Experiments on the short-term development of sine-generated meandering rivers

This paper presents recent works on the simulation of short-term development of sine-generated meandering river in laboratory conditions. The influences of initial system parameters on the evolution process of rivers are investigated, including control over channel sinuousness, channel width and dominant discharge, eventually leading to different results of planforms. Measurements on the bank-line, flow field, bed topography and sediment transport rate were carried out. Braided rivers are easy to produce using non-cohesive sediments in floodplains, whereas environmental temperatures and humidities could influence the fluvial process by their effects on material cohesion. Channelized rivers were obtained in the “High Flow” conditions and the river corridor width was proven to be mainly connected with initial channel sinuousness and water discharge. Sickle-shaped and bamboo leaves-shaped sandbars were formed in the channels during the transformation process of meandering to braiding, the stability degree of sandbars reflects the adaption of channel morphology to hydrodynamic condition. Quantitative analysis confirms the formation of free steady bars, which manifests the free response as a downstream oscillation of the perturbation. Damping length is mainly affected by dominant discharge, channel width is the secondary factor, and channel sinuousness is the weakest factor. The wavelength of steady bars approximately equals to half of the initial streamwise wavelength. Sediment transport rate tends to increase with the increasing of channel sinuousness but stops growing due to the excessive increase of flow route and flow friction. The experiment results could be useful for verifying river pattern discriminant functions and offer a basis for further study on the morphological evolution of large-scale natural rivers, such as Yangtze River.     

黄土高原农牧交错带湿地重构对鸟类多样性的影响

为客观评价生态脆弱地带湿地生态系统变化对鸟类多样性的影响,2017—2018年采用样带法对陕北榆林湿地生态系统重构前后的水鸟变化开展了系统调查。研究结果表明:研究区共有水鸟106种,隶属9目20科55属,分别占陕西全省和全国水鸟总数的88%和40%,其中列入国家Ⅰ、Ⅱ级和省级重点保护鸟类的分别有2、11和14种;列入CITES保护名录的Ⅰ、Ⅱ级重点保护鸟类分别有1、7种;列入IUCN红色名录等级易危、近危和低度关注的分别有3、4和96种;列入国家林业局"三有"名录的有90种;属古北界、广布和东洋界鸟类的分别占65%、25%和10%。种群数量以旅鸟和夏候鸟为主,分别占58%和34%,迷鸟、冬候鸟和留鸟较少,南北不同区域的居留型差异较大;以蒙古高原荒漠湿地鸟类为主,鸻形目、雁形目、鹳形目和鹤形目的鸟类分别占45%、25%、10%和9%,且其数量比湿地恢复保护前增加明显,其余鸊鷉目、鹈形目、红鹳目、隼形目、佛法僧目等的鸟类所占比例较少,数量变化不大。随着湿地生态系统功能不断恢复、区域生态环境不断改善和人们保护鸟类意识的日益增强,以及全球气候变暖,荒漠和黄土区鸟类相互逐渐扩散,研究区内鸟的种类和数量逐年增多,在2010年前记载鸟类共232种,2017年增到280种,2017年调查发现水鸟新记录18种。该研究可为全球最大的遗鸥繁殖地(红碱淖湿地)和繁殖种群及中国鸟类迁移通道保护提供基本依据。     

钦州湾新港区布置对航道水流影响物理模型试验研究

钦州港新建港区位于10万t级东航道和30万t级油码头航道水域,该规划方案对其航道水流及横流均有影响。借助潮流物理模型试验,模拟整个钦州湾海域潮流情况,对规划方案航道水流及横流进行了分析研究。模型试验研究表明:3个方案中30万t级油码头航道流速变化幅度在0.10 m/s以内,西岸线东航道处流速增加幅度均在0.20 m/s以内,方案1增加范围幅度最大。 新港区水流主流在10万t级东航道,方案布置对西侧10万t级东航道水流及横流影响大于方案口门之间30万t级油码头航道,岸线圆滑处理后的方案3东航道横流减少明显。方案布置应尽量利用东航道横流较小的环抱式方案。     

钱塘江嘉绍大桥设计涨潮流速计算

嘉绍大桥河段潮大流急，是涌潮发展、壮大的河段，设计流速预测准确与否关系到桥梁工程施工和运行的安全，应用数学模型来预测设计流速是有效途径之一。应用基于Boltzmann方程的KFVS（Kinetic Flux Vector Spiting）格式，采用WLTF（Water Levelbottom Topograph Formulation）方法和特殊的底坡源项处理技术，实现了计算格式的“和谐”。模型在钱塘江涌潮验证的基础上，求得0．33％设计潮差频率条件下的桥位断面设计涨潮流速为7．83m／s，为桥梁设计提供了重要参数。     

