficient.     

草被覆盖度下坡面流流速变化及缓流机制研究

坡面薄层水流是黄土区土壤侵蚀发生的直接动力条件,探究植被覆盖条件下坡面流水动力学特性及缓流机制,有助于揭示土壤侵蚀发生的水动力学机理。在水槽坡度为12°条件下,通过9个草被覆盖度、7个流量的组合试验,研究了不同植被覆盖度下坡面水流流速变化和缓流机制。结果表明:坡面流流速随着覆盖度的增加整体呈减小的趋势;缓流系数随覆盖度的增加呈先增大后减小的变化规律,当覆盖度大于47.66%时,缓流系数随覆盖度的增加显著减小;以覆盖度47.66%为临界值,高、低覆盖度下缓流系数随雷诺数的变化规律有所不同。最后,建立了模拟草被下的坡面流流速和缓流系数拟合公式,验证结果表明,拟合公式精度较高,可为建立土壤侵蚀预报模型提供参考。     

鹅颈型管道三维水流结构研究

本文通过试验测量了鹅颈型管道水流的三维流速分布（不同层面和断面的纵向、垂向及横向流速分布）与断面压力分布，剖析了鹅颈型管道的三维水流结构，提示出鹅颈型管道边界分离的特点及二次流（弯曲二次流及非圆形断面二次流）的形成机理，提出了鹅颈型管道固有的水流型态，水力特性及概念。     

气液两相水平管流分层--段塞流型转换机制研究

本文根据Stokes溃坝理论 ,提出了一个新的物理模型。通过对段塞单元的稳定性进行分析得出段塞保持稳定的临界液面高度值 ,从而得出分层流向段塞流转换的条件 ,并分析了液体粘度、管径大小对流型转换条件的影响。计算结果与实验值较为吻合     

沭河流域洪水预报的产汇流组合方案优选

针对沂沭泗流域洪水预报问题,选择沭河流域重沟站洪水事件为研究对象,评估了两种产流方法和三种坡面汇流方法的不同组合下洪水模拟精度。 结果表明,CN 曲线数法是研究区最优的产流计算方法,斯奈德单位线和 SCS 单位线均适用于该流域的坡面汇流;CN 曲线数-斯奈德单位线组合是沭河流域最优的产汇流组合方案,洪水预报精度达到乙级以上。