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高拱坝表孔宽尾墩收缩射流水舌的扩散特性与其出口流速分布密切相关,为了求得收缩射流的水力特性,应用RNGk ε双方程湍流模型对高拱坝表孔不同体型及过流量条件下可能出现的降水曲线流态、急流冲击波流态、水跃壅水流态、缓流流态4种流态进行了数值模拟计算,水流自由表面的模拟采用VOF法,得到了溢流水面及流速分布。结果表明,无论在何种流态下,计算所得的水面曲线均与物理模型试验值吻合良好,所得的出口流速分布结构也验证了高拱坝宽尾墩收缩射流水舌不同流态下分散的机理。 相似文献
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水下高速流体射流冲沙是清淤作业的必要手段，如何有效提高射流造浆效率对河(航)道清淤和水库库容修复等工程具有重要价值。采用射流冲刷底泥起动输移试验与高速射流喷头流场数值模拟手段，研究不同水力要素下射流对底床的冲刷效果，分析射流流速分布及衰减规律，探明高速射流底泥冲刷机理。研究结果表明：射流造浆过程中存在最优冲沙距离，使得造浆速率及浑水体浓度增长速度最快；射流中线剖面上横断面射流时均速度分布、最大速度衰减规律具有相似性，不同射流流速下射流初步发展区的射流速度半宽增长率相同；射流冲刷效率与射流发展中的阻力损失和到达床面时的能量损失直接相关，确定合理的射流喷头布置高度有利于提高造浆效率。研究成果对射流造浆能力与速率的提升乃至清淤设备的升级改造提供了有力支撑。 相似文献
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利用声学多普勒流速仪(Acoustic Doppler Velocimetry,ADV)自动测速系统和平面激光诱导荧光(Plane Laser Induced Florescence,PLIF)系统对同向圆射流的速度场和浓度场进行了系统的研究,并与前人的工作进行了比较和讨论。时均特性测量结果表明,射流主体段下游各断面的速度和浓度横向分布是自相似的,且近似可用高斯分布来表示;随着射流向下游传播,射流中心流速逐渐衰减,在强射流区和弱射流区遵循不同的规律;紊动特性测量结果表明,下游各断面的紊动强度横向分布是自相似的。 相似文献
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液动锤射流元件喷嘴临界流速预测与验证 总被引：2，自引：0，他引：2
应用CFD动态分析技术,对SC71B型液动锤内部流场进行了仿真分析,结果表明,其射流元件临界流速为20.305～22.565 m/s,大大低于凭经验预测的40 m/s。为检验这一理论预测结果,对SC71B型液动锤射流元件临界流速进行了实验测定,为21.83 m/s,表明理论预测结果与实测结果高度吻合,证明了基于CFD动态分析的液动锤射流元件临界流速理论预测方法的可行性;同时通过理论分析和实测获得了至今为止液动锤射流元件临界流速的最低值,可为研制油气钻井用低速射流元件驱动控制的液动锤提供重要参考。 相似文献
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为进一步揭示沙波水流运动特性及提高沙波迎流面流速计算精度,采用两种概化模型,通过小水深沙波水槽试验,运用声学多普勒流速仪,对沙波沿程及垂线流速分布进行了测量。基于乐培九次生流理论公式,结合沙波水流特性,假定次生流在沙波迎流面上处于一个不断发展演变的过程,提出了发展函数和修正函数,得到了适用于沙波迎流面的流速垂线分布公式。研究结果表明:相对水深越小,沙波地形对迎流面水流作用越显著,使得上部流速减小、近底流速增大,且越靠近波峰这种现象越明显;建立的沙波流速公式与实测值吻合较好,能够准确地反映出迎流面流速变化规律。 相似文献
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青藏高原隆起及海陆分布变化对亚洲大陆气候的影响 总被引：19，自引：0，他引：19
我们利用经过改进的NCARCCMI动力气候模式并综合出一个40～50MaB．P．的下垫面情景,进行了海陆分布和SST分布由古代到现代、青藏高原由隆起初期、隆起到现代高原一半和现代高度共5个情景的数值试验。结果表明,从古代到现代,模拟的中国气候是变冷的并且东部变湿而西北部变干。青藏高原的隆起是模拟出来的中国变冷的主要原因。青藏高原从隆起初期到隆起到现代高度一半时期中国地区降水是增加的,但当继续隆起后降水却有所减少,尤其是中国西北地区。本文还对海陆分布和SST分布变化以及青藏高原隆起对手风环流的影响作了分析。 相似文献
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以k-ε紊流模型为基础,针对浅水环境垂向射流的水面会有明显突起情况,采用VOF(Volume of Fluid)方法追踪自由面,建立了适合浅水环境垂向平面紊动射流的二维数学模型.对不同入射速度、水深、入射口宽度组合进行了大量的数值模拟实验,对整个流场的分布作了分析,发现自由面的分布特点和速度矢量场的分布特点相对应;中轴线附近的自由面隆起具有自相似性,文中给出了拟合表达式;由于水面的阻滞,中轴线上垂向速度的衰减较自由射流快,衰减规律随水深和射流宽度而异. 相似文献
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《China Geology》2023,6(1):61-69
To study the quantitative relationship between surface sedimentary diatoms and water depth, 67 surface samples were collected for diatom analysis on eight profiles with water depth variation from the muddy intertidal zone to the shallow sea area in North-Central Bohai Bay, China. The results showed that the distribution of diatoms changed significantly in response to the change in water depth. Furthermore, the quantitative relationship between the distribution of dominant diatom species, their assemblages, and the water depth was established. The water depth optima for seven dominant species such as Cyclotella striata/stylorum, Paralia sulcata, and Coscinodiscus perforatus and the water depth indication range of seven diatom assemblages were obtained in the study area above the water depth (elevation) of ?10 m. The quantitative relationship between surface sedimentary diatoms and water depth provides a proxy index for diatom-paleo-water depth reconstruction in the strata in Bohai Bay, China.©2023 China Geology Editorial Office. 相似文献
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藏北高原D105点土壤冻融状况与温湿特征分析 总被引：6，自引：3，他引：3
利用CAMP/Tibet在藏北高原D105点所观测的2002年1月1日-2005年12月31日土壤温度、含水量资料, 分析了该点的土壤温、湿度变化及其冻融特征. 结果表明: D105点40 cm深度以上土壤温度日变化明显, 随着深度增加, 土壤温度日变化相位明显滞后. 各层土壤温度月最高值出现在8-9月, 月最低值都出现在1-2月; 年际气候的差异至少可以反映到185 cm深处的土壤. 土壤冻结和消融都是由表层开始, 土壤随深度增加冻结快, 消融则慢. 冻结期间, 土壤温度分布上部低, 下部高; 消融期间, 则分布相反. 60 cm深度以上的土壤含水量在消融期有显著的波动, 表明60 cm深度以上的土壤与大气之间的水热交换比较频繁. 土壤温度的日变化和平均温度对土壤的冻融过程有较大的影响; 土壤含水量的多少会极大的影响土壤的冻融过程、土壤热量的分布状况以及地表能量的分配. 因此水(湿度)热(温度)相互耦合影响着土壤的冻融过程. 相似文献
