共查询到20条相似文献，搜索用时 62 毫秒
1.
A process was development for researching the finger dynamics using digital image analysis and the soil water content concept
model. Nonuniform wetting front profile expanded vertically under the equalized potential head horizontally. Experimental
data and the present concept model matched adequately. For extending the application of concept model, hysteresis models (Hogarth
in 1988 and Huang in 2005) are compared. The initial temporal and spatial fingered velocity was faster with time under the
same rainfall intensity, as well as fingered width. Besides, the mean fingered velocity also increase with rainfall intensity.
The present concept model expounded the evolution of lingered flow and the hydraulic properties of linger dynamics successfully. 相似文献
2.
Recent research shows that most soils are more or less water repellent. Already subcritical water repellency may cause incomplete soil wetting and preferential flow. Both processes potentially reduce the residence time of water and solutes in the vadose zone, resulting in an enhanced risk of groundwater contamination. The objective of the present paper is, therefore, to evaluate the impact of reduced soil wettability on the soil water infiltration rate and to investigate the tendency towards preferential flow with the analysis of the immobile water content in the infiltration zone. In november 2002, a field experiment was done in a coniferous forest, 30 km N of Hannover, Germany. Soil hydrophobicity was quantified by measuring the contact angles. The hydraulic conductivity of the podsolic sandy soil was measured depth‐dependent with a double‐ring tension infiltrometer in three soil horizons. To quantify possible preferential‐flow effects, a LiBr‐Tracer was added to the infiltrating water to evaluate the mobile water‐content fraction after infiltration. Additionally, infiltration rates of water were compared with infiltration rates of ethanol which were determined after water infiltration at the same locations. Results show that the actual water repellency of field‐moist soil was mainly subcritical (contact angle <90°). Water infiltration rates were reduced due to subcritical repellency by a factor of 3–170 compared with ethanol infiltration rates (exclusion of wetting effects). This spatially variable infiltration behavior was not clearly reflected neither by the small‐scale contact‐angle measurements nor by the analysis of the average immobile soil water content in the infiltration zone. We conclude that this specific infiltration behavior of water caused by small‐scale wettability effects may temporarily reduce the local connectivity of water‐flow pathways. 相似文献
3.
土壤斥水性影响土壤水分运动研究进展 总被引：4，自引：1，他引：3
土壤斥水性广泛存在于各类土壤,是影响植物生长、土壤水分运动以及土壤侵蚀等水土过程的重要因素。该文阐述了土壤斥水性的基本概念,介绍了几种常用的斥水性强度测定方法及适用范围。在此基础上,论文对土壤斥水性如何影响土壤水力性质以及水分运动特征等研究现状作了全面评述,重点讨论了近年来该领域的研究热点,如土壤斥水性影响下的指流观测和理论模拟以及斥水性土壤蒸发过程等。最后,提出了相关研究中亟待解决的若干关键科学问题,主要包括确定土壤斥水性影响指流现象和蒸发过程的物理机制的揭示;考虑土壤斥水性参数的土壤水分运动数学模型的构建;以及对新模型的求解及对数值解的理论分析。由于土壤斥水性对土壤水分运动有重要的关联效应,相关问题的深入研究对进一步认识土壤水分运动的内在物理机制具有重要理论意义,也将为掌握和有效利用土壤斥水性提供实践指导。 相似文献
4.
J. Poulenard J.C. Michel F. Bartoli J.M. Portal & P. Podwojewski 《European Journal of Soil Science》2004,55(3):487-496
Water repellency of volcanic ash soils from the Ecuadorian páramo was studied by a combination of extraction and analysis of water‐repellent products, Molarity Ethanol Droplet values, water contact‐angle measurements by capillary rise, and N2 adsorption isotherms. The undried samples studied are hydrophilic, but exhibit water repellency after moderate drying (48 hours at 30°C). The advancing water contact‐angle measured by capillary rise varies from 78° to 89°. These water contact‐angles decrease strongly after extraction of organic materials by an isopropanol–water mixture. Elemental analysis, infrared spectra and gas chromatography‐mass spectrometry analyses were used to characterize the extracts. The results show that long‐chain fatty acids and more complex non‐polar alkyl components (waxes) are the main water‐repellent materials. The deposition of such extracted materials onto hydrophilic sand leads to the rapid increase of water contact‐angle until values close to those measured on the soil samples are achieved. Assuming a coating of the mineral surface by organic hydrophobic products and using Cassie's law, the water contact‐angle of extracted materials was computed. The values ranged from 100° to 157°. Nitrogen specific surface areas of the soils studied were very small, indicating a low adsorbent–adsorbate interaction on hydrophobic surfaces. These results partially validate the hypothesis of water‐repellent materials that occur as coatings at least after a drying process. 相似文献
5.
