浅水间断问题的水流泥沙及污染物输运数值模拟

发布时间：2018-02-09 09:31

本文关键词： 二维浅水有限体积法 Roe格式植物作用泥沙输运污染物输移　出处：《大连海洋大学》2016年硕士论文　论文类型：学位论文

【摘要】：浅水间断流动如水跃、涌潮、溃坝波、波浪变形等的数值研究,因其具有广泛的工程应用背景,引起了许多学者的研究兴趣。然而,自然界的水流运动过程往往不是孤立的,常伴随有泥沙输移、污染物迁移转化等物理、化学和生物过程。其中,溃坝洪水及其诱发的河床泥沙运动,给下游人民造成重大的生命财产损失。因此,研究动床条件下平面二维溃坝水沙输移的数值模拟,在预测堤坝溃决引起的下游受灾情况和评估溃坝风险控制等方面具有重要的实际意义。另一方面,随着环境污染日趋加重,水环境问题得到越来越多的关注。要实现对污染水体的治理,了解水体的水动力特征,进一步掌握污染物的输运机理十分必要。本文首先基于有限体积法和非结构三角形网格建立平面二维浅水数学模型,将模型主要运用于带有强间断的溃坝洪水模拟以及具有复杂地形的海湾潮汐模拟。模型应用二阶精度的Roe格式近似Riemann解计算网格界面的动量通量,将静水压力项作为源项反映在动量方程中,采用高效的干湿处理技术解决干湿界面的动边界问题。应用模型对6个典型溃坝和3个海湾潮流算例进行模拟,实验结果良好,展示了本模型强大的适应能力和较高的计算精度,说明模型能够用于工程实践中。基于以上水动力模型,考虑平面二维浅水控制方程、泥沙输移方程以及河床变形方程本文建立了平面二维水沙耦合数学模型。其中,浅水控制方程中的连续方程和水动力方程均采用浑水方程,泥沙连续方程中泥沙对流通量采用迎风格式计算。模型同时考虑了植被对水流、泥沙输移及床面冲淤变化的影响。应用模型对5个算例进行模拟,并结合实测资料对数值模拟结果进行了验证分析。计算结果表明:在模拟动床条件下溃坝水流的演进及床面变形等问题上,本文建立的平面二维水沙耦合数学模型具有较高的精确度,同时有较好的复杂地形处理能力。从动床条件下有植物作用的溃坝水流数值模拟这一算例中可以发现,由于滩地植物的存在,植被区的水流流速和溃坝波对下游河床的冲刷影响将减少,但同时植被区河道的泄洪能力也会有所降低,导致洪水在上游区水位提升。基于水动力模型,耦合二维浅水控制方程和物质输运方程,建立平面二维水动力、水质显格式数学模型。模型运用高阶精度的迎风重构插值技术处理网格界面的污染物输运通量,扩散项采用二阶精度的离散方法处理。首先模拟理想条件下旋转流场中纯对流问题以及纯扩散问题,以验证本模型水质模块的计算精度。然后应用本模型模拟法国Gironde海湾盐度分布,以验证在真实地形条件下模型的计算能力。最后应用本模型对庄河海域附近排放的污染物的输运过程进行分析和预测。数值结果表明,在研究水力特性以及预测沿海水域污染物输运过程方面,本文所使用的模型是成功的。
[Abstract]:The numerical study of discontinuous flow in shallow water, such as water jump, tidal bore, dam-break wave, wave deformation and so on, has attracted the interest of many scholars because of its extensive engineering application background. However, the natural water flow movement process is often not isolated. Physical, chemical and biological processes, such as sediment transport, pollutant transfer and transformation, are often accompanied. Among them, dam-break floods and their induced sediment movement on the riverbed cause great loss of life and property to the downstream people. It is of great practical significance to study the plane two-dimensional dam-break water and sediment transport under moving bed condition in predicting the downstream disaster caused by the dam break and in assessing the dam-break risk control. On the other hand, as the environmental pollution becomes more and more serious, More and more attention has been paid to the problem of water environment. It is necessary to realize the treatment of polluted water bodies and understand the hydrodynamic characteristics of water bodies. It is necessary to further understand the transport mechanism of pollutants. Firstly, based on the finite volume method and unstructured triangular mesh, a planar two-dimensional shallow water mathematical model is established. The model is mainly applied to the simulation of dam-break flood with strong discontinuity and the tidal simulation of the bay with complex topography. The model uses the second-order precision Roe scheme to approximate the Riemann solution to calculate the momentum flux at the grid interface. The hydrostatic pressure term is reflected as the source term in the momentum equation, and the dynamic boundary problem of the dry and wet interface is solved by using efficient dry and wet treatment technology. Six typical dam-break and three bay tidal current examples are simulated by using the model, and the experimental results are satisfactory. The strong adaptability and high calculation accuracy of the model are demonstrated. It is shown that the model can be used in engineering practice. Based on the hydrodynamic model above, the two-dimensional shallow water governing equation is considered. In this paper, a two-dimensional coupled mathematical model of water and sediment is established, in which the continuous equation and hydrodynamic equation in the governing equation of shallow water adopt muddy water equation. The upwind scheme is used to calculate the sediment flux in the sediment continuum equation. The effects of vegetation on the flow, sediment transport and bed scour and deposition are taken into account in the model. The model is used to simulate five examples. Based on the measured data, the numerical simulation results are verified and analyzed. The results show that the flow evolution and bed surface deformation of dam-break flow under simulated moving bed conditions are discussed. The planar two-dimensional water-sediment coupling mathematical model established in this paper has high accuracy and good ability of complex terrain treatment. It can be found in the numerical simulation of dam-break flow with plant action under the condition of moving bed. Because of the existence of vegetation, the influence of flow velocity and dam-break wave on the downstream riverbed will be reduced, but at the same time, the flood discharge capacity of the channel in the vegetation area will also be reduced, which will lead to the elevation of the flood level in the upstream region, based on the hydrodynamic model. Coupled with two-dimensional shallow water control equation and mass transport equation, a two-dimensional hydrodynamic and water-quality explicit mathematical model is established. The model uses upwind reconstruction interpolation with high order precision to deal with the pollutant transport flux at the grid interface. The diffusion term is treated by a discrete method with second-order accuracy. First, the pure convection problem and the pure diffusion problem in the rotating flow field under ideal conditions are simulated. The model was used to simulate the salinity distribution of Gironde Bay in France. Finally, this model is used to analyze and predict the transport process of pollutants discharged near the Zhuanghe River. The numerical results show that, The model used in this paper is successful in studying hydraulic characteristics and predicting the transport process of pollutants in coastal waters.
【学位授予单位】：大连海洋大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：X52;TV14

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