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A new approach is proposed to analyze the surface flow and subsurface flow passing over a pervious ground under a uniform rainfall excess. The flow field is divided into two regions that are called water layer and soil layer. To figure out the hydraulic behavior of overland flow on an inclined plane under a rainfall event, the simplified Navier–Stokes equations are employed for the surface water flow, and the flow inside the soil layer is porous media flow, which is governed by Biot's (1956, 1962) theory of poroelasticity. The velocity distribution of overland flow is nonzero at the ground surface. The relation between water depth and slope length was developed first. The profile of surface water flow was then found backwards from the downstream end of the flow section by the Runge–Kutta method. After that, the flow velocity and flow discharge of each layer could also be obtained via the water depth. Finally, the variation of fluid shear stress inside the soil layer is also discussed. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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倒虹吸是输水工程中常见的水工建筑物,研究倒虹吸进口上游的垂向流速分布是明晰其水力学性能的重要内容之一。以南水北调中线工程典型的唐河倒虹吸为研究对象,通过水力学概化模型试验,运用声学多普勒流速仪,实测不同水深和流量组合工况下倒虹吸进口上游的垂向流速分布。试验结果表明,受倒虹吸进口结构的影响,上游垂向流速分布呈现出明显的顶部流速降低和底部流速增加的现象,且淹没度越大、距离倒虹吸进口越近,上述趋势越显著;采用明渠对数型流速分布描述上述垂向流速分布时,其计算误差呈抛物线型分布,采用指数项修正后,新的修正公式可用于计算倒虹吸进口上游垂向流速分布。 相似文献
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Filippo Bandini Alejandro Lopez-Tamayo Gonzalo Merediz-Alonso Daniel Olesen Jakob Jakobsen Sheng Wang Monica Garcia Peter Bauer-Gottwein 《Hydrogeology Journal》2018,26(7):2213-2228
Observations of water surface elevation (WSE) and bathymetry of the lagoons and cenotes of the Yucatán Peninsula (YP) in southeast Mexico are of hydrogeological interest. Observations of WSE (orthometric water height above mean sea level, amsl) are required to inform hydrological models, to estimate hydraulic gradients and groundwater flow directions. Measurements of bathymetry and water depth (elevation of the water surface above the bed of the water body) improve current knowledge on how lagoons and cenotes connect through the complicated submerged cave systems and the diffuse flow in the rock matrix. A novel approach is described that uses unmanned aerial vehicles (UAVs) to monitor WSE and bathymetry of the inland water bodies on the YP. UAV-borne WSE observations were retrieved using a radar and a global navigation satellite system on-board a multi-copter platform. Water depth was measured using a tethered floating sonar controlled by the UAV. This sonar provides depth measurements also in deep and turbid water. Bathymetry (wet-bed elevation amsl) can be computed by subtracting water depth from WSE. Accuracy of the WSE measurements is better than 5–7 cm and accuracy of the water depth measurements is estimated to be ~3.8% of the actual water depth. The technology provided accurate measurements of WSE and bathymetry in both wetlands (lagoons) and cenotes. UAV-borne technology is shown to be a more flexible and lower cost alternative to manned aircrafts. UAVs allow monitoring of remote areas located in the jungle of the YP, which are difficult to access by human operators. 相似文献
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The water column flow velocity of 36 river sections in the river reach between Hankou (Wuhan) and Wuxue of the middle-lower
Changjiang River. Their cross sectional distribution patterns in relation to the river channel morphologies were examined
by using ship-mounted ADCP (Acoustic Doppler Current Profiler) instrument. The results indicate four (I-VI) types of river
channel morphology associated flow patterns: I—laterally deepening riverbed topographic pattern; II—symmetrical to asymmetrical