砂土和黏土的颗粒差异对土壤斥水性的影响 总被引：5，自引：0，他引：5
斥水性土壤广泛存在于自然界中,并且对土壤环境和作物生长等有重要影响。建立理想化的土壤颗粒模型对砂土和黏土的斥水特性进行计算分析。结果表明:当接触角很小时,砂土中不存在斥水现象。随着接触角的增大,砂土斥水性与含水率密切相关,砂土的密实度对其斥水性也有重要影响,当砂土比较密实时,土壤的"亲水"与"斥水"特性对含水率特别敏感,随着含水率的变化,砂土可能由亲水性较好的土壤转变为斥水性土壤;当砂土比较松散时,土壤颗粒的斥水性对含水率并不敏感。当黏土接触角略小于90°且湿润半径b也较小时,黏土也存在斥水现象。如果黏土颗粒的接触角较小或接触角小于90°且湿润半径b较大,黏土总是亲水的。黏土含水率较大时,斥水特性由土壤颗粒的接触角决定。 相似文献
6.
为了研究沙漠干旱区降雨对砂层非饱和带水分的贡献,该文对风积砂层水分入渗过程中的水分存在形式和运移机理进行了理论和力学分析。通过以触点水为主要储水单元的立方布局颗粒模型推导出水分入渗过程中湿润深度的解析表达式,并进行验证。物理和力学分析表明,砂颗粒表面很难形成较厚的薄膜水,砂层非饱和带水分大部分以触点水的形式存在。模型计算结果表明,水分入渗的湿润深度与入渗水量和触点水湿润角有关。模型验证表明,水分入渗湿润深度的解析表达式在风积砂层入渗深度计算中具有一定的适用性,但触点水湿润角与砂颗粒粒径的函数关系还有待进一步研究当设定触点水湿润角为π/4时,比例常数为11.5。该研究可为干旱区农业规划提供依据。 相似文献
7.
Water-repellent(WR) soil greatly influences infiltration behavior. This research determined the impacts of WR levels of silt loam soil layer during infiltration. Three column scenarios were utilized, including homogeneous wettable silt loam or sand, silt loam over sand(silt loam/sand), and sand over silt loam(sand/silt loam). A 5-cm thick silt loam soil layer was placed either at the soil surface or 5 cm below the soil surface. The silt loam soil used had been treated to produce different WR levels, wettable, slightly WR, strongly WR, and severely WR. As the WR level increased from wettable to severely WR, the cumulative infiltration decreased. Traditional wetting front-related equations did not adequately describe the infiltration rate and time relationships for layered WR soils. The Kostiakov equation provided a good fit for the first infiltration stage. Average infiltration rates for wettable, slightly WR, strongly WR, and severely WR during the 2 nd infiltration stage were 0.126, 0.021, 0.002, and 0.001 mm min~(-1) for the silt loam/sand scenario,respectively, and 0.112, 0.003, 0.002, and 0.000 5 mm min~(-1) for the sand/silt loam scenario, respectively. Pseudo-saturation phenomena occurred when visually examining the wetting fronts and from the apparent changes in water content(?θ_(AP)) at the slightly WR,strongly WR, and severely WR levels for the silt loam/sand scenario. Much larger ?θAPvalues indicated the possible existence of finger flow. Delayed water penetration into the surface soil for the strongly WR level in the silt loam/sand scenario suggested negative water heads with infiltration times longer than 10 min. The silt loam/sand soil layers produced sharp transition zones of water content. The WR level of the silt loam soil layer had greater effects on infiltration than the layer position in the column. 相似文献
8.
