| Abstract: |
| \textbf{Abstract.}
The characteristics of velocity distribution and acceleration of an undular bore propagating over a 1:20 sloping bottom are investigated experimentally. The target bore with a water-depth ratio of h1/h0 = 1.70 is tested in a flume, and the investigation area is focused on the swash zone. A flow visualization technique using particle trajectory photography method and a high-speed particle image velocimetry (HSPIV) system for velocity measurement are conducted with the employment of high-speed digital camera and laser sheet. The results of the acceleration are also calculated from the measured velocity value by using Navier-Stokes equation. The investigation on the velocity shifting in the internal flow of the generated bore due to the effect of leading waves is reported. In addition, the variation features of the depth-averaged values of the local and convective accelerations as well as pressure gradient are also discussed. Moreover, the characteristic of flow reversal and formation of shear layer near the sloping bottom are explored. Hence, the generation of a vortex train (or street) is reported due to the existence of shear layer between two opposite currents with one heading in onshore and another in offshore direction near the sloping bottom. |
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