Study on swash zone flow field and foreshore deformation characterizing run-up front as a moving boundary

本文旨在研究冲滩区的水流动力特性，包括水流速度场、泥沙输移和前滩变形，其中冲滩区的水流动力特性需要在冲滩前缘处进行动边界处理，以精确再现冲滩区的水流速度。近十年来，人们对这一课题进行了研究，并建立了基于非线性长波方程的二维波浪模型，但研究主要局限于单色波。在这个项目中，分析扩展到不规则波场。利用1996年在中央电力研究所进行的大型波浪水池实验数据库，研究了爬高波与长周期波的相互作用机制。研究发现，冲浪时间序列数据不受单个来波的影响，而是受长波分量的影响，并对冲浪带的泥沙输移机制进行了定量估算。用荧光色颗粒法测定了输沙率。在前滨地带，通常会形成被称为陡崖的特征地形。提出了一个数值模型来再现包括陡坎在内的冲流带形态。这些分析表明，模拟海滩边坡破坏或崩塌机制是必要的再现前滨海滩变形。考虑冲流区的净输沙率时，砂床的渗流效应也很重要。这些受试者将留在未来的研究中。

The purpose of this study is to investigate the swash zone dynamics including velocity field, sediment transport and foreshore deformation.For the hydrodynamics in the swash zone, moving boundary treatment at a run-up front should be required to reproduce the swash zone velocity precisely. The investigator has been studying this subject for almost one decade, and already developed 2-dimensional wave model based on non-linear long-wave equation.But the study was mainly restricted for monochromatic waves. In this project, the analysis was expanded to irregular wave fields. Using a data-base of large-scale wave basin experiments conducted at the Central Electric Power Institute 1996, interaction mechanism between run-up waves and long period waves was examined. It is found that the time series data of run-up waves are not governed by the individual incoming waves but by the long wave component.For the sedimentation mechanism in the swash zone, quantitative estimations on the sediment transport rate were conducted. Measurements on sand transport rate were done using florescent colored particles. In the foreshore zone, the characteristic topography known as a scarp is often generated. A numerical model to reproduce the swash zone morphology including the scarp was proposed. These analyzes revealed that modeling beach slope failure or avalanching mechanism is essential to reproduce the foreshore beach deformation. Seepage effects into the sand bed are also important to consider the net sediment transport rate in a swash zone. These subjects are remained for the future study.