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Modeling shallow-water hydrodynamics: Rotations, rips, and rivers.

机译：浅水流体动力学建模：旋转，裂隙和河流。

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摘要

Hydrodynamic models are used as a diagnostic tool to understand the temporal variability of shallow-water processes that are difficult to completely resolve with traditional field measurements. For all simulations, modeled quantities are qualitatively or quantitatively compared with available measurements to gain confidence in conclusions derived from the modeled results. In this work we consider both vorticity motions and rip currents, which arise from alongshore inhomogeneities in the wave momentum flux but occur at much different time scales (O(min) vs. O(hours-weeks)). They each have an effect on sediment transport processes and dispersion of sediments or pollutants in the surf zone, which makes understanding their structure and persistence essential.;The vorticity motions of interest here are associated with spatial and temporal wave height variations caused by wave grouping and can exist with either normally or obliquely incident wave conditions. We find that these flows persist for O(1000s) but their lifespan is controlled by the sequence of wave forcing rather than bottom friction as previously hypothesized. These motions can also be observed in combination with either stable or unstable alongshore currents. Our results suggest that, at times, these alongshore propagating wave group forced vortices are misinterpreted as instabilities of the alongshore current.;Alternately, the rip currents considered in this research are controlled by strong wave height gradients in the surf zone generated by the refraction of incident waves over variable offshore depth contours. Thus, this type of circulation is governed by timescales associated with changing offshore wave conditions (O(hours - days)). We consider a four- week time period when variable offshore wave spectra were observed during a large-scale field experiment. The model and data are in good agreement for all wave conditions during the month and estimated model errors are similar to those found previously for alongshore uniform beaches. Through comparisons with remote sensing observations, the model proves it is capable of predicting rip currents when they are observed. Analysis suggests that the direction of the offshore wave spectra will dictate when and where rip currents will appear. We also find that for bi-modal offshore spectra, the relative amount of energy in each spectral mode is a better predictor of rip current development than the peak spectral characteristics.;Finally, some preliminary work to estimate water depths from the combination of hydrodynamic models and available data is also presented. We focus this work in a river meander for our initial tests. A simple analytical model shows skill in predicting the water depth at only one of the two river meanders considered. This discrepancy appears to be related to river curvature and as curvature weakens, the model accuracy decreases. This is hypothesized to be the result of dispersive mixing which is not accounted for in this simple model but confirmation is still required. At the same time, we perform simulations within a river meander to determine the efficacy of using coastal hydrodynamic models in riverine environments where the principles governing the flow are the same. Our initial tests of the Regional Ocean Modeling System (ROMS) suggests that it is able to reproduce the flow through a river meander which opens the door to developing one model that can simulate conditions from upland rivers out to the continental shelf.
机译：流体动力学模型被用作诊断工具，以了解浅水过程的时间变异性，而传统的现场测量很难完全解决这些问题。对于所有模拟，都将建模量与可用测量值进行定性或定量比较，以增强对建模结果得出的结论的信心。在这项工作中，我们考虑了涡度运动和裂隙电流，它们是由波浪动量通量的沿岸不均匀性引起的，但发生在非常不同的时间尺度上（O（min）vs. O（小时-周））。它们各自对冲浪区的沉积物传输过程和沉积物或污染物的扩散都有影响，这使得了解它们的结构和持久性至关重要。此处感兴趣的涡旋运动与波群和水波引起的时空波高变化有关。可以在正常或倾斜入射波条件下存在。我们发现这些流动持续了O（1000s），但是它们的寿命是受波浪强迫的顺序控制的，而不是由先前假设的底部摩擦控制的。这些运动也可以与稳定或不稳定的近岸洋流相结合来观察。我们的研究结果表明，有时这些沿岸传播的波群强迫涡流被误解为沿岸电流的不稳定性;或者，本研究中所考虑的裂隙电流受到由海浪折射产生的海浪区域中强波高梯度的控制。可变的海上深度轮廓上的入射波。因此，这种类型的循环受与变化的海上波浪条件（O（小时-天））相关的时标控制。我们考虑了一个为期四周的时间段，即在大规模现场实验中观察到了可变的近海波谱。该月的所有波浪情况的模型和数据都非常吻合，估计的模型误差与之前在沿海均匀海滩上发现的误差相似。通过与遥感观测的比较，该模型证明了它能够预测观察到的裂隙电流。分析表明，近海波谱的方向将决定裂隙电流何时何地出现。我们还发现，对于双峰离岸光谱而言，每个光谱模式中的相对能量比峰值光谱特征更能预测裂谷电流。;最后，一些初步的工作可以根据水动力模型的组合来估算水深并提供可用数据。我们将这项工作集中在河道上进行初步测试。一个简单的分析模型显示了预测所考虑的两条河曲中只有一条的水深的技巧。这种差异似乎与河流曲率有关，并且随着曲率变弱，模型精度降低。假设这是分散混合的结果，在此简单模型中未考虑此结果，但仍需要确认。同时，我们在河曲中进行模拟，以确定在支配流量原理相同的河流环境中使用沿海水动力模型的效果。我们对区域海洋建模系统（ROMS）的初步测试表明，它能够重现通过河道的水流，这为开发一种模型可以打开大门，该模型可以模拟从陆地河流到大陆架的状况。

著录项

  • 作者

    Long, Joseph W.;

  • 作者单位

    Oregon State University.;

  • 授予单位 Oregon State University.;
  • 学科 Engineering Geophysical.;Engineering Marine and Ocean.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 145 p.
  • 总页数 145
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 海洋工程;
  • 关键词

  • 入库时间 2022-08-17 11:38:26

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