刘学炎的答辩信息.doc

刘学炎的答辩信息：答 辩 人：刘学炎中文题目：溃坝水流数值模拟英文题目： Numerical Simulation Of the dam-break flow 指导老师：熊鳌魁答辩组成员名单：高高 王家楣 毛筱菲 罗薇 陈克强主席：高高委员： 王家楣 教授 毛筱菲 教授罗 薇 教授陈克强 副教授秘书：刘艾明 讲师答辩时间：2009.12.16 星期三下午 4:00答辩地点：工程流体力学研究所 会议室摘 要溃坝作为一种突发性强和破坏性大的灾难，对人民生命财产构成了极大的威胁。因而探讨溃坝问题对于制定地区应急预案，加强区域防洪减灾是十分必要的。溃坝问题计算是进行工程设计、预报预测和管理维护的基础，溃坝计算的主要内容是算出溃坝坝址的流量和水位过程线, 以及下游洪水演进过程中沿程各处的流量、水位、流速、波前和洪峰到达的时间等。国内外学者对这类问题做了大量研究，主要有理论研究、试验研究和数值研究，而由于问题的复杂性，数值研究成为该类问题的主要研究手段。近些年来，国内对溃坝问题做了大量数值研究取得丰富的成果。溃坝水流一维数值模拟主要基于明渠水流运动的圣维南方程。由于它具有物理概念明确、计算简单、计算结果相对可靠等优点,目前仍在实际工程中广泛应用,尤其对于长河段、大尺度的模拟，但是其精度不足。二维数值模拟的研究发展迅速,二维模型主要基于二维浅水方程，数值计算方法包括差分法、有限体积法和有限元法等，二维模型以及一、二维相结合的统一数学模型也逐渐被应用到工程实践中。由于浅水方程做了一定简化和假设，其应用也受到限制。与一、二维数学模型相比,对溃坝水流三维数值模拟的研究相对较少，研究成果也远未达到实际应用的要求,主要是由于三维模型存在模型复杂、计算量大和计算速度慢等缺点。由于商业软件的出现，解决了相当一部分困难，为三维溃坝的研究提供了便利。本文基于商业软件FLUENT分别对二维和三维溃坝水流进行数值研究，目的在于在考察应用N-S方程数值模拟溃坝水流的可靠性的同时，探讨用物理实验和理论分析不易获知的一些溃坝水流基本现象和规律。主要内容如下：采用有试验数据的二维模型模拟在层流和不同湍流模式下二维全溃坝洪水下泄过程，并将得到的各个时段的流场状况与试验结果相比较分析，找出与试验数据吻合较好的湍流模式。采用与实验数据吻合较好的湍流模式模拟二维部分溃坝洪水下泄过程，并分析得到的各个时段的流场状况。采用有试验数据的三维模型模拟在选定的湍流模式下三维溃坝洪水下泄过程，并将得到的各个时段的流场状况与试验结果进行比较分析。通过上述数值模拟和分析，得到以下结论：在对试验模型的二维全溃坝水流在不同的湍流模式下进行数值模拟中，在选取五种湍流模型和层流中模型得到的结果最好，洪水前峰随时间到达的距离和试验结果吻合，自由液面的演化过程也比较好的吻合。*基金项目：本文是水利部江湖治理与防洪重点实验室开放研究基金资助项目（编号R2007-05）在采用模型对3个尺寸相同、溃坝程度不同即全溃坝，顶部三分之二溃溃坝和顶部三分之一溃溃坝的二维溃坝水流进行数值模拟中，得到了结论：不同溃坝方式在所讨论的时间内都存在一段平稳状态；与全溃坝相比，部分溃坝液面变化复杂，并且上游形成的波形也不同；在相同的时间内溃口的大小对推进的距离有影响，特别是在溃坝初期溃口的大小对推进距离影响较大，但到了后期三分之二溃坝水流前锋与全溃坝水流前锋推进距离相差甚少，这说明在剩余坝体低于一定的程度后，在后期对水流前锋的推进距离没有影响或者影响很小。在采用模型对三维溃坝水流进行数值模拟中，在定性上模型能够比较好的模拟溃坝水流结构以及溃坝水流的传播过程，在定量上还是和试验结果有所出入，原因有两方面：首先模拟的对象属于非定常、非线性的复杂水波，甚至含有碎波现象，对很多因素的影响敏感；其次从试验数据可见自由表面是急剧涨落不稳定的，如何在数值计算中平均化处理本身就是个问题。绕障碍物的三维水流的数值计算结果充分再现了复杂的水面波形演化现象，如壅起、回水，反射、干扰等，同时表明障碍物对溃坝水流的传播和水流的内部结构具有显著的影响。关键词： 溃坝；湍流模式；两相流；数值模拟AbstractLocated west of Bohai Bay, near the estuary of Haihe River, Tianjin Port is the port most close to North China, Northwest China and other inland areas in the country. As the maritime gateway to the capital and Tianjin, it is also the east end of the Eurasian Continental Bridge. Tianjin Port, as the main hub of Chinas coastal ports and an important hub for the integrated transport system, is an important node of the modern integrated transport network of Jing-Jin-Ji and the main port for foreign trade. Its also the main transshipment port for the transport of energy supplies and raw materials of North China and Northwest region, northern container trunk port and an important port for the development of modern logistics, which means it has broad development prospects.Dam-break is a sudden and strong destructive catastrophe, so research on the dam-break problem is very necessary for setting up contingency plans and strengthening flood control in the regional. Calculated value of dam-break problem is base for calculations, forecasting and management and maintenance on the engineering, and the main contents is the process of the flood wave propagation speed, wave, water level and flow characteristics with time in the detention basin and downstream areas.Domestic and foreign scholars has done a great deal of research on the problem, there are three major research methods with theoretica research l, experimental research and numerical calculation. Because of complexity in the problem, numerical calculation becomes byandby the main research tool.In recent years,people have done a lot of dam-break problem obtained from research. One-dimensional numerical simulation of dam-break flow is mainly based on open-channel flow movement of Saint-Venant equations, because