本文關(guān)鍵詞：長江口非均勻懸沙濃度垂線分布　出處：《浙江大學(xué)》2016年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 濃度分布 輸沙率 非均勻懸沙 長江口

【摘要】：長江作為中國最長的河流,和京杭大運(yùn)河一起被稱為中國的兩條“黃金水道”。長江口常年豐水多沙,下游航道淤積嚴(yán)重,阻礙航行。1998-2010年,國家分三期工程先后對長江口深水航道進(jìn)行治理,實(shí)現(xiàn)南港-北槽12.5m通航水深目標(biāo)。然而近年來航道仍存在較大回淤量,維護(hù)費(fèi)用高。本文旨在研究長江口非均勻懸沙濃度垂線分布,為分析其常態(tài)回淤原因提供幫助。利用Jasmund-Nikurads對數(shù)流速分布和修正的紊動(dòng)擴(kuò)散系數(shù),通過求解泥沙一維對流擴(kuò)散方程獲得了非均勻懸沙濃度垂線分布的理論公式。在沉降速度中引入修正系數(shù),結(jié)合Larson假設(shè)修正懸沙紊動(dòng)擴(kuò)散系數(shù),同時(shí)以床面平衡濃度作邊界條件,避免了Rouse公式水面含沙濃度為零和床面為無窮的不足,精度也有所提高。隨著懸沙顆粒相對粒徑的增大,懸沙分布更集中在河床附近且曲線梯度增大,同時(shí),公式對均勻沙情形有自適應(yīng)性。懸沙濃度分布隨著懸浮指標(biāo)的減小趨于均勻,當(dāng)懸浮指標(biāo)Ai=2時(shí),懸沙顆粒主要集中在床面至0.2倍水深范圍,當(dāng)懸浮指標(biāo)Ai=0.01時(shí),懸沙顆粒沿整個(gè)水深方向近乎均勻分布。將懸沙濃度與流速之積沿水深方向積分獲得非均勻懸沙單寬輸沙率公式,公式為顯式形式,無需通過數(shù)值積分即可求解。公式考慮了近底層輸沙率對總輸沙率的影響,近底層輸沙率與總輸沙率之比即相對輸沙率跟懸浮指標(biāo)成正比,當(dāng)懸浮指標(biāo)等于2時(shí),相對輸沙率為30%左右。相對輸沙率與相對粒徑(Di/Dm)成正比,相對粒徑大于3以后,相對輸沙率可達(dá)25%以上,忽略近底層輸沙將會(huì)對總輸沙率產(chǎn)生較大影響。作者認(rèn)為,在相對輸沙率所占比重小于5%的情況下,近底層輸沙率對總輸沙率的影響可不予考慮。經(jīng)計(jì)算,長江口懸浮指標(biāo)大于0.15時(shí),應(yīng)考慮近底層輸沙對總輸沙的貢獻(xiàn)。長江口深水航道懸沙濃度全潮周期內(nèi)出現(xiàn)兩次峰值。漲、落急后平衡時(shí)刻懸沙濃度垂線分布較漲、落憩后平衡時(shí)刻均勻。漲急后平衡時(shí)刻濃度分布不及落急后平衡時(shí)刻均勻。大潮期平衡時(shí)刻的懸沙濃度分布較小潮期均勻,枯季平衡時(shí)刻的細(xì)顆粒懸沙含沙量分布較洪季不均勻,粗顆粒和總體含沙量分布較洪季均勻。懸沙單寬輸沙率大潮高于小潮、洪季大于枯季、落潮大于漲潮,自上游往下游呈現(xiàn)出先上升后下降的趨勢,在中部彎曲段達(dá)到最值,凈輸沙指向下游。
[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.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TV148

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