Tsunami surges are frequently simulated by dam-break flows over dry beds. The purpose of this study is to quantitatively investigate the flow kinematics and turbulent characteristics of a surge impacting onto a vertical wall. Based on high-speed videos, the impact process is classified into the initial impact stage, the reflected stage, and the second impact stage. To quantify the flow kinematics, the particle image velocimetry (PIV) technique was used in the non-aerated region, while the bubble image velocimetry (BIV) technique was employed to measure the impact-induced turbulent flow with air entrainment. The measured velocity fields of the impact-induced splash confirmed the feasibility of Ko and Yeh's (2018) model employing a solid-body motion assumption of splash that estimates the impact force by bores and surges at the initial impact stage. Velocity fields and streamlines revealed that the main water body overturned backwards and formed a large two-phase vortex, while a small counter rotating vortex was also formed at the corner of the wall-bed junction. The mean velocity magnitude of the small corner vortex is about two-thirds that of the main water body. The turbulent intensity field was obtained by averaging 20 repetitions of the same experiment. The mean turbulent intensity of these aerated regions is about 3.4 times that of the non-aerated region. Based on a wavelet-transform-based method, the result reveals that the mean turbulence length scale of the aerated region is about two-thirds that of the non-aerated region.

No abstract

No abstract

No abstract

A series of laboratory experiments were conducted to investigate the 2–D kinematic field evolution around a suspended plate induced by solitary waves. The plate–type structure was rigid and suspended above the mean water level, while the solitary waves were generated by the wave maker to simulate the nearshore tsunami waves. The ratio of incident wave height to water depth was in the range of [0.200, 0.333], and the structural suspended height was in the range of [0.067, 0.200]. The velocity field around the deck was measured using the non–intrusive image–based PIV (Particle Image Velocimetry) method. As a result, the flow evolution was categorized into three phases: green water tongue generated, green water overtopping, and flow separation. Flow evolutions in different conditions presented obvious similarities in general but several differences in detail. The measured maximum horizontal and vertical velocities were around 1.9 C0 and 0.8 C0, respectively, where C0 is the maximum flow speed of the incident wave. Ritter’s analytical solution for the dam–break flow problem was examined and compared with the measured data. The accuracy of this solution for the present subject is significant in the period of T ∈ (0.6, 0.9). The adequate experimental data are valuable as a benchmark problem for further numerical model refinement and the improvement of fluid theory.