【作者】 惠二青；

【导师】 江春波；

【作者基本信息】 清华大学 ， 水利工程， 2009， 博士

【摘要】 论文针对生态特征垂向变化较大的植被群落之间水流特性研究较少的现状,选择生态特征垂向均一和变化较大的芦苇、灌木和草本群落,设计了六种群落组合,利用室内水槽试验分析不同流量和植被密度时各种群落之间植被生态特征参数对水流特性和污染物纵向离散的影响。研究结论如下:1)垂向上,植被群落之间水流流速随直径增加而减小,随植被柔韧性增加而增加。灌木完全淹没后,流速垂向分布可以分为两个区域:一个为植被高度范围,另一个为植被冠层以上。植被冠层之上流速分布基本一致,呈对数曲线形式;植被高度范围内流速分布随其生态特征参数的垂向变化不同可以用不同的曲线描述。紊动强度垂向分布曲线上存在三个拐点:一个位于茎干向冠层过渡区域,第二个位于偏转点处,第三个位于冠层顶端处。2)在均匀流条件下,基于水流受力平衡推导植被阻力系数与Darcy阻力因子的关系,结合伯努利方程和Darcy阻力公式计算植被群落阻力系数,通过分析发现其随直径、水深、直径雷诺数、水深雷诺数和相对粗糙高度的垂向变化规律均可以表达为幂函数或指数曲线形式。利用多元非线性逐步回归分析方法建立了植被阻力系数垂向分布计算模型。3)利用改进的单站法计算植被之间污染物纵向离散系数,分析Nepf和Serra扩散模型应用于污染物纵向离散系数计算的可行性,结果表明两个模型在应用于天然植被时精度都比较低。将污染物纵向离散系数与植被直径、阻力系数和直径雷诺数联系起来,建立垂向生态特征参数变化较大的植被群落之间污染物纵向离散系数计算模型。4)将植被阻力分别概化为绕流阻力和底部糙率,建立水深平均的二维水流数值模型。验证结果表明:植被稀疏时,采用绕流阻力或将其概化为底部摩阻应力都可以得到较好的模拟结果。植被稠密时,概化为绕流阻力时计算结果更接近真实值。更多还原

【Abstract】 The hydraulics characteristic of flow among the plant community that vertical ecological character changes steeply was rarely studied. The natural shrubs which vertical characteristics changes steeply and natural reeds which vertical characteristics changes little were chosen as the experimental objects. The six types of communities were designed. The effect of the ecological character on the vertical change of flow characteristics and pollutant longitudinal diffusion was experimental analyzed. The results show:1) In the vertical direction, it is the positive correlation between the velocity and the flexibility of the plant, however it is negative correlation between the velocity and the plant diameter. While shrubs are fully submerged, the vertical distribution of velocity can be divided into two parts: one is within the range of plant height; the other is above the plant canopy. The vertical velocity distribution of the former can be described as the logarithm curve, and the curve shape of the latter is different along with vegetation types. There are three inflexions in the vertical distribution curve of the turbulence density among the plant community. The first lies in the transition zone from the stem to the canopy; the second is located in the plant deflection point; the third is situated in the top of the plant canopy.2) Based on the balance of the force imposed on the plant, the formula between the drag coefficient due to plant community and Darcy friction factor is deduced, which is combined with Bernoulli equation and Darcy friction formula to calculate drag coefficients. The influence factors of vertical distribution of drag coefficient are analyzed. The vertical tendency of drag coefficient with flow depth, diameter, diameter Reynolds number, flow depth Reynolds number and relative roughness height are a declined curve and could be depicted as the power function or exponent function in the different discharges. The calculation models of drag coefficient are built by use of the multiple nonlinear regression analysis method.3) The pollutant dispersion coefficients in the longitudinal direction are calculated by means of the revised single-station method. Nepf model and Serra model’s applicability for the natural vegetation are verified and the results show that the precision of the two models are low. An empirical model is built to calculate longitudinal dispersion coefficient for the natural shrubs using multiple regression analysis method by relating the longitudinal dispersion coefficient to plant diameter, the plan diameter Reynolds number and drag coefficient.4) Chezy coefficient is expressed as the function of the plant ecological character parameter and drag coefficients which are calculated based on the flume experiment result. Drag due to plant was approximately regarded as cylinder-drag or bottom friction, respectively. The two dimensional depth average flow numerical model was built and resolved it by means of TVD-MacCormack scheme. The flume experiment data are validated and show: the calculated result agree well with the measured result among the sparse plants however drag due to vegetation was approximately regarded as the bottom friction or the cylinder-drag; while the drag due to vegetation was approximately regarded as the bottom friction force, the calculated result agree better with the measured result.更多还原