Predicting river width,depth and velocity at ungauged sites in England and Wales using multilevel models

Using a dataset of gauged river discharges taken from sites in England and Wales, linear multilevel models (also known as mixed effects models) were applied to quantify the variability in discharge and the discharge‐hydraulic geometry relationships across three nested spatial scales. A jackknifing procedure was used to test the ability of the multilevel models to predict hydraulic geometry, and therefore width, mean depth and mean velocity, at ungauged stations. These models provide a framework for making predictions of hydraulic geometry parameters, with associated levels of uncertainty, using different levels of data availability. Results indicate that as one travels downstream along a river there is greater variability in hydraulic geometry than is the case between rivers of similar sizes. This indicates that hydraulic geometry (and therefore hydrology) is driven by catchment area, to a greater extent than by natural geomorphological variations in the streamwise direction at the mesoscale, but these geomorphological variations can still have a major impact on channel structure. Copyright © 2008 John Wiley & Sons, Ltd.     

Impacts of climate change and hydraulic structures on runoff and sediment discharge in the middle Yellow River

Due to climate change and its aggravation by human activities (e.g. hydraulic structures) over the past several decades, the hydrological conditions in the middle Yellow River have markedly changed, leading to a sharp decrease in runoff and sediment discharge. This paper focused on the impacts of climate change and hydraulic structures on runoff and sediment discharge, and the study area was located in the 3246 km² Huangfuchuan (HFC) River basin. Changes in annual runoff and sediment discharge were initially analysed by using the Mann–Kendall trend test and Pettitt change point test methods. Subsequently, periods of natural and disturbed states were defined. The results showed that both the annual runoff and sediment discharge presented statistically significant decreasing trends. However, compared with the less remarkable decline in annual rainfall, it was inferred that hydraulic structures might be another important cause for the sharp decrease in runoff and sediment discharge in this region. Consequently, sediment‐trapping dams (STDs, a type of large‐sized check dam used to prevent sediment from entering the Yellow River main stem) were considered in this study. Through evaluating the impacts of the variation in rainfall patterns (i.e. amount and intensity) and the STD construction, a positive correlation between rainfall intensity and current STD construction was found. This paper revealed that future soil and water conservation measures should focus on areas with higher average annual rainfall and more rainstorm hours. Copyright © 2015 John Wiley & Sons, Ltd.     

不同水力压裂顺序下煤层气井组应力干扰效应研究—以沁水盆地柿庄南区块为例

煤层气井常采用井网布置方式进行开发，不同的水力压裂顺序引起不同的应力干扰效应。为了查明不同水力压裂顺序下煤层气井间应力干扰效应，本文以沁水盆地柿庄南区块3组煤层气井网15口井为研究对象，应用ABAQUS 有限元模拟软件，模拟了煤层气井网中3种水力压裂顺序（先周围后中心、对角、先中心后周围）的应力分布特征及干扰效应，提出了相应的水力压裂顺序建议。结果表明：当施工排量为6.00 8.00 m3/min，液量为430.00 580.00 m3时，（1）先周围后中心、对角、先中心后周围压裂时，距中心井、对角线井、周围井不同距离，依次分为应力释放区、集中区和原始应力区。先周围后中心压裂时，中心井三区范围依次为≤15.00 m、15.00 140.00 m、＞140.00 m。对角压裂时，对角线井三区范围依次为≤60.00 m、60.00 150.00 m、＞150.00 m。先中间压裂时，周围井三区范围依次为≤60.00 m、60.00 144.00 m、＞144.00 m。（2）煤层气井网采用四点法布置，井间距超过300.00 m，可有效避免煤层气井之间的应力干扰。降低煤层气井压裂时的施工难度。     