Wettability of soil affects a wide variety of processes including infiltration, preferential flow and surface runoff. The problem of determining contact angles and surface energy of powders, such as soil particles, remains unsolved. So far, several theories and approaches have been proposed, but formulation of surface and interfacial free energy, as regards its components, is still a very debatable issue. In the present study, the general problem of the interpretation of contact angles and surface free energy on chemically heterogeneous and rough soil particle surfaces is evaluated by a reformulation of the Cassie‐Baxter equation, assuming that the particles are attached on to a plane and rigid surface. Compared with common approaches, our model considers a roughness factor that depends on the Young’s Law contact angle determined by the surface chemistry. Results of the model are discussed and compared with independent contact angle measurements using the Sessile Drop and the Wilhelmy Plate methods. Based on contact angle data, the critical surface tension of the grains were determined by the method proposed by Zisman. Experiments were made with glass beads and three soil materials ranging from sand to clay. Soil particles were coated with different loadings of dichlorodimethylsilane (DCDMS) to vary the wettability. Varying the solid surface tension using DCDMS treatments provided pure water‐wetting behaviours ranging from wettable to extremely hydrophobic, with contact angles > 150°. Results showed that the critical surface energy measured on grains with the highest DCDMS loadings was similar to the surface energy measured independently on ideal DCDMS‐coated smooth glass plates, except for the clay soil. Contact angles measured on plane surfaces were related to contact angles measured on rough grain surfaces using the new model based on the combined Cassie‐Baxter Wenzel equation, which takes into account the particle packing density on the sample surface. 相似文献
9.
Although quartz sand with its amorphous surface layer covered with OH groups is completely hydrophilic per se, the contact angle of water with it is > 0°. Natural sand (marine or soil) apparently contains organic hydrophobic substances adsorbed from air and water; this decreases its hydrophilicity, which is not restorable by acid washing and calcination. The H2O2 treatment of acid-washed sand restores its natural hydrophilicity. 相似文献
10.
Soil water repellency is a transient soil property varying with soil–water contact time. The purpose of the present study was to determine the time dependence of the sessile drop contact angle and its relation to repellency persistence estimated using the water drop penetration time (WDPT) test with hydrophobized sand. The contact angle decreased exponentially and almost reached apparent equilibrium after 20 min of soil–water contact time. Time dependence of the contact angle can mainly be attributed to the adsorption of water molecules onto low-energy hydrophobic organic matter surfaces. Contact angles initially greater than 90° decreased to less than 90° within about 40 s. However, the WDPT of these samples was longer than 3600 s. The WDPT responded to the initial contact angle, but not to the contact angle decreased with soil–water contact time. This was considered to be caused by differences in the surface free energy between the surface and the lower layers. Repellency persistence, or the WDPT, can be considered to be the time taken to increase the surface free energy to overcome water repellency, not only on the surface in contact with the droplet, but also in the adjacent layers below the surface. 相似文献
11.
John L. Nieber 《Geoderma》1996,70(2-4):207-229
The mechanism for the growth and persistence of gravity-driven fingered flow of water in initially dry porous media is described. A Galerkin finite element solution of the two-dimensional Richards equation with the associated parameter equations for capillary hysteresis in the water retention function is presented. A scheme for upstream weighting of internodal unsaturated hydraulic conductivities is applied to limit smearing of steep wetting fronts. The growth and persistence of a single finger in an initially dry porous media is simulated using this numerical solution scheme. To adequately simulate fingered flow, it was found that the upstream weighting factor had to be negative, meaning that the internodal unsaturated hydraulic conductivities were weighted more by the downstream node. It is shown that the growth and persistence of a finger is sensitive to the character of the porous media water retention functions. For porous media where the water-entry capillary pressure on the main wetting function is less than the air-entry capillary pressure on the main drainage function, a small perturbation will grow into a finger, and during sequential drainage and wetting the finger will persist. In contrast, for porous media where the water-entry capillary pressure on the main wetting function is greater than the air-entry capillary pressure on the main drainage function, the same small perturbation will dissipate by capillary diffusion. The finger widths derived from the numerical simulation are similar to those predicted by analytical theory. 相似文献
12.
Highway runoff contains pollutants in concentrations that can harm ecosystems of receiving freshwaters. To suggest control measures the hydrological conditions for pollutant transport from road edge to receiving water, and the associated retention mechanisms must be identified. Often, the transfer of highway runoff to receiving water bodies is accomplished by means of roadside swales equipped with gullies and underdrains. It is well documented that infiltration into the swale constitutes the primary runoff removal mechanism, while surface flow across and along the swale is mainly restricted to heavy storm episodes. Dye tracing at four Danish highways was used to describe the hydrological conditions for leaching of highway runoff pollutants through highway swales. At all sites the surface layer of the exposed swale profiles consists of a homogeneous sandy material deposited after construction of the highway, reaching a thickness correlated with, among other things, the road age. The dye solution infiltrated these deposition layers uniformly, replacing all antecedent soil water. The below-swale soil profiles were percolated through more preferential pathways, but contrary to the expectation no earthworm burrows or other biopores played a part. At two sites the preferential flow patterns resembled macroporous flow through physical voids in heterogeneous construction materials (stony loam) and at borders between construction materials with different texture (gravel, clayey till, fine and coarse sand). At the other two sites, which were built almost exclusively from homogeneous sand, the flow patterns resembled fingered flow initiated around thin, deep-running roots from the surface vegetation. The contaminant transport consequences of these flow patterns are discussed. 相似文献
13.
