Dam Break Wave of Thixotropic Fluid

Thixotropy is the characteristic of a fluid to form a gelled structure over time when it is not subjected to shearing, and to liquefy when agitated. Thixotropic fluids are commonly used in the construction industry (e.g., liquid concrete and drilling fluids), and related applications include some forms of mud flows and debris flows. This paper describes a basic study of dam break wave with thixotropic fluid. Theoretical considerations were developed based upon a kinematic wave approximation of the Saint-Venant equations down a prismatic sloping channel. A very simple thixotropic model, which predicts the basic rheological trends of such fluids, was used. It describes the instantaneous state of fluid structure by a single parameter. The analytical solution of the basic flow motion and rheology equations predicts three basic flow regimes depending upon the fluid properties and flow conditions, including the initial “degree of jamming” of the fluid (related to its time of restructuration at rest). These findings were successfully compared with systematic bentonite suspension experiments. The present work is the first theoretical analysis combining the basic principles of unsteady flow motion with a thixotropic fluid model and systematic laboratory experiments.     

Annual variation of fresh water quality in the Gachang Dam reservoir

This paper investigated the relationship between the annual variation of the algae population and the physicochemical properties of the water reservoired in the Gachang Dam in the hopes of serving as a guideline in the production of a clean water supply to regions of the city of Taegu. Summer thermal stratification was formed in the freshwater reservoired in the Gachang Dam and thus dissolved oxygen (DO) decreased according to the depth of the water. The pH of epilimnion was much higher than that of hypolimnion in summer because of the difference in the photosynthesis rate of algae. In July, at the beginning of the rainy season, the amount of total nitrogen (T-N) in the freshwater reached a maximum of 1.92 mg/L without an increase in the amount of total phosphorus (T-P). In August, the concentration of T-P in the freshwater increased steeply and reached 0.12 mg/L.Aulacoseira spp. (diatoms) were predominantly distributed in the freshwater throughout the year andSynedra andAsterionella (diatoms) predominantly populated in the spring. However,Anabaena andMicrocystis (blue-green algae), which caused malodor and a bad taste, flourished predominantly in epilimnion in August when the temperature of the water at the surface region increased to the maximum and the concentration of T-P was sufficiently high.     

Simulation of the St. Francis Dam-Break Flood

A two-dimensional (2D) simulation of flooding from the 1928 failure of St. Francis Dam in southern California is presented. The simulation algorithm solves shallow-water equations using a robust unstructured grid Godunov-type scheme designed for wetting and drying and achieves good results. Flood extent and flood travel time are predicted within 4 and 10% of observations, respectively. Representation of terrain by the mesh is identified as the dominant factor affecting accuracy, and an iterative process of mesh refinement and convergence checks is implemented to minimize errors. The most accurate predictions are achieved with a uniformly distributed Manning n = 0.02. A 50% increase in n increases travel time errors to 25% but has little effect on flood extent predictions. This highlights the challenge of a priori travel time prediction but robustness in flood extent prediction when topography is well resolved. Predictions show a combination of subcritical and supercritical flow regimes. The leading edge of the flood was supercritical in San Francisquito Canyon, but due to channel tortuosity, the wetting front reflected off canyon walls causing a transition to subcritical flow, considerably larger depths, and a standing wave in one particular reach that accounts for a 30% fluctuation in discharge. Elsewhere, oblique shocks locally increased flood depths. The 2D dam-break model is validated by its stability and accuracy, conservation properties, ability to calibrate with a physically realistic and simple resistance parametrization, and modest computational cost. Further, this study highlights the importance of a dynamic momentum balance for dam-break flood simulation.     