水泵站进水池物理模型试验研究

为评估某海水取水泵站的布置设计,对其进行物理模型试验研究.在建模时,需要合理选择模型比尺,使模型与原型符合动力相似,几何相似和运动相似,并正确重现泵吸进口的涡流作用.为了促进系统良好的运行,采取措施对以下几个方面进行测量:设施内的水位,来自每个泵位置的流量,来流类型与水流分布,泵吸处的流速情况,泵室内部的涡流作用.次测试来流分布较差,出现了预旋和旋涡.通过对旋涡出现的原因进行分析,采取了不同的改良措施,有效消除了这些不良现象,保证了泵站取水安全.     

Incipient motion of non-uniform coarse grain of bedload considering the impact of two-way exposure

The incipient motion of bedload is due to the interaction between the flow and sediment.It is stochastically correlated with the flow structure,the sediment gradation and the arrangement of grains on the bed surface.The random position of the sediment on bed can be represented by a hiding factor or an exposure degree.Based on the numerical simulation of the disturbed flow in the interstice of grains,the influence of the two-way exposure degree(the vertical exposure degree and the longitudinal exposure degree) on the coarse grain incipient motion was investigated in this work.Results show that the exposure degree varies with the position of the sediment on the bed,which influences the flow structure around the particle and the incipient motion.In this paper,the major research achievements on this phenomenon include:Firstly,a mathematical model is established for the rolling-pattern incipient motion of the coarse grain under a critical state of moment balance.The influence of the partial disturbed flow is considered.Secondly,the two-way relative-exposure-degree probability distribution functions are developed to reflect the influence of the disturbed flow and the random arrangement of sediments.Thirdly,a formula to calculate the incipient velocity is presented based on the above results,which considers the impact of the two-way exposure degree of sediment particles.     

A study on the stability of laminar open-channel flow over a sandy rippled bed

Many dynamical processes that happen in a river, including the slow change in thewatercourse and the short-term variations in the bedform, are the results of interactionbetween the flow and the sediment in the river system. It is well known that the flow andthe bedforms and the river geometry act upon one another. Their interdependence can beutilized in the differentiation between symptoms and signs. It is paradoxical that deter-minacy exists in randomness and yet determinacy itself can hatch …     

基于阻力规律的床面形态判别方法

床面形态变化是河床演变的重要方面。如何根据水流和泥沙条件,预测床面可能出现的形态,一直是航道整治与泥沙研究所关心的实际问题。水流阻力规律是水流流动及床面形态等综合特征的反映,反演适当的阻力规律表达式,应能够区分出不同的床面形态。本文正是基于这一理念,通过建立包含床面形态参数的河流水流阻力规律表达形式,并结合水槽试验,得到了确定床面形态的无量纲特征参数,以此对不同床面形态进行区分,绘制出相应床面形态划分图,进而得到了高、低能态时不同床面形态间的分界线方程。该方程可用于对河床形态进行判别与预测,对河流整治具有指导作用。     

基于数字图像技术的卵石模糊聚类

为了实现卵石分类数字化,利用数字图像技术获取卵石图像边缘信息,基于最小二乘圆度误差概念构建出一种新的描述卵石形状的参数系统。应用模糊数学原理,使用最大树法对从野外采集的卵石样本进行了模糊聚类识别实验;选取不同的聚类模糊度,结果对应不同的聚类细度、不同的模糊分类准度。对其中一种聚类结果,将实物图与几种标准图进行数据对比确定了图形分类特征,并使用多维平面图法进行聚类结果分析,进一步证明了直观判断卵石形状特征参数与模糊聚类关系的可行性。实验表明,该卵石分类法具有一定的实用性和先进性。     

波流作用下海床稳定性和海底管道局部冲刷分析

针对深水油气开采中的海底管道安全铺设与运营问题,总结和归纳了可用于海床稳定性分析及管道周围局部冲刷预测的方法,并推导了水流作用下平衡冲深和悬跨长度间的关系式.在此基础上,利用Fortran和Visual Basic混合编程技术开发了专用分析程序.结合我国南海某工程海域的实际工程问题,对水流、波浪和波流共同作用下的天然底床稳定性进行了分析,同时给出了管道铺设以后,其局部冲刷的垂向极限平衡深度、横向扩展速率以及初级和次级横向扩展的转折点时刻等.结果表明：水流因素对深水区的底床稳定性起主要决定作用;同时若底床泥沙颗粒粒径越小,则其所起的黏性作用就越大,管道冲刷扩展速度越小.该分析结果为实际海底管道路由设计及工程施工方案的制定提供了技术依据.