發(fā)布時(shí)間：2018-09-06 18:59

【摘要】：樞紐下游局部沖刷問題是影響水工建筑物安全的重要因素，隨著水利樞紐建設(shè)的加快，人們對(duì)樞紐下游局部沖刷問題的研究越來(lái)越重視。本文通過收集已有的水利工程資料，結(jié)合當(dāng)卡模型進(jìn)行了不同流量及不同床沙粒徑的模型試驗(yàn)，分析了樞紐下游沖刷坑的主要影響因素及形成機(jī)理，從不同角度推導(dǎo)了當(dāng)卡下游河床局部沖刷深度的計(jì)算公式，得到以下主要結(jié)論： （1）下游河床受到水流橫向和縱向流速?zèng)_刷形成局部沖刷坑。沖刷坑形成過程主要有三個(gè)階段：開始強(qiáng)烈沖刷階段、隨時(shí)間推移不斷擴(kuò)展階段、沖刷穩(wěn)定階段，前期發(fā)展迅速，后期發(fā)展緩慢。 （2）樞紐下泄流量和下游泥沙中值粒徑是影響水工建筑物下游局部沖刷坑深度與范圍的主要因素，隨著流量的增加，沖刷坑深度、范圍也隨之增大；隨著下游泥沙中值粒徑的增加，，沖刷坑的深度和范圍逐漸變小。 （3）在二元水流基礎(chǔ)上，通過水流連續(xù)性方程推導(dǎo)得到了下游局部沖刷坑深度計(jì)算公式，利用沖刷坑觀測(cè)資料，對(duì)本文公式及現(xiàn)有的樞紐下游局部沖刷坑深度計(jì)算公式進(jìn)行驗(yàn)證表明，現(xiàn)有的公式計(jì)算值與實(shí)測(cè)值誤差較大，本文公式與實(shí)測(cè)值誤差較�。辉诖嘶A(chǔ)上，通過分析誤差原因，對(duì)推導(dǎo)的公式進(jìn)行了修正，得到了當(dāng)卡水電站下游沖刷坑深度計(jì)算公式，為當(dāng)卡下游局部沖刷深度的計(jì)算提供了依據(jù)。 （4）在連續(xù)方程的基礎(chǔ)上，考慮了水流平面擴(kuò)散特性、回流等因素對(duì)下游局部沖刷深度的影響，推導(dǎo)了下游局部沖刷深度公式，依據(jù)水流擴(kuò)散情況，回流強(qiáng)弱程度對(duì)公式的適用條件進(jìn)行分類。
[Abstract]:Local scour problem is an important factor that affects the safety of hydraulic structures. With the acceleration of the construction of hydro-junction, people pay more and more attention to the problem of local scour downstream. In this paper, by collecting the existing water conservancy engineering data and combining the Dangka model to carry out the model tests of different discharge and different bed sand particle size, the main influencing factors and formation mechanism of the downstream scour pit of the project are analyzed. The formula for calculating the local scour depth of the downstream river bed is derived from different angles. The main conclusions are as follows: (1) the downstream riverbed is washed by the lateral and longitudinal flow velocity to form a local scour pit. There are three main stages in the formation of the scour pit: the beginning of the intense scour stage, the continuous expansion of the scour pit over time, the stable scour stage, and the rapid development of the early stage. The later development is slow. (2) the discharge down of the hub and the median particle size of the sediment downstream are the main factors affecting the depth and range of the local scour pit in the downstream of the hydraulic structure. With the increase of the discharge, the depth and the range of the scour pit also increase; The depth and range of the scour pit become smaller with the increase of the median particle size of the downstream sediment. (3) on the basis of binary flow, the formula for calculating the depth of the local scour pit is derived through the flow continuity equation. Based on the observation data of scour pits, the formulas of this paper and the existing formulas for calculating the depth of local scour pits in the downstream of the hub are verified. The results show that the errors between the existing formulas and the measured ones are large, and the errors between the formulas and the measured values are small. By analyzing the error reasons, the derived formula is modified, and the formula for calculating the depth of the scour pit downstream of Dangka Hydropower Station is obtained, which provides the basis for the calculation of the local scour depth in the downstream of Dangka Hydropower Station. (4) on the basis of the continuous equation, Considering the influence of flow plane diffusion and reflux on the local scour depth of downstream, the formula of local scour depth is derived, and the applicable conditions of the formula are classified according to the condition of flow diffusion and the degree of backflow.
【學(xué)位授予單位】：西北農(nóng)林科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TV131.61;TV147

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