Lin, Chang (Department of Civil Engineering, National Chung-Hsing University) | Jeng, Chung-Nan (Department of Civil Engineering, National Chung-Hsing University) | Shieh, Shyh-Jiunn (Department of Civil Engineering, National Chung-Hsing University) | Jeng, Dong-Sheng (Department of Civil Engineering, National Chung-Hsing University)
The characteristics of flow fields in the potential region and bottom boundary layer of finite amplitude standing waves are investigated experimentally for Ursell number ranging from 1.21 to 50.59. Fiber laser Doppler velocimeter (FLDV) was used for quantitative measurement. According to linear standing wave theory, the nodes and anti-nodes are fixed points in the space of wave field and the nodes just locate at the still wave level. However, these specific points are found to be not fixed in the wave field, due to tiny period differences of incident waves generated by a precise wave maker. Therefore, spatial distributions of the highest, lowest, and mean water levels in finite amplitude standing waves were measured first. The positions of the maximum and minimum (mean) wave heights were then determined. The characteristics of time histories of water surface elevation as well as the underlying horizontal and vertical velocities, measured along three sections (i.e. the positions of the maximum and minimum (mean) wave heights and the mid-point between them), are elucidated in detail.
Protection of coastal environments is a vital issue in many countries. To protect residents from the acting of ocean waves, marine structures (such as seawalls, caisson etc.) have been widely used for this protection. The damage of marine structures may come from two failure modes. The first mode is the structural failure, caused by the wave forces acting on the structures (Oumerica, 1994). The second mode is the wave-induced seabed instability (such as liquefaction and scour) in the vicinity of the structure. The velocity and bottom shear stress distribution within the wave bottom boundary layer have direct relationship with the quantity of sediment transport rate. Thus, a better understanding of wave bottom boundary is particularly important for coastal engineers involved in the design of coastal structures.