Developing empirical formulas for assessing the scour of vertical and inclined piers

Abstract

Because scour is one of the main reasons for bridge failure, this study focuses on accurately predicting the maximum scour depth around different vertical and inclined piers. Scouring is an issue of concern in the bridge design process, as most existing equations for predicting local scour near bridge piers suffer from over- or underprediction issues, resulting in higher foundation costs or bridge failure and inaccurate predictions of the scour around piers. The dimensionless maximum scour depths (y_s/D) of vertical and inclined piers were investigated for seven pier shapes with different L/D ratios and four inclination angles (θ) under shallow flow conditions. The inclined pier configuration reduced the y_s/D of the piers. The maximum y_s/D was observed for a rectangular pier with an L/D of 4.5 in both vertical and inclined configurations (θ of 10, 15 and 21°, respectively). The y_s/D was significantly decreased by increasing the angle of the pier from 10 to 30°. The y_s/D of the inclined rectangular piers decreased as θ decreased from 30 to 10° and the L/D ratio increased from 1 to 4.5. The best y_s/D results were obtained for inclined rectangular piers at a θ value of 30° and an L/D ratio of 7.5 compared to other shapes and inclination angles. New equations were developed to predict the local scour depth for circular, square and rectangular bridge piers. The equations yielded excellent results for predicting the maximum clear water scour depth around vertical and inclined piers with inclination angles of 10, 15, 21 and 30°, respectively.     

利用波能平衡方程研究波浪折射——绕射的数学模型及数值模拟

波能平衡方程是研究风浪要素及波能传播问题的很有效的方法，计算较为简单，在海洋学及海岸动力学中得到广泛的应用。本文采用考虑波能侧向传递机制和耗损制约的波能平衡方程组作为研究波浪折射——绕射变形的控制方程。对数学模型用差分法进行了数值模拟，并用两个例题进行了验证     

玲珑金矿田东风矿区深部构造叠加晕研究

东风矿床主要赋存于坡头青主断裂下盘的蚀变带中。在野外地质工作的基础上,运用数学地质分析方法,系统研究了构造叠加晕的特征,建立了构造叠加晕的理想模式。矿区构造叠加晕分析结果显示,金矿成矿具有多期、多阶段的特征,通过研究该区原生晕轴向分带特征,识别出不同成矿阶段所形成的矿体(晕)在空间上具有前尾晕共存的叠加结构,该结构是深部盲矿预测的重要依据。     

利用ArcGIS构建地形图分幅空间数据库

本文利用ArcGIS绑定的脚本语言Python和AML及其空间分析功能,设计了简单可行的算法,并编制了相应的程序,构建了国家基本比例尺地形图分幅空间数据库。首先生成图幅分幅格网,以及对应的网格标识点、图幅编号文件,将标识点与图幅编号文件关联后再与图幅网格叠加即可。该方法充分利用了GIS的空间叠加功能,仅用了极少量的程序代码,没有编程经验的人员可以比较容易掌握,对于各行业应用领域的工作者有很大帮助。     

Cs+水合结构密度泛函理论计算研究

本文用密度泛函理论在WB97XD/gen def2-tzvp基组水平上对[Cs(H2O) n] +(n=1-15)水合团簇结构的振动光谱进行了研究。研究表明,随着水分子数的增加,在气相和液相中,8配位的Cs+ 水合团簇是最稳定的;随着水分子数的增加,Cs-O键长增大,Cs+上的电荷密度减小。当水分子数大于11时,Cs-O键长和Cs+上的电荷密度变化很小。O(H2O)-O(H2O)距离、∠O(H2O)-Cs-O(H2O)°统计结果表明,15个水分子足以形成Cs+的近似饱和水合层。此外,红外光谱显示[Cs(H2O)n]+水合团簇中O-H伸缩振动随着水分子数的增加而发生变化,由此可以作为鉴别水合层位置的一种参考方法。     

基于水化学数据的矿山涌水水源识别:主成分分析与残差分析

涌水是矿山安全生产的重要威胁之一,掌握涌水的水源是预防这类灾害的重要依据。基于多期次的水化学监测数据,提出了利用主成分分析(PCA)和残差分析来识别涌水的水源数量和水源类型。主成分分析能够充分提取高维数据的结构信息,消除变量冗余。残差分析利用主成分分析结果,提取不同的主成分个数重构离子浓度,得出重构离子浓度和原始离子浓度之间的残差,利用残差的结构性信息来判断可能的涌水水源数量和水源类型。结果表明:随保留主成分个数的增加,重构离子浓度的精度越高,离子残差的结构性得到消除且表现出随机性。在实例应用中,通过利用5个主成分重构离子浓度消除了所有主要离子残差结构性,保证了信息的最大程度提取,因此,确定研究矿山涌水水源数量为5个;同时,利用每个主成分对残差结构性的影响程度及离子相关性分析,确定了这5个水源类型为海水、第四系孔隙水、富钙基岩水、富镁基岩水和淡水。     

