【作者】 刘雪兰；

【导师】 陈景秋；

【作者基本信息】 重庆大学 ， 流体力学， 2005， 硕士

【摘要】 长江、嘉陵江一直是重庆生活饮用水、工业用水的主要来源。随着社会经济的发展,长江上游城市生活污水和工业废水排放量日益增加,加之三峡水库蓄水后会使水体的稀释自净能力降低,重庆水污染问题日趋突出。本文以长江和嘉陵江重庆段的汇流区域为研究对象,应用二维有限元数学模型对研究区域的水动力和水质进行了数值模拟。并对模拟结果进行了验证和分析,以期为重庆城区段的水环境资源保护和可持续发展提供科学的数据和参考。本文的数值计算建立在浅水动力学的理论基础上,考虑到实际河流的水面宽度比水深大得多,假设两江汇流段的水平流速沿水深均匀分布,忽略垂向流速和加速度,用三维不可压流运动方程组沿垂向积分,得到二维浅水方程组,来描述河流的流动。结合对流扩散方程,以水动力计算所得流场作为其输入数据,来计算河流中污染物的输运和扩散。其中模拟的污染介质作为保守物质处理,假设其含量和浓度较低,不发生降解行为,也不影响水的流动。数值计算采用有限元模型,用迦辽金(Galerkin)加权余量法对水动力和水质控制方程进行离散,再耦合求解,先后得到两江段的水动力场和污染物浓度扩散场。文中引入了美国的SMS 模型(Surface-water Modeling System),即地表水模拟系统,对重庆两江段的有限元模型进行了前后处理和数值计算。经过实测资料的验证,计算结果符合实际情况,可达到精度要求。两江段的流场结果表明,在位于汇流口下游,河岸边界曲折,且水下地形变化较大的梁沱附近存在很明显的漩涡运动,流速变化剧烈,并在此处形成回水区,造成漂浮物滞留,在自然的水动力条件下很难向下游漂移,建议重点清除这一区域的漂浮物污染。另外,在河道弯曲较大的嘉陵江大桥附近,以及河心高地珊瑚坝附近也存在少量漂浮物短期盘桓的危险。通过对假设点源排放的保守污染物进行扩散模拟,其结果表明,在给定的水动力条件下,污染物的输移和扩散速度较大,不会对研究区域产生较明显的影响;排污初期易在排污口一侧的河岸形成高浓度的污染带,到汇流口以下才能在整个河道达到完全扩散。所以建议污水在排放前进行净化处理,以免恶化排污口下游河岸附近的水质。更多还原

【Abstract】 Yangtze River and Jialing River are the main sources of living and industrial waterin Chongqing. With the development of economy, the living sewage and industrialwaste water into Yangtze River upstream is increasing day by day, in addition, thecompletion of Three Gorges Reservoir will weaken the self-purification of water in thetwo rivers, therefore, the water-pollution problem in Chongqing becomes more andmore severe. This paper takes the confluence of Yangtze River and Jialing River asstudy object, and simulates the hydrodynamics and water quality with two-dimensionalfinite element numerical model. Then validates and analyses the computed results, inorder to provide scientific date and qualitative consultation for the water environmentprotection and sustainable development of Chongqing city.Numerical computation in this paper bases on the theory of shallow waterhydrodynamics. Considering the width is much more than the depth in natural river, theassumption that the horizontal flow velocity in the calculated domain is depth-averageignoring the vertical velocity and acceleration, is taken in this paper. The 2D shallowwater equations, which is depth-integrated of the 3-dimensional incompressible fluidmovement equations, is applied to describe the river’s flow. The diffusion-convectionequation is numerically solved to compute the transfer and diffusion of contaminant,with the hydrodynamics results as its input data. The contaminant is considered asconservative constituent with an assumption that it has a low concentration withoutdecay, and has no influence on the river hydrodynamics.Finite element model is applied to the numerical computation, using the Galerkinmethod of weighted residuals to discrete the hydrodynamics and water qualitygoverning equations. The two kinds of governing equations are solved by combination.The SMS model (Surface-water Modeling System) is introduced to the pro-process,after-process and numerical computation in this paper for the finite element model oftwo rivers in Chongqing. By comparing with measured data, the computed resultsaccord with the reality approximately, the computing accuracy is good enough.The flow result shows that due to the wriggling land boundary and complexunder-water topography, there exists an obvious vortex at Liangtuo which located nearconfluence downstream. The velocity varies acutely in this area, and it becomes abackwater. The drifters will be lingering here and difficult to move downstreamnaturally, so drifters elimination should be paid more attention in this area. In addition, afew of drogues will be lingering temporarily in the area near Jialing River Bridge andisland Shanhuaba, where have a large boundary curvature. Diffusion of conservativeconstituent from the assumed discharge point is modeled, the result shows that, in thegiving hydrodynamic condition, the transfer and diffusion rate of contaminant is high, itwill not influence the calculated domain obviously. In the early stage of sewagedischarging, it forms a pollutant band at the boundary near the discharging point. Thenit will diffuse entirely in the whole riverway down to the convergence. So it is suggestedthat the sewage should be cleaned before discharged, or else it would deteriorate thewaterquality down from discharge point.更多还原