Laboratory study of combined wave overtopping and storm surge overflow of a levee

Combined wave overtopping and storm surge overflow of a levee with a trapezoidal cross section was studied in a two-dimensional laboratory wave/flow flume at a nominal prototype-to-model length scale of 25-to-1. The goal of this study was to develop design guidance in the aftermath of Hurricane Katrina. Time series of water depth at two locations on the levee crown and flow thickness at five locations on the landward-side slope were measured along with horizontal velocity near the landward edge of the crown. New equations are presented for average overtopping discharge, distribution of instantaneous discharge, and distribution of individual wave volumes. Equations are also given for mean flow thickness, RMS wave height, mean velocity, and velocity of the wave front down the landward-side slope.     

中国华南大陆及陆缘地带的大地构造基本格局

华南及陆缘地带主体由扬子块体和华南块体、南海盆地及琼南微块体和台湾岛活动带组成。在多期构造运动、多期岩浆活动和多种力系用下形成了该区浅部和深部独特的结构形式和深层过程。因此,该地区不论在岩相和地球内部圈层耦合,海陆耦合以及壳、幔、核深部物质与能量的交换和演化,地史进程和在东亚大陆动力学研究中均占有极为重要的地位。本文在纵观各地质大家学术观战和构造分类的基础上,基于对该区多年来的岩石圈深部结构、构造     

Scour and burial mechanics of conical frustums on a sandy bed under combined flow conditions

The scour and burial of conical frustums placed on a sandy bed under waves alone (WA) and combined flows (CF) conditions was investigated. The observations indicate that equilibrium burial depth is smaller than burial of other objects such as short cylinders laying on a sand bed under equivalent hydrodynamic conditions. Truncated cone offers less resistance to the flow field due to its more round shape when compared to a horizontally placed short cylinder characterized by sharp edges. A smaller disruption to the flow field translates to less turbulent intensity and to smaller sediment transport capacity of the flow around the object and less burial. The equilibrium burial depth shows a significantly weaker dependency on the Shields parameter than on the Keulegan-Carpenter number, contrary to the case of finite short cylinders. A new empirical predictor based on the relative strength of the wave to the wave plus current velocity, the Keulegan-Carpenter number, and the Shields parameter is proposed for estimating the equilibrium burial of truncated cones under combined flows. Both the Keulegan-Carpenter number and the Shields parameter determine the width of the scour hole around the cone. The former however, is the most dominant parameter influencing the length of the scour hole.     

Numerical simulation of a partially buried pipeline in a permeable seabed subject to combined oscillatory flow and steady current

Hydrodynamic forces exerting on a pipeline partially buried in a permeable seabed subjected to combined oscillatory flow and steady current are investigated numerically. Two-dimensional Reynolds-Averaged Navier-Stokes equations with a k−ω turbulent model closure are solved to simulate the flow around the pipeline. The Laplace equation is solved to calculate the pore pressure below the seabed with the simulated seabed hydrodynamic pressure as boundary conditions. The numerical model is validated against the experimental data of a fully exposed pipeline resting on a plane boundary under various flow conditions. Then the flow with different embedment depths, steady current ratios and KC numbers is simulated. The amplitude of seepage velocity is much smaller than the amplitude of free stream velocity as expected. The normalized Morison inertia, drag and lift coefficients based on the corresponding force coefficients of a fully exposed pipeline are investigated. The normalized Morison force coefficients reduce almost linearly with the increase of embedment depth and that the KC only has minor effect on the normalized Morison coefficients. It is also found that the permeable seabed condition causes a slight increase on the inline force and has a little effect on the lift force, compared with corresponding conditions in an impermeable bed.     

重磁力联合反演在研究复杂盆地基底构造中的应用

本文采用重磁力联合反演方法,计算了民和盆地基底深度和视磁化强度。针对该盆地特点,设计了等效和非均质重力反演模型,在约束条件下分块反演得到准确可靠的基底深度;用基底深度和航磁异常反演基底视磁化强度,根据岩石磁化率参数,判定基底岩性横向分布。该方法不仅能提供盆地基底构造形态,而且能提供基底岩性信息。     

地震触发研究中库仑应力随摩擦系数增加而增大的矛盾及其解决

近年来,通过计算库仑破裂应力变化研究地震触发及断层的相互作用,进而估计地震灾害已经成为国际上研究的热点.研究中,为考察库仑模型触发地震的效果,计算时往往要改变模型参数进行检验,特别是让有效摩擦系数从0.0到0.8之间变化.许多研究人员的计算结果表明,库仑破裂应力随着摩擦系数的增加而增大,即断层上摩擦系数的增大可以导致触发地震能力的提高.这显然与我们的常识相违背:摩擦总是阻碍断层滑动、抑制地震发生的,即断层面上的摩擦越大,地震越是难以被触发.文中通过对库仑破裂应力的计算公式进行详细分析后发现,之所以出现摩擦越大,地震越容易被触发的现象,其原因是研究者在计算中没有考虑在构造应力作用的环境里,摩擦系数本身的变化所带来的附加库仑应力变化.若某个地震使一个位于地下15km的典型断层面上的正应力增加2 MPa,如果只考虑静岩压力,当摩擦系数从0.3增大到0.4后,传统库仑破裂应力变化为0.8 MPa;而综合库仑应力变化则大约为-39.2 MPa.所以,若从整体上来分析断层在地震位错及摩擦系数变化所造成的综合库仑应力改变,就不可能出现库仑应力随摩擦系数增加而增加的不正常现象.由此可见,今后在利用库仑模型研究地震触发问题时,应综合考虑构造应力场及摩擦系数本身变化所带来的库仑应力变化.     

基于改进模糊Borda法的中亚农业投资环境组合评价分析

中亚被认为是丝绸之路经济带沿线最具有投资潜力的地区,对其农业投资环境的评价将有助于我国企业"走出去"到中亚各国开展农业投资合作。通过构建由政治与法律环境、经济与对外开放环境、基础设施与公共服务环境、农业生产环境4个方面27项指标组成的综合评价指标体系,采用改进模糊Borda法的组合模型进行评价分析。结果表明:经济与对外开放环境、基础设施与公共服务环境、农业生产环境是影响中亚国家农业投资环境的主要方面;空间维度上,哈萨克斯坦农业投资环境相对最好,得分均值最高(254.056),乌兹别克斯坦(131.110)吉尔吉斯斯坦(107.158)两国次之,塔吉克斯坦(17.673)和土库曼斯坦(15.886)两国最低;时间维度上,哈、吉、乌三国农业投资环境总体呈趋好态势,而塔、土两国农业投资环境较差,处于不稳定状态。     

浅谈天津市排水规划编制理念

本文简要介绍了天津市排水专项规划编制的必要性、方法、理念及远景展望。希望通过本文,读者能对排水专项规划的编制理念有新的认识和提升,进而对排水规划编制有所帮助。     

组合荷载下超大群桩受力变形模型试验研究

李子沟特大桥是内昆线上的重点工程 ,采用了超大群桩基础。为了进一步完善对超大群桩基础的力学行为的认识 ,应用模型试验分析了在组合荷载作用下超大群桩基础的内力分布特点、群桩的承载性状和受力变形特性。试验结果表明 ,最大弯矩发生在与承台连接附近的桩身处 ,弯矩沿桩身向下随荷载由线性或非线性递减。对于组合加载与水平纵向加载 ,弯矩的极值、沿桩身的变化趋势和受荷载的影响范围不同