波浪要素对水平圆柱杆件水动力系数影响研究

通过试验研究了波浪要素对水平固定圆柱杆件水动力系数的影响。试验利用垂直杠杆原理,提取了杆件在波浪下的水平受力历时曲线,基于改造的莫里森方程,计算了不同波浪要素下的水动力系数C_D和C_M取值。定义分析了新的波高参数KH,周期参数KT和雷诺数Re对水动力系数的影响。研究表明,整体拟合法与四点拟合法获得的水动力系数在数值上差异不大。KH、KT及Re均对水动力系数的取值有较显著影响:1)随着波高KH的增大,C_D、C_M整体呈幂指数衰减,且C_M的衰减更为迅速;2)随着波周期KT的增大,C_D、C_M整体亦呈衰减趋势;3)相同波高条件下,C_M随Re数增大而增大,而C_D值相对稳定。最后给出了波浪条件下水动力系数C_D和C_M的经验计算公式。     

短基线集形变模型反演的正则化解算方法

针对短基线集形变模型反演中法方程系数矩阵呈病态的问题,提出一种正则化稳健解算方法。该方法基于Tikhonov正则化理论,将形变速率求解问题转化为极小化问题,根据L-曲线法选取正则化参数,考虑最小二乘残差各个分量间的关系选取正则化矩阵,实现短基线集形变模型反演的稳健解算。分别采用LS法、岭估计法和Tikhonov正则化法对覆盖北京地区的29景ENVISAT ASAR数据进行处理,反演出研究区沉降速率图。通过对代表不同沉降情况的21个点的均方误差值和时间相干值、整个研究区的均方误差图等的对比分析,表明本文提出的短基线集形变模型反演的正则化稳健解算方法可获取更可靠的形变监测结果。     

Large-eddy simulation of the flow past a circular cylinder at sub- to super-critical Reynolds numbers

Large-eddy simulation of turbulent flow past a circular cylinder at sub- to super-critical Reynolds numbers is performed using a high-fidelity orthogonal curvilinear grid solver. Verification studies investigate the effects of grid resolution, aspect ratio and convection scheme. Monotonic convergence is achieved in grid convergence studies. Validation studies use all available experimental benchmark data. Although the grids are relatively large and fine enough for sufficiently resolved turbulence near the cylinder, the grid uncertainties are large indicating the need for even finer grids. Large aspect ratio is required for sub-critical Reynolds number cases, whereas small aspect ratio is sufficient for critical and super-critical Reynolds number cases. All the experimental trends were predicted with reasonable accuracy, in consideration the large facility bias, age of most of the data, and differences between experimental and computational setup in particular free stream turbulence and roughness. The largest errors were for under prediction of turbulence separation.     

Soil moisture estimation using ERS 2 SAR data: a case study in the Solani River catchment/Estimation de l’humidité du sol grâce à des données ERS-2 SAR: étude de cas dans le bassin de la rivière Solani

Abstract

Abstract The information regarding spatial and temporal variation of soil moisture in a catchment is of utmost importance in hydrological, as well as many other studies. Point measurements from gravimetric and other methods for soil moisture determination are insufficient to understand the spatial behaviour of soil moisture in a region. Microwave remote sensing data from active sensors on board various satellites are increasingly being used to map spatial distribution of soil moisture within the 0–10 cm top surface. The northern part of India has a network of large rivers and canals and, therefore, spatial and temporal distribution of soil moisture in this region has a significant bearing on the hydrology of the region. In this paper, results on estimation of soil moisture from an ERS-2 SAR image in the catchment of the Solani River (a tributary to the River Ganga) in and around the town of Roorkee, India, have been presented. The radar backscatter coefficient for each pixel of the image has been modelled from the digital numbers of the SAR image. Gravimetric measurements have been made simultaneously during the satellite pass to determine the concurrent value of volumetric soil moisture at a large number of sample points within the satellite sweep area. The backscatter coefficient is found to vary from –30 dB to –42 dB for a variation in soil moisture from 30 to 75%. Regression analyses between volumetric soil moisture and both the digital numbers and backscatter coefficients were performed. Strong correlations between volumetric soil moisture and digital number were observed with R ² values of 0.84, 0.75 and 0.83 for bare soil, vegetative and combined surfaces, respectively. A similar trend was observed with the relationship between backscatter and volumetric soil moisture with R ² values of 0.60, 0.89 and 0.67 for bare soil, vegetative and combined surfaces, respectively. These results demonstrate the utilization of SAR data for estimation of spatial distribution of soil moisture in the region of the present study.