Influence of shallowness,bank inclination and bank roughness on the variability of flow patterns and boundary shear stress due to secondary currents in straight open-channels

Boundary shear stress and flow variability due to its interaction with main flow and secondary currents were investigated under conditions that extend previous research on trapezoidal channels. Secondary currents that scale with the flow depth were found over the entire width in all experiments. These findings contradict the widespread perception that secondary currents die out at a distance of 2.5 times the flow depth from the bank, a perception which is largely based on experiments with smooth boundaries. The reported results indicate that a stable pattern of secondary currents over the entire channel width can only be sustained over a fixed horizontal bed if the bed's roughness is sufficient to provide the required transverse oscillations in the turbulent shear stresses. Contrary to laboratory flumes, alluvial river bed always provide sufficient roughness. The required external forcing of this hydrodynamic instability mechanism is provided by the turbulence-generated near-bank secondary currents. The pattern of near-bank secondary currents depends on the inclination and the roughness of the bank. In all configurations, secondary currents result in a reduction of the bed shear stress in the vicinity of the bank and a heterogeneous bank shear stress that reaches a maximum close to the toe of the bank. Moreover, these currents cause transverse variability of 10–15% for the streamwise velocities and 0.2u_*²–0.3u_*?² for the bed shear stress. These variations are insufficient to provide the flow variability required in river restoration projects, but nevertheless must be accounted for in the design of stable channels.     

Nearshore bar migration and sediment-induced buoyancy effects

A 1-D General Ocean Turbulence Model that includes the effects of sediment-induced stratification is shown to simulate the observed onshore and offshore migration of a nearshore sandbar. The only two free parameters of the model, the bed reference concentration and the sediment diffusivity, are taken from the literature, rather than tuned to the data used here. The model results suggest that predictions of onshore bar migration, in which wave-induced sediment transport confined to within a few centimeters of the bottom dominates, are not greatly affected by accounting for buoyancy effects. The model results also suggest that both mean flows and waves transport sediment during offshore bar migration, with different components of transport dominating at different cross-shore locations across the bar-trough bathymetry. Neglecting the effects of sediment-induced stratification results in higher model skill during the largest waves, likely because the excess turbulence production simulated by the non-stratified model is counterbalanced by neglected breaking-wave-generated turbulence. Considering both onshore and offshore migration, the model that includes sediment-induced stratification has higher skill than the model without stratification.     

波浪荷载作用下海底隧道-孔隙海床的动力分析

孔隙海床在波浪荷载作用下其有效应力减小、孔隙水压力增加,这将影响孔隙海床中隧道的稳定性,因此,研究在波浪荷载作用下孔隙海床与隧道的动力响应具有重要的工程意义。本文基于Biot的动力固结理论和弹性动力学理论建立波浪荷载作用下孔隙海床与海底隧道的动力分析模型,并同时考虑海底隧道与海床之间的接触效应、边界效应等对海底隧道内力的影响。最后通过变换海床的变形模量、渗透系数和海底隧道的半径、埋深等,观察其对海床土孔隙水压力和海底隧道内力的影响,为海底隧道的设计提供依据。     

A parcel formulation of Hamiltonian layer models

Starting from the three-dimensional hydrostatic primitive equations, we derive Hamiltonian N-layer models with isentropic tropospheric and isentropic or isothermal stratospheric layers. Our construction employs a new parcel Hamiltonian formulation which describes the fluid as a continuum of Hamiltonian ordinary differential equations bound together by integral transport laws. In particular, we show that this parcel Hamiltonian structure is compatible with the stacking of layers under isentropic or isothermal constraints. The appeal of the parcel formulation is the simplification of various calculations, in particular the derivation of the continuum Poisson bracket and the proof of the Jacobi identity. A comparison and connection is made between the Hamiltonian dynamics of fluid parcels and the Hamiltonian system of partial differential equations. The parcel formulation can be seen as a precursor and tool for the study of Hamiltonian numerical schemes.     