砂层在黄土中发生指流条件的试验研究 总被引：2，自引：1，他引：1
根据层状结构土壤在积水入渗过程中存在发生指流的现象,该文针对黄土地区"垆盖砂"的土壤条件,在室内以西安黄土为主体,对6种不同粒径的砂质双层结构土壤进行积水入渗试验,以观测研究发生指流的现象、机理与条件.研究表明:决定砂质双层结构能否发生指流现象的重要因素,一是入渗水流进入砂层后的稳渗率;二是表征砂层物理特性的饱和导水率;并以二者的比值做为判断发生指流现象的一个重要量化指标.根据试验分析,可将该比值＜0.02作为砂层发生指流现象的临界值.该指标也表明,当进入砂层的稳渗率小于砂层饱和导水率1/50时,即可发生明显的指流现象. 相似文献
14.
后掠式叶片轴流泵固液两相流数值模拟与优化 总被引：5，自引：5，他引：0
针对轴流叶轮在污水固液两相流介质中的磨损问题,该文设计了不同后掠式叶轮结构方案进行优化设计,分别对后掠角度为40°、65°、90°的后掠叶片和原型叶片进行固液两相流数值模拟和试验对比,并分析了不同后掠方案叶轮内固体颗粒的分布特性。数值模拟结果表明,随着后掠角度的增加,叶片压力面固相体积分数会逐渐减少,而叶片吸力面上固相体积分数会先增加后减小,叶轮内固相的径向流动越明显并且叶片后掠角度越大,固相就越难与叶片压力面接触,而越易与叶片吸力面接触;颗粒直径越大,后掠叶片压力面上固相体积分数越大,而叶片吸力面进口边靠近轮毂处的固相体积分数增加;颗粒浓度越大,后掠叶片压力面上固相体积分数减少,叶片吸力面上固相体积分数增加。当优化后的后掠叶片角为90°时,该叶片结构优化了固体颗粒的分布,可大幅降低叶片轮缘处的磨损,提高了轴流叶轮在污水介质中的使用寿命和运行可靠性。 相似文献
15.
不同雨强条件下坡度对坡地产汇流及溶质运移的影响 总被引：6，自引：2，他引：4
为了分析坡度对坡面产汇流和溶质运移的影响,以室内土槽为平台,采用人工模拟降雨实验,研究了坡度为5°,10°和15°,雨强为30,60和120 mm/h条件下植被坡地的入渗总量、坡面流流速、地面径流以及地面径流中Br-,NH4+和NO3-的浓度变化.结果表明,在其它影响因素相同的情况下,随着坡度的增大,坡面平均流速增大,地面径流总量增加,入渗总量减少、地面径流初始产流时间和径流终止时间均呈减小趋势,地面径流中Br-浓度变化不大,变化曲线几乎重合,NH4+浓度总体上呈递减趋势,且随着降雨强度的增大,这种递减趋势越显著,NO3-的规律性不明显.用幂函数关系可较好地拟合出坡面平均流速与坡度的关系. 相似文献
16.
基于薄层水流中的热传递过程，提出测量水流流速的示踪方法，并设计对应的测量系统。在室内试验坡面上，设计不同试验工况(坡度为5°,10°,20°,流量为2,5,8 L/min),以盐示踪法为对照，研究热示踪测量薄层水流流速的可行性及其影响因素。结果表明，测量系统能准确地测得热示踪剂的运移过程；热与盐2种示踪剂测得流速范围为0.408～1.522 m/s,线性拟合斜率为1.006,R2为0.993,表明两者具有显著的线性关系，热示踪法具有较高的可靠性；由于物理属性差异，部分水力工况下示踪剂的释放方式对盐和热的测量结果影响显著，表明此时2种示踪剂测量流速的代表性不同；可采用盐与热联合示踪的方法，取二者测量结果的均值作为薄层水流的平均流速，以提高测量结果的代表性。研究结果可为复杂下垫面、盐渍化和禁用化学成分等特殊坡面上薄层水流流速的准确测量提供新方法和理论参考。薄层水流流速的准确测量对地表水文和土壤侵蚀领域的研究具有重要意义。 相似文献
17.
