Collaborative research: Laboratory and numerical experiments on the response of wave ripples to changes in oscillatory flow

合作研究：关于波动流变化响应的实验室和数值实验

• 批准号: 1225865
• 负责人: J. Taylor Perron
• 金额: $ 25.51万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-15 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1225865&HistoricalAwards=false
• 关键词: Collaborative; research; Laboratory; numerical; experiments

Symmetric sand ripples are among the most common bedforms in modern wave-dominated environments and in the rock record. Whether ancient or modern, visually striking wave ripple patterns are an easily observable signature of the complex interaction of bed topography, turbulent flow, and sediment transport. Ripple spacing is often used as an indicator of ancient wave conditions and water depth, and modern ripples influence bed roughness. However, ripples are often out of equilibrium with respect to rapidly changing wave conditions, and both ancient and modern ripples often contain complicated defects - deviations from straight, parallel crests - that appear to be disequilibrium features but are poorly understood. Our ability to interpret two-dimensional ripple patterns, or to model how those patterns respond to changing wave conditions, is therefore deficient. This project will investigate the mechanisms by which wave ripples respond to changes in wave conditions through a combination of laboratory wave tank experiments, numerical simulations of bedform evolution, and field studies of both ancient ripples exposed in rock outcrops and modern ripples exposed on shorelines. First, in a series of laboratory wave tank experiments, we will use time-lapse photography and image analysis to track the response of rippled beds to step changes in wave forcing, and ultimately produce a phase diagram for different types of wave ripple defects. Second, we will develop a new numerical method for modeling the co-evolution of bed topography and oscillatory flow, and we will use this model to better understand the transient ripple evolution observed in the wave tank. Third, we will compare the results of the laboratory and numerical experiments with ancient ripples in rock outcrops and modern ripples on shorelines. The main outcomes will be a new interpretation of widespread wave ripple patterns, and a new framework for modeling transient bedform evolution.Patterns generated by flows that move sand, such as the ripples that are a common sight along shorelines around the world, are a rich source of information about ancient and modern flow conditions. These bedform patterns can also influence other geologic flows: modern ripples roughen the sandy bed, slowing coastal flows, and ripples in sedimentary rocks can influence permeability, which controls the flow of water, oil and gas beneath the land surface. This research will improve our ability to interpret common irregularities in ancient and modern wave ripple patterns, and will also produce a new computational framework for modeling their formation. In addition to providing an improved explanation for the striking variety of ripple patterns in coastal settings, our results will provide geologists, sedimentologists, and coastal engineers with new tools for predicting the formation and evolution of bedforms, and will aid geophysicists and hydrologists in understanding the controls on reservoir characteristics.

对称沙纹是现代波浪主导环境和岩石记录中最常见的床型之一。无论是古代还是现代，视觉上引人注目的波浪波纹模式都是河床地形、湍流和沉积物运输复杂相互作用的一个容易观察到的特征。波纹间距通常被用作古代波浪条件和水深的指示，而现代波纹影响河床的粗糙度。然而，相对于快速变化的波浪条件，波纹往往是不平衡的，古代和现代的波纹往往包含复杂的缺陷-偏离直线，平行波峰-这似乎是不平衡的特征，但知之甚少。因此，我们解释二维波纹模式的能力，或者对这些模式如何响应不断变化的波浪条件进行建模的能力是不足的。该项目将通过结合实验室波浪槽实验、河床演化的数值模拟以及对岩石露头中暴露的古代波纹和海岸线上暴露的现代波纹的实地研究，研究波浪波纹对波浪条件变化的反应机制。首先，在一系列的实验室波槽实验中，我们将使用延时摄影和图像分析来跟踪波纹床对波浪强迫阶跃变化的响应，并最终生成不同类型波浪波纹缺陷的相图。其次，我们将开发一种新的数值方法来模拟床层地形和振荡流的共同演化，我们将使用该模型更好地理解波浪池中观察到的瞬态纹波演化。第三，我们将把实验室和数值实验的结果与岩石露头的古代波纹和海岸线上的现代波纹进行比较。主要成果将是对广泛的波纹模式的新解释，以及对瞬态河床演化建模的新框架。沙子的流动产生的模式，比如世界各地海岸线上常见的涟漪，是古代和现代流动条件的丰富信息来源。这些床型模式也可以影响其他地质流动：现代的波纹使砂质床变得粗糙，减缓了海岸流动，沉积岩中的波纹可以影响渗透率，从而控制地表下的水、石油和天然气的流动。这项研究将提高我们解释古代和现代波浪波纹模式中常见的不规则性的能力，也将产生一个新的计算框架来模拟它们的形成。除了对海岸环境中各种各样的波纹模式提供更好的解释外，我们的研究结果还将为地质学家、沉积学家和海岸工程师提供预测河床形成和演化的新工具，并将帮助地球物理学家和水文学家了解对储层特征的控制。