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

本研究的目的是研究冲积带的动力学，包括速度场、泥沙输运和前滩变形。对于激流带的流体力学，需要在陡坡锋面处进行移动边界处理，以精确地再现激流带的速度。研究者对这一课题进行了近十年的研究，并建立了基于非线性长波方程的二维波动模型。但研究主要局限于单色波。在本项目中，分析扩展到不规则波场。利用1996年中央电力研究所大尺度波盆试验数据库，研究了上升波与长周期波的相互作用机理。研究发现，上升波的时间序列数据不受单个入射波的支配，而是受长波分量的支配。针对冲积带的沉积机制，定量估算了输沙速率。用荧光色颗粒测定输沙速率。在前滨带，通常会形成被称为陡崖的特征地形。提出了一个模拟含陡坡的冲蚀带形态的数值模型。这些分析表明，模拟滩坡破坏或雪崩机制是模拟前滨滩变形的必要条件。在考虑冲刷带的净输沙率时，沙床的渗流效应也很重要。这些课题留待今后的研究。

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.