Models for Wave-Bottom Interaction and the Formation of Sand Bars and Sand Ridges

波底相互作用及沙坝和沙脊形成模型

• 批准号: 9974116
• 负责人: Jerry Bona
• 金额: $ 9.06万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-08-15 至 2001-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9974116&HistoricalAwards=false
• 关键词: Models; Wave; Bottom; Interaction; Formation

Bona9974116 The overall technical objective of the project is to developthree-dimensional topographical models that describe seabeddynamics in wave-dominated near-shore zones and shelf regionswhere single and multiple sand bars or sand ridges form a centralmorphological feature. The investigator models and analyses theeffects of waves and currents on coastal dynamics. This ischallenging because of the presence of two free surfaces, thewater surface and the movable bottom, both of which change overtime, and which interact with each other through complex,nonlinear processes. The model features nonlinear, dispersive,dissipative partial differential equations to describe theevolution of waves coming in to the shore from deep water. Theseequations, which are of Boussinesq type, are coupled to a modelfor run-up and reflection at the shoreline. Once the evolution ofthe water surface is approximately known, the velocity field inthe bulk of the fluid may then be determined via potentialtheory. This velocity field is then viewed as driving a viscous,sediment-laden boundary layer in which the sediment transport istaking place. The velocity distribution in this layer isdetermined using ideas similar to those pioneered byLonguet-Higgins. By applying conservation of sediment mass in aninfinitesimal form, a differential equation is thereby inferredthat serves to determine the bottom deformation. Thus the entiremodel is somewhat complicated, consisting of a nonlinearinitial-boundary-value problem for the wave motion coupled in anonlocal way to a conservation law for the bottom movement. Thismodel is developed in detail, analysed and implemented as acomputer code. Model predictions are compared with field data.It is also proposed to link the computer code with input from aGeographical Information System, to allow easier deployment ofthe model in real situations. The underlying motivation for the project is two-fold.First, there is a desire to understand both qualitatively andquantitatively some of the fundamental processes that lead to theformation and maintenance of bottom structure in coastal zonesand on continental shelves. This involves a thorough knowledgeof both the wave environment and the dynamics of the bed as it isinfluenced by waves and by currents. Second, and not lessimportant, the project responds to the need for new and moresophisticated tools to aid in the development of strategies todeal with real coastal engineering problems. The project has thepotential to contribute to the study of a number of importantscientific and environmental issues. The ocean margins in NorthAmerica are vast and in many places, troubled. Indeed, erosionof unconsolidated coastlines is a world-wide phenomenon that isnot well understood. Global warming will aggravate theseproblems by increasing sea levels, thus causing shore retreat andproviding a better base for the scour and erosion associated withwave activity. Fragile Arctic coasts and low-altitude regionsare already displaying unmistakable signs of deterioration causedby these global changes. Severe erosion may well spread to othercoast regions within the next half century, and thus there willbe an increased interest in effective prevention methods. Inaddition to "hard" protection schemes such as the construction ofseawalls and the like, there will be an increased demand for"soft" protection strategies that take advantage of naturalprocesses.

Bona9974116该项目的总体技术目标是开发三维地形模型，描述波浪控制的近岸区和陆架区域的海床动力学，在这些区域，单一和多个沙洲或沙脊形成中心地貌特征。调查员模拟并分析了海浪和海流对海岸动力的影响。这是具有挑战性的，因为存在两个自由表面，即水面和可移动的底部，两者都随着时间的推移而变化，并且通过复杂的非线性过程相互作用。该模型以非线性、色散、耗散偏微分方程组为特征，描述了从深水进入岸边的波浪的演变。这些方程是Boussinesq型的，耦合到一个模型，用于在海岸线上的启动和反射。一旦水面的演化近似地知道了，流体整体中的速度场就可以通过位势理论来确定。这个速度场被认为是驱动了一个粘性的、含沙的边界层，泥沙输送在这个边界层中。这一层中的速度分布是用与Longuet-Higgins开创的想法类似的想法来确定的。通过应用极小形式的泥沙质量守恒，从而推导出用于确定底部变形的微分方程。因此，整个模型有些复杂，它由波动的非线性初边值问题和底部运动的守恒律非局部耦合而成。该模型被详细地开发、分析和实现为计算机代码。模型预测与现场数据进行了比较，还建议将计算机代码与地理信息系统的输入联系起来，以便在实际情况下更容易部署模型。该项目的基本动机有两个方面：第一，人们希望从定性和定量两方面了解导致沿海地带和大陆架海底结构形成和维持的一些基本过程。这涉及到对波浪环境和河床动力学的透彻了解，因为它受到波浪和水流的影响。其次，也是不重要的，该项目回应了对新的和更具亲和力的工具的需求，以帮助制定战略来处理真正的沿海工程问题。该项目有可能为研究一些重要的科学和环境问题作出贡献。北美的海洋边缘广阔，在许多地方都很麻烦。事实上，对松散的海岸线的侵蚀是一种世界性的现象，人们对此还没有很好的了解。全球变暖将导致海平面上升，从而加剧这些问题，从而导致海岸后退，并为与海浪活动相关的冲刷和侵蚀提供更好的基础。脆弱的北极海岸和低海拔地区已经显示出由这些全球变化造成的明显的恶化迹象。在接下来的半个世纪里，严重的侵蚀很可能会蔓延到其他沿海地区，因此，人们对有效的预防方法将会越来越感兴趣。除了诸如建造海堤之类的“硬”保护计划外，对利用自然过程的“软”保护战略的需求将会增加。