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明渠非恒定流运动规律及推移质输沙特性的试验研究【作者】刘春晶 【导师】王兴奎

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明渠非恒定流运动规律推移质输沙特性的试验研究

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【作者】刘春晶导师王兴奎
Uo N0pk8B0^-c4E0【作者基本信息】清华大学,水利工程,2005年,博士水利论文vV?C ]6[r

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v#LC Q5@[WjCD|0【中文摘要】 在天然河流中,水流几乎都是非恒定的,特别是在汛期,洪峰涨落频繁,河床的剧烈变化和滩岸溃决一般也是在洪水陡涨陡落的过程中发生的。非恒定流的运动特性及输沙规律的研究对于河流动力学的进展具有重要的理论意义,对水利工程规划和河道整治亦具有重要的实用价值。本文以试验为基础,系统研究了非恒定流的运动特性,取得了以下主要成果: 1 建立了非恒定流输沙的水槽实验系统,在非恒定流生成、水位流量控制和监测、流速和输沙率的测量方面均有新的进展。实验系统可以生成稳定可重复的明渠非恒定流过程,为明渠非恒定洪水波的运动规律、紊动特性及挟沙机理的试验研究提供了便利条件。2 通过水槽试验资料分析,论述比较了恒定均匀流摩阻流速u* 的各种研究方法,其取值将直接影响卡门常数κ、积分常数A 或B、尾流系数Π及悬浮指数Z 等参数。恒定流光滑床面和粗糙床面的摩阻流速与雷诺数的关系遵循统一的规律。少量推移质运动的床面阻力系数有减少的趋势。3 利用实测数据对比了各种单波处理方法及其与多波相位分段平均法之间的差异。单波法具有一定的随机性,而多波相位分段平均法则可以得到更可靠的统计参数。满足试验精度的多波采样时间大约为1000 s 。...更多4 从试验资料的分析得到了明渠流洪水波沿程变形的表达式。初步揭示了洪水波沿程陡涨缓落的变化规律。从Saint-Venant 方程出发,经过简化,推导得出了非恒定流流量过程随水位涨落过程变化的关系,并利用实测资料对Saint-Venant方程组的各项进行了对比,当水流条件变化较为剧烈时,连续方程和运动方程均可能不满足。5 根据试验资料得出了流速~水深和流量~水深最大值出现时刻的相互关系的表达式。分析了明渠流流量特性曲线的绳套现象,其中绳套的相对大小受非恒定流参数Γ的影响。6 非恒定明渠流不同高程上的平均流速、紊动强度及雷诺应力随时间基本同步变化,定床及动床条件的流速分布仍可用对数公式拟合;上部流区的雷诺应力沿垂线基本为线性分布;紊动强度沿垂线分布的变化趋势与恒定流类似。7 除水深较小时段的近水面处,非恒定流各时段的纵向、垂向脉动流速的概率密度均接近正态分布;其中外部流区的纵向流速多为正偏,垂向流速则反之。8 对于低强度的恒定流和非恒定流输沙率,Einstein 公式较Meyer-Peter 公式具有更高的精度。非恒定流推移质输沙率与水流强度的变化并不同步,Φ与ψ之间不再是一一对应的关系;非恒定流的平均输沙率大于恒定流。  还原

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【英文摘要】 Almost all natural river flows are unsteady especially in food seasons. The riverbed experiences drastic transformation and sometimes dyke breaching occurs during the passage of a sharp ascending or descending flood. The study of the unsteady flows together with its influence on sediment transportation is of great significance both in theory and in engineering. The characters of unsteady flows as well as the corresponding bed-load transport have been studied systematically based on experimental evidence. The main results are: 1. A flume experimental system for studying unsteady flows is established. It has the ability to generate unsteady flow, to control and monitor water stage and discharge, and to measure velocity distribution and bed-load transport simultaneously. The system could produce stable and repeatable unsteady flows, which provides convenient circumstances for experiments on the kinetic rules, turbulent characters and sediment transport of unsteady flows in open channels. ...更多2. Various methods to determine the friction velocity u* in steady uniform flows are analyzed and then compared based on experimental data. The quantity of u* directly affects many parameters such as the Karman constant κ, the integral constant B, the wake stress parameter Π, and the suspension index Z. 3. Various methods to obtain the mean and the fluctuating values of velocities in unsteady open-channel flows are analyzed and then compared. It’s shown that it is unconvincing to draw a conclusion based on data within only one flow circle. The ensemble-average method proves reliable while others fail in dealing with data of high-frequency, fast-changing situations. The sampling duration of multiple waves should be larger than 1000 s to ensure accuracy. 4. Expressions of streamwise deformation of open channel flood streams are obtained based on experimental data. Preliminary analysis is proposed of the sharp tiding and tardy edd-tiding rules of the flood stream. The expressions representing the mutual relationships between current velocitywater stage and fluxoccuring time of the maximum water stage are also obtained from the experimental data. Each item in Saint-Venant equation is compared using the experimental data. It shows that the continuous equation and the dynamic equation can not be satisfied when the stream condition varies intensely. 5. Based on the Saint-Venant equation and with some simplifications, expressions are deduced for the variation of unsteady discharge with water stage. The loop phenomenon in the rating curves of open channel flow is analyzed. The comparative loop size is affected by the unsteady parameter Γ. 6. The phases of stream velocity and turbulent intensities at various water depths basically keep synchro. Log-law is still feasible to describe the distribution of current velocities in unsteady open channel flows. The Reynold stress in the outer current field distributes linearly as in the steady flow. The variation tendency of turbulent fluctuation along the water depth is also similar to that of the steady flow. 7. The probability density in both streamwise and vertical directions are approximately in normal distribution, except in the near surface area where the water is shallow. In addition, the majority of longitudinal current velocity tends to positive derivation, whereas the vertical velocity is on the contrary. 8. For weakly sediment discharge in the present experiments, Einstein’s equation is more accurate than the Meyer-Peter’s equation. Due to the time lags between the friction velocity and the bed-load transport, the relation of sediment transport intensity Φand the flow parameter ψis no longer unique in unsteady flows. The long-term average sediment transport in unsteady flow is much more than the steady conditions.  还原水利论文 PI!s;h\;M7Lg

2}?S/gW;V}7dx*~0【中文关键词】 非恒定流; 明渠流; 推移质
Xo%|.D!Wo#j v0【英文关键词】 Unsteady Flow; Open-Channel Flow; Bed-Load水利论文%W"t0kBRM+IV ts:`

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