| Summary: | 碩士 === 中興大學 === 土木工程學系所 === 94 === Abstract
The vortex evolutions induced by a solitary wave propagating over a symmetric cavity were investigated experimentally. The vortex shedding processes were observed qualitatively and measured quantitatively using Phantom Camera and PIV, respectively. The target solitary wave height, H, is 1.4 cm, which gives the dimensionless height ratio (H/h) of 0.15 with h being the depth of water. The depth of cavity D is 3 cm, which gives H/D = 0.47. The characteristics of vortex evolution including trajectory of jet and position of major vortex were discussed in various cases with different gap ratios (G/D = ∞, 2.5, 2.0, 1.0, 0.75, 0.5 and 0.33).
Based on the observation results using flow visualization technique, it is found that the vertical jet ejects in a curvilinear trajectory from the edge to the water surface while the G/D = ∞, 2.5 and 2.0. The vertical jet shifts to the lee side due to the effect of backward velocities generated at the downstream edge of cavity when G/D = 1.0 and 0.75. With the gap ratios of G/D = 0.5 and 0.33, the corresponding vertical jet moves from the cavity to the upstream side. The flow pattern of vortical movement can be categorized to obtain the corresponding trajectory of major vortex Av according to three different sets of gap ratios.
In the analysis of circulation and vorticity for the core of major vortex Av, the phase-average method was utilized in order to precisely obtain the phase-dependent distribution of flow field for vortex shedding process. The results reveal that the magnitudes of vortex strength vary with the gap ratios. When G/D = ∞, both of the corresponding vorticity at the core of major vortex Av and the absolute value of circulation become the largest and have the longest time of energy dissipation. Relatively, the vorticity at center of major vortex Av and the absolute value of circulation are minimum for all the dimensionless time at G/D = 0.33. Moreover, it is found that the vorticity at core and the absolute value of circulation of major vortex Av increase in the beginning and then decrease gradually during dissipation processes.
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