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Numerical modeling of cross-shore sediment transport and sandbar migration.

机译：跨岸沉积物迁移和沙洲迁移的数值模拟。

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摘要

Nearshore processes on barred beaches are studied with a process-based numerical model. The two major goals of the study are to expand the body of knowledge about nearshore processes on barred beaches gaining a better understanding of the physical mechanisms affecting bar migration events and to enhance the numerical model in order to accomplish realistic simulations of bar migration events. The numerical model is used to study the effect of physical processes on the hydrodynamics and morphodynamics in the nearshore environment.The hydrodynamics on barred beaches and mechanics of sediment transport related to bar migration are studied on storm time scales. The numerical model system consists of a linear spectral refraction-diffraction model, REF/DIF S, a quasi-3D nearshore circulation model, SHORECIRC, energetics-based sediment transport models, and a morphological evolution model. A laboratory experiment conducted in the Delta Flume, Netherlands which had an erosive test stage with offshore bar migration followed by an accretive test stage with onshore bar migration is used for modeling purposes and verifications.The sediment transport is driven by the near-bed wave orbital velocities and the undertow current at the bottom. For that reason, accurate predictions of nearshore hydrodynamics are important for predictions of morphodynamics and successful simulations of bar migration events. A number of enhancements are made to the wave and circulation modules of the numerical model system specifically for simulations on barred beaches. The model modifications and enhancements are: (1) a combined breaking wave parameter with a spatial variation in the wave model (2) a method accounting for breaking wave persistence in the wave model (3) a method accounting for the new breaker roller lag in the wave model (4) the dynamic pressure component in the radiation stress forcing (5) a roller contribution with different depth variation options for the short wave forcing in the circulation model (6) wave height instead of water depth as the turbulent length scale in the eddy viscosity calculations in the circulation model (7) a slope term for the default sediment transport formula.The depth-integrated cross-shore momentum balance in the surf zone shows the strong dependence of the mean water level on radiation stresses. The effect of surface shape parameter and the roller face angle on radiation stress and mean water level predictions are investigated. In reality, the organized wave energy is transferred to roller development over a transition distance and the roller does not immediately contribute to the radiation stresses therefore, showing the importance of the roller lag mechanism for mean water level predictions.The cross-shore variation of the vertical momentum balance is studied to observe the variation of forcing agents of the undertow current. The cross-shore pressure gradient is the most dominant forcing term affecting the depth structure of the undertow current. The effect of different depth variations of the roller contribution to the short wave forcing on the undertow current is investigated. The mechanism accounting for breaking wave persistence and the mechanism accounting for the roller lag are shown to be important for predictions of the undertow currents on barred beaches.The performance of the model in predicting offshore bar migration and onshore bar migration events on storm time-scales is investigated. The skewed wave orbital velocities are introduced to the linear wave model by an empirical parametrization method and are found to contribute strongly to the onshore bar migration. The enhancements made to the wave dissipation and roller are found to significantly affect the predicted migration of the bar as well as the maintenance of the trough.
机译：使用基于过程的数值模型研究了禁止海滩上的近岸过程。该研究的两个主要目标是扩大关于禁止海滩上近岸过程的知识，以更好地了解影响酒吧迁移事件的物理机制，并增强数值模型以完成对酒吧迁移事件的真实模拟。该数值模型用于研究物理过程对近岸环境中水动力和形态动力的影响。在风暴时间尺度上研究了封闭海滩上的水动力和与酒吧迁移有关的泥沙运移机理。数值模型系统由线性光谱折射-衍射模型，REF / DIF S，准3D近岸环流模型，SHORECIRC，基于能量学的沉积物输运模型和形态演化模型组成。在荷兰三角洲水槽进行的实验室实验具有模拟测试阶段和近海波轨道，该实验具有海上试管迁移的侵蚀试验阶段，然后是陆上试管迁移的增生试验阶段。速度和底部的拖曳水流。因此，对近岸水动力的准确预测对于形态动力的预测和成功的条形迁移事件模拟非常重要。数值模型系统的波浪和循环模块做了许多增强，专门用于禁止海滩上的模拟。模型的修改和增强是：（1）波动模型中具有空间变化的组合破碎波参数（2）解释波动模型中的破碎波持续性的方法（3）解释新破碎机辊滞后的方法波浪模型（4）辐射应力强迫中的动压力分量（5）循环模型中短波强迫的滚子贡献具有不同的深度变化选项（6）波浪高度而不是水深作为湍流尺度循环模型中的涡流粘度计算（7）是默认泥沙输运公式的斜率项。冲浪区中深度综合的跨岸动量平衡表明，平均水位高度依赖于辐射应力。研究了表面形状参数和辊面角度对辐射应力和平均水位预测的影响。实际上，有组织的波能在过渡距离上转移到滚筒的发育过程中，因此滚筒不会立即对辐射应力产生影响，这表明了滚筒滞后机制对于平均水位预测的重要性。研究了垂直动量平衡，以观察潜流强迫因素的变化。跨岸压力梯度是影响潜流深度结构的最主要强迫项。研究了不同深度的滚子对短波强迫的贡献对拖曳电流的影响。结果表明，解释波浪持久性的机制和解释辊滞现象的机制对于预测禁止海滩上的暗流具有重要意义。该模型在风暴时间尺度上预测近海钢筋迁移和陆上钢筋迁移事件的性能被调查。通过经验参数化方法将斜波轨道速度引入线性波模型，并发现其对陆上钢筋的迁移有很大贡献。发现对波浪消散和滚子的增强会显着影响棒料的预计迁移以及料槽的维护。

著录项

  • 作者

    Cambazoglu, Mustafa Kemal.;

  • 作者单位

    Georgia Institute of Technology.;

  • 授予单位 Georgia Institute of Technology.;
  • 学科 Physical Oceanography.Engineering Geological.Engineering Civil.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 251 p.
  • 总页数 251
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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