长江口非均匀悬沙浓度垂线分布

发布时间：2018-01-04 02:26

本文关键词：长江口非均匀悬沙浓度垂线分布　出处：《浙江大学》2016年硕士论文　论文类型：学位论文

【摘要】：长江作为中国最长的河流,和京杭大运河一起被称为中国的两条“黄金水道”。长江口常年丰水多沙,下游航道淤积严重,阻碍航行。1998-2010年,国家分三期工程先后对长江口深水航道进行治理,实现南港-北槽12.5m通航水深目标。然而近年来航道仍存在较大回淤量,维护费用高。本文旨在研究长江口非均匀悬沙浓度垂线分布,为分析其常态回淤原因提供帮助。利用Jasmund-Nikurads对数流速分布和修正的紊动扩散系数,通过求解泥沙一维对流扩散方程获得了非均匀悬沙浓度垂线分布的理论公式。在沉降速度中引入修正系数,结合Larson假设修正悬沙紊动扩散系数,同时以床面平衡浓度作边界条件,避免了Rouse公式水面含沙浓度为零和床面为无穷的不足,精度也有所提高。随着悬沙颗粒相对粒径的增大,悬沙分布更集中在河床附近且曲线梯度增大,同时,公式对均匀沙情形有自适应性。悬沙浓度分布随着悬浮指标的减小趋于均匀,当悬浮指标Ai=2时,悬沙颗粒主要集中在床面至0.2倍水深范围,当悬浮指标Ai=0.01时,悬沙颗粒沿整个水深方向近乎均匀分布。将悬沙浓度与流速之积沿水深方向积分获得非均匀悬沙单宽输沙率公式,公式为显式形式,无需通过数值积分即可求解。公式考虑了近底层输沙率对总输沙率的影响,近底层输沙率与总输沙率之比即相对输沙率跟悬浮指标成正比,当悬浮指标等于2时,相对输沙率为30%左右。相对输沙率与相对粒径(Di/Dm)成正比,相对粒径大于3以后,相对输沙率可达25%以上,忽略近底层输沙将会对总输沙率产生较大影响。作者认为,在相对输沙率所占比重小于5%的情况下,近底层输沙率对总输沙率的影响可不予考虑。经计算,长江口悬浮指标大于0.15时,应考虑近底层输沙对总输沙的贡献。长江口深水航道悬沙浓度全潮周期内出现两次峰值。涨、落急后平衡时刻悬沙浓度垂线分布较涨、落憩后平衡时刻均匀。涨急后平衡时刻浓度分布不及落急后平衡时刻均匀。大潮期平衡时刻的悬沙浓度分布较小潮期均匀,枯季平衡时刻的细颗粒悬沙含沙量分布较洪季不均匀,粗颗粒和总体含沙量分布较洪季均匀。悬沙单宽输沙率大潮高于小潮、洪季大于枯季、落潮大于涨潮,自上游往下游呈现出先上升后下降的趋势,在中部弯曲段达到最值,净输沙指向下游。
[Abstract]:The Yangtze River, the longest river in China, together with the Grand Canal of Beijing and Hangzhou, is known as China's two "golden waterways". The Yangtze River Estuary is rich in water and sand all year round, and the downstream channel is seriously silted up, hindering navigation from 1998 to 2010. Three stages of the national project have been carried out to control the Yangtze Estuary deepwater channel to achieve the target of 12.5m navigable depth in the Nangang-North Channel. However, there is still a large amount of siltation in the channel in recent years. The purpose of this paper is to study the vertical distribution of non-uniform suspended sediment concentration in the Changjiang Estuary. The Jasmund-Nikurads logarithmic velocity distribution and the modified turbulent diffusion coefficient are used to analyze the causes of normal desilting. The theoretical formula of vertical distribution of non-uniform suspended sediment concentration is obtained by solving the one-dimensional convection-diffusion equation of sediment. The modified coefficient is introduced into the settlement velocity and the turbulent diffusion coefficient of suspended sediment is modified by Larson hypothesis. At the same time, with the equilibrium concentration of bed surface as the boundary condition, the shortage of zero concentration and infinite bed surface of Rouse formula is avoided, and the accuracy is improved. With the increase of the relative diameter of suspended sediment particles. The distribution of suspended sediment is more concentrated near the river bed and the curve gradient increases. At the same time, the formula is adaptive to the case of uniform sediment. The suspended sediment concentration distribution tends to be uniform with the decrease of the suspended index, and when the suspended index Ai= 2:00, the suspended sediment concentration distribution tends to be uniform. Suspended sediment particles are mainly concentrated in the range of bed surface to 0. 2 times water depth, when the suspended index is Ai=0.01. The distribution of suspended sediment particles is almost uniform along the whole water depth. The formula of single wide sediment transport rate of non-uniform suspended sediment is obtained by integrating the product of suspended sediment concentration and velocity along the water depth direction, and the formula is an explicit form. The formula takes into account the influence of near bottom sediment transport rate on total sediment transport rate, and the ratio of near bottom sediment transport rate to total sediment transport rate is directly proportional to suspension index. When the suspended index is equal to 2:00, the relative sediment transport rate is about 30%. The relative sediment transport rate is directly proportional to the relative particle diameter Dip / Dm, and when the relative particle size is greater than 3, the relative sediment transport rate can reach more than 25%. Neglecting the near bottom sediment transport will have a great influence on the total sediment transport rate. The author thinks that if the proportion of the relative sediment transport rate is less than 5%, the influence of near bottom sediment transport rate on the total sediment transport rate can not be considered. When the suspended index of the Changjiang Estuary is greater than 0.15, the contribution of sediment transport near the bottom to the total sediment transport should be considered. The suspended sediment concentration in the Yangtze Estuary deepwater channel has two peaks during the whole tidal cycle. The vertical distribution of suspended sediment concentration increases at the equilibrium time after falling. The concentration distribution of the equilibrium time after rising is less uniform than that of the balance time after falling. The concentration distribution of suspended sediment at the equilibrium time of the spring tide is more uniform than that of the small tide period. The sediment concentration distribution of fine suspended sediment at the equilibrium time in dry season is more uneven than that in flood season, and the distribution of coarse particles and total sediment content is more uniform than that in flood season. The single wide sediment transport rate of suspended sediment is higher than that of low tide, the flood season is larger than the dry season, and the falling tide is larger than the high tide. From the upper reaches to the lower reaches, the trend of rising first and then decreasing, reaching the maximum value in the middle curved section, and the net sediment transport pointing downstream.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TV148

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