东朗水电站坝型方案比选

本文根据东朗水电站坝址地形地质条件及工程区料场料源状况,选取混凝土面板堆石坝、沥青混凝土心墙堆石坝和碾压混凝土重力坝三种坝型进行比选,最终选择混凝土面板堆石坝。     

大坝变形自动监测仪器

混凝土大坝的变形,尤其是坝基和拱座的变形,是衡量工程安全与否的一个重要指标。变形自动监测仪器与人工测读的仪器相比,具有精度高、时间快的优点。本文参考国外资料,提出测斜仪、钻孔变位计、垂线自动监测仪等三种国内外正在试用的电子仪器。将有助于提高并改善大坝设计的经济性和安全性。     

水布垭面板坝智能土石方调配系统研究

由于水布垭面板坝的土石方开挖量超过2 000万方,填筑量超过1 560万方,土石方调配问题关系到整个工程的进展和技术经济效益,为此分析 了水布垭面板坝土石方调配的特点,并根据数学模型,对水布垭面板坝智能土石方调配系统
进行了功能分析和系统设计。计算机仿真结果表明,该系统具有很好的实用性和可操作性, 响应时间约0.5～1 s,优于传统土石方调配结果。     

沙牌RCC拱坝坝肩稳定三维地质模型试验研究

通过三维地质力学模型试验，研究了沙牌RCC拱坝坝体和坝肩的变形规律、破坏机理，综合评价了坝肩的超载安全度，为工程设计提供依据。     

汶川地震余震记录及紫坪铺面板堆石坝余震反应研究

对汶川地震后紫坪铺面板堆石坝台阵余震记录进行了分析,研究实测余震地震动频谱特性等基本特征。选择有代表性的坝址基岩台站记录到的余震地震动作为大坝地震动输入,对紫坪铺大坝进行了三维动力有限元分析,并将计算得到的坝体加速度放大倍数与不同坝高台站的监测数据进行了对比。研究结果表明：实测余震地震动加速度反应谱在短周期部分有一定波动,在周期稍长时随周期增加而衰减,符合地震动反应谱的基本特征;综合实测大坝反应、数值计算结果以及以往实测相关资料,本次紫坪铺大坝余震实测结果反映了土工构筑物反应的一般规律。     

某水库水位的下降对坝体边坡稳定性的影响

水位下降时,一方面坝体内部渗流场会发生变化,土体基质吸力也相应地改变;另一方面,坝体内部土体孔隙水压力、强度参数随水位变化也会改变。因此,库水位变化对边坡安全系数有重要的影响。基于geo-studio软件中的slope/w和seep/w模块来模拟库区水位线的降低和基质吸力对边坡稳定性的影响。结果表明：当水位快速下降的时候,坝体中水位没有相应降低,孔隙水压力没有及时消散,强度参数C、 φ几乎不变,但坝体外部水压力降低,其速率越快,边坡安全系数下降得越明显;水位线缓慢下降时,坝体内部孔隙水压力消散和外部水位线发生同步变化,随着坝体孔隙水压力的消散,坝体内部土体有效应力增加,边坡安全系数逐渐增大,边坡的稳定性相应地变好;与此同时,当坝体内部土体呈饱和状态时,基质吸力为零,基质吸力对边坡稳定性几乎没有影响,随着土体内部水位线的降低,土体由饱和状态逐步变为不饱和状态,基质吸力逐渐增大,坝体的安全系数又逐渐升高,稳定性也随之增强。     

三峡坝址来水变化及水利工程对其影响分析

气候变化和人类活动导致长江流域水资源年际、年内均发生变化。利用不同趋势分析和突变分析法,选取1890—2020年三峡坝址来水资料分析来水变化趋势以及溪洛渡、向家坝、三峡水库建库前后三峡坝址处年均、消落期、汛期、蓄水期来水变化。结果表明：三峡坝址在年均、汛期、蓄水期来水减小趋势显著,消落期减小趋势不显著,三峡坝址来水变化趋势突变时间在1960年左右。溪洛渡和向家坝水库在枯水期向下游补水导致三峡坝址来水增加,造成溪洛渡、向家坝建库后三峡消落期来水比历史反向增大,说明巨型水库对长江上游及金沙江流域水资源时空分布影响较大。