腾格里沙漠沙坡头地区旱季沙层含水量 总被引：2，自引：0，他引：2
[目的]研究腾格里沙漠沙坡头地区旱季沙层含水量、水分来源、水分存在形式、水分平衡等问题,为沙漠地区水分合理利用、沙漠化防治、沙地改良以及沙地农业生产提供科学依据。[方法]利用轻型人力钻打孔取样,进行水分测定。[结果]腾格里沙漠沙坡头地区旱季沙层平均含水量为1%~3%,一般具有分为3层的特点;沙层含水量存在明显的空间差异,洼地平均含水量最大,平坦高地和半固定沙丘中部含水量较低,流动沙丘中上部含水量最低;旱季时期沙层水分以薄膜水形式存在;研究区旱季沙层水分仍为正平衡,主要是由沙层的高入渗率和受蒸发影响深度小决定的;研究区有植被发育之处,在根系的吸水作用下沙层剖面中下部的含水量比无植被的剖面含水量低。[结论]研究区旱季沙层含水量低,空间差异较大,沙层水分仍保持正平衡状态。 相似文献
18.
旋转式喷头空间流道设计及低压水力性能试验 总被引：1，自引：1，他引：0
喷头在低压工况下存在均匀性较差、射程变短及工作不稳定等问题。为了扩宽喷头的工作压力范围,该研究设计了旋转式喷头空间流道结构。以空间流道仰角、中间截面偏置角、出口截面偏置角为因素,以喷头空间流道出口平均速度和旋转驱动力为指标,采用CFD数值模拟正交设计,分析了空间流道结构参数对喷头水力性能的影响,并对旋转式喷头与相同规格的NelsonR33喷头在不同压力工况下进行水力性能对比试验。结果表明：空间流道各参数对喷头出口平均速度影响顺序依次为：空间流道仰角、中间截面偏置角、出口截面偏置角;对喷头旋转驱动力的影响顺序依次为：中间截面偏置角、空间流道仰角、出口截面偏置角。空间流道结构最佳参数组合为：出口截面偏置角为3°、中间截面偏置角为3.5°和空间流道仰角为30°。在工作压力为150及200 kPa下,旋转式喷头的水量分布更为均匀,组合均匀性系数更高。为扩宽喷头工作压力范围以及提高喷头低压下水力性能提供依据。 相似文献
19.
湿沙的风蚀起动风速实验研究 总被引：16，自引：1，他引：16
在土壤风蚀研究中 ,Bagnold建立的干沙子的起动风速与沙粒粒径关系的表达式已被广泛接受。然而 ,沙子含水率是影响沙粒起动风速的重要因子 ,因为沙子在湿润状态下 ,水分子与沙粒颗粒之间的拉张力增加了颗粒间的内聚力。通过风洞模拟实验研究了各种粒径的沙子在湿润状态下的起动风速。实验结果表明 ,湿沙的起动摩阻速度与干沙的起动摩阻速度之比——相对起动摩阻速度能更好地反映沙子含水率对起动风速的影响。建立了湿沙子的起动风速与沙粒粒径和沙子含水率的关系式 相似文献
20.
复式耕整机耕深与耕宽稳定性分析与试验 总被引：1，自引：4，他引：1
针对设计的复式耕整机出现的耕作稳定性问题,结合复式耕整机整体结构及工作原理,从牵引、水平面内受力、机器振动3个角度分析影响耕作稳定性因素,确定影响耕作稳定性关键因素为牵引角、犁体配置斜角、旋耕刀升角。以牵引角、犁体配置斜角、旋耕刀升角为试验因素,以工况耕深稳定系数和工况耕宽稳定系数为性能评价指标进行二次正交旋转组合试验。正交试验结果表明:试验因素对评价指标影响程度从高到低皆为:犁体配置斜角、牵引角、旋耕升角,当各影响因素分别取值为17.3°、27.8°、72.6°时,工况耕深稳定系数和工况耕宽稳定系数分别为91.8%、93.4%。以影响因素最优参数组合为基础进行的验证试验结果表明:试验后工况耕深稳定系数和工况耕宽稳定系数为91.5%、93.1%,与软件分析结果基本一致,且其他耕作指标均达到农艺要求。该研究可为复式整地机械的耕作稳定性研究提供技术参考。 相似文献