本文選題：阻水障礙物群 + 透水密度系數(shù)��； 參考：《浙江大學(xué)》2014年碩士論文

【摘要】：實際情況下,洪水在演進過程中會不可避免地會遇到阻水障礙物群(如植被群和建筑群等),阻水障礙物群的存在對洪水運動和泥沙輸移都有很大的影響。本文通過引入透水密度系數(shù)以考慮阻水障礙物群對洪水運動過程中水流通量的影響,建立了二維動力波洪水和泥沙運動數(shù)值模型,通過對不同情況下帶有阻水障礙物群的洪水演進和泥沙運動進行模擬分析,主要研究成果和結(jié)論如下： (1)分析總結(jié)了植被群和建筑群作為阻水障礙物群在洪水運動過程中的阻力作用,植被群在單位體積上的阻力可以表示為植被群對水流的阻力會因植被自身特性(剛性,柔性,有無樹葉)的不同而變化；而建筑物群在單位體積上的阻力為阻力會因建筑物分布的疏密程度以及形狀尺寸的不同而變化。 (2)在二維淺水運動和泥沙輸移方程的基礎(chǔ)上引入透水密度系數(shù)以綜合考慮阻水障礙物群對水流通量和泥沙輸移通量的影響,從而建立一個新的基于透水密度系數(shù)法的二維動力波洪水和泥沙運動數(shù)值模型。同時,模型還考慮了水流的粘性和紊動擴散作用,以及考慮地形變化影響的水沙耦合作用。本模型采用中心迎風(fēng)格式求解單元界面上的流量和動量通量,并結(jié)合對界面變量的線性重構(gòu),使其具有空間上的二階精度。單元界面上的泥沙輸移通量采用迎風(fēng)格式進行求解。為保證模型的和諧性和穩(wěn)定性,底床坡度項采用中心差分法離散,底床摩擦項和障礙物的阻力項用半隱式法離散。粘性和紊動擴散項,泥沙運動擴散項均采用中心差分格式處理。當庫朗特數(shù)滿足條件時,模型能保證計算水深在任何時刻是非負的,使得模型具有良好的穩(wěn)定性。 (3)模型分別對帶有不同類型阻水障礙物群的定床洪水算例進行驗證分析,結(jié)果表明：透水密度系數(shù)法可以將阻水障礙物群視為一個整體考慮,配置相同的計算參數(shù),網(wǎng)格劃分的疏密對透水密度系數(shù)法下的模擬結(jié)果影響較小,而設(shè)定高程法受網(wǎng)格粗細影響十分顯著。在計算精度和誤差相近的范圍內(nèi),相比設(shè)定高程法,透水密度系數(shù)法具有較高的計算效率,計算耗時僅為其1/50,這表明在洪水演進數(shù)值模擬中,透水密度系數(shù)法比設(shè)定高程法更具優(yōu)勢,這對于洪水風(fēng)險評估和快速防災(zāi)決策極為重要。 (4)通過算例對考慮水沙耦合作用的洪水和泥沙運動數(shù)值模型進行驗證,分析其水動力特征、泥沙運動以及河床變形特征,并利用該模型對阻水障礙物群—水生植被群影響下的洪水和泥沙運動進行計算模擬,分析探討水生植被群的存在及其分布方式對洪水運動、泥沙輸移及底床沖淤的影響。結(jié)果表明：水生植被群的存在雖能有效減小上游河床的沖刷,但由于不利于過流,會使上游水位抬高而增加洪災(zāi)風(fēng)險。同時分析了不同的植被群分布方式對洪水運動和泥沙輸移特性的影響,結(jié)果表明：植被區(qū)沿邊岸分布、寬度減半的方式是既能減小洪災(zāi)風(fēng)險又能維持生態(tài)穩(wěn)定的較為有效的措施。
[Abstract]:In the actual situation, water hindrance barrier group (such as vegetation and building group) will inevitably be encountered during the process of flood evolution. The existence of water hindrance barrier group has great influence on flood movement and sediment transport. In this paper, the permeability density coefficient is introduced to consider the shadow of water barrier group on the flow flux during the flood movement. The numerical model of two dimensional dynamic wave flood and sediment movement is set up. The flood evolution and sediment movement in different cases are simulated and analyzed. The main research results and conclusions are as follows:
(1) the resistance of the vegetation group and the building group as the water hindrance barrier in the flood movement is analyzed and summarized. The resistance of the vegetation group on the unit volume can be expressed as the variation of the resistance of the vegetation group to the water flow due to the characteristics of the vegetation itself (rigid, flexible, and without leaves), and the resistance of the building group to the unit volume is the resistance of the building group. Resistance will vary depending on the degree of density and size of the building.
(2) on the basis of the two-dimensional shallow water movement and sediment transport equation, the permeability density coefficient is introduced to comprehensively consider the influence of the water barrier group on the flow flux and the sediment transport flux, thus a new numerical model of two-dimensional dynamic wave flood and sediment transport based on the permeable density coefficient method is established. This model uses the central upwind scheme to solve the flow and momentum flux on the interface, and combines the linear reconstruction of the interface variables to the two order accuracy in space. The sediment transport flux on the interface is used in the windward format. In order to ensure the harmony and stability of the model, the slope term of the bottom bed is discrete by the central difference method, the friction term of the bottom bed and the drag of the obstacle is separated by the semi implicit method. The viscous and turbulent diffusion term, the sediment movement diffusion term are all treated by the central difference scheme. When the kumatt number satisfies the condition, the model can guarantee the time to calculate the depth of water depth. Carving is nonnegative and makes the model stable.
(3) the model is verified and analyzed for the fixed bed flood calculation with different types of water obstructing obstacles. The results show that the permeable density coefficient method can consider the obstruction of water barrier as a whole consideration, with the same calculation parameters, and the density of grid partition has little influence on the simulation results under the permeable density coefficient method, and the set height is high. In the range of calculation accuracy and error, the pervious density coefficient method has a higher calculation efficiency compared with the set height method, and the time of calculation is only 1/50. This shows that the permeability density coefficient method is more advantageous than the set elevation method in flood evolution numerical simulation, which is the evaluation of flood risk. And rapid disaster prevention decisions are very important.
(4) through a numerical example, the numerical model of flood and sediment movement considering the coupling of water and sediment is verified, and its hydrodynamic characteristics, sediment movement and river bed deformation characteristics are analyzed, and the model is used to simulate the flood and sediment movement under the influence of water barrier group - aquatic vegetation group, and the existence of aquatic vegetation group is analyzed and discussed. The results show that the existence of the aquatic vegetation can effectively reduce the erosion of the upstream river bed, but the water level will be raised to increase the flood risk. The results show that the way to reduce the width of the vegetation along the shore and the width of the vegetation area is a more effective measure to reduce flood risk and maintain ecological stability.
【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】：2014
【分類號】：TV122;TV14

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