锦屏二级水电站深埋引水隧洞群允许最小间距研究

锦屏二级水电站引水隧洞群最大的特点是埋藏深、地应力高、外水压力大。这一极端复杂的赋存环境给4条引水隧洞的中心线间距确定带来了很大的挑战。为此,首先通过流-固耦合的数值计算方法,对洞间岩体塑性区贯通与否、隧洞壁面关键点位移曲线拐点、收敛位移是否超出相关规范共3种判别标准进行分析后,得到引水隧洞群最小理论间距值为50 m。进而在类比与引水隧洞本身相邻的辅助洞和国内外几个典型深埋隧洞的洞径、埋深和间距的基础上,综合确定深埋引水隧洞群的最小允许中心线间距为52 m,为当前设计采用60 m洞间距提供了有力的理论支持。     

斜向波浪对半圆型防波堤作用的实验研究

通过正向与斜向波浪对半圆型防波堤(不开孔出水堤)的实验研究,给出了其水力特性及单位堤长所受的无因次水平波浪力、竖向波浪力和波浪浮托力随各主要影响因素的变化规律,特别指出了斜向波浪力可大于正向波浪力及水平波浪力中波谷作用大于波峰作用发生的条件。     

API圆螺纹连接上卸扣过程中温度场分布的实验研究

粘扣是油套管接头的主要失效形式之一,直接影响油套管的密封性能和连接强度。以J55Φ73.03mm×5.51mmAPI不加厚圆螺纹油管为实验样本,利用TH7102型热像仪对在不同上卸扣速度和扭矩作用下螺纹连接部位温度场的分布进行了动态测试。根据摩擦磨损理论对影响螺纹连接部位温度场的分布和粘扣失效的主要因素进行了研究和总结,实验表明螺纹连接部位温度场分布不均匀,当接箍螺纹外表面温度超过60℃时,油管啮合螺纹一般会出现粘扣失效现象。     

温度和有效应力对砂岩渗透性影响的试验研究

为探讨温度和有效应力对渗透性的影响,在不同温度水平和不同有效应力水平下进行了砂岩的渗透率试验。根据试验结果,初步分析了温度和有效应力对砂岩渗透率及其水力传导系数的影响。试验结果表明,砂岩的渗透率及其水力传导系数都是温度和有效应力的函数:在温度一定的条件下,砂岩的渗透率和水力传导系数均随有效应力的增加而呈负指数规律减小;在有效应力一定的条件下,砂岩的渗透率随温度的升高而减小,但水力传导系数与温度之间的关系函数并非单调函数。因此,在工程实践中不考虑温度和有效应力对岩石 (体)渗透性的影响是不合适的。      

三峡工程永久船闸开挖前后实测应力分布特征

根据实测资料研究了三峡工程区地应力分布特征。三峡工程区浅部和深部的构造应力状态有明显差异,最大水平主应力在浅部表现为NEE向,而深部则表现为NW向,船闸区浅部最大水平主应力方向为NNE向。对永久船闸开挖前后应力分布进行了测量研究。永久船闸开挖前后应力状态有显著的重新调整分布,东西向应力在边坡岩体不同层位（不同高程）有增有减,应力释放量较小;而南北向应力在边坡岩体中上部均减小,应力释放量较大,开挖后坡角部位有应力集中现象。受开挖影响,最大水平主应力方向由开挖前的近NE向发生顺时针方向偏转,变为近东西向。     

含裂隙水脆性材料单轴压缩CT分析

采用CT机配套的自制专用注水加载装置,对含裂隙水压的单裂纹试件进行了单轴压缩破坏的CT（Computerized Tomography）实时试验,对试件被压密→新损伤区产生→裂纹扩展的全过程进行了模拟,得到了各阶段清晰的CT图象及CT数。通过分析,提出了类节理岩体脆性材料的损伤演化率和损伤门槛值概念,并对水压的影响进行了探讨,从细观和三维上初步掌握了类节理岩体脆性材料的损伤演化特性。     

悬挂式帷幕防渗作用的有限元模拟

建立了二维渗流方程的有限元表达式,比较了某工程实例防渗帷幕建造前、后渗流速度和出溢处水力坡降的变化情况。计算表明,除帷幕底部小范围内渗流速度有所上升外,其它地区的渗流速度及下游出溢处的水力梯度均显著降低。在运用悬挂式防渗帷幕时,要注意提高帷幕底部的抗冲刷能力。