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

Bona9974116 该项目的总的技术目标是建立三维地形模型，以描述以单个和多个沙坝或沙脊为中心形态特征的波浪为主的近岸区和大陆架区的海床动态。 研究人员模拟和分析了波浪和海流对海岸动力学的影响。 这是具有挑战性的，因为存在两个自由表面，水面和可移动的底部，这两个表面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。 该模型采用非线性、色散、耗散的偏微分方程来描述波浪从深水向海岸的演化过程。 这些方程，这是Boussinesq型，耦合到一个模型运行和反射在海岸线。 一旦水面的演化近似地知道了，流体中的速度场就可以通过势流理论来确定。 这个速度场被看作是驱动粘性的，泥沙携带的边界层中的泥沙运输isstaking的地方。 在这一层的速度分布isdetermined使用类似的想法，率先由Longuet-Higgins。 应用泥沙质量守恒的无穷小形式，推导出一个用于确定海底变形的微分方程。 因此，整个模型是有点复杂，由一个非线性的初始边界值问题的波动耦合在onlocalway的底部运动的守恒定律。 该模型的详细开发，分析和计算机代码实现。 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连接起来，以便在真实的情况下更容易地部署模型。 该项目的基本动机有两个方面：第一，希望从质量和数量上了解导致沿海区和大陆架海底结构形成和维持的一些基本过程。 这涉及到波浪环境和床的动力学的全面知识，因为它受到波浪和水流的影响。 第二，同样重要的是，该项目响应了对新的和更复杂的工具的需求，以帮助制定处理真实的海岸工程问题的战略。 该项目有可能有助于研究一些重要的科学和环境问题。 北美的海洋边缘很广阔，在许多地方都很麻烦。 事实上，对松散海岸线的侵蚀是一个世界性的现象，但还没有得到很好的理解。 全球变暖将加剧这些问题，增加海平面，从而导致海岸后退，并提供一个更好的基础冲刷和侵蚀与波浪活动。 脆弱的北极海岸和低海拔地区已经显示出这些全球变化造成的明显恶化迹象。 严重的侵蚀很可能在下一个世纪蔓延到其他海岸地区，因此人们对有效的防治方法越来越感兴趣。 除了“硬”保护计划，如建造海堤等，对利用自然过程的“软”保护战略的需求也将增加。

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.