it has a clear physical concept, computing simple and reliable calculation results and so on.It is still widely used in practical engineering, especially for long rivers, large-scale the simulation, but its lack of precision. Two-dimensional numerical simulation which develops rapidly is mainly based on two-dimensional shallow water equations, and numerical methods include finite difference method, finite volume method and finite element method and so on. Two-dimensional model and a two-dimensional combination of a two-dimensional model is also be applied to engineering practice. As assumptions of the shallow water equations made to simplify some of its applications are limited. Compared with a two-dimensional mathematical model and a one-dimensional mathematical model, the research on three-dimensional numerical simulation is relatively less and research achievements cant use in practical engineering,because of its complex model, large amount of and slow computing speed. Since the emergence of business software to solve a considerable number of difficulties, for the three-dimensional dam-break studies have been facilitated.Based on commercial software FLUENT two-dimensional and three -dimensional of dam-break flow were simulated, the main elements of simulation are as follows:The whole discharged process of two-dimensional dam-break flood used experimental model was simulated in laminar and different turbulent modes, analysed and compared with the experimental results in all of the flow field to find a turbulent model in good agreement with the experimental data.The whole discharged process two-dimensional dam-break broken different ways were simulated with selected turbulent model and analyze the situation by all the flow field.Using the selected turbulent model simulated the discharged process of the three-dimensional dam-break flood and will be analyzed and compared with the experimental results in various time periods.Through this numerical simulation and analysis, obtained the following conclusions:Simulated the whole two-dimensional dam-break flood with experimental model in five different turbulence and laminar models, results of the k-model are in good agreement with the experimental results.Compared with experimental results,the advanced distance over time of the flood striker and the evolution of free surface is very good.In order to further study the spread of dam-break flow, two-dimensional of the dam-break of the whole, the one-third part from the top, and the two-thirds part from the top of the dam were carried out using FLUENT, obtained the following conclusions:in discussed time all dam-break flows exist the period of steady state; Compared with the whole dam-break flow, free surface of the part dam-break flows is complexer and the upper reaches of the waveform is also different; In the same times the sizes of dyke breach influence the advancing distance of flows, especially in the initial dam-break flows is prominent, but in the later time two thirds of the dam-break flow is after the whole dam-break flows in a little distance, indicating that the remaining dam less than a certain size, in the latter part of the promotion of forward flow from the right has no effect or little effect.The introduction of k- model to simulate three-dimensional dam-break flow, in the characterization of the k- model can better simulate flow structure and the communication process of dam-break flow,but in quantitative there is a discrepancy with exp