【摘要】：在各類交通運(yùn)輸方式中，水運(yùn)具有能耗低、運(yùn)距長、運(yùn)量大及利于戰(zhàn)備等顯著優(yōu)勢，發(fā)展前景十分廣闊。但是，受自然條件及人為活動(dòng)影響，我國的航道現(xiàn)狀并不理想，普遍存在航道尺度和水流難以滿足船舶通航要求這一問題。 丁壩作為航道整治的主要建筑物，其作用是：束窄河槽、穩(wěn)固河岸、調(diào)整水流流態(tài)以及改變局部河道泥沙沖淤等。據(jù)統(tǒng)計(jì)，在眾多損毀的丁壩中，有相當(dāng)一部分是由壩頭沖刷而導(dǎo)致的，因此對(duì)丁壩壩頭沖刷坑予以研究有助于探索丁壩損毀的根源。為研究丁壩沖刷坑沖刷，首先需要分析坑內(nèi)水流結(jié)構(gòu)，本文采用RNGk~ε三維紊流模型模擬丁壩沖刷坑內(nèi)水流運(yùn)動(dòng)，得到以下結(jié)論： ①丁壩沖刷坑內(nèi)的三維水流結(jié)構(gòu)。水流進(jìn)入沖刷坑時(shí)，從丁壩平面上看，水流在沖刷坑內(nèi)呈現(xiàn)順時(shí)針方向流動(dòng)，同時(shí)會(huì)在沖刷坑內(nèi)形成一些較小的漩渦，這些漩渦的數(shù)目、大小及位置根據(jù)水流條件的不同而各有差異。此外，受坑內(nèi)水流作用的影響，沖刷坑壁面處剪切應(yīng)力大小及分布也不盡相同。 ②水深、流速、沖刷坑深度等因素對(duì)坑內(nèi)水流結(jié)構(gòu)的影響。就水深而言，其在一定范圍內(nèi)增加時(shí)會(huì)相應(yīng)增強(qiáng)沖刷坑內(nèi)的螺旋流和小漩渦，但超過一定深度之后，這種作用反而會(huì)減弱。就進(jìn)口流速而言，其增大會(huì)引起沖坑內(nèi)水流流速和紊動(dòng)強(qiáng)度的增加。就沖刷坑深度而言，隨著深度的增大，沖刷坑內(nèi)流速和紊動(dòng)能均隨之增大，，一旦超過平衡狀態(tài)的深度時(shí)，流速和紊動(dòng)能會(huì)隨之降低。 ③沖刷坑深度公式探討。從力學(xué)角度來看，分析沖刷坑沖刷情況歸根結(jié)底是比較水流對(duì)沖刷坑的剪切應(yīng)力大小與泥沙臨界起動(dòng)剪切應(yīng)力大小，如果前者大于后者，泥沙將會(huì)起動(dòng)，沖刷坑被沖刷。通過分析水深和流速對(duì)沖坑壁面處的剪切應(yīng)力的作用，得出坑深和水深比值與弗汝德數(shù)的關(guān)系，最后借助數(shù)模計(jì)算結(jié)果擬合出兩者之間的代數(shù)關(guān)系式。
[Abstract]:Among all kinds of transportation modes, water transportation has many advantages, such as low energy consumption, long transportation distance, large volume of transportation and benefit to combat readiness, so the development prospect is very broad. However, under the influence of natural conditions and man-made activities, the present situation of the waterway in China is not ideal, and there is a widespread problem that the scale and current of the waterway cannot meet the requirements of the navigation of the ship. As the main structure of channel regulation, the function of spur dam is to narrow the channel, stabilize the river bank, adjust the flow pattern and change the sediment scouring and silting in the local channel, and so on. According to statistics, a considerable part of the damaged groins are caused by the erosion at the head of the dam. Therefore, the study of the scour pit at the end of the dam is helpful to explore the root causes of the damage of the groins. In order to study the scour of groin, first of all, it is necessary to analyze the flow structure in the pit. In this paper, the RNGk~ 蔚 three-dimensional turbulence model is used to simulate the flow movement in the scour pit of the spur dam, and the following conclusions are obtained: 1. When the water flow enters the scour pit, from the plane of the spur dam, the flow of water flows clockwise in the scour pit, and at the same time, there will be some smaller vortices in the scour pit, the number of these vortices. The size and location vary depending on the flow conditions. In addition, the size and distribution of shear stress at the wall of scour pit are different due to the influence of water flow in the pit. (2) the influence of water depth, velocity and scour depth on the structure of water flow in the pit. As far as the depth of water is concerned, the spiral flow and the small vortex in the scour pit will be enhanced when the depth increases within a certain range, but when the depth exceeds a certain depth, the effect will weaken instead. As far as the inlet velocity is concerned, the increase of the flow velocity and turbulence intensity will result in the increase of the flow velocity and turbulence intensity in the scour pit. As far as the depth of scour pit is concerned, the velocity and turbulent kinetic energy in the scour pit increase with the increase of the depth. Once the depth of the equilibrium state is exceeded, the velocity and turbulent kinetic energy of the scour pit will decrease with the increase of the depth of the scour pit. (3) discussion on the formula of scour pit depth. From the point of view of mechanics, the final analysis of scour pit scour is to compare the shear stress of flow to scour pit and the critical initial shear stress of sediment. If the former is larger than the latter, the sediment will start and the scour pit will be scoured. By analyzing the effect of water depth and velocity on the shear stress on the wall of the crater, the relationship between the depth and the ratio of water depth and Froude number is obtained. Finally, the algebraic relation between the two is fitted by the results of numerical simulation.
【學(xué)位授予單位】：重慶交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TV863

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