Flow Characteristics in run-up of periodic waves on nonuni form slope

冲刷带是近岸地区的一部分，其中海滩面交替地被冲冲的海浪覆盖，又被反冲的海浪露出。激流下剧烈的流体运动产生高湍流度，并引起强烈的泥沙运动，导致激流带海滩剖面不断变化。由于水流非常复杂，关于波浪冲刷力学行为的信息相当少。如果我们要更好地了解冲积带的海滩过程，就需要对冲积带下发生的物理过程进行许多研究。这是本研究的主要目的。在波浪池中设置了不同坡度的固定床和活动床模型滩，进行了综合试验。斜波作用下的流场具有高度的非线性和非定常性。此外，水深极浅。因此，测量斜坡上的流速是不可能的。基于自由表面剖面的视频图像，利用非线性长波理论，提出了一种实用合理的流速计算方法。实验结果表明，在井眼坍塌过程中，入射波的模式由波浪形井眼转变为冲刷型井眼。钻孔塌陷在波浪上升过程中起着重要的作用。沉积物输运的底部剪切应力在时间和空间上都有变化，局部流体速度之间存在时间滞后。在对冲积带过程进行建模时，应考虑到本研究的结果。

Swash zone is a portion of the nearshore region in which the beach face is alternately covered by the uprush of the wave swash and exposed by the backwash. Violent fluid motion under the swash flow creates high turbulence and gives rise to a strong sediment movement, which causes constantly beach profile changes in swash zone.Because of the very complex flow, there is fair less information about the mechanical behaviors of wave swash. Many studies of the physical processes occurred under swash have been required if we are better understand beach processes in the swash zone. This is the main purpose of the present study.Comprehensive experiments were made in a wave tank in which model beaches of fixed and movable beds with various slopes were installed. The flow field under swash waves is of high nonlinear and unsteady. In addition, the water depth is extremely shallow. It is, therefore, impossible to measure the flow velocity on a slope. We developed a practical and reasonable procedure for evaluating the flow velocity with the aid of nonlinear long wave theory based on video pictures of the free surface profile.Experiments reveal that mode of incident waves changes from undular bore to swash through the bore collapse process. The bore collapse plays an important role in wave run-up processes. Bottom shear stress contributed to sediment transport is varied temporally and spatially with a time lag between the local fluid velocity.The findings of this research should be taken account of in modeling the swash zone processes.