riverbed topographic pattern; III—relative flat riverbed topographic pattern, and IV—sandbar supported riverbed topographic
pattern. All these correspond to the different patterns of flow velocity distribution. The maximum flow velocity is usually
related to the deeper water depth, but irregular water column distribution of flow current velocity results often from the
vortices’ current associated with river knots. Deeper river water depth is usually identified in the river reach located slightly
downstream to the river knot, where faster flow velocity occurs. Downward change in flow velocity fits semi-log law, showing
an exponential decreasing flow current with the maximum flow velocity near the water surface. However, in the river reach
near the river knots, the water column distribution of flow current velocity does not fit the semi-log law, showing the irregular
flow current pattern. This study, in context of river catchment management, highlights the controls of riverbed morphology
to the flow current structure, which will shed light on the post study of Three Gorges damming in 2009. 相似文献
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确定起伏地表的空间位置是叠前深度域起伏地表偏移成像和速度建模成功的关键。浮动基准面本身就是一个起伏高程面,此外它还定义了CMP道集在其上进行基准面校正的规则。本文分析了确定浮动基准面的常用方法并明确了其在一般情况下所具有的物理意义,指出了即便是基于平均静校正法得到的浮动基准面,在一定条件下也可以直接用于起伏地表叠前深度域偏移成像和速度建模。此外,还讨论了在叠前深度域速度建模中错误地使用浮动基准面数据可能导致深度域成像结果中层位深度的移位和畸变的问题。 相似文献
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Analysis of geological structure and anthropological factors affecting arsenic distribution in the Lahore aquifer,Pakistan 总被引：1，自引：0，他引：1
Akhtar Malik Muhammad Tang Zhonghua Zakari Sissou Bahaa Mohamadi Muhsan Ehsan 《Hydrogeology Journal》2016,24(7):1891-1904
This study investigated the potential factors affecting arsenic concentration in the groundwater system of Lahore, Pakistan. The effects of several factors such as population density (PD), pumping rate (PR), impermeable land use (LU), surface elevation (SE), and water-table elevation (WL) on arsenic concentration were studied in 101 union councils of Lahore. Forty single and multi-factor models were established using geographic information system (GIS) techniques to develop an arsenic contamination map and to investigate the most effective combinations among factors. Additionally, statistical tests were used to evaluate arsenic concentration between classes of the same single factor. The arsenic concentration in the Lahore aquifer varied from 0.001 to 0.143 mg L?1. The highest arsenic concentrations were detected in the Walled City and the town of Shahdara. Among the 40 raster models, groundwater arsenic concentration showed the best matching frequency with single-factor models for PD (50.70 %) and SE (47 %). Thus, PD and SE were used to develop an arsenic distribution raster map, and they were also used to study the effect of aquifer depth on arsenic concentration. PD was found to have hidden latent variables such as PR and LU. The shallow aquifer depth was negatively correlated with arsenic concentration (r?=??0.23) and positively with PR (r?=?0.15). Therefore, when there was high PR in wells with smaller aquifer depth, the arsenic concentration was high. The existing water treatment and alternative water resources are good options, which should be developed to deal with Lahore wells contaminated with arsenic at high concentrations. 相似文献
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川北诺水河景区溶洞分布特征及影响因素探析 总被引：1，自引：0，他引：1
选取诺水河景区48个典型溶洞为研究对象,参阅本地区区域地质图和水文地质图,在对洞穴发育高度、层位、构造位置、发育方向、节理走向,以及地下水和地表水系部分特征进行详细调查前提下,利用最邻近距离法、节理分析法、GIS缓冲区法等方法,对溶洞群的洞口高程分布、洞穴发育方向、空间分布格局、洞穴与构造及地表水系关系等分布特征进行了分析,并对溶洞群分布特征的影响因素进行了探析。结果表明,① 洞口高程分布在空间上具有层级性,在时间上具有阶段性,研究区洞穴主要沿北西西、北东东向发育,并且越接近地表河流洞穴出口分布越多,洞穴群呈凝聚态分布,越接近构造转折端洞穴分布越密集;② 影响洞穴分布的主要因素包括：地层和碳酸盐岩岩性差异,构造派生节理发育状况以及多期次构造变形和构造隆升,地下水的类型和作用,地表水系对地下水系的影响,以及北亚热带季风气候条件下地形的影响等。 相似文献