Analysis of geographical disparities in temporal trends of health outcomes using space–time joinpoint regression

Analyzing temporal trends in health outcomes can provide a more comprehensive picture of the burden of a disease like cancer and generate new insights about the impact of various interventions. In the United States such an analysis is increasingly conducted using joinpoint regression outside a spatial framework, which overlooks the existence of significant variation among U.S. counties and states with regard to the incidence of cancer. This paper presents several innovative ways to account for space in joinpoint regression: (1) prior filtering of noise in the data by binomial kriging and use of the kriging variance as measure of reliability in weighted least-square regression, (2) detection of significant boundaries between adjacent counties based on tests of parallelism of time trends and confidence intervals of annual percent change of rates, and (3) creation of spatially compact groups of counties with similar temporal trends through the application of hierarchical cluster analysis to the results of boundary analysis. The approach is illustrated using time series of proportions of prostate cancer late-stage cases diagnosed yearly in every county of Florida since 1980s. The annual percent change (APC) in late-stage diagnosis and the onset years for significant declines vary greatly across Florida. Most counties with non-significant average APC are located in the north-western part of Florida, known as the Panhandle, which is more rural than other parts of Florida. The number of significant boundaries peaked in the early 1990s when prostate-specific antigen (PSA) test became widely available, a temporal trend that suggests the existence of geographical disparities in the implementation and/or impact of the new screening procedure, in particular as it began available.     

运用GVF Snake算法提取水域的不规则边界

GVF Snake是一种改进型主动轮廓提取算法。本文在详细介绍GVF Snake原理的基础上,重点对GVF Snake的内、外部约束力在边界提取中的作用以及初始边界对提取结果的影响进行了实验研究,提出了初始边界和内部约束力权值的合理设置方法,设计并实现了交互式GVF Snake算法,并用于提取遥感影像上水域的不规则边界。该算法采用种子点区域生长法自动给出水域的初始边界,采用人机交互法设置内部约束力权值,然后运用GVF Snake算法搜索水域的实际边界。实验表明：对于形状极不规则的水域,交互式GVF Snake算法也能方便、快速、准确地获取其边界。     

预压层叠式钻齿型孕镶金刚石钻头的研制

分析了高品质钻头的应用需求,指明了高品质钻头的研究方向。设计了一种层叠式结构钻齿,采用预冷压工艺进行压制后,再经过装模热压烧结的新型孕镶金刚石钻头。给出了此类钻头的原材料选择和制作工艺参数,分析了钻探试验结果。结果表明：预压层叠式钻齿型孕镶金刚石钻头,有利于改善钻进条件,提高钻进效率,有效地实现钻头制造过程中节能降耗,是一种广谱性应用前景的孕镶金刚石钻头新型式。     

江西九瑞矿集区硅质断裂磨砾岩带的厘定及其成岩成矿意义

在九瑞矿集区研究叠合断裂和叠加成矿作用的基础上,我们进一步详细研究了出露在洋鸡山-丁家山-望夫山一线的硅质角砾岩,指出它们不是原先认为的石炭系沉积硅质岩,而应属于一种断裂磨砾岩,并深入探究其形成过程及与成矿之关系.断裂磨砾岩是断裂分带结构成熟的标志之一,多在剪切作用和热液作用下,断裂岩石经硅化-破裂-碎裂-粉碎-研磨,形成具有一定圆度和球度,大小差异较大的磨砾或磨粒,且又会反复的集结-破碎,不断拓宽断裂构造形成磨砾-角砾岩带.本文研究的断裂磨砾岩,呈北东向展布,延长达十几千米.成分上以硅化角砾岩为主,SiO2含量一般大于90％,石英颗粒由隐晶到显晶.一些角砾岩中含Fe2O3较高,有可能是原先的硫化物经氧化形成的褐铁矿.本区洋鸡山-丁家山-望夫山一线产出的断裂磨砾-角砾岩带,很可能是燕山期构造-岩浆-成矿事件的产物.在城门山和武山铜矿,我们之前的工作己发现存在产于泥盆系五通组和石炭系黄龙组层滑构造体系中的黄铁矿角砾岩,则有可能属于海西期同生断裂活动的产物.因此,这些不同的角砾岩具有多阶段活动和叠加成矿的特征.本文还进一步指出,九瑞地区其他层位(如泥盆系与志留系之间、志留系与奥陶系之间)发育的层滑构造体系和断裂角砾岩及热液蚀变岩,也很可能是成矿有利部位,值得今后找矿工作的关注.     

2009年秋季河南一次连阴雨天气成因分析

采用合成分析和动力诊断分析及统计方法,利用NCEP资料和常规气象观测资料对造成2009年9月6-20日河南省北中部地区15 d连阴雨天气成因进行分析.结果表明:200 hPa高空急流的出现并且维持,南亚高压的偏东偏北,副热带高压的偏西略偏北,以及边界层的东北风(或偏东风),是造成此次长连阴雨天气的主要影响因素;200 ...